From: joedees@bellsouth.net
Date: Mon Jan 28 2002 - 01:34:40 MST
On 28 Jan 2002 at 2:10, L' Ermit wrote:
> <snip>
> [Joe Dees 2*] This may apply on the quantum level, but it obviously does not
> apply on the macro level at which i destroyed my sand-painting. Heisenberg's
> Uncertainty principle states that the information we may simultaneously gain
> about a particle's position and momentum cannot exceed a certain multiple of
> the terms. More momentum info. means less position info., and verse-vice-a,
> and this has to do with the empirical limits to which matter/energy can be
> pushed to investigate itself. It was not, as you stated above, about spin,
> which does not change, but
> about position and momentum, which are both changed by the influence of the
> measuring light. I see no problem in ascertaining spin and then performing
> measurements that give one momentum and/or positional info, with the
> heisenbergian constraints that these will be different than they were before
> the spin check, and can not be measured to a degree of precision beyond the
> Heisenberg quotient.
> <snap>
>
> [Hermit 2] The momentum of a particle is a function of the velocity and spin
> (color) and it definitely applies even when we deal with such mundane issues
> as high speed fiber-optic links and indeed we rely upon it when we use
> quantum encryption to secure information from interception on such links. We
> [i]know[/i] that particles evaporate to prevent us from learning this degree
> of information about them - for a trivial and well-known example refer e.g.
> Bell's [aka Cambridge] experiment.
>
> [Hermit 2] Spin, as you (correctly) observed, does not change. Thus having
> determined the spin, we cannot discover the location (within limits) - at
> any time thereafter - for that particle. If the information about the
> knowledge of the spin were not preserved, there would be no way for this to
> be the case.
>
But particles with the same spin may have differing velocities, and
therefore differnet momentums. i do not see how discovering an
unchanging property can militate against discerning info ablout a
changeable property in the way that what we can discover about one of
two changeable properties, position and momentum (or even, say,
velocity), can, through the disruptive expenditure of interacting photons,
limit what we may learn about the other.
>
> Regards
>
> Hermit
>
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