CS Unnikrishnan

Tata Institute of Fundamental Research, Department of High Energy Physics, Faculty Member

Followers

Following

Public Views

C. S. Unnikrishnan is a professor of physics at the Tata Institute of Fundamental Research, Mumbai. He is also a visiting professor at the Raman Research Institute, Bangalore, and was a visiting researcher at the Kastler-Brossel Laboratory (Ecole Normale Superieure) in Paris and the Laboratoire de Physique des Lasers, University of Paris 13. His Ph. D degree in physics is from TIFR, Mumbai, with prior education in BHS, Kalady, Keralam (SSLC - state first rank 1977), Christ College, Iringalakkuda (Pre-degree), U. C. College, Aluva (B. Sc - 1982 Kerala Univ. first rank.) and IIT, Madras (M. Sc. 1984 Gold medal). His research interests are experimental and theoretical aspects of foundational issues in gravity and quantum physics, including quantum optics. The experimental expertise spans the range of precision measurements employing torsion balances, interferometers, laser cooled atoms and Bose-Einstein Condensates (www.tifr.res.in/~filab). He was part of the team that pioneered experimental gravitation studies in India in a special under-ground laboratory at Gauribidanur, Karnataka. He set up the laser-cooling laboratory at TIFR, Mumbai, in which the first Bose-condensate in India was produced and studied in an optical trap. Major theoretical contributions are in the study of dynamics and relativity in the context of cosmic gravity (Cosmic Relativity) and in quantum physics, clarifying the relations between fundamental conservation laws and quantum correlations. Unnikrishnan's cosmic relativity theory unifies dynamics, relativity and gravity by asserting and proving, with a multitude of experimental evidence, that both dynamics and relativistic effects are gravitational consequences of the entire matter in the universe. This grand generalization of the Machian view of dynamics is meant to become the new paradigm for all of fundamental physics. Unnikrishnan is a key member of the IndIGO consortium and the LIGO-India project (www.gw-indigo.org) for setting up advanced gravitational wave detector in India and he is part of the global LIGO Scientific Collaboration for research in gravitational waves.Unnikrishnan has published over 180 research papers in journals and books/proceedings covering several areas of fundamental physics, especially gravitation and quantum physics. This includes several papers addressing some core foundational and philosophical issues in physics pertaining to locality and causality, unobservables, space-time and mind-matter problem.Major interests outside physics research are music and films, especially the process of their creation and structure. His main interest in music is instrumental music on flute and guitar. He has worked on films as an actor and assistant director. He has been a columnist, expressing views on science and society, for Malayalam news magazines Kalakaumudi and Navamalayali.

less

Uploads

Papers by CS Unnikrishnan

Matter, Space, Time, and Motion: A Unified Gravitational Perspective

Space, Time and the Limits of Human Understanding, 2016

This article explores the links between space, time, matter and its motion in the essential conte... more This article explores the links between space, time, matter and its motion in the essential context of the universe they constitute. Conventional and standard physics maintains a nearly dismissive separation between dynamics and the matter-filled universe and indeed between cosmic matter and a priori space-time while asserting their mutual influence in other physical situations through the Einstein equations of general relativity. This can be traced to the incompatibility between the special theory of relativity that rejects a preferred frame and the real situation of a single matter-filled universe in which observers in different states of motion have measurably different experiences. We will argue that the present position cannot be maintained consistent with empirical and physico-logical evidence. The historical fact that all our fundamental theories were formulated and completed before we acquired significant and crucial knowledge about the matter content of the universe and its gravity is contrasted with the unavoidable situation that all our empirical experience and dynamics happens in the presence of all other matter in the universe. A careful analysis leads to a new and necessary paradigm in which several of our notions and even fundamental theories involving space, time and matter need to be reformulated with cosmic gravity as the determining factor. This, when combined with some crucial experimental results, answers several open issues that have been debated for centuries in foundational physics.

New Measurement of the One-Way Speed of Light and Its Relation to Clock Comparison Experiments

The Eleventh Marcel Grossmann Meeting, 2008

Exciting Whispering Gallery Modes in liquid microdrops using sub-micron size tapered fibers

Laser Resonators, Microresonators, and Beam Control XXII, 2020

We report here the observations of high Q (up to 7 x 107) Whispering Gallery Modes in liquid micr... more We report here the observations of high Q (up to 7 x 107) Whispering Gallery Modes in liquid microdrops of a glycerol-water mixture and three different silicone oils, which are excited and detected using high transmission tapered fibers of sub-micron waist sizes. For measuring the real Q values, which are not thermally limited, the laser frequency is scanned fast enough such that the broadband thermal oscillations of microdrops, with frequencies from kHz to 100s of kHz, do not affect the resonance signal. The two standard measurement methods `linewidth measurement' and `cavity ring-down' are used - the first one for resonances with Q <107 and the second one for Q >~ 107. We describe our analysis to show that for the tested liquids, absorption loss plays the dominant role in deciding the maximum value of the measured intrinsic Q of the microdrops. Using the analysis we show that the measured optical Q can be used to estimate a reliable upper limit of the absorption coefficient of liquids.

