Block Time vs Q. Indeterminacy

[Passionflower]

I guess I need some clarification, how can you folks talk about a potential preferred frame in our spacetime which is obviously non-stationary.

 

[ghwellsjr]

I guess I need some clarification, how can you folks talk about a potential preferred frame in our spacetime which is obviously non-stationary.

Since Lorentz Ether Theory (LET) is indistinguishable from Special Relativity (SR) save for the claim that there exists a single preferred frame, Einstein designed his concept of spacetime in such a way that every inertial frame satisfies the requirements for a Lorentz ether frame and therefore can be considered a potential preferred frame.

 

[stglyde]

That's another physical question on which the jury is still out. There is certainly a large school of thought in quantum physics that believes this, but it is not established the way, say, the Earth going around the Sun is.



Tidal gravity is not "just a math model". It's a physical observable. It is true that one is not *forced* to model tidal gravity using a curved spacetime; one could use another model. But in the context of that model, "spacetime curvature" is simply another name for "tidal gravity", so if tidal gravity is real (which it is), then spacetime curvature is real.

PeterDonis. Can you please go to the thread below as I'd like to inquire more about this Tidal gravity and wave function thing which can become off topic in this thead. Thanks.

https://www.physicsforums.com/showthread.php?t=554273

 

[PeterDonis]

PeterDonis. Can you please go to the thread below as I'd like to inquire more about this Tidal gravity and wave function thing which can become off topic in this thead. Thanks.

https://www.physicsforums.com/showthread.php?t=554273

Sure, going there now.

 

[stglyde]

bobc2, what do you make of the following:

http://space.mit.edu/home/tegmark/dimensions.pdf

where Max Tegmark states only 3D space and 1D time is stable. Can you find any flaws in the paper? What is your comment on it?

 

[PeterDonis]

Sure, going there now.

Looks like the thread was locked; possibly because you started asking about spacetime again, which would belong back here, or possibly because it was perceived as pursuing your own speculative theory instead of asking about existing theories.

As far as the items you asked that were about modeling tidal gravity some other way than spacetime curvature, there is an alternate model that views gravity as a masless, spin-2 field on a flat background spacetime. I don't know of a good introductory online reference; I learned about it from The Feynman Lectures on Gravitation:

http://books.google.com/books/about/Feynman_lectures_on_gravitation.html?id=jL9reHGIcMgC

This "field on a flat spacetime" model turns out to be equivalent to the standard curved-spacetime model of GR, except for some concerns about whether the starting assumption of a flat background means the model can't deal with, for example, the FRW spacetimes in cosmology. So instead of viewing tidal gravity as a manifestation of spacetime curvature, you could view it as a manifestation of the massless, spin-2 field. But since the models give exactly the same predictions, one could just as well say that "spacetime curvature" and "massless spin-2 field" are different names for the same thing, the whatever-it-is-that-causes-tidal-gravity.

 

[stglyde]

Looks like the thread was locked; possibly because you started asking about spacetime again, which would belong back here, or possibly because it was perceived as pursuing your own speculative theory instead of asking about existing theories.

As far as the items you asked that were about modeling tidal gravity some other way than spacetime curvature, there is an alternate model that views gravity as a masless, spin-2 field on a flat background spacetime. I don't know of a good introductory online reference; I learned about it from The Feynman Lectures on Gravitation:

http://books.google.com/books/about/Feynman_lectures_on_gravitation.html?id=jL9reHGIcMgC

This "field on a flat spacetime" model turns out to be equivalent to the standard curved-spacetime model of GR, except for some concerns about whether the starting assumption of a flat background means the model can't deal with, for example, the FRW spacetimes in cosmology. So instead of viewing tidal gravity as a manifestation of spacetime curvature, you could view it as a manifestation of the massless, spin-2 field. But since the models give exactly the same predictions, one could just as well say that "spacetime curvature" and "massless spin-2 field" are different names for the same thing, the whatever-it-is-that-causes-tidal-gravity.

