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I don't fully understand the claim that all quantum processes are time-reversible. Aren't there a lot of spontaneous quantum phenomena that aren't?
by Causality1 6y ago
I don't fully understand the claim that all quantum processes are time-reversible. Aren't there a lot of spontaneous quantum phenomena that aren't?
- mikhailfranco 6y agoCorrect. This is the part of QM known as Interpretations, for which people cannot agree on a single viewpoint, and hence do not agree on which axiom to add to the theory. The measurement / collapse / decoherence / forking-of-worlds / entanglement-with-the-environment is either time-irreversible by definition, or time-irreversible FAPP. For example, Penrose proposes that the gravitational field induces one of these time-irreversible processes: https://en.wikipedia.org/wiki/Penrose_interpretation https://en.wikipedia.org/wiki/Penrose_interpretation
- abdullahkhalids 6y agoQuantum processes are described by Schrodinger's equation, that is a linear differential equation in time. Consequently, it's solutions for every possible boundary conditions are always reversible.
- mikhailfranco 6y agoThe Schrodinger Equation is obviously wrong in gravitational scenarios, because it is expressed in a background classical t that does not exist in GR, let alone a future theory of QG.
- Causality1 6y agoSo if you could measure an atom precisely enough you could calculate exactly when it decayed from a heavier atom?
- miltondts 6y agoMeasuring things is kind of problematic. https://en.m.wikipedia.org/wiki/Measurement_problem https://en.m.wikipedia.org/wiki/Measurement_problem
- Causality1 6y agoI'm just saying, theoretically, there's something different about an atom that decayed an hour ago vs one that decayed a year ago?
- effie 6y agoThere are "pure quantum evolution" processes (those described by unitary evolution of ket vector), such as atom sitting forever in its ground state or being in a superposition of different Hamiltonian eigenstates. Those are time-reversible. There are other processes which are not of such kind. Some people don't want to call those quantum processes, but they sure do have a prominent place in QM textbooks. For example spontaneous emission of light from an excited atom or radioactive decay of uranium atomic nucleus. Description of these processes isn't reducible to unitary evolution, instead irreversibility is assumed by employing the golden rule.
- bollu 6y agowhat is the golden rule?
- effie 6y agoFormula that gives rate of transition from one state to a set of many other states, as function of perturbation strength and density of final states. https://en.wikipedia.org/wiki/Fermi%27s_golden_rule https://en.wikipedia.org/wiki/Fermi%27s_golden_rule