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**What is "passive locality"? Bell's Theorem.**

In a current thread about explaining Bell's theorem, the question of "passive locality" came up.

"Passive locality" was introduced by Nelson in 1986. After discussions with Bell he distinguished between "active" and "passive" locality, arguing that for classical realism only active locality is required. Apparently Bell's theorem needs both.

Regretfully I don't manage to understand what it means, let alone the consequences for a good understanding of Bell's Theorem. Even recent follow-up discussions don't make it clear to me...

Can anyone explain it in clear, simple English?

- Nelson's original paper:

http://onlinelibrary.wiley.com/doi/10.1111/j.1749-6632.1986.tb12456.x/abstract

- Recent follow-ups:

http://arxiv.org/abs/0807.3369 Annalen der Physik (Berlin) 18, No. 4, 231 (2009)

http://arxiv.org/abs/0910.4740 Annalen der Physik, 523: n/a. doi: 10.1002/andp.201010462

http://arxiv.org/abs/0910.5660

Harald