Hubble Law & SR: Does Velocity Increase Mass?

[Arman777]

This question will sound mostly stupid but anyways.

We see that galaxies have some velocity due to the Hubble law. Let's take an object that has a recessional velocity of $v$. In SR case assuming the universe is nearly flat, can we say that the galaxy gains mass relative to us ?

I guess in this case the velocity will be low so there won't be any relativistic effect ?

 

[mathman]

Velocities can be high.

 

[Ibix]

Relativistic mass is a deprecated concept nowadays - "mass" is taken to mean "invariant mass", also known as "rest mass", unless otherwise stated.

The limit of a zero-mass density FLRW universe is Minkowski spacetime, equipped with a rather unusual coordinate system (Milne cosmology). In that case, distant test objects "at rest" in this system would be receding, but since you aren't using Einstein coordinates relativistic mass isn't a relevant concept (even if it weren't deprecated).

And in the real world, the mass density isn't zero, so you have curved spacetime and again you can't use Einstein coordinates. So once again, relativistic mass isn't really applicable.

 

[Arman777]

I understand it thanks for your reply