just because it has a formula on it doesn't mean it's a geek t-shirt

I've just started a new course called "Dark Matter, Dark Energy: The dark side of the universe", taught by Dr. Sean Carroll. He's a cosmologist. And he talks really fast.

Interesting side note: cosmologists weren't allowed to win the Nobel Prize until 1973.

Anyway, I didn't entirely understand this completely until I started the class, but gravity is not actually a force. That's because gravity behaves in a universal way through out space (where as forces on earth may not apply in space). Einstein's general relativity theory says that gravity is a component of spacetime, adding a curvature to spacetime.

Spacetime is the point of Einstein's special relativity theory, which is that space and time can't be separated and need to be considered together. The conclusion is that time is no longer absolute (if you've ever had a flight delayed you know what that means - time can go by excruciatingly slow). Anyway, since time and space are no longer absolute Einstein had to figure out a fixed speed limit for the universe. That's why nothing can go faster than the speed of light (in theory).

The curvature in space means that objects can be detected because they curve spacetime via gravity. Picture a flat handkerchief suspended by its four corners. If you put a tennis ball on the handkerchief it will bend around the ball. And if the ball were invisible you'd still know there was something in the handkerchief because you can see a dent where that invisible object is sitting.

Anyway, that's how they know about dark matter even though no one can "see" it. Yet.

The whole point of this post is that people walk around with shirts that say "E = mc2" and people think they're geeks. Well, if they really WERE geeks they would wear a shirt that says: