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IANAP. My (bad) understanding is based on trying to grok Scott Aaron's book on quantumn computing, which AFAIK does a really excellent job educating on, among o

IANAP. My (bad) understanding is based on trying to grok Scott Aaron's book on quantumn computing, which AFAIK does a really excellent job educating on, among other things, WTF quantumn physics. I am open to being horribly wrong, as I don't even know how to properly tell if I know what I'm talking about. That out of the way - The "thing" is neither a particle or a wave, it's a propagating probability amplitude. With one slit, you get a simple probability distribution. With two slits, you get a complex probability distribution, where the amplitudes are summed (and since they can be negative, sometimes sum to zero) The detector adds constraints to the probability amplitudes, zeroing part of the complex probability of the double slit, thus reducing it to a non-complex distribution.

platz 7y ago
Now do you think that propagating probability amplitude is a real physical thing?
- RangerScience 7y ago
  Yes, actually! I just went looking and can't find it, but there was a science paper years ago about dropping.... hydrogen ions into liquid helium? The expectation was that the electrostatic forces would create "bubbles" of empty around the ions, which (the bubbles, not the ions) would then be detected when they reached the bottom. They found those bubbles. They also found many differently sized bubbles, all smaller, in a size distribution correlating to the probability that the ion would pierce the surface tension of the liquid. The interpretation was that the smaller bubbles were the "pieces" of the waveform that traversed the surface tension. This was taken as evidence the waveform is an actual thing that actually exists. I really wish I could find it...
  - notanote 7y ago
    “Can the wave function of an electron be divided and trapped?” https://news.brown.edu/articles/2014/10/electron https://news.brown.edu/articles/2014/10/electron
- leni536 7y ago
  It doesn't make much sense to argue which parts of the equations are real physical. Having said that for me the Aharonov-Bohm effect proves the "reality" of the wave function. https://en.m.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect https://en.m.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect
- TheOtherHobbes 7y ago
  Yes, for mysterious values of "physical". Clearly there is a consistent ordering principle involved, just as there is in entanglement and related phenomena. But you can't look at a single photon/electron/whatever and get this contextual information out of what we know about the physical structure of the object itself. There is no physical marker we can read "inside" a photon that says it's entangled, or that it's passed through two slits by "interfering with itself". So the information - and probably the process itself - is contextual. We don't know where this information lives. But it has to exist somewhere, because we can see the effects of its operation very easily. So it's physical in the sense that we can see physical effects. Photons etc know what they're doing, and we can make excellent predictions about that behaviour. But the exact nature of the entities and relationships that makes this process work, and the way it maps to observable events and properties, remains a mystery. The obvious implication is that what we see isn't really fundamental. Neither field excitations nor the fields of QFT are the ground truth, and there's another layer of reality that generates them - and probably spacetime too. But that layer has some very unusual properties from our POV, and we're going to need some new metaphors to understand it.
- wruza 7y ago
  It’s interesting how classical knowledge offsets what we (me too) feel physical and what we don’t. If you think of particles like they’re hard repulsive spheres, does that make them more “real physical”? Why should matter be fundamental and not be emergent from phenomena that are unlike any of our experience?
phs318u 7y ago
Disclosure: I got my B.Sc (Physics) in 1986 and I barely scraped through (and have been working in IT since), so fair warning. If you were modelling the universe and everything in it, say via a simulation, fancy probability distributions would be a good way of calculating behaviour. What if the "stuff of reality" we're looking for (and trying to map the math to), doesn't actually exist? What if the math is all there is? What if behaviour is all that matters? In primitive cultures, spirits were hypothesised as the animating force behind behaviour of animals, stars, weird people etc. For a long time, it proved a reasonable model until it was supplanted by our more scientific notions of the observable universe. But what if quarks, leptons, photons, are just "spirits" i.e. a good enough approximation given what we know? What if it's "spirits" all the way down? i.e. the only fundamental is the math and everything else is a visualisation (of sorts)? BTW, that kind of speculative question (and an awesome high school physics teacher), are what made me study physics at university. Shame (in one way) I was more interested in rocking out and drinking beer. EDITED TO ADD: don't take anything I post too seriously. If you find yourself rolling your eyes, just downvote me and move on.
- Erlich_Bachman 7y ago
  > What if behaviour is all that matters? Behavior, observation, accurate prediction and empirical evidence is all that matters in science, yes. What difference does it make if you call it "particle" or "just math"? What practical difference does it make? If none then that is not a question of science. It might be an interesting question of philosophy or spirituality, but not for science. Science deals with falsifiable hypothesis and accurate predictions and making functional machines.

platz 7y ago

Now do you think that propagating probability amplitude is a real physical thing?

