Robert McNees
Physicist Julius Robert Oppenheimer was born #OTD in 1904.
He is best known for directing scientific work at Los Alamos during the Manhattan Project, but also made important contributions to quantum mechanics, astrophysics, and relativity that are not as well known!
Photo: Ed Westcott
Robert McNees
There’s an apocryphal story (perhaps due to Oppenheimer himself) that, while a student at Cambridge, he tried to poison his tutor with an apple laced with toxic chemicals.
The tutor, Patrick Blackett, would go on to win the 1948 Nobel Prize in physics.
Robert McNees
I will let others talk about that story, and whether or not it’s true. This thread is about Oppenheimer’s contributions outside the Manhattan Project.
J. Robert Oppenheimer wasn't as prolific as many of his contemporaries. But he had exquisite taste when choosing which problems to work on. Foundational ideas about subjects like anti-particles or black hole formation can be traced back to Oppenheimer.
Robert McNees
Dirac, after the discovery of his eponymous equation, explored the idea of the proton being the positively charged anti-particle of the electron.
A 1930 paper by Oppenheimer scuttled this proposal, pointing out several problems with the interpretation.
Robert McNees
Oppenheimer’s insight prompted Dirac to propose a new particle. In classic Dirac style, he decided to call it the “anti-electron.”
The race was on to observe this particle and give it a name that wasn’t completely terrible!
Ref: https://royalsocietypublishing.org/doi/10.1098/rspa.1931.0130
Robert McNees
Carl Anderson spotted this particle the following year. Tasked with rescuing it from the name "anti-electron," he tried to name it – I’m not joking here – the “positive electron.”
Robert McNees
An exasperated editor from Physical Review stepped in and informed everyone that, no, we will not be using the name "positive electrons," we will instead be calling them "positrons."
Robert McNees
Oppenheimer arrived in Berkeley in 1929 to take a position as an assistant professor, in a special arrangement that also saw him teaching at Caltech. His first doctoral student at Berkeley was Melba Newell Phillips.
Together they discovered the Oppenheimer-Phillips process, where a passing deuteron is polarized by the electrostatic field of a nucleus. The deuteron’s proton is repelled, allowing the nucleus to capture the neutron and form a heavier isotope.
Robert McNees
By the late 1930s, after he was established as a full professor, Oppenheimer turned his attention towards astrophysical problems.
With his students and collaborators he made major contributions to the nascent theory of neutron stars and black holes.
In a 1938 paper with post-doc Robert Serber, Oppenheimer considered the stability of stellar core composed entirely of neutrons.
Robert McNees
This was followed in 1939 by a paper with Volkoff, published alongside work by Tolman. They modeled neutron stars by applying Tolman's self-gravitating perfect fluid solution of general relativity to a degenerate neutron gas.
The Oppenheimer-Volkoff paper was the first serious treatment of the structure of neutron stars, which had been proposed by Baade and Zwicky five or six years earlier. It set the stage for realistic relativistic models of stellar structure.
Robert McNees
About six months later, Oppenheimer and his student Hartland Snyder published the first calculation of black hole formation. This paper is a real gem.
Steffen Christensen
@mcnees I've read a lot of papers with anti-electrons. Never seen a positive electron yet.
Robert McNees
Oppenheimer and Snyder considered a homogeneous sphere of pressureless matter, and showed that as it collapses it "tends to close itself off from any communication with a distant observer; only its gravitational field persists."
Robert McNees
Results established in this paper would make their way into the popular understanding of black holes!
They established the intense red shifting of light, and the fact that witnessing the collapse requires infinite patience for a distant observer but proceeds rather quickly for someone plunging inward.
Robert McNees
By the time WWII got underway, Oppenheimer had already made important contributions across theoretical physics. Perhaps he would have continued to work on gravitational collapse and black holes, or maybe he would have flitted off to some other subject that caught his interest.
The Manhattan Project came next, which is the part that everyone has heard about. I won't bore you. Maybe they’ll make a movie or something.
Robert McNees
After the war Oppenheimer left California to become director of the Institute for Advanced Study.
In 1949 he was brought before the House Un-American Activities Committee for his Communist associations, and they blocked his access to classified material.
https://ahf.nuclearmuseum.org/ahf/history/huac-and-manhattan-project
Robert McNees
It was nonsense, and a hit job, like so many of those HUAC hearings.
This past December, the US government nullified their 1954 decision on the grounds that the whole proceeding had been a flawed. Better late than never, I guess.
https://www.nytimes.com/2022/12/16/science/j-robert-oppenheimer-energy-department.html
Robert McNees
Now, here is the part I want to tell you about.
In 1929, before most of the stuff I wrote about above, Oppenheimer contracted tuberculosis. It wasn't too bad, but it wasn't great, either.
He convalesced with his brother (also a physicist, also attacked by HUAC) at a ranch in New Mexico and fell in love with the place.
As the story goes, when Oppenheimer found out the ranch could be leased he shouted "Hot dog!" He eventually bought the property and named it "Perro Caliente."
Robert McNees
That's the thread. Oppenheimer named his ranch "Hot Dog."
Greg Whitehead
@mcnees That same brother, Frank Oppenheimer, founded The Exploratorium science museum in San Francisco https://en.wikipedia.org/wiki/Exploratorium
minerva koenig
@mcnees Huh. He doesn't look at all like Cillian Murphy.
Robert McNees
@grwster very cool!
Greg Whitehead
@mcnees I was overdue for a visit, so I stopped by today.
It was packed with kids, which is always great to see.
Greg Whitehead
@mcnees That picture of Marilyn Monroe on the wall behind Impossible Triangle morphs into a picture of Einstein as you get closer
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