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“There are only two possible conclusions: if the result confirms the assumptions, then you’ve just made a measure; if the result contradicts the assumption, then you have made a discovery.” “

Enrico Fermi

“..The world seems filled with people who are genuinely, deeply interested in physics but whose lives have taken them in different directions. This book is for all of us..”

― Leonard Susskind
(Quantum Mechanics: The Theoretical Minimum)

On October 18, 1902, theoretical and mathematical physicist Pascual Jordan was born. Jordan made significant contributions to quantum mechanics and quantum field theory. He contributed much to the mathematical form of matrix mechanics, and developed canonical anticommutation relations for fermions.

Pascual Jordan – Early Years
Pascual Jordan was born in Hanover, Kingdom of Prussia, German Empire, as son of Ernst Pasqual Jordan (1858-1924), a painter of landscapes and portraits, and Eva Fischer. One of his ancestors named Pascual Jorda was a Spanish nobleman and cavalry officer who served with the British during and after the Napoleonic Wars. Jorda eventually settled in Hanover, which in those days was a possession of the British royal family. A family tradition dictated that the first-born son in each generation be named Pascual. By the age of fourteen, Jordan was reading books such as August Pauly‘s 1905 work Darwinismus und Lamarckismus and began to think deeply about fundamental questions such as whether organic life was understandable from a purely mechanical and physical perspective.

First Steps in Quantum Theory
Jordan enrolled in the Hannover Technical University in 1921 where he studied zoology, mathematics, and physics. He switched to Göttingen University in 1923, which by then was at the very zenith of its prowess and fame in mathematics and the physical sciences. At Göttingen Jordan became an assistant first to mathematician Richard Courant and then to physicist Max Born.[5] Courant quickly realized that he had an exceptionally talented student and Jordan helped with the writing of Courant and Hilbert’s Methoden der mathematischen Physik. Jordan received his PhD from the University of Göttingen in 1924, working with Max Born and James Franck on the problems of quantum theory. In 1925 Jordan published two seminal papers, one in collaboration with Born and German physicist Werner Heisenberg [4] and one with just Born, that developed Heisenberg’s initial idea of noncommutative variables into a formulation of quantum theory in terms of matrix mechanics — the first working version of quantum mechanics.
Quantum Field Theory
In the following years, in Göttingen and as a Rockefeller fellow in Copenhagen, Jordan helped propel the new theory toward completion, incorporating the wave mechanics approach of the German physicist Erwin Schrödinger [2] with the matrix formulation [2]. The comprehensive mathematical formalism of nonrelativistic quantum mechanics was achieved for the first time in the transformation theory published by Jordan and independently by the English physicist P.A.M. Dirac in 1927.[7] Jordan then put forward the general program of quantum field theory, proposing that relativistic quantum theory should describe all subatomic particles — matter and radiation alike — as quanta of wave fields. Working toward the implementation of this idea, he and the Hungarian-born American physicist Eugene P. Wigner [6] showed in 1928 how the second quantization is capable of describing fermions, in addition to bosons, by introducing the technical idea of an anticommutator (a special matrix operator).

A New Type of Algebra
In 1929 Jordan was appointed as extraordinary professor of physics at the University of Rostock.[3] He went on to pioneer early quantum field theory before largely switching his focus to cosmology before World War II. In 1932, in an attempt to put quantum theory into a new algebraic setting, Jordan tried to establish the basic rules satisfied in the matrix interpretation of quantum theory. He published these ideas in Über die Multiplikation quantenmechanischer Gröβen in 1934. With this work Jordan devised a new type of non-associative algebras, now named Jordan algebras in his honor. Today, von Neumann algebras are also employed for this purpose. Jordan algebras have since been applied in projective geometry, number theory, complex analysis, optimization, and many other fields of pure and applied mathematics, and continue to be used in studying the mathematical and conceptual underpinnings of quantum theory.

World War 2
In 1933, Jordan joined the N**i party, and, moreover, an SA unit. But at the same time, he remained “a defender of Einstein” and other Jewish scientists.[3] Jordan enlisted in the Luftwaffe in 1939 and worked as a weather analyst at the Peenemünde rocket center, for a while. During the war he attempted to interest the N**i party in various schemes for advanced weapons. His suggestions were ignored because he was considered “politically unreliable”. In 1944, before the war ended, Jordan was appointed as an ordinary professor of theoretical physics at the University of Berlin.

