Re: cheating (Re: Understanding the HUP)


"Autymn D. C." <lysdexia@xxxxxxxxxxxxx> wrote in message
news:1124914404.426382.250690@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Ranando King wrote:
> > I agree that too much importance is lain on the HUP. Do to this
indulgance,
> > many misunderstandings proliferate among scientists and hobbyists on
issues
> > involving the HUP. However, the HUP is not bypassable. No matter how
> > accurate equipment becomes, there will always be a limit to how precise
a
> > measurement can be when certain other measurements are made. That
doesn't
> > mean that you cannot infer some things based on the information you can
get,
> > but it does limit your ability to prove those inferences directly in
> > measurement.
>
> Do -> Due
>
> Cheat the HUP:
> http://groups.yahoo.com/group/The_Discipline_Group/message/12206
> http://www.npl.washington.edu/AV/altvw53.html
>
> -Aut
>

No offense Autymn, but little is to be gained from your constant attempts at
being an English teacher in this newsgroup. All but too often I've seen you
post little more than a grammar correction and an insult. My understanding
of the English language as used in the US is comprehensive enough to ensure
that I get my point across whether or not my statements include typos. So
please, refrain from playing editor and stick to the discussion of physics.

Now as for your question...

> Say there's an atom or particle in a box, and roams around like a gas.
> If you bounce a photon off it, you'll know where it is but not where it's
> going because the photon either contributes or steals momentum from the
> particle, depending on both their momenta. So, what if we send photons
> in the box from every direction, or at least from a certain number of
> axes, so that the radiation pressure on the particle is uniform in every
> direction? Would we be able to find its position and momentum to
> arbitrary degrees?

The simple answer to your question is no. The first thing that you have to
consider is that a photon is not an actual particle per se, but rather the
simple physics notation for a single cycle of energy released as an EM wave.
When an actual particle, preferably one that participates in EM
interactions, especially an electron, encounters a photon, it absorbs the
photon.

So, if multiple photons met a particle, the photons themselves having a net
0 momentum, indeed there would be no net momentum change in the encountered
particle. HOWEVER, in order to do such a thing, the photons would have to be
targeted and timed in such a way that they meet the particle simultaneously.
Any time delay at all between the encounters and the particle will have
incurred a change in momentum.

To do such a precise targeting in an experiment would require knowledge of
where the particle is and where it is going to a high degree of accuracy,
i.e. precise knowledge of position and momentum simultaneously. So, in order
to "cheat the HUP", you would need knowledge that violates the HUP.

R.


.

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