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Family members, have you watched the newly released "Oppenheimer" in China?
The film has been widely praised for respecting history in many aspects and restoring many details in place.
But the only part where Einstein appeared was adapted by director Nolan.
In the story, although Einstein does not appear many times or for a long time, he plays a key role as Oppenheimer's mentor and confidant.
In one episode, Oppenheimer finds Einstein by a lake with data and asks whether the chain reaction from the atomic bombing would destroy the entire planet .
Today we already know the answer is no, but for scientists at the time, this was a gamble on the fate of mankind.
……
Historically, there was indeed a mentor-like figure beside Oppenheimer, and he and Oppenheimer also had such a lakeside conversation.
But this man was not Einstein, but another physicist , Arthur Compton .
In the most famous group photo in physics "1927 Solvay Conference Photo", Compton sits in the middle of the second row.
In the same year, he won the Nobel Prize in Physics for his experimental discovery of the Compton effect named after him and his confirmation of the particle nature of electromagnetic radiation.
In the debate about quantum mechanics at that time, Compton neither belonged to Bohr's Copenhagen school, nor joined the opposition camp headed by Einstein, but was an experimental school: he did not stand in line and only focused on the experimental results .
Although not as famous as the theoretical figures in the group photo, Compton is actually a key figure in the entire Manhattan Project.
After the war, he continued to be an experimentalist and made more contributions to the world. The street lights and speed bumps we see today are all related to him.
Let's start with Compton's perspective and revisit how scientists confirmed that the world would not be destroyed during the birth of the atomic bomb.
The possibility of three out of a million is not to be underestimated
Before the atomic bomb was actually built, the scientists of the Manhattan Project discovered a very dire risk:
The atomic bomb explosion relies on nuclear fission, but in the high temperature generated by the explosion, lighter nuclei such as hydrogen may fuse into heavier nuclei and release a lot of energy, just like what happens on the sun.
In July 1943 , Oppenheimer brought this issue to Compton for discussion.
It was Compton who strongly recommended Oppenheimer to be in charge of the entire plan. The high-level executives believed that Oppenheimer lacked management experience, but Compton took a fancy to Oppenheimer's familiarity with the design of the bomb.
Compton later recalled their concerns this way:
If hydrogen can fuse, what about the hydrogen in seawater? Would an atomic bomb detonate the entire ocean? Nitrogen in air is also unstable, although somewhat better than hydrogen...
They speculate that if this starts an uncontrollable chain reaction, both the oceans and the atmosphere will be ignited .
Many years later, Compton told the well-known writer and Nobel Prize winner Pearl Buck that "it is better to accept the slavery of the Nazis than to take the risk of drawing the final curtain for mankind . "
But anyway, the Nazis were also working on their own nuclear weapons, so Compton and Oppenheimer had no choice but to try to quantify the risks while trying to get the bomb out of the way first.
Ultimately Compton decided that he would not proceed with the Manhattan Project if calculations proved that the odds of the Earth being destroyed by an atomic bomb exceeded three in a million .
This story was later published by Pearl Buck in the 1959 issue of Us Weekly
Later, the calculated result was lower than this number, and the plan continued.
In a declassified file, they summarized the relevant calculations at that time, which also used Compton’s previous Nobel Prize achievements:
No matter what temperature it is heated to, it is impossible for the atmosphere to be ignited to produce a chain reaction. Even for a super nuclear bomb with a volume larger than 1,000 cubic meters, the Compton scattering theory will provide additional safety guarantees.
Among them, Compton scattering refers to the collision between high-speed electrons and photons, and the transfer of energy from electrons to photons will consume the heat required for the chain reaction.
The time came two years later.
On July 16, 1945 , the first human nuclear test code-named "Trinity" was carried out in the desert of New Mexico, USA.
Despite the safety of the calculated results, when the explosion did happen, some of the witnesses could not help but worry.
Light is faster than sound. Before hearing the explosion, the silent white light is the only protagonist. In the movie, Nolan also used a silent technique to express this scene.
Emilio Segrè, the Italian physicist responsible for measuring the level of gamma radiation, later admitted, "What impressed me most was the overwhelmingly bright light... I was near Fermi at the time of the explosion... For a moment I feared the explosion even though I already knew it was impossible. would ignite the atmosphere and destroy the planet."
It was also this nuclear test that made Oppenheimer utter his most famous quote:
Now I am death, the destroyer of worlds.
The "Trinity" nuclear test used a plutonium-based atomic bomb.
In the plan at that time, both uranium and plutonium could be used to make atomic bombs, but the material utilization rate of uranium-based bombs was low, and their power was not as good as that of plutonium-based bombs.
Uranium-238 can be converted to plutonium-239 by neutron bombardment, but the plutonium produced in this way is only a small part, and the two must be separated.
Compton was responsible for building nuclear reactors that convert uranium into plutonium and finding ways to separate plutonium from uranium.
In the end, the "Little Boy" dropped on Hiroshima first was a uranium-based bomb that had never been tested before.
The "fat man" dropped on Nagasaki was the plutonium-based bomb that Compton was in charge of.
Throughout the Manhattan Project, Compton played a key role in early planning, recommending Oppenheimer to be in charge, building the reactor, and finally recommending the use of the atomic bomb on Japan.
While the film gives Einstein his role for added drama, there are more lesser-known contributions to Compton's life that are worth exploring.
