Ok here's another question: A friend of mine shook her head in doubt and disbelief when I said that I believe physicists when they say that the universe is constant and is the same everywhere... meaning that the laws of physics don't change whether you are in this galaxy or in another. She believes that the laws of physics that we discovered aren't necessarily the same here as they are somewhere else in the universe. For example the properties of atoms of different elements. How would you prove or explain to a person like that these things are constant. That we don't have to go around the world and test every piece of silver to make sure that it has the same chemical properties in Africa as in Australia. How can we be sure that they are constant without going around and testing them. She believes that just because humans have discovered something that works here on Earth it doesn't necessarily mean that it works the same somewhere else. I asked her what would lead her to believe that it would be any different somewhere else but she insisted that I had to prove to her first that it is constant to begin with. Someone else I talked to about this very question mentioned something about spectroscopy and how through that we know that things are constant. Any help?