Heliophage


The wonder of KamLAND

[The unpublished pilot article — and something of a manifesto, looking back — for my  Music of Science columns ]

Science is more wonderful for the way it works than for the things it talks about

One of the reasons people like to read about the sciences is for the “sense of wonder” science writing can evoke, a vision of order and explication in the universe on scales far beyond the everyday. The neutrino is peculiarly well adapted to this sort of rhetoric, which may be why, 30 years on, I can still remember the station platform on which I was sitting when I read the magazine article by Isaac Asimov which first told me of  their elusive contributions to cosmology.

For a long time only observable as a mysterious absence of energy and momentum in the lab, neutrinos are now known to outnumber all the other known particles in the universe at all; spectacular detectors in deep caverns, or entombed in antarctic ice, monitor the revelatory stream of neutrinos from the core of the sun, and listen for the neutrino screams of distant supernovae. Obviously, this is wonderful stuff.

But not to John Updike.  In his poem “Cosmic Gall”, Updike rhapsodises the spooky ability of neutrinos by the trillion to pass though everyday matter “like dustmaids down a drafty hall”, in ways that seem designed to provide just the amazement science writers strive for. Then he pulls the reader up sharp.

                                      Like tall
and painless guillotines, they fall
Down through our heads into the grass.
At night, they enter at Nepal
and pierce the lover and his lass
From underneath the bed — you call
It wonderful; I call it crass.

However exotic and ethereal neutrinos may be, they are, in the end, just stuff, unimbued with any value or wonder of their own. Unsensed matter; but mere matter, for all that.

He has a point. A lot of the wonder purportedly evoked by accounts of cosmology or the inner workings of the atom has a somewhat ersatz quality, with its  by-the-numbers evocation of Sagan-esque “billions and billions” reverence. At its worst this bleeds into an epistemological power grab based on utterly absurd assertions that understanding, say, where atoms come from forms a necessary part of understanding humanity’s place in the scheme of things. If the “real” answer to the question “where do I come from?” is “stardust”, or some such, then that is also the real answer to “where did my shoe come from”; and an answer that does not distinguish between people and shoes is a pretty poor sort of an answer. Faced with a determined, unimpressed “so what?” — always a reasonable question, for all that it can seem unfair — such evocations of the sense of wonder shrivel to bitter husks.

Yet a good neutrino story can still inspire. Take the recent results from KamLAND, a detector which sits in a repurposed mine under Mt Ikenoyma, in Japan. KamLAND was designed to study neutrinos emitted as part of normal operations by nuclear reactors in Japan and in South Korea; neutrinos go through subtle transformations as they travel, and seeing what the reactor neutrinos looked like after tens or hundreds of kilometres offered a good way of illuminating those subtleties.

Unfortunately, in July 2007 an earthquake shut down the Kashiwazaki-Kariwa nuclear plant, which being both large and nearby provided a great many of KamLAND’s neutrinos. This made the original aim harder to realise — but made it easier to see if the detector could pick up neutrinos from a much larger, much less intense source: the body of the Earth. The Earth contains a lot of radioactive elements, which is one of the reasons why its depths are hot (the other reason is that when you build a planet a lot of heat gets baked in at the beginning, and takes billions of years to seep out).

This summer [ie, that of 2012] KamLAND announced that, of the countless trillions of neutrinos passing through it, it had identified about 100 that seemed very unlikely to come from anywhere but the uranium and thorium in the depths of the earth. That allowed the physicists to calculate that the earth is producing radioactive heat at a rate somewhere between 10 terawatts and 30 terawatts. Human civilisation, by way of comparison, uses a bit more than 10TW, most of it from fossil fuels, ever less of it from Japanese nuclear plants, which have proved rather too vulnerable to the forces that move the earth’s tectonic plates around — forces powered, in part, by the heat given off by the reactions that also produced KamLAND’s neutrinos. The next task is to better define the amount of radioactive heating, which may in turn provide insights into how much more vigorous tectonic motions were in the earth’s deep past.

There is, I think, real wonder here. But it does not lie in the elusive stuff of the neutrinos. It lies in the way faint signs of their passing are elaborated into new knowledge by people making measurements and finessing grants and rethinking experiments and reengineering mineshafts, people bringing together insights from particle physics and astrophysics and the history of the earth. Neutrinos are indeed mere matter. But how people use them to weave webs of ever richer, more complex, more widespread understanding of the world? That is wonderful.

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