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SkepticJ
2005-Jan-18, 01:35 AM
In the movie X2 Wolverine is shot in the head and his Adamantium metal skull stops the bullet. Fine I accept an invincible material for a pseudoscientific movie that is about action and ethics but the bullet he was shot with was lead. Lead is a real material and thus has known and explained properties. When a lead bullet hits a metal wall the bullet spats into a blob; yet the bullet Wolverine's body pushes back out the hole it came in isn't deformed at all. Hmmmmm.

In the movie Back to the Future, Marty McFly travels back in time from 1985 to 1955. There he accidentally causes his someday mother to fall in love with him endangering his existance because his mom won't fall for and boink his dad. Even if time travel to the past were possible this isn't. The reason is it would create a paradox. How could you go back in time to stop your birth; because if you didn't exist you couldn't go back to stop yourself from being born?

In Back to the Future 2 Marty's girlfriend sees herself as an old woman. How would this be possible? If she has skipped over 30 years that means she didn't live those 30 years and thus wouldn't be in the future. In fact her parents must have been worried sick wondering what happened to their daughter for all those years. Poor parents.

In the movie T2 why does the T-1000 walk so slow in the factory? Why does it always look like the same guy? Why would a smart matter robot fight like a human? Wouldn't it be much more effective for it to blob handcuffs onto the Terminator? Why doesn't it adopt a "blade spider" form and kick some serious tail? If it did anything rational it would have won. You couldn't stop it. It can't break.

The whole reason humans exist in the future on the Matrix Earth is to be a power source for the robots. It is true humans produce voltage and heat. In the real future and in an open system we may have small electronic devices that run off our body heat. The problem in The Matrix is a little thing scientists like to call the Second Law of Thermodynamics(Entropy) Creationists like to use this to try to debunk Organic Evolution. This "argument" shows just how hopelessly stupid they are. But it would work to destroy the world of The Matrix because no solar energy to input energy into the system is getting in. Geothermal energy would work; but why don't the robots just use that? Or just the fusion mentioned in the movie? Someone really needs to slap the Wachowski Brothers.

When the good guys get killed when they are in The Matrix their bodies in reality spit up blood. What?! They died a neurological death. Flat lines on an electroencephalograph machine would be realistic though.



Your turn.

V-GER
2005-Jan-18, 01:56 AM
Skeptic wrote:

How could you go back in time to stop your birth; because if you didn't exist you couldn't go back to stop yourself from being born?

I've often wondered about this myself and the conclusion I've come to(that I find plausible) is that if you go to the past, you immediately start
a new time line since you didn't exist there if the first place, therefore, what ever you do won't affect the time line from which you left. When you return to the future, you arrive in the future of the time line you just created when you went back in time. How can there be a future in the time line that just got created?Well, the blink of an eye that you use for time travel is actually a lot longer time for those in real time(?)


In Back to the Future 2 Marty's girlfriend sees herself as an old woman. How would this be possible? If she has skipped over 30 years that means she didn't live those 30 years and thus wouldn't be in the future

I agree, she couldn't have seen herself because she had not yet gone back. Now the question remains, if you go back in time during your own life time and see yourself what happens? can same matter occupy same space?(according to Timecop, it can't but that's a Van Damme movie...)

Gullible Jones
2005-Jan-18, 02:45 AM
In Armageddon, a small fission bomb in a relatively shallow shaft blows up an iron asteroid the size of Texas. That is simply not possible. Also, the massive iron asteroid has a bizarre irregular shape, probably impossible for such an object.

In Alien, FTL ships use rocket engines.

In Tar Fle... Erm, Star Trek, (any series) phaser beams - these are made of gamma rays, people! - are visible as beams of light (even in space!) and can be seen moving. Also, "photon torpedoes" (antimatter bombs, no less) produce ridiculously small explosions - one should be enough to total any battleship.

Also in Star Trek, Vulcans - who come from a planet with a surface gravity of about 1.2 gees - are quite obviously at least twice as strong as humans.

Similarly, alien species in Star Trek manage to keep the same level of strength as is typical of their species despite extended stays in 1 gee environments.

In Deep Space 9, the wormhole doesn't look like a wormhole.

V-GER
2005-Jan-18, 02:57 AM
Also in Star Trek all aliens(or at least the vast majority) seem to have
a planet wide culture and only one ethnic group. Only exceptions seem to be of political nature. Still, Trek rocks.
And one photon torpedo is more than enough to destroy a ship without shields, also on Star Trek.

Gullible Jones
2005-Jan-18, 03:38 AM
Vulcans have a variety of diferent skin colors, as do Romulans and Klingons... And the reason for the planet-wide culture is that almost all the alien species have star-faring civilizations. Yes, I know that the idea of star-faring civilizations having a single culture is stupid, but hey, at least they have an excuse. ;)

(As for the "Star Trek rocks" comment... Well, Stephen Hawking may be a Trekkie, but I sure ain't.)

Enzp
2005-Jan-18, 06:05 AM
Yes, I would have to say there is some nitpicking here.

In no particular order:

Vulcan with 1.2 time earth gravity yet they are twice as strong. SO? Chimpanzees are quite a bit stronger, yet they are not only smaller than we but also live in the same gravity as we. I think that nitpick mixes the Superman rationale for his strength with the Star Trek characters. An angry chimp can pull your arm right off.

I always had real trouble with SUperman by the way. If something about the different sun gave him his powers, then all his people had the natural ability to fly and see through things as soon as they got out of their solar system. ANd our lighter gravity? Apparently it was only gravity at home preventing him from throwing locomotives across the room and squeezing coal into diamonds. I can't toss around 200 ton locomotives at Krypton, but these 100 tons jobs on earth are nothing.

I enjoy Star Trek, but don't recall ever being told that phasors were gamma ray beams. I've seen all the episodes, did I forget? (As a rule of thumb, I disregard things in Star Trek books as made up) Even if they were using gamma rays, remember it is a phasor, so the beam would be in some way phased with respect to the rest of the world to give it its effect. Phased how? Who knows? Temporaly? DImensionally? After all, the transthater is the basis of a lot of this technology, but I don't believe they ever explained just what a transthater was or did.

Likewise the photon torpedo. I don't recall it being an antimatter bomb. There were times when they sent antimatter out after something, so it is a distinct thing from the torpedo. The torpedo may run on a bit of antimatter, but it is a photon torpedo, not an antumatter torpedo. Again we don't know how they work.

The DS9 wormhole doesn't look like a wormhole? WHich wormhole are you using as exemplary? All the wormholes I ever saw were... were... were... um imaginary, so they can look like whatever you want.

I am not sure about the BTTF girlfriend. There is no problem going 30 yrs into the future and seeing your self as old as long as you go back before you have lived those 30 yrs.. That is to say, you go to the future and see yourself and go EEEK. Then you go back home and thirty years later some young girl steps up and looks at you and goes EEEK. it is only a problem if you go and decide to stay - that skips the 30 yrs, but the first example does not.

teddyv
2005-Jan-18, 03:38 PM
In Armageddon, a small fission bomb in a relatively shallow shaft blows up an iron asteroid the size of Texas. That is simply not possible. Also, the massive iron asteroid has a bizarre irregular shape, probably impossible for such an object.

I also wonder how they were able to drill into an iron formation using no obvious cooling for the bit.

Amadeus
2005-Jan-18, 04:01 PM
In Armageddon, a small fission bomb in a relatively shallow shaft blows up an iron asteroid the size of Texas. That is simply not possible. Also, the massive iron asteroid has a bizarre irregular shape, probably impossible for such an object.

I also wonder how they were able to drill into an iron formation using no obvious cooling for the bit.

I thought it was some kind of comet... Didn't it have a tail?

About the cooling, it's an iron body in space. I would say that is pretty cold as it was so wouldn't the asteroid/comet act as a massive heat sink?

worzel
2005-Jan-18, 05:35 PM
Skeptic wrote:

How could you go back in time to stop your birth; because if you didn't exist you couldn't go back to stop yourself from being born?

I've often wondered about this myself and the conclusion I've come to(that I find plausible) is that if you go to the past, you immediately start
a new time line since you didn't exist there if the first place, therefore, what ever you do won't affect the time line from which you left. When you return to the future, you arrive in the future of the time line you just created when you went back in time. How can there be a future in the time line that just got created?Well, the blink of an eye that you use for time travel is actually a lot longer time for those in real time(?)


In Back to the Future 2 Marty's girlfriend sees herself as an old woman. How would this be possible? If she has skipped over 30 years that means she didn't live those 30 years and thus wouldn't be in the future

I agree, she couldn't have seen herself because she had not yet gone back. Now the question remains, if you go back in time during your own life time and see yourself what happens? can same matter occupy same space?(according to Timecop, it can't but that's a Van Damme movie...)
If you could go back and branch off a new timeline from where you arrived then why couldn't you branch off a new timeline when you go forward, seperate from the one where you stayed behind to age as normal? It would seem logical to me that the act of timetravelling causes the split, whichever way you go.

Nowhere Man
2005-Jan-18, 05:53 PM
In the movie X2 Wolverine is shot in the head and his Adamantium metal skull stops the bullet. Fine I accept an invincible material for a pseudoscientific movie that is about action and ethics but the bullet he was shot with was lead. Lead is a real material and thus has known and explained properties. When a lead bullet hits a metal wall the bullet spats into a blob; yet the bullet Wolverine's body pushes back out the hole it came in isn't deformed at all. Hmmmmm.
Whether or not the bullet was deformed, I'd expect the nice, intact adamantium skull to be full of brain puree afterwards. Not even super mutant healing powers should be able to deal with that.

Fred

SeanF
2005-Jan-18, 05:57 PM
If you could go back and branch off a new timeline from where you arrived then why couldn't you branch off a new timeline when you go forward, seperate from the one where you stayed behind to age as normal? It would seem logical to me that the act of timetravelling causes the split, whichever way you go.
That's what happened in the Star Trek: The Next Generation episode "Yesterday's Enterprise."

The Enterprise-C travelled forward in time and ended up in a future in which they had disappeared without a trace . . .

V-GER
2005-Jan-18, 07:43 PM
Gullible Jones wrote:

Vulcans have a variety of diferent skin colors, as do Romulans and Klingons

They do?aside from Voyager's Tuvok? What about Cardassians?Bajorans
and, well who cares really....
Still I think Trek is a great show. It's only normal that certain scientific facts must be sacrified for entertainment values like
sounds in space and we actually seeing the phaser ray as it moves forward etc.

worzel wrote:

why couldn't you branch off a new timeline when you go forward, seperate from the one where you stayed behind to age as normal

Because you left to the future, you never stayed behind to age.

teddyv
2005-Jan-18, 08:14 PM
About the cooling, it's an iron body in space. I would say that is pretty cold as it was so wouldn't the asteroid/comet act as a massive heat sink?

No; you could also say that the earth is a large heat sink (the crust anyway). Drilling through rock is going to generate lots of heat right at the bit face. Thats why lots of mud/water/polymers are pumped down to drill string. If the bit isn't cooled it will shatter or turn into slag.

frenat
2005-Jan-18, 08:55 PM
In T2 the T1000 was walking slow in the factory because it was damaged. The T1000 can take a lot of punishment but only so much. If you watch the deleted scenes, you can see where the T1000 was having trouble keeping it form and it hands and feet were spontaneously morphing to different materials that they touched. As for blobbing handcuffs onto the terminator, once material has separated from the T1000's body, it doesn't hold it's form for very long. The T1000 can't control it's pieces that aren't connected. As for always looking like the same guy, I think that was ego on the part of the T1000 and of course lack of additional actors. The rest can be explained in two words "plot device".

worzel
2005-Jan-18, 09:49 PM
worzel wrote:

why couldn't you branch off a new timeline when you go forward, seperate from the one where you stayed behind to age as normal

Because you left to the future, you never stayed behind to age.
Did you see the word "branch" in that sentence? The point is that if history can branch when you go back, then why can't it branch when you go forward?

SkepticJ
2005-Jan-18, 10:07 PM
In T2 the T1000 was walking slow in the factory because it was damaged. The T1000 can take a lot of punishment but only so much. If you watch the deleted scenes, you can see where the T1000 was having trouble keeping it form and it hands and feet were spontaneously morphing to different materials that they touched. As for blobbing handcuffs onto the terminator, once material has separated from the T1000's body, it doesn't hold it's form for very long.


The scenes were left out of the final cut which means they aren't movie cannon. Honestly how could you damage a machine that is composed of billions of tiny machines or however it was supposed to work? Try breaking Silly Putty and NOT being able to put it back together again. The only thing that could destroy or even damage the T-1000 was a vat of molten steel.

Nope wrong here to. Earlier in the movie "his" claws stay intact while stuck in the car trunk lid. Also in the foundry scene how do the blobs of nanite alloy come together after thawing back out if they can't talk to each other from a distance?

My nit picks still stand.

SeanF
2005-Jan-18, 10:57 PM
worzel wrote:

why couldn't you branch off a new timeline when you go forward, seperate from the one where you stayed behind to age as normal
Because you left to the future, you never stayed behind to age.
Did you see the word "branch" in that sentence? The point is that if history can branch when you go back, then why can't it branch when you go forward?
Yes, but if you branch out when you travel, so you've got a "you're still here" branch and a "you're gone" branch, when you travel to the future, why would you end up in the "you're still here" branch? :)

worzel
2005-Jan-18, 11:28 PM
worzel wrote:

why couldn't you branch off a new timeline when you go forward, seperate from the one where you stayed behind to age as normal
Because you left to the future, you never stayed behind to age.
Did you see the word "branch" in that sentence? The point is that if history can branch when you go back, then why can't it branch when you go forward?
Yes, but if you branch out when you travel, so you've got a "you're still here" branch and a "you're gone" branch, when you travel to the future, why would you end up in the "you're still here" branch? :)
Yes, I realized my idea was basically flawed just after I posted it :) but not much more than causing a branch when you go back in time, which was my point. There's also the question of suprising yourself, the one who stayed behind would remember the unsuccessful attempt at a time leap and therefore expect to meet himself sometime in the futre.

V-GER
2005-Jan-19, 12:41 AM
worzel wrote:

Yes, I realized my idea was basically flawed just after I posted it but not much more than causing a branch when you go back in time, which was my point. There's also the question of suprising yourself, the one who stayed behind would remember the unsuccessful attempt at a time leap and therefore expect to meet himself sometime in the futre.

But my take on this is that there is no self that left behind. When you go to the past you leave this present and because you didn't ever exist in the past as your present self, you create a new branch. However when you go back to the future, you will arrive to the future of the branch you just created and not create another one. English isn't my first language so it is a bit diffucult for me to explain this. And maybe it is flawed but I came up with it because it was more plausible for me than other theories where a traveller to the past would change existing history and therefore our reality might change all the time without us knowing it.

worzel
2005-Jan-19, 12:52 AM
worzel wrote:

Yes, I realized my idea was basically flawed just after I posted it but not much more than causing a branch when you go back in time, which was my point. There's also the question of suprising yourself, the one who stayed behind would remember the unsuccessful attempt at a time leap and therefore expect to meet himself sometime in the futre.

But my take on this is that there is no self that left behind. When you go to the past you leave this present and because you didn't ever exist in the past as your present self, you create a new branch. However when you go back to the future, you will arrive to the future of the branch you just created and not create another one. English isn't my first language so it is a bit diffucult for me to explain this. And maybe it is flawed but I came up with it because it was more plausible for me than other theories where a traveller to the past would change existing history and therefore our reality might change all the time without us knowing it.
Yes, I see your point, and you express yourself very well in English, if you don't mind me saying so.

