PDA

View Full Version : Time travel from ring lasers....



publius
2006-Nov-14, 12:55 AM
Art Bell had Dr. Ron Mallet from U of Conn. Dr. Mallet thinks he figured out how to make time travel possible. Here's a brief Wiki page on him, with links to his main papers on it:

http://en.wikipedia.org/wiki/Ronald_Mallett

What I find interesting about this is it involves some things I was rambling about from the Coriolis metric and the "Sagnac" circularly constrained null (light) geodesics. :)

Frame dragging is apparently the "key" to time travel, which in GR means closed time-like geodesics and/or world lines are possible. Frame dragging is the way time-like curves can be bent around into closed paths. So far, the mass-energy-velocity needed to "close the loop" has been so enormous that it is just an academic thought-experiment (such loops are thought to exist between event horizons in the Kerr metric -- but "thankfully" hidden behind the outer horizon where we would never be able to see it or learn any information about what would happen).

But Mallet thinks he's figured out a way to do with much less energy. He claims that the space-time metric of a beam of light going around in a circle can do the proper frame dragging contortions --actually two beams of light going around in opposite directions (note this would have sort of a "shearing" effect).

Now, normally, as above with regular mass, the energy to close the loops would be astronomical, but he says that the "slowing of light" to a crawl by those Bose-Einstein condensates has the effect of amplifying the effect. [And there are criticisms of his EFE solutions here, before anyone gets too excited -- they say he's wrong, but he thinks he's right].

Anyway, from what I understood him to say last night, he needs a few terawatts of laser power, going around in circles in some BE condensate near absolute zero, and he thinks he'll make a region with closed time-like curves just big enough for some neutrons to squeeze through and be able to observe any funny effects he expects.

I think he said he needs about $1/4 million to do that, and now has the funding and is going to try it.

Now, I pose to you all, what do you think? :D

-Richard

antoniseb
2006-Nov-14, 02:50 AM
I think that it won't work, but if he promises to do the measurements very carefully and report his findings, it might be worth a quarter million.

PhantomWolf
2006-Nov-14, 03:32 AM
Chump change if it works, but I doubt it will.

publius
2006-Nov-14, 04:47 AM
Speaking of the funding, Ol' Art, always looking for a conspiratorial angle, asked him if any military/government types were interested in what he was doing. Mallet laughed and said he actually had been approached by some government types who off the record offered him all the funding he would need to try it, but at the price of signing his work away and going secret. He wants to keep this all public with no strings attached and turned them down.

Which brings up an interesting question. What would the powers that be do if it looked like someone was actually going to suceed in making a time machine? Me, while I'd be all in favor of testing the concept, there's no way in heck or high water I'd let someone start messing with time travel on his own. :)

And second, if Mallet's tests were successful, would you want anyone to know about it?

I mean, time travel is so far-fetched, you figure it won't work, and so no harm in letting this guy play around. But if it turned out to be true, things would get serious quickly. Would you want it to made public knowledge that time travel is possible, meaning others in other countries might try it as well?

-Richard

grav
2006-Nov-14, 04:57 AM
Now you asked what we think, so this is not a theory, just my opinion.

Time is a measure of motion, nothing more. To travel back in time means reversing the motion of everything within a certain perimeter. The problem is that light and particles that decayed or were emitted prior to that point must all be brought back. This would require a perimeter of at least an equal distance that light travels during the reversal time. To reverse time in the absolute sense would mean reversing the motions of all of the particles in the universe, which in turn would require more energy than the universe contains. Even if that were possible, it would require a gate through which to pass, unless space is expected to just open up on its own. So time could only be reversed to the point where the gate was initially created, or else we must produce a wormhole and/or a singularity. But even then, we have a problem. If we are to conserve energy, and yet some of this energy is transported to the past, then there is a defiency of energy after the point at which it was sent back. Yet more would exist in the past. But at some point the past would become the future, so that extra energy would still exist. So how could we have a deficiency of energy in the future and extra energy at the same time? Unless, of course, we are also talking alternate universes. In that case, though, we would not really be sending energy into the past, but to another universe.

astromark
2006-Nov-14, 10:09 AM
Well, what do I think.?
Frame dragging is if I have caught it right the effect of motion and gravity. The speed of light has been proven to be altered by strong gravity force. I am sorry but as yet have not seen the case for time travel experiments as anything other than a wast of money and time. It will not. Can not. For more reasons than we could list. It can not be done.
( As he disappeared in a cloud of smoke..... back to the future.)
No. I would sagest experiments in forms of propulsion that might get us near to light speed. Would be a better direction of the budget expenditure.

