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g99
2002-Jul-25, 10:33 PM
What is gravity? Is it a particle? A Wave? something of both? Or something unlike anything else?

Also On ships like on Star Trek and on Star wars, would not making an artificaial gravity field equal to earth really screw up the earths orbit and oceans? Would not a gravitational object coming up next to earth pose a serous threat to it? Also how would the moon be affected? Makes you think that making a artificail grav generatior a bad thing. Hmmmm...

_________________
"The chickens is coming!!!"
"Watch out for falling coconuts!!"
"If you are on a train going the speed of light and you fall forward flat on your face, was your nose travelling faster than the speed of light?"

<font size=-1>[ This Message was edited by: g99 on 2002-07-25 18:34 ]</font>

Silas
2002-Jul-25, 11:00 PM
What is is, I dunno...

But if we could make artificial gravity, I don't think it would be a problem. Ideally, it would be just another form of "elevator," useful to lift heavy things from one height to another.

But...that's science fiction at this point; nobody really knows...

Silas

GrapesOfWrath
2002-Jul-26, 02:58 AM
If what we perceive as gravity is just a warp in space, then a gravity "generator" (as opposed to a gravity source, like the moon) might just warp the space below the spaceship and unwarp it above it--its affect would only be felt within the ship, and wouldn't disrupt the planetary field at all.

Or, we could wear gravity boots.

Peter B
2002-Jul-26, 03:11 AM
g99

It's worth remembering that the reason spaceships in sci fi series always seem to have artificial gravity is a matter of production cost. It's a heck of a lot cheaper to have people walking just like they do here on Earth than to go to the expense of making them float in zero G or bounce in low G.

I'm sure that researchers into artificial gravity don't rely on sci fi shows for inspiration.

<font size=-1>[ This Message was edited by: Peter B on 2002-07-25 23:12 ]</font>

g99
2002-Jul-26, 03:50 AM
yah i know, I love the famous if there's air there is gravity thing that is popular in Sci-Fi. But is there a way to create a antigravity thingy (wave, particle, or something) and shoot it at the gravity sorce to cancel our the gravity? I am not an expert in physics (by far), but i do know that when you send our a sound wave and a opposing sound wave of the exact same frequency and wavelength, but opposite they will cancel eachother out. The same with mater and anti-matter.

Wouldn't that be cool? Have Anti-grav rec rooms where you can fly about in your pleasure (or do naughtier stuff with your significant other). Another point is, if we do create a anti-grav room on earth would that disrupt the grav field around the room? Also could we use this grav feilds to power a ship? Have a lesser gravity behind and greater gravity in front? A gravity drive...


_________________
"The chickens is coming!!!"
"Watch out for falling coconuts!!"
"If you are on a train going the speed of light and you fall forward flat on your face, was your nose travelling faster than the speed of light?"

<font size=-1>[ This Message was edited by: g99 on 2002-07-25 23:51 ]</font>

roidspop
2002-Jul-26, 04:53 AM
The best antigravity thingy I know of is to stop resisting it. Just fall. As long as you're falling freely, no weight. For skydivers, this doesn't last long...air drag builds up until at about 120 mph (straight down), drag equals a big, fat air mattress...no more weightlessness. For astronauts...no air drag; no weight indefinitely...the perpetual fall. Aieee. For aircraft, engines can overcome drag, so you can stretch out weightlessness during a plunge to about 30 seconds. For around $5K, you buy a bunch of freefall time...the Russians will fly you on repeated "zero-gee parabolas" in a big cargo plane. It's not the Vomit Comet...the Splurtnik maybe?

But there's some stuff going on with what might turn out to be something very much like real AG. A physicist named Podkletnov claims to have produced what amounts to antigravity above a spinning superconducting magnet. NASA has tried to reproduce these results; I believe they're still working on it. Another physicist named Ning (?) is working on what might be a more efficient version of the same sort of thing. I'm crossing my fingers that we might be seeing the end of rocketry and the beginning of true spaceflight. And no thanks; I really don't need any shoreline property in Atlantis.

Wiley
2002-Jul-26, 05:04 PM
On 2002-07-26 00:53, roidspop wrote:
The best antigravity thingy I know of is to stop resisting it. Just fall.

It does help if you miss the ground. /phpBB/images/smiles/icon_smile.gif
(Tips hat to Douglas Adams.)



But there's some stuff going on with what might turn out to be something very much like real AG. A physicist named Podkletnov claims to have produced what amounts to antigravity above a spinning superconducting magnet. NASA has tried to reproduce these results; I believe they're still working on it. Another physicist named Ning (?) is working on what might be a more efficient version of the same sort of thing. I'm crossing my fingers that we might be seeing the end of rocketry and the beginning of true spaceflight. And no thanks; I really don't need any shoreline property in Atlantis.


The physicist's name is Ning Li (for more info see the space.com article (http://www.space.com/businesstechnology/technology/anti_grav_000928.html)). However I would not hold your breath for an antigravity shield. I suspect this a Pascal's wager on NASA part, but I would've prefered the $2 million already boondoggled to go exploration of Pluto or something similar. The dissenting view is explained in Scientific American's Ask the Experts (http://www.sciam.com/askexpert_question.cfm?articleID=000112A7-67A3-1C71-9EB7809EC588F2D7&pageNumber=1&catID=3) column. A brief snippet from Lawrence Crum's response:


In summary, simple shielding of gravity is not possible. Not only would it violate the laws of gravity, it would provide a perpetual motion machine, thereby violating the principle of conservation of energy.

