The Science of Discworld IV

an inflationary universe by a factor of one googolplex – ten to the power ten to the power one hundred. So an explanation not involving inflation, although it requires an extraordinarily unlikely initial state, is massively more plausible than an explanation that does involve inflation.
    A few mavericks have been devising alternatives to the standard model all along, but now mainstream cosmologists are also having to rethink the theory. There is no shortage of ideas. In some, there is no Big Bang; instead, there is a kind of revival of the steady-state universe, in which a suitably clumpy distribution of matter can survive for hundreds of billions of years, perhaps indefinitely. The redshift is not caused by expansion, but by gravity. Dark matter is not needed to explain rotation curves: instead, relativistic inertial dragging, in which rotating matter carries space along with it, might do the job.
    Perhaps more radical is the proposal that either our theory of gravity, or our theory of motion, need to be modified slightly. In 2012 the particle physicist and Nobel prize-winner Martinus Veltman, when asked ‘Will super-symmetry explain dark matter?’, replied: ‘Of course it won’t. People have been looking for this stuff since the 1980s and are just talking ballyhoo. Isn’t it more likely that we don’t understand gravity all that well? Astrophysicists believe in Einstein’s theory of gravity with a fervour that is unbelievable. Do you know how much of Einstein’s theory has been tested at the distances of galaxies where we “see” dark matter? None of it.’ fn2
    The best known proposal here is MOND, Modified Newtonian Dynamics, suggested in 1983 by Mordehai Milgrom. The basic idea is that Newton’s second law of motion may not be valid for very small accelerations, so that acceleration is not proportional to the force ofgravity when that force is very weak. There is a tendency to assume that MOND is the only alternative to general relativity; the correct statement is that it is the most extensively explored one. Robert Caldwell, fn3 in a special issue of a Royal Society journal devoted to cosmological tests of general relativity, wrote: ‘To date, it appears entirely reasonable that the observations may be explained by new laws of gravitation.’ In the same issue Ruth Durrer fn4 pointed out that the evidence for dark energy is weak: ‘Our single indication for the existence of dark energy comes from distance measurements and their relation to redshift.’ The rest of the evidence, she says, merely establishes that distances estimated by redshift measurements are larger than those expected from the standard cosmological model. Something unexpected is going on, but it might not be dark energy.
    Our confidence that we know how our universe began is being shaken. Some modified version of the Big Bang may well be correct – but then again, maybe not. When new evidence comes along, scientists change their minds.
    Though perhaps not quite yet.
    fn1 Actually, Lemaître’s doesn’t, not in its original formulation. Instead of a point singularity at a finite time in the past, it has a hyperspherical singularity infinitely far in the past.
    fn2 Martinus Veltman, coming to terms with the Higgs,
Nature
490 (2012) S10-S11.
    fn3 Robert R. Caldwell, A gravitational puzzle,
Philosophical Transactions of the Royal Society of London
A (2011) 369 , 4998-5002.
    fn4 Ruth Durrer, What do we really know about dark energy?
Philosophical Transactions of the Royal Society of London
A (2011) 369 , 5102-5114.

NINETEEN
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DOES GOD WIGGLE HIS FINGERS?

    Marjorie had been lost in her furious thoughts for an unmeasured length of time which, as it turned out, was about five minutes. These were broken into by Mustrum Ridcully, who had given her an appropriate nudge. She shook herself, stood up straight (which she generally did anyway) and said brightly, ‘This is going to be round two; yes?’
    Ponder Stibbons hurried over, detected a certain look in her eye, and said, ‘Really, Miss Daw, please leave it all to the Archchancellors. After all, it is
our
business.’
    Marjorie smiled: not the smile she had for a good book well read and catalogued and subsequently handed to the appropriate reader – a process she thought of as carrying
the flame
. fn1
    The chamber was buzzing as people poured in, chattering. Lord Vetinari, apparently refreshed, was ascending the stairs to the podium. The gavel dropped like thunder and, almost