Is spacetime an absolute reference frame?

Re: Spacetime

No, because the notions of being "at rest relative to spacetime" or "in motion relative to spacetime" have no physical meaning.

 

Re: Spacetime

What do you mean by "used as a benchmark"? I don't think it'd be meaningful to say you're accelerating "relative to spacetime" either, though acceleration is absolute (you know you're accelerating because you feel G-forces).

 

Re: Spacetime

I think it would be misleading to say it's rotating relative to spacetime since spacetime doesn't have any landmarks that you can measure your motion relative to. I would probably say it's rotating relative to inertial frames of reference (coordinate systems), frames that can be identified because the equations for the laws of physics take a particular form when stated in terms of their coordinates. But maybe others would have different ways of describing what's going on here.

 

Re: Spacetime

I agree that it's relative to an inertial frame. I'm not sure exactly what Greene says, but maybe there's an idea that the global inertial frames of special relativity reflect the symmetries of the flat metric - which can be colloquially identified with spacetime, and which in general relativity becomes curved and further identified with the gravitational field?

 

Re: Spacetime

Isn't the aether a concept used as an absolute reference frame? In fact, i'm sure Einstein said relativity was unthinkable without one.

Today, we've replaced the word aether for the zero-point energy field, which acts like a quantum aether.

 

Re: Spacetime

Einstein only said that spacetime was similar to an aether in the sense that it has physical properties of its own, but in relativity it is unlike the traditional notion of aether in that it doesn't have any rest frame of its own, so it is meaningless to talk about your velocity relative to spacetime (whereas it would make sense to talk about velocity relative to the aether). For example, see the last paragraph of http://www.tu-harburg.de/rzt/rzt/it/Ether.html [Broken] where he writes:

The same is true of quantum fields, quantum field theory is Lorentz-symmetric so quantum fields look the same way in every frame, they don't have a rest frame.

 

Re: Spacetime

That's quite interesting. Langevin's concept of aether was that it remained always at rest with regard to a particle or object in any frame. And maybe that was the later conclusion of Poincare and Lorentz. Therefore in following the motion of a particle translating between a laboratory frame and a frame moving in tandem with the particle, length and time contraction arises.

http://en.wikisource.org/wiki/The_R...trons_to_Other_Branches_of_Science#cite_ref-1