Ok.

Say. Can you think of an experimental setup that we average person can afford that can test for local lorentz invariance? Like some electronics apparatus that can be modified to become sensors for a rough test of orientation and boost lorentz symmetry or CPT symmetry? Think and brainstorm for an hour then please share. Thanks.

 

[stglyde]

Looks like the thread was locked; possibly because you started asking about spacetime again, which would belong back here, or possibly because it was perceived as pursuing your own speculative theory instead of asking about existing theories.

As far as the items you asked that were about modeling tidal gravity some other way than spacetime curvature, there is an alternate model that views gravity as a masless, spin-2 field on a flat background spacetime. I don't know of a good introductory online reference; I learned about it from The Feynman Lectures on Gravitation:

http://books.google.com/books/about/Feynman_lectures_on_gravitation.html?id=jL9reHGIcMgC

This "field on a flat spacetime" model turns out to be equivalent to the standard curved-spacetime model of GR, except for some concerns about whether the starting assumption of a flat background means the model can't deal with, for example, the FRW spacetimes in cosmology. So instead of viewing tidal gravity as a manifestation of spacetime curvature, you could view it as a manifestation of the massless, spin-2 field. But since the models give exactly the same predictions, one could just as well say that "spacetime curvature" and "massless spin-2 field" are different names for the same thing, the whatever-it-is-that-causes-tidal-gravity.

Googling "massless, spin-2 field on a flat background spacetime", there are indeed many researches about this.. interesting.. it's about going to flat minkowski space with spin 2 gravitons. Now how about going a step further backward.. like minkowski field on an Newtonian spacetime. I mean.. if we can remove the space curvature in GR by going to massless spin 2 field on a flat spacetime.. what is it not possible to move further back... like space+time field on Newtonian absolute space and time.. or something akin to it?

 

[nitsuj]

Ok.

Say. Can you think of an experimental setup that we average person can afford that can test for local lorentz invariance? Like some electronics apparatus that can be modified to become sensors for a rough test of orientation and boost lorentz symmetry or CPT symmetry? Think and brainstorm for an hour then please share. Thanks.

I think Tom Tom's have come down in price.

I hope it's okay I did someone else's homework

 

[stglyde]

Googling "massless, spin-2 field on a flat background spacetime", there are indeed many researches about this.. interesting.. it's about going to flat minkowski space with spin 2 gravitons. Now how about going a step further backward.. like minkowski field on an Newtonian spacetime. I mean.. if we can remove the space curvature in GR by going to massless spin 2 field on a flat spacetime.. what is it not possible to move further back... like space+time field on Newtonian absolute space and time.. or something akin to it?

After writing this. It slowly dawns on me there is indeed such thing. It's Lorentz Ether Theory which occurs in the backdrop of absolute space and time... just like how you can model massless spin-2 field on flat spacetime. You can actually take one step backward... LET field on absolute space and time! Now how do you connect gravity to Newtonian. There is one. It's called General Lorentz ether theory applied to Newtonian space and time! And all this appears not to be falsifiable! Is this 100% such that no experiment ever will distinguish them??

 

[atyy]

After writing this. It slowly dawns on me there is indeed such thing. It's Lorentz Ether Theory which occurs in the backdrop of absolute space and time... just like how you can model massless spin-2 field on flat spacetime. You can actually take one step backward... LET field on absolute space and time! Now how do you connect gravity to Newtonian. There is one. It's called General Lorentz ether theory applied to Newtonian space and time! And all this appears not to be falsifiable! Is this 100% such that no experiment ever will distinguish them??

LET has absolute space and time in the sense that it is physics in a preferred frame (an inertial frame). LET, however, still has Lorentz invariance, not Galilean invariance. GR/massless spin-2 fields also have Lorentz invariance. Is it possible to find a theory of gravity which is well-approximated as a Lorentz invariant spin-2 field at low energies, but which has Galilean invariance at high energies? At present, no such theory has been discovered. There are, however, non-gravitational theories which have Galilean invariance at high energies and Lorentz invariance at low energies: http://www.nature.com/nature/journal/v438/n7065/abs/nature04233.html.