Sticks
2006-Nov-14, 10:44 AM
This reminds me of a sci-fi story I did at one of my universities I attened, using caricatures of myself and other friends.

In it I was the research student who had stumbled across a strange effect whilst investigating fundamental particles that had implications for time travel. The powers that be used the "potential danger of a time machine" to justify blasting away at the university lab to destroy it and save humanity. (later on we find that was just an excuse as they wanted to cover up ileagal bio-weapons they had the university work on)

Anyway the time travel was done by pumping out accelerated anti-chronons into the universe to "drive it backwards" but in effect, like pushing on a massive object it pushed you back in time, except you device stayed behind. In the story the hero version of me had to find the experiment in the past, just before the attack to jury rig it to send them forward back to the present.

So to sum up, if anyone did get close to a working time machine, I would expect them to meet with a "fatal accident" planned by TPTB :shifty:

grav
2006-Nov-14, 02:10 PM
I just realized that time travel would require, not a wormhole or some such, but more like some sort of protective shell, to keep that within the shell from reversing, while the rest of the universe is all simultaneously reverted for all motion. But since that would require much, much more energy than the universe contains (to reverse all energy), the best we could do is send out a sort of shock wave from the origin that reverts some matter to its original form as it passes through, so the further one gets from that origin, the less the time is reversed in comparison. But even then, the wave could not catch up to all of what has been emitted in the same time (and how it should do this anyway is another matter), and so would not be capable of reversing things exactly like they were, so it would probably just end up destroying most things anyway, as they would simply fall back apart or disintegrate in the process. The only real practical use of time travel, then, is to reverse the "aging" of the object within the shell, as a sort of "fountain of youth", and leave the rest of the universe alone, sort of like rewinding a tape. But again, most of the processes that have already taken place for that object will have lost light and particles to the rest of the universe, especially if it depends on everything the object has come in contact with in the rest of the universe during its "lifetime", so to try to reverse time for it would leave these gaps unfilled, and then it would probably fall apart or disintegrate in this case also, unless the time reversal was very minute. And to "rewind" an object that has not undergone too many atomic or chemical processes would reverse it to practically the same way it is now, so there would be no point, unless all of these processes themselves ocurred within the shell to begin with and are properly contained.

Mister Earl
2006-Nov-14, 04:54 PM
I've got one dollar that says that if he fires this thing up and it works, he starts getting information from the future, the very first message will be DUCK!

korjik
2006-Nov-14, 05:20 PM
Now, normally, as above with regular mass, the energy to close the loops would be astronomical, but he says that the "slowing of light" to a crawl by those Bose-Einstein condensates has the effect of amplifying the effect. [And there are criticisms of his EFE solutions here, before anyone gets too excited -- they say he's wrong, but he thinks he's right].

Anyway, from what I understood him to say last night, he needs a few terawatts of laser power, going around in circles in some BE condensate near absolute zero, and he thinks he'll make a region with closed time-like curves just big enough for some neutrons to squeeze through and be able to observe any funny effects he expects.

I think he said he needs about $1/4 million to do that, and now has the funding and is going to try it.

Now, I pose to you all, what do you think? :D

-Richard

He wants to put terawatts into a ring shaped BEC, and he thinks he could do it for $250,000? I might believe a quarter billion, would expect a quarter trillion, but cant believe quarter million

publius
2006-Nov-14, 05:54 PM
He wants to put terawatts into a ring shaped BEC, and he thinks he could do it for $250,000? I might believe a quarter billion, would expect a quarter trillion, but cant believe quarter million


Remember we're talking power, not total energy. The tiny amount of energy necessary to propel the proverbial flea motorcycle halfway around a BB could make a terawatt if moved/released fast enough.

