Through two doors at once

By Anil Ananthaswamy

This is a good history of the double slit experiment in physics.

Amongst other things, the book describes a variation of the double slit experiment that took place on the canary islands. This experiement confirms that QM & Nature really doesn't want you to know the position and velocity of a partical, even if it means going back into the past to erase the evidence.

1. Start out with the normal double slit experiement. This shows that a partical can be a wave.

2. Put filters in front of the two slits such that horizontal polarized photons only pass through one slit and vertical polarized photons pass through the other. The double slit experiement still works. If you know the polarization of the photon, then the interference goes away.

3. Create a stream of engtangled photons. Send on half of the engtagled pair to the slits. Send the other away.

4. If you put a polarizer in front fo the photos that were fired away from the experiment, then the interference pattern goes away when you use the polarizer to filter out H or V photons. Filtering entangled photons still causes interference patterns to happen, or go away, as appropriate.

5. Move the filter added in step #4 miles away from the experiment. Randomly choose the polarization position after the entangled particle has hit the screen. The interference pattern will still appear (or dissappear) even if you choose to look at the entangled-away-photon long after the entangled-slit-photon has hit the screen.