Nobody has explained why we should worry about
the foundations of quantum mechanics better than John Bell:
...conventional formulations of quantum theory,
and of quantum field theory in particular, are unprofessionally vague and
ambiguous. Professional theoretical physicists ought to be able to do
better. Bohm has shown us a way.
J.S. BELL
Speakable and Unspeakable in Quantum Mechanics
It would seem that the theory [quantum mechanics] is exclusively concerned
about "results
of measurement", and has nothing to say about anything else. What
exactly qualifies some physical systems to play the role of
"measurer"? Was the wavefunction of the world waiting to jump for
thousands of millions of years until a single-celled living creature
appeared? Or did it have to wait a little longer, for some better
qualified system ... with a Ph.D.? If the theory is to apply to
anything but highly idealized laboratory operations, are we not
obliged to admit that more or less "measurement-like" processes are
going on more or less all the time, more or less everywhere. Do we
not have jumping then all the time?
The first charge against "measurement", in the fundamental axioms of
quantum mechanics, is that it anchors the shifty split of the world
into "system" and "apparatus". A second charge is that the word
comes loaded with meaning from everyday life, meaning which is
entirely inappropriate in the quantum context. When it is said that
something is "measured" it is difficult not to think of the result
as referring to some preexisting property of the object in
question. This is to disregard Bohr's insistence that in
quantum phenomena the apparatus as well as the system is essentially
involved. If it were not so, how could we understand, for example,
that ``measurement'' of a component of ``angular momentum" ... in
an arbitrarily chosen direction ... yields one of a discrete set
of values? When one forgets the role of the apparatus, as the word
``measurement'' makes all too likely, one despairs of ordinary
logic ... hence "quantum logic". When one remembers the role of the
apparatus, ordinary logic is just fine.
In other contexts, physicists have been able to take words from
ordinary language and use them as technical terms with no great harm
done. Take for example the ``strangeness'', "charm", and "beauty"
of elementary particle physics. No one is taken in by this "baby
talk". ... Would that it were so with "measurement". But in fact
the word has had such a damaging effect on the discussion, that I
think it should now be banned altogether in quantum mechanics.