How Does the Expansion of Space Affect Electromagnetic Wave Speed?

[eternalakin]

Whats the effect of shrinking and stretching of space on the propagation speed of electromagnetic waves. This is in reference to the direct correlation of the propagation speed to the fundamental properties of empty space viz. permittivity and permeability of free space. Do the permittivity and permeability of empty space change when it is shrunk or stretched significantly ?
Ofcourse the effect can't be tested in a lab so far or can it ?
c = 1/√ε0*μ0

 

[Simon Bridge]

Welcome to PF;

Whats the effect of shrinking and stretching of space on the propagation speed of electromagnetic waves.

Nothing.

This is in reference to the direct correlation of the propagation speed to the fundamental properties of empty space viz. permittivity and permeability of free space. Do the permittivity and permeability of empty space change when it is shrunk or stretched significantly ?

No, it isn't.

Of course the effect can't be tested in a lab so far or can it ?

IIRC the evidence is indirect from observation of distance galaxies.

It's been a while since I've visited this subject though and the state of the art may have moved on since then. My previous thinking (in a nutshell) was: since the Hubble expansion is in the metric, and E-Mag is Lorentz invariant, then I would not expect E-Mag constants to change with the metric.

I have seen the occasional paper suggesting an expansion model that assumes some alteration to c, but none I've seen appear to add anything to existing theory.

 

[Naty1]

There are many possible answers to your question as I read it...since you posted this in cosmology, I'm wondering what you had in mind via the term 'propagation speed'. 'Speed' in curved spacetime is not well defined because neither time nor distance are well defined.

Some possible answers:

The speed of light is always 'c' locally. Locally, c = 1/√ε0*μ0, as you posted.

Light at the Hubble radius, where recession velocity is c, is not closing any distance towards us right now, but will be in the future.

Light just inside the particle horizon is receding from us right now, but can reach us in the future.

 

[Chronos]

Bear in mind, in an expanding universe, we have a cosmic event horizon; which is not necessarily the same as the particle horizon.

 

[marcus]

...
Light just inside the particle horizon is receding from us right now, but can reach us in the future.

Light just inside the Cosmic Event Horizon is receding from us right now but can reach us in the future. Assuming it's aimed at us. The CEH is currently 16.4 Gly

Light just inside the particle horizon is receding from us right now, and always will recede, and can never reach us. The particle horizon is currently around 46 Gly.

 

[Chronos]

The confusing part about the CEH is light from the particle horizon can reach us in the past, but, light from the
CEH cannot reach us in the future.

 

[Naty1]

yes...thanks...{edit: Glad someone is checking on me!}

I saw this rather nice explanation somewhere and saved it...too bad I didn't utilize it!

In an expanding universe, an observer may find that some regions of the past cannot be observed ("particle horizon"), and some regions of the future cannot be influenced (event horizon).

So this 'particle horizon' is the surface of last scattering from where CMBR originates...

I think we can say for our universe, with our expansion 'an observer WILL find'...
[and I'll be lucky if I remember to hit 'submit reply' key' !]