The Science of Discworld IV Judgement Da - By Terry Pratchett, Ian Stewart Page 0,68

July 2012) a prominent climate change sceptic. In an analysis aimed at refuting claimed evidence of man-made global warming, the Project (funded by groups that support lobbying to resist action on climate change) made a fresh analysis of historical data on the Earth’s temperature over the last two hundred and fifty years. In the event, the study was entirely in line with, and strengthened, the existing evidence in favour of man-made global warming. The analysis showed that during that period, the Earth’s average land temperature increased by 1.5°C. Nearly two thirds of that rise occurred in the last fifty years.

Muller promptlyfn1 announced that his previous concerns about possible errors of data collection and analysis had proved unfounded. ‘Last year,’ he said, ‘I concluded that global warming was real and that the prior estimates of the rate of warming were correct. I’m now going a step further: humans are almost entirely the cause.’

That’s the difference between scepticism and denial.

There are two big philosophical problems about laws of nature. What are they? Where do they come from?

To complicate matters, the phrase itself can mean several different things. The philosopher Thomas Hobbes, who published Leviathan in 1651, proposed essentially God-given laws: ‘The first law of nature is that every man ought to endeavour peace, as far as he has hope of obtaining it’ – which determined what humankind should do. Another usage was that of John Locke, an early Fellow of the Royal Society, who cheerfully assumed that God had ruled against slavery: ‘The state of nature has a law of nature to govern it, which obliges every one: and reason, which is that law, teaches all mankind, who will but consult it, that being all equal and independent, no one ought to harm another in his life, health, liberty, or possessions.’ Fine: consult reason and produce a system with liberty for all. That’s all right to start with, perhaps. But then you must make exceptions: for witches, of course; or for children caught stealing bread; or for malefactors in general. For a given value of ‘mal’.

Laws of nature in these senses were much nearer to human laws than is our common usage today, physical law. Examples are the law of gravity and Ohm’s law about the relation between voltage, current and resistance in electrical circuits. This meaning seems much closer to ‘how things work’, and it will be our starting point.

In The Nature of Physical Law, Richard Feynman wrote that in order to discover a law of nature, we start with a hypothesis, like Newton’s theory of gravitational attraction. Then we do some calculations, to see if examples fit our hypothesis. If all goes well, we call it a theory and try it out on many other examples. To the extent that these examples get wider and wider – from the famous applefn2 to the Moon, to planetary orbits, then to the discovery that large heavy spheres attract each other very slightly in the laboratory, and that galaxies seem to have gravitational interactions with each other over vast distances – we can then elevate the theory to the status of a law.

That brings us back to the Large Hadron Collider and its dramatic discovery of the Higgs boson, a long-sought fundamental particle that sorts out the masses of the other sixteen particles in the ‘standard model’ of particle physics. What was once wild surmise has now become respectable orthodoxy, and the standard model has now taken a giant leap towards becoming a law of nature. However, it hasn’t yet attained that status, because the current state of knowledge leaves some alternatives open.

At the end of 2011, if you were an optimist, the Higgs was barely visible, a statistically insignificant bump on a graph at an energy of about 125 GeV (billion electronvolts). By the middle of 2012, the same bump had achieved five-sigma significance, meaning that the chance that it was spurious was less than one in two million. On 4 July 2012 CERN, the European laboratory that administers and runs the LHC, announced the existence of the Higgs.

Well, a Higgs. Higgs-like. Sort of Higgsy. (A theory called super-symmetry, currently popular among mathematical physicists, predicts at least five Higgses. Maybe this is just the first.) The observations did fit the predicted behaviour of the Higgs, a specific theoretical construct, but some key properties of the real particle have not yet been measured. No one can be certain that those will fit too, until suitable data have been collected. But now the particle