The Science of Discworld IV

that in a re-run of history, our ‘law’ for quantum systems really could have turned out very different, giving Schrödinger no reason to introduce his puzzling cat.
    Whether our current physical laws are special and unique, or a different set would work just as well, there is something more to say about laws in general. And about their exceptions, and especially about transcending them. By that word we don’t mean that the laws are disobeyed. We mean that they become irrelevant because of a change in context, like the way a jumbo jet transcends gravity by using air-flow past its wings.
    We’ll take Ohm’s law as an example, because it appears to be simple.
    Matter is basically of two kinds with regard to electricity: either it’s an insulator, or it’s a conductor. If it’s a conductor, Ohm’s law applies: current equals voltage divided by resistance. So, for fixed resistance, a greater current requires a greater voltage. However, resistance need not be fixed, and this possibility lies behind some natural anomalies, like the way that lightning changes the insulating gas of the atmosphere into a conducting ionised path for the lightning strike, or ball lightning, which essentially folds up into the surface of a sphere. Being anomalies, these phenomena are automatically interesting. We can also play tricks with variable conductors of electricity, starting with thermionic valves (vacuum tubes) in the 1920s and continuing with semiconductors like transistors. The computer industry is built upon this trick.
    The discovery of superconducting alloys –
no
electrical resistance – near zero Absolute temperature was a very interesting anomaly, which, as new alloys have been found that exhibit no resistance athigher and higher temperatures, promises to give us a whole new energy technology. The interesting items are those that
differ
from the Ohm’s law picture: the witches, the spacecraft.
    Ohm’s law is intimately involved with stories about electricity distribution. By describing these problems, and their solutions, we can show how leaving the law to ‘work its will’, but changing the context, can completely alter the situation. From there we can go from Feynman’s position – that laws determine the context as well as the content of natural events – to a more progressive view.
    Electricity distribution to households is made difficult by the resistance of the cables, which causes a lot of electrical energy to be dissipated from the transmission lines as heat. Ohm’s law implies that the same amount of power can be transmitted, with lower losses, by making the voltage higher and the current lower. However, this would supply homes with very high-voltage electricity, and accidents would be fatal.
    The trick is to use alternating current, back and forth fifty or sixty times a second. Transformers can change the voltage of alternating current, so it can be high for transmission and then reduced to not-very-lethal values when it gets to our homes. Today we could stick to direct current, using modern electronics to change the voltage, but that option wasn’t available when the distribution system was being created. We’ve now invested so much in alternating current systems that we can’t easily change them, even if that turned out to be a good idea. This trick dodges the Ohm’s law problem of resistance, hence energy loss. Even now, more than a third of the energy can be lost in long transmission lines, but that’s still far more efficient than the 70% loss delivered by the low-voltage direct current systems of the 1920s. By changing the parameters, by going to low-current high-voltage alternating current, we can to some extent change the rules.
    Too many physicists seem to have a mind-set that considers physics to be
all of reality
, simply because it is concerned with all the basic structure of matter. In
The Character of Physical Law
, Feynman says:
    The same kinds of atoms appear to be in living creatures as in non-living creatures (
sic
); frogs are made of the same ‘goup’ as rocks, only in different arrangements. So that makes our problems simpler; we have nothing but atoms, all the same, everywhere.
    In the same book, he says:
    Probably the most powerful single assumption that contributes most to the progress of biology is the assumption that everything animals do the atoms can do, that the things that are seen in the biological world are the results of the behaviour of physical and chemical