Saturday, November 27, 2010

Do NBA players experience time differently than shorter people?

Sometimes things are true but just don't make sense. Physics for example: if you have two clocks and hold one slightly higher than the other -- about a third of a meter in the following experiment -- the clocks will run at different speeds. Strange but true. In "Channeling Einstein and Bending Time", scientists do just that. I think a corollary is that taking lots of trips zipping around in airplanes makes you younger (although you might feel older) -- I'll have to think about that more. What is an everyday example of this spacetime stuff? GPS. From the article:
Previously, this could only be seen on much larger scales, like clocks on GPS satellites running faster than clocks on earth. The NIST aluminum ion clock shows that time is moving measurably faster or slower based on even the slightest changes in gravity or velocity. ...
Sean Carroll, a theoretical physicist at the California Institute of Technology, says that this finding drives home that the laws of physics can apply at any size.
"To me, it means a lot that we can measure the fact that spacetime is curved here in my house," he says. "This abstract idea from Einstein ... it really happens. It's measureable. It's always a good thing to get data that tests these ideas."
The strange thing about GPS is that both general and special relativity apply, one making it appear that the GPS satellites' clocks run slower than ours on earth, and the other making the orbiting clocks run faster. RC Davison summarizes:
The changes in time due to these properties of relativity total to an increase of about 38,700 ns/day and will conspire to make your GPS receiver build up errors in location that could cause it to be off on the order of kilometers after several hours—up to 10 km (6 miles) per day! The system is designed to correct for these errors by setting the atomic clocks on board the satellites to run slower than their corresponding reference on Earth before launch, so that once in orbit, and the effects of relativity take hold, the satellite’s clocks speed up and very closely match the reference on Earth.