I am a heretic. There, I've said it. My heresy? I don't believe that quantum computers can ever work.
I've been a cryptographer for over 20 years and for all that time we've been told that sooner or later someone would build a quantum computer that would factor large numbers easily, making our current systems useless.
However, despite enormous amounts of money spent by research councils and government agencies, the things are stuck at three qubits. Factoring 15 is easy; 35 seems too hard. A Canadian company has started selling computers they claim are quantum; scientists from Google and NASA said they couldn't observe any quantum speed-up.
Recently, the UK government decided to take £200m from the science budget and devote it to found a string of new "quantum hubs". That might be a bad sign; ministerial blessing is often the last rites for a failing idea.
So will one more heave get us there, or is it all a waste of time?
An answer is suggested by the beautiful bouncing droplet experiments of Yves Couder, which started ten years ago.
He found that if you vibrate a tray of oil vertically at 4g and 30Hz, then droplets will bounce indefinitely on the oil and will even move about and interact with each other, displaying many of the phemonena of quantum mechanics. The droplets show single-slit and double-slit diffraction, tunnelling, Anderson localisation and quantised orbits. Perhaps, with a big enough oil tray, we could even implement a quantum computer using oil drops – but it would just be an analogue computer, so you couldn't expect any magical speed-up.
Could the droplet experiments be trying to tell us something about physics more generally? Mainstream physicists used to believe that matter and the forces that act on it were probably waves in an underlying ether, but the supporters of a wave theory of matter (notably Einstein, Lorentz and de Broglie) were out-argued at a 1926 conference in Belgium by the Young Turks who were just inventing quantum mechanics, such as Bohr, Heisenberg, Schrödinger and Dirac, whose view became the new orthodoxy.