Time Travel Theories Debunked by Hong-Kong Researchers

[Lord Loss]

Researchers in Hong-Kong (Pr. Shengwang of the Hong Kong University of Science and Technology, and his colleagues). prove that a particle cannot accelerate past light-speed, debunking most current time-travel theories. Other theories, however, such as Einstein's General Relativity Theory, remain intact.

This discovery probably means a lot of other stuff, beyond time travel.

French Article Here: Sorry, I couldn't fidn an english version. (http://synchro.sympatico.ca/actualite/sciences/physique_impossible_de_voyager_dans_le_temps/0720653a)

EDIT: Wrong Forum. Please move to Friendly Banter.

[Mewtarthio]

Wait, wasn't it already impossible to go past light speed? :smallconfused:

[Z3ro]

Not really new, though I would like to point out that lots of things have been "proven", then later proven wrong.

Though I always thought the current favorite theory for FTL travel was the Star Trek version, i.e. you can't move objects through space FTL, but nothing says you can't move space itself FTL. So just come up with a way to put something in a space bubble, and away you go.

[Tengu_temp]

Though I always thought the current favorite theory for FTL travel was the Star Trek version, i.e. you can't move objects through space FTL, but nothing says you can't move space itself FTL. So just come up with a way to put something in a space bubble, and away you go.

That's not how real physics work.

[Cog]

That's not how real physics work.
Miguel Alcubierre (http://en.wikipedia.org/wiki/Alcubierre_drive) might disagree with you.

[Eakin]

... At the press conference announcing their results, Abraham Lincoln appeared riding a flying stagecoach pulled by velociraptors and encouraged scientists to keep trying, they'd figure it out eventually

[Cespenar]

Ah, physicists and their cute little games. :smalltongue:

[Eldonauran]

So, particles can't move faster than light ... We knew this already. :smallconfused:

You really want to time travel and/or move FTL? Get into quantum physics.

[golentan]

*Squee!*

You humans and all your theories and experiments. It's just *so cute* how hard you try to understand a world that is simply beyond your ability to comprehend it. :smallbiggrin:

[Trixie]

Miguel Alcubierre (http://en.wikipedia.org/wiki/Alcubierre_drive) might disagree with you.

Except it still doesn't move faster than light, and is fictional anyway.

[Zen Monkey]

Good news everyone!

All you have to do is get the ship to hold still and move the entire universe around it. Nothing is impossible if you believe in the power of science!

Now, if anyone needs me, I'll be in the angry dome.

[Z3ro]

That's not how real physics work.

Not how they work yet.

[JoseB]

Except it still doesn't move faster than light, and is fictional anyway.

Point of order: Alcubierre's drive is not fictional, it is *hypotetical* and theoretically possible. That is VERY different (in the context of physics, I interpret "fictional" as meaning "it will break the laws of physics and is not possible at all").

Alcubierre's drive is based on sound mathematics. The results are consistent with the equations of relativity, and the mathematics are correct. We may not have the slightest idea of how to actually implement it (if at all), but that doesn't automatically mean that it is impossible, or that it will remain so forever.

A good example of this "theoretically possible" thing would be antimatter: When Dirac predicted the existence of antimatter in 1928, based *ONLY* in the fact that it was mathematically consistent and didn't violate any laws of physics as known at the time, most scientists thought he was being silly. Until the positron was discovered in 1932, that is. That earned him the Nobel Prize in 1933.

Another good example would be the concept of a "space elevator". It is theoretically possible, but we have no idea of how to build one on Earth (maybe fibers of carbon nanotubes might be used to create a belt or string possessing the humongous tensile strength and minimal weight necessary for the project, but we don't know -- that doesn't prevent many institutions and agencies from working on it, though. Possibly because, as a matter of fact, space elevators on places with a weaker gravitational field were possible with the technology available in 1978, as this paper from that time mentions (http://www.frc.ri.cmu.edu/~hpm/project.archive/1976.skyhook/papers/scasci.txt)).

