Saturday, October 01, 2005

Expansion of the Universe

This is cool (yes I know, I should be packing). Physicist Richard Price was asked a simple question by a high school student:

"He asked me if, as space expands, we all get bigger too," says Price. "I knew the standard answer was 'no', but I couldn't explain why not. And when I consulted my colleagues, neither could they."

So he decided to investigate:

Since atoms are made up mostly of empty space, with electrons "orbiting" the nucleus at distances typically many hundreds of times its diameter, it seemed reasonable to ask whether the electrons would be dragged away from the nucleus by the stretching of space. Price decided to examine the simplest system, that of a hydrogen atom, with one negative electron orbiting a positive proton. He found if the force involved - electromagnetic in the case of atoms - binding the system together is stronger than a certain critical value, the system will be entirely unaffected by the cosmological expansion.

What does it all mean you ask:

"This means that the solar system - which is quite tightly bound by gravity - doesn't expand. Your desk doesn't expand. Your dog doesn't expand," says Price. "But clusters of galaxies, which are only loosely bound by gravity, will feel this effect."

Price also found that the atoms never experience just a little stretching - either they must totally ignore the expansion of the universe or they will be completely torn apart. "This all-or-nothing effect is a startling result," says Roy Maartens, a cosmologist at the University of Portsmouth in the UK. "This question has been knocking around since the 1930s, but nobody has found this before."

The moral of the story, to me, is that you should try to explain science to as many people as possible, because the questions they ask may lead you to some interesting research.

Actually there is a second moral of the story:

Andrew Jaffe, an astrophysicist at Imperial College London in the UK believes the effect becomes interesting in so-called "big rip" cosmologies in which the universe is not only expanding, but the expansion is accelerating.

"Price's calculation still holds in this case, but you start to see the opposite effect," says Jaffe. The expansion of the universe accelerates drastically. First it overpowers gravity, ripping apart solar systems, and next the electromagnetic forces are overwhelmed. "The planets are torn apart, and then you and me, and finally the atoms that make us up are destroyed," says Jaffe. "That's not a particularly fun way to end."

Now if we could only get a restauraunt at the end of the universe...