Tom Jonard on Quantum Mechanics #3

Physical Reality is non-local.

Locality is the idea that effects are restricted in time and space, i.e. localized.

There is an old joke I like that does, "Time is nature's way of keeping everything from happening all at once."  Well all joking aside space-time is now thought to separate objects and events somewhat.  This was not always the case.  Newton thought that gravity propogated instantaneously.  Light was thought to do the same before the middle of the 19th century.  Einstein did not discover the speed of light but set it as a general speed limit for signals and processes.  In doing so he basically set limits on how events in one part of the universe can effect those in another.  Parts of the universe whose light hasn't had time to travel to us can never effect us.

I was tempted to discuss non-local effects under the failure of classical of reality but I chose not to becuase locality is more a physicist's notion than a common sense one and therefore deserves special treatment.  Common sense is out to lunch on this one -- a lot of people believe in non-local effects.  At least 50% of what is known as parapsychology describes what can only be termed non-local effects.  So many people believe these things that it is pointless to try and describe as the "common sense" that effects are only local.  Having said this I should point out that because QM allows non-local effects does not mean that it supports parasphychology in any way.  (And neither do I.)

Protons and electrons behave something like spinning balls of charge (as revealed by their deflection in a magnetic field).  However unlike the spinning of a ball particle spin can have only 2 orientations -- call them up and down.  Exactly half of all protons have either up or down orientation when their spin is measured.  Measure one of these groups (say all the down electrons) by turning the measuring apparatus 1/4 turn so that up and down become left and right and the result is again split 50/50.  (Now the really odd thing is that if you then measure one of these groups (say left) with the apparatus again oriented up and down you will find they are once again split 50/50!)  The spin orientation of particles (that have not been measured before in the same orientation) appears to be random.  Which means that any time you measure the spin of any particle it has of 50/50 chance of being either up or down.

It is possible to create two protons such that their spins are somehow entangled -- no matter how far the two particles are separated.  If you measure the spin of one of the two protons you may find that it is up.  If you do and then you measure the spin of the other you will find that it is down!  But the spin of any one proton is entirely random.  The same must be true even of each of our pair of entangled protons.  So their spins cannot be "fixed" at their creation.  It must be that measuring the spin of one of these protons somehow determines the spin of the other.  The measurments can be made far enough apart that no signal could travel from one proton to the other and still respect the speed of light speed limit.  So however one proton "determines" the spin of the other it is both non-local and non-causal.

Two entangled protons seem to form a single system which is spread over the distance between them in space-time however large that may be.  This suggests interesting possibilities (if only we knew what they were).  One question raised is whether distant parts of the universe are connected non-locally and what this would mean.  This is possible because according to the Big Bang theory of Cosmology everything in the universe, every particle and quantum of energy, was once in the same place at the same time -- in the begining.

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Created June 2, 2001, 
© 2001, Thomas A. Jonard