M
Max Power
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Kathianne said:No, I don't see "why" they "must."
Okay.
Let's say you fire 100 photons at the screen through 2 slits. For the first 50 you cover the first slit, and for the second 50, you cover the second slit (or you can randomly cover each slit if you want). You will get a pattern on the screen that corresponds to the addition of two one-slit patterns.
Now, if you fire 100 photons through the 2 slits, leaving both of them open. Intuition tells you that since each photon should travel through one of the slits, you will get the same pattern as above, but you do not. The resulting interference pattern corresponds to two slits being open, (this is the one in the picture). This means that each photon somehow interacts with BOTH slits at the same time.