<font size=-1>[ This Message was edited by: Wiley on 2002-07-26 13:05 ]</font>

<font size=-1>[ This Message was edited by: Wiley on 2002-07-26 13:06 ]</font>

nebularain
2002-Jul-26, 05:21 PM
On 2002-07-26 13:04, Wiley wrote:
[quote]
On 2002-07-26 00:53, roidspop wrote:
The best antigravity thingy I know of is to stop resisting it. Just fall.

Or better yet, just don't look down!
(Tips hat to Wile E. Coyote.)
/phpBB/images/smiles/icon_razz.gif

Wiley
2002-Jul-26, 05:45 PM
On 2002-07-26 13:21, nebularain wrote:
Or better yet, just don't look down!
(Tips hat to Wile E. Coyote.)
/phpBB/images/smiles/icon_razz.gif



Ah, my name sake.

SpacedOut
2002-Jul-26, 06:30 PM
On 2002-07-26 13:04, Wiley wrote:
…I suspect this a Pascal's wager on NASA part…,


Maybe a dumb question – What’s a Pascal wager?

[fumble fingres]

<font size=-1>[ This Message was edited by: SpacedOut on 2002-07-26 14:31 ]</font>

Wiley
2002-Jul-26, 08:38 PM
On 2002-07-26 14:30, SpacedOut wrote:

Maybe a dumb question ? What?s a Pascal wager?



Pascal's wager is bet you have no hope of winning, but the payoff is so great if you win, you take the bet anyway. The lottery is a perfect example of Pascal's wager.

I don't think NASA actually expects the gravity shield to work, but if it does, the rewards are enormous. Of course, no one has ever won betting against the first law of thermodynamics.

AJ
2002-Jul-26, 09:10 PM
A quick question on gravity. How fast do the effects of gravity travel? I remember reading in the Honor Harrington book series (sci-fi) that they used gravity pulses to communicate faster than light. Is that possible? For example if the sun were to just disappear (no explosion or anything just go to zero mass) would it take eight minutes (appx time for sunlight to reach earth) before earth stopped traveling in a circle/orbit and flew off in a straight line?

-AJ

David Hall
2002-Jul-26, 10:04 PM
I think it's pretty conclusively been determined that even gravity has to obey "c". This cosmic speed limit is built into the very fabric of space and time, so it's impossible for anything to travel faster than that. The effects of gravity may stretch out infinitely in space, but it still has to have the time to reach whatever it is affecting.

traztx
2002-Jul-26, 10:08 PM
On 2002-07-26 18:04, David Hall wrote:
I think it's pretty conclusively been determined that even gravity has to obey "c". This cosmic speed limit is built into the very fabric of space and time, so it's impossible for anything to travel faster than that. The effects of gravity may stretch out infinitely in space, but it still has to have the time to reach whatever it is affecting.


I wonder how that was demonstrated.

David Hall
2002-Jul-26, 10:19 PM
Ok, maybe I should have said determined theoretically. I am not aware of any experiments that have demonstrated this conclusively. I think we're still trying to work out exactly how gravity propigates. But I'm fairly confident that all of the working theories have to take c as the limit. Otherwise I'm sure we would have heard something about it before now.

But then again, I'm no physicist. There is a good chance I'm wrong. I probably shouldn't have opened my mouth here. /phpBB/images/smiles/icon_smile.gif

Phobos
2002-Jul-26, 10:36 PM
Artificial Gravity - Easy, and you dont need either high tech, or spinning spacecraft.

What you do need is the ability to constantly accelarate or decellarate your spacecraft at 10 metres per second per second (speed up or slow down makes no difference except the direction of gravity).

The problem with accelaration is it is very fuel intensive, but assuming you have a fix for this then just build your spacecraft any shape you like and point it in the direction you want up to be (or down if you are slowing down).

The net result is perfect artificial g throughout the spacecraft.

Whilst this is energy intensive it does mean that you cut down your journey time considerably.

Phobos

Wiley
2002-Jul-26, 10:48 PM
On 2002-07-26 18:19, David Hall wrote:
Ok, maybe I should have said determined theoretically. I am not aware of any experiments that have demonstrated this conclusively. I think we're still trying to work out exactly how gravity propigates. But I'm fairly confident that all of the working theories have to take c as the limit. Otherwise I'm sure we would have heard something about it before now.


General Relativity says that changes in gravity are transmitted in the form of waves which propagate at the speed of light. Gravity waves have yet to be detected directly. The Taylor and Hulse binary pulsar (http://www.psc.edu/science/Taylor/Relativity.html) provided the first indirect evidence of gravity radiation by showing a decrease in orbital energy: the two pulsars are getting closer and their orbital velocities are increasing. The LIGO (http://www.ligo.caltech.edu/LIGO_web/about/) will attempt to detect gravity waves directly.



But then again, I'm no physicist. There is a good chance I'm wrong. I probably shouldn't have opened my mouth here. /phpBB/images/smiles/icon_smile.gif


Nonsense. If you had opened your mouth, your smiley would look like /phpBB/images/smiles/icon_razz.gif or /phpBB/images/smiles/icon_biggrin.gif or perhaps /phpBB/images/smiles/icon_lol.gif.
/phpBB/images/smiles/icon_smile.gif


<font size=-1>[ This Message was edited by: Wiley on 2002-07-26 18:52 ]</font>

g99
2002-Jul-26, 11:39 PM
So if gravity is a wave can we send out a "Anti-Grav" wave of the opposite magnitude and amplification and wavelength to cance out the gravity?

