I heard that, at the Quantum level, events can happen out of order making causality invalid. Thus the future can happen in the present and the present in the future. Is this true?


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    $\begingroup$ Where did you hear/read this? $\endgroup$ – Johannes Jul 15 '13 at 16:30
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    $\begingroup$ I remember reading about this in the future. $\endgroup$ – Olin Lathrop Jul 15 '13 at 21:35
  • $\begingroup$ The Elegant Universe $\endgroup$ – Neo Jul 15 '13 at 22:32
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    $\begingroup$ Of all the classical things that quantum mechanics changes around or redefines or invalidates, quantum mechanics doesn't change the concept of time at all. Whoever said this may have in mind some dubious ideas about quantum gravity which have no experimental or sound theoretical foundation. $\endgroup$ – Michael Brown Jul 16 '13 at 11:17
  • $\begingroup$ arxiv.org/abs/quant-ph/0105101 $\endgroup$ – Count Iblis Jul 5 '16 at 21:17

In quantum field theory causality is preserved. See for example the answers to In QFT, why does a vanishing commutator ensure causality?. I'm afraid the subject is a bit technical, but I think it would be hard to give a popular science level explanation of how causality is preserved in QFT.

I don't know how causality is preserved in string theory, but the question Causality in String Theory asks this very question and the reply indicates that causality is preserved.

So it is not true that causality is invalidated at the quantum level.


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