On Wed, Aug 1, 2018 at 11:34 PM Brent Meeker <[email protected]> wrote:
> > > On 8/1/2018 3:46 PM, Jason Resch wrote: > > > > On Wed, Aug 1, 2018 at 1:39 PM Brent Meeker <[email protected]> wrote: > >> >> >> On 8/1/2018 3:51 AM, Bruno Marchal wrote: >> >> >> On 31 Jul 2018, at 21:46, Brent Meeker <[email protected]> wrote: >> >> >> >> On 7/31/2018 9:11 AM, Bruno Marchal wrote: >> >> >> On 30 Jul 2018, at 22:27, Brent Meeker <[email protected]> wrote: >> >> >> >> On 7/30/2018 9:58 AM, John Clark wrote: >> >> >>> > >>> *Forget collapse.* >> >> Many, perhaps most, physicists do exactly that because they believe in >> the "Shut Up And Calculate" quantum interpretation and are only interested >> in predicting how far to the right a indicator needle on a meter moves in a >> particular experiment. But for some of us that feels unsatisfying and would >> like to have a deeper understanding about what's going on at the quantum >> level and wonder why there is nothing in the mathematics that says anything >> about a wave collapsing. >> >> >> That's not true. "The mathematics" originally included the Born rule as >> part of the axiomatic structure of QM. >> >> >> In the usual QM, yes. But this use a vague notion of observer, and a >> seemingly forbidden process, a projection (a Kestrel!), I mean forbidden if >> we apply the wave to the couple observer-particle. >> >> >> >> >> Most of all they want to know what exactly is a "measurement" and why it >> so mysterious. >> >> >> The problem with the Born rule was that its application was ambiguous: >> >> >> Ah! Exactly. >> >> >> >> Where was the Heisenberg cut? Why was "the needle basis" preferred? But >> decoherence theory has given answers (at least partially) to those >> questions. Given those answers, one can just replace "collapse" with >> "discard", i.e. discard all the predicted possible results except the one >> observed. Is there really any difference between saying those other >> predictions of the wf are in orthogonal, inaccessible "worlds" and saying >> they just didn't happen. That seems to be Omnes approach. He writes, >> "Quantum mechanics is a probabilistic theory, so it only predicts >> probabilities.” >> >> >> >> OK, but the honest, and perhaps naive inquirer would like to have an idea >> about what are those probabilities about, and where they come from. >> >> >> That was the source of resistance to Born's paper. Physicists assumed >> that probability could only arise from ignorance of an ensemble. Since >> there was no ensemble in Heisenberg's (or Schroedinger's) QM they resisted >> the idea. Lots of attempts were made to reintroduce ensembles, or at least >> virtual ensembles, so that they could feel comfortable with having a >> probabilistic theory. Omnes' is just saying "Get over it!"; probabilities >> are fundamental. >> >> >> >> Yes, but he said all this after defending Everett (or its own better >> version of Everett). Then, this introduces a notion of ensemble (the set of >> all consistent histories), and, at least in some book, just ask us to be >> irrational and to dismiss the ensemble at make probability fundamental, >> only to make the “other worlds” disappear. In one book he lakes clear that >> such a decision is irrational, and that he makes it because he dislike of >> find shocking the idea that all quantum possible outcome are realised. It >> is a bit like a christian who understand the evolution theory, but add that >> it makes just God having invented evolution instead of Adam. >> >> >> >> There's nothing irrational about discarding that which is not observed >> and keeping that which is observed. >> > > It is irrational if it results in a significantly more complex, ad hoc, or > nonsensical theory. > > > So it's irrational if it postulates infinitely many unobservable worlds. > Nothing is more sensible than discarding that which is unobservable. > > See, I can be just as snarky as you. > I was being serious. This explains my position well: https://www.scientificamerican.com/article/multiverse-the-case-for-parallel-universe/ Remember: Parallel universes are not a theory—they are predictions of certain theories. To me, the key point is that if theories are scientific, then it's legitimate science to work out and discuss all their consequences even if they involve unobservable entities. For a theory to be falsifiable, we need not be able to observe and test all its predictions, merely at least one of them. My answer to (4) is therefore that what's scientifically testable are our mathematical theories, not necessarily their implications, and that this is quite OK. For example, because Einstein's theory of general relativity has successfully predicted many things that we can observe, we also take seriously its predictions for things we cannot observe, e.g., what happens inside black holes. Likewise, if we're impressed by the successful predictions of inflation or quantum mechanics so far, then we need to take seriously also their other predictions, including the Level I and Level III multiverse. George even mentions the possibility that eternal inflation may one day be ruled out—to me, this is simply an argument that eternal inflation is a scientific theory. [...] George also mentions that multiverses may fall foul of Occam's razor by introducing unnecessary complications. As a theoretical physicist, I judge the elegance and simplicity of a theory not by its ontology, but by the elegance and simplicity of its mathematical equations—and it's quite striking to me that the mathematically simplest theories tend to give us multiverses. It's proven remarkably hard to write down a theory which produces exactly the universe we see and nothing more. The theory that branches we don't observe don't exist is a needless complication to the simplicity of QM, one not motivated by evidence, and introduces all kinds of unintended baggage (priviledged reference frames, magical observers, discontinuity, violations of unitarity, FTL effects, perhaps even solipsism). Jason -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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