Phobos
2002-Jul-27, 01:03 AM
On 2002-07-26 19:39, g99 wrote:
"If you are on a train going the speed of light and you fall forward flat on your face, was your nose travelling faster than the speed of light?"


Couldn't resist answering your tag ...

As the train gets closer to the speed of light, it's mass will increase. Just before you reach the speed of light the mass of you and the train should be sufficient to turn into a black hole. Once you are a black hole you cannot fall over as you are a singularity.

Phobos

Ring
2002-Jul-27, 03:15 AM
On 2002-07-26 18:48, Wiley wrote:

General Relativity says that changes in gravity are transmitted in the form of waves which propagate at the speed of light.



Once again please excuse me for being overly picky, but changes in gravity are normally transmitted as nothing more than a changing field. Gravitational "waves" require a time varying quadrupole moment, and they cause a massive object to oscillate transversely to their direction of propagation.

Curiously, the embedded field of a gravitating mass points directly at the object's present position with no velocity or accelerational time delay (to first order). If this weren't true there could be no such things as gravitational waves. The same is true for the electric field of a charged particle (velocity correction only) and this, in turn, is what enables EM waves to exist.

g99
2002-Jul-27, 03:28 AM
On 2002-07-26 21:03, Phobos wrote:


On 2002-07-26 19:39, g99 wrote:
"If you are on a train going the speed of light and you fall forward flat on your face, was your nose travelling faster than the speed of light?"


Couldn't resist answering your tag ...

As the train gets closer to the speed of light, it's mass will increase. Just before you reach the speed of light the mass of you and the train should be sufficient to turn into a black hole. Once you are a black hole you cannot fall over as you are a singularity.

Phobos


How does mass increase? Does that not break the rule of conservation of matter? Do you suddenly gain a couple of trillion, trillion, trillion tons (metric or standard? /phpBB/images/smiles/icon_smile.gif )in a couple of seconds? But theoretically would your nose be travelling faster than light IF you can fall over? Or am i misinterpreting this. Does your gravitation mass increse making it seem like your physical mass increases?

Here is another theory, if you were going faster than the speed of light, would your body not physically be able to fall over because of the speed barrier? Would it be like hitting a invisible wall?

I have another idea of how to make a anti-grav devcice. Find out what in our atoms the gravity is actually affecting and somehow block that interaction by some sort of gravity shielding device. That way we don/t affect the gravity field of anything except around us. But this won't crerate artificial gravity , we would actualy have to think of something else, like maybe buid a ship around the core of a neutron star?

GrapesOfWrath
2002-Jul-27, 04:24 AM
On 2002-07-26 23:28, g99 wrote:
Does that not break the rule of conservation of matter?

Another convervation law? This place is getting way too conservative. I'm moving to a new universe.

thkaufm
2002-Jul-27, 05:01 AM
So if gravity is a wave can we send out a "Anti-Grav" wave of the opposite magnitude and amplification and wavelength to cance out the gravity?

At some point in space between two massive bodies isn't this sort of what happens?

Tom

g99
2002-Jul-27, 05:15 AM
On 2002-07-27 01:01, thkaufm wrote:
So if gravity is a wave can we send out a "Anti-Grav" wave of the opposite magnitude and amplification and wavelength to cance out the gravity?

At some point in space between two massive bodies isn't this sort of what happens?

Tom


So that means that there is some sort of horse lattitudes in space? Now gravity (wind) so any object there gets stuck. So would not there be a amalgamation of asteroids, comets and other junk in that area?

P.s. There is not a law for the conservation of matter? I thought that went along with conservtion of energy. Opps i guess i better take physics again. /phpBB/images/smiles/icon_smile.gif

<font size=-1>[ This Message was edited by: g99 on 2002-07-27 01:15 ]</font>

David Hall
2002-Jul-27, 08:10 AM
On 2002-07-27 01:15, g99 wrote:

So that means that there is some sort of horse lattitudes in space? Now gravity (wind) so any object there gets stuck. So would not there be a amalgamation of asteroids, comets and other junk in that area?


Yep, actually there are such points. In a two-body orbiting system there are 5 points where the two bodies gravities cancel out. These are called the LaGrange Points (http://www.physics.montana.edu/faculty/cornish/lagrange.html) L1-L3 are unstable, that is, a slight push would be enough to send them moving away from the point, so objects don't collect there, but they can reside temporarily. L4 and L5 are stable points, and objects there tend to stay there. There are many Trojan (http://antwrp.gsfc.nasa.gov/apod/ap020724.html) asteroids in the Lagrange Points of Jupiter, and dust clouds have been detected in the Lagrange points of Earth.

_________________
<font size="-1">PLEASE NOTE: Some quantum physics theories suggest that when the consumer is not directly observing this product, it may cease to exist or will exist only in a vague and undetermined state.</font>

<font size="-1">(fixed link)</font>

<font size=-1>[ This Message was edited by: David Hall on 2002-07-27 04:12 ]</font>

DStahl
2002-Jul-27, 08:56 AM
We went round-about on the nature of gravitational propagation on a thread in the Against the Mainstream section a couple of months ago.

