If we fire one photon at a time, why don't all of the photons hit the barrier exactly in between the two slits? How come each photon goes in different directions? (some go through top slit, some go through bottom slit, and the rest hit the barrier at different altitudes) If the photon firing gun is stationary in between the slits (longitudinally) and always points perpendicular to the barrier, why doesn't 100% of the photons travel in a straight line and hit the barrier halfway between the two slits??
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People often interpret "particle" as a point-like being or something negligible in size. But photons' sizes definitely cannot be ignored in the double-slit experiment. Further, in quantum mechanics, the particle nature of photons refer to their energy come in packets and is not about their sizes. They are not point-like things. Each photon goes through both slits as a wave does.
Yuan John Jiang
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Your question is very specific. Let us ignore that your conception is actually wrong, and take your particle viewpoint to the extreme.
When a gun shoots a particle, one-by-one, there is recoil. There is vibration from the Earth that the gun has to be secured somehow. (And no, I am NOT invoking uncertainty principle.) There is no such thing as a gun that can fire particles exactly tracing the trajectory of an earlier particle. There is some actual spread.
Yes, if you have a very small spread, then it is likely to fire particles that hit the middle of two widely separated slits. When this happens, you get that the barrier with the slits is blocking the passage. This case actually defines what it means to be widely separated.
Given any small spread, the slits can be moved closer until the spread and the slits will overlap. Then, and only then, will the double slit experiment start to be discussed in the way that is envisioned to be discussed. You have simply ignored the point of discussing the experiment, and instead got worked up on a technicality.
Classically, light is a wave, and the size of the wave is necessarily huge compared to the slits. In fact, you can visibly see the how macroscopically large the resulting wavefunction is, on the viewing screen behind the slits. All those pictures are made with photons that are localised onto tiny atoms making up the viewing screen, much smaller than the macroscopically large wavefunction.
Then you can speak about how the wave is passing both slits at once. And confuse yourself over the particle trajectories and the interference pattern.
naturallyInconsistent
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