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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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It sounds like you haven't considered or answered the Rietdijk-Putnam Argument.

The argument makes a huge leap, from perception to ultimate reality, that I cannot accept. It's not epistemologically sound. The perception does not determine reality, only apparent reality. Actual reality is still there, even if its perception has been distorted by space or speed.

And Penrose's modification seems extremely confused.

I simply argue that apparent planes of simultaneity are artifacts of perception. Actual simultaneity is perfectly possible and objective, if not objectively perceivable.

 

 
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Anenome... so whose plane of simultaneity matches your idea of the "real" universe? You, or someone travelling at a different velocity? Which reference frame will you choose as the privileged one (arbitrarily, untestable, and in violation of the principles of relativity, and in violation of Occam's Razor)?

Since the Earth is continually undergoing acceleration, you almost certainly do not have a plane of simultaneity matching the universe at any given time. Consequently points distant from you in space must also be distant in time to lie in the "true present" and be real, according to your ideas. At one moment, points in the direction of one constellation and in your distant future are "real", while points in the direction of another constellation and in your distant past are "real". 6 months later, when the Earth is in a different position in its orbit, it will be the opposite.

GR's general covariance says that the laws of physics remain valid under any coordinate system. But what if the real coordinate system in the universe is one attached to my fingertip, and all the other coordinate systems only apparently work?

"And Penrose's modification seems extremely confused."

Or more likely, you are confused.

 

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@baxter: You're not rebutting what I have written. And all your quotes of Mises, Hoppe only go to make my case.

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baxter replied on Wed, Dec 5 2012 10:52 AM

Your "case" is a special one indeed.

Clayton, I showed that Mises was perfectly tolerant of non-Euclidean geometry. He did not embarass himself and AE by attacking commonly-accepted physics. (GR is now several decades older than in Mises's time and yet it still withstands experimental assaults.)

Probably you are not as lucky as Mises and do not have a mathematician/physicist as a brother. It might help reduce your childish rage against the inductive sciences if you cracked open a math book every now and then.

 

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Clayton, I showed that Mises was perfectly tolerant of non-Euclidean geometry. He did not embarass himself and AE by attacking commonly-accepted physics. (GR is now several decades older than in Mises's time and yet it still withstands experimental assaults.)

Probably you are not as lucky as Mises and do not have a mathematician/physicist as a brother. It might help reduce your childish rage against the inductive sciences if you cracked open a math book every now and then.

Rather than dropping ad hominems and taking pot-shots, why not quote a specific claim (I've made plenty) with which you disagree, state why you disagree, and we can go from there?

And who is "intolerant" of non-Euclidean geometry??

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Ooooh, Clayton asked for someone to quote a specific claim so that they can actually debate. I can just tell that Clayton is frothing at the mouth with rage!

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>Clayton: human geometry is Euclidean

This is simply wrong. Gravitational physicists, who are human beings, often employ and think about non-Euclidean geometry.
Even nuclear physicists must employ the non-Euclidean hyperbolic geometry of special relativity and its Minkowski metric.

Sailors need to use non-Euclidean geometry: https://sites.google.com/site/hendricksphysics/where-is-our-destination/non-euclidean-geometry-for-sailors

I have used non-Euclidean geometry with my friends when playing "cylindrical chess".

Again I refer you to von Mises: "Present-day epistemology looks upon [the assumptions of Euclid] as freely chosen postulates, the starting point of a hypothetical chain of reasoning".

Do you think Mises errs? Presumably he was referring to human epistemology, not alien epistemology.

>Clayton: what we are ultimately describing are not the phenomena "way out there" or the phenomena "way down there"... we are describing the numbers on the screen. That's it

So do you think that a piece of bread is a real thing, or is it merely a conceptual trick used to summarize visual, taste, olfactory, and tactile sensations and a means of staving off death?
Are the people you are conversing with real, or are they abstractions? Is economics a science of the imaginary?

 

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Here's a great article on Less Wrong discussing a lot of the issues we are.

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Gravitational physicists... Sailors... cylindrical chess...

None of which are perceptual space, that is, space-as-we-experience it. The physics of gravitation do not present themselves to my senses. Spherical and cylindrical geometries do have Euclidean representations, which is why we can easily visualize them.

It appears you may have misunderstood me when I said "human geometry" - I don't mean "any geometry humans can construct" but the geometry that humans don't need to construct. The geometry that's "built-in" to our brains and our language. That geometry is Euclidean. Exclusively so.

do you think that a piece of bread is a real thing

Yes.

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As I already said, there is no doubt that the mathematics of SR describe the physics of the world. The problem is that the mathematics of SR do not necessarily imply a speed-limit of light.

The principle of relativity does i.e. all laws and physical constants are invariants. This is a metaphysical principle without which physics becomes meaningless. The mathematics of SR can be deduced from radiation being spherical in all frames (which is a consequence of vacuum permeability and permitivity being fundamental constants).

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The principle of relativity does i.e. all laws and physical constants are invariants. This is a metaphysical principle without which physics becomes meaningless.

In context, I would say that this is circular reasoning. What is the speed of sound? Surely, it is either a physical constant as you say or physics is meaningless?

The mathematics of SR can be deduced from radiation being spherical in all frames (which is a consequence of vacuum permeability and permitivity being fundamental constants).

Again, this is circular, since assigning permeability and permittivity a status as "fundamental constants" is one and the same as assuming that there is no aether and that the speed of light is, thus, some kind of universal constant.

