Ultimate geekitude

This post from Physics Geek reminded me of my favorite Ditch Day Stack of ALL TIME:

I believe this happened in the 60's. As you may be aware (see link above), on Ditch Day, Caltech Seniors lock their room doors and go off campus, leaving a series of puzzles behind for the underclassmen to solve to figure out how to open their door for a prize.

Anyway, the seniors left at 7 am and all that was on this particular door was a hose sticking out from under the door, and a note saying that only the proper substance could be poured through the hose to open the door. The only clue as to what that was was this: "0.693"

The underclassmen sat all day and stared at the door, they couldn't figure out what 0.693 meant..... Finally at 4:30, 30 minutes before they would have to give up, one of them jumped up and ran out the door. He returned a few minutes later with a steaming jug and poured the contents down the hose, and the door opened, just before 5.

The answer below the fold for those of you who would like to take a guess as to what was in the jug....

0.693 is the natural log of 2, or ln2. LN2 is a common name for liquid nitrogen.

Pouring the (-80 deg C) liquid nitrogen into the hose froze the lock mechanism, allowing the door to be pushed open.