When one reads George Sudarshan’s many seminal papers on a variety of subjects, one becomes aware of how unique he is. On the one hand, he has been enormously prolific—authoring over 400 important papers—and his work is credited with elucidating several important topics in physics and impacting many leading physicists.

The deep common thread lying at the core of his efforts is an attempt to resolve the fundamental conflict between descriptions of objects ("being") and processes ("becoming"). There is a unifying theme in George's work—irreversible processes and transformations (including decay, measurements, etc) in strictly reversible dynamical quantum systems. The understanding of this contradiction is still unsolved, and is fundamental. Through what can be categorized as seven quests, George has made major contributions in trying to piece this puzzle together. These seven of George's major Science Quests are the focus of a symposium Sudarshan: Seven Science Quests. His efforts are ongoing—The Quest continues.

Physics is the study of Existence and Change. These changes may be viewed as Transformations of the Physical system, generated by physical quantities of the system. Quantum mechanics has unified processes and the physical quantities. These changes should be reversible for closed systems. The observed irreversibility should therefore involve Open systems. Thus, for example, from reversible dynamics one can calculate quantum mechanical decay rates and probabilities.

Open quantum systems (such as non-equilibrium thermodynamics) demand generalized quantum states which are "mixed" and stochastic dynamical processes. The formulation of this in terms of Dynamical Maps was first given by Sudarshan and collaborators. (See the Open Quantum Systems topic on the FOGS site.)

The transformations in a closed system are intimately related to symmetry groups. While symmetries are present in both classical and quantum mechanics, by virtue of the superposition principle they are manifested more obviously in quantum mechanics.

In the domain of particle physics they lead to selection rules and sum rules, which have dominated the field for several decades and have yielded very valuable clues for physics in the microphysical domain such as the relation between electromagnetic properties and masses of elementary particles by Sudarshan and collaborators. In the realm of Relativistic mechanics a careful analysis by Currie, Jordan and Sudarshan led to the "No Go" theorem. (See the Symmetry topic on the FOGS site.)

When the wave functions of many (strictly identical) particle systems are considered we find that all integer spin particles have symmetric wave functions and obey Bose statistics while half integer spin particles have anti-symmetric wave functions and obey Fermi statistics. This regularity was believed to emerge only from relativistic quantum field theory. However Sudarshan showed that there is a simpler basis if we consider rotationally invariant field theories, not necessarily relativistic. This is related to the symmetry properties of the scalar products; symmetric for integer spin and anti-symmetric for half integer spin. The relation then becomes applicable to phonons and electrons in metals also. (See the Spin Statistics topic on the FOGS site.)

The theory of Relativity is characterized by a group of transformations and any physical system is a realization of this group. One such realization is furnished by Tachyons (particles traveling faster than light). Their unusual properties were first pointed out by Bilaniuk, Deshpande, and Sudarshan. If Tachyons exist they necessitate a critical re-examination of the principle of causality. (See the Tachyons topic on the FOGS site.)

Quantum Mechanics deals primarily with amplitudes, with probabilities being the squared absolute value of the amplitudes for change. Hence changes in amplitude are proportional to the time for "small" times. Consequently the probabilities are quadratic in time; and the rate tends to vanish for very small times. This is the Quantum Zeno Effect discovered by Misra and Sudarshan. (See the Quantum Zeno Effect topic on the FOGS site.)

Physics is primarily an experimental subject. In the domain of nuclear physics no law of beta radioactivity could reconcile all the data. In 1956-57 a critical analysis of all the data showed their internal inconsistency. The discovery of the left handed V-A interaction by Sudarshan and Marshak led to the unification of all weak interactions and to the possibility for the subsequent electro-weak unification a decade later. (See the V-A Interaction topic on the FOGS site.)

It was the study of light that led to Quantum Theory. But this did not cover the phenomena of Optical Coherence. Since light is quantum mechanical , there should be a quantum theory of coherence. The first formulation of this was by Sudarshan in 1963 and it showed that the typical quantum effects, photon antibunching, negative intensity correlation and squeezed light should obtain. All these are now well established experimentally. (See the Quantum Optical Coherence topic on the FOGS site.)

The common thread running through all these investigations is the study of existence and change in physical systems.