On Wed, Aug 7, 2019 at 5:03 AM smitra <[email protected]> wrote: > On 06-08-2019 20:00, 'Brent Meeker' via Everything List wrote: > > On 8/6/2019 6:38 AM, Bruno Marchal wrote: > > > >>> If the QC does its task effectively, the output basis qbits will > >>> be put into definite states, > >> > >> Relatively to the observer, but in the global state, the observer > >> will inherit the superposition state, by linearity of the tensor > >> products and of the evolution. > > > > In something like Shor's algorithm there is only one final state with > > non-vanishing probability. Yet this is the kind of algorithm that > > Deutsch cites as proving there must be many worlds. > > > > Deutsch's does mention this, but his main argument is that you could in > principle implement entire observers within a QC, simply because the > universe is ultimately quantum mechanical and observers are internal to > the universe. Note that locality implies that observations cannot be > fundamentally based on permanent records due to environmental > decoherence.
I note that Deutsch does not believe in the non-locaility implied by violation of the Bell inequalities. Non-locality is now an accepted part of the understanding of quantum mechanics and of decoherence. If you do an experiment in the lab and make an observation > then there are still only a finite number of physical degrees involved > in the entanglement with the observed quantum system. Whatever it > physically means to have observed a definite outcome would remain > unaffected when performed within a sufficiently large QC simulation that > doesn't undergo decoherence itself (although it will end up simulating a > decohering system). > The trouble with that argument is that in any simulation, you get to set the rules of physics that obtain. There is then no guarantee that the results of your simulation have any relation to physics in the real (unassimilated) world. For decoherence to work, all that is required is a sufficient number of environmental degrees of freedom for multiple copies of the result to be recorded by the "environment as witness", in Zurek's words. Quantum Darwinism then ensures that the result is permanent and irreversible. Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLSBG4yDbXZs%2BfiMqfa0fRV0rsOLXH8XRrnk5t-RReJBGA%40mail.gmail.com.