Let's keep in mind that if the luminiferous aether were to be detected by an experiment, all the mathematics of relativity would still work just fine. The difference would be that the speed of light could vary from place to place and could possibly even become arbitrarily large under the right physical conditions.

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>Clayton: Spherical and cylindrical geometries do have Euclidean representations

Non-Euclidean manifolds can be envisaged as lying in a Euclidean manifold with a greater number of dimensions. But this involves introducing additional assumptions and is of little practical value in relativity.

>Clayton: which is why we can easily visualize them.

I'm not sure what you can visualize. I have had some success in visualizing four-dimensional objects.

>Clayton: The physics of gravitation do not present themselves to my senses.

It is the same with economic phenomena. Fortunately, one equipped with a brain can contend with "that which is not seen".

>Clayton: I would say that this is circular reasoning.

Relativity is not "circular reasoning". It's empirically backed up.

Again I refer you to von Mises:

"A tautology must ex definitione be the tautology - restatement - of something said already previously. If we qualify Euclidian geometry as a hierarchical system of tautologies, we may say: The theorem of Pythagoras is tautological as it expresses merely something that is already implied in the definition of a right-angled triangle... But the question is: How did we get the first - the basic - proposition of which the second - the derived - proposition is merely a tautology? In the case of the various geometries the answers given today are either (a) by an arbitrary choice or (b) on account of its convenience or suitability." - Ultimate Foundation of Economic Science p. 17

I would say inane philosophical hand-wringing is "circular", because it gets you nowhere. I doubt philosophical e-peen measuring contests will assuage your jealousy of the hard sciences.

 

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>Clayton: which is why we can easily visualize them.

I'm not sure what you can visualize. I have had some success in visualizing four-dimensional objects.

The point is that cylinders and spheres are part of ordinary perceptual space. The artwork on a baseball, soccer-ball or basketball is easily visualized in the mind. Thus, we may use visual reasoning to supplement verbal reasoning to great advantage in these geometries, something that we cannot do with many non-Euclidean geometries.

>Clayton: The physics of gravitation do not present themselves to my senses.

It is the same with economic phenomena. Fortunately, one equipped with a brain can contend with "that which is not seen".

That only goes to prove my point - ordinary perceptual space occupies a privileged place in human knowledge. To visualize a 4D cube, for example, you need to use some kind of metaphor, or you have to depict particular aspects of the cube such as the topological arrangement of its edges and vertices but in no case can any human being "visualize" a 4D cube because visualization is, by definition, 3-dimensional and 3 != 4.

>Clayton: I would say that this is circular reasoning.

Relativity is not "circular reasoning". It's empirically backed up.

I didn't say "relativity is circular reasoning" and I gave an argument which you did not answer. Try again.

Again I refer you to von Mises:

"A tautology must ex definitione be the tautology - restatement - of something said already previously. If we qualify Euclidian geometry as a hierarchical system of tautologies, we may say: The theorem of Pythagoras is tautological as it expresses merely something that is already implied in the definition of a right-angled triangle... But the question is: How did we get the first - the basic - proposition of which the second - the derived - proposition is merely a tautology? In the case of the various geometries the answers given today are either (a) by an arbitrary choice or (b) on account of its convenience or suitability." - Ultimate Foundation of Economic Science p. 17

A tautology is not circular reasoning unless the person positing the tautology is attempting to deny that it is, in fact, tautologous. Circular reasoning is fallacious because it presents itself as an argument when it is actually a tautology.

I would say inane philosophical hand-wringing is "circular", because it gets you nowhere. I doubt philosophical e-peen measuring contests will assuage your jealousy of the hard sciences.

The "hard sciences" are just another subject of philosophy. Basic philosophical errors - such as the petitio principii implicit in the many-universes interpretation, which I explained in an earlier post - mitigate against the possibility of doing hard science. Stated another way, you can't do advanced philosophy very well (which is what the hard sciences really are) if you are making amateur mistakes in basic philosophy.

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the petitio principii implicit in the many-universes interpretation

Clayton, I'm not a fan of MWI (Many Worlds Interpretation) either. It is arbitrary, extremely weighty metaphysical baggage which has no scientific value. But I have trouble seeing the "petitio principii" fallacy there as you claim to. I simply see it as a ridiculous axiom that can be adopted at almost any time to sweep any kind of scientific ignorance under the rug. For example, before "F=ma" was discovered, we could have said the universe splits into an infinity of copies each time an object is pushed, and the object moves at a different velocity in each of the new universes.

The "ensemble" interpretation of quantum mechanics (http://en.wikipedia.org/wiki/Ensemble_interpretation) is far more humble and satisfying. It is silent regarding the possibility of a deeper "(nonlocal) hidden variables" explanation. Per Einstein: "unnatural theoretical interpretations... become immediately unnecessary if one accepts the interpretation that the description refers to ensembles of systems and not to individual systems."

There are also many other interpretations of QM besides MWI.

 

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a ridiculous axiom that can be adopted at almost any time to sweep any kind of scientific ignorance under the rug. For example, before "F=ma" was discovered, we could have said the universe splits into an infinity of copies each time an object is pushed, and the object moves at a different velocity in each of the new universes.

Precisely. The point of a theory is to explain the phenomena. To explain phenomena is to rule out all possibilities but those that comply with some regularity (law). Thus, to invoke all possibilities to explain a phenomenon is not to explain it since no possibilities have been ruled out. Thus, the many-worlds or "all possibilities" explanation is not an explanation at all, it's just a tautology masquerading as an explanation. Which is the definition of petitio principii.

QED

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