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

Concerning the constancy of the speed of light......
I am in 2nd year of an undergrad physics degree.
A Christian friend of mine maintains that the universe was created 5000 years ago, he is very adamant about this.
When I confronted him with some cosmological evidence he answered me by saying, "that can all be explained by the fact that the speed of light is slowing down." (!!!)
Having only just taken a first course in special relativity, I don't have the confidence to construct a watertight defence of this physical constant.
I would like a coherent argument to present him with.
He is quite adept at debunking much of modern science in order  to support creationalism,
Could you also send me archives of arguments against creationalism.
Then I will be ready to argue it out with him.
Thanks.

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