In any case, going by what I can read in the link provided by the OP (and it is a rather short abstract of the whole thing, it seems), I would say that those guys in Hong Kong have discovered the wheel. It was already well known that photons don't go over the speed of light in a vacuum (notation: c). If you mess with them, you may slow them down, but nothing will make them shoot faster than c. It is generally agreed that the only way to achieve superluminic communications or transport is either to mess with spacetime to make a bubble of spacetime move faster than light relative to the rest (Alcubierre), to "fold" spacetime itself to "join" distant points (wormholes) or to achieve control over quantum effects (quantum entanglement appears to be superluminal -- check Bell's theorem (http://en.wikipedia.org/wiki/Bell%27s_theorem) and the tests of Bell's theorem (http://en.wikipedia.org/wiki/Bell_test_experiments), which -although exposed to loopholes- have been repeated enough times and in enough different ways that most physicists agree in that certain quantum effects are non-local, which implies superluminal influences. However, although you may have superluminal quantum influences, it appears to be impossible to use them to send anything that is not random bits).

In fact, when I first read the OP, I thought that those Hong Kong researchers had been able to prove the inexistence of tachyons (tachyons are yet another example of something theoretically and mathematically possible that doesn't violate relativity, yet are veeeeeeery weird: They are hypothetical particles that *ALWAYS* go *FASTER* than c -- They would never slow down enough to even reach c, much less going below it).

[Kane]

Saw this elsewhere. I suppose it bears mentioning that the scientists doing this research were doing so in a country that has outlawed time travel.

[Mono Vertigo]

{Scrubbed}

[nerd-7i+42e]

Huh? We've known particles can't travel faster than light since relativity.

[Spiryt]

And my grandpa still sleeps restfully.

[Dr.Epic]

Wait, wasn't it already impossible to go past light speed? :smallconfused:

Not for team Gurren. Otherwise that last end fight in the series would have taken forever.

[Tyndmyr]

Haha, the fools! I've been travelling forward in time for...*checks watch*...29 years now! You'll never stop me!

[enderlord99]

Haha, the fools! I've been travelling forward in time for...*checks watch*...29 years now! You'll never stop me!

At 1 second/second?

[tyckspoon]

Huh? We've known particles can't travel faster than light since relativity.

Strictly, we've known it's impossible to accelerate a sub-light particle to faster than light. The math does permit for some faster-than-light effects, and some of them, mostly dealing with quantum entanglement, are observable. Tachyons as mentioned up-thread are a possibility (although I don't think anybody knows how we would actually detect them, should they exist, because they're highly unlikely to interact with our dull sub-light matter in any identifiable way), and if you have enough energy of the right variety to play with you can change local properties of space-time so that the speed of light is different, and thus appear to be going 'faster' than light to an outside observer.

[Eurus]

Strictly, we've known it's impossible to accelerate a sub-light particle to faster than light. The math does permit for some faster-than-light effects, and some of them, mostly dealing with quantum entanglement, are observable. Tachyons as mentioned up-thread are a possibility (although I don't think anybody knows how we would actually detect them, should they exist, because they're highly unlikely to interact with our dull sub-light matter in any identifiable way), and if you have enough energy of the right variety to play with you can change local properties of space-time so that the speed of light is different, and thus appear to be going 'faster' than light to an outside observer.

"That's why we raised the speed of light in 2208!"

[Cobalt]

At 1 second/second?

He's a madman.

[RandomNPC]

He's a madman.

Does he have a box?

[enderlord99]

Does he have a box?

:smallconfused:

[turkishproverb]

I always have to hesitate on trusting Chinese studies, simply because it's a country that so dislikes sharing research.

Mind you, that one theiry wasn't the odd thing about that type of sub particle. Or even the faster than light problem about certian types of particles. The odd thing was the way they could be made to "communicate" for lack of a better term faster than lightspeed.


Does he have a box?

I got it.

[golentan]

Does he have a box?

I should hope so. And a bow tie. Bow ties are cool.

[Ravens_cry]

Huh? We've known particles can't travel faster than light since relativity.

Relativity is a theory to explain how the world works. One of its predictions is that particles can't travel faster than light. This result demonstrates that experimentally.

[RebelRogue]

No amount of observations can ever disprove the existence of something.