All reputable physicists that I wrote to and that I know of agree that gravity propagates at the speed of light. However, just as with electrical fields the laws of physics require an adjustment to the vector of attraction which, in smoothly varying systems, makes the vector of attraction point at the instantaneous position of the attractor rather than the position it occupied one lightspeed-propagation transit time in the past.

I think it was Kip Thorne that wrote that physicists have a toolkit of equations that treat gravity as a field in flat spacetime, and this toolkit is very useful in describing the genesis of gravity waves (the quadrupolar time-varying fields described by someone in a previous post). They have another toolkit of equations that treat gravity as a geometrical curvature of spacetime, and this is spectacularly successful in describing things like black holes. Quantum physicists are working on quantum gravity, and perhaps that will include a zero-mass 'graviton' as the particle which mediates the gravitational force. If that works out, then there will be a third toolkit of equations.

But Thorne's point was that it is actually uninteresting to him which of these alternate descriptions is "really" gravity: when the equations from the toolkits are applied to the same problem they give exactly the same predictions. Therefore it's experimentally impossible to distinguish between them, and they can all be regarded as scientifically correct.

That material is in Thorne's book for lay audiences, "Black Holes and Time Warps: Einstein's Outrageous Legacy." It is one of my favorite science books of all time. Your local library probably has a copy... /phpBB/images/smiles/icon_wink.gif

Don Stahl

Addendum and caveat: I have a great tendency to misremember stuff that I've read some time in the past. I'll see if I can look that passage up and verify what I've written.

<font size=-1>[ This Message was edited by: DStahl on 2002-07-27 05:11 ]</font>

DoctorDon
2002-Jul-27, 12:57 PM
On 2002-07-26 23:28, g99 wrote:
How does mass increase? Does that not break the rule of conservation of matter?


The mass does not increase in the sense of there being "more stuff". What happens is this: at slow speeds, if you apply a force to a mass, you get a certain acceleration, and we call the constant of proportionality between those two quantities "the mass".

F=ma; Force = mass times acceleration

As you get closer to the speed of light, the same amount of force produces less acceleration. If you still want mass to be defined as "the proportion between force and acceleration", then mass has to increase in order to keep the equation valid (if F stays the same and a goes down, then m must go up). However, if you want to think of mass as "the amount of stuff" (relativity theory calls this the "rest mass"), then it is more accurate to say "the same amount of force produces less acceleration". It is a property of space, not of matter. Saying "the mass increases" is just a shorthand way of saying "the same force produces less acceleration", and I think it's misleading, because it gives people the impression that "more stuff" appears out of nowhere. Still, it's in all the textbooks, because they think it's easier for people to get the concept if they frame it in terms of something familiar (F=ma). I disagree.

Don

Phobos
2002-Jul-27, 03:02 PM
On 2002-07-26 23:28, g99 wrote:


On 2002-07-26 21:03, Phobos wrote:

Couldn't resist answering your tag ...

As the train gets closer to the speed of light, it's mass will increase. Just before you reach the speed of light the mass of you and the train should be sufficient to turn into a black hole. Once you are a black hole you cannot fall over as you are a singularity.

Phobos


How does mass increase? Does that not break the rule of conservation of matter? Do you suddenly gain a couple of trillion, trillion, trillion tons (metric or standard? /phpBB/images/smiles/icon_smile.gif )in a couple of seconds? But theoretically would your nose be travelling faster than light IF you can fall over? Or am i misinterpreting this. Does your gravitation mass increse making it seem like your physical mass increases?

Here is another theory, if you were going faster than the speed of light, would your body not physically be able to fall over because of the speed barrier? Would it be like hitting a invisible wall?

I have another idea of how to make a anti-grav devcice. Find out what in our atoms the gravity is actually affecting and somehow block that interaction by some sort of gravity shielding device. That way we don/t affect the gravity field of anything except around us. But this won't crerate artificial gravity , we would actualy have to think of something else, like maybe buid a ship around the core of a neutron star?


The following link explains why would expect you to turn into a black hole before you reached light speed;

The Effects of the Special Theory of Relativity
(http://members.aol.com/soccer1800/astronomy/rel.html)


The first strange result of traveling close to the speed of light is that your mass increases. This results from the famous equation E=Mc^2. The E is energy, the M is mass, and the c is the speed of light. The faster you travel, the more energy you use. Since energy equals mass your mass increases when you travel close to the speed of light. Partical accelerators are designed to allow for and increase in mass with increasing speed.

So basically as a result of special relativity as you get closer to the speed of light your mass increases. At light speed you would have infinite mass, so therefore before you reach light speed you will obtain sufficient mass to turn into a black hole !

Phobos

<font size=-1>[ This Message was edited by: Phobos on 2002-07-27 11:06 ]</font>

g99
2002-Jul-27, 05:54 PM
On 2002-07-27 08:57, DoctorDon wrote:


On 2002-07-26 23:28, g99 wrote:
How does mass increase? Does that not break the rule of conservation of matter?


The mass does not increase in the sense of there being "more stuff". What happens is this: at slow speeds, if you apply a force to a mass, you get a certain acceleration, and we call the constant of proportionality between those two quantities "the mass".

