When two become one, we say they are married. By the text above, we see that marriage is a process that occurs only after the wedding. It makes sense! The only way two can become one is if those two things are first joined together. The process of joining two things together is called fusion. Fusion takes place continuously in the universe in stars. To replicate the same reaction on earth requires that atoms be heated to millions of degrees. In other words, fusion requires activation energy. Without this activation energy, you can bring two atoms together, but nothing will happen.