phonon:
Take what happens when you set a flame under a lump of table salt. The individual atoms all start rattling around a tad more enthusiastically, setting up waves of vibrations. In 1932, the Soviet physicist Igor Tamm realised he could treat these waves as particles, mathematically at least. He called them phonons.
Phonons have since become a staple, helping us for instance to understand processes such as superconductivity, in which electrons flow through a material with zero resistance, and opening the way for devices that turn heat into electricity (see “Five particles that don’t exist – yet could change our world“). Because they emerge from the movements of more traditional particles, phonons are called emergent particles or quasiparticles. “Phonons are not actually real,” says Jon Goff, a physicist at Royal Holloway, University of London. “They are really just a way of simplifying a very complicated problem.”
A mathematical construct, it seems. But then they jam this into my brain:
Phonons, magnons and the like exist in a kind of twilight world: useful to work out how things work, but doubtful as entities in their own right. But these half-existing particles aren’t even the half of it. Quasiparticles can exist, it turns out, even when nothing is there.
That discovery first came in 1947, with a seminal moment for the history of computing. William Shockley, a solid state physicist at Bell Labs in New Jersey, and his team were trying to perfect the transistor, an on-off switch for electrical current. They were using semiconductors, materials whose atoms are deficient in electrons. It had been known for a decade or so that this would create gaps of nothingness, like the empty square in a sliding puzzle. But no one thought these “holes” were anything more than the absence of an electron. Shockley proposed that the hole was actually a particle in its own right, something like an electron that carried positive charge.
Even when nothing is there. Roll that around in your head for a while.
(“Holes in reality”, Andrea Taroni, NewScientist, 10 September 2016, paywall)