They've got terawatt lasers now based on this. The total energy is not that high, it's just released very fast (and usually concentrated in a very small volume as well).

From what I gather, he's looking to do something similiar, lots of energy in a small space released very fast, which will give him a small window to see if some neutrons are affected the way he thinks they will be. This will confirm if space-time is behaving the way he thinks it will.

Now, if you want to make something that could allow a macroscopic object to go through some closed time-like loop, then you're talking some serious money and serious energy.

-Richard

astromark
2006-Nov-14, 06:41 PM
What would happen if we were to do this..... BOOM !
Didn't there used to be a planet between Mars and Venus ?
If we can not yet contain a fission reactor for more than a few Milli seconds, How do they turn this thing off. Please conduct these experiments some place else.... Andromeda maybe.
Yes, I think this is nonsense. Time can not flow back wards.

korjik
2006-Nov-14, 06:57 PM
What would happen if we were to do this..... BOOM !
Didn't there used to be a planet between Mars and Venus ?
If we can not yet contain a fission reactor for more than a few Milli seconds, How do they turn this thing off. Please conduct these experiments some place else.... Andromeda maybe.
Yes, I think this is nonsense. Time can not flow back wards.

There are quite a few fission reactors that have been going for years.

publius
2006-Nov-15, 12:56 AM
What would happen if we were to do this..... BOOM !
Didn't there used to be a planet between Mars and Venus ?
If we can not yet contain a fission reactor for more than a few Milli seconds, How do they turn this thing off. Please conduct these experiments some place else.... Andromeda maybe.
Yes, I think this is nonsense. Time can not flow back wards.


Don't worry -- there's no danger that Mallet is going to blow anything up -- well, on the scale you're thinking of at least, nor any temporal paradoxes to be caused yet -- he's just going to see if his ring laser makes the space-time metric he thinks it will.

And I think there is some confusion here about time travel in GR. Time does not have to flow backwards. Indeed the proper time of a time traveller would be flowing normally relative to him as always. He just moves backwards in someone else's time, ours watching him. :)

To see how this works, consider one your typical SR space-time diagrams, say a simple x-t 1D - 1T space-time. Consider the time-like geodesics. These are just straight lines of a slope between -c and +c. Sitting there stationary, our path is just x = 0. We move along that x = 0 line at c. That's us moving through time at our own proper clock rate.

Now, imagine taking that x = 0 line and bending it around. That's what gravity does to geodesics. It curves them. Now imagine bending that x = 0 line around so that crosses itself at some point, and you come back to the same point in time and space you were in the past. That is a closed time-like curve, and that's how time travel in GR would work.

In flat space-time, you can see that to bend a path back around like that, one would have to go faster than light relative to an inertial observer. Bending around, that world line would have to have a slope > c at some point. And that prevents you from doing that.

But gravity, however, can indeed bend the geodesics around in closed time-like curves like that. Frame dragging (gravitomagnetism) is what can do it.

GR solutions with these time-loops exist. Now, that's some solutions to some equations, and no one has any idea if anything like that is really possible, nor any inkling of what it would be like physically to be in a space-time like that. Ron Mallet may soon find out. :)

-Richard

BISMARCK
2006-Nov-15, 03:47 AM
I'll be interested to see what happens.

astromark
2006-Nov-15, 09:16 AM
yes I understood all of that... Frame dragging and all. I am teasing you and I should not. So I'm Sorry. I still do not think that you could bend it the 360deg you would need. The event horizon would tear you to bits way before you got close enough to test this experiment. Some things we just can never do. In order for you to reach that point to see yourself leaving you would need to be traveling at a rate greater than c. That is not possible. Just as well as some of the things from my past I do not want to see again. Even as a laboratory test I can not comprehend this working.
Korjik., what fission reactor where? am I being misunderstood. I do not think that a fission reactor has worked for more than a few seconds any where on Earth. The containment plasma field is just to expensive and complex to sustain for more than a brief burst. Long enough to know it can work but, not actually a running fission reactor process. If this is wrong ( and it could be ) please direct me to the evidence of this.

swansont
2006-Nov-15, 11:45 AM
Korjik., what fission reactor where? am I being misunderstood. I do not think that a fission reactor has worked for more than a few seconds any where on Earth. The containment plasma field is just to expensive and complex to sustain for more than a brief burst. Long enough to know it can work but, not actually a running fission reactor process. If this is wrong ( and it could be ) please direct me to the evidence of this.

