R: Heisenberg uncertainty principle for macroscopic objects

[Paolo Cavallo <ton0621@IPERBOLE.BOLOGNA.IT>]

----- Original Message -----
From: Margaret Mazzolini <mmazzolini@SWIN.EDU.AU>
To: <PHYS-L@LISTS.NAU.EDU>
Sent: Friday, December 17, 1999 9:52 AM
Subject: Heisenberg uncertainty principle for macroscopic objects


> It's more years than I care to count since I studied (or taught)
quantum
> mechanics, so I need a bit of help with a discussion I am having ... I
> had thought that the standard popular science type discussion of
> Heisenberg's uncertainty principle, where it is claimed that there is
a
> ridiculously small but non-zero probability that an elephant could
> quantum-tunnel through a wall, was falacious because the uncertainty
> principle doesn't apply to a macroscopic, incoherent assembly of
> particles like an elephant. Am I wrong?

Some months ago I read a beatiful but difficult book by Roland Omnes,
_Understanding Quantum Mechanics_. I'm not sure I understood the whole
argument! But I would answer (following Omnes) that:
1. _There is_ a ridiculously small probability for tunnelling of
macroscopic object - in general, for superposition effects in the
macroscopic world.
2. Effects are even smaller because of decoherence of phase on a very
large number of particles; decoherence is a very efficient and rapid
process.
3. The physical meaning of ridiculously small probabilities is
controversial and perhaps there is none: events associated with such
small probabilities must be assumed as never occurring.

Forgive my bad English. I'm from the wide area audience of PHYS-L
outside North America. In the recent controversy, I vote with
neo-Luddites, being myself a tech fan.

Best regards,

Paolo Cavallo - ITALY