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## Einstein Pedometer App Measures Relative Time Gain148

cylonlover writes "Among other things, Einstein's theory of special relativity says that as an object's velocity increases, time as experienced by the object will slow down when compared to another object traveling at a lower velocity. This means that a 'relatively' short round trip on a space ship traveling at close to the speed of light would see you arrive home having aged less than those back on Earth. While the greater the velocities involved, the greater the effect, the theory applies to all relative movement. Now there's an iPhone app that will let you know just how many extra nanoseconds you've gained by getting moving as opposed to sitting on your rear end."

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## Einstein Pedometer App Measures Relative Time Gain

• #### Re:relative to what? (Score:5, Interesting)

on Monday April 11, 2011 @11:12AM (#35782588)

It isn't just about math. These effects have been proven experimentally - just not by sending a human off to Alpha Centauri. Follow the references for more relativity fun. [wikipedia.org] I personally find length dilation to be the most interesting and difficult to get my head wrapped around.

Fun thought experiment:

A 100m rocket speeds toward a 90m hangar building at .99C. As the rocket passes through the open doors of the hangar the operators of the building close both sets of doors while the rocket is entirely inside the building. This is possible because of the length dilation happening at the high relativistic speeds (the rocket is compressed to less than 90m from the view of the hangar).

But from the point of view of the ship, it is the hangar that is approaching at .99c. Therefore the hangar is foreshortened - even shorter than 90m - leaving more than 10m too much rocket hanging out. What do each of the door operators and the pilot of the rocket see happening?

This is a fun use for all that math you learned to figure out relativity. Even though both frames of reference see things in entirely incompatible ways, both versions of the truth are entirely consistent via relativity.. Fun!

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