A long time ago, in between undergrad and grad school, I had a job as a New York City foot messenger.
It was pretty cool. I got to know the subway system with startling accuracy. I delivered stuff to Annie Leibovitz's studio weekly. And I got to peer into the lives of many an investment bank.
But the best part of the job was the elevators — those long, high-speed elevator rides.
Being a physics student, I knew about Albert Einstein's famous recognition that riding on an upwardly accelerating elevator would be the same as feeling the "force" of gravity while being stationary on a planet's surface. It was this equivalence that led him to key parts of the General Theory of Relativity.
Being the dork that I was, I kept a red ball with me — so that every time I got on an elevator, I could toss it upwards at the exact moment the elevator accelerated upwards or downwards. If I caught it just right, the ball would seem to hang in the air for a moment, like gravity had been canceled.
Everyone else in those workday elevators thought I was nuts — but it always blew my mind.
To illustrate the point I was trying to work out back then, here is a great video from the Museum of Science and Industry in Chicago. As is often the case, I initially found this video on the great site The Kids Should See This.
Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester and author of the upcoming book Light of the Stars: Alien Worlds and the Fate of the Earth. His scientific studies are funded by the National Science Foundation, NASA and the Department of Education. You can keep up with more of what Adam is thinking on Facebook and Twitter: @adamfrank4