[PD] Feedback discussion

[Mathieu Bouchard]

On Wed, 16 Sep 2009, Chris McCormick wrote:

> On Tue, Sep 15, 2009 at 04:00:09PM -0400, Mathieu Bouchard wrote:
>> Instantaneousness is a myth. It does not exist in nature.
> I thought that at the moment it looks quite a lot like the collapse of a wave
> function of an electron being measured is instantaneous.

Damn, my sentence was too short. Yes, I agree that those events are as 
instantaneous as instantaneousness can be... but cause-effect 
relationships always take nonzero time... they can't be strung 
continuously in time. Eventually, between a chosen original cause and 
final effect, picking intermediate causes and effects will eventually come 
to an end, as you will find each event leading directly to another, each 
after a certain nonzero delay. Thus a feedback loop can only have a 
nonzero feedback time.

(but then, a number of things that we'd casually count as events don't 
count in this concept of physics, and thus we are free to imagine them as 
continuous as we like, or as non-existent as we like; e.g. a change in 
position doesn't count, a change in speed does).

I think that an event ("collapse") could also appear to have a duration, 
but only as an artifact of limited measurability (time-energy 
uncertainty), and I think that physicists prefer seeing events as 
instantaneous with unknown timing, but to make sure I'd have to ask them.

...

But there are surely tricky phenomena that can be thought of as both a 
feedback loop and not a feedback loop, in which case the appearance of 
instantaneous feedback would be a mirage due to the way of writing the 
math formulas...

  _ _ __ ___ _____ ________ _____________ _____________________ ...
| Mathieu Bouchard, Montréal, Québec. téléphone: +1.514.383.3801