Ok.

Say. Can you think of an experimental setup that we average person can afford that can test for local lorentz invariance? Like some electronics apparatus that can be modified to become sensors for a rough test of orientation and boost lorentz symmetry or CPT symmetry? Think and brainstorm for an hour then please share. Thanks.

Test Maxwell's equations (which have Lorentz symmetry). In particular test that the speed of light is as predicted by Maxwell's equations: http://www.physics.umd.edu/icpe/newsletters/n34/marshmal.htm (I've never tried this, I'd be interested to know if it really works).

There is also what is commonly advertised as a test of length contraction by measuring the magnetic field due to a current: http://physics.weber.edu/schroeder/mrr/MRRtalk.html.

 

[PeterDonis]

Ok.

Say. Can you think of an experimental setup that we average person can afford that can test for local lorentz invariance? Like some electronics apparatus that can be modified to become sensors for a rough test of orientation and boost lorentz symmetry or CPT symmetry? Think and brainstorm for an hour then please share. Thanks.

See here for a good summary of tests of Lorentz invariance:

http://relativity.livingreviews.org/Articles/lrr-2005-5/

 

[PeterDonis]

I mean.. if we can remove the space curvature in GR by going to massless spin 2 field on a flat spacetime..

I think you may be misunderstanding what the massless spin-2 field model does. It does not "remove" the spacetime curvature; it shows that the massless spin-2 field is *equivalent* to curvature. (And it's *spacetime* curvature, not just space curvature.)

what is it not possible to move further back... like space+time field on Newtonian absolute space and time.. or something akin to it?

If this were possible, it would have been done in the late 19th or early 20th centuries; everybody was looking for a theory like this, in order to try and reconcile Maxwell's Equations with Newtonian physics, and nobody found one.

 

[stglyde]

I think you may be misunderstanding what the massless spin-2 field model does. It does not "remove" the spacetime curvature; it shows that the massless spin-2 field is *equivalent* to curvature. (And it's *spacetime* curvature, not just space curvature.)

I know. It's just like the strings in flat spacetime but the gravitons causing effect equivalent to curvature and we can't know.

If this were possible, it would have been done in the late 19th or early 20th centuries; everybody was looking for a theory like this, in order to try and reconcile Maxwell's Equations with Newtonian physics, and nobody found one.

Have you forgotten Lorentz Ether Theory. Here's the analogy.

1. massless spin2 field in flat minkowski is equivalent to General Relativity
2. actual length contraction, etc. in absolute space and time is equivalent to Newtonian Absolute Space and Time

 

[PeterDonis]

1. massless spin2 field in flat minkowski is equivalent to General Relativity
2. actual length contraction, etc. in absolute space and time is equivalent to Newtonian Absolute Space and Time

I see the similarity: both examples involve something that's postulated to be part of a physical theory but is "unobservable" (the flat background spacetime and the "absolute rest" frame). But the two examples are not quite the same. In the massless spin-2 field example, there's no need to commit to any particular state of motion as being "at rest". You just have to accept that the flat background is unobservable, because all actual physical measurements are governed by the "curved" metric produced by the massless spin-2 field.

With LET, you have to believe that there is some particular state of motion that corresponds to "absolute rest", we just have no way of ever telling which one it is by experiment. Also, the "absolute rest" frame in LET, corresponding to the "absolute rest" state of motion, is *not* a Newtonian absolute space/time. It's a Lorentz inertial frame; there's just no way of knowing *which* Lorentz inertial frame it is. LET is *not* a theory that adds Lorentz length contraction/time dilation "on top of" Newtonian absolute space and time; there is no such theory, because Newtonian absolute space and time is incompatible with Lorentz invariance (it would require Galilean invariance, corresponding to an infinite speed of light).

