Every time transistors shrink, they get closer to the point where they can shrink no further—for if the law continues on its merry way, transistors will be the size of individual silicon atoms within two decades.

More to the point, they have already shrunk to a size where every atom counts. Too few atoms can cause their insulation to break down, or allow current to leak to places it is not supposed to be because of a phenomenon called quantum tunnelling, in which electrons vanish spontaneously and reappear elsewhere. Too many atoms of the wrong sort, though, can be equally bad, interfering with a transistor’s conductivity. Engineers are therefore endeavouring to redesign transistors yet again, so that Dr Moore’s prediction can remain true a little longer.