We are all enslaved to time. Even if we do nothing, we are spending time. And, time is a mystery. But, physics states that time as we perceive it is an illusion. The concept of the illusion of time is explicit from a relativistic point of view.
Time is constantly moving towards the future. Even if you stop, the time won’t. Things are ageing and everyone is. I bet there is not a single person in this world who has not thought of stopping this monotony of time. Everyone wants to escape from this bondage. On this quest to solve this mystery that time is, Albert Einstein made a remarkable breakthrough. He figured out that time is not universally constant and can be slowed down!
Time According to General Relativity
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Time indefinitely marches towards the future in a constant way, that was the concept of time before Einstein’s relativistic interpretation. Relativity stated – the speed of light in a vacuum is constant. This constancy of the speed of light led to an amazing conclusion, time and space are relative to the speed of the observer. So, this means the speed can have an effect on how we observe time and space. Further generalization saw that gravity also can affect our perception of time and space.
Since time and space, both showed similar observational effects on the basis of the observer, it was necessary to address both as one. Hence time was added as the fourth dimension.
The Relative Nature of Time
The relative nature of time means that the clock slows down if our speed increases, a phenomenon called time dilation. So, if we accelerate to speed 90% of the speed of light for 160 days according to our clock, we would have passed 365 earth days. This is because the clock at Earth is almost stationary and it does not show any time dilation. Not just speed but gravity also have effect similar effects, as already stated and further details of relative nature of time are provided in our separate article here.
The flow of time is not constant, it’s proven mathematically as well as experimentally, but this is not the end of the story. This attribute of time has a profound implication. It implies that this flow of time that we perceive maybe just an illusion, an illusion of time.
Illusion of Time
Time is observer-dependent. So, observation of time at a distant place depends on the state of the observer. If we consider looking up in the stars, what we see is past because light from stars can take millions of years to get here. But the point of time that we see depends upon our speed. It is possible with the variation of the speed of two observers at one instant that one may see a star at one point of time while the other may see at another point of time.
It can be explicit from one example. Consider you and your friend are moving towards each other. Then, both of you observe a star which is behind one of you and in front of others as you meet one another. According to your speed and distance between you and the star, the observation made by you and your friend may differ. This is because due to your velocity, your individual clocks are not synchronized. If one of you see that the star is exploding, the other may see the star has already exploded. You and your friend may argue there but both of you are true.
Now, the complexity arises. Each one of you has a different present than the other and some future events for your friend are included in your present. Does this make sense? It does not until we can relinquish the thought that time is moving towards the future.
Now, let’s generalize this example. If we have multiple people moving with multiple velocities as there were two before, it is possible that they might span each and every moment of time; past, present and future. So, the conclusion is there is no real difference between past, present and future. This is just an illusion of time.
Has Future Already Happened?
Has the future already happened? This is an obvious question brought in by the concept of the illusion of time. And the answer is – Yes, this theory suggests that the future has already happened and there is no difference between past, present and future at all. These points of time must co-exist if the relativistic interpretation of time is correct.
Even though the future has already happened, time will go at this same pace unless we decide to travel in time. The co-existence of past, present and future won’t introduce a great deal of difference though. If we are set to measure, there is past, there is a future and there is present. Our speed may mess with our experience of present Universe and lead us to a different path in time but we are marching towards future again, a different future may be, which may include different points in time.