Re: wavelengths of macroscopic bodies

From: Neil (paradoxer_at_lykose.com)
Date: 08/16/04 

Date: 16 Aug 2004 13:56:03 -0400

"Charles J. Quarra" <disposablemailaccountfornews@yahoo.com.ar> wrote in message
news:bc979c06.0408091425.528ca2fa@posting.google.com...
>
>
> Hi,
>
> Frequently, in introductory quantum mechanics books the relation
> between wavelength-momentum is used uncospicuously for macroscopic
> objects, probably for didactic purposes, however i see a problem with
> that extrapolation: if one would go on and adding the momenta of the
> composite objects to obtain a "body-momenta", then one should ask if
> why that cant extrapolate to, for example, light beams (as the one you
> got on a laser). If there is a system in which one can fulfill the
> condition of coherent constructive propagation is in the laser light.
> A laser pulse has a lot more total momenta than its constitutive
> photons (each produced by an individual atom line) however one doesnt
> see this "total momenta wavelength" at
> work in the physics of these systems, at least nothing
> im aware.
>
> any insights about this?

I think a better way to put this is to borrow from Galileo. In criticizing the
Aristotelian physics, he asked: if bodies fall at a rate proportional to their
mass, then what would happen to two rocks tied together? Is the string
incidental (leaving the rocks falling at their individual rates), or does it
"count" to making the pair into a "single object?" Would it matter if we tied
them loosely, versus gluing the strings on, etc. The whole matter of what
constitutes a "single object" is revealed to be ambiguous, and suspect for
determining physical properties. *However*, this is exactly the dilemma for QM!
Think of it: if we define wavelength as per the mass "of a particle," what
happens in Galileo's case? It's hard to tie particles together, but why would
one "collection" (like a nucleus) behave as "an" object, and some other
association (positronium?) perhaps behave as two objects, with wavelengths
according to what should count as "one" object? How about an atom: why can't the
orbiting electrons show wavelength properties relevant to the individual masses
of electrons, as when atoms diffract through crystals, etc? I have heard some
discussion of this, but was never really satisfied. What does anyone know, and
what experiments have been done? What "individualization" of collections can be
found, under what criteria?

N. Bates