Re: Concerning the constancy of the speed of light......

Every atom gives off radiation at its own characteristic frequencies.
If the atom is moving towards or away from us, this frequency will be 
shifted.  By looking at the frequencies of distant stars, scientists have 
observed that these distant stars are all traveling away from us, and that
their velocities are roughly proportional to their distance from us.  From
this we can deduce that the universe is expanding.  By measuring how
far away distant galaxies are, and how fast they're traveling you can
figure out how long ago they must have started traveling from some common
point (or roughly how old the universe is).

If your friend is trying to say that the shift in frequency is due to the
speed of light being different in the past, I've got a simple experiment
for them to try.  Point a telescope at some distant galaxy and measure 
the speed of light.  Although its difficult to measure the speed of light
accurately, in order for it to be responsible for the large shifts in
frequencies that we observe the effect should be noticeable.

Its my guess that your friend will not attempt this experiment.  In order
to believe that the universe is only 5000 years old, one must disbelieve
thousands and thousands of experiments carried out in field after field.
One must disbelieve physics, astronomy, biology, chemistry, geology, and
probably several other fields of science that I'm leaving out.  Its one
thing to suggest that a varying speed of light is responsible for the
shift in frequencies that we observe, but this suggestion must be logically
extended and its consequences must be examined.  The speed of light is a
fundamental constant that appears in all sorts of equations.  What 
consequence does the speed of light being different have on all those 
equations?  Why do galaxies in every direction have the same frequency 
shift and the shift get larger according to their distance from us?  
According to his suggestion, this would be determined solely by 
the age of the galaxies so this would suggest that the universe was created
in layers, like the layers of a onion, with the outermost layers created
first, and the earth smack-dab in the middle!