From: Hal Finney (hal@finney.org)
Date: Fri Sep 20 2002 - 14:43:16 MDT
Ross Finlayson wrote:
> It's like if we were standing next to each other a million light years
> away from a source of coherent light, each holding a [polarized] lens. If
> the photons go through one then they go through the other. Similarly, if
> we are each holding a lens at a given angle a couple million light years
> away from each other, if it goes through one it goes through the other,
> and if it doesn't go through one then it doesn't go through the other.
Actually it doesn't work like this. Coherent light is light where all
the photons have the same properties: the same wavelength, phase and
polarization.
See http://isaac.exploratorium.edu/~pauld/activities/Laser_light.html
for a description of some easy experiments to demonstrate these facts.
Light coming from a laser will have a particular polarization state;
let's suppose it is vertically polarized. Then if you pass it through
a slantwise oriented polarizer, half the photons will get through.
Each photon will independently have a 50% chance of making it. The result
for each photon is not the same as for all the others.
If we try your experiment, each of us sees a different photon from the
coherent light source. If our polarizers are oriented at the same angle,
then each photon has the same chance of getting through each polarizer,
but the result for any given photon is random. If some particular photon
gets through your polarizer it doesn't mean that there is a corresponding
one which is guaranteed to get through mine.
To get the "spooky action at a distance" you need a different kind of
photon, an entangled photon pair. In the entangled state, neither photon
individually has a well-defined polarization. But it is guaranteed that
the two photons, when measured, will be in a common polarization state.
In that case, if one gets through your polarizer then the paired photon
will get through mine at the same angle.
Hal
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