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It has always fascinated me that time is symmetrical in classical physics while, in life, we all experience the flow of time in only one direction. There is no preference as to the direction of time in classical physics, the only exception being in thermodynamics where, with the introduction of entropy, there is a preferred direction for time's axis. Physical systems evolve in the direction in which their entropy increases (sorry for not being precise...) Personally, I have never truly accepted thermodynamics as a full theory as it never truly 'explains' why entropy must increase.

But, in quantum theory, there seems to be a preferred direction for time, too. And this has nothing to do with entropy? The collapse of a wave function in a measurement seems to dictate a direction of time. Could this be a better explanation for the direction of time or maybe even for thermodynamics? (Ok, maybe not thermodynamics...)

Qmechanic
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user56718
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  • possible duplicate of Is the collapse of the wave function inherently time asymmetric? – John Rennie Aug 06 '14 at 07:10
  • somewhat related but not exactly the same. My focus was on the direction of time. In thermodynamics, the arrow of time or entropy is due to the statistical nature of a system consists of large number of components which is not very satisfying as an "explanation" of the direction of time. But, in the quantum mechanics case, the collapse of weave function is due to observation, and arrow-of-time is really about a series of observations. So, if we accept quantum mechanics, we can "accept" asymmetric of weave function collapse and hence the arrow-of-time? – user56718 Aug 06 '14 at 07:41
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    The trouble is that the collapse of the wave function is just one interpretation. In the Many Worlds Interpretation there is no collapse. The argument about QM and the arrow of time has generated and continues to generate much heat but little light. – John Rennie Aug 06 '14 at 11:18
  • "Never accepted thermodynamics as a full theory..." And rightly you shouldn't because we talk about the "Laws" of Thermodynamic, not the "Theory" of Thermodynamics. A Law is a statement of observations. The law is that entropy of an isolated system will increase over time. A law doesn't need to explain itself, it is what it is. P.S. You should accept thermodynamics as a valid set of Laws – Jim Aug 06 '14 at 13:47

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