SkepticJ
2005-Jan-19, 01:47 AM
In the movie Jurassic Park 2 the Green Peace nut(I don't feel like looking up his name.) said that only humans hunt when they aren't hungry. Not true. Just about anyone with a cat has seen dead lizards, mice, insects ,birds etc. that their cats bring up from time to time. They only sometimes eat them.

Ilya
2005-Jan-19, 05:13 AM
Vulcan with 1.2 time earth gravity yet they are twice as strong. SO? Chimpanzees are quite a bit stronger, yet they are not only smaller than we but also live in the same gravity as we. I think that nitpick mixes the Superman rationale for his strength with the Star Trek characters. An angry chimp can pull your arm right off.

Little known fact -- a chimpanzee could never throw a rock as fast, or punch as hard as a human. Their arms are very strong but SLOW. Arms of all primates act as force-reducing levers, with muscle attachments very close to the joint. When you bend your arm, your bicep contracts less than an inch, but that motion is levered to much longer, faster and weaker, sweep of your hand. Ape muscles attach further from the joint, so the force reduction is not as great. Chimpanzee bicep actually produces about as much force as male human's bicep, but the lever makes the difference. Which is why chimpanzees never punch each other in fights -- it would be completely ineffective. Instead, they grab and rend.

swansont
2005-Jan-19, 01:29 PM
In Alien, FTL ships use rocket engines.


I don't recall where the Nostromo was claimed to be FTL.

Reacher
2005-Jan-19, 03:13 PM
Whether or not the bullet was deformed, I'd expect the nice, intact adamantium skull to be full of brain puree afterwards. Not even super mutant healing powers should be able to deal with that.

Fred

I don't quite see what you're getting at here... The Adamantium skull stopped the bullet, so the bullet should have been deformed. The bullet did not get to his brain, because of the adamantium plates.

teddyv
2005-Jan-19, 03:27 PM
Whether or not the bullet was deformed, I'd expect the nice, intact adamantium skull to be full of brain puree afterwards. Not even super mutant healing powers should be able to deal with that.

Fred

I don't quite see what you're getting at here... The Adamantium skull stopped the bullet, so the bullet should have been deformed. The bullet did not get to his brain, because of the adamantium plates.

I think he's getting at that the force of impact of the bullet would still be translated into the body (internal damage).

ZaphodBeeblebrox
2005-Jan-19, 03:47 PM
Whether or not the bullet was deformed, I'd expect the nice, intact adamantium skull to be full of brain puree afterwards. Not even super mutant healing powers should be able to deal with that.

Fred

I don't quite see what you're getting at here... The Adamantium skull stopped the bullet, so the bullet should have been deformed. The bullet did not get to his brain, because of the adamantium plates.

I think he's getting at that the force of impact of the bullet would still be translated into the body (internal damage).

Yeah ...

Pesky Little Thing, Called Conservation of Momentum ...

His Brain, would've been Shaken, not Stirred!

Moose
2005-Jan-19, 03:49 PM
I think he's getting at that the force of impact of the bullet would still be translated into the body (internal damage).

Right, just like the guy who shot Wolverine had his hand crushed by the recoil... #-o

(Yes, I know. That's my point, actually. The impact to the adamantium skull plates would have been spread about a wider area and the shock ultimately cushionned by his neck muscles. [edit again, I suppose he could have been concussed, but I expect his mutant regeneration abilities would have fixed that right up.])

Reacher
2005-Jan-19, 03:49 PM
Ah, ok, fair enough.

ToSeek
2005-Jan-19, 04:49 PM
Vulcan with 1.2 time earth gravity yet they are twice as strong. SO? Chimpanzees are quite a bit stronger, yet they are not only smaller than we but also live in the same gravity as we. I think that nitpick mixes the Superman rationale for his strength with the Star Trek characters. An angry chimp can pull your arm right off.

Little known fact -- a chimpanzee could never throw a rock as fast, or punch as hard as a human. Their arms are very strong but SLOW. Arms of all primates act as force-reducing levers, with muscle attachments very close to the joint. When you bend your arm, your bicep contracts less than an inch, but that motion is levered to much longer, faster and weaker, sweep of your hand. Ape muscles attach further from the joint, so the force reduction is not as great. Chimpanzee bicep actually produces about as much force as male human's bicep, but the lever makes the difference. Which is why chimpanzees never punch each other in fights -- it would be completely ineffective. Instead, they grab and rend.

On the other hand, chimps (and the other apes) can undo bolts with their bare hands that it took a human with a wrench to tighten. (Zoos have had to account for this!)

Gullible Jones
2005-Jan-19, 08:28 PM
Ahh... Thanks Ilya.

(I was wondering if there were differences in the amino acid composition of human and chimp muscle proteins sufficient to account for the strength difference... I know that chimps are partially arborial, so I was thinking that stronger prehensile limbs would be favored, perhaps leading to more efficient muscles...)

lti
2005-Jan-20, 09:27 AM
Re: X2.
The fact that the bullet is not smushed means that it clearly didnt stop on his adamantium skull (the movie does not even say whether or not his skull is protected with adamantium so this is merely conjecture on SkepticJ's account). The bullet smashed through his skull and into his brain, knocking him out. his mutant healing powers then forced the bullet out and fixed his brain and skull. U dont think thats possible? Then i challenge u to prove his mutant healing powers arent up to the challenge.

Re: timetravel.
When u start talking about diverging timelines as if that is what happes u have clearly been watching too much sci fi. two words: Plot Device.
the way i see time is merely as a linear progression. fact: marty goes back in time to 1955 and has interactions with his mother. this has happened before he has born. when his mother tells the story of her courtship the first time this fact should have been mentioned.
This logic follows that u cant change time, so multiple timelines are redundant. what ever u do back in time, is what happened in the first place, so its ur actions that create the world u expect.

Whichever way a tv show tries to deal with it is merely for plot and to complain about it is the same as complaining that a fictional wormhole doesnt look right.
(star trek has as many different ways of dealing with time travel as it has episodes featuring it)

the fact chimps can untighten bolts that humans cant is testament to the greater mechanical advantage their arms bestow them.

Re: superman.
It is not soley (if at all) through Krypton's greater gravity that Superman has super powers on Earth. It is due to our yellow sun. Our yellow sun provides him with all his super powers (which have greatly varied through the years of his mythos) his abilities of flight, superstrength, laser vision, superspeed etc. all come because of his exposure to yellow sunlight.

It isnt meant to be scientific.

teddyv
2005-Jan-20, 03:39 PM
Re: X2.
The fact that the bullet is not smushed means that it clearly didnt stop on his adamantium skull (the movie does not even say whether or not his skull is protected with adamantium so this is merely conjecture on SkepticJ's account). The bullet smashed through his skull and into his brain, knocking him out. his mutant healing powers then forced the bullet out and fixed his brain and skull. U dont think thats possible? Then i challenge u to prove his mutant healing powers arent up to the challenge.

IIRC, in the original X-Men, an x-ray was performed on Wolverine which suggested adamatium plates on his skull. But its been a while. :-?

Sock Munkey
2005-Jan-20, 07:16 PM
What bugs me about T2 is the apparent lack of reason with which the T-1,000 was attacked. They just kept on shooting it ineffectually when they should have been trying to elctrocute it, throw acid on it, or stuff it into a microwave.

Doodler
2005-Jan-20, 07:25 PM
In Back to the Future 2 Marty's girlfriend sees herself as an old woman. How would this be possible? If she has skipped over 30 years that means she didn't live those 30 years and thus wouldn't be in the future. In fact her parents must have been worried sick wondering what happened to their daughter for all those years. Poor parents.

On of the things tapped on in Back to the Future was parallel time lines. Its possible to pass it off on them having stepped into a future timeline where they had lived out those 30 years.

Of course, the other side of that coin that got me was, if they did only make a brief stopover in time, why didn't their older selves remember it?

Doodler
2005-Jan-20, 07:30 PM
In Armageddon, a small fission bomb in a relatively shallow shaft blows up an iron asteroid the size of Texas. That is simply not possible. Also, the massive iron asteroid has a bizarre irregular shape, probably impossible for such an object.

I also wonder how they were able to drill into an iron formation using no obvious cooling for the bit.

I thought it was some kind of comet... Didn't it have a tail?

About the cooling, it's an iron body in space. I would say that is pretty cold as it was so wouldn't the asteroid/comet act as a massive heat sink?

No, having drilled on steel that was left to sit overnight in subfreezing temperatures, I can tell you from first hand experience that steel subjected to abrasion with metal gets REAL hot REAL fast. As I was drilling through a mere 1/2" of metal, I could watch the frost on the surface retreat within a minute from the area where the drill was working. In fact, heat contraction caused the hole to close on the bit and throw the magnetically achored drill off the beam, shattering the bit.

Jason
2005-Jan-20, 07:35 PM
What bugs me about T2 is the apparent lack of reason with which the T-1,000 was attacked. They just kept on shooting it ineffectually when they should have been trying to elctrocute it, throw acid on it, or stuff it into a microwave.

I'd like to see you try to stuff a living metal killing machine into a microwave. :)
And where are you going to get enough industrial-strength acid to throw at it and do any appreciable damage?
Sure if you're given unlimited time and resources you can probably come up with a few ways to kill the thing, but they had their hands full in the movie with just trying to keep alive.

Shooting it at least slows it down somewhat (as it stumbles or takes time to re-form body parts).

Doodler
2005-Jan-20, 08:15 PM
What bugs me about T2 is the apparent lack of reason with which the T-1,000 was attacked. They just kept on shooting it ineffectually when they should have been trying to elctrocute it, throw acid on it, or stuff it into a microwave.

I'd like to see you try to stuff a living metal killing machine into a microwave. :)
And where are you going to get enough industrial-strength acid to throw at it and do any appreciable damage?
Sure if you're given unlimited time and resources you can probably come up with a few ways to kill the thing, but they had their hands full in the movie with just trying to keep alive.

Shooting it at least slows it down somewhat (as it stumbles or takes time to re-form body parts).

If the thing was entirely liquid metal, there had to be some level of conductivity to it. Why not massive levels of electricity?

Moose
2005-Jan-20, 08:46 PM
Well, the T-80 (Arnie) tasked with defending the Connors had had it's learning mode dip-switch set off. Barring any special tactical programming other than "get Connors clear and hide them", it would have to go with what it knew: "See target, shoot stuffing out of target. If that fails, find bigger gun and repeat."

Once the Connors got the T-80 into learning mode, it immediately realized that it would have to get very creative to destroy the T-1000. Every action and contingency it took afterwards was towards that end.

lti
2005-Jan-20, 08:48 PM
would passing electricity through it damage it anyway?

why didnt they shoot at its legs. knocking them off would have slowed its advance more than blasting away at its chest.

it wasnt indestructable, as the damage done to it by the liquid nitrogen showed.

Why is it that liquid nitrogen seems to be the solution in every movie?

Jason
2005-Jan-20, 09:19 PM
why didnt they shoot at its legs. knocking them off would have slowed its advance more than blasting away at its chest.
Probably because it's a lot harder to shoot a running man in the legs than in the chest.

SkepticJ
2005-Jan-20, 09:58 PM
it wasnt indestructable, as the damage done to it by the liquid nitrogen showed.

No, the nitrogen only froze it so it couldn't move. Then like a dummy T-80 shot the frozen form and it shatterd. This allowed it to thaw out faster than a large solid body would. Only huge amounts of heat, enough to break the chemical bonds of the T-1000's nanomachines was enough to destroy it as I already said. Quite convenient that a steel smelting factory was there huh? Other than that or large amounts of strong acid it's unstoppable and unbreakable(where it can't fix back like new after a few seconds).

lti
2005-Jan-21, 12:17 AM
the freezing process did damage it. presumably the individual nanomachines were damged by being frozen.

regardless, the T-1000 showed signs of damage after the freezing process. Yes, the only way to destroy it completely was to destroy the individual parts which the molten iron seemed to do quite nicely.

Paul Beardsley
2005-Jan-21, 12:28 PM
In the movie Back to the Future, Marty McFly travels back in time from 1985 to 1955. There he accidentally causes his someday mother to fall in love with him endangering his existance because his mom won't fall for and boink his dad. Even if time travel to the past were possible this isn't. The reason is it would create a paradox. How could you go back in time to stop your birth; because if you didn't exist you couldn't go back to stop yourself from being born?

The film was about the dangers of time-travel paradoxes.

It's true that the film didn't address the fact that if Marty stopped existing, he wouldn't have been there to prevent his own existence in the first place. But perhaps they worked on the principle that once you're deleted from the time line, you stay deleted - even if that means Marty's parents failed to get together for some reason other than his interference.

The whole "if I could travel back in time I could change what happened" idea is fallacious, so all time travel stories based on that premise are logically flawed - examine them closely and they will unravel sooner or later. Back to the Future was one of the better-thought-out stories based on the fallacy, and as such it works on its own terms.


In Back to the Future 2 Marty's girlfriend sees herself as an old woman. How would this be possible? If she has skipped over 30 years that means she didn't live those 30 years and thus wouldn't be in the future. In fact her parents must have been worried sick wondering what happened to their daughter for all those years. Poor parents.

Huh???

The fact that she sees herself as an old woman 30 years in the future simply means she knows she's destined to return to the present before too long so that she will get to live out her life and eventually become the old woman she saw.

Yes, she's skipped across 30 years, but her parents aren't going to be worried about her because she skips back 30 years afterwards, so from the parents' point of view she's only been gone an hour (or whatever it was).

Gas Giant
2005-Jan-21, 12:30 PM
Well, the T-80 (Arnie) tasked with defending the Connors
Wasn't it a 101? The one from the first movie was a "Cyberdyne Systems model 101" according to Reese.

Paul Beardsley
2005-Jan-21, 12:34 PM
Right, just like the guy who shot Wolverine had his hand crushed by the recoil... #-o

Did that actually happen? Argh! That is just too stupid! Surely someone in the camera crew, or the best boy or the grip, would have intervened and said, "That makes no sense!"

It made me think about the early unmanned probes to the moon - the ones that simply impacted on the surface. I can imagine a team of scientists looking at the launch pads to see if they crush at the moment of impact - and from that they can determine the hardness of the moon's surface.

Gas Giant
2005-Jan-21, 12:36 PM
The fact that she sees herself as an old woman 30 years in the future simply means she knows she's destined to return to the present before too long so that she will get to live out her life and eventually become the old woman she saw.
The big problem with BttF2 wasn't Jennifer, it was Old Biff. When Doc and Marty return to 1985 and find the hellish world Biff's millions have caused, Doc explains that they can't go back to 2015 to stop Old Biff getting hold of the almanac, because they were now on a different time line. So how did Old Biff get back to his 2015 from the 1955 where he gave Young Biff the book?

Moose
2005-Jan-21, 01:13 PM
Right, just like the guy who shot Wolverine had his hand crushed by the recoil... #-o

Did that actually happen?

No, it didn't. That's my point. The shooter does not have his/her hand or shoulder crushed by the recoil. And the person taking the bullet doesn't get thrown back ten feet, even though the total force of impact is the same on the shooter and the shot.

Why?

Because the recoil of the shot is spread out over a wide area and cushionned either by the hand/arm, or by the shoulder and ribcage. This happens without turning the shooter's innards into goo.

