Originally Posted by shawnhcorey

I accept the Big Bang Theory as a reasonable explanation but not as the only one.

Einstein's General Theory of Relativity states that time runs slower in a gravity well than in free space. A clock on the Earth's surface runs slower than one in orbit. This has been shown.

As time goes on, more and more mass has appeared in our universe. This has created a deeper gravity well. Time runs slower now than it did in the past. Therefore light, which travels at a constant speed, travels less distance now than it did in the past. This gives the illusion that the universe is expanding.

The figure of 13.7 thousand million years is given as the age of the universe since, if you run the expansion backward and assume a constant rate of expansion, this is the number you'll get. That's if you accept the universe is expanding.