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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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G.E. Moore had a similar argument, saying that since we cannot define things without further definitions that communication is impossible unless the premises in discussion have been experienced. For instance, yellow is impossible to explain to a blind person.

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Autolykos:

It's interesting that there are basically two separate notions of "time" which have been discussed in this thread. One can be described as something like "simultaneity or non-simultaneity of observations". The other can be described as "causality". Relativity theorists use the former notion of "time" exclusively, although they still accept the existence of causality.

Interestingly enough, while relativity theorists think that the simutaneity or non-simultaneity of multiple observations is dependent on the observer's frame of reference, IIRC they conversely think that causality is not. The question then is whether Newton's notion of "absolute time" is actually analogous to causality rather than simultaneity.

At very close to the speed of light, and viewed from different inertial references, an effect can appear to an observer to happen before its cause. But that it just a figment of being so close to light-speed, and causality is in-fact preserved.

 
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Suggested by AJ

thetabularasa:
Time itself is a construct we use to measure rates of objects relative to other perceived objects, thus the measurement of time itself does not exist; however, the dimension of time appears to exist (it must as I mentioned just above), but time being a physical property seems to be an oxymoron.

This is where I say time is better viewed as being rate. Time indicates a measurement, and all measurement is subjective; but to deny rate is to deny the truth that the object traveling to another object (location) faster than another object traveling to the same "location" will arrive there sooner than the slower object. I suppose rate and speed would mean the same time, and time would be the subjective interpretation of rate as a dimension of its own.

Thoughts? Am I completely right or wrong? Curious to see some responses.

Well, all that was a bit confusing. But I think you're right in one sense. I spoke realier of time being a 'half-dimension.' You're right that it's not a physical dimension and that time only moves forward (which is why I call it a half-dimension, a dimension you can only move one way in). Thus it would be perfectly reasonable to quantify time as a rate or multiplier in a particular area depending on how much gravity is extent in that area.

You could speak of time as being 0.99991% on the surface of the earth, due to gravity, whereas the satellites in orbit are experiencing 0.9992% time passage. 1.0 time would mean a section of space which has a zero-gravity reading. This is effectively impossible however, so getting to 1.0% time would be just as impossible as achieving 1.0 x the speed of light, reaching it is asymptotic.

The key is the relationship between gravity and time, and inertia and time.

The inertia one still throws me and seems to have some logical failures. Like if moving faster can actually slow your rate of time passage compared to a non-moving thing, like the planet, how does the universe know that you're moving away from the planet and not that the planet is moving away from you? It would have to be tied either to changes in inertia, which I think is increasingly possible, or there is a universal reference point of zero-speed, which physicists strongly doubt.

But as for gravity and time, it's a well established link. Stronger gravity = slower passage of time.

 
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Anenome:

thetabularasa:
Time itself is a construct we use to measure rates of objects relative to other perceived objects, thus the measurement of time itself does not exist; however, the dimension of time appears to exist (it must as I mentioned just above), but time being a physical property seems to be an oxymoron.

This is where I say time is better viewed as being rate. Time indicates a measurement, and all measurement is subjective; but to deny rate is to deny the truth that the object traveling to another object (location) faster than another object traveling to the same "location" will arrive there sooner than the slower object. I suppose rate and speed would mean the same time, and time would be the subjective interpretation of rate as a dimension of its own.

Thoughts? Am I completely right or wrong? Curious to see some responses.

Well, all that was a bit confusing. But I think you're right in one sense. I spoke realier of time being a 'half-dimension.' You're right that it's not a physical dimension and that time only moves forward (which is why I call it a half-dimension, a dimension you can only move one way in). Thus it would be perfectly reasonable to quantify time as a rate or multiplier in a particular area depending on how much gravity is extent in that area.

You could speak of time as being 0.99991% on the surface of the earth, due to gravity, whereas the satellites in orbit are experiencing 0.9992% time passage. 1.0 time would mean a section of space which has a zero-gravity reading. This is effectively impossible however, so getting to 1.0% time would be just as impossible as achieving 1.0 x the speed of light, reaching it is asymptotic.

The key is the relationship between gravity and time, and inertia and time.

The inertia one still throws me and seems to have some logical failures. Like if moving faster can actually slow your rate of time passage compared to a non-moving thing, like the planet, how does the universe know that you're moving away from the planet and not that the planet is moving away from you? It would have to be tied either to changes in inertia, which I think is increasingly possible, or there is a universal reference point of zero-speed, which physicists strongly doubt.

