If you were to ask me “What’s the time?”, I could just have a look at my watch and let you know the time. However, what might I say if you were to ask me “What is Time?”. Indeed, that isn’t easy to reply as it appears.
Since our birth, we realize we have grown up. Furthermore, we realize we will keep on growing every year. So does the universe. May it be us, or the universe, or anything which is aging up, progress in years up in light of the fact that the time is moving forward. However, for what reason does the time moves forward? Why it’s not moving backward or remaining for what it’s worth consistently. Here the second law of thermodynamics comes to the rescue saying that the total entropy of a system either increments or stays steady in any unconstrained cycle. All in all, it is saying that a system generally, will in general develop to the most steady state which is the state of equilibrium. In the majority of the systems, the most equilibrium state is the state which has the most disorder(entropy). Alright now hold this thought for some time.
Let’s quickly go back to the 1600s to meet the grandfather of Physics. Imagine you are throwing up a ball in your room. It’ll go up and return to your hand. Regardless of whether you did this in your room or you did it on your lawn or out and about, the laws of physics wouldn’t change. This is called ‘Space Translation Symmetry’. By the by, you’d come by a similar outcome assuming you did likewise at 8 am or at 4 pm or at midnight. This is called ‘Time Translation Symmetry’. Along these lines, we have a surprising symmetry called ‘Time Reversal Symmetry’ which says that we can’t recognize the distinction between backward and forwards in time. For example, if you record the above-mentioned scenario of catching a ball, you cannot simply say if the video clip is played forward or backward simply by checking the ball out.
Okay now again to the point. Now, as indicated by thermodynamics, it is more probable for a system to evolve from a state of low probability to a state of high probability. In any case, for each state that evolves to higher entropy, there is a contrary state that evolves to lower entropy. One should simply flip the direction of velocities of all the molecules. Then, at that point, they will go all return to the manner in which they came. This is allowed due to the time symmetry nature of Newtonian mechanics which I stated previously. So it is like having two states of heads and tails. So how is it that one could say that it is more probable to evolve towards higher entropy? It is like saying that it is more likely to get heads as the result of any number of flips. This is called Time Reversibility Paradox. So as indicated by this contention universe has an equivalent likelihood of evolving towards higher entropy and evolving towards lower entropy. As such, time ought to go backward as regularly as it goes forwards.
The universe began at an extremely low entropy state at the big bang and ever since, it is evolving towards higher entropy. Also, one day it will arrive at the equilibrium state. It will fluctuate around there since it is the most probable state. But on occasion, it might have some abatement in entropy. This isn’t impossible. Just exceptionally improbable. It could work out in the event that we stand long enough. Very much like getting 1,000 heads in succession on the off chance that we flip a coin adequately long. What’s more, these decreases in entropy are quickly followed by the increases back to comfortable equilibrium.
This all happens in light of the fact that we began at an exceptionally improbable state of low entropy. If we started at the equilibrium then the decrease in entropy happens just as often as the increase. Hence there is no universal direction of time, but only pockets of backward and forwards. The second law of thermodynamics which says that the entropy is predominantly liable to increment possibly holds on the off chance that we assume, that we began at an exceptionally low state of entropy. However, there is no legitimate thinking to that assumption. It exactly occurred at the big bang. For what reason did our universe begin in such an improbable state? This is currently one of the biggest perplexing questions in cosmology.
Now, you realize that the direction of time or the arrow of time, whatever you call it, isn’t built into our universe yet it is an aftereffect of the manner in which it began. We won’t generally go to ‘The Future’. We are evolving to a state where we will fluctuate between ‘The Past’ and ‘The Future’.