The bite of the HUP is that it leads to a mathematical contradiction if you assume that a particle has a determinable position and a determinable velocity at the same time. This is not, repeat not, an epistelogical problem. It is not that we cannot _know_ both the position and the velocity. The principle, which can be mathemetically proven, states that the particle doesn't _have_ both a position and a velocity simultaneously, and that we determine which one it has when we make the observation of one or the other. This is not the only instance of mind-dependence in QM, either.
And yes, the problem is that practice is the test of truth: QM is as verifified as any scientific theory in history. It allows predictions that are highly reliable down to multiple decimal points. So yes, the theory is almost certainly true. And the most natural interpretations of it are the the fundamental structure of the world, the matter that is in motion, depends on what we think. That's what bites. Practical tests of our best theories suggest that idealism is true. Not as a philosophical interpretation, but as a physical theory. No dount QM will be incorporated and perhaps partly superceded by some Grand Unified Field Theory. But no one expects the HUP to be changed. Like the micro- and macro-determinism that people once thought was necessarily true, but which QM has also refuted, it plays havoc with standard notions of realism. And it's a pretty slender reed to say that maybe, who knows, our current best theory of the world that is well-confirmed and highly predictive will be replaced bt one that confirms Lenin's metaphysical prejudices. I wouldn't count on it. --- Charles Brown <[EMAIL PROTECTED]> wrote: > Andie: > 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. > > ^^^^^^ > CB: Wasn't the term "materialism" used before > "realism" for this concept ? > Doesn't this debate originate with Feuerbach, Marx > and Engels ? Or does > Bacon refer to "realism" or "materialism" ? > > > Yes, this is the crux of the dispute, but QM's claim > to have proven same is > suspect, no ? How do they prove that there is "no > there there" ? Also, this > is not an issue that would be proved > "mathematically". That would be like a > thought experiment, i.e. remaining in the realm of > ideas, which is to say an > idealist method. Idealism is what is in dispute. > > How can QM prove that there will not ever arise a > "theory" that demonstrates > that, ahha, the particle _does_ have position and > velocity independently of > the effort to measure them ? It can't. > > Not having a "determinate" position or velocity > means _we_ can't determine > it . Us not being able to determine it is at best a > sort of Kantian > unknowable thing-in-itself. But future science may > discover a way for us to > determine it. Heisenberg and others can't foreclose > that future > possibility. > > > > ^^^^^^ > > 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. > > ^^^^^ > CB: But surely Schrodinger's cat is a thought > experiment. Nothing like this > has ever actually been done with a cat, no ? > > Surely they are not claiming that the cat only comes > into existence upon the > choice of a slot. > > > Maybe we bring in Heidegger: why does the cat exist > rather than not exist > :>)? > > ^^^^^^ > > 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. > > ^^^^^ > CB: Predictive practice _is_ the test of reality. > > > > 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 > > ^^^^^^ > > CB: Not being able to determine something is not the > same thing as its just > being an idea rather than objective or outside of > our minds. It doesn't > follow from the Heisenberg principle -that the act > of measuring one aspect > of the particle forecloses simultaneously measuring > another aspect - that > the particle only exists in the mind of the > measureer. All that results from > that is a sort of half-Kantian, unknowable "half" of > the thing-in-itself. > And how can anybody foreclose the possibility of > future scientific theory > overcoming this limitation ? > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
