The basic problem that QM poses for realsim is this. Realism normally commits us to the idea that there is a world, in this case physical, that is independent of our minds. QM seem to tell us in lots of ways that the world is not independent of our minds. For example, Heisenberg's uncdertainty principle tells us that we cannot determine, simultaneously, the position and velocity of a particle.This "cannot determine" is not epistemological, it's not that the particle has a position and a velocity, but we can't know them them both at the same time. It is possible to prove mathematically that it doesn't have a determiate position and/or velocity unless we choose to measure one or the other, and if we choose to measure position (say), it hasn't got a determinate velocity. QM is full of this sort of thing. For example, there is Schrodinger's cat, about whom there is no fact of the matter whether it is alive or dead until we choose which slit to let the photons pass through.
It's a _real_ problem for realism. And it is worse than it looks, because this isn't just microlevel stuff. QM is true at every level -- we just can't observe Q effect at the level of mid-sized objects. Mostly. I gather engineers can do things with them. But the real point is that the natural interpretation of QM is antirealistic. Bohr's "Copenhagen" interpretation is basically logical positivistic, this stuff is just (as John Wheeler told me in freshman physics when my mind was boggling) a bunch of equations. Not a description of the "real" world, just a predictive device. There are various attempts to get out of the paradoxes. My own favorite is the Many Worlds hypothesis, suggested by my adoption of David Lewis' possible worlds semantics, to which the MWH bears analogies. On this view, all the quantum possibilities are real existing worlds -- we happen to live in one of them, but the others, for example, the one where we chose to measure the velocity rather than the position of the particle, are equally real. A popular science writer named Paul Davies has a good nontechnical presentation of this idea in a book called Other Worlds. I used to know the maths for this stuff, it's gone the way of my Latin (which went much longer ago). But trust me, and ask them as still knows the maths, Daniel Davies, for example, there is no easy out. jks --- Charles Brown <[EMAIL PROTECTED]> wrote: > http://www-theory.chem.washington.edu/~trstedl/quantum/quantum.html > What is the importance of quantum mechanics? > > The following are among the most important things > which quantum mechanics > can describe while classical physics cannot: > > * Discreteness of energy > <http://www-theory.chem.washington.edu/~trstedl/quantum/quantum.html#Discret > eness> > * The wave-particle duality of light and > matter > <http://www-theory.chem.washington.edu/~trstedl/quantum/quantum.html#Duality > > > * Quantum tunneling > <http://www-theory.chem.washington.edu/~trstedl/quantum/quantum.html#Tunneli > ng> > * The Heisenberg uncertainty principle > <http://www-theory.chem.washington.edu/~trstedl/quantum/quantum.html#Heisenb > erg> > * Spin of a particle > <http://www-theory.chem.washington.edu/~trstedl/quantum/quantum.html#Spin> > > > ^^^^^^^^ > > CB: None of these pose a problem for materialism in > the sense of holding to > the existence of objective reality. Being limited to > a probable measurement > of a phenomenon doesn't contradict the concept of > objective reality. See > Engels's discussion of chance and necessity in > _Anti-Duhring_ within a > framework of materialist conception. > > The test of theory is practice. Quantum mechanics > allows "us" to do more, > make personal computers for example, in practice. > This is a confirmation of > materialism, not a refutation of it. > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