F=ma; Force = mass times acceleration

As you get closer to the speed of light, the same amount of force produces less acceleration. If you still want mass to be defined as "the proportion between force and acceleration", then mass has to increase in order to keep the equation valid (if F stays the same and a goes down, then m must go up). However, if you want to think of mass as "the amount of stuff" (relativity theory calls this the "rest mass"), then it is more accurate to say "the same amount of force produces less acceleration". It is a property of space, not of matter. Saying "the mass increases" is just a shorthand way of saying "the same force produces less acceleration", and I think it's misleading, because it gives people the impression that "more stuff" appears out of nowhere. Still, it's in all the textbooks, because they think it's easier for people to get the concept if they frame it in terms of something familiar (F=ma). I disagree.

Don


Hmmm...very interesting. I have never heard f=ma in that way. I have always heard it in the usual terms. Thanks...

I think i am actually getting it. This is a first /phpBB/images/smiles/icon_smile.gif.

So If you constantly gain mass to a infinite amount, how come the light particles do not all become black holes? Why is space not one giant black hole? I can understand that they are not accelerating anymore, but the initial acceleration of the particles would produce a giant black hole in the center of every star, would it not? Or do the particles start out at the speed of light, thus no acceleration, and thus no mass change?



_________________
"The chickens is coming!!!"
"Watch out for falling coconuts!!"
"If you are on a train going the speed of light and you fall forward flat on your face, was your nose travelling faster than the speed of light?"

<font size=-1>[ This Message was edited by: g99 on 2002-07-27 13:54 ]</font>

Kaptain K
2002-Jul-27, 11:07 PM
Phobos and g99, please go back and reread Doctor Don's post. The rest mass does not increase. Only the relativistic mass increases (to keep the equation F=ma in balance). In other words, to the force pushing the object, the mass seems to increase (acceleration per unit force decreases). The mass, as perceived by the rest of the universe, does not change. In other words, an object with a rest mass of one gram moving at 0.999...c may have the relativistic mass of a small planet (with corresponding energy release if it hits something) but gravitationally, it is still only one gram and is not going to turn into a black hole.

g99
2002-Jul-28, 12:07 AM
But still, would a particle of light have the relativistic mass of a black hole? or does it start out at the speed of light, so there is not acceleration, and thus no relativistic mass change?

Donnie B.
2002-Jul-28, 02:02 AM
Light always propagates at the speed of light (or less, in media other than a vacuum), when measured by any observer. This is the very essence of relativity.

So it's senseless to talk about what happens as light "accelerates". It doesn't.

What's more, light has zero rest mass, so there's no mass to increase. It does, of course, carry energy, and so can be said to exert a pressure, but it's not quite the same kind of pressure as is exerted by, say, the molecules of gas in a diver's air tank.

DoctorDon
2002-Jul-28, 03:21 AM
On 2002-07-26 16:38, Wiley wrote:

Pascal's wager is bet you have no hope of winning, but the payoff is so great if you win, you take the bet anyway.


That's not how I've always heard it defined. The definition I've heard is when you are faced with a situation where there is a proposition A which may or may not be true. If the conditions are such that the consequences of winning or losing a bet based on the proposition that A is true are much greater than the consequences if A is false, then Pascal said it's best to bet that A is true, since you are risking less if you lose and win more if you win. The classic example of such a wager is where A is "God exists". Pascal said you should believe in God because it's the least risky scenario. If he doesn't, he can't reward or punish you for your choice, but if he does, he can, so better to behave as if he does.

Although this does get trotted out quite a bit by certain missionaries I have encountered, I think it is theologically ludicrous (Despite the ample evidence that hordes of people think about it this way, religion is not about greed for reward and/or fear of punishment.), and mathematically dubious (as it assumes mere belief in God is sufficient to earn the reward in question, and it also fails to put much weight on the idea of having wasted your life behaving as if there were a God if it turns out there isn't).

> The lottery is a perfect example of Pascal's wager.

I disagree. First of all, the known improbability of winning the lottery weights the choice a priori. I think Pascal's wager demands no prior information be known on whether the proposition is true. Also, without the threat of punishment, the loss category in the event of A being true does not provide enough of a risk to balance out the known loss if A is not true. I.e., if A is true and I buy a ticket, I win big. If A is not true and I buy a ticket, I lose a little. If A is true and I don't buy a ticket, I lose nothing, and if A is not true and I don't buy a ticket, I also lose nothing. That clearly pushes the answer to not buying a ticket, escpecially given the improbability factor, which is not how I understand a Pascal's Wager to operate.

But then, I've never heard Pascal's Wager refer to anything but the belief in God question, so perhaps I am generalizing it incorrectly.

Don

Phobos
2002-Jul-28, 03:32 AM
On 2002-07-27 20:07, g99 wrote:
But still, would a particle of light have the relativistic mass of a black hole? or does it start out at the speed of light, so there is not acceleration, and thus no relativistic mass change?


Light has no mass and is best thought of as matter completly converted into energy.

Phobos

DoctorDon
2002-Jul-28, 03:39 AM
Wow, lots of deep questions flying around here. Let me see if I can answer a couple of them...



The first strange result of traveling close to the speed of light is that your mass increases. This results from the famous equation E=Mc^2. The E is energy, the M is mass, and the c is the speed of light. The faster you travel, the more energy you use. Since energy equals mass your mass increases when you travel close to the speed of light.

Gack! Oh, no, no, no. This is completely and utterly wrong. The only part that is right is the definitions of the letters. The rest is wrong. Please don't get misled by this. Please see my description for a more accurate explanation of why the "mass increases".

