My son is a PhD student in astronomy. Every time I talk to him I learn something new. Here's what I learned that's relevant to this post:
Our galaxy, Milky Way, resides in a local group of about 54 galaxies. They orbit around each other (more or less) and over time will all collide and form one huge super galaxy. By the time that happens, all the other galaxies in the universe will have receded so that astronomers here will no longer be able to detect those galaxies. The will be so far away that their light can no longer reach us. That means, in the very distant future, we will have absolutely no way of measuring how large the universe is and, because by then the background radiation from the Big Bang will be so low as to be undetectable, we will have no way of figuring out how old the Universe might be. In short, we'll be inside a large galaxy surrounded by an infinity of empty space.
In the shorter term, and less depressing, is this:
Milky Way, our galaxy, has about 300 billion stars (not the 100 billion referenced in the TED talk).
Andromeda, the nearest large galaxy, is three times the size, with some 1 trillion stars.
Milky Way and Andromeda are on a collision course. Brace yourselves, we'll crash into each other in about 4 or 5 billion years.
So I asked my son, when that crash (intersection is the word I think astronomers prefer) occurs, how many stars will actually collide. Oh, he said, we're not sure but no more than ten. Ten, out of 1.3 trillion stars. Which tells you just how vast interstellar distances are.
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