Eli5: Does time have a structure?
In: Physics
That’s an ambiguous question but I’ll answer as best I understand it.
Classical physics views time as a dimension similar to the three physical dimensions. (I’m not going to get into multidimensional physics). This means it treats the past and future the same way it treats going up/down or left/right, from the mathematics there is no reason why we can’t travel back in history just like we can drive to work. This is what a theoretical time machine does, it moves us in time like a car moves us in space.
Quantum Mechanics, a branch of special physics, says that time and space exist in discrete pieces. A good way to understand this is to think of molecules; I can have one molecule of water or I can I have 2 molecules. I cannot have 0.25 or 1.7765 molecules of water, it must exist in whole molecules or not at all. Same with space and time, I can *this* moment of time, or *that* moment of time, but there is nothing in between. This is the origin of the phrase “a Quantum Leap”, the infinitesimally small gap between existing in place and time and jumping forward to the next place and time. (although that phrase often gets misused to mean the exact opposite thing, a gigantic leap forward.)
In terms of why we perceive time as always traveling in one direct and can’t travel backwards in time, you introduce a concept called Entropy, a measurement of order/disorder in a system. For example, if I had a perfectly ordered deck of cards by number and suit, that would be called a Low Entropy system. If I throw those cards in the air and gather them they are now all disordered and it becomes a High Entropy system. The world around us is constantly becoming increasingly disordered, increasingly high entropy system. This movement of reality from low to high entropy is the best example we have of why time flows in a specific direction, always towards higher entropy.
No. Time moves differently depending on the perspective of the observer and what amount of gravity they’re experiencing. Jupiter is a really really big planet, so of you jumped on it you’d fall faster, and that gravity would also make time slightly slower, you wouldn’t notice anything but if you want back to earth your watch would be behind compared to one that stayed on earth while you were gone. If you jumped into a black hole and back out, you’d be years if not decades behind.
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