Donnie B. is quite right that a photon does not accelerate. It has no rest mass, so it cannot move at any other speed than the speed of light. [The fact that light moves slower when not in a vacuum has to do with how light interacts with the atoms in the material. Since any material is mostly empty space between the atoms, you can think of the light waves as racing at the speed of light through the vacuum between the atoms, but being slowed down by all the interactions it has along the way through the macroscopic material. (Okay, so that's a gross simplification, but I think it's not wrong within its limitations.)]

However, folks are getting to a more subtle point. While the relativistic mass does not curve space the way the rest mass does, general relativity *includes* energy in Einstein's Equations for the curvature of space. For that matter, *pressure* can cause space to curve, too. So I think it's a valid question to ask whether a particle accelerated near the speed of light, or an energetic photon, would collapse into a black hole. I believe the answer is that it's just not possible to give a single particle that much energy, massless or no. They would use that energy to decay into something else before you could get anywhere near energetic enough. And they're moving so fast you can't constrain enough of them in a small enough space to cause collapse, either. That would be my guess, but I'm not an expert. I'll ask the Relativist down the hall.
Yours,

Don

Phobos
2002-Jul-28, 03:40 AM
On 2002-07-27 19:07, Kaptain K wrote:
Phobos and g99, please go back and reread Doctor Don's post. The rest mass does not increase. Only the relativistic mass increases (to keep the equation F=ma in balance). In other words, to the force pushing the object, the mass seems to increase (acceleration per unit force decreases). The mass, as perceived by the rest of the universe, does not change. In other words, an object with a rest mass of one gram moving at 0.999...c may have the relativistic mass of a small planet (with corresponding energy release if it hits something) but gravitationally, it is still only one gram and is not going to turn into a black hole.


Put yourself in the driving seat of your 1gm spacecraft with the relativistic mass of a small planet. Your spacecraft will be pushing with the required 1 planet force and will in turn be receiving an equal and opposite reactive force of 1 planet pushing back to aquire the required accelaration.

Keep accelarating and our spacecraft will keep receiving ever greater forces pushing againt it - what will happen when our spacecraft requires more than the weight of an entire galaxy to continue its quest to reach light speed ?

I suspect it would be a black hole before it ever reached the velocity described above.

Phobos

SpacedOut
2002-Jul-28, 09:11 AM
Wiley and DoctorDon – Thanks for the descriptions of a “Pascal’s wager”. I had never heard of it before – now to do some more research.

John Kierein
2002-Jul-28, 10:27 AM
In the book "Pushing Gravity" I describe the cause of gravity as being a push from overwhelmingly long wavelength cosmic background electromagnetic radiation. The graviton becomes a quantization of the shadow cast by a mass in this radiation field and it travels at the speed of light. As masses aproach c the are slowed as though they increase in mass per the above discussion on the relation between force and acceleration. This provides a "reason" for special relativity. These are not yet the mainstream.

g99
2002-Jul-28, 04:02 PM
back to one of my original questions...What does gravity actually attach to or push? Is there a physical interaction or is it purely ralativistic?

John Kierein describes "The graviton becomes a quantization of the shadow cast by a mass in this radiation field and it travels at the speed of light." Is this a explanation of how gravity works? If so(or if not) can someone explain this in more stupid person lanugage for me? I did not get a degree in physics, only anthropology with some astronomy and geography, so i am not a physics expert (that is why i started this discussion /phpBB/images/smiles/icon_smile.gif).

Donnie B.
2002-Jul-28, 04:35 PM
Here's a good link about Pascal's Wager, with arguments pro and con...

http://plato.stanford.edu/entries/pascal-wager/

Espritch
2002-Jul-28, 06:05 PM
How does mass increase? Does that not break the rule of conservation of matter? Do you suddenly gain a couple of trillion, trillion, trillion tons (metric or standard? )in a couple of seconds? But theoretically would your nose be travelling faster than light IF you can fall over? Or am i misinterpreting this. Does your gravitation mass increse making it seem like your physical mass increases?

As I understand it, as you accelerate closer to the speed of light, added energy can't accelerate you so it converts to mass instead. Time also slows down as you get closer to light speed, so if you started to fall over, your nose would become frozen in time so you would just sort of stand there leaning until the ship decelerated and you could tumble on over.

Woops! I just noticed I missed a whole page of this thread. People have already addressed this much better than I did. You should ingnore this post.

<font size=-1>[ This Message was edited by: Espritch on 2002-07-28 14:13 ]</font>

roidspop
2002-Jul-28, 06:21 PM
There is not a law for the conservation of matter?

...there is in chemistry. Or there was. I don't know if there's a Law of Conservation of Conservation Laws or not.

beskeptical
2002-Jul-28, 07:47 PM
Dr Don: "The mass does not increase in the sense of there being "more stuff". What happens is this: at slow speeds, if you apply a force to a mass, you get a certain acceleration, and we call the constant of proportionality between those two quantities "the mass".

F=ma; Force = mass times acceleration

As you get closer to the speed of light, the same amount of force produces less acceleration. If you still want mass to be defined as "the proportion between force and acceleration", then mass has to increase in order to keep the equation valid (if F stays the same and a goes down, then m must go up). However, if you want to think of mass as "the amount of stuff" (relativity theory calls this the "rest mass"), then it is more accurate to say "the same amount of force produces less acceleration". It is a property of space, not of matter. Saying "the mass increases" is just a shorthand way of saying "the same force produces less acceleration", and I think it's misleading, because it gives people the impression that "more stuff" appears out of nowhere. Still, it's in all the textbooks, because they think it's easier for people to get the concept if they frame it in terms of something familiar (F=ma). I disagree."

