What's the Meaning Behind Google's Bouncing Balls Logo

As I've mentioned before, I love Google. Today's logo has me stumped though. Here's what it looks like when you load the page.

Then when you wait a second, the balls fall into place.

Plus, it's interactive! Run your mouse through them and the balls are repelled from the mouse!

I've been trying to figure out what it's all about, but I can't find anything. In the course of searching, I did, however, discover this interesting fact: 6 Nobel Laureates were born on September 6th and another Nobel Laureate died on September 6th. Weird huh?

If someone figures out what the logo is referring to, please let me know because I'm baffled.