And the shot? Well, while a lead (and especially hollow point) bullet spreads out to a wider area upon impact, that area is still very small. The skin gets punctured.

If Wolverine had adamantium plating on his skull, his brains would not have turned into goo (perhaps concussed, though), because the force of the impact would have been spread and cushionned by his neck muscles, the same way our unarmored heads aren't splattered by a seat-belted crash-stop.


Wasn't it a 101? The one from the first movie was a "Cyberdyne Systems model 101" according to Reese.

Gas Giant, I've been looking around, and I've seen references to T-80 and/or T-100 (movie novelization filtered through lousy memory), T-800 (IGN's review of the T3:Redemption game) and T-850 (a movie review from someone who didn't "get" who sent Arnie in the first place), as well as T-101 (another review) all referring to Arnold's character.

IMDB (T3 page) refers to Arnold's character both as T-800 (plot summary) and T-101 (review). IMDB also refers to Arnold's character as T-800 Model 101 in the T2 page credits, but also as the Series T-101, Model T-800 in the review.

Wikipedia calls it a "Cyberdyne Systems Model 101 800 Series Terminator", and labels a screencap "T-800 terminating".

TimH
2005-Jan-21, 03:38 PM
In the movie Back to the Future, Marty McFly travels back in time from 1985 to 1955. There he accidentally causes his someday mother to fall in love with him endangering his existance because his mom won't fall for and boink his dad. Even if time travel to the past were possible this isn't. The reason is it would create a paradox. How could you go back in time to stop your birth; because if you didn't exist you couldn't go back to stop yourself from being born?

Which is why Marty as Mom-to-be starts to fall for he starts to fade from reality



<Snip> Why would a smart matter robot fight like a human? Wouldn't it be much more effective for it to blob handcuffs onto the Terminator? Why doesn't it adopt a "blade spider" form and kick some serious tail? If it did anything rational it would have won. You couldn't stop it. It can't break.

As Arnie explains on the way out of town (before John orders him to go to the hospital for a rescue), the T1000 can't form 'machines'. Something to do with a limitation with moving parts. Stabbing/cutting/bludgeoning impliments are ok, anything complex won't work.

worzel
2005-Jan-21, 04:04 PM
As Arnie explains on the way out of town (before John orders him to go to the hospital for a rescue), the T1000 can't form 'machines'. Something to do with a limitation with moving parts. Stabbing/cutting/bludgeoning impliments are ok, anything complex won't work.
I.e. topologically it could only be a sphere, but you could make handcuffs out of a sphere.

Ricimer
2005-Jan-21, 04:29 PM
x2: Right, he'd likely be concussed, and I'd argue he did take a chunk of internal damage, afterall, he was knocked out for a couple of minutes. So the bullet either had some effect, or he decided to take a nap. Your pick.

And yes, the bullet should have been deformed, even if it did penetrate the skull. Upon impact with a body most bullets deform to a certain extent.

SeanF
2005-Jan-21, 04:31 PM
And yes, the bullet should have been deformed, even if it did penetrate the skull. Upon impact with a body most bullets deform to a certain extent.
Maybe his healing power repaired the bullet before ejecting it . . . 8-[

Jason
2005-Jan-21, 04:35 PM
The big problem with BttF2 wasn't Jennifer, it was Old Biff. When Doc and Marty return to 1985 and find the hellish world Biff's millions have caused, Doc explains that they can't go back to 2015 to stop Old Biff getting hold of the almanac, because they were now on a different time line. So how did Old Biff get back to his 2015 from the 1955 where he gave Young Biff the book?
Here's a theory: Old Biff was able to return to the original 2015 because he left from 1955 before the original time line had been diverted into Biff's world (before Young Biff had made his first bet using the sports book).

There's a cut scene on the BttF2 DVD that shows that shortly after Old Biff returns the DeLorean in 2015 he fades from existence. That probably confuses things even more.

Krel
2005-Jan-21, 07:10 PM
[quote="Moose"]

No, it didn't. That's my point. The shooter does not have his/her hand or shoulder crushed by the recoil. And the person taking the bullet doesn't get thrown back ten feet, even though the total force of impact is the same on the shooter and the shot.

Why?

Because the recoil of the shot is spread out over a wide area and cushionned either by the hand/arm, or by the shoulder and ribcage. This happens without turning the shooter's innards into goo.

And the shot? Well, while a lead (and especially hollow point) bullet spreads out to a wider area upon impact, that area is still very small. The skin gets punctured.


quote]

Actually a bullet is traveling faster when it leaves the barrel then on ignition due to the expanding gases from the casing. The longer the barrel, the higher the velocity. When the bullet enters a body most damage is done by the shock wave passing though the tissue. The higher the velocity, the deeper the penetration. That is why the .45 acp is so good against people, we have a pretty shallow cross section, so slow and heavy is better. A Bear on the other hand is pretty thick so a higher velocity for deeper penetration is better.

In an semi-automatic pistol or rifle, the weapon is designed to absorb some of the force so that the shooter doesn't take the abuse. The Hunters that used to fire the old Express rifles used to suffer nerve damge from the recoil.

Even if the skull is plated the force will still be transmitted through it. Think of the old toy that is five ball bearings suspended from a frame. You lift one ball bearing and let it fall and hit the next one. The force is transmitted though the other three and the ball bearing on the other end jumps. Unless there is something to absorb the velocity of the bullet, the brain is going to recieve the shockwave.

David,

John Dlugosz
2005-Jan-21, 08:45 PM
And yes, the bullet should have been deformed, even if it did penetrate the skull. Upon impact with a body most bullets deform to a certain extent.

Maybe whatever power repairs his body decided to restore the bullet too, in case it was something important that he wanted back?

SkepticJ
2005-Jan-21, 09:34 PM
Maybe whatever power repairs his body decided to restore the bullet too, in case it was something important that he wanted back?

Unlikely because his "healing power" is only biological regeneration like salamanders and other animals have, it just is supposed to work MUCH faster; seconds instead of weeks to months.

Moose
2005-Jan-22, 01:46 AM
Actually a bullet is traveling faster when it leaves the barrel then on ignition due to the expanding gases from the casing. The longer the barrel, the higher the velocity.

... And the stronger the recoil. "Equal and opposite reaction". To borrow an old joke: "It's not just a good idea, it's the LAW."


When the bullet enters a body most damage is done by the shock wave passing though the tissue.

The "Hydrostatic shock" hypothesis? I've never seen any convincing evidence supporting this, although I do admit I haven't cared enough to go looking for any.


In an semi-automatic pistol or rifle, the weapon is designed to absorb some of the force so that the shooter doesn't take the abuse. The Hunters that used to fire the old Express rifles used to suffer nerve damge from the recoil.

Uh huh. Pretty much my point, though. The shooter doesn't get pulverized because the force of the recoil either gets spread or redirected.


Even if the skull is plated the force will still be transmitted through it. Think of the old toy that is five ball bearings suspended from a frame. You lift one ball bearing and let it fall and hit the next one.

Yes, which is why I say the neck muscles would ultimately absorb the force of the shot if there was no give to the adamantium plating.

Same example, except put a bean bag directly behind the last bearing. Now how far do you think the last ball bearing is going to go?

Paul Beardsley
2005-Jan-22, 09:29 PM
The big problem with BttF2 wasn't Jennifer, it was Old Biff. When Doc and Marty return to 1985 and find the hellish world Biff's millions have caused, Doc explains that they can't go back to 2015 to stop Old Biff getting hold of the almanac, because they were now on a different time line. So how did Old Biff get back to his 2015 from the 1955 where he gave Young Biff the book?
Indeed. Because stories about changing history are fundamentally nonsensical, there will always be a lapse in logic somewhere - and it's to the film's credit that this particular lapse is reasonably well buried...

...Unless you think about it even a little bit! Old Biff nicks the time machine, goes off to do what he does, then returns to his present and leaves the time machine so that its owners can recover it. Strange motivation, given that a time machine is a fairly handy thing to own, and given that he himself doesn't appear to be benefitting from the new timeline - it's another Biff who's living in luxury!

But the essence of storytelling is to gloss over bits that don't make sense, and to highlight the bits that engage the audience. This is doubly true for stories about changing history.

Gullible Jones
2005-Jan-22, 10:17 PM
If the neck muscles absorbed the shock, the brain would still get enough to mash it pretty good.

As for the hydrostatic shock business... Is there any evidence for that, i.e. ruptured cells relatively distant from the point the bullet struck? And if you got hit in a vulnerable spot (chest, shoulder, head, etc.) wouldn't the formation of a large, ragged hole in whatever place it was due to the bullet's momentum be enough to kill you?

Paul Beardsley
2005-Jan-22, 11:09 PM
As a matter of interest, which films do you care about? (This is addressed to anyone who wants to answer.)

For instance, I couldn't care less if there was a gaping logical hole in a film about Spiderman or The X-Men because I find the premise of these films totally banal and uninteresting and infantile and just plain rubbish.

On the other hand, if a film is very appealing but has a few minor plotholes in it, I am more prepared to either overlook the plothole or else attempt to explain it away.

Moose
2005-Jan-22, 11:55 PM
If the neck muscles absorbed the shock, the brain would still get enough to mash it pretty good.

Hence the earlier reference to the possibility of a concussion rather than the crucible of goo some have been expecting.

Remember, the total energy delivered by the bullet is equal to what the shooter had to deal with. Ordinarily, the bullet's force is spread over a very small area. In Wolverine's case, the area the shock is spread into is his entire head and shoulders, assuming there is no give to the adamantium plating.

If it does compress at all, then there's the possibility of a brain injury.

Without that compression, the only shock to his brain is that of a high velocity, deforming light object colliding against a stationary uncompressable object orders of magnitude more massive.

And we already know the cop was able to fire the gun without injuring his hand or wrist.


As for the hydrostatic shock business... Is there any evidence for that, i.e. ruptured cells relatively distant from the point the bullet struck?

Nope. Especially considering people actually do have a fair chance at surviving a gunshot wound if they are treated early enough.


And if you got hit in a vulnerable spot (chest, shoulder, head, etc.) wouldn't the formation of a large, ragged hole in whatever place it was due to the bullet's momentum be enough to kill you?

As I see it, having a piece of deforming lead passing through you, at any velocity high enough to puncture skin once, tearing a quarter-sized hole through major organs and blood vessels is likely to be plenty to kill you, or not, entirely depending on what it's torn its way through.

Once it's punctured skin, the bullet's velocity basically determines whether it punctures it's way out the other side, or bounces back to tearing even more.

In general, the higher the velocity (and the less deformable the bullet), the more survivable the round is likely to be.

Kebsis
2005-Jan-23, 12:17 AM
Arguing about time travel inconsistancies has always seemed kinda silly to me. Why wouldn't you be able to kill your grandfather in the past? Because that doesn't make logical sense? Most of the universe that we do understand doesn't make much logical sense, why would traveling through time be required to?

Maybe you could go back in time to 1940, kill your grandfather, then go to 1950 and have a beer with him. Whose to say that the two events are related to each other at all?

Paul Beardsley
2005-Jan-23, 08:49 PM
Arguing about time travel inconsistancies has always seemed kinda silly to me. Why wouldn't you be able to kill your grandfather in the past? Because that doesn't make logical sense? Most of the universe that we do understand doesn't make much logical sense, why would traveling through time be required to?

This does sound like an "against the mainstream" view.


Maybe you could go back in time to 1940, kill your grandfather, then go to 1950 and have a beer with him. Whose to say that the two events are related to each other at all?

Er, everybody?

Kebsis
2005-Jan-25, 02:36 PM
But why? Why does one instance in time have to be related to another at all? The point being that we have a limited understanding of how time works at all, right? So how can we apply standard logic to it when standard logic doesn't even work for all the stuff we do understand?

It reminds me of when the resturant at the end of the universe was being described in HGTTG. Everything about it should have been impossible but there it was. Why? Because we have no clue how time actually works.

How can this view be 'against the mainstream' when there really isn't any mainstream view at all? It's simply an unknown.

ToSeek
2005-Jan-25, 03:00 PM
But why? Why does one instance in time have to be related to another at all? The point being that we have a limited understanding of how time works at all, right? So how can we apply standard logic to it when standard logic doesn't even work for all the stuff we do understand?



Causality seems pretty well established to me. If we line up dominoes (either literally or figuratively), we don't see them fall in random order but one right after the other.

Kebsis
2005-Jan-25, 03:36 PM
I get the feeling I'm not explaining myself well. That makes sense because this isn't a theory or anything, just something I've been chewing on.

Let me put it this way. What if time is like a film reel. A series of moments moving by which to us looks like it is a continuous video. the 'present' being the frame currently being imaged.

If you could step outside of the reel and look at the previous frames, ie time travel, and alter them, what would happen to the frames in front and behind the one you altered? Nothing, right?

Of course I don't know this, anymore than I know that time is continous and, assuming traveling through time was possible, that altering events in the past would change stuff in the present. But I guess that's what I'm saying; that it's such an insane idea to begin with that really anything goes within it's context.

ToSeek
2005-Jan-25, 03:43 PM
I get the feeling I'm not explaining myself well. That makes sense because this isn't a theory or anything, just something I've been chewing on.

Let me put it this way. What if time is like a film reel. A series of moments moving by which to us looks like it is a continuous video. the 'present' being the frame currently being imaged.

If you could step outside of the reel and look at the previous frames, ie time travel, and alter them, what would happen to the frames in front and behind the one you altered? Nothing, right?

Of course I don't know this, anymore than I know that time is continous and, assuming traveling through time was possible, that altering events in the past would change stuff in the present. But I guess that's what I'm saying; that it's such an insane idea to begin with that really anything goes within it's context.

It falls into a category of questions we sometimes get on here that are along the lines of "If you could [do something that goes completely against the known laws of physics], what would happen?" Well, it's a little hard to say considering that we're relying on the known laws of physics to figure out what would happen. So, yes, maybe you're right. Maybe I'm right. Given the premises, there's no way of telling.

Paul Beardsley
2005-Jan-27, 12:33 PM
Hi Kebsis

My "against the mainstream" remark was mainly directed at your comment,


Most of the universe that we do understand doesn't make much logical sense, why would traveling through time be required to?

Because I don't think the first bit is true. The stuff we understand generally makes sense, because otherwise we wouldn't understand it, we'd merely observe it. For instance, I observe that when I drop a lead weight, it falls to the ground; when I drop a helium-filled balloon, it rises to the ceiling. I understand what is happening because someone explained the relevant bits of gravity and bouyancy to me - and so it makes logical sense.

As for time travel into the past, well, as I understand it, it is theoretically possible, but so difficult that it will probably be forever beyond our capability. But even if it turns out that the theories are wrong and that it is not possible at all, it's still reasonable to consider the logical consequences. If the logical consequences are... well, illogical, then it would suggest that either time travel is completely impossible, or there's faulty reasoning going on.

As I see it, there is faulty reasoning going on the moment people start to consider the consequences of time travel. People often ask, "What if I went back in time and killed my father before I was conceived?" The very question is wrong! It should read, "What if I went back in time and attempted to kill my father..." or, better still, "What if I attempted to go back in time with a view to killing my father..." or still better, "...to kill the man whom I am fairly sure is my father..."

For oft-discussed reasons, it is clearly impossible to kill your own father before you were conceived. Therefore, you can say with certainty that if you set out with the intention of going back in time to kill your own father before he had impregnated your mother, you would fail in your task somewhere along the way. Time travel means you know the outcomes of some intentions.