[Gaius Marius]

No amount of observations can ever disprove the existence of something.

I am not sure. Just by observing your post, I can disprove the existence of accuracy in it.

[JoseB]

Relativity is a theory to explain how the world works. One of its predictions is that particles can't travel faster than light. This result demonstrates that experimentally.

First of all, the experiment has nothing to do with "particles" but with photons, which have peculiarities that distinguish them from your average subatomic particle (namely, their lack of mass, for one).

And if this experiment had been done with subatomic particles, it still wouldn't have shown anything new, because relativistic effects were already abundantly demonstrated by simply observing the behaviour of subatomic particles in particle accelerators.

As I mentioned earlier in post #13, what these people in Hong Kong appear to have done is reinvent the wheel. This particular property of photons (that they won't go faster than c, the speed of light in a vacuum) was also very well known and checked out.

So, either these scientists have discovered something in the line of "the Sun rises at dawn", or (perhaps more likely) the press write-up made available is so bad that it doesn't make sense and doesn't really explain what it is these scientists have found.

[Liffguard]

(perhaps more likely) the press write-up made available is so bad that it doesn't make sense and doesn't really explain what it is these scientists have found.

I'd be inclined to believe this explanation. The quality of science reporting in the english speaking world is generally atrocious. I'm a complete layman when it comes to the sciences and even I have to cringe at most science stories in mainstream newspapers or on TV news shows.

[Ravens_cry]

First of all, the experiment has nothing to do with "particles" but with photons, which have peculiarities that distinguish them from your average subatomic particle (namely, their lack of mass, for one).

How about we call it both (http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality) and leave it at that?


And if this experiment had been done with subatomic particles, it still wouldn't have shown anything new, because relativistic effects were already abundantly demonstrated by simply observing the behaviour of subatomic particles in particle accelerators.

As I mentioned earlier in post #13, what these people in Hong Kong appear to have done is reinvent the wheel. This particular property of photons (that they won't go faster than c, the speed of light in a vacuum) was also very well known and checked out.

So, either these scientists have discovered something in the line of "the Sun rises at dawn", or (perhaps more likely) the press write-up made available is so bad that it doesn't make sense and doesn't really explain what it is these scientists have found.
It's hard to tell, I don't read French so I am forced to resort to more technological solutions. Something may have been lost in either the translation from French to English or Science to Layman. Or, again, both.
My point was that we have not 'known' this because of relativity, relativity just predicted, which this and other, earlier experiments have verified. Pedantic? You be the judge. I personally think it is an important distinction between the theory and the law.

[JoseB]

How about we call it both (http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality) and leave it at that?

It's hard to tell, I don't read French so I am forced to resort to more technological solutions. Something may have been lost in either the translation from French to English or Science to Layman. Or, again, both.
My point was that we have not 'known' this because of relativity, relativity just predicted, which this and other, earlier experiments have verified. Pedantic? You be the judge. I personally think it is an important distinction between the theory and the law.

It's OK. I guess that we will not know what these people have really done until a longer, better article or paper is published. I speak French, and I could see that the article in the OP didn't really explain things.

It never hurts to re-do experiments from time to time to see if we may have missed something (a very famous example was the announcement in 1923 by Theophilus Painter that humans have 48 chromosomes in 24 pairs. It was only in 1956 that Tijo and Levan repeated the experiment and found that humans had only 46 chromosomes in 23 pairs. It seems that Painter's preparations broke chromosome 1 in two and he counted it double (http://www.nature.com/scitable/topicpage/human-chromosome-number-294)). However, I still think in this case that, if they truly have done what that article says (and that as big "if", given the average quality of science news in the mainstream press), their experiment doesn't really add to what we already knew.

[The_Final_Stand]

Light photons cannot go faster than the speed of light.

In other news, people have been observed to die when they are killed.

[turkishproverb]

Light photons cannot go faster than the speed of light.

In other news, people have been observed to die when they are killed.

:xykon: I knew there was a reason we kept this guy around

[Ravens_cry]

It's OK. I guess that we will not know what these people have really done until a longer, better article or paper is published. I speak French, and I could see that the article in the OP didn't really explain things.

