History

Re: Time Travel is Impossible

Blargg — Mon, 10 Dec 2012 17:36:45 GMT

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.

Re: Time Travel is Impossible

AJ — Mon, 10 Dec 2012 17:19:44 GMT

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.

Re: Time Travel is Impossible

AJ — Mon, 10 Dec 2012 17:17:34 GMT

Sorry for the delay, Anenome.

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.

Anenome:
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.

Anenome:
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.

"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.

Anenome:
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?

Anenome:
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.

Re: Time Travel is Impossible

Clayton — Fri, 07 Dec 2012 04:02:37 GMT

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 -

Re: Time Travel is Impossible

Anenome — Thu, 06 Dec 2012 23:43:28 GMT

Yeah, I think MWI is reeeeediculous.

Re: Time Travel is Impossible

baxter — Thu, 06 Dec 2012 22:33:04 GMT

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.

Re: Time Travel is Impossible

Clayton — Thu, 06 Dec 2012 22:19:53 GMT

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

Clayton -

Re: Time Travel is Impossible

baxter — Thu, 06 Dec 2012 20:46:38 GMT

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.

Re: Time Travel is Impossible

Clayton — Thu, 06 Dec 2012 10:59:56 GMT

>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.

Clayton -

Re: Time Travel is Impossible

baxter — Thu, 06 Dec 2012 02:20:38 GMT

>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.

Re: Time Travel is Impossible

Clayton — Thu, 06 Dec 2012 00:57:20 GMT

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.

Clayton -

Re: Time Travel is Impossible

banned — Thu, 06 Dec 2012 00:39:18 GMT

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).

Re: Time Travel is Impossible

Clayton — Wed, 05 Dec 2012 23:53:37 GMT

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.

Clayton -

Re: Time Travel is Impossible

Clayton — Wed, 05 Dec 2012 23:47:35 GMT

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

Clayton -

Re: Time Travel is Impossible

baxter — Wed, 05 Dec 2012 21:14:21 GMT

>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?