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The Possibility of Paradox-Free Time Travel
relliker writes in with word of a paper up on the ArXiv by Seth Lloyd and co-workers, exploring the possibility that "postselection" effects in non-linear quantum mechanics might allow paradox-free time travel. "Lloyd's time machine gets around [the grandfather paradox] because of the probabilistic nature of quantum mechanics: anything that this time machine allows can also happen with finite probability anyway... Another interesting feature of this machine is that it does not require any of the distortions of spacetime that traditional time machines rely on. In these, the fabric of spacetime has to be ruthlessly twisted in a way that allows the time travel to occur. ... Postselection can only occur if quantum mechanics is nonlinear, something that seems possible in theory but has never been observed in practice. All the evidence so far is that quantum mechanics is linear. In fact some theorists propose that the seemingly impossible things that postselection allows is a kind of proof that quantum mechanics must be linear."
http://timecube.com/ ... obviously.
I have neither the capacity nor the will to vet the paper, but it should be noted that ArXiv is not peer reviewed. While experimentalists use it as a place to publish pre-prints of their papers and will typically only put them up after the papers have been accepted, but theorists use the medium as a substitute for publishing and so many wacky and untrue claims get put up there.
Time travel leads to Parallel universes that make paradox not happen in the one you left.
Am I the only person who has noticed the Authors name? Seth Lloyd = Sith Lord I think we should be very cautious of these findings.
The problem with all of those approaches is that they assume a "meta-time" (even if not stated as such) that will alter the PRESENT based upon changes in the FUTURE.
That's how a photograph that you have right (taken in the future) now will change based upon events that have not happened yet.
Once you get past that, you understand that there is no "grandfather paradox". If it exists in the current time then it exists in the current time. The future will not reach back and "clean up" the present to make it more acceptable to the future.
Obligatory cartoon linkage:
http://www.smbc-comics.com/
You can dress up pseudoscience with a bunch of equations, but tell me how this is based on any type of actual science. If this is science, then Deepak Chopra must be an actual genius...
I'm not an expert but it does seem like a lot of physicists are just lost in their own little worlds. I realize science is a process, but spending valuable time "researching" time travel, before we can even explain what time or even gravity is, seems like skipping over the hard work to spend time on "fun stuff".
http://www.smbc-comics.com/
Has nobody anything snarky to say?
They are too busy trying to build postselection time machines. Expect to lose your first post status as soon as one of them succeeds.
The Tao of math: The numbers you can count are not the real numbers.
Yes, but the keys will be postselected to be in the worst case possible.
The Tao of math: The numbers you can count are not the real numbers.
The movie "Primer" had an interesting take on avoiding paradoxes. http://video.google.com/videoplay?docid=3909854615539675694# (entire movie online)
Insightful and funny are really the same thing, except one has a punch line.
Or, we go with the simple, elegant solution to the problem...it's not possible.
t
Now, if we can just hook in the logic circuits of a Bambleweeny 57 Sub-Meson Brain to an atomic vector plotter suspended in a strong Brownian Motion producer (say a nice hot cup of tea)...
It must have been something you assimilated. . . .
And if you travel outside of your light-cone? (other then math breaking down)
6.8SPC TR of 550, l xwind at 6, drift rt at 26" drops 77". AT has 503 ft-lbs at 1403 fps. FT 0.86
Quantum mechanics is a big tease. It seems whenever it's about to give you Jetsons or Stargate technology, there's always a big fucking loophole or caveat. You can go into the past, but you can't come back and/or die; you can travel faster than light, but the universe will end before you reach your destination; you can predict the future, but will change it in the process without knowing what the change is; you can date 3-breasted aliens, but they all have penises, or whatever. (Okay, I made up the last one.)
There must be a God, because nature wouldn't find a way to tease us with so many Almost's and fuck with our minds in so many different ways that QM does.
Or maybe it's the anthropic principle keeping us from destroying the universe with time weapons?
Something odd is going on. Time for a congressional investigation.
Table-ized A.I.
As far as I can tell, the article is saying that if you impose a condition in the present, you cause the past to change so that it matches. This process of imposing a condition must affect the quantum mechanical properties of whatever you are checking, similar to a quantum computer.
