Re: [Phys-L] causality

[John Denker <jsd@av8n.com>]

On 2/7/19 2:36 PM, bernard cleyet wrote:

> Somewhere I read that the K-K transform implies causality — the
> argument was (even more so now) beyond my intelligence.

My thesis advisor loved to ask about that on oral exams
for admission to candidacy.  Woe betide the chump who
thought the Kramers-Kronig relations were evidence for
causality.  The follow-up question was:

  What requires us to integrate around the contour
  clockwise instead of counterclockwise?

I once knew a guy who wrote his PhD thesis on a slightly
fancier version of this topic, about time-reversibility
(and therefore non-causality) in the fundamental equations
of quantum mechanics:
  http://files.untiredwithloving.org/thesis.pdf