Monday, March 27, 2017

Do you believe in miracles?

Tristan Casabianca has kindly drawn my attention to an article he published last year which discussed the case for the authenticity of the Turin Shroud – by which I mean the claim that it is not just an artifact made during the period traditionally ascribed to the life of Jesus Christ but that it was the cloth used to wrap his body between the Crucifixion and the Resurrection. It’s a thoughtful and provocative article, but I don’t agree with very much of it.

I won’t go into the evidence for and against the age and provenance of the Shroud here (see here instead). Suffice to say, it is still hotly contested, with several researchers arguing that the radiocarbon dating performed in 1988, which placed the Shroud in the 13th-14th century, was flawed in some respect or another. I’ve not seen convincing evidence to doubt that very careful study, but I do wish it could be repeated. I also think however that, based on the evidence we have to date, it is very hard to understand how the image of a bearded man was formed on the linen. It doesn’t seem to be painted on. It’s deeply intriguing, tantalizing question. In the interests of full disclosure, I don’t believe that Jesus of Nazareth was the resurrected son of God, and I find it extremely unlikely that this artifact which turned up in 14th-century France had anything to do with him. But that is just my opinion.

Casabianca’s article is concerned not so much with weighing up the arguments as with establishing the framework within which we should think about them. In particular, he takes issue with my comment in a 2008 column in Nature Materials that “the two attributes central to the shroud’s alleged religious significance – that it wrapped the body of Jesus, and is of supernatural origin – are precisely those neither science nor history can ever prove.” Casabianca in effect asks: really? Ever?

And in this much he is right: saying such and such can never happen is, when viewed philosophically, a contentious claim. It amounts to ruling out possibilities that we can’t be sure of. To take an extreme example: we might say that time travel contravenes the laws of physics as we currently know them, but can we really state as a philosophical absolute that there will never come a time when it becomes possible to travel back in time and witness at first hand the events that took place in Palestine around 33 AD? It sounds absurd to suggest such a thing (outside of Michael Moorcock’s splendid Behold The Man), but I’m not sure that a philosopher would accept such a ban as a rigorous principle, any more than we could deny the possibility that any other feature of (or indeed all of) our current understanding of the universe is utterly mistaken. I’m not sure that it is terribly meaningful to leave such possibilities open, though – in general when we say something is impossible, we mean it seems impossible according to our current understanding of the universe, and what more could we expect of such a statement than that?

But Casabianca is more specific. He says that of course we do come to accept some historical truths, even about the distant past. We accept that tomb KV62 discovered by Howard Carter is the tomb of Tutankhamen. So why should we consider it a theoretical impossibility that we could prove the Shroud to be the burial shroud of Jesus of Nazareth (even setting aside for the moment his theological status)?

Again, philosophically I don’t see how one could exclude that theoretical possibility. But could it ever happen, given what we have to go on? There is a possibility that Jesus of Nazareth was a real person – this seems rather likely to me, though I have no deep knowledge of the matter. How might we link this object to him? We could perhaps establish that the previous dating study was wrong, and find good reason to believe the Shroud was in fact made within, say, the two centuries bracketing the time Jesus is supposed to have lived. We might find pretty compelling evidence that it came from the Middle East, perhaps being able to localize it fairly well to Palestine, and also that it was probably used in a burial ritual. To be clear, none of this has been by any means proved right now, and some evidence argues against it – but in principle it seems plausible that it could happen.

What then? Casabianca offers no line of argument that could link this artifact to the person of Christ. Might we find his name inscribed on it somewhere? No, we will not. Might we be able to link the style of weaving to one specific to Nazareth at that time? If that were possible, surely it would have been done already. It seems to me that you have to think about what might be demonstrated historically in the light of the capacity of the artifact in question to hold the information required for that demonstration. I see no reason to think that the Shroud contains the kind of evidence needed to make such a definitive identification of provenance, and more than a random pot excavated in Birmingham can be linked to a specific Iron Age Brummie beer maker named Noddy. Whether one can exclude that as a “theoretical philosophical possibility” seems pretty irrelevant.

Casabianca goes on to point out that several historians do claim that there is good evidence for concluding that the Turin Shroud is the authentic burial wrapping of Jesus. And indeed they do. But it seems a very curious argument to say that it is valid to make this historical claim simply because some people do so. Simply, such claims are made; whether there are, or can be, adequate grounds for making them is another matter entirely.

Casabianca certainly goes too far, though, when he proposes that “to explain the image on the Turin Shroud, the Resurrection hypothesis is the most likely of all the hypotheses, even when compared with natural hypotheses.” There are several problems with this suggestion.

Casabianca suggests that it follows from “a historiographical approach (the ‘Minimal Facts Approach’)”, which I take to be some kind of Occam’s razor position. Even if you buy the usefulness in Occam’s razor for determining the preferred solution to a body of facts (and there is no philosophical or empirical justification for it), the idea becomes meaningless here. There is no calculus that allows you to make a quantitative comparison between a natural explanation of events that stays within the laws of physics and a supernatural explanation that does not. Is the explanation “God did it” economical because you can say it in three very short words? Or (as I think) does the idea that the laws of physics can be arbitrarily suspended by some unknown entity in fact incur an overhead of hypotheticals compared to which the demands of string theory look like a trifling concession? However you look at it, to afford supernatural explanations so casually doesn’t look like careful reasoning to me.

