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I also don't understand this. AFAIK "particle" in this context means quantized unit rather than contiguous solid object. And I see no reason why a quantized un

I also don't understand this. AFAIK "particle" in this context means quantized unit rather than contiguous solid object. And I see no reason why a quantized unit of a wave can't propagate through two slits simultaneously. But my level of understanding here is YouTube level so if you know more please correct me.

ithkuil 2y ago
I trust the physics works out. The problem in these discussions is how to build an intuition about the underlying physical model. I fail to have an intuition of how can a quantized unit of wave propagate through both slits. I know that the equations say that the probability of finding the particle at a given location is given by the amplitude squared of the wave function (Born rule). The image that a "quantized unit of wave propagates through two slits simultaneously" doesn't help me build any further intuition. Do the two parts going through the two different paths carry half the unit? Clearly that's not the case otherwise they wouldn't be quanta anymore. So does it mean that the entire wavefront is "one unit" no matter how spread out? But in that case, "one unit" of what?
- HarHarVeryFunny 2y ago
  If one just sends photons through a narrow single slit, then the pattern that builds up on the screen (if you send multiple photons, and record their positions) will be a banded diffraction pattern. If you have two slits, with a detector to determine which slit the photon went thru, then it'll behave as if it only went thru one of the two slits, at random, and what'll build up on the screen will be the two (slit A + slit B) overlayed diffraction patterns. Finally, if you have two slits with NO detector, then what will build up on the screen is the interference pattern as if the photon had gone thru both slits simultaneously and the two resulting banded diffraction patterns interfered with each other. So, what SEEMS to be happening in this case is that the quantum state of the system post-slit is that of the photon simultaneously having gone thru both slits, each slit having diverted it per diffraction, and then these diffraction patterns (probabilities) interferering. Wave collapse can only be happening after this interference (if it was before then there would only be one diffraction pattern and no interference), presumably when quantum state interacts with the screen. So, yeah, it seems that the "photon" does "go" through both slits, but this is a quantum representation, not a classical one.

ithkuil 2y ago

I trust the physics works out. The problem in these discussions is how to build an intuition about the underlying physical model. I fail to have an intuition of how can a quantized unit of wave propagate through both slits. I know that the equations say that the probability of finding the particle at a given location is given by the amplitude squared of the wave function (Born rule). The image that a "quantized unit of wave propagates through two slits simultaneously" doesn't help me build any further intuition. Do the two parts going through the two different paths carry half the unit? Clearly that's not the case otherwise they wouldn't be quanta anymore. So does it mean that the entire wavefront is "one unit" no matter how spread out? But in that case, "one unit" of what?

HarHarVeryFunny 2y ago
If one just sends photons through a narrow single slit, then the pattern that builds up on the screen (if you send multiple photons, and record their positions) will be a banded diffraction pattern. If you have two slits, with a detector to determine which slit the photon went thru, then it'll behave as if it only went thru one of the two slits, at random, and what'll build up on the screen will be the two (slit A + slit B) overlayed diffraction patterns. Finally, if you have two slits with NO detector, then what will build up on the screen is the interference pattern as if the photon had gone thru both slits simultaneously and the two resulting banded diffraction patterns interfered with each other. So, what SEEMS to be happening in this case is that the quantum state of the system post-slit is that of the photon simultaneously having gone thru both slits, each slit having diverted it per diffraction, and then these diffraction patterns (probabilities) interferering. Wave collapse can only be happening after this interference (if it was before then there would only be one diffraction pattern and no interference), presumably when quantum state interacts with the screen. So, yeah, it seems that the "photon" does "go" through both slits, but this is a quantum representation, not a classical one.