But as for gravity and time, it's a well established link. Stronger gravity = slower passage of time.

 

When I read about spacetime, though, it almost seems mystical, like you pointed out.

Anenome:

how does the universe know that you're moving away from the planet and not that the planet is moving away from you?

This is why I insist time, or at least as we commonly perceive it going "forward" like you mentioned, cannot exist. Direction is completely relative to perspective. We in the States could insist that the Chinese are standing upside down right now, but they aren't according to their perspective; we are. Past and future do not exist; only the present exists, and everything is changing in it.

Anyhow, I'll check back tomorrow or later.

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AJ replied on Fri, Nov 30 2012 8:14 PM
thetabularasa:

G.E. Moore had a similar argument, saying that since we cannot define things without further definitions that communication is impossible unless the premises in discussion have been experienced. For instance, yellow is impossible to explain to a blind person.

It's similar, but here the issue is not about the mind of the listener, but the mind of the speaker. Suppose I talked about a fourth primarily color, but said I could not vizualize it. From my perspective, the words "fourth primary color" are just words in search of a referent. From your perspective they must also be words wanting for a referent, but additionally if I try to propound a theory based on this term - and especially if I stand to get some of your tax dollars if people accept my theory - you might start to suspect I'm bluffing or leveraging my position of authority to allow me to get away with something a nobody could not.

I question the implicit premise of this whole business wherein the burden in the communication is on the listener rather than the speaker. If your theory is complex I may make the effort to figure it out, but if the very terms of your theory appear incoherent and you offer no clarification that allows me to see what you mean by them, why should I continue to listen? If a theorist wants to be taken seriously without relying on authority or laurels, he or she had best make it comprehensible - at the very least imaginable! But I think if you asked most of the modern physicists they would tell you that even they cannot imagine these things.

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AJ replied on Fri, Nov 30 2012 11:36 PM
Oops, I accidentally hit "suggest as answer." There are some answers here, though.
Anenome:
The inertia one still throws me and seems to have some logical failures. Like if moving faster can actually slow your rate of time passage compared to a non-moving thing, like the planet, how does the universe know that you're moving away from the planet and not that the planet is moving away from you?
Exactly. Imagine that the universe consists of only you and the planet. Then there is no difference between visualizing the planet moving away from you and you moving away from the planet. These are praxeologically identical actions. It is impossible to visualize any kind of universal non-moving reference point without inserting a third object (or second observer), which would just push the problem back (how does the universe know the second observer isn't moving while you or the planet remain still?).
Anenome:
Stronger gravity = slower passage of time.
Assuming the data are reliable as well as significant versus the margin of error, they would only show that clocks moved more slowly under stronger gravity. However, it is hardly surprising that certain processes happen more slowly under gravity. Mechanical clocks would run slow due to friction, and hourglasses would run faster. Who knows by what mechanism the atomic clocks were slowed down. It may be via a known effect or an unknown one, but it certainly can't be due to empty space "warping" as General Relativity would have it. More precisely, it is simply incoherent in human communication to say that the concept known as space warped or curved or bent, as the only thing a human can conceive of doing these things is a physical object. It is therefore not proper to say that any data whatsoever proved or lent evidence to such a "theory."

"But still, what if the equations predict accurately?" There are many reasons why an equation may "predict" the results of experiments, and only one of those is "because the theory is sound." For instance, Newton's law of gravitation predicts the results of many experiments accurately, but Newton himself pointed out that there was no theory of gravitation behind it. It is merely a summary of the observed data (so it's no feat that it could predict the trend would continue). As new data come in, equations are updated. GR may be such a case. There are also many ways to massage equations as well as to privilege a popular theory in the design and interpretation of experiments. Remember that a lot of jobs and grant money are on the line. Even barring any of that, though, one thing is certain: an irrational theory is no theory at all. We need to search for another explanation if we want to unlock the secrets of the universe instead of just cataloging patterns of measurements.

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Temperature, pressure, entropy, energy, etc. are state variables of thermal systems.

You experience four "dimensions" or spatial variables all the time in physical reality. Clocks do not run more slowly in a higher gravitational field because of friction or anything like that. In fact, consider the relativistic effects on GPS satellites, with astronauts, etc. Remember, these are all RELATIVE concepts. In your own reference frame, there is no difference whatsoever. But when you start juxtaposing reference frames, you see the length contraction, time dilation, and so forth. Look up special relativity experiments.

