A tuning fork struck once rings pure and long. But if you shake the fork itself while it sounds, the tone wavers and dies out quickly. Something similar happens to electrons in any piece of matter. Atoms in a lattice never stay put: thermal vibrations keep them jittering. These jitters disrupt the synchronized quantum dance of electrons, and in a metal, you get the familiar electrical resistance.
The authors of the work showed how to calculate this process from first principles, without artificial fitting parameters. They took a method that tracks electrons over time and added the effect of the jittering lattice, as if the tuning fork were placed on a vibrating table. In metals, from a single “snapshot” of random atomic displacements, a decay law naturally emerges, resembling friction in a fluid. And in transparent dielectrics, the same jitter surprisingly does not spoil the picture: high harmonics (very pure shades of emission) come out sharp, without blurring.
The key trick is to rescale from a large fragment of the lattice down to a single unit cell. It turns out that the decay is governed mainly by how the occupation of electronic levels changes (the diagonal of the density matrix), rather than by the damping of off-diagonal “connections.” This is like a choir where singers don't so much lose hearing of each other as simply move from one part to another, and the overall sound changes. This approach, for the first time, allows realistic spectra and conductivities to be obtained directly from simulation without fitted lifetimes.
In copper at room temperature, atoms oscillate with an amplitude of about 5% of the distance between them, as if a violin string were constantly vibrating on its own, even without a bow.