Denazification and PostWar Career
Wolfgang Pauli [8] declared Jordan “rehabilitated” to the authorities some time after the war, allowing him to regain academic employment after a two-year period and then recover his full status as a tenured professor in 1953. Jordan went against Pauli’s advice, and reentered politics after the period of denazification came to an end under the pressures of the Cold War. He secured election to the Bundestag standing with the conservative Christian Democratic Union. In 1957 Jordan supported the arming of the Bundeswehr with tactical nuclear weapons by the Adenauer government, while the Göttinger 18 (which included Born and Heisenberg) issued the Göttinger Manifest in protest. This and other issues were to further strain his relationships with his former friends and colleagues.

Later Years
Pauli worked on an idea of Paul Dirac about a time-varying gravitational constant in the framework of a scalar-tensor theory, which he developed already in the 1940s and which he presented in his book Gravity and Space in 1952. A similar theory (Brans-Dicke theory) was formulated later by Carl H. Brans and Robert Dicke, whereby the emphasis of their consideration lay in an implementation of Mach’s principle. Thus he explained the continental drift as consequence of an expanding globe (expansion theory). This explanation is considered as refuted today. From 1963 to 1967 he was president of the Academy of Sciences and Literature in Mainz.

Pascual Jordan died on Juli 31, 1980, in Hamburg at age 77.
Credit: Sci Hi Blog

🎈 🎉 It's the birthday of Niels Bohr, the architect of quantum mechanics!

🇩🇰 ⚛️ Born in 1895 in Copenhagen, Niels Bohr was a Danish physicist whose journey into the quantum domain began with his revolutionary model of the atom in 1913.

🧠 💡 At a time when classical physics faltered to explain atomic behaviors, Bohr introduced a quantum model where electrons existed in distinct energy levels around the nucleus, leaping between these orbits without traversing the space in between. This bold postulation not only explained why atoms have stable structures but also shed light on the spectral lines of hydrogen, a phenomenon classical physics found perplexing.

⚡️ 😳 But Bohr didn't stop there. He played an integral part in the development of quantum mechanics, a theory that provides a comprehensive description of nature at the smallest scales. His principle of complementarity, which asserts that different experimental setups reveal different aspects of quantum systems, became a cornerstone of quantum mechanics and continues to influence our understanding of the quantum world.

📕 🤯 Bohr's appreciation for the mysterious nature of quantum mechanics can be encapsulated in his often-quoted words: "If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet."

In 1905, Albert Einstein published the first explanation of the photoelectric effect, but at the time, it was impossible to resolve the timescales that were relevant for this effect. For a long time, physicists assumed the effect was instantaneous.

Einstein was eventually awarded the 1921 Nobel Prize in Physics “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect.” Parenthetically, when he gave his Nobel Prize lecture, it was not in Stockholm in December 1922 (Einstein was in Japan at that time), but in the middle of the summer of 1923, in Gothenburg – a unique event in the history of the Nobel Prize. His talk did not concern the photoelectric effect but the theory of relativity, the theory for which he was never awarded a Nobel Prize.

The fundamental question that this year’s physics laureates made it possible to pose was “what is the timescale for the photoelectric effect?” When an atom or a surface absorbs sufficient energy from incoming light, it can transfer that energy to an electron, which is then emitted with a kinetic energy equal to the photon energy minus the binding energy of the electron. The complex dynamics of atomic photoemission results in a small time delay, and the question is how small this time delay is. Before the window to attosecond science was opened, one could assume that the process occurred instantaneously, and so the research focus was on the energetics. This is the foundation of photoelectron spectroscopy.

The 2023 Nobel Prize in Physics has been awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier “for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter.

The 2023 physics laureates Pierre Agostini and Ferenc Krausz demonstrated ways to create shorter pulses of light than were previously possible.

