With relativity in the picture, time becomes a little bit complex than we observe. The Relativity Theory talks about the individual perception of time and how each and every single particle in the universe has a time of its own!
Every particle in the universe experiences time in its own pace, one second at a time. Right now with our calculation of time reaching accuracies up to Femto (10-12) and even yocto (10-21) seconds! We’ll stick with one ‘standard’ second in our discussion. All the particles (matter) in the universe experience time in the same pace however dilated or accelerated it may appear for some other particle observing it. Our physical body and its experience of time explain how this works.
An astronaut floating in space, far away from Earth and a man standing on the surface of Earth watch their wristwatches ticking time at the same pace, one second at a time, but the cosmological time the astronaut experiences is different than the Earth-bound man’s time. The reason is gravity. The gravitational force, though depends on matter in the first place, is strong enough to slow down matter’s flow (time).
The strength of the gravitational force at any point in space decides how much it can influence time. The greater the gravity, the lesser the time a body experiences. Here, the Earth-bound man sits in the gravity of Earth, ageing perfectly in the pace we humans evolved in. Earth’s steady gravity and its influence on matter is the reason for the steady ageing process in all living beings.
The astronaut floating far away in space has a totally different experience. When devoid of gravity’s influence, he feels his psychological time flow at a steady pace. If he starts counting numbers for every second he experiences, he would end up counting 86,400 for all the seconds in one standard Earth day. If he continues counting, he would observe his body’s (matter) ageing process slowed down compared to his time count (in seconds).
If he started the exercise when he was 30 years old and counted to 30 years in seconds – that is 946,080,000 – he would end up in his sixtieth birthday, but his physical body would’ve aged only a few years, say 4 or 5! With body’s ageing depending on the cosmological time and the effects of gravity, his ageing would be slowed down! But his psychological time, independent of any influence (even gravity), works at the same steady rate.
It is this slowdown in the cosmological time that is explained as time dilation in the Theory of Relativity.
