Re: TECH: Quantum Head Job

From: Anders Sandberg (
Date: Wed Oct 10 2001 - 04:23:32 MDT

On Wed, Oct 10, 2001 at 02:07:31AM -0400, wrote:
> Quantum communications?
> Isn't that process you describe similar in many respects to "ansible"
> communication (Ursula LeGuin ref.)?? If I recall correctly, two particles are
> given identical properties and then moved apart great distances. Then by
> modulating the spin (or other quantum) characteristics of one of the
> particles, it affects the twin exactly the same, regardless of distance, and
> hence a communication device independent of the speed of light or relative
> distance. Can anyone expand on this or tell me if I am off base in this
> subject? I am by far no expert, just a big scifi fan!

This is roughly the idea. What LeGuin (and a lot of other authors) did
was to assume that you could send information through these coupled
particles. What really happens is that two particles are created that
are 'entangled': the spin (or some other property) of one is related to
the spin of the other. So when you measure the spin of one, you will get
a definite result (which is entirely random) - and if you measure the
other and then compare the results you will find that they match,
despite each measurement being essentially a random coin-flip. The
problem is that you can't change the other particle on the other end by
doing stuff to the particle at the near end, and the shared information
is just a random number (good for crypto, though).

Anders Sandberg                                      Towards Ascension!                  
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y

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