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Does somebody know of good papers about potential links between computation complexity and why we do not observe large scale quantum behaviours ? As a basic com

by madlag 13y ago

Does somebody know of good papers about potential links between computation complexity and why we do not observe large scale quantum behaviours ? As a basic computer guy, I have always suspected that the large computer that is running our universe does not have the resources to handle quantum entanglement on a large number of particules, and has to fallback to some classical approximation to be able to run the full simulation in real time ;-)

kremlin 13y ago
why would it have to run it in 'real time'? what's the difference between this universe being simulated by a very slow computer in the super-verse, vs being simulated by a very fast computer in the super-verse? for us, I'd argue there's no difference at all.
- maxerickson 13y ago
  Not always a fan of linking xkcd, but: http://xkcd.com/505/ http://xkcd.com/505/
- madlag 13y ago
  That's right, thanks for this point.
gus_massa 13y ago
Superconduction and superfluity are examples of macroscopic quantum phenomena. I’m not sure they can be classified as entanglement, but the fundamental reason is at least as weird as entanglement and I think they would be also very difficult to simulate. There is also a correction of the law for Ideal gases. It’s more important when the temperature is low and the quantum effects are more visible. Essentially, let’s suppose that you have a lot (~1E23) of identical atoms/molecules in a gas. In some gases the atoms/molecules can’t be in the some quantum state at the same place (fermions) and in other gases they can be (bosons). Moreover, the particles are all identical, so you can’t label them and can’t track them. This causes an “apparent repulsion” in the fermions gasses and an “apparent traction”. It’s not a real force, it’s only a statistical effect that looks like a attraction/repulsion. (It’s a little more complicated because the positions and velocities are not discrete, so “the same place” is more difficult to define.) (I can’t find a link to a direct simple measurement.) More info: http://en.wikipedia.org/wiki/Fermi_gas http://en.wikipedia.org/wiki/Fermi_gas and http://en.wikipedia.org/wiki/Bose_gas http://en.wikipedia.org/wiki/Bose_gas
- madlag 13y ago
  Of course there are some large scale (~150km http://iopscience.iop.org/1367-2630/8/9/193/fulltext/ http://iopscience.iop.org/1367-2630/8/9/193/fulltext/ ) or large number of particles quantum effects that are usually very carefully crafted , but the majority of the matter that surround us does not show such behavior, so I still wonder about this ;-) That said, thanks for the reminder !
Strilanc 13y ago
I don't know about links to computational complexity, but in the many worlds interpretation the "classical approximation" is explained by "quantum decoherence". 1: http://en.wikipedia.org/wiki/Quantum_decoherence http://en.wikipedia.org/wiki/Quantum_decoherence 2: http://lesswrong.com/lw/pp/decoherence/ http://lesswrong.com/lw/pp/decoherence/

by madlag 13y ago

kremlin 13y ago

why would it have to run it in 'real time'? what's the difference between this universe being simulated by a very slow computer in the super-verse, vs being simulated by a very fast computer in the super-verse? for us, I'd argue there's no difference at all.

maxerickson 13y ago
Not always a fan of linking xkcd, but: http://xkcd.com/505/ http://xkcd.com/505/
madlag 13y ago
That's right, thanks for this point.

gus_massa 13y ago

Superconduction and superfluity are examples of macroscopic quantum phenomena. I’m not sure they can be classified as entanglement, but the fundamental reason is at least as weird as entanglement and I think they would be also very difficult to simulate. There is also a correction of the law for Ideal gases. It’s more important when the temperature is low and the quantum effects are more visible. Essentially, let’s suppose that you have a lot (~1E23) of identical atoms/molecules in a gas. In some gases the atoms/molecules can’t be in the some quantum state at the same place (fermions) and in other gases they can be (bosons). Moreover, the particles are all identical, so you can’t label them and can’t track them. This causes an “apparent repulsion” in the fermions gasses and an “apparent traction”. It’s not a real force, it’s only a statistical effect that looks like a attraction/repulsion. (It’s a little more complicated because the positions and velocities are not discrete, so “the same place” is more difficult to define.) (I can’t find a link to a direct simple measurement.) More info: http://en.wikipedia.org/wiki/Fermi_gas http://en.wikipedia.org/wiki/Fermi_gas and http://en.wikipedia.org/wiki/Bose_gas http://en.wikipedia.org/wiki/Bose_gas

madlag 13y ago
Of course there are some large scale (~150km http://iopscience.iop.org/1367-2630/8/9/193/fulltext/ http://iopscience.iop.org/1367-2630/8/9/193/fulltext/ ) or large number of particles quantum effects that are usually very carefully crafted , but the majority of the matter that surround us does not show such behavior, so I still wonder about this ;-) That said, thanks for the reminder !

Strilanc 13y ago

I don't know about links to computational complexity, but in the many worlds interpretation the "classical approximation" is explained by "quantum decoherence". 1: http://en.wikipedia.org/wiki/Quantum_decoherence http://en.wikipedia.org/wiki/Quantum_decoherence 2: http://lesswrong.com/lw/pp/decoherence/ http://lesswrong.com/lw/pp/decoherence/