Well now it finally makes sense. I just took for granted the mass increasing was something everyone understood but me. I was trying to figure out how energy was being converted into mass as I see other posters were. I agree using the easier explanation in text books does a disservice in the long run. Look how many people either have it wrong or don't have it at all.


Dr Don: "That's not how I've always heard {Pascal's Law} defined. The definition I've heard is when you are faced with a situation where there is a proposition A which may or may not be true. If the conditions are such that the consequences of winning or losing a bet based on the proposition that A is true are much greater than the consequences if A is false, then Pascal said it's best to bet that A is true, since you are risking less if you lose and win more if you win. The classic example of such a wager is where A is "God exists". Pascal said you should believe in God because it's the least risky scenario. If he doesn't, he can't reward or punish you for your choice, but if he does, he can, so better to behave as if he does.

Although this does get trotted out quite a bit by certain missionaries I have encountered, I think it is theologically ludicrous (Despite the ample evidence that hordes of people think about it this way, religion is not about greed for reward and/or fear of punishment.), and mathematically dubious (as it assumes mere belief in God is sufficient to earn the reward in question, and it also fails to put much weight on the idea of having wasted your life behaving as if there were a God if it turns out there isn't).

That's a bit of a twisted way to look at risk benefit analysis. What are the risks, (or costs) of doing x, and, what are the benefits of doing x; how does it compare to the risks, (costs) of not doing x?

I think Pascal's Law makes it sound like some mysterious logic. For example, proposition x is that you may or may not get an infectious disease for which there is a vaccine. The risk of giving a vaccine might be 1 really bad outcome per 10 million doses. The risk from the disease might be 2 really bad outcomes per 1,000 cases. If you find that the rate of disease is higher than 1 in 10 million persons, then the vaccine is a safer bet. (The trick is to recognize which population to count yourself in, the world or the Americas or just North America.)

<font size=-1>[ This Message was edited by: beskeptical on 2002-07-28 15:53 ]</font>

g99
2002-Jul-28, 07:53 PM
On 2002-07-28 14:21, roidspop wrote:

There is not a law for the conservation of matter?

...there is in chemistry. Or there was. I don't know if there's a Law of Conservation of Conservation Laws or not.


Hmm... A law to conserve laws about conserving stuff...Damn those sientists and their many rules. I say we propose a law to go against all laws that conserve laws that conserve laws. (say that 5 times fast!)

g99
2002-Jul-29, 12:21 AM
Woohooo..This topic is flaming!!!

Ring
2002-Jul-29, 03:18 AM
The only energy that curves space is energy that cannot be transformed away.

This is either the rest mass of an individual particle or the mass of a system of particles that has a center of momentum frame. This also means that a system of photons can have mass.

m^2 = E^2-p^2

c = 1
m = mass
E = energy
p = momentum

So if a system of photons has a center of momentum frame then m = E

Edit: I didn't know you can't use the sup BB code. Why is that?

<font size=-1>[ This Message was edited by: Ring on 2002-07-28 23:23 ]</font>

David Hall
2002-Jul-29, 07:06 AM
On 2002-07-28 23:18, Ring wrote:

Edit: I didn't know you can't use the sup BB code. Why is that?


The software for this board is open source, and I think it only uses a stripped-down version of the BB code, so it looks like many functions haven't been incorporated into it.

I believe you can still use the HTML codes though. Let's see:

E=MC<sup>2</sup>

Yep, no problem there.
_________________
<font size="-1">PLEASE NOTE: Some quantum physics theories suggest that when the consumer is not directly observing this product, it may cease to exist or will exist only in a vague and undetermined state.</font>

<font size=-1>[ This Message was edited by: David Hall on 2002-07-29 03:07 ]</font>

Ring
2002-Jul-29, 02:48 PM
On 2002-07-29 03:06, David Hall wrote:


The software for this board is open source, and I think it only uses a stripped-down version of the BB code, so it looks like many functions haven't been incorporated into it.

I believe you can still use the HTML codes though.





Thanks, I was laboring under the delusion that HTML had been completely disabled.

Wiley
2002-Jul-29, 05:18 PM
On 2002-07-26 23:15, Ring wrote:


On 2002-07-26 18:48, Wiley wrote:

General Relativity says that changes in gravity are transmitted in the form of waves which propagate at the speed of light.



Once again please excuse me for being overly picky, but changes in gravity are normally transmitted as nothing more than a changing field. Gravitational "waves" require a time varying quadrupole moment, and they cause a massive object to oscillate transversely to their direction of propagation.



I think you're confusing waves with radiation. The only requirement for a wave is that it satisfies the wave equation; radiation, however, decays at 1/distance. Gravitational radiation does require a quadrapole moment, but non-radiating waves do not. A "changing field" is a wave, if it is the solution to the wave equation; it does not have to radiate.

Wiley
2002-Jul-29, 05:54 PM
On 2002-07-27 23:21, DoctorDon wrote:


On 2002-07-26 16:38, Wiley wrote:

Pascal's wager is bet you have no hope of winning, but the payoff is so great if you win, you take the bet anyway.


