Paul Dirac: A Genius Scientist with No Ambition for Fame

9 min readAug 10, 2020

Outside the physics community, the name “Paul Dirac” is quite unfamiliar. But, within the physics community, Paul Dirac is a person of high-esteem, regarded as being in the same league as Newton, Maxwell or Einstein.

The Nobel committee declared him as one of the winners of the Nobel Prize in Physics for the year 1933, but he refused to accept the prize, because he believed that, it would bring publicity for him. When Rutherford told him, “A refusal will get you much more publicity”, he accepted it, reluctantly! In his life, he turned down most honors including the knighthood offered to him in 1953.

“Of all Physicists, Dirac has the purest soul”
- Niels Bohr
“Of the three founders of modern quantum mechanics, Heisenberg and Schrodinger can claim to have caught the first glimpses of the theory. But it was Dirac who put them together and revealed the whole picture”
- Stephen Hawking

Dirac with Heisenberg in Chicago in 1929

Why is Paul Dirac so important for Physics?

Paul Dirac is one of the founders of modern Quantum Mechanics (current version of QM) and the author of many of its most important subsequent developments. Students who do a major in Physics, in the senior year, begin learning Quantum Mechanics with the famous/infamous Bra-ket notation, introduced by Paul Dirac.
He combined the Special Theory of Relativity with Quantum Mechanics, which led him to discover something, known as “The Dirac Equation”. Dirac equation is considered as one of the most beautiful equations in Physics
He introduced the concept of “antimatter” which plays a central role in particle physics and cosmology.
He took the first step in the foundation of Quantum Field Theory, one of the most vital areas of physics today.

Paul Dirac

1902: Born in Bristol, England on August 8

1918: Enrolled at University of Bristol in Electrical Engineering, at his Father’s suggestion

1921: Completed Honors degree with First Class

1921–23: Studied Mathematics at U of Bristol

1923: Enrolled to University of Cambridge for PhD in Physics

1925: First met Heisenberg, with whom he continued a lifelong friendship

1926: PhD

1927: First met Einstein, though the contact between them remained minimal afterwards

1932: Became the Lucasian Professor of Mathematics at Cambridge, the same chair once held by Newton

1933: Received Nobel Prize in Physics, at the age of 31

1984: Passed Away, on October 20

Paul Dirac (center) with Director Robert Oppenheimer (left) and Abraham Pais (right), during a tea party in November 1947, at Princeton University’s Institute for Advanced Study

Dirac and Oppenheimer (father of the atomic bomb) spent some time together in Göttingen. Then, in one of these days, Dirac noticed that Oppenheimer wrote poetry. Dirac asserted, “Robert, I do not understand how a man can work on the frontiers of physics and write poetry at the same time.”

“Why not?” Oppenheimer asked.

“In physics, you want to tell something that nobody knew before, in words which everyone can understand. In poetry, however, you go on to describe something that everybody knows about, in incomprehensible ways.”

Dirac and Feynman at a conference in Poland in July 1962

American physicist, Richard Feynman, born in 1918, grew up idolizing Dirac. About 40 years later, they met in Poland at a conference.

Feynman spoke at length, as he wanted to describe new ideas to his hero. Dirac, perhaps intimated by Feynman’s over-enthusiasm, remained quiet all along.Feynman started to see that it was extremely difficult to get anything out of Dirac. But then, after a long silence, Dirac says, “I have an equation. Do you have one too?”

Dirac also went on to explain as to why he spoke so little, “There are always more people willing to speak than there are to listen.”

Shifting from Relativity to Quantum Mechanics

At Cambridge, as a research student Dirac had to have a supervisor who would advise on, or determine, the research topic on which he would work. Dirac wanted to have Ebenezer Cunningham as his supervisor and to pursue research in the theory of relativity. Cunningham was a specialist on relativity, but he did not want to take on any more research students. At first Dirac felt disappointed not to have Cunningham as his supervisor.

Dirac was later assigned to Ralph Fowler. Fowler’s field was not relativity, his main interests were in the quantum mechanics for atoms and statistical mechanics. In the summer of 1923, Dirac was ignorant of quantum theory and he initially found it much less interesting. But as Fowler’s research student, he was forced to learn the new subjects and soon discovered that they were far from uninteresting. Dirac worked hard to improve his knowledge Within a year, Dirac became fully acquainted with the quantum mechanics for atoms.

A brilliant, successful career as a researcher

Old vs Modern Quantum Mechanics:

The old quantum mechanics was developed between 1900–1924 by Max Planck, Neils Bohr & others which had a lot of limitations. The more general view of quantum mechanics was initiated after, a French PhD student, Louis de Broglie in 1924, provided a new hypothesis: particles (like electrons) could behave as waves. This idea was moved forwarded by Schrodinger, Heisenberg and a new quantum theory came into light in 1925, called “modern quantum mechanics”

In the old quantum theory, we could think about particles moving in normal ways. The electrons orbit the nucleus just like planets orbit the sun. But this was wrong. The new quantum theory says that tiny particles behave in ways that are totally different from normal objects that we can see. In fact, it is impossible to know exactly where they are or what they do.