It never hurts to re-do experiments from time to time to see if we may have missed something (a very famous example was the announcement in 1923 by Theophilus Painter that humans have 48 chromosomes in 24 pairs. It was only in 1956 that Tijo and Levan repeated the experiment and found that humans had only 46 chromosomes in 23 pairs. It seems that Painter's preparations broke chromosome 1 in two and he counted it double (http://www.nature.com/scitable/topicpage/human-chromosome-number-294)). However, I still think in this case that, if they truly have done what that article says (and that as big "if", given the average quality of science news in the mainstream press), their experiment doesn't really add to what we already knew.
Perhaps. This (http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.106.243602)article gives a clearer idea on what the experiment showed. The Wikipedia on FTL page mentions the idea an individual photon (http://en.wikipedia.org/wiki/Faster-than-light#Quantum_mechanics) could go faster than the cosmic "speed limit" had to do with the uncertainty principle, so the experiment may have more pertinence than thought. I agree that mainstream news often doesn't do the best job at reporting Science news,

[Dvandemon]

In other news, people have been observed to die when they are killed.

Unless you are a MAN!

[Lord Vampyre]

I am not sure. Just by observing your post, I can disprove the existence of accuracy in it.

I believe what he means is that nothing can ever be truly proven. And since to disprove something, you are proving its negative, then nothing can ever be disproven.

However, we can observe something, but that observation is not in and of itself proof.

Now, physics has a few laws that we tend to abide by. These laws have never been proven, merely observed. In order for physics to work, these laws have to remain true. If at any point these laws are shown not to work under the right circumstances, new rules will be invented to show that the old rules were merely simplifications of the new rules. This has actually happened quite a few times in science.

[tyckspoon]

I believe what he means is that nothing can ever be truly proven. And since to disprove something, you are proving its negative, then nothing can ever be disproven.


eh.. not quite. You can disprove an absolute statement pretty easily- either "This thing does not happen" or "This thing always happens this way." Simply record something either happening that wasn't supposed to, or something happening in a different way than it is expected to. Proving something works 100% the way you say it does, on the other hand, is pretty much impossible; you can gather an overwhelming body of evidence and get everybody using your claim because it's the best current explanation, but you generally can't guarantee nobody will ever find an exception.

[enderlord99]

Another way to debunk time travel:

Velocity=distance/time
X/X=1
Temporal Velocity=1

[pendell]

I am not sure. Just by observing your post, I can disprove the existence of accuracy in it.

Sig-worthy.

Respectfully,

Brian P.

[Lord Vampyre]

eh.. not quite. You can disprove an absolute statement pretty easily- either "This thing does not happen" or "This thing always happens this way." Simply record something either happening that wasn't supposed to, or something happening in a different way than it is expected to. Proving something works 100% the way you say it does, on the other hand, is pretty much impossible; you can gather an overwhelming body of evidence and get everybody using your claim because it's the best current explanation, but you generally can't guarantee nobody will ever find an exception.

Actually disproving something tends to be slightly more complicated than that. The fact that you observed something to happen differently than what the original theorem predicted, probably means that not all of the variables had been accounted for. Thus, you haven't actually disproven anything. You have merely shown that you will get different results with the new set of variables. Unfortunately observation in science is not in and of itself proof.

[windweaver]

Does he have a box?

No. He's just a madman. On the other hand I most certainly am, a madman with a box. It's bigger on the inside :smallwink:

[shawnhcorey]

Not really new, though I would like to point out that lots of things have been "proven", then later proven wrong.

Though I always thought the current favorite theory for FTL travel was the Star Trek version, i.e. you can't move objects through space FTL, but nothing says you can't move space itself FTL. So just come up with a way to put something in a space bubble, and away you go.

So far, all theories on this involve negative energy and no-one has figured out how to create this. On the other hand, during the hyper-inflation of the universe (https://secure.wikimedia.org/wikipedia/en/wiki/Cosmic_inflation), the distances between parts of it grew at speeds greater than the speed of light. Of course, there was no movement or change in momentum, so this doesn't really count.