That's not how I've always heard it defined. The definition I've heard is when you are faced with a situation where there is a proposition A which may or may not be true. If the conditions are such that the consequences of winning or losing a bet based on the proposition that A is true are much greater than the consequences if A is false, then Pascal said it's best to bet that A is true, since you are risking less if you lose and win more if you win.


Yep. I was trying to generalize it to the non-theological world. Not too successfully. I had taken the final result, belief in God results in eternal life (W) or little cost(L), but I neglected the setup. Oops.

Gsquare
2002-Jul-30, 10:06 PM
On 2002-07-27 19:07, Kaptain K wrote:
Phobos and g99, please go back and reread Doctor Don's post. The rest mass does not increase. Only the relativistic mass increases (to keep the equation F=ma in balance). In other words, to the force pushing the object, the mass seems to increase (acceleration per unit force decreases). The mass, as perceived by the rest of the universe, does not change. In other words, an object with a rest mass of one gram moving at 0.999...c may have the relativistic mass of a small planet (with corresponding energy release if it hits something) but gravitationally, it is still only one gram and is not going to turn into a black hole.



I rather agree with you Kaptain K, gravitational mass does not increase as velocity increases.....however many would disagree and I think Einstein to be one of them. This, of course, is no trivial issue.

For example, in trying to account for the fully observed precessional advance of Mercury's perihelion (43 arcsec/century) above the non-relativistic prediction, ONE of the necessary factors (in post Newtonian analysis) is the calculation of Mercury's gravitational increase due to its orbital speed.
Without such assumption (i.e. the velocity dependent modification of gravitational force), GR's prediction of the required precessional amount would be inadequate.

G^2

Comments, Kaptain ? Doc Don?







<font size=-1>[ This Message was edited by: Gsquare on 2002-07-30 23:08 ]</font>

Donnie B.
2002-Jul-31, 01:51 AM
Hmmm... if the gravitational mass does increase, then I guess we have an answer to the burning question, "could a sufficiently advanced technological society find a way to close the universe?" Sure, just accelerate a lot of masses up to near-light speeds, and let them attract all those distant galaxies back into a Big Crunch.

You could do it with ultra-huge cyclotrons so the masses stay in the neighborhood instead of flying off to infinity...

Gsquare
2002-Jul-31, 03:35 AM
I have re-edited my previous post (7/30) for clarity.

G^2

tjm220
2002-Jul-31, 05:32 PM
I rather agree with you Kaptain K, gravitational mass does not increase as velocity increases.....however many would disagree and I think Einstein to be one of them. This, of course, is no trivial issue.

For example, in trying to account for the fully observed precessional advance of Mercury's perihelion (43 arcsec/century) above the non-relativistic prediction, ONE of the necessary factors (in post Newtonian analysis) is the calculation of Mercury's gravitational increase due to its orbital speed.
Without such assumption (i.e. the velocity dependent modification of gravitational force), GR's prediction of the required precessional amount would be inadequate.

G^2

Comments, Kaptain ? Doc Don?



Mercury isn't moving fast relativistically.

Wiley
2002-Jul-31, 06:00 PM
On 2002-07-31 13:32, tjm220 wrote:



For example, in trying to account for the fully observed precessional advance of Mercury's perihelion (43 arcsec/century) above the non-relativistic prediction, ONE of the necessary factors (in post Newtonian analysis) is the calculation of Mercury's gravitational increase due to its orbital speed.


Mercury isn't moving fast relativistically.


I believe its curvature, not speed, they are interested in. The closer to the sun, the more pronounced the curvature, and the larger the descrepency between measurement and Newtonian gravity. See the table below.

___________GR___observed
Mercury__42.98___43.1 +-0.1
Venus____8.65____8.62
Earth____3.85____3.84
Mars_____1.36____1.35

(from Ohanian and Ruffini, Gravitation and Spacetime, 1994)



<font size=-1>[ This Message was edited by: Wiley on 2002-07-31 14:02 ]</font>

Gsquare
2002-Jul-31, 11:06 PM
I believe its curvature, not speed, they are interested in. The closer to the sun, the more pronounced the curvature, and the larger the descrepency between measurement and Newtonian gravity. See the table below.

----------GR-----observed
Mercury__42.98___43.1 +-0.1




Thanks Tjm220 and Wiley for your responses.

First, Wiley ...Curvature is only part of the calculated difference. The GR predicted discrepancy (43 arcsec.) given above is the total precessional correction (above Newtonian) which INCLUDES calculations of BOTH speed and curvature effects. (Notice in my post I said speed was "ONE" of the factors).

This fact is not commonly known and is the whole point of my first post. Thus, without including the amount due to speed of Mercury, the GR calculation would not total the required 43 arcsec. and Gen. Relativity would be inadequate to explain the precessional anomoly.

The implication are obvious and worthy of discussion.

G^2


Tjm220....Even though Mercurial speed is not considered 'relativistic', over the course of a century the cumulative effect is significant and needs to be accounted for IF you are making the assumption that there is a modification in gravitational force due to velocity. This assumption is made and is included in the Gen. Relativitic precessional calculation in order to achieve the required 43 arcsec/century deficiency.

G^2





<font size=-1>[ This Message was edited by: Gsquare on 2002-07-31 19:33 ]</font>

<font size=-1>[ This Message was edited by: Gsquare on 2002-07-31 22:29 ]</font>