Time travel may or may not be possible. If it is possible, I see no reason for it to be less subject to logic than, say, galaxy formation or rocket flight.

nomuse
2005-Jan-27, 07:33 PM
Hrm. Are you saying causality can not be violated?

Or is it possible to build a logical framework that contains causality violations?



The movies generally lean towards implicit causality -- although things may look as if they are changing, at the end of the movie it is shown that everything --surprise! -- worked out with a terrible neatness to reprise the original history.

Of course, most movies can't resist the last shot of the quarter buried in Tut's tomb or the bullet hole in the armor, or something else that takes everything they just spend an hour and a half saying and tosses it out the window.

However, that isn't the worst problem of movie (and cheap fiction) time travel. As a friend of mine points out, it isn't conservation of causality -- it's conservation of history books. The time traveller can eat, drink, defecate, speak with people, carry materials around....blow up buildings, shoot hundreds of extras dead...as long as they never mess with anything that has a name.

Aka blowing up half of Constantinople is fine with causality, but don't you dare touch Hagia Sophia; History has Heard of It.


I can't think of any of the recent SF by scientifically trained writers that allows simple causality violations. They seem to use mostly closed loops (like "By Hit Bootstraps"), or resort to Many Worlds. And then there's Baxter's "Time Ships," invoking a super-causality to resolve violations inside the "simple" causality of most of the book.

Careless
2005-Jan-27, 07:59 PM
What bugs me about T2 is the apparent lack of reason with which the T-1,000 was attacked. They just kept on shooting it ineffectually when they should have been trying to elctrocute it, throw acid on it, or stuff it into a microwave.
How about tossing the piece of its arm off the car, giving it back to the t-1000? I guess there's a chance you could be tracked with it, but at least try to put it someplace it can't get it back.

Paul Beardsley
2005-Jan-27, 08:39 PM
Responding to nomuse:

It is my belief that causality cannot be violated. In fact it is stronger than that - it's my belief that the very idea of causal violation is without basis.

People have this idea in their heads that if, say, a time traveller went back to 1800, it would be an 1800 that hadn't previously had a visit from a time traveller. Even though the word "previously" has no meaning in this context.

In fact, as soon as we learn that the time traveller arrived safely in 1800, we can say with certainty that the past 205 years of history includes whatever contribution the time traveller made.

I don't see the "conservation of history books" as a problem. If the time traveller visits the middle ages and is armed with a gun, then yes, he can attempt to shoot people. If he attempts to shoot a peasant working in a field, or a very minor knight in armour who happens to be passing, then from the time traveller's point of view, several outcomes are possible. The gun will jam; the gun will fire but the bullet will miss the target; the gun will fire and the bullet will kill the unfortunate knight or peasant. The time traveller does not know which of these possible outcomes will be the actual outcome until he actually pulls the trigger. (And if he kills the knight, then yes, the act will leave a bullet-hole in the armour.)

But if the time traveller attempts to shoot an historical character whose fate is known (e.g. he tries to shoot Abraham Lincoln before 1865) then there will be fewer possible outcomes. The gun will jam, or it will fire but the bullet will miss. Again, he won't know which of these possible outcomes will be the actual one until he pulls the trigger. Indeed, circumstances might even prevent him from being in a position to even try to shoot the former president.

There's nothing magical that distinguishes recorded history from the forgotten stuff of the past. The only difference is that the time traveller knows some endeavours might end in failure, and some endeavours will end in failure.

Doodler
2005-Jan-27, 09:10 PM
As a matter of interest, which films do you care about? (This is addressed to anyone who wants to answer.)

For instance, I couldn't care less if there was a gaping logical hole in a film about Spiderman or The X-Men because I find the premise of these films totally banal and uninteresting and infantile and just plain rubbish.

On the other hand, if a film is very appealing but has a few minor plotholes in it, I am more prepared to either overlook the plothole or else attempt to explain it away.


You're dismissing the whole point of this thread by saying you're either willing to forgive, or simply don't care. Gotta help me with that one.

As for the bolded part, I tried a few times to reply to that, and decided I'd be better off sitting back and gnashing my teeth. Some people liked those movies, in spite of their completely fanstastical premises, but I imagine not everyone keeps that in mind.

Doodler
2005-Jan-27, 09:19 PM
Responding to nomuse:

It is my belief that causality cannot be violated. In fact it is stronger than that - it's my belief that the very idea of causal violation is without basis.

People have this idea in their heads that if, say, a time traveller went back to 1800, it would be an 1800 that hadn't previously had a visit from a time traveller. Even though the word "previously" has no meaning in this context.

In fact, as soon as we learn that the time traveller arrived safely in 1800, we can say with certainty that the past 205 years of history includes whatever contribution the time traveller made.

I don't see the "conservation of history books" as a problem. If the time traveller visits the middle ages and is armed with a gun, then yes, he can attempt to shoot people. If he attempts to shoot a peasant working in a field, or a very minor knight in armour who happens to be passing, then from the time traveller's point of view, several outcomes are possible. The gun will jam; the gun will fire but the bullet will miss the target; the gun will fire and the bullet will kill the unfortunate knight or peasant. The time traveller does not know which of these possible outcomes will be the actual outcome until he actually pulls the trigger. (And if he kills the knight, then yes, the act will leave a bullet-hole in the armour.)

But if the time traveller attempts to shoot an historical character whose fate is known (e.g. he tries to shoot Abraham Lincoln before 1865) then there will be fewer possible outcomes. The gun will jam, or it will fire but the bullet will miss. Again, he won't know which of these possible outcomes will be the actual one until he pulls the trigger. Indeed, circumstances might even prevent him from being in a position to even try to shoot the former president.

There's nothing magical that distinguishes recorded history from the forgotten stuff of the past. The only difference is that the time traveller knows some endeavours might end in failure, and some endeavours will end in failure.


There are other ways of preserving causality in the event of time travel. BttF crudely explored this in the second movie. You go back and kill your grandfather, this creates a split, a parallel time line. In one history, your grandfather has a son/daughter, who in turn has you. In the new history, your grandfather is dead, your parent will never exist, and neither will your future counterpart. In that sense, the paradox never exists. The question then remains, where do you go home to? Are you linked to the new timeline or are you linked to the old one? That's the real trick.

This is the root of a plothole in that series. In the first movie, you could directly affect your past, in the second, you're interference creates a new timeline. No one linked to the old past changed or was at risk, they were only trapped in the new reality. As for Old Biff vanishing, I'd say since he was the nexus of the time change, he was most directly affected by the shift. Kind of a temporal epicenter. The removal of the scene made the movie more consistent with the premise that changing the past this time around didn't shift original future's past, but created a new one.

nomuse
2005-Jan-27, 09:49 PM
Oh, I am quite aware there is nothing magical about recorded history. What I was pointing out is that most movies and a great many books don't seem to know it. At their worst, they seem to think it doesn't matter if Henry the VIII is now a tall, asian, woman from the future, as long as the name is the same and the Holbien portrait can be faked.

My problem is thus; all the while the Time Traveller is attempting and failing to assasinate Lincoln, he is impinging upon that time...being seen by people, adding wear to surfaces; a multitude of tiny changes just because of his presense. Now, the butterfly wing flapping in Burma doesn't always cause a Monsoon in Madagascar -- but some of those changes are going to snowball.

Really, it makes more sense for the universe to either disallow time travel completely, or deal with the potential travellers more efficiently, as in Niven's "Rotating Cylinders..."

Doodler
2005-Jan-27, 10:02 PM
Oh, I am quite aware there is nothing magical about recorded history. What I was pointing out is that most movies and a great many books don't seem to know it. At their worst, they seem to think it doesn't matter if Henry the VIII is now a tall, asian, woman from the future, as long as the name is the same and the Holbien portrait can be faked.

My problem is thus; all the while the Time Traveller is attempting and failing to assasinate Lincoln, he is impinging upon that time...being seen by people, adding wear to surfaces; a multitude of tiny changes just because of his presense. Now, the butterfly wing flapping in Burma doesn't always cause a Monsoon in Madagascar -- but some of those changes are going to snowball.

Really, it makes more sense for the universe to either disallow time travel completely, or deal with the potential travellers more efficiently, as in Niven's "Rotating Cylinders..."

Why not let the changes occur? Why must time be so fragile? Honestly, I'm just curious. I always found it unusual that some minor tweak in one planet's history is thought to cause a paradox that's going to unravel the whole works.

nomuse
2005-Jan-27, 10:36 PM
I just re-read Beardsley's post above. As I understand, the twin ideas here is that time is moderately self-healing; one time traveller makes an impact not really different from any local figure; and that the time traveller is indeed capable of making "changes," but only from his point of view.

Rephrasing Paul for my own illumination, the time traveller will fail to shoot someone he knows wasn't shot, he can shoot someone he knows was shot, and he can shoot or not shoot someone he didn't know was shot. But regardless of what he knows about what is possible, his actions are pre-ordained.

Time machines may not violate causality, but they sure throw a monkey wrench into free will.

Doodler
2005-Jan-27, 10:55 PM
I just re-read Beardsley's post above. As I understand, the twin ideas here is that time is moderately self-healing; one time traveller makes an impact not really different from any local figure; and that the time traveller is indeed capable of making "changes," but only from his point of view.

Rephrasing Paul for my own illumination, the time traveller will fail to shoot someone he knows wasn't shot, he can shoot someone he knows was shot, and he can shoot or not shoot someone he didn't know was shot. But regardless of what he knows about what is possible, his actions are pre-ordained.

Time machines may not violate causality, but they sure throw a monkey wrench into free will.


Sorry, but you're implying some force acting to stop a time traveller from doing anything, when in reality he's doing a lot just by being there. What if he's carrying a future mutation of a virus that the past has no method of fighting? Will some mystical force prevent millions from dying at the hands of a new strain of bird flu that shouldn't exist for another hundred years? Free will is irrelevant, once you have time travel, you've got scads of opportunity to wreak havoc on the timestream without free will entering the equation. Following the same tack but a different current. What if someone goes back to England at the start of the bubonic plague outbreak with a few hundred doses of tetracycline and nips the Black Death in the bud before it blossoms? Will time affect chemistry too?

Interesting thought, but you're treading close to divine intervention to support it.

nomuse
2005-Jan-27, 11:45 PM
Heh. Well, I'm no phycisist -- it doesn't bother me at all to crack causality wide open, to have the time traveller change a past without the slightest influence on their own past, with changes propagating up the time stream in all disorder. I also, as a writer, would prefer to assume that the mainstream of events coheres -- that stepping on one butterfly won't change the future, but wiping out a species might.

A large part of the fun of a time-travel story is to look for seemingly innocuous things that create large changes later on. But here we get away from the moment of the time travel and into the results, the alternate history.

Unfortunately there is a built-in literary problem in alternate history stories. You don't write one without doing a lot of research. Maybe with a pre-existing interest in the period you mean to write about. Problem is, after all your reading about General Lee, how can you NOT put the man in some military position and have the fun of using him -- irregardless of how much you've mucked with the rest of the world around him? So you end up with stories in which Dinosaurs stroll the streets beside humans, but you can still buy a 1957 deSoto with pink upholstery.

Doodler
2005-Jan-28, 12:27 AM
Now I see where you're going, you can change local events, and probably cause a lot of chaos in the the area you visit, but the overall picture still progresses forward. The ripples only propogate so far in the pond, so to speak. Affect the life of someone who had no major contribution to society, and nothing happens to the overall stream. Take out a well known figure, and the world responds accordingly, but the timing of events not directly related to that individual proceed fairly unabated.

nomuse
2005-Jan-28, 05:43 AM
Um, yeah, but remember the old show "Connections," hosted by James Burke? The particular shape and name of a technology, a fashion, a country might come from an unlikely-sounding series of seemingly unrelated elements. The supermarket dependent on the canned food invented for the civil war, etc.

As far as I know current thinking is that most political, social, and even scientific developments come because the time is ready for them; Europe was ready for a war and didn't need an assasinated arch-duke to start it, there was enough hue and cry about church corruption so if Martin Luther hadn't been, someone else would have tacked a few words to a church door, and shutting up Copernicus didn't keep the Earth in the center for very much longer.

But that is far from saying the final result is going to look that familiar.



Jumping back to the causality thing; it isn't that the universe is some sort of malevolent intelligence, acting to protect causality. Rather, it is that when you have ruled out the impossible, what remains, no matter how improbable, is the truth. Causing Abraham Lincoln to not exist is impossible, therefor, the truth will range from the time-travelling assasin's gun misfiring, to him missing the day and not getting to Lincoln until he is at Ford's Theater, to some other person stepping into the stove-pipe hat and beard, to some incredible conspiracy by the Federal Congress to hide the fact that Lincoln is gone.

Paul Beardsley
2005-Jan-28, 07:43 AM
I just re-read Beardsley's post above. As I understand, the twin ideas here is that time is moderately self-healing; one time traveller makes an impact not really different from any local figure; and that the time traveller is indeed capable of making "changes," but only from his point of view.

That's more or less what I said. I'm not sure about the phrase "self-healing" though, because that suggests damage has been done.

The time traveller does indeed affect the people around him, but the effect he has merely contributes towards established history.


Rephrasing Paul for my own illumination, the time traveller will fail to shoot someone he knows wasn't shot, he can shoot someone he knows was shot, and he can shoot or not shoot someone he didn't know was shot. But regardless of what he knows about what is possible, his actions are pre-ordained.

Time machines may not violate causality, but they sure throw a monkey wrench into free will.

That's the other thing I'm trying to move away from.

Free will does not allow us to do what we like. You can't simply say, "I choose to become a major author!" But you can say, "I shall attempt to learn the craft of writing and storytelling. I shall put aside so many hours each week to write. I shall send stories to editors." And so on.

In fact, even that's oversimplified. The exercise of free will is a near-endless series of attempts. Most attempts succeed - attempting to get out of bed in the morning, attempting to drive to work and so on. But the outcome of each attempt is subject to circumstances.

Time travel doesn't restrict free will, but it sometimes gives that impression because it allows us to see the ultimate outcome of a long series of attempts.

I'll address the other posts later. (Edited to add: I'll attempt to address the other posts later.)

Paul Beardsley
2005-Jan-28, 09:41 AM
You're dismissing the whole point of this thread by saying you're either willing to forgive, or simply don't care. Gotta help me with that one.

Well, the ones you don't care about, you don't care about.

Others are perfect, or nearly so, so they don't need justifying. For me, Blade Runner came close - you can watch it specifically to spot inconsistencies or logical lapses, and you'll only find a small number of them, all of them easy to overlook.

But there's a middle category that you like even though you know it's flawed. So you either ignore the flaws, or attempt to justify them. For me, Terminator 2 fits into that category. I was wondering what films fit into other people's middle category.


As for the bolded part, I tried a few times to reply to that, and decided I'd be better off sitting back and gnashing my teeth. Some people liked those movies, in spite of their completely fanstastical premises, but I imagine not everyone keeps that in mind.

No offence was intended. All I'm saying is, I can't abide that kind of film, so it goes into my "don't care" category. Sure, other people like them. My wife does. When Spiderman 2 came out, I had to get a friend to take her to the cinema!

The TV series Goodnight, Sweetheart is my favourite TV series of all time, but if you loathe and detest it and put it in your "don't care" category, that's fine with me!

jofg
2005-Jan-28, 02:39 PM
I can understand the concept of time-travel to the past - events have already occurred so they exist in some osft of time-line. I can even grasp having a time traveller go to the past, then forward again to the future (as long as the future is no further than the point where he/she original travelled back in time) - but how can there be time travel to the future? How could I travel 10 years to the future to witness or experience events that have not yet occurred? And if I can, then that means that all future events have already occurred, so I in reality have no control (or freewill).

