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Time Travel is Impossible

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thetabularasa posted on Wed, Nov 28 2012 3:28 PM

The quantum physics discussion in my Holiday Dinner Table thread got me thinking about time and space, what is bendable, what isn't, whether General Relativity is a viable theory and so forth, and naturally I started considering the possibility of time travel. Here's how I know it is impossible:

Time doesn't exist. It is a manifestation of the human imagination. Things change; the world changes, we change and everything seems to be in flux somehow. Even if an object takes millenia to destruct and end, it inevitably does, similar to entropy, I suppose, in the sense that there is a systematic degradation involved in all things. Nevertheless, my point is that things are always changing, and of course distances between objects exist, but time itself does not exist. It is merely a subjective measurement system.

Prove me wrong if you must!

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Anenome replied on Wed, Nov 28 2012 11:21 PM
 
 

hashem:

Oh ok I thought you were talking about seeing into the future lol.

...No >_>

To the person within strong gravity, time outside his frame of reference would appear to travel faster depending on the strength of that gravity.

To the persons outside that gravity, the person in strong gravity would appear to have time moving slower, depending on the gravity strength difference.

So, when I wrote about seeing stars explode and galaxies collide, that's not seeing into the future, but rather the idea that under strong enough gravity the person in that gravity could see in a few seconds light that was generated over the span of thousands or millions of years.

It'd probably be pretty bright :P There's an energy shift when time goes through a gravity effect. Ordinary light could blue-shift to, say, become gamma radiation. So, you might not even see much if it all gets massively blueshifted :P

 
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hashem replied on Wed, Nov 28 2012 11:31 PM

Watching some videos that are opening new dimensions into the future of my mind. Will comment back when I'm less ignorant.

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AJ replied on Wed, Nov 28 2012 11:42 PM
Define "time" and you'll know whether it can dilate.
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Everything is traveling through time. That should make it clear why time-travel in the fictional sense is impossible. Time is nothing else but the the causal relation.

Because time is the causal relation, it too is governed by the law of conservation (causality implies conservation). The conservation law is the essence of physics - if matter cannot be created or destroyed, then whenever the distribution of matter is altered from equilibrium, a surplus and deficiency are created simultaneously. For example, if you mount a fan in your window and push air out of your house, this increases the pressure outdoors and decreases the pressure indoors by precisely the same extent (per volume). If you move a billiard ball from one end of a billiard table to the other end of the billiard table, the density of billiard balls on the end from which it was removed must decrease and the density on the end to which it was moved must increase.

Perhaps not quite as obviously, this same principle operates in time. If you strike a billard ball and it moves across the table unimpeded, no motion is deducted from the ball, except by friction which we are neglecting. If you strike the exact same ball with exactly the same force, angle, etc. and place another billiard ball in its path, something different will happen to the struck ball - its motion (energy) will be reduced when it encounters the ball in its path. In order to impart motion (energy) to a body, motion (energy) must be given up to exactly the same extent by the causal body.

By definition, the effect cannot be the cause, so time travel is not even coherent, let alone possible.

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Isn't causality just the intuition our minds have for conceptualizing experience of time?

I mean, living for all our lives in "normal" flow of time ingrained the implications ("causality") so deeply in our minds that we take causality for granted. Add to this cultural and genetic inheritance of our ancestors living for all their lives in "normal" flow of time.

What makes you believe causality is actually fundamental? I am not denying it is, BTW, I am just unsure.

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What makes you believe causality is actually fundamental? I am not denying it is, BTW, I am just unsure.