Discovery of optoelectronic hypothesis wins Nobel Prize
Compton was born in a scholarly family. His father was the president of the University of Worcester, and his mother was named "Mother of America" in 1939.
In addition, there are two older brothers in the Compton family, and all three of them are Ph.D. students from Princeton University.
Eldest brother Carl Compton and second brother Wilson Compton served as presidents of MIT and Washington State University respectively.
Among them, the eldest brother Carl is also closely related to the Manhattan Project.
△ Compton (left) and elder brother Carl
We return to Compton himself, who in 1916, at the age of 24, received his Ph.D.
After graduation, he first worked as a physics teacher at the University of Minnesota, but he did not choose to continue working in the physics field, but went to Westinghouse to work.
Compton improved the sodium lamp there , and our common yellow light street lamp is a sodium vapor lamp.
He also developed aviation instruments for the U.S. Army Signal Corps during World War I.
But Compton did not forget his original intention because of these. He still had a deep love for physics. In 1919, Compton went to the Cavendish Laboratory of Cambridge University in England for further study and returned to the field of physics.
Compton's mentors are also well-known figures - Rutherford who proposed the atomic structure model and GP Thomson who won the Nobel Prize for electron diffraction experiments.
△ Rutherford (left) and GP Thomson
There, he studied the scattering and absorption of gamma rays , which laid the foundation for the later discovery of the Compton effect.
In the scattering experiment of gamma rays, Compton found that some phenomena could not be explained by the theory at that time.
This question remained in Compton's mind. After returning to the United States, he switched to X-ray scattering experiments.
So there was Compton's most famous achievement - the discovery of the Compton effect .
The Compton effect experimentally confirmed Einstein's optoelectronic hypothesis. This achievement was also highly praised by Einstein.
He found that after X-rays are scattered by some substances, light with longer wavelength (frequency and lower energy) will appear in the scattered light.
At the same time, Compton also found a quantitative relationship between the incident light and the scattered light wavelength:
(Among them, Δλ is the difference between the incident wavelength λ0 and the scattering wavelength λ, h is Planck’s constant, c is the speed of light, m is the rest mass of electrons, and φ is the scattering angle. )
At first, Compton tried to explain it with classical electromagnetic theory, but soon found that it was as unexplainable as the phenomenon of gamma rays.
So he thought of Einstein's light quantum theory, which successfully revealed the secret behind the phenomenon from the perspective of photon and electron collision.
It is this discovery that verifies the particle nature of light (electromagnetic wave) and the wave-particle duality .
After that, the voice of doubting and denying the light quantum theory disappeared in the academic circle.
In 1927, Compton won the Nobel Prize in Physics for this achievement .
In the 1930s, Compton's research direction quietly changed, and he began to study cosmic rays .
△ In 1933, Compton and his students studied cosmic rays
People at that time already knew its existence, but what kind of matter cosmic rays are has always been an unsolved mystery.
Compton and other researchers traveled to many corners of the world and eventually found that cosmic rays are 15% stronger at the poles than at the equator.
Ultimately Compton proposed that cosmic rays consist of charged particles rather than photons as speculated by Millikan et al., and this fitted the observed phenomenon nicely.
In addition to studying physics, he is also an inventor
After World War II ended in 1946, Compton returned to the University of Washington and served as the ninth president of the school.
After eight years as president, Compton, 62, retired from UW in 1954 but continued to teach until 1961.
During this period, Compton also unlocked another identity of himself-an inventor.
Compton's invention of the speed bump goes down in history along with X-ray scattering and cosmic rays.
At that time, the transportation in the United States had begun to see a scale, and the number of cars owned had reached a certain level.
Compton, as principal, was also annoyed by the random traffic on campus.
Previously, in order to solve the safety problem of pedestrians crossing the road, some places raised the sidewalk on the road to achieve the purpose of slowing down the car.
But this method will bring danger when the vehicle accelerates. In the end, after repeated research, Compton designed a "hump" speed bump composed of bumps with slopes to solve this problem.
Since then, this speed bump has been applied all over the United States and has become the originator of modern speed bumps.
In 1962, this legendary figure in the physics world died in Berkeley, California, at the age of 69.
To commemorate Compton, NASA named the gamma-ray observatory after him, a star belonging to him appeared on the Celebrity Walk in St. Louis, and there was a Compton crater (named after him and his brother) on the moon... …
△ Compton Gamma Ray Observatory
One More Thing
I believe you have already understood Compton's story and achievements, but you may still have a question about Oppenheimer:
In real history, did Oppenheimer recognize Einstein?
The answer is to know, but the relationship between the two is different from that described in the movie.
In his autobiography, Oppenheimer wrote:
Although I had known Einstein for twenty or thirty years, we did not become close colleagues and friends until the last decade of his life.
参考链接：
[1]https://nautil.us/the-day-oppenheimer-feared-he-might-blow-up-the-world-355603/
[2]https://www.insidescience.org/manhattan-project-legacy/atmosphere-on-fire
[3]http://large.stanford.edu/courses/2015/ph241/chung1/docs/buck.pdf
[4]https://thebulletin.org/2015/07/trinity-now-and-then
[5]https://en.wikipedia.org/wiki/Arthur_Compton
[6]https://www.sinoconcept.co.uk/purchasing-guides/everything-about-speed-bumps/what-is-speed-bump/who-invented-speed-bumps/