I Is there a physical explanation for the relationship between light and space?

[Buckethead]

Look,if you have an isolated ring with stress, you can deduce a state without stress that the isolated ring rotates relative to. Thus, even though the ring is isolated, it physically defines its own nonrotating reference.

Interesting. I can accept that this is true, but it sure is abstract! It just seems impossible that it can be this way.

 

[Buckethead]

This doesn't make any sense. How could you even have two rings without spacetime? If there is no geometry then in what sense is there a ring, let alone two rings? Doesn't what you are describing as a "two rings" presuppose geometry?

I should have been more careful with my wording. What I meant to ask was if it was necessary to first compare the ring with spacetime, then compare spacetime to the second ring to determine if one ring is rotating relative to the other, or would it be possible to just compare one ring to the other directly to get the same result. But I'm not sure this is a valid question anymore. I'm getting the sense that trying to determine whether a ring is feeling forces due to spinning or not simply by math alone is not possible. That only a measurement (by accelerameters) can be used to determine this. I suppose this is just one of those mysteries up there with why light always travels at c.

 

[Buckethead]

In other words, spacetime is a model that we use in order to tie together lots of different observations and give a compact explanation for all of them. But the model is not the observations. It's a model.

Right, again, we can know spacetime by its properties, but that does not give us the ability to know spacetime as anything other than a math model.

 

[Buckethead]

There would be a Doppler effect with the observation, I'll use my own choice of light. Even if the ring was luminescent, and uniformly, or at least consistently so, this would be seen.

Interesting, although if the object were not rotating and instead was being orbited by an observer the Doppler shift would still be seen.

 

[Buckethead]

Common sense, another term for experience, does not apply in the depth of space or in a black hole or inside and atom because we cannot experience and survive these places.

This seems to be true, but we have to be careful to not use that excuse as another type of god of the gaps where if we stumble upon a paradoxical situation such as the mystery of spacetime, that we don't just throw our hands up and say, "Welp, looks like another one of natures mysteries that we are not allowed to make sense of".

 

[Dale]

What I meant to ask was if it was necessary to first compare the ring with spacetime, then compare spacetime to the second ring to determine if one ring is rotating relative to the other, or would it be possible to just compare one ring to the other directly to get the same result.

The comparison to the other ring is pretty much irrelevant. You can determine the rotation of one ring (without reference to the other) either by comparing it to spacetime (using accelerometers) or directly (measuring the stress in the ring).

I'm getting the sense that trying to determine whether a ring is feeling forces due to spinning or not simply by math alone is not possible. That only a measurement (by accelerameters) can be used to determine this.

This is true, but I am not understanding what you feel is at all surprising about that. I mean, you cannot determine anything about an object through math alone. Why should spinning be determined through math alone? Indeed, to me that would be far more surprising.

 

[nitsuj]

The problem is that this physics, like quantum physics, is in physical terms but outside the boundaries of our day to day human experience. It is described in mathematics because everyday terms like door and chair and teddy bear really do not apply. Our everyday experience is pretty well described by Newton's physics for 90 percent of it and the other ten percent we gloss over till someone starts measuring and observing closely finding discrepancies. Then it gets weird and the Newtonian space of our daily experience cannot be reconciled. Common sense, another term for experience, does not apply in the depth of space or in a black hole or inside and atom because we cannot experience and survive these places.

Are you talking about measurement accuracy, our ability to perceive comparatively microscopic physical effects or our ability to understand them? The logic between the theories is vastly different, contradictory and as easy to spot as the difference between a chair and a teddy bear, or to speak your language 0≠1

fyi Newton physics describes 0% of our, or anythings daily experience. It does make very accurate predictions, but lacks the SUPER axiom that, as seen in this thread, changes everything.

I haven't seen anything in this thread that suggests they're applying "everyday experience" [Newtonian physics] to this imaginary physics scenario

The question was simply put, simply answered , rinse repeat, and maybe is better understood now.

 

[pervect]

If someone asked in a post "Is this frame rotating relative to space-time", I'd ask them what they meant. It'd be unclear at best. I'd also not word my answer in those terms, I'd pick some different ones I felt was less ambiguous as well, as I wouldn't want my words to be interpreted differently later and by other people.

In the one problem I worked where it made a difference, I'd talk about whether something was rotating "relative to the fixed stars" or "relative to a gyroscope". This is a bit clearer, though it may possible to improve it further. Both make more sense to me than talking about "rotating relative to space-time".

A problem I was working on a while ago where it made a difference -might provide some insight. Consider a frame on block sliding on the floor of Einstein's elevator. It - it seemed to be generally better understood when I said that a gyroscope attached to the sliding block would precess. It's logically equivalent to say that the block rotates relative to a gyroscope, but it seemed to cause less confusion when I assumed what I'd call "the fixed star frame".

In this example in particular, if someone asked "is the block rotating relative to space-time", the answer is not very clear. It's clearer IMO to say that the block is not rotating relative to the fixed stars, but a gyroscope attached to the block would precess.

 

[Herman Trivilino]

If someone asked in a post "Is this frame rotating relative to space-time", I'd ask them what they meant. It'd be unclear at best.

I agree. It would make me think they might be referring to space-time as a substance of some sort. What you could say is that it's rotating in some specified reference frame. That reference frame is used to define the space and time coordinates. Is space-time, a, some naturally-occurring thing whose creation we attribute to Nature; or is it, b, a model created by the human intellect? Or is there some third option? Perhaps we use the term space-time in more than one way, so that in one way we mean a but in the other we mean b?

 

[PeterDonis]

I'd talk about whether something was rotating "relative to the fixed stars" or "relative to a gyroscope".

The second is better, IMO, since it's local. When you make "relative to a gyroscope" rigorous, you end up talking about the vorticity of the congruence of worldlines that describes the object.