There are several reasons why.

a) To explain is to give a reason, which is to give a cause. Hence, any explainable phenomenon is causal. This does not tell us that all phenomena are causal unless all phenomena are explainable which is, of course, not obviously the case. (In fact, I believe it is not the case that all phenomena are explainable by us, but more on that later). But we can at least say that acausality may never feature in any coherent explanation. Thus, to explicitly invoke acausality in an explanation is to engage in contradiction. This makes almost any video featuring Michio Kaku virtually unwatchable.

b) Causality implies conservation (if the world is causal, you cannot have entities and forces popping into/out-of existence). Conservation of all physical variables (except entropy) is perhaps the most well-established fact of physics. While this does not prove the antecedent, it is strongly consistent with it.

c) The most subtle aspect of the issue has to do with the complexity of explanations. We can rank explanations in order of their complexity and when explanations are so ranked, it turns out that there is a concrete reason why Ockham's razor is the case - simpler mechanisms are more probable than complex mechanisms, ceteris paribus. In other words, if you have a set of phenomena A, and two or more explanations (mechanisms) that are consistent with A, the simplest mechanism is to be preferred because if we imagined mechanisms being assembled at random, the simplest mechanism is more likely to occur. I'm stating this in very imprecise language for the sake of communicating the essence of the argument. For more information, search "kolmogorov complexity" "chaitin" "solomonoff induction", etc.

When applied to physical systems, this idea suggests that random phenomena (acausal phenomena) are the most improbable of all. This reinforces point a) above and gives it a more specific meaning... there's a reason why we should treat random phenomena as incoherent... the implied "explanation" is maximally complex.

Finally, on the point of our inability to explain everything, this goes into the fact that a computation system of complexity X cannot fully explain phenomena of complexity greater than X. Again, I'm using extremely imprecise language (caveat). The brain is not infinitely complex and, thus, it can only explain phenomena of a certain complexity. There is no reason to suppose that the Universe itself (its fundamental operation) is less complex than the human brain. Hence, there is no reason to expect that we can explain all real phenomena. This has some implications to the nature of noise/randomness in physical theories.

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Andris Birkmanis:

Isn't causality just the intuition our minds have for conceptualizing experience of time?

I mean, living for all our lives in "normal" flow of time ingrained the implications ("causality") so deeply in our minds that we take causality for granted. Add to this cultural and genetic inheritance of our ancestors living for all their lives in "normal" flow of time.

What makes you believe causality is actually fundamental? I am not denying it is, BTW, I am just unsure.

I've thought about this a bit. Causality is absolutely dependent on the nature of time, on time being essentially a half-dimensional (meaning, moving forward at a steady rate in essentially a single direction, from one moment to the next).

If you think about one dimensional time, where you could move backwards or forwards (the classic concept of time-travel in most stories), causality breaks down entirely, effects can become causes, and you reach the typical time paradoxes. Also, many dismiss the question of god with the question "who created god" which is really a question about causality, but we know that time itself began with the big bang--as one of the consequences of special relativity (or is it general? meh, one of those), meaning there was no causality before time began, there could not be, which invalidates that question about god, significantly muddying the impact of such a question. God as the "causeless cause" makes perfect sense if you understand that time did not come into being before god.

On the next level is two dimensional time, where one could move sideways in time. It's kinda hard to imagine this one. But, you could for instance, begin a conversation with someone, then shift sideways and go fishing for ten years, then come back to that same moment in the conversation and continue as if nothing had happened and your conversation partner would not experience 10 years as having passed, because for him it wouldn't have, it would be just a moment.

Time in that concept would be fluid, and also causality breaks down there as well. Also, there may be no such thing as scarcity in different concepts of time. Each moment passes for us now and is lost, but in a two dimensional-time universe, each moment in time an object exists could be selected out of that moment and taken elsewhere, and each moment in time would be essentially infinitely divisible, thus if there's one copy of an item at any point in time to any other point in time, that continuity could populate the rest of time-space with that object. Which is a pretty freaky thing to think about.

I can't really imagine what a third dimension to time could possibly add to the mix. Possibly not much of anything.

 
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AJ:

Comparison is an action, hence for the purposes of physics (rather than the loose sense of everyday talk), "time" is a verb. One can travel through an object or space, but one cannot travel through a comparison! Perhaps something else is meant by "travel through time," but that awaits coherent definition.

Exactly how I'm approaching it.

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Andris Birkmanis:

Isn't causality just the intuition our minds have for conceptualizing experience of time?

I mean, living for all our lives in "normal" flow of time ingrained the implications ("causality") so deeply in our minds that we take causality for granted. Add to this cultural and genetic inheritance of our ancestors living for all their lives in "normal" flow of time.

