Now it is assumed that the dark energy is in some way responsible for time running exclusively forward, ie. that we can't go back into the past.
Time is one of the factors that we take for granted. We all know that it can't go back, but we rarely ask ourselves why this is so. Why does time go in only one direction - forward?
One direction of time
And while we, mere mortals, accept this as inevitable the fact, scientists are constantly confused by this issue. The mystery is even greater when we consider that certain physical processes are reversible in time.
Take, for example, gravity - it always works the same, regardless of which direction time is moving. Our planet would orbit around the Sun in the same way, only in the opposite direction, if time would suddenly begin to run backward and we wouldn't feel any change.
However, there is an aspect of the universe that is completely dependent on the direction of the flow of time - this is the second law of thermodynamics. It says that a closed system (like our Universe) always strives for a state of increasing disorganization. This rule is also called Entropy.
The second law of thermodynamics states that bodies increasingly move away from each other, despite the force of gravity.
What does entropy represent in practical terms?
Because of the second law of thermodynamics, a broken egg can't be suddenly brought back together, nor what died can revive. What is done cannot be undone, things are deteriorating, everything ages and falls apart, the past cannot be returned ... The universe is constantly striving for disintegration, chaos and disorganization.
Complex systems - like planets, stars, human beings and the like, require an enormous amount of energy to be produced, which only increases the overall amount of entropy of the system. The second law of thermodynamics is a mechanism that makes time unidirectional. So, now we know how it works. Still, it doesn't give us the answer to the question of why this is so.