[Sipex]

I dunno, taking some theories, there could be ways to move faster than the speed of light but only if the following are true:

1) The universe rapidly expanded during the creation of itself.
2) There's no friction to stop the expansion of the universe, so everything must be moving at the same speed it was moving at the beginning of time. As shown in space, planets keep spinning and orbiting because there's no friction to slow this down.
3) The speed of light is currently the speed everything is moving + the speed of light.

Therefore light is technically already moving faster than the speed of light (in a non-moving vaccuum at least).

I'm not a physicist so feel free to point out what I got wrong.

[shawnhcorey]

I dunno, taking some theories, there could be ways to move faster than the speed of light but only if the following are true:

1) The universe rapidly expanded during the creation of itself.

Yes, but no movement or change in momentum occurred. Just the distances between objects increased.


2) There's no friction to stop the expansion of the universe, so everything must be moving at the same speed it was moving at the beginning of time. As shown in space, planets keep spinning and orbiting because there's no friction to slow this down.

The expansion of the universe was not caused by movement, so fiction of any type is not a consideration.


3) The speed of light is currently the speed everything is moving + the speed of light.

The speed of light is constant with respect to the observer. You can't add the speed of light to the speed of the observer. See Special Relativity (https://secure.wikimedia.org/wikipedia/en/wiki/Special_relativity) for details.


Therefore light is technically already moving faster than the speed of light (in a non-moving vaccuum at least).

I'm not a physicist so feel free to point out what I got wrong.

There is no absolute frame of reference. The best you can get is an inertial frame of reference (https://secure.wikimedia.org/wikipedia/en/wiki/Inertial_frame_of_reference).

[Liffguard]

2) There's no friction to stop the expansion of the universe, so everything must be moving at the same speed it was moving at the beginning of time. As shown in space, planets keep spinning and orbiting because there's no friction to slow this down.

Shawnhcorey already covered most of it. It's worth expanding on this. The expansion of the universe is not the movement of objects further into space. It is the expansion of space. It is not expanding into anything, the space in which it is possible for things to expand is itself expanding.

Also, space is not a vacuum. Not even deep intergalactic space. Sure, from the point-of-view of a scale that humans are comfortable with it's practically a vacuum for all intents and purposes but there is matter there. Just extremely rarefied, so there is some friction.

[Sipex]

Ah, I figured there were some off points but bringing it up helped clarify.

I learned something, hooray.

[Thajocoth]

I thought this up a long time ago:

Let's assume someone invents time travel. From this moment onward, there are infinite people who will interact with time travel. It is possible for time travel to somehow hurt someone badly enough for them to try to stop it. If it is possible, and there are infinite people, by probability, it will eventually happen. The person will use time travel to the moment right before time travel is invented. They stop the invention from occurring. The new future with time travel ceases to exist and is replaced by one without time travel. As far as the universe knows, someone spontaneously came into existence with memories of things that never occurred, and stopped someone else from doing something.

[Douglas]

I thought this up a long time ago:

Let's assume someone invents time travel. From this moment onward, there are infinite people who will interact with time travel. It is possible for time travel to somehow hurt someone badly enough for them to try to stop it. If it is possible, and there are infinite people, by probability, it will eventually happen. The person will use time travel to the moment right before time travel is invented. They stop the invention from occurring. The new future with time travel ceases to exist and is replaced by one without time travel. As far as the universe knows, someone spontaneously came into existence with memories of things that never occurred, and stopped someone else from doing something.
It's a fairly common theory that even if time travel is possible it cannot allow travel to before the creation of the time machine.

For myself, I think that the Novikov self-consistency principle (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle) is correct.

[Thajocoth]

It's a fairly common theory that even if time travel is possible it cannot allow travel to before the creation of the time machine.

For myself, I think that the Novikov self-consistency principle (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle) is correct.

I believe that the idea of a paradox doesn't make sense. If you go back in time and kill your father, you don't get born, sure... But you still exist and have all the memories of growing up. That's not a paradox in my opinion. As far as the universe knows, you spontaneously existed with memories of events that will not occur. The idea that everything will always coincidentally work out to having been that way all along seems far too complex and far fetched to me.

