# Fermilab

## Inquiring Minds

All About Light Main Page  |  Classical  |  Relativistic  |  Quantum

 Relativistic - Time Dilation Experiments c and Einstein  |  c Top Speed  |  Speed & Speed  |  Faster than c? Mass Gain  |  E=m*c^2  |  Age Slower  |  Time Dilation  |  Twin Paradox Dopper Shift  |  Ticketed  |  Simultaneity  |  Competition  |  Fast Strudel Paradox? No!  |  Confusions  |
On the previous page I stated that time goes slower for moving objects.

This time slowing prediction was actually VERIFIED in many many different ways in many many experiments. Oneof the nicest is an experiment with elementary particles called MUONS. These particles are unstable and decay intoelectrons and other particles called neutrinos.

The lifetime of muons, if they do not move, has been measured in laboratories. Now, if you measure the lifetime of muons moving at a very high speed (close to the speed of light), you notice that it is much longer than the lifetime of the stationary muons.

It is easy to measure speed of muons. Then it is possible to calculate their lifetime in our frame of reference. Physicists compared the prediction from relativity theory and the results of experiment, and they matched very well.

Another nice experiment has proved that time slows down in a moving frame of reference. This experiment uses MUONS again and is based on the same idea as described above. This time we use COSMIC muons. It is a known fact that there is a flux of cosmic high-energy particles entering our atmosphere. These cosmic particles produce high-energy muons at a very high altitude. The lifetime of stationary muons is so short that even if they moved with the speed of light, they could not reach Earth. They would already decay high in the atmosphere. But various experiments show, that there is a pretty much constant flux of muons reaching Earth.

Conclusion: Moving muons live longer in our frame of reference; than in their own, therefore they can reach Earth.

For those interested, I show the formula for relativistic time dilation.

On the next page, I will discuss the Twin Paradox, which is related very closely to this time dilation business.

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