Astronaut’s life in space is exciting. this is second part of Astronaut’s life in space. You can read first part An astronaut’s Life in Space

“Time is but a stubborn illusion”.These were the words told by one of the greatest Physicists of all time, Albert Einstein, referring to the fact that even time is not absolute or it doesn’t have a standard reference, and of course, it is relative in nature.
When everyone had assured themselves that time is absolute and it’s the same for all observers, then arrived Einstein’s Special Theory of Relativity which gave us the idea that even time varies as per the observer’s reference frames and their speed, and also their position in a gravitational field. The term that describes all these things is called time dilation, an occurrence making astronauts aboard space stations aging slower than those on earth.

Time dilation effect on Astronaut’s life

Astronaut's life in space with atomic clock
Atomic Clock

It’s the difference in the elapsed time measured by two clocks. Time dilation can be said to occur due to two major reasons: Gravitational effect of a massive body and increasing speed of a body.
Measurement is different for all of us in the fabric of spacetime as spacetime isn’t flat but curved. Spacetime gets warped due to the presence of a massive body. This causes time to slow down near a massive body. This is called gravitational time dilation. Imagine you are travelling to the centre of the earth. The closer you are to the centre, the slower the time becomes due to strong gravitational effects of the earth. The astronauts aboard the ISS must feel time speeding up as they are far away from the centre of the earth in a weaker gravitational field, ultimately leading to ageing faster than us, which in fact doesn’t happen. But why? Wait. Another reason for time dilation is the increase in the speed of the body.
According to the special theory of relativity,
Time(moving frame)=Time(rest frame) x{ 1- ()2}0.5
The ISS moves almost 7.8 kilometres per second, which makes time appear to move slower than that on earth, which means the astronauts have less time than us making them age slower than their earthlings.

Aging of Astronauts
Time dilation of two clocks

This animation shows Time Dilation Between two Clocks
According to calculations, time at ISS lags 0.007s behind us for every six months. So it would take more than 100 years on ISS to warp ahead by 1s. This is called relative time dilation.
But earlier we had a question as to why time doesn’t get slower for the astronauts due to their presence in a weaker gravitational field. The answer is that the relative time dilation has much more effect on the astronauts than the gravitational time dilation. But there’s a place around 3,174km above the earth’s surface where both gravitational effects and relative effects cancel out each other.
Time also varies for people living in the mountains and those on the surface. Time dilation was proved by an experiment where an atomic clock, which gives more precise time than our ordinary clock, was sent to the orbit, and another clock was placed on the surface of the earth. Later it was seen after the return of the atomic clock was that the clock placed on the surface showed fractions of seconds more than that of the one sent to the orbit, concluding that time slows down on clocks moving at really higher speeds.
So when you become an astronaut and travel to space and live aboard the space station and come back to earth after six months of space explorations, you’ll be 0.007 seconds younger than your fellow earth-mates of your same age. Sometimes even people ask whether their hair on the legs should grow faster than that on their head as the leg hair is nearer to the earth’s center than that on the head. So what do you think of this crazy question? Let me know in the comments below.

Author: Som Abhisek.

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