[Douglas]

I believe that the idea of a paradox doesn't make sense. If you go back in time and kill your father, you don't get born, sure... But you still exist and have all the memories of growing up. That's not a paradox in my opinion. As far as the universe knows, you spontaneously existed with memories of events that will not occur.
From the perspective of the resulting timeline, your initial appearance has no cause and could only result from an absurdly unlikely combination of randomness - something on the order of taking a billion smashed glasses, throwing the pieces of them at a table one glass at a time, and each and every glasses spontaneously reassembling itself on impact due entirely to random chance. Not going to happen.


The idea that everything will always coincidentally work out to having been that way all along seems far too complex and far fetched to me.
This, on the other hand, merely requires an insanely complex computation to determine what combination of events would form a consistent loop. The universe has effectively infinite computational power with regard to determining the proper outcome of physical events, so this is a trivial problem and not an obstacle at all.

[Thajocoth]

This, on the other hand, merely requires an insanely complex computation to determine what combination of events would form a consistent loop. The universe has effectively infinite computational power with regard to determining the proper outcome of physical events, so this is a trivial problem and not an obstacle at all.

I do not believe that the universe has any computational power or performs any computations at all. It's not a computer, it's a universe. Just a collection of matter, energy, and maybe undiscovered things, but maybe not. It does not need itself to be consistent. It has no way or reason to care.

At least, in my opinion. And I'll leave this at that.

[Sipex]

If you could go back in time to stop the creation of the time machine and therefore change history then the universe would require multiple timelines.

That said, that means you'd be in an infinite loop.

1) The time machine is invented and someone goes back to stop it.
2) The time machine isn't invented due to 1 and no one goes back to stop it.
3) The time machine is invented because no one goes back to stop it...

etc

[Douglas]

I do not believe that the universe has any computational power or performs any computations at all. It's not a computer, it's a universe. Just a collection of matter, energy, and maybe undiscovered things, but maybe not. It does not need itself to be consistent. It has no way or reason to care.

At least, in my opinion. And I'll leave this at that.
True, the universe does not "need" itself to be consistent, and I'd go even further and say that the universe caring about it is a meaningless idea - the universe doesn't have a mind that could care about anything in the first place.

However, pretty much all of modern science rests on the foundational assumption - which matches all observations to date - that the universe IS consistent. Whether it needs to be consistent or not is irrelevant, it simply is consistent as a basic fact of existence.

As for the universe not performing any computations: in the sense of some cosmic background computer taking input and calculating what should happen and thereby determining what does happen, maybe not. In the sense of producing results as if that computation took place, most certainly yes. You see an object traveling at X location and Y velocity, you calculate that at T time it will be at Z location according to the laws of physics, you check, and lo and behold the object is indeed there! How does the universe decide this? The object's course is the same regardless of whether you perform your computation, yet it matches what that computation would say anyway. How did the universe figure it out?

The universe may not operate by calculating everything, but it does follow a set of rules that produce results that can in theory be calculated. The difference between those rules producing "X particle will follow Y path" and "Z collection of 2903875984302578902347509238457238 particles will go through list of events E" is a matter of scale and complexity, not fundamental nature. As far as the universe is concerned, the rules it operates by are simply true facts; any amount of complexity or scale they might involve is nothing more than an irrelevant side note. If holding to those rules requires a bizarre sequence of events that would take a sun-sized quantum computer a trillion years to figure out, then so be it, that sequence of events is what happens even if it's only a millisecond's worth of history on a subatomic scale; further, the process of determining what that sequence is has no effect whatsoever on when or how it happens or how any observers might perceive it. Figuring out such an enormously complex interaction is, as far as the universe is concerned, effectively instantaneous and free no matter how difficult it might be for a sentient observer to calculate it independently.

So, for the idea of time travel coincidental consistency being false because it's too complex, I say nonsense. It might take a galaxy-sized maximally efficient computer a billion times the age of the universe to figure out a combination of coincidences that make a consistent timeline for a single occurrence of time travel, but for the universe such a degree of complexity is as inconsequential as the single smallest hair on your left thumb is for you.

[Al'izh'dheg]

Light photons cannot go faster than the speed of light.