RangerScience 7y ago
Yes, actually! I just went looking and can't find it, but there was a science paper years ago about dropping.... hydrogen ions into liquid helium? The expectation was that the electrostatic forces would create "bubbles" of empty around the ions, which (the bubbles, not the ions) would then be detected when they reached the bottom. They found those bubbles. They also found many differently sized bubbles, all smaller, in a size distribution correlating to the probability that the ion would pierce the surface tension of the liquid. The interpretation was that the smaller bubbles were the "pieces" of the waveform that traversed the surface tension. This was taken as evidence the waveform is an actual thing that actually exists. I really wish I could find it...
- notanote 7y ago
  “Can the wave function of an electron be divided and trapped?” https://news.brown.edu/articles/2014/10/electron https://news.brown.edu/articles/2014/10/electron
leni536 7y ago
It doesn't make much sense to argue which parts of the equations are real physical. Having said that for me the Aharonov-Bohm effect proves the "reality" of the wave function. https://en.m.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect https://en.m.wikipedia.org/wiki/Aharonov%E2%80%93Bohm_effect
TheOtherHobbes 7y ago
Yes, for mysterious values of "physical". Clearly there is a consistent ordering principle involved, just as there is in entanglement and related phenomena. But you can't look at a single photon/electron/whatever and get this contextual information out of what we know about the physical structure of the object itself. There is no physical marker we can read "inside" a photon that says it's entangled, or that it's passed through two slits by "interfering with itself". So the information - and probably the process itself - is contextual. We don't know where this information lives. But it has to exist somewhere, because we can see the effects of its operation very easily. So it's physical in the sense that we can see physical effects. Photons etc know what they're doing, and we can make excellent predictions about that behaviour. But the exact nature of the entities and relationships that makes this process work, and the way it maps to observable events and properties, remains a mystery. The obvious implication is that what we see isn't really fundamental. Neither field excitations nor the fields of QFT are the ground truth, and there's another layer of reality that generates them - and probably spacetime too. But that layer has some very unusual properties from our POV, and we're going to need some new metaphors to understand it.
wruza 7y ago
It’s interesting how classical knowledge offsets what we (me too) feel physical and what we don’t. If you think of particles like they’re hard repulsive spheres, does that make them more “real physical”? Why should matter be fundamental and not be emergent from phenomena that are unlike any of our experience?

phs318u 7y ago

Disclosure: I got my B.Sc (Physics) in 1986 and I barely scraped through (and have been working in IT since), so fair warning. If you were modelling the universe and everything in it, say via a simulation, fancy probability distributions would be a good way of calculating behaviour. What if the "stuff of reality" we're looking for (and trying to map the math to), doesn't actually exist? What if the math is all there is? What if behaviour is all that matters? In primitive cultures, spirits were hypothesised as the animating force behind behaviour of animals, stars, weird people etc. For a long time, it proved a reasonable model until it was supplanted by our more scientific notions of the observable universe. But what if quarks, leptons, photons, are just "spirits" i.e. a good enough approximation given what we know? What if it's "spirits" all the way down? i.e. the only fundamental is the math and everything else is a visualisation (of sorts)? BTW, that kind of speculative question (and an awesome high school physics teacher), are what made me study physics at university. Shame (in one way) I was more interested in rocking out and drinking beer. EDITED TO ADD: don't take anything I post too seriously. If you find yourself rolling your eyes, just downvote me and move on.

Erlich_Bachman 7y ago
> What if behaviour is all that matters? Behavior, observation, accurate prediction and empirical evidence is all that matters in science, yes. What difference does it make if you call it "particle" or "just math"? What practical difference does it make? If none then that is not a question of science. It might be an interesting question of philosophy or spirituality, but not for science. Science deals with falsifiable hypothesis and accurate predictions and making functional machines.