Oh, Atom, Where Art Thou?

Had our first physics club meeting of the year last week. I'll have the minutes up soon, but I'll give you a preview: lots of good ideas and good attendance including a couple alums. Alums are always welcome - stop by and say "hi!"

Speaking of alums, I got the following message from an alum, who knew I enjoyed good puns (and bad ones, too, for that matter):
"Atoms have mass!?!? I did not know they were catholic"
I attempted to respond with more amusing wordplay:
"Ah... since you used the small letter c, you must mean that you did not know that atoms were universal. Last I checked, no matter where you look in the universe, you can expect to find at least one atom within about a meter. Sounds universal to me"

Well, not only was my response not that funny, it was also WRONG! Can you see where I made my mistake?

My mistake was in assuming that the places where you would be furthest from an atom would be the least dense places in the universe, where the density is about one atom per cubic meter, so you might expect to be within about a meter of an atom there. In actual fact, it is the most dense places in the universe where you are farthest from an atom.

Consider the dense interior of the Sun (or any star). The matter there is so dense that the electrons are ripped from the atoms, leaving separated ions and electrons, a state of matter called a plasma. I would say that at the center of the Sun, then, you are about 700 thousand kilometers from the nearest atom.

It could be argued that interior of the Sun still contains atoms, albeit ionized atoms. Consider then a neutron star, which is hundreds of trillions of times more dense than the Sun. A neutron star is so dense that there are no longer individual atoms, and the electrons have been fused with the protons. The net result is an immense mass of neutrons. At the center of a neutron star, you are surrounded by neutrons, not atoms. At the center of the typical neutron star, you would be about 12 kilometers from the nearest atom.

Shall we go even denser? Though we have never seen inside a black hole, it is pretty certain that atoms would be obliterated as matter collapses to extreme densities upon forming a black hole. At the center of our galaxy there is a supermassive black hole. At the center of that black hole, you might be a few trillion meters from the nearest atom - that's a long way to go to find an atom, approximately the distance from here to Pluto!

Maybe atoms aren't so catholic after all.

_{(Image: Astronomy Picture of the Day)}