You are confusing fusion (combining nuclei) with fission (splitting them).

Kaptain K
2006-Nov-15, 04:38 PM
If your local newspaper carries the Non Sequitur comic strip, There is a humorous take on time travel in this coming Sunday's (11/19) strip.

antoniseb
2006-Nov-15, 04:43 PM
There is a humorous take on time travel in this coming Sunday's (11/19) strip.

I read this strip faithfully, but didn't know there was a look-ahead feature.

Kaptain K
2006-Nov-15, 04:56 PM
There isn't. I work in the production side of a newspaper. We receive the Sunday comics a week in advance. One minor perk to a mind-numbingly dull job.

Van Rijn
2006-Nov-15, 08:47 PM
There isn't. I work in the production side of a newspaper. We receive the Sunday comics a week in advance. One minor perk to a mind-numbingly dull job.

And here I thought you had come back in time, but you had to come up with that all too mundane answer. *sigh*

astromark
2006-Nov-16, 10:00 AM
I was not confusing fusion with fission... I just can't spell. I should have checked that. You should never spoil a story with the facts.
So where am I going to see this cartoon ?
A NZ paper? Sunday star times or what.

Van Rijn
2006-Nov-16, 10:16 AM
Google "Non Sequitur". There are several web sites where it can be found, like:

http://www.gocomics.com/nonsequitur/

Squashed
2006-Nov-16, 02:10 PM
Now, I pose to you all, what do you think? :D

-Richard

I think it is possible to make time stop but not go backwards and so someone could stop themselves and then restart themselves into their future (missing out on all the fun prior to the future moment) but not go backwards into the past.

I also have reason to believe that time dilation is merely a fundemental slowing of energy interactions, sort of like freezing food, and nothing more -- which would be useful for spacetravel but not historical research into the past (unless the participant tells about the history conditions of the present in a first-person account to those in the future).

I think Grav has a valid point (http://www.bautforum.com/showpost.php?p=865747&postcount=5) about time and its applications to physics.

grav
2006-Nov-17, 03:47 AM
I think Grav has a valid point about time and its applications to physics.Thanks. I try to see how some others think about time travel, like time is something that we actually travel through, with substance, but it makes no sense to me. Motion occurs in all directions and at varying rates. It is only the frame of reference that we use to measure it, such as a clock, that must always travel forward (or repeat cycles) consistently to be of any use to us, for comparison. I also try to see how travelling faster than light would accomplish this, but to do so would violate the very foundation the theory it is based upon, that nothing can travel faster than light to begin with, and would therefore render it null and useless. Even if one could, the result is not even negative time or space-time, but sqrt(-1), placing the object travelling at this speed outside of our geometry, and universe. And then, how would one slow down in order to re-enter with nothing to relate "slowing down" to? The speed of light, after all, is not absolute, but only relative.

I have, however, had some fun entertaining the thought of what a so-called time machine might entail. I find myself fascinated by the idea, usually thinking about it on the way to work. Let's say I created a time machine that could somehow reverse all of the motion in the universe at the same time. So I say goodbye to my friends, take a sip of water from a cup and pitcher on the counter, and climb in. The machine has glass walls so I can see what's happening outside of it. As I turn the dial, all motion steadily begins to slow down. I watch my friends moving more and more slowly until their motions finally stop. Then I turn the dial a little further and they begin slowly moving backwards. What would I see? Well, since I am no longer present, things would be a little different than they were when moving forward. The cup on the counter stays where it is. My friends are saying goodbye to noone. And talking backwards. They don't know I'm not there because they can't remember the future. I am simply rewinding "time". Their neural processes are being erased. Everything retraces its steps, but light that would have normally reflected off of me when I was there hits the floor and walls instead. The water that I poured into a cup remains where it was and so does the pitcher, even though those actions were initially caused by me. It is as if time is still running forward, but I have simply reversed the "polarity" of the universe, and am now absent from it.

