swimming causes rising sea levels

This cartoon from the New Yorker (28 August, 2006) reminds me of the time when a couple friends called me from Las Vegas, as they were walking down the strip. Apparently inspired by the immensity of the buildings, my friend wanted to know if I thought Earth could get heavier. I'm the science guy they knew, so he was going to me.

He thought that if people built a whole bunch of stuff where there wasn't anything before—say casinos on a flat desert plain—then the Earth would have more mass than it did before.

His wife thought not. I agreed. All the building materials had to come from somewhere.

The same goes for the obese people in the cartoon. Since we're mostly water, I'm not sure this new theory would fly. It's a good try though.