According to the usual explanation, polarized lenses work by only allowing light with a specific kind of polarization. It’s a simple explanation, and makes a lot of sense.
Why is it then, than when I look at a screen with two polarized glasses, one at an angle from the other, the image does not dim in the overlapping region, when it does in the glass closer to my eyes?
In: 3
The screen itself has a polarised filter so you are encountering the three-filter paradox. It’s a quantum mechanical effect: https://youtu.be/zcqZHYo7ONs
In a nutshell:
The photons do not have an underlying “true” polarity. If they did, you would rightfully expect holding your second pair of glasses at 45 degrees to cancel *more* light than just your one pair of glasses.
Instead, the photons have a *probability* to cross each polarizing filter, depending on the orientation of the last polarization they went through. When passing from the screen (polarized one way) through your one pair of glasses (polarized the other way) the photons have a very low probability of crossing. However, when you introduce another filter at 45 degrees there’s a much higher likelihood that the polarized light from the screen will pass through it AND there’s a higher likelihood that the light from the 45 degree filter will pass through your first pair of glasses.
This adds up so that filter A, B, and C let through more light together than if you just had A and C.
Adding more filters turned incrementally between one another will effectively cancel out the polarization effect. Essentially, each filter serves as a rung on a ladder or a step on a staircase – going from the bottom directly to the top is almost impossible, but if you have a step in the middle it becomes much easier to get up.
Yes, this is very counter-intuitive – like a lot of quantum phenomena.
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