The real universe is both gravitational and thermodynamic. In some contexts, the thermodynamic model is more appropriate and thermodynamics provides a good model. In other contexts, a gravitational model is more appropriate. There are yet other contexts: molecular chemistry involves different types of forces again. It is a mistake to shoehorn all natural phenomena into the thermodynamic approximation or the gravitic approximation. It is especially dubious to expect both thermodynamic and gravitic approximations to work in the same context, when the way they respond to coarse-graining is diametrically opposite.
See? It's simple. Not magical at all ...
Perhaps it's a good idea to sum up our thinking here.
The 'laws' of thermodynamics, especially the celebrated Second Law, are statistically valid models of nature in a particular set of contexts. They are not universally valid truths about the universe, as the clumping of gravity demonstrates. It even seems plausible that a suitable measure of gravitational complexity, like thermodynamic entropy but different, might one day be defined -call it 'gravtropy', say. Then we might be able to deduce, mathematically, a 'second law of gravities', stating that the gravtropy of a gravitic system increases with time. For example, gravtropy might perhaps be the fractal dimension ('degree of intricacy') of the system.
Even though coarse-graining works in opposite ways for these two types of system, both 'second laws' -thermodynamic and gravitic -would correspond rather well to our own universe. The reason is that both laws are formulated to correspond to what we actually observe in our own universe. Nevertheless, despite this apparent concurrence, the two laws would apply to drastically different physical systems: one to gases, the other to systems of particles moving under gravity.
With these two examples of the misuse of information-theoretic and associated thermodynamic principles behind us, we can turn to the intriguing suggestion that the universe is made from information.
Ridcully suspected that Ponder Stibbons would invoke 'quantum' to explain anything really bizarre, like the disappearance of the Shell Midden People. The quantum world is bizarre, and this kind of invocation is always tempting. In an attempt to make sense of the quantum universe, several physicists have suggested founding all quantum phenomena (that is, everything) on the concept of information. John Archibald Wheeler coined the phrase 'It from Bit' to capture this idea. Briefly, every quantum object is characterised by a finite number of states. The spin of an electron, for instance, can either be up or down, a binary choice. The state of the universe is therefore a huge list of ups and downs and more sophisticated quantities of the same general kind: a very long binary message.
So far, this is a clever and (it turns out) useful way to formalise the mathematics of the quantum world. The next step is more controversial. All that really matters is that message, that list of bits.
And what is a message? Information. Conclusion: the real stuff of the universe is raw information. Everything else is made from it according to quantum principles. Ponder would approve.
Information thereby takes its place in a small pantheon of similar concepts -velocity, energy, momentum -that have made the transition from convenient mathematical fiction to reality.
Physicists like to convert their technically most useful mathematical concepts into real things: like Discworld, they reify the abstract. It does no physical harm to 'project' the mathematics back into the universe like this, but it may do philosophical harm if you take the result literally.
Thanks to a similar process, for example, entirely sane physicists today insist that our universe is merely one of trillions that coexist in a quantum superposition. In one of them you left your house this morning and were hit by a meteorite; in the one in which you're reading this book, that didn't happen. 'Oh, yes,' they urge: 'those other universes really do exist. We can do experiments to prove it.'
Not so.
Consistency with an experimental result is not a proof, not even a demonstration, that an explanation is valid. The 'many-worlds' concept, as it is called, is an interpretation of the experiments, within its own framework. But any experiment has many interpretations, not all of which can be 'how the universe really does it'. For example, all experiments can be interpreted as
'God made that happen', but those selfsame physicists would reject their experiment as a proof of the existence of God. In that they are correct: it's just one interpretation. But then, so are a trillion coexisting universes.
Quantum states do superpose. Quantum universes can also superpose. But separating them out into classical worlds in which real-life people do real-life things, and saying that those superpose, is nonsense. There isn't a quantum physicist anywhere in the world that can write down the quantum-mechanical description of a person. How, then, can they claim that their experiment
(usually done with a couple of electrons or photons) 'proves' that an alternate you was hit by a meteorite in another universe?
'Information' began its existence as a human construct, a concept that described certain processes in communication. This was 'bit from it', the abstraction of a metaphor from reality, rather than 'it from bit', the reconstruction of reality from the metaphor. The metaphor of information has since been extended far beyond its original bounds, often unwisely. Reifying information into the basic substance of the universe is probably even more unwise. Mathematically, it probably does no harm, but Reification Can Damage Your Philosophy.
LETTER FROM LANCRE
Granny Weatherwax, known to all and not least to herself as Discworld's most competent witch, was gathering wood in the forests of Lancre, high in the mountains and far from any university at all.
Wood gathering was a task fraught with danger for an old lady so attractive to narrativium. It was quite hard these days, when gathering firewood, to avoid third sons of kings, young swineherds seeking their destiny and others whose unfolding adventure demanded that they be kind to an old lady who would with a certainty turn out to be a witch, thus proving that smug virtue is its own reward.
There is only a limited number of times even a kindly disposed person wishes to be carried across a stream that they had, in fact, not particularly desired to cross. These days, she kept a pocket full of small stones and pine cones to discourage that kind of thing.
She heard the soft sound of hooves behind her and turned with a pine cone raised.
'I warn you, I'm fed up with you lads always on the ear'ole for three wishes—' she began.
Shawn Ogg, astride his official donkey, waved his hands desperately.52
'It's me, Mistress Weatherwax! I wish you'd stop doing this!' 'See?' said Granny. 'You ain't havin'
another two!' 'No, no, I've just come up to deliver this for you ... ' Shawn waved quite a thick wad of paper. 'What is it?'
'Tis a clacks for you, Mistress Weatherwax! It's only the third one we've ever had!' Shawn beamed at the thought of being so close to the cutting edge of technology.
'What's one of them things?' Granny demanded. 'It's like a letter that's taken to bits and sent through the air,' said Sean.
'By them towers I keep flyin' into?' 'That's right, Mistress Weatherwax.'
'They move 'em around at night, you know,' said Granny. She took the paper.
'Er ... I don't think they do ...' Shawn ventured. 'Oh, so I don't know how to fly a broomstick right, do I?' said Granny, her eyes glinting.