New App Aims to Teach Special Relativity Hands-On

Many people have at least heard of Albert Einstein’s famous theory of special relativity, or its key formula E=mc2. Understanding that theory and how it affects the complex relationship between space and time in the universe is another matter entirely.

Carnegie Mellon University Professor of Physics Ira Rothstein hopes to make understanding general relativity a little easier with a new smartphone app that lets anyone experiment with and learn how different aspects of special relativity, like time dilatio and length contraction, work.

First published in a 1905 paper, Einstein’s theory of special relativity boils down to how time and space are perceived in different frames of reference. Whereas time will pass at the same rate for two people going about their lives normally, even if they’re on different parts of the Earth, if one person were put on a rocket that traveled at a rate approaching the speed of light, the cosmic speed limit, then time for them would pass much slower than to people outside of the rocket. This means when and if they returned to Earth, everyone they know would have aged much more than they have.

No human has ever traveled anywhere near the speed of light, however, so it’s difficult to relate this theory to our everyday lives. Four years ago, Rothstein set out to change that by designing his app.

"Normally, when you teach physics on the computer, you have this virtual world you play in," Rothstein said. "The idea of this app is to actually try to experience it first-hand."

When people hear the term "Einstein’s Theory of Relativity," they automatically think its above their heads. Terms like "Spacetime" and the " E=mc2" equation are easier to understand than you think. 

The app, named Relatively Simple, uses one’s own movements to help make special relativity seem more approachable. To model the time dilation effect, the user can walk around with their smartphone to see how the passage of time on their own clock starts to move slower than the clock for a person in the app who is not moving. For length contraction, a ruler for the user appears to shrink as they start to move around faster, while a ruler for the person in the app who is standing still remains the same. Helpful animated videos throughout the app give lessons on why and how these effects happen.

"The idea is to develop an intuition about special relativity," Rothstein noted.

Rothstein has developed the app with students from Carnegie Mellon’s Entertainment Technology Center and with funding from the university’s Berkman Faculty Development Fund. One day, it may even end up being built into a smartphone game that classes could be designed around.

"My primary goal was just to do something cool and see if people like it," Rothstein said.

The app can be downloaded for iPhone’s from the Apple Store  and for Android phones from the  Google Play Store.


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