This video shows a rudimentary double slit eraser experiment. He sends photons through a double slit with a polarization film before the double slits (with a 90 degree difference) to obtain "which-way" information. Thus, the interference pattern at the end screen is gone.

Afterwards, he adds another uniform polarizing film after the double slits to erase the "which-way" information of the photons.

The result is that there is an interference pattern at the end screen.

  1. if we were to fire single photons would we get the same result? (I assume yes)

  2. Did the wave function collapse after the double slit and then re-emerge after the second polarizing film which erased the which way information or did the photon remain as a wave function throughout its flight path until it reached the end detector? (or perhaps it is impossible to know)

  3. What effect did the second film have on the photons? Did it change their polarity or just absorb those photons with non-matching polarity?


1 Answer 1


The experiment is likely not performing as claimed. Most slit experiments polarize before the slits and the laser should be highly polarized to begin with. Typically half the photons are absorbed for unpolarized light at a polarizer, these are collapsed. The transmitted photons have the same wave function all the way through. Probably 100% of the photons were blocked on one side and 100% transmitted on the other, by adding a 45 deg polarizer half of the transmitted photons were blocked.


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