Any comments?

Paul Beardsley
2005-Jan-28, 03:16 PM
jofg, the way to travel into the future is to slow down your personal time, so that every minute that passes for you, a year passes for the rest of the world. Wait however many minutes you want (say ten) then get your personal time back to the same rate as the world's time. Hey presto, you're ten years in the future, but you've only aged ten minutes.

This can be done by travelling at near-light speed, or by subjecting yourself to intense gravitational fields. In practical terms it's much harder than I made out in the first paragraph, but the theory is quite simple. Well, a lot simpler than the travel-into-the-past theory!

lti
2005-Jan-29, 08:06 AM
the majority of people here write as if time travel is theoretically possible as opposed to simply a plot device invented by authors or directors to give an entertaining story.

as such many of u seem to be unable to see the woods through the trees so to speak. Paul Beardsley seems to be the only person to touch on the fact that it would be logically impossible to change history without resorting to a plot device such as an alternate timeline.

Others say it is impossible to go to the future but not the past. what logic is there in that statement? When we travel into the past, it is for the people back then as if someone has arrived from the future. Would u also say that it is impossible for some from 1800 to come forward to our time?

Ofcourse einstein's theories of relativity predict we can dilate time and so engineer situations where we can observe the distant future. ofcourse this is a one way trip unless we through a few negatives into the maths.

Reinforcing Beardsley's post, id like to reiterate that following causality it is impossible to change history.
if, say, a time traveller went back to 1800, it would be an 1800 that hadn't previously had a visit from a time traveller. Even though the word "previously" has no meaning in this context.


If a time traveller was trying to asasinate hitler, he would fail because we know that hitler was not asasinated. In fact it isnt a new version where there is a failed asasination atempt, but it is merely the way hostory always took place. the concept of 'changing' time is completely meaningless.



If you could step outside of the reel and look at the previous frames, ie time travel, and alter them, what would happen to the frames in front and behind the one you altered? Nothing, right?
this is also an interesting point to ponder. although it isnt the same as what i have been saying, how could u argue otherwise?

Paul Beardsley
2005-Jan-29, 10:56 AM
Here's another way of looking at it.

Suppose there's a football match between (say) Manchester United and Chelsea. You don't see the game but you learn that the score is 2-0 to Man U. That's all you learn at this stage.

A bit later, someone who recorded the game lends you the recording and you watch it, concentrating on one particular Chelsea player.

The player is performing well. Sometimes he gets very near to the Man U goal. He shoots, and the ball is heading directly for the goal. But the Man U goalie saves it.

And so it goes on. No matter how close Chelsea get to scoring a goal, and no matter how well their goalie performs, the end result it 2-0 to Man U. There is no divine intervention involved to prevent this Chelsea player from scoring, and he is certainly exercising his free will (within the constraints of the rules of football, of course). The result is 2-0 simply because that is how it turned out.

Note, by the way, that the outcome of the football match might seem pre-ordained to the person watching the video, whereas it would not have seemed so to the players involved at the time.

Now, suppose this player had actually visited the future and learnt that the score was 2-0. What could he do to get a different outcome? Make more of an effort, perhaps?

I maintain that causality is conserved, not by some divine preserving force, but simply because there is no logical basis for it to be violated, even if time travellers are involved. This is because:

1. A time traveller's arrival in the past is as much a part of history as any other event taking place at that time.

2. To change an outcome, the time traveller would need to know all the events that contributed to it.

3. The results of the time traveller's own actions are subject to a myriad of external influences, not all of which can be known. Kicking a football in the direction of a goal is one thing; scoring a goal is not necessarily the same thing.

nomuse
2005-Jan-29, 11:49 AM
Heh. I thought I understood. I also thought I was able to write that I understood. Well, my writing was never that clear.

The problem is we don't have language to divorce time from causality, or to stand outside of progression. Language is also emotional; every way outside of mathematics that you describe an event, it will cause an emotional reaction by your reader.

My choice of "ordain" was poor...but how else to put it? Standing outside of time, the events "are." The time traveller was "always" there and always did whatever it is they did. The only one to be discomfitted is the time traveller, as we rarely get so clear an idea of what the consequences of our actions are. Or maybe it is better looked at as a different vision of the future. If I build a wall today, I have only guesswork as to whether it will be standing fifty years from now. If a time-traveller builds a wall, he has had the opportunity to know, exactly, that there will be a wall in such a place fifty years from then.


As I understand it, these questions are closer to the heart of most science fiction than we like to admit. For doesn't FTL travel or communications implicitly introduce the possiblity of causality violation?

Paul Beardsley
2005-Jan-29, 12:48 PM
Heh. I thought I understood. I also thought I was able to write that I understood. Well, my writing was never that clear.

I'm not saying you haven't understood, nomuse. I'm just trying to clarify my views in order to respond to a number of points raised by various people on this thread. It's also becoming clearer in my own mind as we all engage in this discussion.

nomuse
2005-Jan-29, 06:56 PM
Absolutely Paul. Discussing this stuff clarifies for me, too -- and I hope for everyone.

eburacum45
2005-Jan-30, 10:19 AM
The idea of travelling back in time without changing history is kind of difficult to achieve in practice;
the mere appearance of a time traveller in the past introduces a myriad chains of cause and events which may not have been there before. Only in a very few cases could a time traveller go backin time and fit in to the pre-existing flow of events; his or her actions would be very constrained, and he or she would have to operate without freewill.

If you really wanted to change the score of the match you would find out who scored the goals and prevent them from scoring. If you didn't succeed the first time you could go back for another go untill you are the entire Chelsea team, the ref, the linesmen and all the spectators too.
Let's see if Man U win then.

eburacum45
2005-Jan-30, 10:33 AM
And time travel to the future is not only possible, but obligatory.

One way that the universe is supposed to prevent backwards time travel is by the establishment of a Cauchy horizon; if a path opens up in the geometry of space time which would allow violations of causality, then an event horizon is formed, just as impassable (in the wrong direction) as the event horizon around a black hole.

The other way that the universe is supposed to prevent the creation of closed timelike loops is via the virtual particle racetrack: when a time loop is formed, virtual particles find a pathway around the loop and suddenly exist in the same location twice; because this process is achieved in no time at all, the number of such virtual looped particles instantly becomes infinite- causing a massive release of radiation and destroying whatever space-time distortion has allowed the closed timelike loop tp occur. Instantly.

Paul Beardsley
2005-Jan-30, 01:11 PM
The idea of travelling back in time without changing history is kind of difficult to achieve in practice;
the mere appearance of a time traveller in the past introduces a myriad chains of cause and events which may not have been there before.

Before what?

I'm guessing your answer is, "Before the time traveller set out on his journey." If so, my argument is that "before" is meaningless in this context.

I think the problem is, we've been conditioned to think of time as moving, or people moving along time. This is of course an illusion, brought about by the fact that each "frame" of time (to borrow the film analogy) is a development of each previous frame.

Instead of saying, "I was born in 1963 etc," it's better to say, "At 1963 the infant me is born; at 1967 the child me has an accident on a swing; at 1993 the 30 year old me is getting married, and so on.

In keeping with this timeline approach, we can say, at 1800 the 30 year old time traveller arrives; at 1975 the time traveller is born, at 2005 the 30 year old time traveller sets off for 1800. As I see it, there's no point on this timeline that can meaningfully be called "before".


Only in a very few cases could a time traveller go backin time and fit in to the pre-existing flow of events; his or her actions would be very constrained, and he or she would have to operate without freewill.

Without freewill? I don't buy that. "Constrained" inasmuch as his/her actions will be consistent with what is known to have happened, but that still leaves a lot of scope.

It is of course easy to envisage scenarios where one's presence or actions are bound to disrupt causality. But, as I've said, for the situation to come about, a long chain of by-no-means-guaranteed events must be successfully completed. And we know that the chain will break somewhere because we know the actual outcome.


If you really wanted to change the score of the match you would find out who scored the goals and prevent them from scoring. If you didn't succeed the first time you could go back for another go untill you are the entire Chelsea team, the ref, the linesmen and all the spectators too.
Let's see if Man U win then.

If time travel turned out to be that easy, we'd probably discover that the Man U team had their own time machine and are using it to preserve the status quo.

Paul Beardsley
2005-Jan-30, 01:23 PM
And time travel to the future is not only possible, but obligatory.

Are you talking about time dilation here?

I take it you're not talking about "moving into the future at a rate of one second per second" because that's clearly not time travel. It's as meaningless as saying St Paul's Cathedral is moving through London at a rate of one metre per metre.


One way that the universe is supposed to prevent backwards time travel is by the establishment of a Cauchy horizon;
[Snip]


If these theories are correct, then obviously all this musing is academic. My worry, though, is that scientists are looking for ways of ruling out time travel simply because they think time travel will give rise to these paradoxes - in which case, they are in the position of pre-Keplerian astronomers who felt compelled to fudge orbital data because they thought planetary orbits had to be circular.

A Thousand Pardons
2005-Jan-30, 01:34 PM
And time travel to the future is not only possible, but obligatory.

Are you talking about time dilation here?

I take it you're not talking about "moving into the future at a rate of one second per second" because that's clearly not time travel.
I think he is talking about moving into the future, since he mentions it is obligatory. I wouldn't say it is so clear that it is not time travel.

How would you measure time travel then? Against what standard?

Paul Beardsley
2005-Jan-30, 02:26 PM
I think he is talking about moving into the future, since he mentions it is obligatory. I wouldn't say it is so clear that it is not time travel.

Part of my earlier argument was that time doesn't move, nor do we move along it. My newborn self is at 1963, my 20 year old self is at 1983, and so on. No travel is involved - any more than St Paul's is travelling through London. (This is not something I came up with - I first encountered it in a book by Paul Davies in the early 1980s, and I don't think it was original to him.)


How would you measure time travel then? Against what standard?

Personal time against world time. If you're travelling at seven tenths of the speed of light, you could say that for every second you experience, the folks back home are experiencing two seconds.

Fortis
2005-Jan-30, 05:54 PM
How would you measure time travel then? Against what standard?

Personal time against world time. If you're travelling at seven tenths of the speed of light, you could say that for every second you experience, the folks back home are experiencing two seconds.
But if those folks strapped a huge rocket to the earth and set off after you until you were both at rest relative to each other, then would that mean that you were no longer travelling through time, and that your ability to travel through time depends on what other people are doing?

eburacum45
2005-Jan-30, 06:18 PM
If you're travelling at seven tenths of the speed of light, you could say that for every second you experience, the folks back home are experiencing two seconds.

Yes; that is one way of measuring time travel in the forward direction. If you want to visit 2 Million AD, you can set off in a Nearly-As-Fast-As-Light ship to Andromeda, turn round before you get there and come back; or you could buzz around near the event horizon of a supermassive black hole (which would also cause time dilation), or you could wait on Earth (perhaps in frozen sleep); in any event, you will get to 2 million AD(but you won't get back).


...your ability to travel through time depends on what other people are doing?
Yep; that's relativity...


As far as Man U going back in time as well, is concerned- yes, you see that if you have unlimited time travel, causality goes right out the window. The world would be shoulder to shoulder time tourists.

Paul Beardsley
2005-Jan-30, 07:01 PM
But if those folks strapped a huge rocket to the earth and set off after you until you were both at rest relative to each other, then would that mean that you were no longer travelling through time, and that your ability to travel through time depends on what other people are doing?

Yes. Of course, both you and the folks back home (where "back home" is much closer, and much less stationary, than you probably thought when you first set out) are travelling in time relative to the inhabitants of some other world that hasn't had a blimmin' great rocket strapped to it.

And if you strapped rockets to every single object in the universe then you'd be synchronised with the universe once more, assuming they're all moving at the same velocity.

Paul Beardsley
2005-Jan-30, 07:22 PM
As far as Man U going back in time as well, is concerned- yes, you see that if you have unlimited time travel, causality goes right out the window. The world would be shoulder to shoulder time tourists.

Causality doesn't go out the window at all, it just leaves us in the same situation I described early on - the time travellers are still as much a part of the era they're visiting as anyone else living at that time; they would still need to know all the events that contributed to an outcome in order to change that outcome; and the results of each time traveller's action would still be subject to a myriad of external influences - more than ever, in fact, as they would include those of other time travellers.

It's analagous to those polygon things where the number of faces minus the number of edges plus the number of vertices equals some constant. At first sight, you think you only have to draw a random line between two other lines to upset the equation - only to find that no matter how many random lines you throw in, the equation still stands.

Granted, it seems somewhat unlikely that there are time tourists everywhere, which suggests time travel will never be unlimited. But that doesn't mean it's not possible at all.

Humots
2005-Jan-30, 07:49 PM
they would still need to know all the events that contributed to an outcome in order to change that outcome; and the results of each time traveller's action would still be subject to a myriad of external influences

This would hold if the time travellers wanted some specific outcome, but what about a time traveller who just wants to mess things up? He could set off a bomb at some point in history, like the Constitutional Convention, killing dozens of people important to history.

Once we allow time travel, it's hard to see how people could go back in time but somehow be prevented from making a change, no matter what they tried to do or how they tried to do it.


- more than ever, in fact, as they would include those of other time travellers

That's one way. Poul Anderson used that in his novel "The Corridors of Time." Two waring factions in the future, both with time travel. A character suggests trying to prevent an enemy attack before the fact, and the reply is "A superior enemy force would show up to stop us."

Paul Beardsley
2005-Jan-30, 09:32 PM
This would hold if the time travellers wanted some specific outcome, but what about a time traveller who just wants to mess things up? He could set off a bomb at some point in history, like the Constitutional Convention, killing dozens of people important to history.

That's a specific outcome. We know a bomb did not go off during the Constitutional Convention (I assume - I don't know much US history!), therefore an attempt to set off a bomb at that point would fail.

The chain of attempts still applies. You have to obtain the bomb, you have to ensure it doesn't go off prematurely, you have to gain access to a time machine, you have to arrive at the right location, you have to have the opportunity to light the fuse, you have to avoid time travellers who hunt bomb-carrying time travellers for sport, and so on. In other words, a whole bunch of circumstances. You cannot know all the circumstances, but you can know the outcome: the bombing attempt failed.


Once we allow time travel, it's hard to see how people could go back in time but somehow be prevented from making a change, no matter what they tried to do or how they tried to do it.

As I see it, it's not so much that time travellers couldn't make a change; rather, they didn't.

Humots
2005-Jan-30, 09:59 PM
I believe I understand what you mean by didn't.

A time traveller could go back and look through the window while the Constitution was being signed, but if he tried to toss in a hand grenade, something would happen to stop him, because something did happen to stop him.

The situation could be simplified. For example, in In L. Sprague deCamp's story "A Gun for Dinosaur", a man tries to go back in time to shoot someone who didn't get shot. As soon as he tries to do anything that didn't already happen, he gets thrown back to the present. His gun doesn't jam, a dinosaur doesn't eat him.

In another story, deCamp explains why the same time machine can't bring back information from the future. The machine can go to the future, but if it tries to come back with information that would create a difference, the same force prevents the machine from returning.

eburacum45
2005-Jan-31, 06:26 AM
To allow this kind of time travel which does not change history it is neccessary to place severe limits on the freedom of action of the travellers; otherwise every new wave of time travellers would change history to suit themselves.