What makes you believe causality is actually fundamental? I am not denying it is, BTW, I am just unsure.

No, causality exists regardless of time. True, time is how we perceive it, but take a light switch. If the switch is in the downward position and the light is off, and then I flip the switch and the light is on, what we know is that I caused the light to turn on. Granted we perceive a laps in time, an amount of time that allows me to flip the switch, but this perception is nothing more than a subjective measuring system to understand what actually happened.

Now it gets sticky when you think of sequence (which itself implies time too): could the light switch be off and on at the same time? Logically we know that it cannot. So one might say that there is a measure of time between the light being off and on; it would have to be since the light cannot be off and on at the same time. But there is the catch: ...at the same time. Really what I'm saying is that objects or an absolute states of existence (both off and on or here and there or alive and dead or cat and dog) cannot be contradictory; basically, paradoxes cannot exist. My point, though, is that fluctuation (change) is constant, and there is no way to speak of this fluctuation except by way of time. It is a measurement to gauge the change.

Now of course we can induce change, such as my flipping the light switch from off and on. I have free will, so I can manipulate objects and change their states of existence. But what am I doing other than changing their states of existence? In other words, sequence doesn't exist; only fluctuation. Concepts like time and sequence are our own constructs we use to measure fluctuation and communicate or conceive the concepts.

Any thoughts? I'm thinking out loud, never really gone down this route before, friends.

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AJ replied on Thu, Nov 29 2012 6:59 AM
Doing well, TR. Time is just a measure of change (i.e., motion). Paradox is the hallmark of an incoherent theory. Clear definitions and modern physics are like oil and water.
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thetabularasa:
Nevertheless, my point is that things are always changing, and of course distances between objects exist, but time itself does not exist. It is merely a subjective measurement system.

Yet distances between objects can change, can't they?

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hashem replied on Thu, Nov 29 2012 8:59 AM

Ok so I was watching some videos on special relativity and time, both supporting and opposed to it. I'm not an expert by any standard, but it seems at a bare minimum there's a definition game problem. It seems to be conflating perception of light with whatever definition of time supports the theory (the theory that time isn't just a concept about difference and distance, but something mystical, simultaneously not-physical and manipulatable) in any given context.

Again, I could be confused and probably am, but that's what I got from watching a few videos regarding both sides of the issue of special relativity and time.

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hashem:

Ok so I was watching some videos on special relativity and time, both supporting and opposed to it. I'm not an expert by any standard, but it seems at a bare minimum there's a definition game problem. It seems to be conflating perception of light with whatever definition of time supports the theory (the theory that time isn't just a concept about difference and distance, but something mystical, simultaneously not-physical and manipulatable) in any given context.

Again, I could be confused and probably am, but that's what I got from watching a few videos regarding both sides of the issue of special relativity and time.

Yes. If one can commit to the premise that there is no physicality to time, then one must admit that it does not exist. If it exists, it exists; if it does not exist, it does not exist. Sounds silly/sarcastic to say it like that, but I agree, hashem: time doesn't exist, therefore time travel is impossible.

 

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Blargg replied on Thu, Nov 29 2012 12:01 PM

On the next level is two dimensional time, where one could move sideways in time. It's kinda hard to imagine this one. But, you could for instance, begin a conversation with someone, then shift sideways and go fishing for ten years, then come back to that same moment in the conversation and continue as if nothing had happened and your conversation partner would not experience 10 years as having passed, because for him it wouldn't have, it would be just a moment.

Reminds me of the time travel scene in K-PAX: Adios aloha

Time is implicit. If you talk about travel in it, the implicit one becomes an explicit one that you're traveling in, and a new implicit one gives basis for the notion of travel in the explicit one. But the explicit one isn't time anymore, just another dimension that can be moved freely in.

In your description above of two-dimensional time, you basically lay out a bunch of timelines, where you can jump across them. But then you describe a third dimension, the implicit time in which you move forward in one timeline, jump to another for a while, then jump back to the first timeline. This implicit time is then the only time in your example.
 

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Clayton, do you know of any good books that go into all that?

Freedom of markets is positively correlated with the degree of evolution in any society...

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