Register to reply

Realism in the vein of EPR and Bell

by DrChinese
Tags: bell, realism, vein
Share this thread:
DrChinese
#19
Jan3-13, 01:09 PM
Sci Advisor
PF Gold
DrChinese's Avatar
P: 5,378
Quote Quote by mbd View Post
DrChinese, I am very sorry for having gone out of my way to create an extremely simple, no math necessary, self-evident, example of a system that can violate Bell's Inequality.
The "counter-example" fails as I have detailed. And it is hardly self-evident. You may as well say it is self-evident that 1=0. I have commented on each of your references. None of these have anything whatsoever to do with your personal local realistic theories.

Last chance: retract or provide the specifics.
DrChinese
#20
Jan3-13, 01:17 PM
Sci Advisor
PF Gold
DrChinese's Avatar
P: 5,378
Quote Quote by jk22 View Post
In QM treatment of EPRB it is seen from the onset that the measurement disturbs the system since suppose we measure 1st particle with + then
psi_before equals ((+-)-(-+))/sqrt2 and
psi_after equals* (+-)
since both differ we conclude there was a disturbance.

Hence we cannot use the EPR criterion of existence of elem. of phys. reality.
You have made a good point, and I am sure Bohr would agree with you! In QM the system is disturbed.

However, if you ASSUME that there was no such disturbance (as EPR does), then the criterion applies. (Of course there was something of a circular nature to the EPR argument.) They say:

"On the other hand, since at the time of measurement the two systems no longer interact, no real change can take place in the second system in consequence of anything that may be done to the first system."
mbd
#21
Jan3-13, 02:05 PM
P: 53
Quote Quote by DrChinese View Post
You have made a good point, and I am sure Bohr would agree with you! In QM the system is disturbed.

However, if you ASSUME that there was no such disturbance (as EPR does), then the criterion applies. (Of course there was something of a circular nature to the EPR argument.) They say:

"On the other hand, since at the time of measurement the two systems no longer interact, no real change can take place in the second system in consequence of anything that may be done to the first system."
There is nothing circular about the EPR argument. It is a standard proof by contradiction.

The assumption is that special relativity applies to all physical phenomena. With this assumption, measuring the first cannot change the second. QM, though, predicts a change to the second. So, either special relativity does not exclude "spooky action" or QM is an incomplete theory.
DrChinese
#22
Jan3-13, 02:35 PM
Sci Advisor
PF Gold
DrChinese's Avatar
P: 5,378
Quote Quote by mbd View Post
There is nothing circular about the EPR argument. It is a standard proof by contradiction.

The assumption is that special relativity applies to all physical phenomena. With this assumption, measuring the first cannot change the second. QM, though, predicts a change to the second. So, either special relativity does not exclude "spooky action" or QM is an incomplete theory.
Wrong again! EPR says that if their assumptions are correct, then QM is incomplete. That is circular reasoning because their assumptions will be contested by reasonable people. For an assumption to work, it must be agreeable to someone contesting (ie agreeable to both sides).

EPR assumes no action at a distance - such as QM's application of the HUP non-locally - and concludes QM is incomplete. That conclusion is not generally accepted and never has been (although there were a number of scientists who accepted this early on).

What was accepted from EPR is that IF QM is complete, then the reality of a particle here is dependent on the nature of a measurement there. This is now generally accepted as being the case, although that assessment is somewhat more recent (post Bell).
berkeman
#23
Jan3-13, 03:44 PM
Mentor
berkeman's Avatar
P: 41,041
Thread closed for Moderation...


Register to reply

Related Discussions
Bell's Inequality: Must we ditch locality, realism... or something else? Quantum Physics 49
Bell's theorem: Local realism v. counterfactual determinism Quantum Physics 0
Blood pressure in the vein Introductory Physics Homework 2
Mathematical expression of Bell's local realism Math & Science Software 79
Local Realism After Bell Quantum Physics 24