SV: Capacity of the brain

Shmuel (Seymour J.) Metz nospam at nsf.gov.invalid
Fri Oct 22 13:44:51 EST 1999


Ignatios Souvatzis wrote:

> - You can't measure the state of a system without influcencing it.

Sounds good, but it's wrong, at least in QM. In QM if you perform the
same measurement twice in succession, the second time will not affect
the state. Of course, as a practical matter it's difficult to perform
the exact same measurement, but we're talking Physics here, not
Engineering. See P.A.M. Dirac's "Principles of Quantum Mechanics", 3rd
edition, for a lucid description; it's dated, but still considered to be
a useful reference.

> - Modern quantum theory predicts that this happens even if said photons
>   travel off in opposite directions, and the measurement is done at
>   seperated places! (In fact, doing this kind of measurements can tell
>   us whether an alternate quantum physics with hidden variables, leading
>   to more causality und thus looking less strange, is possible; which is
>   one of the reasons why this experiment was done!)

It's more complicated than that. The combination of Bell's Theorem and
the Aspect experiment tells us that you can't explain the observed
behavior of matter with a hidden variables theory that has local
causality. Hidden variables are not ruled out, but we're stuck with the
"spooky action at a distance" that Der Alter objected to.

Of course, there's no guaranty that nonsocial interactions will allow
transmission of superluminal signals.

-- 

Shmuel (Seymour J.) Metz
Reply to host nsf (dot) gov, user smetz



More information about the Neur-sci mailing list