Why is special relativity a local phenomenon?

[sunrah]

Where does the requirement come from that special relativity applies only locally? It is not immediately obvious from the two postulates. I'm asking because this is important for the validity of the Hubble Law.

 

[Nugatory]

Where does the requirement come from that special relativity applies only locally? It is not immediately obvious from the two postulates. I'm asking because this is important for the validity of the Hubble Law.

Special relativity applies only locally because special relativity is exact only for a flat spacetime, and spacetime is not globally flat. Thus, we can only use special relativity across regions of spacetime that are small enough that the curvature and gravitational effects are negligible.

 

[sunrah]

Thanks. I thought that spacetime was flat and with no discernible non-trivial topology. Do you mean that the gravitational effect of galaxies and clusters is enough to invalidate SR on large scales.?

 

[Boing3000]

invalidate SR on large scales.?

What I have read from Nugatory in post #2 is that SR is not a large scale theory. So how could it be invalidated on scales it is not working in ?

 

[sunrah]

That's splitting hairs. Invalidate here means that any application of SR over large distances would be invalid.

 

[Boing3000]

I don't understand what you mean. SR does not explains why an apple falls. Does it invalidate SR in our mind ? Is a hammer invalid because I cannot use it on a screw ?

 

[bcrowell]

I thought that spacetime was flat and with no discernible non-trivial topology.

You're probably thinking of the average spatial curvature on cosmological scales. That's different from the spacetime curvature, which is definitely nonzero. GR describes gravity as curvature, so if there were no spacetime curvature, there would be no gravity in the universe.

 

[jedishrfu]

I think @Nugatory and @bcrowell answered your question and so we'll close the thread here.