- #36
rkastner
- 264
- 38
My concern is laid out in the paper I've linked: the unitary-only approach to explaining 'apparent collapse', i.e. the emergence of the macroscopic world, doesn't work, because it assumes what it is trying to prove. One can see this also on p. 14 of Wallace's big book on the Everett Interpretation, as I note here:(from https://arxiv.org/abs/1603.04845):
"The insistence on 2 [the universe has initially separable, localizable degrees of freedom such as distinguishable atoms] appears, for example, in Wallace’s invocation of “additional structure on the Hilbert Space” as ostensibly part of the basic formalism (Wallace 2012, p. 14-15). Such additional structure–preferred sets of basis vectors and/or a particular decomposition of the Hilbert space–is imposed when quantum theory is applied to specific situations in the laboratory. However, what we observe in the laboratory is the already-emergent classical world, in which classical physics describes our macroscopic measuring instruments and quantum physics is applied only to prepared quantum systems that are not already entangled with other (environmental) degrees of freedom.
If the task is to explain how we got to this empirical situation from an initially quantum-only universe, then clearly we cannot assume what we are trying to explain; i.e., that the universe began with quasi-localized quantum systems distinguishable from each other and their environment, as it appears to us today. Yet Wallace includes this auxiliary condition imposing structural separability under a section entitled “The Bare Formalism” (by which he means Unitary-Only), despite noting that we assign the relevant Hilbert space structures “in practice” to empirical laboratory situations. The inclusion of this sort of auxiliary condition in the “bare formalism” cannot be legitimate, since such imposed structures are part of the application of the theory to a particular empirical situation. They thus constitute contingent information, and are therefore not aspects of the “bare formalism,” any more than, for example, field boundary conditions are part of the bare theory of electromagnetism. These separability conditions are auxiliary hypotheses to which we cannot help ourselves, especially since the most general state of an early quantum universe is not one that comes with ...distinguishable degrees of freedom. Thus, the addition of this condition amounts to ...circular reasoning, or (at worst) outright affirming of the consequent, illicitly propping up the claim that quasi-classical world “branches” naturally appear in an Everettian (unitary- only) picture. "
So the problem is that, in unitary-only evolution, the universal state must be considered to have distinguishable features from the very beginning in order to 'derive' the distinguishability attributed to 'einselection'. The latter does the heavy lifting in the purported 'explanation' of the emergence of the macroscopic world. But in order to get that, there must be a 'system of interest', distinguishable from its 'environment'--which presupposes someone who can identify ('be interested in') at least a semi-localized system. But if, for example, the initial universal state consisted only of systems in eigenstates of momentum, nobody would ever have a localizable 'system of interest'. So right away there is an hoc tooling of the universal state such that it will yield us what we want. This sort of hand-tooling of the initial state is required in a unitary-only model in order to get even apparent collapse (but not in a collapse model like TI). As noted above, Wallace smuggles this hand-tooling in as ostensibly part of the 'bare formalism', when clearly it is not--it is application of the formalism along with specific auxiliary conditions obtaining empirically. If the whole point is to account for determinate empirical experience, then unitary-only theorists cannot assume that from the outset! When challenged on this, they basically assert that it's necessary because that's the only possible explanation--another logical fallacy (see the above paper for details on this point).
The reason I brought up the existence of a genuinely preferred observable is that this is a common objection to the TI solution. It also arises as a concern among unitary-only researchers as well. So I'm pointing out that energy/momentum are the preferred observables.
And yes of course you can find nonrelativistic QM as a limit of the relativistic theory. But Nature operates relativistically--she doesn't stop particle creation just because we're not paying attention that domain at the moment. This is why position/time are not ontologically fundamental properties of quantum systems, yet energy/momentum are. Similarly, the orbit of Mercury doesn't stop precessing just because we're not paying attention that.
