“In the 1928 book The Nature of the Physical World, which helped to popularize the concept, Eddington stated:
Let us draw an arrow arbitrarily. If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointing towards the future; if the random element decreases the arrow points towards the past. That is the only distinction known to physics. This follows at once if our fundamental contention is admitted that the introduction of randomness is the only thing which cannot be undone. I shall use the phrase ‘time’s arrow’ to express this one-way property of time which has no analogue in space.”
“The arrow of time is the “one-way direction” or “asymmetry” of time. The thermodynamic arrow of time is provided by the Second Law of Thermodynamics, which says that in an isolated system, entropy tends to increase with time.”
Even people who teach this kind of stuff may forget it and take a compartmentalized view that it only applies to physical systems. In their interactions with the world they may assume that nothing is final, it can always be undone, one may be able to talk one’s way out of any situation and that revocability can hold true. Yet in common parlance we have; “don’t lock the stable door after the horse has bolted” and “too much water under the bridge”. Both of which point at some irrevocability. There may be a short time at which things can be reversed (a bit) but after that, the reversal is no longer possible.
Strangely the “cleverer” you are the more you might believe in your god-like abilities of revocability. Time’s arrow does not exist for you, only mere mortals. It is with this mind-set that some politicians cannot resist opining. Somehow this cleverness can forget the second law of thermodynamics, if it had ever encountered it in the first place.
We can get into cause and effect, action and consequence, to see that unless you have a DeLorean time machine, time flows only one way on the macroscopic scale. Everyone kind of knows this, yet it does not influence our actions as much as it might. Science fiction aside we cannot turn the clock back and start over. There is no “undo” button in real life.
Regret can stem back to when the stable door was left open and before the Pooh stick passed under the bridge, but that doesn’t change the new situation. No matter how much we might want revocability it can never be exact, only partial at best. We cannot go back to the initial conditions in the event flow. All one can do is learn from what might be termed a mistake. We have the notion of “too late” and it is real enough.
Some seemingly small actions of ours can create an inordinate amount of mess and kerfuffle. These are evidence of an increase in entropy, according to the second law. A mess once generated is very hard to clean up. Time’s arrow is given flight and it bifurcates on its journey. And even should the mess be cleared up things are never the same again. Yeah, this kind of stuff keeps Jeremy Kyle in work.
There are some things in life, in the human sphere, which are irrevocable and so Time’s Arrow applies. There is no going back. Some things which are not random but intended also cannot be undone, though their consequences may not initially have been considered.
You cannot step in the same river twice.