That’s all the more so given that there are so many unknowns and uncertainties about the Shroud image in the first place. Reports are contradictory and confused, technical issues are challenged, and quite frankly it has been pretty much impossible to perform careful, well checked science on this material at all, since the Roman church has made access to the samples so restricted. Put simply, we can’t be sure what facts we are proposing to explain.

Coming back to Casabianca’s contention, could science ever prove that the Shroud is of supernatural origin? Of course, scientists will rightly say that this is a semantic contradiction, since if new knowledge shows that what we have previously considered “supernatural” actually happens, it then just becomes part of the “natural”. But the real issue here is whether there could ever be incontrovertible evidence that such things as God, resurrections and divinely ordained virgin births may happen. Casabianca mentions the example of the stars spontaneously forming the sentence “God exists” in the sky. I for one am happy to say that, were that to happen, I would be given pause. My hierarchy of explanations would then be something like: It is a hoax or weird illusion; I have lost my mind; it is aliens; it is the Supreme Being saying hello. I have no problem of principle with working my way through that progression. Yes, I’m open to persuasion that God exists and that Christ rose from the dead and left his imprint in a cloth through supernatural means. Which rational person could not be?

But to accept such things on the basis of fuzzy and often rather poor science conducted on a jealously guarded scrap of old linen doesn’t seem terribly logical to me. To believe that a supreme being would have set us a puzzle of this kind, so hazily written and laced with red herrings, false trails and contradictions, to test our faith seems positively perverse. You would almost need to believe that He had set out not to challenge science but to traduce it. Such a God can’t be logically excluded from existence, but He does not interest me.

Tuesday, January 24, 2017

Killing the cat?



This graphic from New Scientist, and conversations last night at the Science Museum, got me thinking. Using Schrödinger’s cat as a way to illustrate the differences between interpretations of quantum theory is a nice idea. But it suffers from the flaw that challenges the entire thought experiment. In order to be able to talk about the scenario in quantum terms, we need to be able to express it in quantum terms. But we can’t, because “live cat” and “dead cat” are not well-defined quantum states.

What, you can’t tell a live cat from a dead cat? Nonsense! Well yes, it is; but that’s not we’re asking here. What quantum property is it, exactly, that characterizes the superposition state, and that will enable you, unambiguously and in a single shot, to distinguish the two classical states? Live and dead are not quantum variables, and I’m not at all sure that they can be correlated even in principle with quantum variables that can be placed in superposition states.

Schrödinger’s point was not, in any case, that these are two different states of a macroscopic object, but that they are logically exclusive states. The paradox lies not in “two states at once”, but in “two contradictory states at once”. He was pointing not to “weird behaviour” predicted by quantum theory, but to logical paradoxes.

And this is why the Many Worlds Interpretation doesn’t resolve the problem. Yes, it looks as though it does: both outcomes are true! As New Scientist puts it here, “The universe splits. Your cat is dead, but in a parallel world it remains alive.” (Or, as Rowan Hooper points out, vice versa.) But wait: your cat? Who is you? Whose cat is it in the other world?

Brian Greene, in The Hidden Reality, tells us: that is you too! They are both you. Oh, so that sentence reads “Your cat is dead, but your cat remains alive.” Greene isn’t troubled by the fact that this is not how “you” works. But nevertheless, this is not how “you” works.

David Deutsch and Max Tegmark say, ah language! What should we trust more, language or maths? Contingent sounds, or timeless equations? But here language is articulating something that underpins maths, which is logic. Schrödinger realized that, but his point seems to be forgotten (by some). I don’t have time to go into it here (my forthcoming book will), but individual identity is a logical construct. You can’t wish it away with fantasies about “other yous”. I am trying to resist the topical urge to suggest that the Many Worlds interpretation offers us “alternative facts”, but that is terribly hard to do. So folks, the second option here is far more problematic than it looks.

What about the first? Let me say first of all that in neither the Copenhagen nor the Many Worlds interpretation is the cat “simultaneously alive and dead”. Not only is there no way of expressing that in quantum mechanics (at least, no one has articulated one), but in any event the proper statement of the situation is that “We can say nothing about the state of the cat, other than that live and dead are both possible outcomes of an observation”. That might sound like a pedantic distinction, but it will not be possible to make sense of quantum mechanics without it.

Now, I would hesitate to call the Copenhagen interpretation the “standard” interpretation, since there is no consensus, nor even a majority view, about which is the correct interpretation of quantum mechanics, at least among those who think about foundational issues. What’s more, the “Copenhagen interpretation” is not a single thing: Heisenberg expressed it differently to Bohr, and Wheeler had his own view too, as did others. However, I think Bohr would have said something like this: after observation, we have acquired now information that has changed our view of the cat’s condition (assuming it can be expressed in quantum terms at all) from an indeterminate to a determinate one. Some Copenhagenists, such as Pascual Jordan, spoke of this in causative terms: our observations produce the results. In that view, it seems acceptable to say that “Your measurement killed the cat” (although since we cannot say that it was previously alive, we might need to say more strictly “Your measurement elicited a dead cat”). But I’m not at all sure that Bohr would have seen causation at work in the measurement, as if “wavefunction reduction” is a physical effect that kills the cat. (That’s really the third, “objective collapse” option, which is given the least problematic representation here.) I think Bohr might have said something along the lines that “Observation allows us to speak about the classical state of the cat. And look, it is a dead one!”

So, which way will you vote? Bear in mind, however, that there are other option available, not all of them mutually exclusive. And that you won’t be able to prove that you’re right, of course.