So basically, if your granddad rigs up a machine that kills him depending on the quantum state of a particle, and then he leaves that particle in an indeterminate quantum state until he has your dad and your dad has you, and then you collapse that particle's waveform into the state that would have killed him, he will have died back then. And somehow paradox is avoided.
Wha?
i'd hit it so hard, if you pulled me out you'd be the king of britain [bash.org]
I can accept FTL travel as maybe possible, but time travel seems farfetched to me. It means that every single state that the universe has ever been in is preserved (somewhere) in it's exact state. We're not talking about the awareness of the state being preserved on the speed-of-light boundary away from the location of the state, it's the actual state, in a way that can be modified and changed. Does this even seem reasonable? How could all that be stored?
Not only that, it means that a change in one of those states will instantly change every subsequent state. So when you travel back, everything will be different. This is really hard to believe.
Qxe4
But if I'm going BACK in time, I'm taking some aspirin, toothpaste, deodorant, and toilet paper with me. I hope the machine is big enough.
Don't forget your towel you insensitive clod!
My ignorance is just as good as your knowledge.
Pretty much, yep. Because you are now existing at a prior point in the chain of causality. So you've already accepted either:
1. circular causality (and a supreme janitor who cleans up the past to keep the future tidy) (and how would you tell the difference) or
2. effect without cause (because you exist prior to your parents giving birth to you).
“The Encyclopedia Galactica has much to say on the theory and practice of time travel, most of which is incomprehensible to anyone who hasn’t spent at least four lifetimes studying advanced hypermathematics, and since it was impossible to do this before time travel was invented, there is a certain amount of confusion as to how the idea was arrived at in the first place. One rationalization of this problem states that time travel was, by its very nature, discovered simultaneously at all periods of history, but this is clearly bunk. The trouble is that a lot of history is now quite clearly bunk as well.”
The concept of a paradox is entirely a human concept - in other words, it's in the eye of the observer. The universe wouldn't "classify" you going back in time and killing your great-grandparents before you were born as a paradox, simply because the universe is not an observer. It would happen - so what - "It is what it is". That would just be part and parcel of the way the universe works in that particular case.
Attempting to say that this would result in a paradox as far as the universe is concerned is anthropomorphizing the universe to an absolutely unforgivable degree. Sure, it makes for a good time travel story, but the universe won't lose any sleep over it, any more than it does for me writing "The next phrase is false." "The previous phrase is true." "Both the previous phrases are true" "The previous phrase is true" There's no paradox. The universe doesn't suddenly go wonky, and cats mate with dogs, etc.
Grandfather paradox: Go back in time, shoot your grandfather... now your father wasn't born, you weren't born. Which means your grandfather doesn't get shot, so you get to be born, etc... the universe flip-flops your time travel forever, the record is skipping for eternity.
I personally like Primer and it's time machine concept. You could go back to yesterday and kill yourself, that version of you would die but you would not disappear. Also if you kept the yesterday you from going in the time machine you now have 2 of yourself that you're stuck with. No paradoxes, it runs more a computer program or a flowchart.
Grandfather paradox requires a sort of feedback loop in time where the universe seemingly gets stuck in a cycle until things resolve themselves.
Cwm, fjord-bank glyphs vext quiz
Neither. Assuming he's right (and the Technology Review article correctly reproduced his claims; I haven't actually read the arXive article yet), he proved that you cannot have non-linear quantum mechanics without time travel. Given that some people try to resolve the measurement problem by adding nonlinearities, that's certainly an interesting result.
The Tao of math: The numbers you can count are not the real numbers.
I think it's the first one, but only because I'm pretty sure it can be rephrased thus:
"He proved that paradox-free time travel is possible through postselection of quantum teleportation by postselecting the condition that quantum mechanics is non-linear."
However, I believe this phrasing assumes that the probability of quantum mechanics being non-linear is nonzero, so if I just divided by zero, I apologize.
Let q be a radix > 1. I am in ur base-q, killing 10 d00ds.
Yesterdays SMBC had a good point:
You can not have any motivation or objective if you are going to travel otherwise the act of time travel is a paradox. SMBC put it thusly: if you are travelling to change some outcome, and you succeeded, you would not have had the motivation to time travel to make that change.
SMBC's conclusion was that only nitwits have the capacity to time travel and the fact that there seem to be so many confirms that time travel must be going on right now.
