What if you threw a baseball at 90% the speed of light?

Randall Munroe, the creator of the excellent comic strip XKCD, has started answering fun gee-I-wonder questions using science and math in a new blog called What If?. Start from the beginning. It’s incredibly entertaining and surprisingly educational.

The answer to the question in the headline:

Everything within roughly a mile of the park is leveled, and a firestorm engulfs the surrounding city. The baseball diamond is now a sizable crater, centered a few hundred feet behind the former location of the backstop.