According to Einstein/Special Relativity, time is relative, meaning, my version of time is different from the version of time for everything else in the universe. How old are you? The question is: are you biologically as old as you think you are?
What is time?
Time is the occurrence of events relative to a particular frame of reference.
What do you mean by “relative to a particular frame of reference”?
If you’re standing still on a road, a Ferrari zipping past you would appear to be traveling really fast - relative to you, but if you were moving next to the Ferrari at the same speed, it becomes no different from you both not moving at all. You are the frame of reference here.
Time can relatively speed up, & it can also slow down or even stop completely. Why does time slow down next to a black hole? It’s because there’s very little that can happen to anything close to it. The closer you get, the less things can happen other than everything continuing to fall towards its event horizon. As far as you’re concerned, time is passing normally. However, relative to an observer watching you from far away, you would appear to be moving slower & slower as you get closer to the black hole (i.e. time slowing down). At the black hole’s singularity, where its gravity is at its strongest, time effectively stops because no events can happen at all. If you manage to escape the black hole’s gravity & return to the person observing you, they would be many years older than you by the time you reach them. This is known as time dilation.
Conversely, the more that can/is happening around you, the faster time moves. When you lead a very busy life, you’re literally aging faster relative to others around you who lead less-busy lives (just like the black hole example, you won’t actually feel it yourself). However, we don’t realize this because we all use the same timekeeping systems & calendars even though the time we’re measuring is different for each one of us. Of course, the difference between our versions of time is limited to a certain degree because we’re all sharing the same planet & affected almost equally by its gravity & the Sun’s gravity. So if you have a very busy life & you just celebrated your 32nd birthday today (according to the standard Georgian calendar that people all around the globe use regardless of how busy their lives are), you could actually be a few hours or days late because in reality, you turned 32 sooner relative to the other people in your life.
So if we think of time as a train moving forward, it’s not a single train for everyone. Everyone actually has their own train, & these trains are not moving at the same speed. Some trains are further ahead than others.
Quran: A day to God is equivalent to a thousand years for us
Surah Al-Haj, verse 47:
“And indeed, a day with your Lord is like a thousand years of those which you count.”
