In 1957 the Chinese language-American theoretical physicist TD (Tsung-Dao) Lee, who has died aged 97, turned the second-youngest scientist to win a Nobel prize. He did this with one other Chinese language émigré to the US, Chen Ning Yang, who was 4 years older than he was. They turned Nobel laureates for physics for work that overthrew the extensively accepted “parity legal guidelines” – that the forces performing on the elemental subatomic particles are symmetric between left and proper. Within the standard description, they overthrew the idea of “mirror symmetry”.
Earlier than Lee and Yang questioned this basic precept, it was believed that the mirror picture of any course of shows a sequence of occasions that would equally properly happen in the actual world. In impact, there is no such thing as a method to inform whether or not you might be viewing an actual occasion or its mirror picture. This was properly established within the acquainted case of electromagnetic forces and the robust pressure that binds atomic nuclei. For instance, the mirror picture of an electrically charged particle being steered in a single route by electrical or magnetic forces reveals a sequence that’s realised in the actual world just by reversing the route of the mentioned forces.
Within the mid-50s, physicists have been puzzled by the behaviour of what have been generally known as unusual particles. Amongst these have been two generally known as “tau” and “theta”, with an identical plenty, lifetimes, and different properties however for one: the taus decayed into two particles (pions) whereas the thetas decayed to a few. In quantum concept the mathematical description of an excellent or odd variety of pions on this scenario differs; within the jargon, the quantum state has respectively “even-parity” or “odd-parity”. The assumption that parity is preserved implied that the tau and theta should be totally different particles, the tau having even-parity and the theta, odd.
At a convention in April 1956, Yang mentioned the tau-theta puzzle. The proof was mounting that the tau and theta have been in actuality one and the identical, but the legislation of conservation of parity contradicted that. With hindsight, the reply was there in plain sight – tau and theta are the identical and parity conservation isn’t a basic reality. Nonetheless, the axiom of parity conservation, or mirror symmetry, was thought to be to date past query that within the ensuing debate solely Richard Feynman was ready to ask: “Does nature have a means of distinguishing proper or left handedness uniquely?”
Yang and Lee began poring over information and verified that whereas there was conclusive proof that mirror symmetry is sweet for electromagnetic and robust forces, the weak pressure liable for some types of radioactivity had not been sufficiently properly examined to both affirm or deny parity conservation. And it was this pressure that was liable for the decays of tau and theta. They raised the likelihood that the tau and theta are certainly however one, and that the decays to 2 or three are linked, by way of quantum discipline concept arguments, to a violation of mirror symmetry.
Their paper Query of Parity Violation in Weak Interactions was printed in October 1956 and took the physics group by storm. Amongst many sceptics was Wolfgang Pauli, who quipped: “I don’t consider that the Lord is a weak left-hander.”
Yang was based mostly on the Institute for Superior Examine at Princeton, New Jersey, and Lee at Columbia College, New York. Inside days, a colleague of Lee’s at Columbia, Chien-Shiung Wu, arrange an experiment through which she examined parity conservation in weak interactions following a template proposed of their paper. This concerned measuring the directional properties of the electrons emitted within the decays of radioactive cobalt-60.
This constructed on a key statement by Lee and Yang, that nuclei of cobalt-60 atoms carry angular momentum, which behaves in a different way from unusual momentum below mirror reflection. So, measure the correlation between the instructions – momenta – of the decay merchandise (electrons) and the angular momentum of the cobalt nucleus. If there may be any correlation, this may seem totally different in a mirror, and by implication parity be violated. The one means for parity symmetry to be true could be for there to be no correlation in any respect.
After a number of months of labor, the extremely delicate experiment proved conclusively that there’s a correlation and due to this fact parity symmetry isn’t a basic property. The information was sensational: the weak interplay cracks the mirror; nature can distinguish left from proper completely. This turned a founding property of at this time’s normal mannequin of particles and forces. Among the many many purposes of parity violation, spanning now seven many years, has been identification of the Higgs boson.
Born in Shanghai, TD was the third of six youngsters of Ming-Chang Chang and Tsing-Kong Lee, a service provider. After highschool in Shanghai, he studied physics at Chekiang (now Zhejiang) College (1943-44) and, later, on the Nationwide Southwest Related College in Kunming.
In 1946, he received a Chinese language authorities fellowship to do a PhD in the US. below the steerage of Enrico Fermi on the College of Chicago. After finishing this in 1950 he did postdoctoral work on the College of California, Berkeley, and the Institute for Superior Examine, Princeton, and in 1953 joined Columbia College as an assistant professor. Three years later, on the age of 29, he turned Columbia’s youngest ever full professor.
Lee printed a number of books on science, and along with the Nobel he received the Albert Einstein award in 1957. At a reception to mark his retirement from Columbia, in 2012, he in contrast his work to gardening: “You is probably not cultivating new species, however you may nonetheless preserve the outdated lovely issues occurring.”
In 1950 Lee married Jeannette Hui-Chun Chin. She died in 1996, and he’s survived by his sons, James and Stephen, a brother and a sister.
