Chien-Shiung Wu’s exclusion from the list of Nobel laureates in 1957 remains one of the greatest injustices in the history of physics. Particle physicist Jack Steinberger called it the “biggest mistake in the Nobel committee’s history”, Tsung-Dao Lee and Chen Ning Yang – the recipients of the 1957 prize – thanked her in their acceptance speech and later pleaded with the Nobel Committee to acknowledge her work, and even J. Robert Oppenheimer publically stated that it should have been awarded to her. So who was Chien-Shiung Wu, and why haven’t more people heard of her? 

1950s, Columbia University. It was an exciting time in particle physics, with more and more new research and discoveries happening every day in the emerging field of high-energy physics. Scientists were working on identifying and fitting together all the pieces in what would become the Standard Model, a jigsaw puzzle of a table that classifies all known elementary particles in our universe. The Standard Model, or “SM”, covers three out of four of what are called “fundamental forces” – these are named electromagnetic, weak, and strong interactions (the fourth, gravity, is absent). Up until 1956 it was believed that a concept called the conservation of parity held true for all particle interactions. The idea of parity is essentially that if everything in our world was flipped, the behaviour of everything in that mirror image world would be identical, except for the reversal of left and right – as an example, the hands on clocks would instead move anticlockwise, but except for this direction change, their motion would still be identical to the clockwise clocks. This notion that every “clock” has its “anticlock” quickly became an important idea when it came to attempts to identify particles in the SM, this symmetry between two identical but opposite particles.

Enter: Lee and Yang. Both theorists, they began to realise that although experiments had been conducted that confirmed parity was indeed conserved for both electromagnetic and strong particle interactions, there was no experimental data to suggest that this was the case for weak particle interactions. In fact, there was no experimental data at all, as scientists up until that point had just assumed that because it was true for two out of the three interactions, that it must also be true in the third case. Yang and Lee mathematically theorised that might not actually be the case, and came up with an idea for how this could be experimentally proven in a laboratory setting. This was groundbreaking work that had the potential to reshape how the laws of particle physics were understood; however, there was one problem – neither Yang or Lee were experimentalists. 

Experimentally verifying a result such as this in a lab setting is an exact and demanding science. Things that work out precisely and tidily on paper oftentimes rarely translate to the real world in such a neat fashion. The obvious choice of experimentalist to oversee and run this was Chien-Shiung Wu, who was renowned for her expertise and precision, and so it was that Yang and Lee asked her to conduct this experiment for them. It was imperative that the lab conditions and apparatus setup be of the highest standard of experimental accuracy possible, especially in this proposed experiment. Wu’s method ended up involving, amongst other things, using liquid gases to cool radioactive cobalt to a temperature below -150ºC while also applying a constant uniform magnetic field in order to align the spin axes of the atomic nuclei! – a massive experimental undertaking.

Wu’s experiment proved that parity was indeed not conserved under weak particle interactions, as Yang and Lee had proposed. Idea became action became proof became Nobel prize. In their acceptance speeches Yang and Lee thanked Wu, and attempted to nominate her for a future prize – in fact, attempts to nominate her were made a further seven times until 1966, at which point the Nobel committee stopped publishing publically the lists of nominees – however the fact remains that only for Wu’s diligent and exact laboratory work the theory of parity conservation would have never been disproven beyond any doubt. There would have been no Nobel prize for Yang and Lee, and their prediction would have remained just that, a prediction. 

It seems incredible to think that the list of laureates for the Nobel Prize in Physics, that pinnacle of recognition of human achievement, has at times been fallible, but this is what Wu’s story tells us. Wu herself wrote about this experience in a letter, saying: “Although I did not do research just for the prize, it still hurts me a lot that my work was overlooked for certain reasons”.  It is more important than ever that, when we celebrate the discoveries and work of our Nobel laureates throughout history, we also learn about those – like Chien-Shiung Wu – whose work was never officially recognised, and take the time to applaud and celebrate their crucial contributions and scientific achievements that underpin our understanding of the world and the field of physics today.

You can read more about Chien-Shiung Wu’s life and work in this article (written by her granddaughter):

Image source: By Science Service (Smithsonian Institution) – Restored by Adam Cuerden – Flickr: Chien-shiung Wu (1912-1997), No restrictions,

Sarah Joyce | JS TP

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