Thanks for your questions and for your open-mindedness regarding TI. (My latest submission to the arxiv on TI, discussing how it explains the microscopic origin of irreversibility and thus the 2nd law of thermodynamics, has been placed on hold. The paper is an invited submission to Entropy. It can be viewed here: http://philsci-archive.pitt.edu/id/eprint/12718 )
"The insistence on 2 [the universe has initially separable, localizable degrees of freedom such as distinguishable atoms] appears, for example, in Wallace’s invocation of “additional structure on the Hilbert Space” as ostensibly part of the basic formalism (Wallace 2012, p. 14-15). Such additional structure–preferred sets of basis vectors and/or a particular decomposition of the Hilbert space–is imposed when quantum theory is applied to specific situations in the laboratory. However, what we observe in the laboratory is the already-emergent classical world, in which classical physics describes our macroscopic measuring instruments and quantum physics is applied only to prepared quantum systems that are not already entangled with other (environmental) degrees of freedom.
If the task is to explain how we got to this empirical situation from an initially quantum-only universe, then clearly we cannot assume what we are trying to explain; i.e., that the universe began with quasi-localized quantum systems distinguishable from each other and their environment, as it appears to us today. Yet Wallace includes this auxiliary condition imposing structural separability under a section entitled “The Bare Formalism” (by which he means Unitary-Only), despite noting that we assign the relevant Hilbert space structures “in practice” to empirical laboratory situations. The inclusion of this sort of auxiliary condition in the “bare formalism” cannot be legitimate, since such imposed structures are part of the application of the theory to a particular empirical situation. They thus constitute contingent information, and are therefore not aspects of the “bare formalism,” any more than, for example, field boundary conditions are part of the bare theory of electromagnetism. These separability conditions are auxiliary hypotheses to which we cannot help ourselves, especially since the most general state of an early quantum universe is not one that comes with ...distinguishable degrees of freedom. Thus, the addition of this condition amounts to ...circular reasoning, or (at worst) outright affirming of the consequent, illicitly propping up the claim that quasi-classical world “branches” naturally appear in an Everettian (unitary- only) picture. "
So the problem is that, in unitary-only evolution, the universal state must be considered to have distinguishable features from the very beginning in order to 'derive' the distinguishability attributed to 'einselection'. The latter does the heavy lifting in the purported 'explanation' of the emergence of the macroscopic world. But in order to get that, there must be a 'system of interest', distinguishable from its 'environment'--which presupposes someone who can identify ('be interested in') at least a semi-localized system. But if, for example, the initial universal state consisted only of systems in eigenstates of momentum, nobody would ever have a localizable 'system of interest'. So right away there is an hoc tooling of the universal state such that it will yield us what we want. This sort of hand-tooling of the initial state is required in a unitary-only model in order to get even apparent collapse (but not in a collapse model like TI). As noted above, Wallace smuggles this hand-tooling in as ostensibly part of the 'bare formalism', when clearly it is not--it is application of the formalism along with specific auxiliary conditions obtaining empirically. If the whole point is to account for determinate empirical experience, then unitary-only theorists cannot assume that from the outset! When challenged on this, they basically assert that it's necessary because that's the only possible explanation--another logical fallacy (see the above paper for details on this point).
The reason I brought up the existence of a genuinely preferred observable is that this is a common objection to the TI solution. It also arises as a concern among unitary-only researchers as well. So I'm pointing out that energy/momentum are the preferred observables.
And yes of course you can find nonrelativistic QM as a limit of the relativistic theory. But Nature operates relativistically--she doesn't stop particle creation just because we're not paying attention that domain at the moment. This is why position/time are not ontologically fundamental properties of quantum systems, yet energy/momentum are. Similarly, the orbit of Mercury doesn't stop precessing just because we're not paying attention that.
Thanks for your questions and for your open-mindedness regarding TI. (My latest submission to the arxiv on TI, discussing how it explains the microscopic origin of irreversibility and thus the 2nd law of thermodynamics, has been placed on hold. The paper is an invited submission to Entropy. It can be viewed here: http://philsci-archive.pitt.edu/id/eprint/12718 )
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