In other news, people have been observed to die when they are killed.

Best. Summation. Ever! :smallbiggrin:

[shawnhcorey]

I do not believe that the universe has any computational power or performs any computations at all. It's not a computer, it's a universe. Just a collection of matter, energy, and maybe undiscovered things, but maybe not. It does not need itself to be consistent. It has no way or reason to care.

At least, in my opinion. And I'll leave this at that.

I disagree. At its simplest, a calculator is nothing but a bunch of electrons running around a circuit. But they calculate because they has consistent behaviour. Same with the rest of the universe.

[Lamech]

I believe that the idea of a paradox doesn't make sense. If you go back in time and kill your father, you don't get born, sure... But you still exist and have all the memories of growing up. That's not a paradox in my opinion. As far as the universe knows, you spontaneously existed with memories of events that will not occur.From the perspective of the resulting timeline, your initial appearance has no cause and could only result from an absurdly unlikely combination of randomness - something on the order of taking a billion smashed glasses, throwing the pieces of them at a table one glass at a time, and each and every glasses spontaneously reassembling itself on impact due entirely to random chance. Not going to happen.



The idea that everything will always coincidentally work out to having been that way all along seems far too complex and far fetched to me.
This, on the other hand, merely requires an insanely complex computation to determine what combination of events would form a consistent loop. The universe has effectively infinite computational power with regard to determining the proper outcome of physical events, so this is a trivial problem and not an obstacle at all.Umm... the second one is the "unlikely" one. See for the first we basically have something springing from a the first time line. The previous existence used to have you getting born, but the new one has changed. No strange degree of unlikeliness. In the second example we can get the strange glasses one. Build a time machine, and make it robust enough that it breaking down is much more unlikely than your example with the glasses. Program it so when the glasses are thrown it will check to see what it has from the future and if the glasses are in order then it will do one of
a) If the glasses are together it does nothing.
b) If the glasses are NOT together and it did NOT get a "1" from the future it sends a "1"
c) If the glasses are NOT together and it got a "1" from the future it sends a "0".
The only consistent solution is all the glasses are all together.

Basically incredibly stupid stuff results if time travel is possible. Also fun fact, if you CAN go back and kill your grandfather time travel always removes itself from the time line. Sort of, the new timeline can have people from the future, but nothing going to the past.
Here's why: Your machine changes the past, so now one of two things happens: a) the new time line has someone time traveling b) the new time line has no time traveling. If its a) we repeat the process and keep repeating it until we get "b". If we never get "b" we don't have a way of progressing.

[Douglas]

Umm... the second one is the "unlikely" one. See for the first we basically have something springing from a the first time line. The previous existence used to have you getting born, but the new one has changed. No strange degree of unlikeliness.
Ah, but that "previous existence" does not exist. It cannot cause anything because it never happened and never will. There is only a single timeline, not a series of overwritten timelines, and it contains all of its own causes. If a cause would get eliminated by a time travel event, then it does not exist and consequently cannot have an effect - that's a basic assumption of Novikov's principle, and in fact the consistency principle's whole point is explaining how that could be compatible with time travel without paradoxes. Your appearance is not you arriving from an alternate future, it's you spontaneously assembling from thin air by random chance.

There are theories with multiple timelines and other such things where the idea of a time traveler arriving from a future that will not happen in the timeline he shows up in makes sense, but Novikov's self-consistency principle is about the idea of a single timeline that contains all of the causes for its own effects.


In the second example we can get the strange glasses one. Build a time machine, and make it robust enough that it breaking down is much more unlikely than your example with the glasses. Program it so when the glasses are thrown it will check to see what it has from the future and if the glasses are in order then it will do one of
a) If the glasses are together it does nothing.
b) If the glasses are NOT together and it did NOT get a "1" from the future it sends a "1"
c) If the glasses are NOT together and it got a "1" from the future it sends a "0".
The only consistent solution is all the glasses are all together.

Basically incredibly stupid stuff results if time travel is possible. Also fun fact, if you CAN go back and kill your grandfather time travel always removes itself from the time line. Sort of, the new timeline can have people from the future, but nothing going to the past.
Here's why: Your machine changes the past, so now one of two things happens: a) the new time line has someone time traveling b) the new time line has no time traveling. If its a) we repeat the process and keep repeating it until we get "b". If we never get "b" we don't have a way of progressing.
About the bolded part...

