First, a big, fat disclaimer: I do not understand physics. I know that gravity keeps me from floating into space, thanks to the earth's rotation or something. I know there's something called "Planck's constant," even though I have no clue what it is (or who Planck was). I know about inertia, mostly from firsthand experience. And that's pretty much that.
Still, I find the Einstein's Pedometer app kind of fascinating.
A poetically brief description on the app's iTunes page lays it all out in two sentences, which for unexplained reasons are broken into three lines:
According to Einstein's theory of relativity,
When you move faster, time slows.
This application is using GPS and Lorentz transformations, to calculate how much time you get.
So, add "Lorentz transformations" to the list of things I don't understand.
A review of the app on Gizmag.com puts it in layman's terms:
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. … 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.
To calculate just how much time you've gained by walking to the shops, the Einstein's Pedometer app uses the iPhone's GPS capabilities and the Lorentz transformation, which describes how two observers' varying measurements of space and time can be converted into each others frame of reference. A quick stroll round the neighborhood with Einstein's Pedometer yielded me an extra 0.00021440 nanoseconds than if I'd stayed at my desk doing something else, like working.
More motivation to head out for a run, if you needed one.
And hey, don't laugh: Over enough years, those fractions of nanoseconds can really add up. Maybe to a whole nanosecond!