 

[stglyde]

I see the similarity: both examples involve something that's postulated to be part of a physical theory but is "unobservable" (the flat background spacetime and the "absolute rest" frame). But the two examples are not quite the same. In the massless spin-2 field example, there's no need to commit to any particular state of motion as being "at rest". You just have to accept that the flat background is unobservable, because all actual physical measurements are governed by the "curved" metric produced by the massless spin-2 field.

With LET, you have to believe that there is some particular state of motion that corresponds to "absolute rest", we just have no way of ever telling which one it is by experiment. Also, the "absolute rest" frame in LET, corresponding to the "absolute rest" state of motion, is *not* a Newtonian absolute space/time. It's a Lorentz inertial frame; there's just no way of knowing *which* Lorentz inertial frame it is. LET is *not* a theory that adds Lorentz length contraction/time dilation "on top of" Newtonian absolute space and time; there is no such theory, because Newtonian absolute space and time is incompatible with Lorentz invariance (it would require Galilean invariance, corresponding to an infinite speed of light).

Uhm.. if this is so. How come when Lorentz discovered the Lorentz Transformation. He didn't immediately explore Minkowski Spacetime. He actually thought the physical length contracting was enough to explain it. It took Einstein to discover the Minkowski mechanism. So it could be assume Lorentz Transformation as Lorentz thought it can be an addition to Newtonian absolute space and time.

 

[PeterDonis]

Uhm.. if this is so. How come when Lorentz discovered the Lorentz Transformation. He didn't immediately explore Minkowski Spacetime. He actually thought the physical length contracting was enough to explain it. It took Einstein to discover the Minkowski mechanism. So it could be assume Lorentz Transformation as Lorentz thought it can be an addition to Newtonian absolute space and time.

Actually, Einstein didn't discover Minkowski spacetime; Minkowski did. (Yes, I know things aren't always named after the people who actually discovered them, but in this case it happened that way.) You may be using the term "Minkowski spacetime" more generally than it's normally used; normally it doesn't just refer to SR in general, but to the particular geometric object, a 4-dimensional manifold with a particular metric, that can be used to model SR. As I said, Einstein didn't come up with that; Minkowski did, and Einstein only adopted it when it became clear to him that he needed a geometric model for general relativity, and that Minkowski's flat spacetime was the limiting case of that model when gravity is absent.

I'm not familiar enough with Lorentz's papers to know whether he thought at first that his results could be explained by just adding on length contraction to Newtonian space and time. But I don't think it really matters, because Einstein's 1905 relativity papers did make it clear that that wasn't possible; that to make kinematics consistent with the speed of light being constant for all observers, you *had* to give up Newtonian space and time.

 

[stglyde]

Actually, Einstein didn't discover Minkowski spacetime; Minkowski did. (Yes, I know things aren't always named after the people who actually discovered them, but in this case it happened that way.) You may be using the term "Minkowski spacetime" more generally than it's normally used; normally it doesn't just refer to SR in general, but to the particular geometric object, a 4-dimensional manifold with a particular metric, that can be used to model SR. As I said, Einstein didn't come up with that; Minkowski did, and Einstein only adopted it when it became clear to him that he needed a geometric model for general relativity, and that Minkowski's flat spacetime was the limiting case of that model when gravity is absent.

I'm not familiar enough with Lorentz's papers to know whether he thought at first that his results could be explained by just adding on length contraction to Newtonian space and time. But I don't think it really matters, because Einstein's 1905 relativity papers did make it clear that that wasn't possible; that to make kinematics consistent with the speed of light being constant for all observers, you *had* to give up Newtonian space and time.

Thanks for the important distinctions. I'm interested in all this because I'm looking for lorentz violations.

How do you think the quantum vacuum connect with spacetime? Is the quantum vacuum inside spacetime or is spacetime inside the quantum vacuum? They say the quantum vacuum doesn't have a rest frame.. so it's like its connected to spacetime as if part of the manifold.

