To respond to the SEED article at slightly greater length… We can start by trying to get a grip on what they mean by “realism”. Zeilinger himself says “to give up realism about the moon, that’s ridiculous”. So the so-called rejection of realism doesn’t involve anything like the abandonment of belief in reality (whatever that could mean), just an abandonment of belief in the reality of some things. Calling that a rejection of realism may be rhetorical excess; it is as if I believed there was a cake in the cupboard, discovered there wasn’t, and as a result proclaimed that realism about the cake had been falsified.
However, Zeilinger says, “on the quantum level we do have to give up realism”. So what does that mean? We believe in things made of particles (like the moon), but not the particles themselves? We believe that big things, like the moon, have properties, but that small ones, like particles, do not? In the end, it seems we are to abandon the belief that small things have properties before we look. No, wait, we are to abandon the belief that small things have the properties we see them to have before we looked. Well, what if they had some other property before we looked, and then the act of looking (measuring, more precisely) perturbed them into a new state with new properties? That would seem to be entirely consistent with what they describe, but what does that have to do with the ‘falsification of realism’?
Do I sound exasperated? Pardon me. It is just that there is so, so much nonsense propagated by physicists in the name of physics, and then further passed on by credulous people who are in no position to make an independent judgement about what they’ve been hearing. The situation is something like this: We have quantum mechanics, which works experimentally. Traditionally, the quantum states (wavefunctions) are not regarded as the fundamental reality of things, they’re just a quasi-statistical description which happens to work. So, on the one hand, we have a variety of attempts to explain what the fundamental reality might actually be, and on the other hand, we have—complacency, basically. A frame of mind which is content to use QM as it is, apply it, extend it, but not to dig deeper. Returning to the attempts at a deeper explanation, we have, as SEED mentions, Bohm’s theory, which is a nonlocal theory. So long as quantum mechanics continues to work experimentally, Bohm’s theory will never be falsified, because it makes exactly the same predictions as quantum theory. On the other hand, Leggett apparently produced a nonlocal theory which does make slightly different predictions. Zeilinger’s group did the experiments, quantum mechanics was right, Leggett was wrong—and this is trumpeted as a falsification of realism on the quantum level, for absolutely no good reason that I can see. It is, I suppose, a falsification of the particular postulates that Leggett was trying to uphold, but calling this a falsification of realism is like saying that not finding the cake in the cupboard was a falsification of realism.
To respond to the SEED article at slightly greater length… We can start by trying to get a grip on what they mean by “realism”. Zeilinger himself says “to give up realism about the moon, that’s ridiculous”. So the so-called rejection of realism doesn’t involve anything like the abandonment of belief in reality (whatever that could mean), just an abandonment of belief in the reality of some things. Calling that a rejection of realism may be rhetorical excess; it is as if I believed there was a cake in the cupboard, discovered there wasn’t, and as a result proclaimed that realism about the cake had been falsified.
However, Zeilinger says, “on the quantum level we do have to give up realism”. So what does that mean? We believe in things made of particles (like the moon), but not the particles themselves? We believe that big things, like the moon, have properties, but that small ones, like particles, do not? In the end, it seems we are to abandon the belief that small things have properties before we look. No, wait, we are to abandon the belief that small things have the properties we see them to have before we looked. Well, what if they had some other property before we looked, and then the act of looking (measuring, more precisely) perturbed them into a new state with new properties? That would seem to be entirely consistent with what they describe, but what does that have to do with the ‘falsification of realism’?
Do I sound exasperated? Pardon me. It is just that there is so, so much nonsense propagated by physicists in the name of physics, and then further passed on by credulous people who are in no position to make an independent judgement about what they’ve been hearing. The situation is something like this: We have quantum mechanics, which works experimentally. Traditionally, the quantum states (wavefunctions) are not regarded as the fundamental reality of things, they’re just a quasi-statistical description which happens to work. So, on the one hand, we have a variety of attempts to explain what the fundamental reality might actually be, and on the other hand, we have—complacency, basically. A frame of mind which is content to use QM as it is, apply it, extend it, but not to dig deeper. Returning to the attempts at a deeper explanation, we have, as SEED mentions, Bohm’s theory, which is a nonlocal theory. So long as quantum mechanics continues to work experimentally, Bohm’s theory will never be falsified, because it makes exactly the same predictions as quantum theory. On the other hand, Leggett apparently produced a nonlocal theory which does make slightly different predictions. Zeilinger’s group did the experiments, quantum mechanics was right, Leggett was wrong—and this is trumpeted as a falsification of realism on the quantum level, for absolutely no good reason that I can see. It is, I suppose, a falsification of the particular postulates that Leggett was trying to uphold, but calling this a falsification of realism is like saying that not finding the cake in the cupboard was a falsification of realism.