In this scenario, energy is conserved because I am not present in the reversal, but I am still present in the machine. If I stop it at some point, others would think I just vanished and re-emerged from the machine, because their memories have been reversed to that point. Even though I just built the machine the day before, I could reverse time indefinitely, but everything I had contact with would now act differently. One disturbing part of all this, though, is that this would mean that our consciousness is not real, that our destiny is predetermined, and that we are simply going through the motions. If I then went back and kept my parents from ever meeting, it would have no consequence on me whatsoever. I already exist, but I am only reversing everything else. I am still trying to determine, however, what would happen to that cup and pitcher if I went back to a point before the counter was put in, for instance. The worker installing it (or uninstalling it) would undoubtedly cause it to fall and break or some such. Would his cuts still heal, since the polarity of the universe is reversed? He would never have even known it was there since he is simply going through the reverse motions of what he did before. Nor would he react to it, since his mind only remembers the past, which is constantly being erased. What also of the time machine? Would I eventually be run over by a bulldozer going in reverse as the construction of the building is undone? How about people that would have normally walked through the area the machine now sits? Would they just stop when they encounter the machine, or would they continue to go through the motions of what they would have done at that particular point in "time", because of what their brains "untell" them should be happening, even though their position has now changed? This could get very hazardous for everyone. I guess it would all depend on the precise physics one employs to reverse motion in the first place. My absence during the reversal and the placement of the time machine would both make a difference as to how things look when I reverse it. Even if the time machine was placed safely out of the way, I could never go back to precisely how things used to be because my absence would change things more and more considerably the further back I went. It would be like placing one path for motion on top of another, or even replacing it, so that things would eventually, if rewound far enough, appear to begin moving forward again as I sit watching from the machine.

Ken G
2006-Nov-17, 10:15 PM
Note that there are more mundane ways of creating timelike loops in spacetime, on the scale of elementary particles. Virtual particles do it all the time, but we want real particles here. Still, you can do it simply by colliding two very high energy photons, letting them annihilate into an electron-positron pair, and then the bring the electron-positron pair back together again to annihilate back into two photons a little later. One can view that whole process as a single electron that is created when it scatters a photon backward in time (photons move effortlessly in either time direction, being their own antiparticle), moves forward in time until it scatters a backward-time photon into a forward-time photon, at which point the electron will scatter backward in time and return to the point of its initial creation. The difference between this scenario, which is really just a particular interpretation of a process that does not violate cause and effect rules, and a true closed loop in spacetime is apparently that a true loop can indeed violate cause and effect rules. But this part is not so clear to me-- it sounds like he is saying he might be able to make a neutron go forward in time, act on it, and then have it follow a spacetime loop such that it propagates the information of that act backward in time. That's what he will have to show that he has done to make it interesting, it's the information that counts. My guess is, some process he has overlooked will bite him-- it has happened over and over again, the universe guards its rules of cause and effect more jealously than any other. There's always some subtle way to insure that information does not go faster than light, and does not go back in time.

publius
2006-Nov-17, 10:43 PM
But this part is not so clear to me-- it sounds like he is saying he might be able to make a neutron go forward in time, act on it, and then have it follow a spacetime loop such that it propagates the information of that act backward in time. That's what he will have to show that he has done to make it interesting, it's the information that counts. My guess is, some process he has overlooked will bite him-- it has happened over and over again, the universe guards its rules of cause and effect more jealously than any other. There's always some subtle way to insure that information does not go faster than light, and does not go back in time.

Ken,

When Mallet was speaking about this with Art, he was talking in general audience mode and didn't go into serious detail about things. Listening, I could surmise some of those details. I'm not sure if his prelimary test, the one he's got the money for is actually going to try to close a time loop or not, just see if space-time is acting like his EFE solutions say it will.

He mentioned neutron spin, and I so I surmised he will be looking for the "tidal B_g" push of a spinning particle off geodesics. Ie, if the frame dragging is there and acting like he thinks it will, he will see neutrons get pushed around in some specific way.

