[HN Gopher] Quantum Mischief Rewrites the Laws of Cause and Effect
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       Quantum Mischief Rewrites the Laws of Cause and Effect
        
       Author : rbanffy
       Score  : 39 points
       Date   : 2021-03-13 19:20 UTC (3 hours ago)
        
 (HTM) web link (www.quantamagazine.org)
 (TXT) w3m dump (www.quantamagazine.org)
        
       | yarg wrote:
       | I've thought about similar things, it seems to me to be a sort of
       | retroactive causality.
       | 
       | It seems to me that there will be mutually exclusive states of
       | reality existing in different spatial contexts; it's only at the
       | meeting of light cones that the contradiction is reconciled (the
       | likelihood of superposition mutex events is zero).
        
       | antiquark wrote:
       | How is this not a perpetual motion machine:
       | 
       | > engines normally need a hot and cold reservoir to work, with a
       | quantum switch they could extract heat from reservoirs of equal
       | temperature -- a surprising use suggested a year ago by Oxford
       | theorists.
        
         | lumost wrote:
         | This is something akin to maxwell's demon. All Quantum
         | processes save for measurement are reversible, and as such many
         | thermodynamics concepts don't apply or don't apply in all
         | circumstances.
        
       | darig wrote:
       | Dibs on Quantum Mischief band name
        
       | wizzwizz4 wrote:
       | This is an interesting, but obvious-in-retrospect, consequence of
       | superposition. Amplitude is contributed by all paths, but it's
       | contributed _to a state_ (a way-that-the-universe-could-be). The
       | history is irrelevant, unless it has an effect on the final state
       | - which is always true in the macroscopic world, thanks to the
       | second law of thermodynamics and historians and space probes and
       | chaos theory, but not always true in the microscopic world, where
       | things are simpler.
       | 
       | This means that multiple histories contribute to a final state-
       | of-the-universe: If A-B-C and A-D-C are indistinguishable
       | (because C is the same state as C) then they _both_ contribute
       | amplitude - in layperson 's terms, both histories are happening
       | in parallel, then combining when they get to the same state.
       | 
       | If you've got states X and Y, and you're doing something like XOR
       | swap, then you can go (X, Y) - (X^Y, Y) - (X^Y, X) - (Y, X) _or_
       | (X, Y) - (X, X^Y) - (Y, X^Y) - (Y, X). This isn 't fundamentally
       | different from the ABC / ADC case; it _obviously_ follows that
       | this would happen too, though I 'd never though it of it before.
       | 
       | Very thought-provoking article.
        
       | optimalsolver wrote:
       | See also retrocausality, aka backwards causation:
       | 
       | https://en.wikipedia.org/wiki/Retrocausality
       | 
       | https://aeon.co/essays/can-retrocausality-solve-the-puzzle-o...
        
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