> On 7 Aug 2019, at 15:08, Bruce Kellett <[email protected]> wrote: > > On Wed, Aug 7, 2019 at 7:39 PM Bruno Marchal <[email protected] > <mailto:[email protected]>> wrote: > On 7 Aug 2019, at 02:19, Bruce Kellett <[email protected] > <mailto:[email protected]>> wrote: >> On Wed, Aug 7, 2019 at 10:04 AM smitra <[email protected] >> <mailto:[email protected]>> wrote: >> On 07-08-2019 00:45, Bruce Kellett wrote: >> >> > 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. >> >> If you measure the z-component of a spin polarized in the x-direction, >> then however astronomically large the number of environmental degrees of >> freedom there are that get entangled with the spin, it's still a finite >> number. One minute after the measurement all the degrees of freedom that >> can be entangled are within one light-minute of the experimental set-up. >> So, the recording of the result in the environment are going to be a >> superposition of the two possible recordings. >> >> It is called the "relative state" interpretation for a reason. The >> entanglement with the environmental degrees of freedom that leads to the >> recording of the result in the environment is relative to each possible >> experimental outcome. Within the decoherence time (typically of the order >> of a few nanoseconds or less) these "relative states" become effectively >> orthogonal, and the measurement becomes irreversible. Because there is no >> longer any possibility of interference between the results, there is no >> longer any superposition. > > > That does not follow. There is no more a possibility to detect the > interference. > > What exactly is the difference between something that it is impossible in > principle to detect and something that does not exist?
It is like the difference between the human existence and the human non existence, for an alien situated in a very far away galaxy. The fact that this alien cannot detect us does not make the human disappearing. It is like the other side of the moon before we built rocket. It is like taking our theory at fave value, instead of eliminating some terms in the equation by sheer coquetry. You are questioning the whole physical realism, which might be a progress. > > That does not make the other terms of the wave vanishing, they become just > inaccessible, or … you introduce something non linear in QM. > >> You guys seems so desperate to hold on to a superposition that no longer has >> any practical consequences. > Yes, because we are not interested in practical matter, but in conceptual > understanding. > > Conceptual understanding of what? Things that do not exist? Only about things which exist. But we have to take our theories seriously, as this help to abandon them, or improve them, in front of facts and problems. > >> Get used to it -- measurements have definite outcomes. That is the fact that >> has to be incorporated into your theory. > > That’s like coming back to collapse, if not to 'shut up and calculate', > frankly. > > No, it is recognising the reality that the theory is designed to describe and > predict. We can’t decide this without understanding the theory, and its relation with some possible reality. Bruno > > 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] > <mailto:[email protected]>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/CAFxXSLT4%2BARSoPQEwUmckXuNgwZgCT4iA2_FFh11d924j%3DMcrA%40mail.gmail.com > > <https://groups.google.com/d/msgid/everything-list/CAFxXSLT4%2BARSoPQEwUmckXuNgwZgCT4iA2_FFh11d924j%3DMcrA%40mail.gmail.com?utm_medium=email&utm_source=footer>. -- 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/C8E6FF38-B320-4286-AB38-C227B4BCE762%40ulb.ac.be.