If he doesn't see what he expects, then his solutions were wrong. If he does see it, then things get interesting, and it's "More power, Scotty!"...."But, Captain, my poor engines are putting out all they can. Anymore, and she's gonna blow!". "Damn it, Mr.Scott, more power! She's hold together. You hear that ship, I said hold together!" If he does achieve closed time loops there, I'm not too sure he even knows exactly what those neutrons will do, other than he should see something strange. He said something about seeing more or less total neutrons that went in.

Mallet believes in a "many worlds" interpretation, and thinks that's how you get around the Grandfather paradox. There's all sorts of other possibilities, too, but that's what he believes. Just go back in time, start another parallel branch, and never get back on the original time line.

Another thing I wonder is if Mallet has taken into account the effect of the possible time-travelling mass-energy itself on his space-time. I remember that was what killed some other close-time loop solution. You could open the door so to speak, but the space-time was so unstable, the slightest mass-energy trying to go through that door would collapse it. And the only way around that was "negative mass-energy", whatever that would be to take with you to cancel your own energy out.

Anyway, that might be what kills it.

-Richard

publius
2006-Nov-17, 10:59 PM
Ken,

And another thing I'm not sure about is if closed time loops in GR is the same thing as "time reversal" in quantum theory. I mean with the latter, aren't you really "running proper clocks backwards"? That is, truly reversing the proper time? With a closed world line in GR, the proper time along that path is still positive, your own proper clock is running normally, you just go back relative to some else's time coordinates (such as the coordinate system you are specifying the solutions in). Your own clock runs foward, just gets warped so that foward time direction for you is backwards to what it was before.

-Richard

Ken G
2006-Nov-17, 11:07 PM
Just go back in time, start another parallel branch, and never get back on the original time line. That's probably why he expects he might see more or fewer neutrons-- they're either coming from or going to other parallel worlds. So he thinks the laws of cause and effect can bridge between parallel worlds. Certainly possible, but again, the evidence so far in "mundane" situations is that the universe conspires to make sure cause and effect work in our own world, to within the confines of the Heisenberg uncertainty principle. My money says it finds a way to do that here too, but it sounds like an interesting thing to test.


You could open the door so to speak, but the space-time was so unstable, the slightest mass-energy trying to go through that door would collapse it.Yeah, that's just the kind of thing the universe I know and love would do to avoid having its precious rules be violated beyond the finite reach of constructive interference that is the uncertainty principle.


And the only way around that was "negative mass-energy", whatever that would be to take with you to cancel your own energy out.
I'll bet if you took some of that with you, it would either also cancel the ability to propagate information back in time, or it would get killed in some other way. If I'm right, it certainly suggests that there must be some deeper theory that enforces the rules of information transit, which I vaguely call the rule of cause and effect. I frankly don't know if such a theory exists yet or not, there is certainly a lot in string theory that's pretty magnificent and bizarre.

eburacum45
2006-Nov-17, 11:56 PM
there must be some deeper theory that enforces the rules of information transit, which I vaguely call the rule of cause and effect. I frankly don't know if such a theory exists yet or not, there is certainly a lot in string theory that's pretty magnificent and bizarre.
Something like the Cronological Protection Conjecture (http://en.wikipedia.org/wiki/Chronology_Protection_Conjecture)?

Ken G
2006-Nov-18, 12:02 AM
Yes, that's just what I had in mind, but that's not really a theory-- just an element that theories might need to possess.

Michael Noonan
2006-Nov-18, 01:22 AM
Something like the Cronological Protection Conjecture (http://en.wikipedia.org/wiki/Chronology_Protection_Conjecture)?


Maybe all of time does not need to be turned around.

Time travel may have very different effects depending on the scale. If the effect is quantum only then it may be only the particles that experience a reverse aging process but for the object they form time still appears to go forwards. If this is the case then the genius of Einstein is magnifient. Imagine knowing that if your brain was correctly preserved it would regenerate. Were there very strict instructions that had to be followed and under no circumstances any damage to be done to the structure of the brain like sectioning for instance.

Cheers