Is time reversal possible?

v. 3 n. 44

If time is defined in terms of entropy (things get simpler), time reversal is unlikely since this would contradict the principle of increasing entropy from thermodynamics, which also forbids perpetual motion machines.

There is a program with "reversed time" in a quantum computer. * However, computer experimentation is not as conclusive as physical experimentation.

It was discussed recently that if time is explained in terms of virtual particles, the speed of light and causality, then time reversal may not be possible, as follows. **

Recall that virtual particles were said to be responsible for preventing the speed of light to be infinite. If light speed was infinite, causality would be violated. This means that, in effect, everything would happen at once, to include for instance reception of radiation from all the stars in the universe reaching us at the same time and turning the Earth into a cinder.

Virtual particles could also be the origin of time. Even if there was no light, visible or otherwise, there would still be virtual particles in the ground-state quantum vacuum in a range of frequencies. Such movement in and out of existence would be the only thing happening in such a simple universe. Something happening implies the existence of time, and in this case the origin of time.

Within this simple universe model containing particles coming into and out of existence at certain lifespans from practically infinite to practically instantaneous, a conventional photon that is assumed to be an independent entity would have to make its way through a gauntlet of virtual particles (be absorbed by an adjacent virtual particle, which would re-emit to another virtual particle, etc., in this thesis). Assuming such an independent conventional photon was to try to retrace its steps (go back in time) it would have to locate the same path it took to reach its present location. But the path no longer exists since the virtual photons making up the original path no longer exist.

In this way mathematical and computer models permitting time reversal might not be physically possible.

* Scientists Have “Reversed Time” Inside A Quantum Computer, And The Implications Are Huge | IFLScience

** i.e., (4) An explanation of time from the frequency of virtual particles | LinkedIn

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