Why Can Time Not Be Reversed
Why Can Time Not Be Reversed — Before the fact that time cannot be reversed, my heart grows quiet. We often wish, "if only I could go back to then." But for the same reason a broken cup does not reassemble, the days that have flowed do not gather again. At first this felt cruel. Yet looking closely, because time does not return, every moment is one-time-only, and being one-time-only, precious. If we could live twice, today would weigh nothing. The arrow of time ages us and, at once, makes this very moment one that will not come again, and so makes it shine. That it cannot be reversed is another name for that it is precious.
A film of a rolling ball looks fine run backward. But run a film of a cup shattering in reverse, and anyone sees at once that it is backward — for broken shards never gather into a whole cup. Most laws of physics hold equally forward and back, so why does the world we live in have a clear before and after, a past and a future?
This question is one of physics' deepest riddles. Newton's equations, and those after them, hold the same when time is reversed; nowhere in the formulas is an arrow saying "from past to future." Yet we have never, for a single moment, gone from future to past. The one who wrestled this contradiction head-on was, again, Boltzmann. He realized the direction of time is not a basic law but something that emerges from the probabilities of countless particles.
The core of the insight is one body with entropy. For a broken cup's shards to gather again is not physically impossible — only the chance of the particles arranging exactly so is unimaginably small. The ordered state of a whole cup is rare; the scattered state of broken shards overwhelmingly common. So the world always flows toward the common, the more scattered, and we feel the direction of that flow as "time passing." The arrow of time is not inside the clock but in the whole universe's flow from order to disorder. Even that we remember the past and not the future is because forming a memory, an order, increases the universe's entropy. Time does not flow — scattering itself is time.
- We leave photographs and diaries because time flows only one way. Unable to return, humans build devices to hold the moments that have passed.
- Food spoiling and iron rusting is how entropy, not the clock, tells the time. We gauge how much time has passed by the degree of scattering.
- Even a computer giving off heat as it calculates expresses the same law: erasing information and making order must always be paid for in scattering.
往, 가버린 것은 돌아오지 않는다는 그 한 방향의 흐름이 곧 시간의 화살이다.
Meet this hanja in Cheonjamun →Before the fact that time cannot be reversed, my heart grows quiet. We often wish, "if only I could go back to then." But for the same reason a broken cup does not reassemble, the days that have flowed do not gather again. At first this felt cruel. Yet looking closely, because time does not return, every moment is one-time-only, and being one-time-only, precious. If we could live twice, today would weigh nothing. The arrow of time ages us and, at once, makes this very moment one that will not come again, and so makes it shine. That it cannot be reversed is another name for that it is precious.
