Experiment with faster-than-light "spooky" quantum effect at 18km | Hacker News Reader

Experiment with faster-than-light "spooky" quantum effect at 18km

physorg.com

5 pointsmojuba3 comments

There's an old 1997 article that explains this kind of experiments and their possible applications in a bit more detail:

http://www.cebaf.gov/news/internet/1997/spooky.html

I never got how this is supposed to be "spooky". To me it is common sense. To whit:

If a spin 1 particle (say, a photon) is "tweaked" by adding energy to it in some way, like say, being in the presence of a strong magnetic field, there is a chance it could briefly decay into two spin 1/2 particles (say an electron and an anti-electron). If the electron flies over to village A and is measured to have an "up" spin, and the anti-electron flies over to village B, if the electron had been measured to have an "up" spin in village A, why then naturally it should come as no surprise that the anti-electron in village B will be measured to have a "down" spin, due to conservation of spin laws. Spin 1 is decomposible into two spin 1/2 particles, so 1/2(electron) + 1/2(anti-electron)=1(photon). The spin can be up or down, not both, so if one particle has "up" spin, the other necessarily has "down" spin.

I have never understood why this is all supposed to be so "spooky". It is just simple common sense based on known conservation laws. Spin is conserved. If a spin 1 particle decays into two particles, and one is "up spin 1/2" then by necessity, not by any kind of "spookiness" but by basic necessity, the other particle will be "down spin 1/2".

Conservation laws are not "spooky". They are high school physics. So I really don't understand sensationalist articles like this, other than to try to get a "reaction" from the ill-informed.

It is getting spookier with experiments where each photon, say, hits a semi-opaque mirror and chooses a path randomly. The Geneva experiment was doing precisely that:

You start with an ultraviolet photon and split it into two photons. One goes one way and the other goes another way, both to identical interferometers. Entering its own interferometer, each photon must make a random decision as to whether it will travel a long pathway through the device or a short one. Then you look for a correlation between the pathways taken by the photons in their respective interferometers.

If the timing between the photons is exactly adjusted, each twin seems to know what the other is doing and matches its choice of pathway to coincide with that of its distant partner. (upd)

From http://www.cebaf.gov/news/internet/1997/spooky.html

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