Time tourism is only one of the problems you would encounter if time travel was possible and easy; worse would be the time refugees, immortal emigrants from the end of time (crunch, rip or heat death, whatever).

They come back to our era (and before) and live their lives into the deep future until the physical conditions of the universe become too uncomfortable and then they come back again. If time travel does not have severe restrictions on its utility the universe instantly fills up with immortal time travellers who already know every detail of history. In fact this sort of mass emigration actually increases the mass of the universe and changes its physical characteristics.

lti
2005-Jan-31, 07:09 AM
there arent waves of time travelers. they allready were there the first time. there is only 1 version of history, not repeats with different characters and diferent events.

the absense of time travelers today would be proof that one can not travel back in time.

A Thousand Pardons
2005-Jan-31, 11:27 AM
I think he is talking about moving into the future, since he mentions it is obligatory. I wouldn't say it is so clear that it is not time travel.

Part of my earlier argument was that time doesn't move, nor do we move along it. My newborn self is at 1963, my 20 year old self is at 1983, and so on. No travel is involved - any more than St Paul's is travelling through London. (This is not something I came up with - I first encountered it in a book by Paul Davies in the early 1980s, and I don't think it was original to him.)
I knew what you were talking about. But look at your example. Your newborn self is at 1963 in a hospital, your 20 year old self is at a pub. They don't move either. They're stationary.

You can't then say that there was no travel involved in getting from the hospital to the pub. Similarly for the time dimension.



How would you measure time travel then? Against what standard?

Personal time against world time. If you're travelling at seven tenths of the speed of light, you could say that for every second you experience, the folks back home are experiencing two seconds.
Sure, but that's all relative. If you take two folks back home, then isn't one of them experiencing one second for every one second--just what you thought eburacum45 meant, but said (http://www.badastronomy.com/phpBB/viewtopic.php?p=407759#407759) could not be true?

Paul Beardsley
2005-Jan-31, 12:10 PM
I knew what you were talking about. But look at your example. Your newborn self is at 1963 in a hospital, your 20 year old self is at a pub. They don't move either. They're stationary.

You can't then say that there was no travel involved in getting from the hospital to the pub. Similarly for the time dimension.
[quote]

There is travel, but not through time. It took me twenty years to travel from a maternity ward in Nottingham to a pub in Portsmouth. (Needless to say this was a very indirect route.)

[quote="A Thousand Pardons"]Sure, but that's all relative.

Yes. Time travel (in the context of time dilation when moving at near-light velocities, for instance) is generally expressed in terms relative to a clock or person who has not been accelerated to near-light velocities.


If you take two folks back home, then isn't one of them experiencing one second for every one second--just what you thought eburacum45 meant, but said (http://www.badastronomy.com/phpBB/viewtopic.php?p=407759#407759) could not be true?

I didn't say it could not be true, I said it did not count as travel. It sometimes feels as if it's travel, sure - especially when our youthful years seem ever further away. But if you think something is travelling, you should be able to say what it's travelling relative to, and at what rate. If we divide out the units of the expression "one second per second" we get 1s/s = 1. I don't know what meaning you'd give that, but to me it sounds like not moving at all.

Paul Beardsley
2005-Jan-31, 02:16 PM
The situation could be simplified. For example, in In L. Sprague deCamp's story "A Gun for Dinosaur", a man tries to go back in time to shoot someone who didn't get shot. As soon as he tries to do anything that didn't already happen, he gets thrown back to the present. His gun doesn't jam, a dinosaur doesn't eat him.

The trouble with this scenario is, we'd have to identify a mechanism that gets time travellers "spat out" in this way. There might be such a mechanism, but it sounds a bit artificial to me.

(It also reminds me of the Morphail effect from Michael Moorcock's Dancers at the End of Time series.)


In another story, deCamp explains why the same time machine can't bring back information from the future. The machine can go to the future, but if it tries to come back with information that would create a difference, the same force prevents the machine from returning.

That's almost indistinguishable from saying time travel into the past is impossible!

eburacum45
2005-Jan-31, 03:26 PM
But all these effects are necessary, if we are to suppose a form of time travel which does not change history.
For example, if you cant change the score of the Chelsea v Manchester match, you simply send a bomb. Or, more peacefully, but just as effectively, perhaps,
a sofa...
(HHGTTG)

"Eddies in the Space-Time Continuum."
"Is he. And this is his sofa, is it?".

To prevent simple random acts of surrealism we must imagine some kind of cosmic censorship principle with respect to time travel, one which allows acts of no consequence but which prevents sofas.

A Thousand Pardons
2005-Jan-31, 03:44 PM
I didn't say it could not be true, I said it did not count as travel. It sometimes feels as if it's travel, sure - especially when our youthful years seem ever further away. But if you think something is travelling, you should be able to say what it's travelling relative to, and at what rate. If we divide out the units of the expression "one second per second" we get 1s/s = 1. I don't know what meaning you'd give that, but to me it sounds like not moving at all.
So, 1 second per 2 seconds sounds like time travel to you, but 1 second per 1 second does not? I don't see much difference.

Paul Beardsley
2005-Jan-31, 09:27 PM
For example, if you cant change the score of the Chelsea v Manchester match, you simply send a bomb.

I've already addressed the sending-back-a-bomb scenario.

Paul Beardsley
2005-Jan-31, 09:46 PM
So, 1 second per 2 seconds sounds like time travel to you, but 1 second per 1 second does not? I don't see much difference.

It's a ratio.

One means your self at 2015 is only five years older than your self at 2005, whereas everybody else is ten years older.

The other means your self at 2015 is as much older as your self at 2005 as everybody else.

I can see how you could argue that that's not actually "travel", it's merely a "stretching" of your timeline. But the upshot is that you can hope to see future years that you'd otherwise not expect to live to see. Which is what most people mean by time travel.

SkepticJ
2005-Jan-31, 10:26 PM
The absense of time travelers today would be proof that one can not travel back in time.


The "absense" of timetravelers today could be explained by them not wanting to reveal themselves. If you said you were a timetraveler you'd be commited unless you could prove it. Much easier to not say anything.
If you were a spy in Russia back in the Cold War would you go walking around saying you were a spy? They could even have cloak suits where we can't see them. Or timetravelers could be small robots that look like houseflies, gnats, ticks, lizards etc. If they are here we don't have to know about it. Like aliens. This is one of the reasons I think alien abduction stories are so stupid, in addition to being a skeptic that demands proof. If aliens have the technology to get here from hundreds, thousands, millions or billions of lightyears away they would have tech so advanced that we couldn't detect them. We wouldn't know they are here. They would also wipe memories if need be, and their tools would be much more advanced than dentist picks. :roll: Active optical camo is already being worked on, stealth for RADAR isn't hard etc. What kind of tech will we have in millions of years, which is the amount of time aliens would have on us.

Humots
2005-Jan-31, 11:57 PM
The trouble with this scenario is, we'd have to identify a mechanism that gets time travellers "spat out" in this way. There might be such a mechanism, but it sounds a bit artificial to me.

I can easily see such a mechanism as being a basic part of whatever principles govern travelling in time. And it's simpler than identifying a mechanism that organizes events so as to prevent a time traveller from changing anything.

For example, I can see something like "You must understand that while in the past, you will be in an unstable state, like a needle balanced on its tip. If you try to change anything significant, the needle falls over."

Rather than "the time equations clearly show that if you try to shoot John Wilkes Booth, every person in the area will suddenly trip and fall on you."


That's almost indistinguishable from saying time travel into the past is impossible!

No, it means that you can't travel to a part of the past where it is too easy to introduce a significant change. You can go back millions of years and leave footprints and dead dinosaurs, but you couldn't go back to 1963 and throw Lee Harvey Oswald out the window.

Someone going to 2100 and simply looking out a window is liable to see something of importance. "Hey! Where is everybody?"

Moose
2005-Feb-01, 12:44 AM
Time travel works if you eliminate the concept of free will. If our quantum particles are the balls in an interdimensional billiards game, then there are no paradoxes. Someone goes back in time and fails to kill JWB because he went back in time and failed to kill JWB. It had to happen because it happened. No more, no less.

Determinism writ very large. :P

Paul Beardsley
2005-Feb-01, 08:24 AM
Time travel works if you eliminate the concept of free will. [Snip]

We've done the free will thing.

Paul Beardsley
2005-Feb-01, 08:52 AM
I can easily see such a mechanism as being a basic part of whatever principles govern travelling in time. And it's simpler than identifying a mechanism that organizes events so as to prevent a time traveller from changing anything.

But time would somehow have to "know" that some acts would change history (and so it has to return the traveller to a place where he can do no harm) whereas other acts wouldn't.

I'm not suggesting there's a "mechanism that organises events". I'm saying that past outcomes are the result of a myriad of circumstances leading up to that outcome - including, in some cases, the contribution of a time traveller.


For example, I can see something like "You must understand that while in the past, you will be in an unstable state, like a needle balanced on its tip. If you try to change anything significant, the needle falls over."

If you've been physically delivered into the past, you're there. Why should your presence be unstable?

Put another way, what if someone from 1864 travels a year into the future, learns of JWB's assassination of Prez Lincoln, then returns to the present. What if he tries to kill JWB? Where will he be spat to?


Rather than "the time equations clearly show that if you try to shoot John Wilkes Booth, every person in the area will suddenly trip and fall on you."

It's more a case of, "Don't try to shoot JWB prior to the assassination. We know that the assassination succeeded, therefore we know that if there were any attempts to avert it, they obviously failed. That includes any attempt you might have made."


No, it means that you can't travel to a part of the past where it is too easy to introduce a significant change. You can go back millions of years and leave footprints and dead dinosaurs, but you couldn't go back to 1963 and throw Lee Harvey Oswald out the window.

Again, time would have to know which is which.


Someone going to 2100 and simply looking out a window is liable to see something of importance. "Hey! Where is everybody?"

What you see is what you get - that's the essence of time travel! Returning to the present, you can say with some authority that at some point in 2100 there will be no people visible from a certain window.

eburacum45
2005-Feb-01, 08:58 AM
The cosmic censorship principle that you seem to be proposing doesn't sound like it would work to me; it appears to be -
you can only travel back in time if you don't change anything.

This cannot be managed on a voluntary basis- the only way to allow inconsequential time travel is for you to go back to perform a set of actions that already exists.
This sort of time travel would only allow a vanishingly small number of time travel events.

Otherwise very time you go back you change an almost infinite number of tiny things- you absorb certain oxygen molecules and certain photons, simply by going back in time you change the mass of the universe; and the effects of chaos theory mean that the universe is changed forever just by the fact of you being there.

if time travel is possible then every person from the future, billions of years of humans, robots and evolved chimpanzees will want to travel back in time to visit certain events; the assassination of Lincoln for instance...
they will all want to go back not once, but as often as they can afford the fare as well; Instantly every historical event has quadrillions of people attempting to observe the action.


The only way to have time travel which does not change the past is to avoid all time travel at all. It is impossible to have such information paradoxes; if relativity is correct then this rules out faster than light travel as well.

Paul Beardsley
2005-Feb-01, 11:20 AM
This is starting to go round in circles. I feel too ill to discuss it much longer.


The cosmic censorship principle that you seem to be proposing doesn't sound like it would work to me; it appears to be -
you can only travel back in time if you don't change anything.

This cannot be managed on a voluntary basis- the only way to allow inconsequential time travel is for you to go back to perform a set of actions that already exists.
This sort of time travel would only allow a vanishingly small number of time travel events.

On the contrary there would be only a few "forbidden" events.


Otherwise very time you go back you change an almost infinite number of tiny things- you absorb certain oxygen molecules and certain photons, simply by going back in time you change the mass of the universe; and the effects of chaos theory mean that the universe is changed forever just by the fact of you being there.

You are speaking as if your arrival in the past is an addition to established history. As if there was an 1800 (say) in which you did not make an appearance; in which you did not absorb those photons or those oxygen molecules. Yes, you'd affect the world around you, but those effects are as much a part of history as the effects of anyone else around in 1800.

I accept, though, that time travel into the past means the mass of the universe will fluctuate.


if time travel is possible then every person from the future, billions of years of humans, robots and evolved chimpanzees will want to travel back in time to visit certain events; the assassination of Lincoln for instance...
they will all want to go back not once, but as often as they can afford the fare as well; Instantly every historical event has quadrillions of people attempting to observe the action.

If travel to absolutely any point in space and time was readily available, then it's difficult to imagine how this problem (christened the Golgotha effect by SF writer Garry Kilworth) can be avoided. Leaving aside the fact that there are only so many seats in Ford's Theatre, of course...

But from what I can gather from the physics involved in time travel, it's always going to be difficult to do. There might even be a natural limit to the number of possible time journeys in a given region.


The only way to have time travel which does not change the past is to avoid all time travel at all. It is impossible to have such information paradoxes; if relativity is correct then this rules out faster than light travel as well.

And it might even be that time travel is completely impossible.

But the point of my argument is, if time travel into the past is, in some circumstances, possible, don't dismiss it just because of the supposed paradoxes and arguments about free will. Most of these can be addressed quite readily; others might be addressable in due course.

A Thousand Pardons
2005-Feb-01, 04:26 PM
So, 1 second per 2 seconds sounds like time travel to you, but 1 second per 1 second does not? I don't see much difference.

It's a ratio.
They're both ratios. Of the same quantities.


One means your self at 2015 is only five years older than your self at 2005, whereas everybody else is ten years older.

The other means your self at 2015 is as much older as your self at 2005 as everybody else.
Right.


I can see how you could argue that that's not actually "travel", it's merely a "stretching" of your timeline.
Actually, I'm not aguing that--your argument is that one is not time travel, the other one is. That seems inconsistent to me.

But the upshot is that you can hope to see future years that you'd otherwise not expect to live to see. Which is what most people mean by time travel.
I've never heard that before. :)

What about seeing future years that I had not been certain of living to see? Why isn't that "time travel"?

Paul Beardsley
2005-Feb-01, 04:43 PM
Actually, I'm not aguing that--your argument is that one is not time travel, the other one is. That seems inconsistent to me.

Okay, imagine you bought a plant. You measure it one month and it's two metres high. You measure it the following month and its height is still two metres. The growth over that period is 2m/2m, which is to say 1. In other words, no growth has taken place.

OTOH, if when you next measure the plant, the height is 4m, then the growth is 4m/2m, which is to say it has doubled in height. Growth has occurred.

Referring to my own timeline again, my newborn self is at 1963, and my 20 year old self is at 1983. There's no time travel involved. However, if my 20 year old self was located anywhere other than 1983, that would be time travel.


What about seeing future years that I had not been certain of living to see? Why isn't that "time travel"?

I think I'll let you sort that one out for yourself. I'm too ill to debate any further.

A Thousand Pardons
2005-Feb-01, 05:22 PM
Okay, imagine you bought a plant. You measure it one month and it's two metres high. You measure it the following month and its height is still two metres. The growth over that period is 2m/2m, which is to say 1. In other words, no growth has taken place.

OTOH, if when you next measure the plant, the height is 4m, then the growth is 4m/2m, which is to say it has doubled in height. Growth has occurred.

Referring to my own timeline again, my newborn self is at 1963, and my 20 year old self is at 1983. There's no time travel involved. However, if my 20 year old self was located anywhere other than 1983, that would be time travel.
What is it you are using in your ratio, in the timeline examples?

