Is spacetime an absolute reference frame?

• chuckset
In summary: 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...would occur in the laboratory frame, and the translation would be observed as an increase in the speed of light in the laboratory frame.

chuckset

Is spacetime an absolute reference frame?

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

So, is spacetime only used as a benchmark for accelerated motion?

chuckset said:
So, is spacetime only used as a benchmark for accelerated motion?
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).

For Newton's thought experiment about two rocks in deep space that will pull taut, with respect to what is it rotating? I'm trying to read Brian Greene's book "The Fabric of the Cosmos" but I'm getting very confused. Forgive me if this is a stupid question.

chuckset said:
For Newton's thought experiment about two rocks in deep space that will pull taut, with respect to what is it rotating? I'm trying to read Brian Greene's book "The Fabric of the Cosmos" but I'm getting very confused. Forgive me if this is a stupid question.
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.

Ok thanks for your responses and thanks for helping me!

JesseM said:
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.

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?

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.

ManyNames said:
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.
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:
Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it.
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.

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JesseM said:
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

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

1. Is spacetime an absolute reference frame?

No, according to the theory of relativity, spacetime is not an absolute reference frame. It is relative and can be affected by the presence of massive objects.

2. What is the concept of spacetime?

Spacetime is the mathematical model that combines the three dimensions of space and the dimension of time into a four-dimensional continuum. It is used to describe the physical universe and how objects move through it.

3. How does the theory of relativity explain spacetime?

The theory of relativity states that the laws of physics are the same for all observers in uniform motion. This means that the measurement of time and space can vary depending on the observer's frame of reference, leading to the concept of spacetime as a relative rather than absolute reference frame.

4. Can spacetime be distorted?

Yes, according to the theory of relativity, massive objects such as planets and stars can cause distortions in the fabric of spacetime. This is known as gravitational lensing and has been observed and measured by scientists.

5. How does the concept of spacetime impact our understanding of the universe?

The concept of spacetime has revolutionized our understanding of the universe by providing a unified framework for describing the laws of physics and how objects move in the universe. It has also led to the development of technologies such as GPS, which rely on precise measurements of time and space.

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