Illustration of Tau

1971-1977 Tau

The book of science

Tom Sharp

Yung-su Tsai, Martin Lewis Perl particle physics Illustration of Tau


Electron, muon, and tau carry exactly the same charge, and the same spin, but have progressively larger masses and shorter lifetimes. Too bad making tau is not very practical, unless you have your own positron-electron accelerator.

Time dilation / length contraction

People wondered how muons and tau could penetrate solids as deep as they do, considering their ultra-short lifetimes; however, FitzGerald and Einstein had already explained length-contraction and time dilation. From its own point of view, a particle traveling near the speed of light sees great distances in a small span, and from our point of view, a particle traveling near the speed of light appears to age extremely slow.


Its energy has to go somewhere, so when a fast charged particle is decelerated or deflected, it emits “braking radiation”— like the noise of a crash landing.


For electron, e. For muon, the Greek μ (mu). For tau, the Greek τ short for τρίτον meaning “third”— (tau, rho, iota, tau, omicron, nu).

Like the tau particle, I am the third Frederick in my paternal line—my grandfather, Frederick Lee, whom I shall designate with the symbol “Λ” (Lambda), my father, Frederick James, otherwise Frederick “Ζ,” and me, Frederick “Τ.”

See also in The book of science:

Readings in wikipedia: