# Time Dilation

## As the velocity of an object approaches the speed of light it appears to move more slowly through time to a stationary observer.

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The Fountain of Youth?

### Could time dilation possibly be the answer to eternal youth?

Credit: Unknown

Albert Einstein, a German-born theoretical physicist, is one of the most famous scientific icons in history. [Figure1]

You may have heard of Albert Einstein, one of the most iconic figures in the history of science. Having published the theory of special relativity in 1905, he brought up an interesting concept called time dilation. Time dilation states that if two observers are moving relative to each other or are differently located relative to a large gravitational mass, there will be a time difference between their respective frames of reference. Time will slow down in the case that a high speed is achieved, but will speed up in areas of lower gravity.

Credit: NASA

After spending a significant amount of time in space, astronauts return to Earth with a slightly slower rate of aging. [Figure2]

Time dilation is not easily observable in our daily lives. However, it has been proven in a few instances. Consider astronauts, especially those who spend six months or more in satellites such as the International Space Station (ISS). After returning to Earth, these astronauts end up having gained an extra 0.007 seconds of life. However, while in space, they actually experience an accelerated aging process! Researchers have continued to work towards preventing this, so that space travel can be made much more comfortable. And who knows -- maybe some day, we will be able to use space to add several extra years to our lives!

### Creative Applications

1. If the gravity experienced by astronauts in space is less than the gravity on Earth, why do they end up aging slower rather than faster (considering the time difference rather than the physical aging)?
2. Read and understand the first three entries of this link, about the Hafele-Keating experiment on time dilation.
3. Out of the two pieces of evidence regarding time dilation that you just read about (astronauts in space and the Hafele-Keating experiment), choose the one you prefer and explain your choice.

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