During the fall of 1925 and the following winter, the formulation of the new quantum mechanics was attended by stiff competition, primarily between the German physicists (Heisenberg, Jordan, Born, and Pauli) and Dirac in England. The Germans had the great advantage of formal and informal collaboration, while Dirac worked on his own. Even had he wanted to (which he did not), there were no other British physicists with whom he could collaborate on an equal footing. That he lost the competition under such circumstances is no wonder. In spite of all his productivity and originality, most of his results had also been obtained by other physicists who, more often than not, had published their works a little before Dirac.

At that time Dirac was twenty-three years old. He was still a student, barely known to the Continental pioneers of quantum theory. The German physicists were surprised to learn about their colleague and rival in Cambridge. “The name Dirac was completely unknown to me,” recalled Max Born, another important physicist in Quantum Mechanics.

The difficult Quantum Field Theory

In February 1927, Dirac wrote a famous paper “The quantum theory of the emission and absorption of radiation”. This paper marked the beginning Quantum Electrodynamics (QED) which is the part of Quantum Field Theory (QFT). To note, QED describes how light interacts with materials.

Image Source: https://www.jstor.org/stable/94746?seq=1

Relativity + Quantum Mechanics= The Beautiful Dirac Equation

When Dirac went to the Solvay Conference (a famous conference at that time) in October 1927, he could look back at two years of successful involvement in quantum mechanics. He still lived in the shadow of Heisenberg and the other German theorists and that he had not yet produced a deep and really novel theory, a theory nobody else had thought of. This lacking were fulfilled by in 1932 with Dirac’s celebrated relativistic theory of the electron, one of the great landmarks in the history of science.

“If Dirac had patented his equation, like some people are now patenting human genes, he would have become one of the richest men in the world.”
- Stephen Hawking

A bold step and the prediction of Anti-matter

An electron’s spin can be of two types: spin up and spin down. In May 1927, Pauli had proposed that the electron satisfy a two-component wave equation (corresponding to spin up and spin down)

Although Dirac’s equation achieved spectacular successes, it was also a source of great trouble, because Dirac’s wave functions had four components. The question: Why four? led to monumental confusion about which, in the 1960s, Heisenberg recalled: ‘Up till that time [1928], I had the impression that, in quantum theory, we had come back into the harbor, into the port. Dirac’s paper threw us out into the sea again.

From the outset, Dirac had correctly diagnosed the cause for this doubling of the number of components. There are two with positive, two with negative energies, each pair with spin up and down.

What to do with the negative energy solutions? He went on to speculate that negative energy solutions may be associated with particles whose charge is opposite to that of the electron.

In the meantime, Hermann Weyl (German Mathematician) had made a new suggestion regarding the extra two components: “It is plausible to anticipate that, of the two pairs of components of the Dirac quantity, one belongs to the electron, one to the proton.” In December 1929, Dirac dissented: “One cannot simply assert that a negative energy electron is a proton, since this would violate charge conservation if an electron jumps from a positive to a negative energy state.” Rather Dirac suggested the idea of hole which acts like a particle with positive energy and positive charge.

Then, in May 1931, Dirac bit the bullet: “A hole, if there were one, would be new kind of particle, unknown to experimental physics, having the same mass and opposite charge of the electron.”

Dirac eventually called the new particle anti-electron and made the first prediction of antimatter, completely theoretically. Just in the following year, Carl Anderson made the first announcement of experimental evidence for the anti-electron.

The prediction and subsequent discovery of the positron rank among the great triumphs of modern physics. The detection of the positron was considered by nearly everyone as a vindication of Dirac’s theory.

Dirac made several other significant contributions in Physics!

An Overview of Dirac’s Research

Analysis of Dirac’s publications results in the following observations:

1. Dirac wrote more than 190 publications, the first in 1924 and the last sixty years later. Although he was a prolific author, the length of his publication list is by no means exceptional. The greatness of Dirac’s publications lay not in their number, but in their quality and originality.

2. The years 1925–33 are the heroic period in Dirac’s life, during which he emerged as one of the principal figures in twentieth century science and changed the face of physics. He himself has called those years in his scientific career “the exciting era”.

3. After 1934, Dirac’s productivity fell sharply. The decline during the period from 1935 to 1945 was not a result of the war, since almost half of the publications during the period were written between 1940 and 1945; if the classified works on war-related research are included, Dirac was in fact more productive during the war period than in the five previous years.

4. In the first two periods, 1924–34 and 1935–45, most of Dirac’s publications were research papers, but in the last period, 1946–84, he increasingly produced nonresearch publications.