:smallamused: http://smileydatabase.com/s/512.gif http://smileydatabase.com/s/514.gif http://smileydatabase.com/s/532.gif http://smileydatabase.com/s/517.gif http://smileydatabase.com/s/528.gif http://smileydatabase.com/s/490.gif

Yeah, good luck building something that robust without being god. Seriously, you're talking about a degree of reliability where the possibility of critical components undergoing spontaneous existence failure is significant. Or the possibility of brownian motion cancelling the signal exactly by pure coincidence. The kind of engineering where "what happens if an antimatter bomb spontaneously forms from vacuum and detonates inside the machine?" is a serious question that must be taken into consideration. If you're able to build something that robust, you can probably pull off the glasses trick trivially easily without resorting to time travel.

[Lamech]

Ah, but that "previous existence" does not exist. It cannot cause anything because it never happened and never will. There is only a single timeline, not a series of overwritten timelines, and it contains all of its own causes. If a cause would get eliminated by a time travel event, then it does not exist and consequently cannot have an effect - that's a basic assumption of Novikov's principle, and in fact the consistency principle's whole point is explaining how that could be compatible with time travel without paradoxes. Your appearance is not you arriving from an alternate future, it's you spontaneously assembling from thin air by random chance.This? (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle) You're using that as one of your premises? Circular logic. Your using that principal to claim that this version of time travel doesn't work. That IS the principal.


Yeah, good luck building something that robust without being god. Seriously, you're talking about a degree of reliability where the possibility of critical components undergoing spontaneous existence failure is significant. Or the possibility of brownian motion cancelling the signal exactly by pure coincidence. The kind of engineering where "what happens if an antimatter bomb spontaneously forms from vacuum and detonates inside the machine?" is a serious question that must be taken into consideration. If you're able to build something that robust, you can probably pull off the glasses trick trivially easily without resorting to time travel.Then its just a matter of degree. Make it significantly more robust than a human. Change the glasses example to "Person X dying". Now I can kill people from anywhere. Inane improbable things still happen.

[Douglas]

This? (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle) You're using that as one of your premises? Circular logic. Your using that principal to claim that this version of time travel doesn't work. That IS the principal.
My entire participation in this thread started with a statement that my opinion on time travel paradoxes is that Novikov's principle is correct. Everything since then sprang from refuting the idea that it's implausibly complex and unlikely. Novikov isn't the principle I'm basing my arguments on, it's the subject the arguments are about.


Then its just a matter of degree. Make it significantly more robust than a human. Change the glasses example to "Person X dying". Now I can kill people from anywhere. Inane improbable things still happen.
In most cases I'd predict that you'd end up with a normally unstable ambiguous signal instead of murder-by-consistency. Like how in computers 0s and 1s are represented by high and low voltages with circuits designed to force the voltage towards one end or the other; with a signal like that, a time travel circuit might end up with a medium voltage so precisely in the middle that it can't be determined at all which of 0 or 1 it's supposed to be. You can devise other signal mechanisms, of course, but I'm not sure it's possible to eliminate that kind of ambiguity - it's the kind of problem where "solving" it tends to do nothing more than introduce a new set of goalposts for the problem.

It might in principle be conceivable to make something like what you're suggesting with Novikov-consistent time travel, and maybe even get around the ambiguous signal problem, but I doubt it would ever be feasible as a way to force large scale events. Small scale, yes, and the potential for computations using time loop logic (http://en.wikipedia.org/wiki/Novikov_self-consistency_principle#Time_loop_logic) is of quite substantial interest, but in that kind of computation an ambiguous signal is actually a valid acceptable outcome that yields information. I suspect that the signal ambiguity problem is sufficiently intractable to render schemes that absolutely require unambiguous signals - which the kind of thing you're suggesting inherently does - infeasible.

Anyway, it is my opinion that Novikov's view of time travel is the one that makes the most sense and is most likely correct - if time travel is possible at all.