David M. writes (Feb. 22):
"I think quantum theory tells us that
when the rock is not being measured
it is spreading out as a mere probability
of being a rock, so not so static or present?"
=====
Jorge: Yes David, quantum theory says something of the
sort. It uses some cute equations called wave
functions which relate to a particle by saying that
the probability of finding a particle, within a given
volume element, is proportional to the size of that
volume element.
If we were to call a rock a particle, the size of
the particle (rock) is so large that, for all
practical purposes, the said probability is as closest
to 'absolute certainty' as one could get.
As 'absolutely certain' of winning all the prizes of a
(honest) lottery if we buy all the tickets.
Put in other words: quantum mechanics would consider
said rock as being pretty much static and/or present
in a given portion of space. In other words there is
no detectable 'spreading out of the probability'
regarding the position of the rock.
Since, for the case of a rock, Quantum Mechanics
and Classical (Newtonian) Mechanics give exactly the
same description, we don't use Quantum Mechanics for
rocks. Contrary to widespread opinion, scientists much
prefer simple equations to complicated ones; no point
of using a hefty wave function if an alternative
concise, simple, equation would give exactly the same
results.
You are probably aware of this, but for the
benefit of others that keep bringing-in Q.T., it might
be convenient to say here that the above
considerations hold not only for a rock but for a
grain of sand and even for a particle a millionth's
times smaller than a grain of sand. Meaning that, for
all practical purposes in our daily lives we can
blissfully forget about quantum mechanics and rely
entirely on old Newton's.
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