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According to my understanding. Since Einstein, physicists have thought of space and time as forming a four-dimensional structure known as “spacetime.” But space differs from time in some very fundamental ways. In space, we’re free to move about as we wish. When it comes to time, we’re stuck. We grow older, not younger. And we remember the past, but not the future. Time, unlike space, seems to have a preferred direction — physicists call it the “arrow of time.” Some physicists suspect that the second law of thermodynamics provides a clue. It states that the entropy of a physical system (roughly, the amount of disorder) rises over time, and physicists think this increase is what gives time its direction. (For example, a broken teacup has more entropy than an intact one — and, sure enough, smashed teacups always seem to arise after intact ones, not before.) Entropy may be rising now because it was lower earlier, but why was it low to begin with? Was the entropy of the universe unusually low 14 billion years ago, when the Big Bang brought it into existence? Recent computer simulations seem to show how the asymmetry of time might arise from the fundamental laws of physics, but the work is controversial, and the ultimate nature of time continues to stir passionate debate. All of this is theory by the physicists but I feel like there is more reasons just other than these 2. If time is considered the 4th dimension then we should be able to travel back and forth right? I am just looking for a curious group of people to add their perspective and reasoning on why time only seem to flow in only one direction? So I can get a even depth understanding on other people's perspective and reasoning and the topic itself.

Krish
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  • @VincentThacker not really because that post was focusing on these points

    What do physicists mean by time?

    How does time flow?

    Why is there an arrow of time But none of it answers my question of why time only flows in that only one direction and about entropy , spacetime and the flow of time itself. I would prefer if you were to give your own opinions on this. Thanks :)

     – Krish Jun 17 '21 at 02:33
  • There is really no such thing as the antithesis of diffusion. Entropy rises over time, so the Universe should have started with low entropy. – shawn_halayka Jun 17 '21 at 02:38
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    This post has too many questions in one. Please focus on the most important single question, and edit to delete the others – Dale Jun 17 '21 at 03:21
  • Einsteinian relativity (which includes both 1915's General Relativity and the 1929 Einstein-Cartan theory, identical to GR only in vacuum, that was worked out by Einstein and the mathematician Cartan) is sometimes referred to as "the spatialization of time", so you'd probably grasp the subject more easily if you'd refer to "the flow" of time (whose origin probably dates from the use of medieval "water clocks") as passage through it: Time is a dimension, and is definitely not any substance or energy that "flows". – Edouard Jun 17 '21 at 03:30

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