But another way to say this is, you can only choose objectives that either already happened in your past or are inevitable no matter what you do.
For example, You could however travel with the objective of sinking the Titanic, but not the objective of preventing the sinking. If you saved the titanic, it would never occur to you to try to save the titanic.
For example, If your objective was to save Abe Lincoln and you succeeded, then it never would have occurred to your pre-travel self that you needed to go back and save abe lincoln.
What all this adds up to I think is that time travel is still forbidden but observational time travel-- gathering information-- is not forbidden.
THere is an interesting proof regarding the computability of any proposition by David Wolpert that shows time travel is forbidden unless the information you gain by doing so is probabilistic or faulty. That is he proves rigorously that it is not possible to answer any arbitrary true/false question about the past with perfect fidelity. Thus time travel that preserves information with fidelity is forbidden. Error prone time travel is however allowed.
Some drink at the fountain of knowledge. Others just gargle.
it does not require any of the distortions of spacetime that traditional time machines rely on.
Wait, did I missed the part where time machines were something traditional or common or anything like that ?
Seriously, time travel became mainstream and nobody told me ?
Segmentation Fault in "Life, Universe and Everything" at line 42. Don't Panic.
I'm completely with the parent.
While I don't think that you can call pseudoscience the exploration of the implications of a theory that are unlikely to be possible in practice, let's assume it's pseudoscience. So what? It was pretty interesting read, at worst it will serve as an inspiration to some science fiction author. It's interesting. You know why? Because it is "fun stuff"! Also, as the parent stated, exploring the theoretical possibilities provides better understanding of the model, allows you to improve the model and might allow you to find the boundaries where the model stops being correct. Also, making advances in the part that don't apply in practise might improve the understanding of the practical part of the model. Infinitesimals don't seem to exist in our universe, but the models that explore their properties closely have been the basis for most of the physics.
Also, I might not understand the article completely, but it, along with another report that was posted to Slashdot less than an year ago, seems to show a method of time "travel" that doesn't allow to send information back in time at all. Seems reasonable, and not against anything that I know about the world I'm living in. It would completely blow out my idea of time -- I'm a firm believer that only the current moment exists, and you can't affect or travel to previous ones, and that other interpretations of time are merely implementation details of the physical models we use -- but these results wouldn't be against any physics I know. Also, even if there is an experiment that confirms that this paper isn't bullshit, and it is empirically proven that this kind of time "travel" is possible, the results won't have a single interpretation. I wouldn't be surprised even if someone builds another model that doesn't involve any time travel that explains the same empirical results.
Yes, someone needs to verify the premises and the conclusions, I don't have good enough knowledge to do that myself on the first read, but I didn't see any mistakes pointed out by the GP, only baseless claims, so I'd rather go with the article and/or the paper. I have a direct question for the GP: We have no idea what time is, OK. Suppose that our current theoretical model allows for time travel (which would seem to be the case unless the article is full of mistakes). Are you denying that testing them would allow us to be closer to understanding what time is?
If time travel existed at some point in the future, we would have had evidence of its existence in the past...
Seven puppies were harmed during the making of this post.
Yes, but what if with the act of time travel with motivation you also create an alternate reality where the titanic didn't sink or abe lincoln survived? Is there some rule where you must be attached to your original timeline?
John Titor
Sig: I stole this sig.
Citation needed.
David Deutsch, Quantum mechanics near closed timelike lines, Phys. Rev. D 44, 3197–3217 (1991)
The Tao of math: The numbers you can count are not the real numbers.
we'll always be
just apes in a tree
rewriting history since 2109
Now wouldn't this effectively get around the grandfather clause, since you have basically created a closed loop? Because unless I missed something you could alter the past while giving your future self the knowledge of what you have done, thus allowing him to do the same and closing the loop.
I'm no expert, but the idea that the universe is a sort of cosmic small claims court judge who will grudgingly let you off the hook for your liabilities if you ticked all the right boxes on form TT-8710 seems... far-fetched to me.
"...always new atoms but always doing the same dance, remembering what the dance was yesterday." -Richard Feynman
'Dead simple', huh !?! Are you an economist or an administrative policy writer by any chance ?
Non-Linux Penguins ?