science, video

Time Dilation with Carl Sagan

Google street-view mock-up of final scene of The Planet of the Apes.

Image created by Brook Boley

Remember the scene where Charlton Heston finds the remains of the Statue of the Liberty? In The Planet of the Apes, I mean. Sorry, I just gave the ending away. It’s a classic trope (the “Earth all along“). And it’s a classic pop culture reference to time dilation.


I recently ran across Carl Sagan’s explanation of time dilation, the phenomenon in which perspectives of time can vary–the concept of relativity that Einstein laid out. The most famous example being the relative slowing of time as you move faster—basically, the reason why Charlton Heston’s mission aboard the Icarus was 18 months for him but more than 2000 years back on Earth, during which time apes evolved, learned English, and took over.

Relative velocity isn’t the only cause of time dilation, but it’s the one Carl Sagan discusses here. The other big factor is gravity—the closer you are to a major source of gravity, like a planet, the slower time passes for you relative to objects farther from the planet.

This is from episode 8 of Sagan’s famous Cosmos series (which I’ve never actually seen). I like the pastoral Italian setting, and especially the opening scene in which Sagan uses a near-collision to illustrate his first point about the speed of light. And while the time dilation thought experiment has a certain poignance, I love the way Sagan supercharges his pronunciation of the Italian names Paolo and Vincenzo. He sounds more Italian than the Italian kids.


[Photo illustration by Brook Boley from Gizmodo’s “50 of the Most Insane Things Never Seen on Google Street View“]