How much better are physical possibilities than logical ones?

[Rivendale]

As a fictional character, Sheldon exists outside time, so his endorsement of my views must carry exceptional weight and I am grateful for it.

[Gadianton]

Quantum measurement is only simple in theory. The devices and processes that do it, that amplify atomic-scale phenomena into things we can see, are extremely complicated.

I used to have this mini-keyboard that came with a laser pointer. Useless, except one day I drove a couple nails close together into a board and then shot the laser through the gap, beholding the interference band on my garage wall. One more life thing checked off.

I partially get what you're saying about leveraging microscopic events. Tell me where I'm going wrong: in your terms, decoherence = And to Or? In the two slit experiment, an interference band shows up, revealing the position of photons, thus decoherence happened. Measurement must be identical to decoherence; or at least, all decoherence is measurement? But there isn't much leveraged on an everyday two-slitter. I was thinking in nature something like two-slitting must happen regularly.

But can't the same weirdness that is amplified by the micro-detectors you're talking about be mimicked using dumber gear? I can't think of an example yet, but the motivation would be something like that suggestion by Wheeler. One of my favorite examples. So, I'm outside at night doing two slit experiments and watching interference bands show up. A couple light years away, an alien has a powerful telescope trained on the slits in my driveway...a dumb version of that scenario, as such a telescope would be advanced technology.

[Gadianton]

How do we make the move to every imagined myth happened somewhere on a many worlds view? I'm not seeing how many worlds would entail this. There's a slim possibility there's a God therefore there's a God in some world but not his one or another one because there's also a possibility there's no God? I'm struggling to see how our imagining something into existence puts something into existence. While there's a possibility Harris did whatever it was 75 times we can say it happened in some world, I don't see that as saying the same thing as there really is a world conceived of by L Ron Hubbard. If we don't have spirits inside us, how is it possible to say we would in another world?

God transcends quantum probability because in the ontological argument, God inhabits all logically possible worlds, of which all physical possibilities are a subset.

There is a division between what is logically possible and physically possible, I don't think all mythologies and every logically consistent imaginable scenario are physically possible. However, some aspects of mythology could very well be physically possible.

Now what is physically possible in the world of QM? Dropping the mike 75 times seems pretty mundane but is it really? We seem to be invoking some kind of contra-causal, anomalous event; specifically, something that makes no sense. That's what seems to be the intent. The later examples, suddenly speaking in another language that you don't know, how is that physically possible? Once you cross a line where matter spontaneously arranges itself into weird things, you can't really prevent religiously inspiring anomalies from happening from there. Like, suddenly, the personage of Moroni popping into existence and delivering plates to Joseph Smith. It's not that more far-fetched then the neurons in your brain suddenly happening to arrange themselves such that Hungarian emits from your mouth. And so it depends on what is meant in the 75 mic drop examples as to how innocent it is compared to Moroni appearing.

[Physics Guy]

Not all wave interference is quantum interference. Classical waves can all show it—light waves, sound waves, even water waves. Diffraction is also a classical wave phenomenon.

Classical physics isn’t fundamentally true, but quantum systems can emulate it very well. So just seeing interference and diffraction is kind of like catching Clark Kent in the act of turning in a story to the Daily Planet. He’s really Superman but you didn’t see him being super.

Wave interference is only weird if a single particle does it. So to claim a quantum measurement, you need a detector that can register individual atoms or photons or whatever.

Young’s double-slit experiment used a really faint light in a really dark room, and it did have a quantum detector: photographic film. It didn’t show the two-slit interference pattern at all—at first. It showed individual specks, where a single photon had hit an individual film grain. If he left the film there in the faint light for longer before developing it, he got more specks. And if he left it long enough, the specks made out an interference pattern in pointillistic shading. Using a strong light so that you can see the whole pattern form instantly, though, isn’t non-classical. That’s what you’d also see if light were classical and photons didn’t exist.

Decoherence isn’t necessarily measurement, though measurement is a case of decoherence. Decoherence is the loss of interference effects, just like what happens with light that isn’t monochromatic enough. Lots of things besides measurement can cause it. After you’ve measured a photon, it’s a speck, and it’s not going to interfere with anything, so that is decoherence.

The relationship isn’t trivial. Scenarios in which information gets effectively recorded somewhere, even if no-one sees it, bring decoherence to quantum systems, with measurable effects that can even be dramatic, even if no energy or momentum changes hands but only information.

[Gadianton]

I had a feeling if I posted that, I'd be at risk of unchecking the box. My defense to keep the box checked: My understanding is that the interference of classical waves produces a different pattern than that of quantum waves. Granted, I don't have such a great eye that I observed the pattern on my garage wall, and probably already a couple IPA's into it anyway, said, "Yep, that's it! Let's check the box." I assumed, given it was a laser, that the interference pattern I saw must be quantum interference. If the classical kind of interference can also happen with a laser shooting through two nails, then it's checkmate and I have to uncheck. I assumed that enough experiments have been done with lasers that it is established as always a different pattern than water's (or bullets) when going through two slits. 100% of the time. Don't soften the blow, this isn't Sic et Non, and around here, we're happy to learn that we're wrong about something. If it's possible I saw something other than quantum interference, let me know. (I'm reading your account of Young as confirming that a laser in my scenario would produce the same pattern as if light were a classical wave, and so the box has to be unchecked)

Wave interference is only weird if a single particle does it

to be sure, because I either missed this, forgot about it, or the youtube videos I watched in the past were wrong: Normal light, or my laser through the nails interferes like a stream of water in the same scenario. The shift in pattern only happens at one quanta at a time?

[Physics Guy]

No, laser light as light is perfectly classical. It's just like what you'd get from a radio station, if the radio station could broadcast at 10^15 Hz. In fact we can't make AC current to drive a wire antenna at such insanely high frequencies, so to make light in optical frequencies we use atoms as our antennas. It's not so hard to make atoms emit light, but it's trickier to get a lot of them all to emit light at the same frequency; the process by which atoms emit light collectively like that is very quantum mechanical. The end product, though, is an ordinary classical light wave that is just really monochromatic. It's kind of like the way Santa's elves use their magic to produce ordinary toys that say Mattel on the label.

The interference patterns of light waves are different in detail from those of sound or light waves, because the wavelengths are much shorter, and because there's very little dispersion of light waves, at least through most reasonably transparent media. There is nothing specially quantum mechanical about light wave interference patterns, though. The only special thing about laser light is that it's monochromatic—it contains a very narrow range of frequencies—so interference effects show up much more strongly. Interference patterns usually depend on frequency, so if your light includes many frequencies then you see many patterns superimposed, and they can easily average out to just a blur. That doesn't happen with lasers.