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 of gravity 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 Durrerfn4 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
* * *
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 immediately, so did the noise.
‘Ladies and gentlemen, I ask the wizards of Unseen University to defend their ownership of the Round World, although it appears to me that stewardship might be a better and more appropriate term. It also occurs to me that I haven’t even seen this curious thing. It is apparently reasonably small, so I will have it on my podium right now, so we can all visualise what is at the centre of today’s little escapade. It will be brought to me at once.’
Ponder Stibbons was dispatched in haste to the university and returned, breathless, carrying the padded baize bag. Against a background of laughter, giggles and outright tittering, he gently put the contents of the bag on a tripod in front of the Patrician, who himself seemed somewhat amused by what had been placed before him.
There was a twinkle in his eye as he said, ‘Excuse me if I seek for clarity, gentlemen, but could this indeed be a living world with a population of millions? Over to you, Archchancellor. I must say I am all agog!’
‘In fact, your Lordship, I will delegate this job firstly to Ponder Stibbons, head of the Inadvisably Applied Magical facility. What he does not know about quantum – yes, I am afraid we must