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Can someone provide or point to a layman's definition of "realism" in quantum mechanics? Recently on a call-in podcast I listen to, a caller has claimed that t

by jere 14y ago

Can someone provide or point to a layman's definition of "realism" in quantum mechanics? Recently on a call-in podcast I listen to, a caller has claimed that the following article shows that a) realism has been disproven and b) that proves we are all in a computer simulation: http://physicsworld.com/cws/article/news/2007/apr/20/quantum-physics-says-goodbye-to-reality http://physicsworld.com/cws/article/news/2007/apr/20/quantum... >Now physicists from Austria claim to have performed an experiment that rules out a broad class of hidden-variables theories that focus on realism -- giving the uneasy consequence that reality does not exist when we are not observing it Sure. Anyway, I'm certain this guy is equivocating, but I don't even know where to read up on the relevant topics. And I read articles like these and they keep using the word realism without defining it.

toufka 14y ago
Philosophically (as written by Einstein, Heisenberg, etc.) there are three assumptions about the world - of which one is broken by the quantum world. We do not know which one. Depending on your interpretation of the Schrodinger equation you can interpret the breaking in any of the three ways. This article says its realism - but as far as I know there is no way to prove its realism and not one of the others. One of these cannot hold: - Realism, Locality, or Separability Realism - Einstein's idea of 'elements of reality' - the idea that things actually are material and unchanging. Their properties are constant unless acted upon (ie a Hydrogen atom at time1 and point1 has a constancy of properties at time2 and point2). You could imagine a universe that had, as a property of the universe, atoms change mass every other day - just for the hell of it. Locality - The idea that a system can only be affected by things within its lightcone - no effect can travel faster than the speed of light. And two objects must be 'local' before they can interact. Separability - any system separated by non-trivial space/time can be considered independent of each other. The idea that 1/2mv^2 does not include every other part of the universe in trying to figure out what m or v are. Not quite the same as locality - as it would still require local interactions, but that net of interactions could be so thick and pervasive as to prevent any meaningful isolation of any system. As is stated above, these concepts fall out of the EPR experiment.
- Anderkent 14y ago
  Do you have any sources for the separability part? From what I remember, the three assumptions should be realism (the universe would exist even if no one would 'observe' it), locality or counter-factual definiteness - the ability to talk and reason on results of measurements that have not been performed.
  - toufka 14y ago
    Search this article - it explains much of the original rationale: http://plato.stanford.edu/entries/qt-epr/ http://plato.stanford.edu/entries/qt-epr/
- platz 14y ago
  That's interesting. At first glance, it seems like we invented Separability just to make things easier for us. In my head I'd always assumed that forces diminish continuously; But I guess that's what I get for thinking of force as something different from a particle. If all force is particles, I suppose it makes sense.
- jere 14y ago
  Thanks for the explanation. I was still confused about how "things actually are material and unchanging" led to "reality does not exist when we are not observing it." You pointed me in the right direction though and I'm convinced that the term is being abused by the caller: >Realism in the sense used by physicists does not equate to realism in metaphysics. The latter is the claim that the world is in some sense mind-independent http://en.wikipedia.org/wiki/Local_realism#Local_realism http://en.wikipedia.org/wiki/Local_realism#Local_realism http://arxiv.org/pdf/quant-ph/0607057v2.pdf http://arxiv.org/pdf/quant-ph/0607057v2.pdf If papers are being written about how "local realism" should be banned from scientific discussion, I'm fairly certain it isn't appropriate for laymen to bandy about the term and then make wild ass philosophical assertions based on it.

by jere 14y ago

toufka 14y ago

Philosophically (as written by Einstein, Heisenberg, etc.) there are three assumptions about the world - of which one is broken by the quantum world. We do not know which one. Depending on your interpretation of the Schrodinger equation you can interpret the breaking in any of the three ways. This article says its realism - but as far as I know there is no way to prove its realism and not one of the others. One of these cannot hold: - Realism, Locality, or Separability Realism - Einstein's idea of 'elements of reality' - the idea that things actually are material and unchanging. Their properties are constant unless acted upon (ie a Hydrogen atom at time1 and point1 has a constancy of properties at time2 and point2). You could imagine a universe that had, as a property of the universe, atoms change mass every other day - just for the hell of it. Locality - The idea that a system can only be affected by things within its lightcone - no effect can travel faster than the speed of light. And two objects must be 'local' before they can interact. Separability - any system separated by non-trivial space/time can be considered independent of each other. The idea that 1/2mv^2 does not include every other part of the universe in trying to figure out what m or v are. Not quite the same as locality - as it would still require local interactions, but that net of interactions could be so thick and pervasive as to prevent any meaningful isolation of any system. As is stated above, these concepts fall out of the EPR experiment.

Anderkent 14y ago
Do you have any sources for the separability part? From what I remember, the three assumptions should be realism (the universe would exist even if no one would 'observe' it), locality or counter-factual definiteness - the ability to talk and reason on results of measurements that have not been performed.
- toufka 14y ago
  Search this article - it explains much of the original rationale: http://plato.stanford.edu/entries/qt-epr/ http://plato.stanford.edu/entries/qt-epr/
platz 14y ago
That's interesting. At first glance, it seems like we invented Separability just to make things easier for us. In my head I'd always assumed that forces diminish continuously; But I guess that's what I get for thinking of force as something different from a particle. If all force is particles, I suppose it makes sense.
jere 14y ago
Thanks for the explanation. I was still confused about how "things actually are material and unchanging" led to "reality does not exist when we are not observing it." You pointed me in the right direction though and I'm convinced that the term is being abused by the caller: >Realism in the sense used by physicists does not equate to realism in metaphysics. The latter is the claim that the world is in some sense mind-independent http://en.wikipedia.org/wiki/Local_realism#Local_realism http://en.wikipedia.org/wiki/Local_realism#Local_realism http://arxiv.org/pdf/quant-ph/0607057v2.pdf http://arxiv.org/pdf/quant-ph/0607057v2.pdf If papers are being written about how "local realism" should be banned from scientific discussion, I'm fairly certain it isn't appropriate for laymen to bandy about the term and then make wild ass philosophical assertions based on it.