If you are using the other people, then that would be akin to using other plants for comparison. Since the other plants would have grown too, the ratio in the second example would be 4m/4m--no growth. So, that's inconsistent, again.

Paul Beardsley
2005-Feb-01, 06:19 PM
Okay, imagine you bought a plant. You measure it one month and it's two metres high. You measure it the following month and its height is still two metres. The growth over that period is 2m/2m, which is to say 1. In other words, no growth has taken place.

OTOH, if when you next measure the plant, the height is 4m, then the growth is 4m/2m, which is to say it has doubled in height. Growth has occurred.

Referring to my own timeline again, my newborn self is at 1963, and my 20 year old self is at 1983. There's no time travel involved. However, if my 20 year old self was located anywhere other than 1983, that would be time travel.
What is it you are using in your ratio, in the timeline examples?

If you are using the other people, then that would be akin to using other plants for comparison. Since the other plants would have grown too, the ratio in the second example would be 4m/4m--no growth. So, that's inconsistent, again.

Whatever. I'm really too tired for this.

A Thousand Pardons
2005-Feb-01, 06:31 PM
Get some rest Paul the future will be here any minute :)

Paul Beardsley
2005-Feb-01, 07:54 PM
Get some rest Paul the future will be here any minute :)

Thanks. If my head doesn't explode from this cold or flu I might even see tomorrow!

Humots
2005-Feb-02, 12:01 AM
But time would somehow have to "know" that some acts would change history (and so it has to return the traveller to a place where he can do no harm) whereas other acts wouldn't.

Time doesn't need to "know" anything. The idea is that paradoxes are not allowed. If you try to do something that would create a vast disturbance in the time stream, you get returned. As long as you don't, you stay.

If you prevent Lincoln's assassination, history would be completely altered and you probably would not even exist. Then you didn't go back, you didn't shoot Booth, Lincoln did die, history didn't get changed, you did go back, etc.


Put another way, what if someone from 1864 travels a year into the future, learns of JWB's assassination of Prez Lincoln, then returns to the present. What if he tries to kill JWB? Where will he be spat to?

The idea is, once he knows this, he can't return to his original present. The time machine would spin its wheels trying to move him.


What you see is what you get - that's the essence of time travel! Returning to the present, you can say with some authority that at some point in 2100 there will be no people visible from a certain window.

I didn't mean that no one happened to be visible. I mean looking out a window and seeing a serious lack of people where people should be. As in seeing a city that has obviously been abandoned for fifty years. Or for a better example, all the signs are in Arabic.

SkepticJ
2005-Feb-02, 12:07 AM
How about time travel only to the future? There's a novel here somewhere--> http://nobeliefs.com/death%26timetravel.htm

Paul Beardsley
2005-Feb-02, 11:17 AM
I've emerged from my sick bed to engage in the sometimes frustrating but often enjoyable debate again. I doubt I'll be here long though.



But time would somehow have to "know" that some acts would change history (and so it has to return the traveller to a place where he can do no harm) whereas other acts wouldn't.

Time doesn't need to "know" anything. The idea is that paradoxes are not allowed. If you try to do something that would create a vast disturbance in the time stream, you get returned. As long as you don't, you stay.

As I probably said, this makes for good drama in fiction (we've mentioned de Camp and Moorcock) but it still feels too artificial.

Another way of explaining the "didn't rather than couldn't" thing, imagine an assassination similar to that of JFK. When the gunman fires, his victim is due east of him - at 90 degrees. Because of the distance, the gunman would have missed if he was aiming at 89 or 91 degrees.

So, to avert the assassination, you have only to nudge the gun by a degree. Make it ten degrees to be sure. So,

assassin's aim + nudge = 90 + 10 = 100. Presto, the victim is saved!

But there are more variables than this. It's a gusty day, the gunsight is not aligned correctly, the gunman is nervous and so on. So we know the outcome but not the contributing variables:

unknown1 + unknown2 + unknown3... + unknownN = 90

Now, if you do get to nudge the gunman (and that's a big if), you are merely contributing to the variables:

unknown1 + nudge + unknown2... + unknownN = 90


I didn't mean that no one happened to be visible. I mean looking out a window and seeing a serious lack of people where people should be. As in seeing a city that has obviously been abandoned for fifty years. Or for a better example, all the signs are in Arabic.

Nice scenario! Thing is, though, what happens when (if) you return to your own time? It's one thing to know that there are Arabic signs in a city, but how can that knowledge enable you to avert it? If you warn the government, and they take you seriously, they might well take the very action that will increase the likelihood of bringing this future about. In which case there's no paradox, so time doesn't spit you back to 2100. Similarly, if you return home and choose not to mention it. But what if you return home, mention it, and the government take action that actually averts this future? Do you get spat out just before you mention it? In other words, what is the deciding point?

eburacum45
2005-Feb-04, 03:48 PM
One way of looking at it is sum-over-histories.
You could study history, and acquaint yourself with the sequence of events;
then you go back in time, and act however you want; but only those actions which lead to the known final state of history as it existed will have consequences- if you manage to change history, this means that you did not go back in time in the first place and so that particular timeline, or chain of causality if you like, simply ceases to exist.

So you are left with the illusion of free will, but no real freedom of action.

In fact there might be a number of ways that could result in the final state of 'known' or observed history, that state that existed before the time traveller set off; so the time traveller could act in a number of different ways, and a number of different chains of causality could occur; but as long as they all end up in the same final state they would all be permitted. These different timelines would converege upon the final state, and the final state would be indistinguishable.
Or several different outcomes may yet be possible without changing known history;
For instance you might go back in time to find out the identity of Jack the Ripper; as there are many candidates for the perpetrator of the crime, it could be that any of them is guilty,
and the time traveller would select one at random from all the available candidates, crystallising history rather than actually changing it.

Humots
2005-Feb-05, 02:22 AM
Nice scenario! Thing is, though, what happens when (if) you return to your own time? It's one thing to know that there are Arabic signs in a city, but how can that knowledge enable you to avert it? If you warn the government, and they take you seriously

It's not a given that I'm some lone explorer. My trip to the future could be a government experiment. They're eager to hear about what I saw, and to go over it in depth.


they might well take the very action that will increase the likelihood of bringing this future about.

Does this mean "the future is destined to happen and nothing, not even foreknowledge, can change it; in fact it may even make it happen"? If not, that's a reason never to try to stop anything from happening, because trying might cause it.


Similarly, if you return home and choose not to mention it. But what if you return home, mention it, and the government take action that actually averts this future? Do you get spat out just before you mention it? In other words, what is the deciding point?

The idea is if there is a high enough probability that I will mention it and the government will succeed in averting it, I can't come back. There doesn't have to be a deciding point. Or if free will of some kind is involved, then yes, I might get spat out just when I make up my mind to tell.

Here's some other possibilities. I find out that a well-known drug can cure AIDS. Or I discover the identity of a serial killer who has several victims to go. Or I learn that a major disaster will be caused by a simple, easily-prevented equipment failure.

Paul Beardsley
2005-Feb-05, 11:19 AM
Does this mean "the future is destined to happen and nothing, not even foreknowledge, can change it; in fact it may even make it happen"? If not, that's a reason never to try to stop anything from happening, because trying might cause it.

As I see it, that's the only model that makes sense. As I indicated in my last post, an event that is known to have happened is an expression on the right hand side of an equals sign; the events that contribute towards this known event happening are all on the left hand side. They include other known events, and unknown events (such as wind direction, unpredictable moods of people involved, actions of various time travellers and so on).

If someone precious to you is killed, and you get the chance to go back in time, then yes, you are running the risk of putting yourself into the left hand side of the equation - which is to say you might discover that you contributed towards the person's death.

Because there are so many unknowns on the left side of the equation, there is no need to invoke a spitting-out mechanism in order to conserve causality.


Here's some other possibilities. I find out that a well-known drug can cure AIDS. Or I discover the identity of a serial killer who has several victims to go. Or I learn that a major disaster will be caused by a simple, easily-prevented equipment failure.

It's easy to come up with scenarios that seemingly lead to changing history. As I see it, that simply means they are unlikely to come about. Or if they do, they will rely on a chain of events.

In the serial killer case, the chain of events is, You discover killer's identity AND you get access to a time machine AND you successfully arrive at a convenient location before all the victims have been killed AND you get the police to take you seriously... A single break in this chain means your plan will fail. And since we know the outcome is that five (or whatever) people are going to die, then you know the chain WILL break.

A Thousand Pardons
2005-Feb-05, 11:32 AM
It's easy to come up with scenarios that seemingly lead to changing history.
We have a bit of a skewed perception of time, anyway. I've pointed out before, that there is a conversion factor between time and space--c. To properly compare distance with time, you have to multiply time by c. So, if you want to "travel" a distance of one second, that's the equivalent of 300,000 kilometers--most of the distance to the moon. Takes some effort, even if you're not going up to the moon.

Humots
2005-Feb-05, 07:24 PM
In the serial killer case, the chain of events is, You discover killer's identity AND you get access to a time machine AND you successfully arrive at a convenient location before all the victims have been killed AND you get the police to take you seriously... A single break in this chain means your plan will fail. And since we know the outcome is that five (or whatever) people are going to die, then you know the chain WILL break.

Nope. The chain of events is I have access to a time machine and I go into the future with the government's backing and I find out among other things that a serial killer is John Smith and that he's going to kill several more people before he's caught. When I come back, I tell the police about John Smith with the government vouching for me, and they look for proof, haul him in for questioning, warn the future victims, etc.


As I see it, that's the only model that makes sense.

Here's another hypothetical case. This is taken from the novel "The Quincunx of Time" by James Blish. He does an interesting take on the idea of foreknowledge.

In the novel, a faster-than-light (in fact, instantaneous) communications device has been invented, and is in limited use. A government security officer is receiving information from someone who has an uncanny knowledge of future events.

The informant has access to a prototype of the communications device and has made an interesting discovery: it can receive messages that will be sent in the future. She finds herself hearing future messages of all kinds, including one addressed to her by her future self, instructing her to take the actions she has taken. This includes eventually telling the security officer all of the facts, and then using the communicator in his office to send the message she is hearing. Her opinion is that all of this is destined to happen, so all she can do is to rationalize that all of her actions are correct and moral (which they are, if a bit complex).

However, the security officer's science advisor (who invented the communicator) points out that they can effectively mess things up by not letting her use the office communicator to send the message. She can still send the message with her own communicator, but then a significant part of the message will be false. This means that the information they are receiving is only potentially true. The foretold events have to be made to happen.

My question is, what if a person receives knowledge of a future event of a sort that requires his active, willing cooperation over a long period of time in order to come true? And I do mean willing. No blackmail, no death threats, and no disaster if it doesn't happen. What if he balks?

Paul Beardsley
2005-Feb-05, 09:23 PM
Nope. The chain of events is I have access to a time machine and I go into the future with the government's backing and I find out among other things that a serial killer is John Smith and that he's going to kill several more people before he's caught. When I come back, I tell the police about John Smith with the government vouching for me, and they look for proof, haul him in for questioning, warn the future victims, etc.

It's still a chain of events that add up to an intended outcome which is incompatible with the actual outcome. So once again we can be sure that it will break at some point.

The moment you acquire the identity of the serial killer, you know that someone has lied to you about the identity, or you'll have an accident on your way back to the present, or John Smith turns out to be in partnership with someone who agreed he'll finish the job if temporal police intervene... (That's assuming the chain doesn't break before you get access to the time machine, AND that you get the killer's ID.)

Re "The Quincunx of Time" idea:


My question is, what if a person receives knowledge of a future event of a sort that requires his active, willing cooperation over a long period of time in order to come true? And I do mean willing. No blackmail, no death threats, and no disaster if it doesn't happen. What if he balks?

It reminds me of the Young's Slits experiment used for single electrons or photons. The quality of the photon detector actually affects the experiment.

I'll give more thought to the Blish idea in due course. (I'm feeling a little less ill now, thank you for asking!)

Someone mentioned sum-over-histories here earlier, and on the BABBling board someone posited the idea of a time machine sending back information, such as, you're going to die tomorrow in a train crash. The question was raised, so can't you just stay in bed instead of catching the train?

The obvious response to this is, the "prophecy" of the person's death in a train crash was sent back to the person after they'd died in a train crash. So their death in the train crash occurred after they'd a) got on a train and b) had already received warning of their death on said train. Which means they either a) decided to take their chances, and died as predicted, or b) avoided the train, in which case they never would have had the warning.

Which suggests that the person raising the hypothetical situation was thinking of the prediction as a contingent possibility, and not the ultimate outcome.

As I see it, if you ever get an actual view of the future, it's the final deal - the one that's going to come about after you've done all the, "Oh no, I'll do anything to avert that!" nonsense.

So you wouldn't get a die-on-the-train prophecy - unless you were the sort of person who'd get on the train anyway. ("I'm not going to let some namby-pamby guaranteed prediction put me off getting on that train - I'm needed at work!") The timeline would know that a) you normally catch the train and b) you'd avoid catching the train if you knew it was going to crash. So it would show you the actual future - one in which you catch the bus - and you'd think, "It's not like me to catch the bus. But there must be a good reason why I do." And so you do.

eburacum45
2005-Feb-06, 10:31 AM
I think I can see the distant glimmer of a mechanism here;

You live in 2030, say, and learn about the history of the period you are going to visit, and go back in time to 2005 like the Meddling Monk fully prepared to change history; when you get there you act in what ever way you like, but any action you take that changes history significantly causes a paradox so that timeline disappears.

Only that timeline survives which has a chain of events which leads to the state of history that existed in 2030 before you left.
So you can make as many choices as you like, but if you make the wrong one you disappear.

There could actually be a large, perhaps infinite set of correct paths; but this set will be smaller than the set of incorrect paths.

Alternately the alternate timelines created could continue to exist, but have no influence on, or communication with, the version of 2030 that you set off from. I have to say I tend to favour this interpretation myself.

Paul Beardsley
2005-Feb-06, 03:33 PM
I think I can see the distant glimmer of a mechanism here;

I've read your post twice (and the earlier one) but I'm still not clear what you're driving at. Are you saying there are infinite timelines? Or that more than one past can lead to a single present?

Not that I'm too worried about the Meddling Monk changing history - this is a man who loses his wristwatch in 1066, and requires a pull-down blackboard to remind him to wipe out Harald Hadrada's Viking fleet!

eburacum45
2005-Feb-06, 04:02 PM
I am sorry about this thread hijack, by the way; time travel should have been a separate thread, but so it goes.


Are you saying there are infinite timelines? Or that more than one past can lead to a single present?

I would say both are possible; but if the sort of time travel we are discussing does not change history, then the actions of the time traveller are limited to those which result in the known state of history when he or she set off.
It is quite possible that the time traveller could act in a large number of different ways, and all of them converge on a single final state. This is similar to the sum-over-histories concept in quantum physics, which explains how a single particle can interfere with itself; the particle takes all possible paths.
to arrive at a particular state in history, the past can have taken many forms, all of which are true, and all of which converge on a single moment in time- the moment of observation.

Humots
2005-Feb-06, 09:50 PM
As I see it, if you ever get an actual view of the future, it's the final deal - the one that's going to come about after you've done all the, "Oh no, I'll do anything to avert that!" nonsense.

So you wouldn't get a die-on-the-train prophecy - unless you were the sort of person who'd get on the train anyway. ("I'm not going to let some namby-pamby guaranteed prediction put me off getting on that train - I'm needed at work!")

