- #1
benjayk
- 8
- 0
As I understand it wavefuctions of individual particles are incomplete descriptions of a system because ultimately a wavefunction describes a system and cannot be reduced to individual particles (which would exclude things like entanglement).
So the only way to have a good idea how a system behaves in QM is to make many many precise measurements of a system, to find all the subtle ways in which the wavefunction of the system is not reducible to the wave function of the individual parts (like correlations between measurements of parts).
That by itself is not a problem and makes sense.
The only thing that I don't get is how that is applied in practice. Because here it seems that in most cases only very specific wavefunctions are considered relevant even for macro systems. That is, it is assumed that the wavefunction of the macro behaviour doesn't include much (if any) information that goes beyond the individual wavefunction of the constituent parts.
Sometimes this is justified through our observations about decoherence. But I don't get how that works given that our notion of decoherence mostly describes decoherence of particles or small systems, not decoherence of systems in general (in which case there may be no correlations between individual particles, but still between bigger systems). It seems we just don't know the wavefunction of (remotely) macro systems because this would require *very* difficult to make measurements. Thus we can make no precise statements about its decoherence. From this also follows that we can't make any statements about subtle macro entanglement and phenoma related to it (psi, quantum brain or other quantum processes in nature).
But given that it is mostly taken for granted that practically relevant macro entanglement does not exist (as commonly seen in discussion regarding psi, where it is claimed it is against the laws of QM), either there is an implicit hypothesis at work here (like "the macro wave functions don't involve any large scale correlations") or I don't understand the reasons for excluding such possibilities, or even regarding them as unlikely.
I think I understand the most basic concepts of quantum mechanics, but not much beyond that, so please answer using simple concepts. :)
So the only way to have a good idea how a system behaves in QM is to make many many precise measurements of a system, to find all the subtle ways in which the wavefunction of the system is not reducible to the wave function of the individual parts (like correlations between measurements of parts).
That by itself is not a problem and makes sense.
The only thing that I don't get is how that is applied in practice. Because here it seems that in most cases only very specific wavefunctions are considered relevant even for macro systems. That is, it is assumed that the wavefunction of the macro behaviour doesn't include much (if any) information that goes beyond the individual wavefunction of the constituent parts.
Sometimes this is justified through our observations about decoherence. But I don't get how that works given that our notion of decoherence mostly describes decoherence of particles or small systems, not decoherence of systems in general (in which case there may be no correlations between individual particles, but still between bigger systems). It seems we just don't know the wavefunction of (remotely) macro systems because this would require *very* difficult to make measurements. Thus we can make no precise statements about its decoherence. From this also follows that we can't make any statements about subtle macro entanglement and phenoma related to it (psi, quantum brain or other quantum processes in nature).
But given that it is mostly taken for granted that practically relevant macro entanglement does not exist (as commonly seen in discussion regarding psi, where it is claimed it is against the laws of QM), either there is an implicit hypothesis at work here (like "the macro wave functions don't involve any large scale correlations") or I don't understand the reasons for excluding such possibilities, or even regarding them as unlikely.
I think I understand the most basic concepts of quantum mechanics, but not much beyond that, so please answer using simple concepts. :)