Cherrill Spencer From the USA

A true recollection written by Dr Cherrill Spencer, Particle Physicist and Accelerator Magnet Engineer, for the 5th International Conference on Women in Physics:

Adventures with Alligators, Sharks and Dirac

Here is my story of my day out with Dirac. Yes, that Dirac who formulated the Dirac equation in 1928 and won the Nobel Prize with Schr�dinger in 1933 for “the discovery of new productive forms of atomic theory”. Who would have thought he was alive and well and living in Tallahassee, Florida in 1977? But there he was, sitting in the front row of the audience for my colloquium on the particle physics experiment I had worked on during my previous post-doctoral research associateship. And when Professor Dirac, the founder of quantum electrodynamics, told me in question time that he didn’t believe in the Feynman diagram I had used to explain how we had collided an electron and a positron and made a muon and anti-muon, I was completely flustered and had to appeal to the other theoretical physicists in the auditorium for help. Nevertheless, Dirac sought me out at the reception that followed and praised me for my youthful enthusiasm for physics. Then he told me that he’d be joining me the next day in a tour by car of northern Florida with the head of the Physics Department at Florida State University, Professor Joe Lannutti, and Assistant Professor of Physics, Ron Diamond.

So that’s how I came to be sitting in the back of a car for a day out with arguably the most famous physicist of the twentieth century. But no-one had told me that Dirac was also famous for being very precise, quite shy, and bordering on autistic in his social interactions. As we drove to some Florida swamps to take a boat ride to see some alligators I was ready to pepper him with questions about his life at Cambridge University, how he came up with his equation that describes the behaviour of electrons and predicted the existence of anti-matter, and why he’d come to work at Florida State University when he’d had the choice of any university in the world for where to go after his mandated retirement from Cambridge. When he didn’t answer my first question right away I asked him a different one and after three un-answered questions I took a break to wonder what was wrong with them. Then, after what felt like an age, Dirac answered my first question in a carefully thought-out way; to start with I was a bit confused because I supposed he was answering my most recent question, but then I realised what he had answered was my first question, asked over 5 minutes before! Having learnt how to converse with Professor Dirac I spread out my questions and waited patiently for his short but precise answers as we sped in the car towards the Gulf of Mexico to go for a swim after our boat ride.

The tide was out at the deserted beach and one had to wade from shore over 50 metres to reach water deep enough to swim in. But first, Professor Dirac had to check the water temperature, which he did by throwing a thermometer on a string into the water and dragging it back after a minute or two to read it. After Dirac declared that the water was warm enough to swim in we four took off our outer clothes, having put on our swimming costumes before we set out, and waded into the calm Gulf water with no-one else in sight. Dirac was further out than I was and swimming slowly parallel to the shore when I saw what I thought was a shark’s fin gliding above the water a few metres beyond him. Oh dear, I thought, I’m going to have to save the most famous physicist in the world, who established the general theory of quantum mechanics about 45 years earlier, from a shark attack, so I shouted out “Professor Dirac, there’s a shark over there!”. He stood up (the water was not deep) and looked at where I was pointing, “Oh no”, he said, “that’s not a shark’s fin, that’s a dolphin’s fin.” and proceeded to explain the difference in their fin shapes, a subject he had apparently studied in preparation for swimming in Florida. You can imagine my great relief.

After a sea-food dinner at a restaurant, Professor Lannutti drove us back to Professor Dirac’s house in Tallahassee where his wife Margit invited us in for a cup of coffee and to find out about our sight-seeing trip. While we chatted with her, Professor Dirac disappeared into the back of their house and eventually returned with a pile of presentation boxes which he opened up one by one to show me what was inside. They each contained one of the many prizes and honours that Professor Dirac had received over his lifetime, for example, the Royal Medal, the Copley Medal, the Max Planck Medal, his Order of Merit and his Nobel Prize medal. What a treat it was to see all those medals and to read their accompanying citations. As we left, Mrs Dirac pulled me aside and told me that Dirac had NEVER BEFORE brought out his prizes to show anyone and I must have been a good influence on him. That was a marvelous remark to hear at the end of my amazing day out with Dirac.