Based on the view you've presented, everything from the beginning to the end of time is fixed and immutable. Then time travel is really of no use. You can't change the past, you can't get information from the future unless you aren't going to act on it. So why bother?

The idea that a specific mechanism such as presented in de Camp's story prevents changing the past or getting information from the future preserves freedom. Events are not rigidly determined, you are just blocked from obtaining certain knowledge.

I realize that disliking the consequences of an idea is not in any way disproof. But to me, the idea that time is of necessity fixed from beginning to end is an extraordinary claim requiring extraordinary proof.

Also, the true situation may be beyond our understanding. In the Blish story I mentioned, the final decision was to make all the events of the future reported by the communicator happen. Abd the reported events were of disasters prevented and wars averted. The messages never contained the date of a death, because the people sending them had a strict rule that such dates were never mentioned. The conclusion was that some kind of free will was operating to make good choices, but it was operating beyond individuals.

Paul Beardsley
2005-Feb-07, 08:21 AM
Based on the view you've presented, everything from the beginning to the end of time is fixed and immutable. Then time travel is really of no use. You can't change the past, you can't get information from the future unless you aren't going to act on it. So why bother?

Is this really how my view looks?

I'm not saying everything from the beginning to the end of time is fixed and immutable. What I am saying is that nothing that has been done can be undone.


The idea that a specific mechanism such as presented in de Camp's story prevents changing the past or getting information from the future preserves freedom. Events are not rigidly determined, you are just blocked from obtaining certain knowledge.

I don't follow this reasoning at all. According to my model, attempts to undo established events simply won't succeed. There is no contrived mechanism involved.

As far as we can see, there is nothing about the working of time that suggests time has a way of spitting people into the future (or blocking them from the past if they're planning on doing temporal mischief). Lots of people have tried to do things that didn't actually come to fruition - why treat time travellers differently?


I realize that disliking the consequences of an idea is not in any way disproof. But to me, the idea that time is of necessity fixed from beginning to end is an extraordinary claim requiring extraordinary proof.

Probably. But as it's not what I said, I feel no compulsion to provide the extraordinary proof.

Humots
2005-Feb-07, 11:58 PM
We've probably beaten this to death, but how about one last time. The last word is yours.


I'm not saying everything from the beginning to the end of time is fixed and immutable. What I am saying is that nothing that has been done can be undone.

And nothing happening in the future can be prevented, foreknowledge or no. That sounds pretty fixed and immutable to me.


I don't follow this reasoning at all. According to my model, attempts to undo established events simply won't succeed. There is no contrived mechanism involved.

But if they don't succeed, why not? Saying that the attempts won't succeed "because they didn't" doesn't cut it for me.


As far as we can see, there is nothing about the working of time that suggests time has a way of spitting people into the future (or blocking them from the past if they're planning on doing temporal mischief). Lots of people have tried to do things that didn't actually come to fruition - why treat time travellers differently?

Spitting people is just a possible mechanism. The intent is to answer the question I asked above: if attempts to change or prevent things do not succeed, is there a common reason based on the nature of time travel that explains why?

We don't know the working of time, so we don't know how time travel would work, or what its limits would be.

Lots of people have tried to do things and succeeded. Time travellers could try many times.

For me, the bottom line is: if time travel exists, then it is valid to ask if events can be changed or prevented. Most of the serious arguments I have read do not say "Time Travel is possible, but you couldn't change or prevent anything"; they say "Time Travel is impossible because if it existed, you could create paradoxes by changing things."

I can believe that changes to the past are not possible, but to say "you can't because you didn't" does not tell me why. And I want to know.

SkepticJ
2005-Feb-08, 12:21 AM
And nothing happening in the future can be prevented, foreknowledge or no. That sounds pretty fixed and immutable to me.

But the future hasn't happened yet. I can choose to buy a car and get a lemon by accident. But a me from the future couldn't come back and tell me not to buy that car because if I didn't then the future me would have no reason to come back to tell me to not buy said car. A future me can't intentionally keep me from typing this message because if I stop me then I have no reason to come back to stop me. Get it? You can't change the past unless alternate timelines can break off. You can determine the future and present because it's not fixed yet, once an event happens though you can't change the fact it happened. Take heating a sealed container of water for example. You heat the water to just below boiling then turn the stove off. The water loses heat to the room thus cooling off. The water is back to like it was before, at room temp. But the fact that it was heated before it cooled off can't be changed.

Gillianren
2005-Feb-08, 08:12 PM
exactly. it's not that you can't change the future; clearly, we can and do all the time. it's that you don't know what causes a future, so you can't avoid it. as far as travel to the past is concerned, the past is static. it happened. so your future self can't change the present, because it's your future self's past.

I don't know who brought up the plague example (which was badly thought out; the earliest outbreaks of plague known were in Greece over 2000 years ago), but it wouldn't work, because we know that a third of the population of Europe died. it already happened. your vials could get broken; your test subjects could be allergic. something would happen so that the Black Death spread over Europe (predominantly starting in the 13th Century, w/the last outbreak in England in 1665), no matter what you did.

Paul Beardsley
2005-Feb-09, 08:50 PM
We've probably beaten this to death, but how about one last time.

There are other points for the making.


The last word is yours.

That would be the day! :)


And nothing happening in the future can be prevented, foreknowledge or no. That sounds pretty fixed and immutable to me.

As others have suggested, from our point of view the future is up to grabs. You, and I, and everyone who lives after this moment will try to do certain things, and some will come to pass, and some won't, and still other things will occur due to accidents, forces of nature and so on.

But from the point of view of someone in the future after a specific event, that event is fixed. To them, it's a past event. The people of the past have exercised their free will, and the results of that past exercise in free will are there to see.


For me, the bottom line is: if time travel exists, then it is valid to ask if events can be changed or prevented. Most of the serious arguments I have read do not say "Time Travel is possible, but you couldn't change or prevent anything"; they say "Time Travel is impossible because if it existed, you could create paradoxes by changing things."

This is the crux of what I'm trying to get past. Time travel might be impossible, but that's not how it's looking at the moment; more to the point, I do not buy the argument that seems to say, "Well, time travel has to be impossible because if it was possible there'd be some difficult stuff to deal with." Indeed, not every serious article dismisses it like this; J. Richard Gott's Time Travel In Einstein's Universe is worth checking out.


I can believe that changes to the past are not possible, but to say "you can't because you didn't" does not tell me why. And I want to know.

Because your presence in the past is as much a part of the past as anything else in the past. You might as well say, "Why can't Napoleon win the battle of Waterloo?"

But to come at it from another angle...

The model I advocate can clearly apply to some situations. A time traveller goes into the past with the specific intention of changing history, but while in the past they fall asleep at a crucial moment, or their gun jams, or they end up doing something to cause the very thing they sought to prevent.

So it can apply to some situations. But the important thing is, it can be envisaged.

The other scenario - that of changing history - can not be envisaged. Yeah yeah, we all think we can imagine scenarios where we assassinate a tyrant before he's risen to power. But if you try to think it through, you run into problems even before you get to the paradoxes.

Let's suppose, in 2011, a bloke called Steven Jenkins comes to power. Over the course of several decades he becomes a tyrant. Then in 2050, a 30 year old woman called Sally Gatiss travels back to 2010 to assassinate him.

Now, according to my model, she must fail. The world's timeline looks like this:

Pre-2010, various stuff happens.
2010, 30 year old Sally Gatiss arrives from the future. She attempts, unsuccessfully, to kill Steven Jenkins.
2011, Steven Jenkins comes to power.
2020, Sally Gatiss is born.
2050, Sally Gatiss sets out on her assassination mission.
Post-2050, various other stuff happens.

Okay, so let's suppose Sally has gathered so much material on the past fifty years, and is so skilled with a sniper rifle, that her mission is bound to succeed.

How do we then present the timeline? Perhaps we can have two entries for 2011 - "originally Steven Jenkins came to power at this point, but this time round he simply rots in his grave". But what does "originally" and "this time" mean? When, from the world's point of view, did things change? Point to somewhere on the timeline where it changed! Done that? You can't, can you? Even granting Sally her own timeline, you can't point at a place on her timeline where things change. Change must come with time, or something. But when people talk of changing a past event, they are (probably unconsciously) inventing a non-existent new dimension of time - the time during which time changes. You hear nonsense-talk about, "Well, that would have happened before the time traveller changed history." What does it mean???

As I say, that's before you even get to the paradoxes - the place later on in the timeline where Steven Jenkins has been long dead and so Sally Gatiss has no motive for going back to kill him. In other words, the changing-the-past scenario cannot be envisaged.

Perhaps time travel, if it can happen at all, only happens occasionally. Maybe you don't have time to prepare, or you can't know your destination. In which case, it's easy to imagine that you'll arrive somewhere where you simply don't know enough to make changes. But what if it's not so constrained? Suppose Sally Gatiss can go back a second time and have another go?

Well, it might be that the first time Sally had her sniper gun aimed carefully at Steven Jenkins. She aimed, she fired. And somehow she missed. So after reporting back to her resistance leader in 2050, and getting a more accurate gun, she goes back to the same day in 2010 for another go. She installs herself in a different vantage point but shoots at the same time. And again she misses.

After some head-scratching, she realises what happened: the bullets from the first and second attempt collided in midair just before they hit Steven Jenkins.

Again, this scenario - unlikely as it might sound - can be envisaged. The alternatives, where (say) the second attempt succeeded, cannot be. Because if Sally missed the first time, but hit the second, what did Sally see the first time? Did she shoot, and miss, but see Steven die? If so, why did she make the second attempt? And when did it change from Steven not dying to Steven dying? Where on the timeline did this happen?

Since we can envisage the conservation-of-causality model for very simple instances, and for slightly more complicated instances, it seems reasonable to me that this sort of scenario might apply for complicated, multiple trip situations.


Spitting people is just a possible mechanism.

It's not a mechanism, it's a solution without a cause. Just like the "if you go into the past you become invisible" or "a new timeline splits off". Yes, it sorts your problems out, but there's no reason to suppose it will happen.

eburacum45
2005-Feb-09, 10:03 PM
There is a name for your theory of time travel; the Novikov consistency conjecture (a.k.a the principle of self-consistency).
from here (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle)

The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture, is a principle developed by Dr. Igor D. Novikov to solve the problem of paradoxes in time travel.

Stated simply, the Novikov consistency principle says that if an event exists that could give rise to a paradox, then the probability of that event happening is zero. Rather than consider the usual models for such a paradox, such as the grandfather paradox in which a time-traveller kills his own grandfather before he ever meets his grandmother, Novikov used a mechanistic model which was more amenable to mathematics; a billiard ball being fired into a wormhole in such a way that it would go back in time and collide with its earlier self, thereby knocking it off course and preventing it from entering the wormhole in the first place.

Novikov found that there were many trajectories that could result from the same initial conditions. For example, the billiard ball could knock itself only slightly astray, resulting in it going into the past slightly off course, which winds up causing it to knock its past self only slightly astray; this "sequence" of events (actually a causal loop) is completely consistent and does not result in a paradox. Novikov found that the probability of such consistent events was nonzero, and the probability of inconsistent events was zero, so no matter what a time traveller might try to do he will always end up accomplishing consistent non-paradoxical actions.

---------snip-------------------
The Novikov consistency principle assumes certain conditions about what sort of time travel is possible. Specifically, it assumes counterfactual definiteness which is the assertion that there is only one timeline and that multiple alternate timelines do not exist or are not accessible.

Humots
2005-Feb-10, 12:14 AM
There is a name for your theory of time travel; the Novikov consistency conjecture (a.k.a the principle of self-consistency).
from here (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle)

Further on, under Chronology Protection Conjecture:
---------snip-------------------

However, the ideas of the chronology protection conjecture are completely serious. Many attempts to generate plausible scenarios for closed timelike curves have been suggested, and all seem either implausible, or contradict other principles of physical law, or appear to be contradicted by experimental observations. The question then arises: is this apparent prohibition a global constraint of physics, in the same way as a conservation law, or is it a series of accidental coincidences?


Aha! "A global constraint of physics" is precisely the kind of prohibition that I have been talking about.

eburacum45
2005-Feb-10, 01:04 AM
My anti-time travel rant;
http://www.orionsarm.com/intro/WhyNoTimeTravel.html

Paul Beardsley
2005-Feb-10, 09:06 PM
eburacum45:

Thank you for the Novikov link. I've been trying for longer than I can remember trying to track that down. Trouble is, without knowing Novikov's name, it ain't easy.

As to the rant, though - the content is exactly the stuff that we have been challenging over the course of this hijacked thread. We have

whole galaxies of material particles will begin to exist in space
time reference that did not have them before
If the Novikov conjecture is true (and it's the only one that's remotely credible) there's no question of time travellers arriving in locations that they weren't in before. If there is a location in space-time that is known to not have been visited, then a time traveller's visit to the location is a zero-probability event.

the collapse will get closer to the present day, until it eventually happened yesterday and we will cease to exist.
Where does this "eventually" come from? This is that total-figment-of-the-imagination-plucked-from-the-air-meta-time-thingie that people unthinkingly use whenever they try to argue that history is prone to changes by time travellers. "Eventually" suggests a longish period of time - so whereabouts on the timeline does this transition take place? Between what dates does it change from present day to yesterday?

And really, how many time travellers would it take to compare to the mass of an average moon, let alone something big enough to accelerate the collapse of the universe?

Finally, Azimov's name is spelled Asimov. I'm not usually so picky, but when you appeal to authority, you should get the authority's name right. :)

eburacum45
2005-Feb-11, 09:58 AM
Oh yes, there are quite a few spelling mistakes on the OA site; we are gradually working through them...
the massive time travellers are actually a parable; they are representative of the acausal particles that are thought to accompany closed timelike loops. Without some sort of moderation these particles- which appear instantly- would turn all time machines into singularities or supernovae.

If time travel changes history, then there has to be more than one state of history. Therefore these different states have to be separate one from another; they do not however appear to be separated by physical distance, but superimposed; closely related timelines interact as can be seen in the twin slit experiment. One theory is that every random oscillation of an atom, every random creation of a virtual particle pair, greates a new timeline. This suggests that there is a new timeline for every cubic planck length of space multiplied by the age of the universe in planck lengths of time;
a number so large that it can barely be written down using exponentials.

This idea does not appeal to cosmologists;they wonder where the energy would come from to create these additional universes. So the Novikov conjecture seems tempting. However the predeterminism of this concept seems at odds with the Uncertainty Principle; if you already know the outcome of a process, then the Uncertainty Principle cannot apply to time travelling particles.
The four main possibilities of time travel are these (from Visser,1995);
The Radical Rewrite conjecture; this uses something called non-Hausdorf manifolds, and leads to multiple timelines.
The Novikov conjecture - allows closed timelike curves, forbids inconsistencies.
The Chronological Protection conjecture- this allows space-time distortions such as wormholes (which have the potential for becoming closed timelike curves) but they collapse or are otherwise blocked when CTC's develop
The 'boring physics conjecture'; all forms of traversible space time distortion ae forbidden.

So you pays your money and you takes your choice.

ToSeek
2005-Feb-11, 07:24 PM
This suggests that there is a new timeline for every cubic planck length of space multiplied by the age of the universe in planck lengths of time;
a number so large that it can barely be written down using exponentials.


No sweat:

(((28 billion light years)^3) / ((1.6 * (10^-35) meters)^3)) * ((13.7 billion years) / ((10^-43) seconds)) = 1.96189421 10^244