I would suggest you read what we say about decoherence in our paper. We specifically covered that topic because we know many people think decoherence solves the observer problem. Even the founders of decoherence, like Zeh and Joos state categorically that decoherence doesn’t solve that problem. And I would point out that if Weinberg is correct that there is no way to formulate quantum without running into consciousness, then that would also include the decoherence interpretation. Unless you are claiming Steven Weinberg doesn’t know about decoherence.
One thing not in our paper is the claim by the 2003 Nobel Laureate, A. J. Leggett who said:
“_Let us now try to assess the decoherence argument. Actually, the most economical _
tactic at this point would be to go directly to the results of the next section, namely that it is experimentally refuted!” A. J. Leggett, Testing the Limits of Quantum Mechanics: Motivation, state of Play, Prospects," J. Phys.: Condens. Matter 14 (2002) R415–R451, R429
He discussed several experiments in the section of his paper he refers to in the above quote but the most easily understandable experiment is the one where buckeyballs (fullerenes C60 and C70) produce an interference pattern. _Wave–particle duality of C60 molecules | Nature
Decoherence says environmental interactions cause loss of coherence and thus loss of the ability for things like interference patterns to be formed. Leggett points out that in order to carry out this experiment the Buckeyballs must be heated to high temperatures. If we observe an electron as it is going through a slit, no interference pattern is produced. But with the buckeyball experiment, each molecule interacts between 6-8 times with the thermal radiation field, meaning each molecule has had loads of thermal interaction and environmental interaction both before and at the slits. He raises the question of why this much interaction with the environment doesn’t cause the coherence to leak away. He says:
"Secondly, the molecules of the beam are by no means in their ground state with respect to their internal degrees of freedom; indeed, it is estimated that the average energy associated with these is approximately 5.8 eV, distributed over the 174 degrees of freedom of vibration of the C60 molecule. Moreover, four of these modes are infrared active, i.e. couple strongly to the black-body radiation field, and from the known Einstein coefficients it is estimated that three or four quanta are emitted (and absorbed) during the passage of a molecule through the apparatus. Thus, the interaction of the system with its ‘environment’ is by no means ‘weak’!
"Why, nevertheless, does decoherence not destroy all possibility of observing QIMDS in this experiment? The main reason, of course, is that in free space the motion of the centre of mass is not directly coupled to the internal degrees of freedom (the ‘diver’s theorem’; cf section 4). However, this observation does not in itself eliminate the problem, since there is an indirect coupling via the interaction of the infrared-active vibrational modes with the blackbody radiation field; if the final state of the radiation field is appreciably different depending on which slit the molecule passed through, this should be enough to decohere the superposition and thus destroy the diffraction pattern." A. J. Leggett, Testing the Limits of Quantum Mechanics: Motivation, state of Play, Prospects," J. Phys.: Condens. Matter 14 (2002) R415–R451, R434
As you know, decoherence says that if something has a large number of degrees of freedom it will decohere rapidly. Buckey balls have 174 degrees of freedom which is quite sufficient for the theory, yet it didn’t decohere.
When we wrote our paper, I was very insistent that we cover decoherence because we knew your objection would arise. Decoherence tries to ‘collapse’ the wavelet without any conscious being needed. But as I pointed out, even the founders of decoherence don’t believe they succeeded at that. Go look as Schlosshauer’s long quotation in our paper. http://themigrantmind.blogspot.com/2019/05/quantum-soul.html