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AJ:
Anenome:
The inertia one still throws me and seems to have some logical failures. Like if moving faster can actually slow your rate of time passage compared to a non-moving thing, like the planet, how does the universe know that you're moving away from the planet and not that the planet is moving away from you?
Exactly. Imagine that the universe consists of only you and the planet. Then there is no difference between visualizing the planet moving away from you and you moving away from the planet. These are praxeologically identical actions. It is impossible to visualize any kind of universal non-moving reference point without inserting a third object (or second observer), which would just push the problem back (how does the universe know the second observer isn't moving while you or the planet remain still?).

This is why theorists still speculate some kind of at-rest ether of sorts. It's some property of space-time itself.

I think the answer is bound up in the frabric of space-time. Basically if you're in strong gravity, it means space-time is denser in that region of space, like it's been condensed there by gravity almost like a higher-pressure gas. This is what physicists means by curving space-time. A curve is a metaphor for the two-dimensional explanation of space-time, where gravity is viewed as the effect of a bowling-ball on a blanket.

But when you take that metaphor into 3d it's much harder for people to visualize curving in three dimensions.

You have to imagine an omni-directional pinch towards a gravitational center. I like to think of it in term of rarification and thickification (my terms). Where strong gravity is, space is in a sense 'thinner' and where it's not it's thicker.

Thus, the strange effects of special relativity may be a result of passing through a large amount of space-time in any one instant.

That's one kind of 'objective observer' or spatial reference point, one way the universe knows who's actually moving faster than who. And it means space is a tangible thing after all. That's actually one of the great discoveries of modern physics, and perhaps something that not many people commenting in this thread may realize, that space is not merely nothing, but actually has discernible properties. Space is in fact 'something,' just something on so basic a level that we cannot yet interact with it. Space exists underneath even quantum mechanics.

Now, if you want to have your mind blown, I can lay out another problem I've been working on for a few years. It's the problem of inertia. We know that all matter is simply energy that takes up space. energy fluctuating in a stable region of space, almost like energy wrapped around space somehow. This is how matter is made from pure energy at extremely high levels of energy.

Scientists can create matter from energy and do so in the lab every day, so I don't think anyone should challenge the above.

The paradox is thus. Why do we have inertia at all if we are made of pure energy? A related question is, why doesn't matter simply pass through other kinds of matter--but that's a harder problem.

Now, I think I have a solution. Been lots of talk about a god-particle to explain this, but I think I have another explanation from another point of view.

All the energy inside your body is already moving at the speed of light, it's just doing so in an extremely small amount of space. We know this to be true. So, when you move in any direction, even the slightest bit, that energy grinds against the speed of light and has to come to rest at a higher energy level, even if that energy level is only slightly higher by your small action.

At the same time, to slow down your momentum would have the opposite effect, of moving all the energy in your body to a lower energy state in order to preserve the speed of light. And that's why you experience intertial resistance to movement when an object is in motion or at rest, equally. Also explains why objects with more mass are harder to move, there's more energy in them grinding against light-speed by volume.

AJ:
Anenome:
Stronger gravity = slower passage of time.
Assuming the data are reliable as well as significant versus the margin of error, they would only show that clocks moved more slowly under stronger gravity. However, it is hardly surprising that certain processes happen more slowly under gravity. Mechanical clocks would run slow due to friction, and hourglasses would run faster. Who knows by what mechanism the atomic clocks were slowed down. It may be via a known effect or an unknown one, but it certainly can't be due to empty space "warping" as General Relativity would have it. More precisely, it is simply incoherent in human communication to say that the concept known as space warped or curved or bent, as the only thing a human can conceive of doing these things is a physical object. It is therefore not intelligible to say that any data whatsoever proved or lent evidence to such a "theory."

I think you'll find if you study up on this that you're wrong about this. It cannot be a gravity effect slowing the clock in any physical sense. There are very easy ways to test for that, for one thing, and secondly the atomic clocks rely on electromagnetic interactions, not physical ones, and aren't gravity sensitive. It can only be time slowing down. Honestly.

AJ:
"But still, what if the equations predict accurately?" There are many reasons why an equation may "predict" the results of experiments, and only one of those is "because the theory is sound." For instance, Newton's law of gravitation predicts the results of many experiments accurately, but Newton himself pointed out that there was no theory of gravitation behind it. It is merely a summary of the observed data (so it's no feat that it could predict the trend would continue). As new data come in, equations are updated. GR may be such a case. There are also many ways to massage equations as well as to privilege a popular theory in the design and interpretation of experiments. Remember that a lot of jobs and grant money are on the line. Even barring any of that, though, one thing is certain: an irrational theory is no theory at all. We need to search for another explanation if we want to unlock the secrets of the universe instead of just cataloging patterns of measurements.

