“Product of optimism and knowledge is constant”, well-known Soviet theoretical physicist Lev Landau said when he was making fundamental contributions to understanding physics. Today, on his 111th birthday, we give a tribute and tell you why should you know about this legendary figure in physics.

### A Born Talent

Born in Baku on this day, Landau was described by his classmates as a ‘shy boy’ in the class and had struggles in relating to his peers. Needless to say, he always was brilliant in Math and Physics in school, and learnt to differentiate when he was just 12 and integrate when he was 13. He had his first ever publication published when he was a mere 18 year old teenager. The publication was called *Theory of the Spectra of Diatomic Molecules*. He further went on to completing his PhD when he was only 21 year old and later earned a Rockefeller fellowship and a Soviet stipend, because of which had him the opportunity to study with the father of the atom, Nobel Laureate Niels Bohr. Elected to the USSR’s Academy of Sciences in 1946, Ladau also received the Lenin Science Prize for his monumental Course of Theoretical Physics which is a ten-volume study written with his student Evgeny Lifshitz, and is still widely used as a graduate-level physics reference text.

### Notable Contributions To Quantum Mechanics And Its Uses Today

Landau made several contributions in the field of quantum mechanics. Here are some of the key ones:

**1.Density matrix:** He along with John von Neumann had discovered the density matrix in quantum mechanics, which represents the statistical state of a system in quantum mechanics. This theory is highly used in quantum mechanics in decomposition matrices, in pure and mixed states which have several applications such as light polarizability

**2.Diamagnetism:** Landau discovered the quantum mechanical property of diamagnetism in a free electron gas. Discovered in 1930, Landau diamagnetism is the diamagnetism of free electrons in an external magnetic field. It is used in the study of magnetism

**3.Superfluidity:** R=Nobel prize. It is the property of a fluid of zero viscosity. And therefore flows without loss of kinetic energy. This phenomena is used in Astrophysics, high-energy physics and quantum gravity. It also helps in the understanding of the Standard Model

**4.Second-order phase transitions: **Microscopic states of the system are important to be determined in order to calculate thermodynamic properties like the free energy, entropy, specific heat, and so on. While introducing the theory of “continuous” second-order phase transitions, Landau claimed that they “may also exist” along with the majority of first order phase transitions, the latter being discontinuous, displaying ‘jumps’ of their physical properties. Several advancements have since then been made in these transitions and are used in thermodynamics and solid state physics

**5.Ginzburg–Landau theory of superconductivity: **Landau’s second-order phase transitions theory gave rise to the phenomenological Ginzburg-Landau theory of superconductivity. It is used in the study of superconductors and also in String Theory

**6:Fermi liquid: **Also called as Landau Fermi liquid theory, this is a theoretical model of interacting fermions that describes the normal state of most metals at sufficiently low temperatures. The key idea is the notion of adiabaticity and the Pauli exclusion principle

**7.Landau damping:** Landau damping is the exponential decrease of longitudinal space charge waves in plasma, as a function of time. It is used to understand the wave-particle interaction in plasma, or a similar environment. It also has applications in theoretical physics

**8.Landau pole: **A concept in quantum electrodynamics pointed out by Landau and his colleagues, it is the momentum scale at which the coupling constant of a quantum field theory becomes infinite, and has applications in statistical physics

**9.Two-component theory of neutrinos: **Proposed by Landau, this was first theoretical idea about neutrino mass. It has experienced several advancements and is now widely used in particle physics

**10.S matrix singularities: **S-matrix theory was a proposal for replacing local quantum field theory as the basic principle of elementary particle physics. The S-matrix relates the infinite past to the infinite future in one step, without being decomposable into intermediate steps. Although not thoroughly proposed by Landau, he had contributed to proposing some aspects of this theory. It was further led to string theory.

### Interesting Facts

One of the very interesting facts of this genius mind is that he used to keep a list of names of physicists that he ranked on a logarithmic scale, from 0 to 5. His ranking had Isaac Newton at 0 and Albert Einstein at 0.5 and the rank 1 was awarded to the founding fathers of quantum mechanics, Niels Bohr, Werner Heisenberg, Satyen Bose, Paul Dirac and Erwin Schrödinger, and others. He had also ranked himself at a 2.5, later promoting at 2.