I’ve heard of the double-slit experiment with electrons as described by Richard Feynman being carried out in such manner that electrons were sent out one at a time. I’m not sure whether or not I understood the experiments and its results well, but it seems that the final appearance of the screen showed the same interference pattern which is created by the phase shift resulting from changes in the path lengths of both waves when electrons are emitted all at once or as a flux.
Is this what really happens? How can the screen show the same interference pattern?
Yes that’s really what happens. I don’t think anyone has succeeded in coming up with a “how” answer that satisfies intuitions that humans have developed to fit an environment considerably different than the subatomic one, though.
Because the single electron passes through both slits, and interferes with itself…
The pilot wave interpretation seems pretty intuitive to me, even though most people who know more than I do don’t like it; something to do with local realism or something.
I’m on my phone so I can’t give you a link but there is a great veritasium video that sold me on this idea. When I get home I will try to find it, unless someone else does first.
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I’m given to understand that all particles have a wave function. The wave function of tiny, very fast moving things like photons or electrons is very noticeable. The wave functions of big, slow-moving things, say a baseball pitched straight at a baseball bat at 90 mph has a negligible wave function … but not a zero wave function. A PBS cartoon guide to physics said there is an infinitesimal possibility that the Mighty Casey didn’t strike out – the baseball passed through the bat. But admitted its most likely he struck out.
This explanation would seem to imply that photons should have more of a wave function than electrons do. But I never seen corroboration of that.
Here it is:
I would love to know why this is the default explanation for laymen.
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It’s not so much that they “have” a wave function, it’s more a matter that we find that mathematical representation to have predictive properties. And we can’t even say that something like photon is a particle in the sense of being a tiny, physical thing. We use math to represent reality, but don’t confuse the math with reality.
Correction: I would love to know why this isn’t the default explanation
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The PBS Space Time guy agrees with you…
Because it doesn’t offer testable differences from the other hypotheses.
To add to the weirdness, if you put a detector at one of the slits that rings when a photon passes through the slit, the interference pattern disappears. Feynman used say that no one understands quantum mechanics, but people can learn to calculate with it.
That’s why I said “for laymen”: it’s a lot easier to get your head around. It doesn’t lead to the type of confusion exhibited in the OP.
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There may be reasons why it is wrong, but it does give a good visual demonstration of why the double slit experiment works the way it does, as well as a few other quantum weirdness phenomena. It is at least as right as using a trampoline to demonstrate gravity, and probably much more so.
And it may not be wrong, either, even if it does seem to be somewhat frowned upon in the physics community.
When I took my first QM class in college, I remember one particular lecture where the professor was writing equations on the board, and telling us about some strange aspect of QM as we all scribbled our notes frantically trying to keep up. At one point he turned around, looked at us and said: “By the way, no one understand this stuff. You just become more comfortable with it over time.” That actually made us feel a lot better!
Well the problem with picking an explanation for laymen that is not generally accepted by physicists is that it ends up as something budding physicists have to unlearn.
What does pilot wave explanation “give up”, relative to other explanations?
Pilot wave: Non-locality. What does this mean exactly. Wikipedia says it does not conflict with relativity because no information/communication occurs. Anything else?
Copenhagen: Observer "creates " reality. Particles move through both slits at the same time.
Many worlds: Continual astronomical (cosmological?) exponential reduplication of the universe, presumably with every quantum interaction (that is unthinkable number of universe “splitting” events every nano-second!).
Did I get that right? Any other good ones?
John Cramer’s Transactional Interaction Transactional interpretation - Wikipedia
even if equivalent, does pilot wave cause special challenges, calculation-wise?
Bohmian mechanics (aka pilot wave theory) is one of the major interpretations of quantum mechanics and has been favoured by some important QM theorists (e.g. John Bell). Its big achievement and appeal is providing a realist explanation of quantum physics, which side-step some of the major interpretational issues of QM such as the measurement problem; its unappealing aspects are that, realism and non-locality in combination, are difficult to reconcile with relativity and that despite being realist it still contains elements that are downright strange to our classical intuition. Like any interpretation of QM, whether you favour it depends on your point of view on its interpretational problems.
This may be in the videos above (I haven’t watched them), but Bohmian trajectories in the double slit experiment: INSPIRE
If you don’t choose an interpretation in which particles have trajectories (which of course is the case for most interpretations), then you can only look at the double slit experiment in the abstract and esoteric world of wavefunctions.
I’m pretty sure that every interpretation uses the same calculations (hence, the popular slogan “Shut up and calculate!”)