That's true, but theories are usually revised to become more precise on edge cases. They don't usually revamp all the past work completely. Sometimes they do conceptually. For instance, Netwon's laws were great for everything except the edge cases at extreme speeds of light and gravity. His math is still used to send ships into orbit, because it would be a major pain to use GR's calculus to do the same thing with only a marginal improvement at such slow speeds.

Have you read of the experiment that prove space-curvature due to gravity via bending light around the sun during an eclipse?

According to the theory of general relativity, stars with light rays that passed near the Sun would appear to have been slightly shifted because their light had been curved by its gravitational field. This effect is noticeable only during eclipses, since otherwise the Sun's brightness obscures the affected stars. Eddington showed that Newtonian gravitation could be interpreted to predict half the shift predicted by Einstein.

Eddington's observations published the next year[4] confirmed Einstein's theory, and were hailed at the time as a conclusive proof of general relativity over the Newtonian model. The news was reported in newspapers all over the world as a major story. Afterward, Eddington embarked on a campaign to popularize relativity and the expedition as landmarks both in scientific development and international scientific relations.

I think it's dangerous to state conclusively that X is an irrational theory and therefore to reject. I can easily see people pulling that sort of reasoning about Austrian economics or libertarianism's free society. When the math works out, as proved by experimentation, there's nothing more rational that that.

 
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AJ replied on Sat, Dec 1 2012 2:22 AM
To avoid rehashing too much, here's an older thread that covers the main point I want to make. The Prezi presentation there is the heart of the heart of it.
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hashem replied on Sun, Dec 2 2012 11:47 AM

thetabularasa:
Past and future do not exist; only the present exists

Yes.

hashem:
Matter exists in its current arrangement. When we speak of "the past" or "the future", we're speaking figuratively about imaginary nonexistent arrangements of matter. Time, past, and future are figures of speech; they're concepts.

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Ludwig von Mises:
ACTING man distinguishes the time before satisfaction of a want is attained and the time for which the satisfaction continues.
Keep the faith, Strannix. -Casey Ryback, Under Siege (Steven Seagal)
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"time travel" is a pleonasm of sorts. Youre already doing it. Its free-fall through the fourth dimension.
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Malachi:
"time travel" is a pleonasm of sorts. Youre already doing it. Its free-fall through the fourth dimension.

I agree. Which is why it's been called a 'half-dimension,' it's regular travel in one direction only. The present is omni-present, meaning everyone's always in the same temporal reference frame. Where it gets confusing is the idea of relative time passage despite co-local temporal frame, ie: that one person could be moving through time slower or faster than another, yet both remain in the 'present' reference frame. There's no way to move outside that 'present' reference frame, thus no way to achieve time travel.

But in strong gravity you could approximate traveling into the future by slowing your personal reference frame, leaving you in a future far beyond the amount of time passed in your own reference frame. But it would only have the effect of transporting you into a far off 'present' while having much less time pass for yourself.

Strange that it should be true, but from everything we know now, it is possible.

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You could speak of time as being 0.99991% on the surface of the earth, due to gravity, whereas the satellites in orbit are experiencing 0.9992% time passage.

No you can't. In SR, there is no proper frame. You can choose a proper frame but it's only valid for a particular problem.

Like if moving faster can actually slow your rate of time passage compared to a non-moving thing, like the planet, how does the universe know that you're moving away from the planet and not that the planet is moving away from you?

It doesn't. That's the point of SR, there is no proper frame. When you are in an accelerating frame things become different, because you can tell whether one frame is accelerating relative to the other (this is also GR and requires a more complex derivation of space-time geometry that I haven't fully learned). BTW, the answer to this problem is that both the observer in the "moving" frame and the observer on the "non-moving" frame see each others clocks going slower.

It would have to be tied either to changes in inertia, which I think is increasingly possible, or there is a universal reference point of zero-speed, which physicists strongly doubt.

Both are incorrect. Inertia is a frame invariant (othewise energy and momentum are not conserved in frames). And there is no such concept as an invariant zero-speed, because speed is a relationship and must necessarily be measured relative to other things.

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