lester welch

In the example usually given to illustrate entanglement - two
correlated photons - if one of the photons has a second interaction
producing more particles/photons and then a third,, etc. one would
have a multitude of entangled particles. The measurement of any one
wouold determine the state of the others. It the original two photons
were created early in the life of the universe could not the entire
universe be entangled? Any measurement would determine the state of
the universe - the "wave function" of the universe would "collapse."

oh no

Thus spake Lester Welch <lester.welch@gmail.com>


The photons in the usual example are observable. For a photon to produce
more particles it must be a) off mass shell, b) extremely energetic.
This kind of thing is seen in high energy scattering, but not in EPR
type set-ups.

If you have n entangled particles and measure one particle the remaining
n-1 particles will still be entangled. In general you will need n-1
measurements to complete disentangle an entangled state of n particles.

The point you make about the early universe is, in essence, a good one
and I do not know why it is overlooked by cosmologists. Except of course
that we do not, as yet, have a mathematical theory with which to
properly describe it. The horizon problem shows that the early universe
can be regarded as large number of causally disconnected regions. This
is a problem because if they are causally disconnected there is no
reason that they should be all the same - there should be random
differences which are not observed.

Usually people try to get round the horizon problem by invoking
"inflation", which amounts to a claim that the universe was expanding
faster than itself and should be clear nonsense. In fact there is no
reason to invoke inflation if one realises that some form of quantum
description of an initial entangled state will be needed, and that such
a condition leads naturally to the observed homogeneity and isotropy.

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

If you have 2 pairs of entangled particles and the first one of the
first pair interracts with a the first one of the the second pair the
second ones of the two pairs become entangled while the first remain
unentangled. This is called swapping of entanglement. I think you can
not entangle new particles without loosing entanglement in the middle.

There is also a process called sudden death of entanglement.

By the way entanglement is very fragile and if the ent.paticles do not
propagate in optic fibers or vacuum the entanglement is lost soon.

Ilian