Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 21/05/2013 21:30:01

Title: Has the speed of light changed as the universe expands?
Post by: thedoc on 21/05/2013 21:30:01
Ray Gorman asked the Naked Scientists:
   
I am familiar with the idea of an expanding universe… That not just the distance between galaxies in increasing, but the ACTUAL space between galaxies (or everything for that matter) is expanding. Does this not alter the speed of light at various ages of the universe, especially if the speed of light is a constant? So, if you're looking at the universe from the "outside"- at 6.5 billion years ago, is the relative distance light travelled in a second LESS than it travels today since the SPACE itself has expanded?
 
Thanks, really enjoy the show over here in the colonies!

What do you think?
Title: Re: Has the speed of light changed as the universe expands?
Post by: Pmb on 19/05/2013 21:11:22
Quote from: thedoc on 19/05/2013 19:30:02
Ray Gorman asked the Naked Scientists:
   
I am familiar with the idea of an expanding universe; that not just the distance between galaxies in increasing, but the ACTUAL space between galaxies (or everything for that matter) is expanding.

Does this not alter the speed of light at various ages of the universe, especially if the speed of light is a constant?

So, if you're looking at the universe from the "outside"- at 6.5 billion years ago, is the relative distance light travelled in a second LESS than it travels today since the SPACE itself has expanded?
 
Thanks, really enjoy the show (http://www.thenakedscientists.com/HTML/podcasts/) over here in the colonies!

What do you think?
No. The speed of light does not change with time.
Title: Re: Has the speed of light changed as the universe expands?
Post by: Bill S on 19/05/2013 22:45:24
Quote
No. The speed of light does not change with time.

João Magueijo.  (Faster Than the Speed of Light.  2002) disagreed with that statement, have his views gained any following?
Title: Re: Has the speed of light changed as the universe expands?
Post by: imatfaal on 20/05/2013 13:20:36
Quote from: Bill S on 19/05/2013 22:45:24
Quote
No. The speed of light does not change with time.

João Magueijo.  (Faster Than the Speed of Light.  2002) disagreed with that statement, have his views gained any following?

On a regular basis some science crew state that one or more of the constants of space actually vary spatially or temporally - alpha (~1/137) the fine structure is the most common mover as it is an absolute fundamental constant (no units) and seems to be completely arbitrary.  I am pretty sure that no one has yet put forward a convincing argument that these important physical constants should change or have changed.

Is the fine structure constant really constant (http://en.wikipedia.org/wiki/Fine-structure_constant#Is_the_fine-structure_constant_actually_constant.3F)

I would heartily recommend Sir Martin Rees' pop-sci classic just six numbers for a discussion on how much could change with a variation of fundamental constants
Title: Re: Has the speed of light changed as the universe expands?
Post by: yor_on on 20/05/2013 18:21:49
I don't really know  :)

But we find 'c' to be a constant locally defined, in a two way experiment. And we can all agree on those experiments showing us the same thing. 'c' is a distance that light propagates in a specific time, defined by electric radiative oscillations, or mechanical. Assume that a distance change, aka a expansion. As long as we stay the same that shouldn't matter for our definition of 'c', as we will measure up a same distance (locally defined) anyway.
Title: Re: Has the speed of light changed as the universe expands?
Post by: David Cooper on 21/05/2013 19:10:08
The question only makes sense if you add Newtonian time to the model, but even when you do that you find that the speed of everything else changes to match the new speed of light to the point that no difference can be detected.