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What is the difference between a preferred state of rest and a preferred state of velocity?


Simplico

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10 hours ago, mistermack said:

Sorry, but that's not right at all. It would only be right, if the one point of view was incompatible with the other.

If you postulate that the laws of physics apply equally in every frame, which of course I'm not disputing, then they would inevitably apply in a "real" frame in the same way as every other frame. What's the difference between saying that there is no preferred frame, and saying that there is no preferred frame available?

My argument for years now has been that the speed of light RESTRICTS us from observing reality, and relativity is just the consolation prize that we can use to recreate a working model. It's not reality, but it's all we can achieve and we're lucky to have it.

If your focus is on reality, then this is philosophy.

If your focus is on physics, then you have to work out a model and discuss it in your own thread in speculations.

10 hours ago, mistermack said:

Imagine that somebody tomorrow discovered a previously undetected form of light, call it L2. Instead of travelling at c, L2 travelled almost infinitely fast. So as far as we could tell, even from billions of light years away, you were seeing the present.

What would that do to relativity? What would you consider reality, what you were seeing with L2, or what you observed with ordinary light? Just because there is no way for US to observe simultaneous events, does that mean there ARE no simultaneous events?

It's the unfortunate slow speed of light that's stopping us from observing reality. What we CAN see, is reality for us, it's all we've got, but it's not what's actually out there. 

If this L2 interacted with anything, then causality goes out the window.  Game over, man.

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23 hours ago, swansont said:

But we have looked at it, and looked at it carefully, for >100 years. And the framework of the consideration is that there is no way to test for it (i.e. it exists but has relativistic symmetry), and that of some new framework of thought were found it would not change physics at all, since we've already agreed that in this scenario there is no physical test that can distinguish the frame, which is synonymous with saying there is no preferred frame of reference.

 

 

In principle you could run tests from a base that is at a much greater speed wrt the CMBR than have ever taken place in the >100 years and see if the relativistic symmetry still holds. So far we have only done this from a base of a fraction of a percent of c wrt to the CMBR.

This is just an example. I am not arguing against relativity per se. It is obviously the best we have, and it's based on our best assumptions. But you, I or anyone else having no reason to disbelieve it does not make something 100% certain. The level of certainty can still increase from whatever it might be today, or we might find something unexpected.

 

 

Edited by J.C.MacSwell
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4 hours ago, J.C.MacSwell said:

In principle you could run tests from a base that is at a much greater speed wrt the CMBR than have ever taken place in the >100 years and see if the relativistic symmetry still holds. So far we have only done this from a base of a fraction of a percent of c wrt to the CMBR.

We have run tests on things moving very fast wrt the CMBR. Muon decay, and particles in accelerators.

 

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12 hours ago, J.C.MacSwell said:

Measured from a base with start and finish points moving how fast wrt to theCMBR?

Moving at a large fraction of c.

Why do you need "a base" and start and finish points?

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1 hour ago, swansont said:

Moving at a large fraction of c.

Why do you need "a base" and start and finish points?

Measured wrt your base, lab, space station etc Some reference frame at a fraction 1% of c. (wrt anything else is calculated)

It is very reasonable to assume the tests would have the same results if done from a base at greater speed (wrt Earth or wrt the CMBR) given that we don't have much choice...but if we did have a choice, if we could just as easily make the tests from some spaceship at greater speeds, would we be 100% confident that those assumptions are reasonable and not bother?

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2 hours ago, mistermack said:

It's a gigantic expansion of the notion of the universe, if every incident that ever happened or ever will happen is lying around somewhere. 

While that is indeed the basic idea, I should clarify that the notion of “event” in GR is not the same as the term “event” in everyday speech. A GR event is simply a point in space at an instant in time, meaning a point on a 4-dimensional manifold. When you describe a real-world object that persists over a period of time, then this becomes a collection of events, i.e. a world line in spacetime. 

But yes, in GR terms, the “universe” is the collection of all points in space at all instances of time.

2 hours ago, mistermack said:

You also have the problem of random uncertainty. You have to have every possible incident lying about, not just the actual ones. That makes for a gigantic expansion of a gigantic expansion, of something that was unbelievably gigantic to start with. 

GR is a purely classical model, meaning it does not account for any quantum effects, such as uncertainties in measurement outcomes. That is what I meant when I mentioned that everything is deterministic in GR.

You can try to interpret QM in the context of spacetime, which basically leads you to the “many worlds” interpretation. That is indeed a gigantic collection of events!

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