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| date | 2001-03-27:11:40 |
| Metaphysics |
Here's the difference between realism and reality for the specific experiment I described yesterday. Two polaroid filters are placed on either side of the calcium atom source, and they are set with an angle of zero between their transmission directions. Photons are detected coming from the source for a long enough time that we think 100000 pairs have been emitted, then one or both of the polaroids are rotated so that they have 10 degrees between their transmission directions and data are again accumulated, and so on.  If realism is true, then both photons in each pair must share a real common plane of polarization, and the number of pairs that have both photon detected looks like the curve shown: low at zero, peaking at around 30 degrees, and falling off again above, but never close to zero. This is because even if the polaroids are at 90 degrees to each other photons pairs whose common plane of polarization is anywhere in between zero and 90 degrees to the polaroids will still have a non-zero probability of transmission through both. Unfortunately for realism, reality does not conform to realist expectations. There's a sense in which realists should be heartened by this: reality in fact behaves so weirdly that there's no doubt at all that there is a reality out there, independent of us! No subjectivist could ever dream up such strange behavior--this is akin to Descartes' argument that external reality must exist because otherwise he would not be able to conceive of anything greater than himself. If reality were not this way I'm damned sure no one would have suggested it. Ergo, there is a mind-independent reality, and it is not pre-packaged into categories or natural kinds. The argument I've presented here is for a specific experiment, and uses a specific, naive realist model to predict in detail what the result of that experiment should be. Realists are open at this point to start singing and dancing around the problem by inventing bold hypotheses that posit some mysterious interaction between the polaroids, the atom, God, Athena and the Furies which will account for the results without giving up their cherished belief that things just are members of a particular category and just have particular universal properties or attributes independently of a knowing subject that categorizes them to be that way. The argument I've presented here is a concrete version of John Bell's much more general (but correspondingly more abstract and difficult for the non-physicist to appreciate) argument that shows that no realist account that does not assume there is an interaction between the widely separated photons can explain the data. That is, any realist account must say that once one photon interacts with a polaroid it must somehow influence the plane of polarization of the other photon to make the probability of detecting both photons dependent only on the angle between the polarizers. And to ensure angular momentum is conserved, this interaction must take place instantaneously, over arbitrarily large distances. My next task is to show why positing such an instantaneous interaction at a distance would be a bad move for a realist, and then to move on to a conceptualist view of this problem, jettisoning realist baggage as I go. This is a difficult journey to make, and perhaps too steep a hill to climb without first providing some more detailed conceptualist account of the more temperate climes of ordinary science. But nothing worthwhile was ever achieved by a person with merely reasonable goals. Before leaving the description of this experiment, let it be said that I'm intimately familiar with the issues surrounding experimental violations of Bell's Inequalities. I consider Aspect's "delayed choice" work to be definitive, and do not believe that any of the criticisms of it are sufficient to change it's conclusions. In particular, some critics have pointed out that the two photons are not emitted at precisely the same time, as there is an intermediate state between them. If anything, this should make the results even more mysterious to the realist, who has to posit how the detection of one photon can affect the properties of another that hasn't even been emitted yet! And of course, such cavils are in any case not relativistically invariant--there are frames in which the second photon is always emitted after the first. And other work using parametric down-conversion as the source of photon pairs has address these and other quibbles more directly. So for the purposes of this discussion I take it as given that reality is correctly described by quantum mechanics, because in an entirely ordinary sense, this is in fact the case. |
| Humans |
The claim is sometimes made that the free press has nothing to gain from being biased. The difficulty is that in a society where getting on for half of my income is disposed of by people who work for the government and over whom I have no effective means of control, people who work for the government have a lot more power than I do to respond to--that is reward--bias in the press than I have power to respond negatively to it. So yesterday I noticed two different headlines in two major Canadian newspapers: the first saying that the Prime Minister was refusing to release some personal financial documents related to a minor bit of graft and influence peddling he is alleged to have committed some years ago, the second saying that the Prime Minister wanted to release said documents. Guess which paper is going to get rewarded by whom? Both headlines were true, in the sense that the PM has refused to release the documents on the grounds that doing to would be to expand the scope of parliamentary intrusion into the Prime Minister's personal dealings in a way that would have a negative effect on the PM's autonomy into the far future. It's not just his private affairs that are at issue, but the private affairs of all who come after him. This is a reasonable argument, and he has been given reasonable advice to refuse on this basis. It's also true that he is on record as saying that if was just a matter of his own privacy, he'd turn over the documents. So both headlines are correct. But no one would be likely to claim that both don't reflect the bias of their respective papers. This isn't a rant against the yellow press, however. It's just an observation that all thought requires selection of what's important, and that depends on your beliefs and values. This is the way humans are, and one of the things that makes giving a plurality of views a hearing necessary to the workings of a free society. |