# Fermilab

## Inquiring Minds

All About Light Main Page  |  Classical  |  Relativistic  |  Quantum

 Relativistic - Wanna Be Younger Than Your Twin? 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  |
At first glance, this title seems to suggest something crazy. By definition, TWINS are ALWAYS the same age!

Mr. Einstein said NOOO, this is not necessarily true. The twins will be the same age only if the time passed at the same rate for both of them.

Is this always so?

No!

One of the consequences of Einstein's theory is that time slows down in moving frames of reference.

This means that anybody who is moving ages slower than others who are stationary. Notice that I am not suggesting that one can travel backward in time, I am just saying that both you and your twin will get older, but at a different rate.

Suppose you have a twin sister and she goes for an intergalactic trip at a very high speed. She takes a clock with her. Suppose she comes back to Earth after 10 years of her clock time. When she comes back to Earth, it might very well happen that on Earth 1,000 years have passed! ( Exactly how much time has passed on Earth depends on her speed.)

We will discuss this twin issue in more detail on the Twin Paradox page.

But first, one might think that, this time slowing down business is very strange. Is it a fiction, or has it been verified in experiments? I will show you on the next page.

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