Virtually everyone agrees that the act of measurement is nothing more than the entanglement of the 'experiment' system with the 'observer' system, and that as far as physics is concerned, that's the only thing that matters.
As I pointed out, Hugh Everett does not agree.
He describes observation as being performed by an automatically functioning with sensory gear and a memory.
The observer has to create a memory record in memory for a measurement to occur.
It's on page 9 on his thesis:
Quantum theory was barely understood when Everett wrote his thesis. In particular, quantum mechanics as operator theory on Hilbert spaces was only starting to become understood, and Bell's theorem had not yet been proven. An article written 50 years ago has little bearing on what physicists think today.
But anyway, the distinction of 'creating a memory' does not apply when you consider the observer and experiment together as a single quantum system. All quantum systems are reversible and follow unitary transformation laws. This means that no information can ever be lost or created within a quantum system.
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