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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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In any case we can agree that physicists generally suck at philosophy. Something like 58% of physcists adopt MWI. But MWI has no known measurable consequences.

I still choose to rely on the experimentation that reveals the 4D hyperbolic geometry of the universe, again and again, rather than what my feeble eyes perceive.


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Yeah, I think MWI is reeeeediculous.

Autarchy: rule of the self by the self; the act of self ruling.
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I still choose to rely on the experimentation that reveals the 4D hyperbolic geometry of the universe, again and again, rather than what my feeble eyes perceive.

False dichotomy. Go back to my post on the human brain as a telescope/microscope.

Clayton -
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AJ replied on Mon, Dec 10 2012 10:17 AM

Sorry for the delay, Anenome.

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.

Well that's at least potentially a physical hypothesis, if you mean that there are actually little objects (balls?) existing at higher or lower densities and it is these balls that collide with the clock hands and slow them down. That would be a rational (=visualizable) theory. However, I am not sure that the rest of physics can be done with such little balls.

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.

If "space" actually means "a bunch of objects floating in space," this - at the very least - is a puzzling use of language.

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.

"Study up on this"? If the language used is incoherent, no amount of additional words will make a difference - unless those are clarification of the definition. I'm going to have to ask you to define "time" before I can assess whether it is possible for time to slow down, because the only way I can see to define it, it cannot do so.

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.

This is the problem: these "laws" are not theories, they are just summaries of the observed patterns. Newton never claimed to have a hypothesis, he just found a simple equation that describes the motion of planets, etc. That is nifty, but it tells us nothing about the physical mechanism of attraction or why planets attract each other rather than, say, repelling each other. Why be satisfied with this?

If you asked a scientist how a volcano worked and he just gave you an equation that predicted eruption times and amounts, extrapolating from past eruption data, would you be satisfied with such a "theory"? What if you wanted to know if pouring buckets of ice into the volcano would be an effective way of stopping it from erupting? Would he just tell you to try it out (run an experiment) and report back? Then create some new, better equations ("theories")? Isn't there something more than this?

When the math works out, as proved by experimentation, there's nothing more rational that that.

Math is not physical theory. Math can be used to describe and summarize what we already know in a more useful form, but it doesn't explain the underlying physical mechanisms that produced the observed phenomena. 

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AJ replied on Mon, Dec 10 2012 10:19 AM

As for "energy," that doesn't sound like a physical object at all. Definition?

Regarding the points made by others about relativity, if it is merely a measurement effect and says nothing about what is actually going on from a purely physical perspective, it may be useful for engineering, but what use does it have for theorizing? What we have here is a strange delineation of terms, wherein observing, data-gathering, curve-fitting, equation-making, extrapolation, experimenting, and testing are all mixed together with theorizing, which is imagining what could be going on "under the hood" to produce the phenomena we can detect. This just makes a mess of the terminology.

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Blargg replied on Mon, Dec 10 2012 10:36 AM

I found a quote by Feynman on this along with a discussion about tangible things and constructed things.

It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. However, there are formulas for calculating some numerical quantity and when we add it together it gives “28″—always the same number. It is an abstract thing in that it does not tell us the mechanisms or the reasons for the various formulas.

Another interesting page asking what energy really is, pointing out the inconsistencies in common definitions.

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