We still haven't refuted Dirac sea of Electrons where the vacuum is composed of negative sea of electrons. If this were true. Then lorentz violations could be detected at this sector. I wonder if the quantum vacuum can also have spontaneous symmetry breaking where if you can alter it at certain configuration from the default ambient background.. it would no longer follow lorentz symmetry.. and hence lorentz violations detected. What are the arguments that makes it impossible that the quantum vacuum can change default mode to another phase or level?

 

[PeterDonis]

Thanks for the important distinctions. I'm interested in all this because I'm looking for lorentz violations.

The living reviews site I linked to earlier gives a good summary of where we stand on this. If there are particular things in there that you have questions about, you should probably start a separate thread.

How do you think the quantum vacuum connect with spacetime? Is the quantum vacuum inside spacetime or is spacetime inside the quantum vacuum? They say the quantum vacuum doesn't have a rest frame.. so it's like its connected to spacetime as if part of the manifold.

Any quantum vacuum state has to respect Lorentz invariance; in this sense it "doesn't have a rest frame". However, a quantum state that looks like the vacuum to inertial observers will *not* look like the vacuum to accelerated observers. See here for an overview:

http://en.wikipedia.org/wiki/Unruh_effect

So in this sense there is not a unique "quantum vacuum"; which quantum state is the vacuum can depend on your state of motion (inertial vs. accelerated). In curved spacetime this effect is used to show that black holes emit Hawking radiation:

http://en.wikipedia.org/wiki/Hawking_radiation

We still haven't refuted Dirac sea of Electrons where the vacuum is composed of negative sea of electrons.

Only in the sense that the predictions of Dirac's "hole theory" are formally equivalent to those of standard quantum field theory (at least, as far as I know they are). But standard QFT makes the same predictions without requiring the existence of the infinite sea of negative energy electrons, so Occam's Razor implies that such a sea does not exist.

I wonder if the quantum vacuum can also have spontaneous symmetry breaking where if you can alter it at certain configuration from the default ambient background.. it would no longer follow lorentz symmetry.. and hence lorentz violations detected. What are the arguments that makes it impossible that the quantum vacuum can change default mode to another phase or level?

The quantum vacuum can certainly undergo spontaneous symmetry breaking: that's the current theory of how the inflationary epoch in cosmology ended (by the vacuum undergoing a phase transition from the symmetric "false vacuum" to the symmetry-broken "true vacuum"):

http://en.wikipedia.org/wiki/Inflation_(cosmology)

But as far as I know, this did not involve any violation of Lorentz invariance. I don't know that anyone has proposed spontaneous symmetry breaking as a mechanism for Lorentz violation. If anyone has, I would expect the living reviews site I linked to to talk about it.

 

[stglyde]

Actually, Einstein didn't discover Minkowski spacetime; Minkowski did. (Yes, I know things aren't always named after the people who actually discovered them, but in this case it happened that way.) You may be using the term "Minkowski spacetime" more generally than it's normally used; normally it doesn't just refer to SR in general, but to the particular geometric object, a 4-dimensional manifold with a particular metric, that can be used to model SR. As I said, Einstein didn't come up with that; Minkowski did, and Einstein only adopted it when it became clear to him that he needed a geometric model for general relativity, and that Minkowski's flat spacetime was the limiting case of that model when gravity is absent.

I'm not familiar enough with Lorentz's papers to know whether he thought at first that his results could be explained by just adding on length contraction to Newtonian space and time. But I don't think it really matters, because Einstein's 1905 relativity papers did make it clear that that wasn't possible; that to make kinematics consistent with the speed of light being constant for all observers, you *had* to give up Newtonian space and time.

Hi PeterDonis, please go to this related thread where I mentioned about LET, FTL and SR (in order not to make it off topic here) and mentioned about the above where one of them commented:

"I would drop the first assumption immediately and say that the second is also questionable. Dropping the first assumption is sufficient to reject PeterDonis' argument.

Pls address message #19 in:

https://www.physicsforums.com/showthread.php?t=554741&page=2