On Thu, Jul 1, 2021 at 1:07 AM John Clark <[email protected]> wrote:
> On Mon, Jun 28, 2021 at 7:46 PM Bruce Kellett <[email protected]> > wrote: > > *> I think John's trouble here is that he still adheres to David Deutsch's >> concept of worlds. Deutch talks as though every component of a >> superposition is a separate world. This leaves Deutsch no language to talk >> about decohered worlds, pointer states, and all the other usual apparatus >> of quantum interpretations.* >> > > Not so, "superposition" is just a word that means a collection of > particles that exist in very different physical states at exactly the same > time, in other words it's a word that people like to use when they just > don't want to say that the universe has split. In Many Worlds if the > mathematics says that 2 things could happen then 2 things do happen. > Usually when a universe splits the two never recombine again, that's why we > usually don't see weird quantum effects in our everyday lives, and that's > why making a Quantum Computer is hard. But If the difference between > universes is very very small > That seems a bit arbitrary. Exactly how is this "very very small difference" quantified? It all looks much more like an arbitrary "just so" story rather than a well-defined physical theory. Bruce > then a skilled experimenter can make them become identical again and > recombine, and that produces interference. However the difference between > the universes rapidly grows larger and the task of making them identical > again rapidly becomes more difficult, so when the difference becomes > larger than the microscopic level the possibility of them becoming > identical again becomes ridiculously small, like in classical physics and > the possibility that by pure random chance all the air molecules in the > room you're in right now will go to the other side of the room and you'll > suffocate to death. That's why you never see somebody as large as a human > being use quantum tunneling to walk through a brick wall even though such a > thing is theoretically possible. > > We don't always see a superposition of states, in fact usually we don't. > If you flip a coin and it comes out heads then you are NOT living in the > world where it came out tails. In a roughly similar way if you do the two > slit experiment and see that the photon goes through slit A then you are > not living in the world where the photon went through slot B. But the 2 > slit experiment can be a little different from the simple coin toss > example. > > If after the universe splits and the photon goes through both slits they > then hits a photographic plate (or a brick wall) then both photons in both > universes are destroyed and thus there is no longer any difference between > the two, so the universes will merge back together. Then and only then you > will see evidence that the photon went through both slits (aka. > Interference) on the photographic plate even if you send the photos through > one at a time. > > If you got rid of the film (or the brick wall) and let the photon head out > into > infinite space after it passes the slits then the two universes will > never recombine, and so of course you will never see a interference > effect. The beautiful part of the theory is that it doesn't have to > explain what an observer is and that's why a brick wall will work just as > well as a photographic plate. > > A measurement, if for some reason you'd like to use that word, is a change > made in the universe, and it doesn't matter if that change is made in a > conscious being or not. In one universe the photon hits the screen at point > X, and in another universe the photon hits the screen at point Y, and in > yet another universe the photon doesn't hit the screen at all because it > doesn't pass through either slit. If there happens to be an observer > watching all this he splits too, and they all have different memories about > what happened. And it doesn't matter if nobody is watching, the universe > splits anyway. In Many Worlds if you like you could replace the word > "measurement" with the word "change" and you don't need to use the word > "observer" at all, so you don't need to ponder the question of if a > cockroach can observe things and make the universe split. > -- 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/CAFxXSLS-vjjWBvv48vDB7N0S96XVTWckRudf_KbBG709%2BzuL1Q%40mail.gmail.com.
