E =mc{squared} How Did He Arrive At This ?

[SpaceTiger]

I remember he rejected a major part of his discoveries, but I don't remember which. He refused to believe, I think that the universe was expanding.

You're thinking of his original model of the universe that included a cosmological constant. He later said it was a mistake to include it because the observations showed an expanding universe. This implied that he believed those observations. However, I think he had a problem with black holes. I'm not an expert on the history.

Why is this? Science is absolute is it not? Once you prove something, its proven and should be accepted?

He didn't prove that his theory applied to all situations. It probably doesn't. Newton's certainly didn't.