\nIn quantum mechanics, it’s just as natural to go forward in time as going backwards. And if you look at a typical Feynman diagram, you can turn the diagram either way. Where does this transition from time symmetry at the quantum level,...\nIn quantum mechanics, it’s just as natural to go forward in time as going backwards. And if you look at a typical Feynman diagram, you can turn the diagram either way. Where does this transition from time symmetry at the quantum level, to time asymmetry at the macro level occur?
To understand its irreversibility, we have to look for other irreversible processes in nature to see if there is any correlation - such as in thermodynamics, Entropy.
Entropy is a measure of disorder, but a more rigorous definition has to do with information. Entropy is related to the amount of information necessary to describe a system. Thus, information is directly tied to entropy. And if entropy of the universe is always increasing, it means that the information necessary to describe the universe must also be increasing.
If we have two gases on the two sides of a chamber and allow the gases to mix, they'll mix together and not unmix. This is a one way process, from an ordered state of two separate gases, to a disordered state of a mixtures. The process evolves from one state to the other, and you cannot go back to the prior state. This is similar to the one way direction of time.
It's important to point out that it is not impossible for the mixture of gases to go back to the prior ordered state. It is a statistical impossibility but not a physical impossibility.
Does increasing entropy cause the forward flow of time? Time and entropy seem to be related. But how do we know one is the cause of the other? If you could reverse time, you would see a scrambled egg going back to being unscrambled.
If increasing entropy was directly responsible for the forward flow of time, it would be logical to presume that decreasing entropy would cause the backward flow of time. The inside of your refrigerator decreases entropy by removing heat. But time does not run backwards inside your refrigerator.
The best definition of time in physics is that time is the process that brings the unknown future into a recorded past via the present. This requires an increase in information because every moment that goes by is recorded as a definite past which are events that have definitely happened. This was not knowledge until it happened. When it happened, it became new information and thus added to the total information in the universe. More information is more entropy.
Physicist Lee Smolin suggests that what distinguishes the past from the present is a kind of knowledge that is gained once indeterminate quantum events consisting of only probabilities in the present, become a classical definite past.
So what seems to separate the past from the present is whether it is knowable or not.The change from quantum indefinite present to a classical definite past is what defines the arrow of time. This points always in the forward direction as the quantum present constantly churns out a classical past.
Note that although it is established that information is related to entropy, both Smolin’s paper and my extrapolation of his paper to information are not established theories, but conjecture.
This means that entropy must have been much lower earlier in time, near the big bang. How did the universe get to this low entropy state at the beginning? If entropy only increases, one hypothesis is that one day the universe will be in a state with no useful energy, only radiation and heat. Then nothing can happen - no physical movement, no chemistry, not even thoughts in brains.
If nothing happens in the entire universe, and not even thoughts or consciousness can exist, does time still continue to move forward? I’m not so sure. \n
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