Pierre Agostini and his research group in France succeeded in producing and investigating a series of consecutive light pulses, like a train with carriages. They used a special trick, putting the “pulse train” together with a delayed part of the original laser pulse, to see how the overtones were in phase with each other. This procedure also gave them a measurement for the duration of the pulses in the train, and they could see that each pulse lasted just 250 attoseconds.

At the same time, Ferenc Krausz and his research group in Austria were working on a technique that could select a single pulse – like a carriage being uncoupled from a train and switched to another track. The pulse they succeeded in isolating lasted 650 attoseconds and the group used it to track and study a process in which electrons were pulled away from their atoms.

These experiments demonstrated that attosecond pulses could be observed and measured, and that they could also be used in new experiments.

Now that the attosecond world has become accessible, these short bursts of light can be used to study the movements of electrons. It is now possible to produce pulses down to just a few dozen attoseconds, and this technology is developing all the time.

The 2023 Nobel Prize in Physics has been awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier “for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter.”

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Women who have been awarded the Nobel prize in physics;
1.Marié Curié in 1903 for the study of spontaneous radiation discovered by Becquerel.
2. Maria Goeppert Mayer in 1963 for the discovery of nuclear shell structure.
3. Donna Strickland in 2018 for the discovery of chirped pulse amplification.
4. Andrea M. Ghez in 2020 for the discovery of supermassive compact object at the center of our milkyway galaxy.
5. Anne L'Huillier in 2023 for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter.

The Feynman technique of learning:
1. Pick and study a topic.
2. Explain the topic to someone, like a child, who is unfamiliar with the topic.
3. Identify any gaps in your understanding.
4. Review and simplify!

Second law of thermodynamics states that the entropy in an isolated system always increases. Any isolated system spontaneously evolves towards thermal equilibrium—the state of maximum entropy of the system

Centrifugal force is considered a pseudo vector (or axial vector) because of the way it behaves under coordinate transformations. To understand this, let's first clarify what centrifugal force is:

Centrifugal force is the apparent outward force that seems to act on an object moving in a circular path, away from the center of rotation. It is often invoked to explain why objects in a rotating reference frame, like a spinning merry-go-round, tend to move away from the center.

Now, the reason why centrifugal force is a pseudo vector lies in how it responds to changes in coordinate systems:

1. **Direction**: In a rotating reference frame, like one attached to the spinning merry-go-round, the centrifugal force points outward from the axis of rotation. So, it has a specific direction in this frame.

2. **Transformation**: However, when you switch to an inertial (non-rotating) reference frame, the centrifugal force seems to disappear. It is not a true vector in the sense that its direction does not remain the same under coordinate transformations. In the inertial frame, there is no centrifugal force; instead, it's actually a result of inertia and the object's tendency to move in a straight line unless acted upon by a force (Newton's first law).

Because of this difference in behavior under coordinate transformations, the centrifugal force is classified as a pseudo vector or axial vector. True vectors, like displacement or velocity, maintain their direction in all coordinate systems, while pseudo vectors do not.

A pseudo vector (also known as an axial vector) and a null vector are two distinct mathematical concepts:

1. Pseudo Vector (Axial Vector):
- A pseudo vector, or axial vector, represents a quantity that has both magnitude and direction but transforms differently under coordinate transformations compared to regular vectors.
- It arises in certain physical contexts, such as angular momentum and torque, where the direction of the vector is important but the transformation properties differ from regular vectors.
- Pseudo vectors are associated with cross products and have an antisymmetric transformation law.

2. Null Vector:
- A null vector, on the other hand, is a vector with zero magnitude and no specific direction. In other words, it is a vector whose components are all zero.
- Null vectors are often used in linear algebra and physics to represent the absence of a physical quantity or a point in space with no displacement from a reference point.
- They play a role in vector spaces and can be used to describe degenerate cases or as placeholders in mathematical equations.

In summary, the main difference is that a pseudo vector has magnitude and direction but transforms differently under coordinate transformations, while a null vector has zero magnitude and no specific direction, representing the absence of a quantity or a point in space.

The self-induced emf is also called the back emf as it opposes any change in the current in a circuit. Physically, the self-inductance plays the role of inertia. It is the electromagnetic analogue of mass in mechanics.So, work needs to be done against the back emf in establishing the current.