raisin bread universe

So I’ve downloaded a series of lectures from iTunes U about astronomy. UC Berkeley’s Alex Filippenko teaches a course called Astronomy C10: Introduction to General Astronomy. On my computer, the lectures in this series are all neatly numbered, but on my phone, it’s a jumble. So I pick one at random. Not only does this end up being lecture number 32 out of the 41 lectures in this course, I am actually admonished by Professor Filippenko during this lecture, who warns his students to listen to the lectures in order, if they can’t attend class.

Great. First day and I’m getting an F.

This lecture is called “The Age of the Universe”. Right up my alley. I love this stuff. He talks about the ‘red shift’ of light coming from distant galaxies and how Edwin Hubble, for whom the Hubble Space Telescope is named, figured out that the galaxies around us--every galaxy that we can see beyond our immediate neighborhood--is flying away from us. The farther they are, the faster they go.

So yes, I’ve heard this before. Along with the caveat that even though it looks like we’re in the middle, and all the galaxies are flying away from us, we’re not really in the middle. But things never added up for me. How is it, I asked myself, that the furthest galaxies are moving away faster than the closer ones, and the further away they are, the faster they’re bugging out? It all seems so linear, and when you draw lines in space, tracing back where they all came from, all the lines point back to us. It certainly seems like we’re in the middle.

The problem, I think I discovered tonight, is the balloon image; the huge, inflationary object I think of when I think of a universe after a Big Bang, swelling outwards from the center, and getting bigger as it moves through time.

Dr. Filippenko fixed that tonight. By making raisin bread.

As he talked, I imagined raisin bread dough; dense, sticky, full of raisins and yeast, evenly distributed in the mix. As the raisin bread cooks, all of the spaces between the raisins expand as the yeast does its work. The raisins themselves don’t expand, but to each of the raisins, each and every other raisin appears to be moving away from it in every direction. AAAAhhhh! It’s the space between the galaxies that is expanding, and we all move away from each other, and no matter what raisin you are, all the other raisins are moving away from you.

And here’s the kicker. When raisins A, B and C started out in the dough, they were all 1-inch apart. After an hour in the oven, they were all 2-inches apart. From raisin A’s perspective, B is now 2-inches away, but raisin C, who used to be just 2-inches away, is now 4-inches away.

That’s right. The distance between A and B changed at a rate of 1in/hr while the distance between raisins A and C changed at a rate of 2in/hr. Twice the speed!

Dr. Filippenko didn’t talk about raisins X, Y or Z, but I imagined them shooting out through the side of the oven in defiance of the constant speed of light.