Physics in the ‘Once Given’ Universe: New Perspectives on Dynamics, Relativity, Quantum Spectra and the Spin-statistics Connection

Recent Developments in Theoretical Physics, 2009

Popper's Experiment, Uncertainty Principle, Signal Locality and Momentum Conservation

Foundations of Physics Letters, 2000

An experiment proposed earlier by Karl Popper in his critique of the Copenhagen interpretation wa... more An experiment proposed earlier by Karl Popper in his critique of the Copenhagen interpretation was realized recently by Kim and Shih. We show that the Copenhagen interpretation is consistent with the results, contrary to Popper's expectation. We examine the role of signal locality and momentum conservation in Popper's experiment and in the realization by Kim and Shih.

Experimental Perspectives on the Interplay between Quantum and Gravity Physics

There is a rich history of experimental effort that has been aimed at exploring the effects of gr... more There is a rich history of experimental effort that has been aimed at exploring the effects of gravitational fields on the elementary building blocks of matter: atoms, nuclei and subatomic particles, including the photon and neutrino. Much of this work was originally empirically motivated, with many of the investigations driven simply by curiosity over how the gravitational field might affect either various attributes of the quantized states of matter or the behavior of fundamental particles. More recently, searches for novel or anomalous aspects of gravity (torsion, screening effects, etc.) have employed “exotic” matter (eg., spin-polarized substances, superconductors, etc.) the properties of which can be understood only in terms of quantum mechanics. Substantial theoretical developments have often either preceded or accompanied that class of experiments. All of this reflects the desire of experimental physics to contribute insight into the problem of the interplay between quantum ...

On Fresnel Aether Drag, `Moving' Images, and Relativity

Physical review letters, 2019

I show the decisive difference between genuine transverse Fresnel drag of light in a moving mediu... more I show the decisive difference between genuine transverse Fresnel drag of light in a moving medium and the "spatial shift" measured with a time dependent interference pattern of light traversing a homogeneous finite medium (J. Leach et al., PRL 100, 153902 (2008)). In the latter case, the relative velocity and spatial shift are in fact zero and the `movement' is an elementary visual illusion, easily made superluminal. Three separate proofs are given for this fact. What is recorded in the experiment is just the difference between a time dependent space-fixed pattern and its time lagged version. This has no relevance to relative motion of any physical entity, Fresnel drag or relativity.

Download

On Einstein's resolution of the twin clock paradox

Current Science, 2005

Einstein addressed the twin paradox in special relativity in a relatively unknown, unusual and ra... more Einstein addressed the twin paradox in special relativity in a relatively unknown, unusual and rarely cited paper written in 1918, in the form of a dialogue between a critic and a relativist. Contrary to most textbook versions of the resolution, Einstein admitted that the special relativistic time dilation was symmetric for the twins, and he had to invoke, asymmetrically, the general relativistic gravitational time dilation during the brief periods of acceleration to justify the asymmetrical aging. Notably, Einstein did not use any argument related to simultaneity or Doppler shift in his analysis. I discuss Einstein's resolution and several conceptual issues that arise. It is concluded that Einstein's resolution using gravitational time dilation suffers from logical and physical flaws, and gives incorrect answers in a general setting. The counter examples imply the need to reconsider many issues related to the comparison of transported clocks. The failure of the accepted vie...

Strong in Small and Weak at Large: Thoughts and Bounds on Higher-Dimensional Gravity

International Journal of Modern Physics D, 2008

Gravity in a higher-dimensional scenario is one of the most topical of research subjects due to t... more Gravity in a higher-dimensional scenario is one of the most topical of research subjects due to the possibility of decisive results from experiments. The field exhibits duality of various kinds. On the one hand, the weakness of gravity and the hierarchy issues are handled with some success as one cascades from a larger number of small dimensions with strong gravity to a smaller number of dimensions of larger space with weaker effective gravity. On the experimental front, the highest energy accelerator and the weakest energy mechanical oscillators available to us today are simultaneously focussed at the TeV scale to address new features in gravity physics. This intriguing scenario and its conceptual and phenomenological aspects are examined here, with new results from considerations of hitherto-unexplored higher-dimensional gravitomagnetic effects at the atomic scale.

Measurement of the Casimir Force in the Range Above 5 Microns and Detection of the Finite Temperature Effect

The Eleventh Marcel Grossmann Meeting, 2008

Photoassociation of ultracold metastable helium atoms

2003 European Quantum Electronics Conference. EQEC 2003 (IEEE Cat No.03TH8665), 2003

Photoassociation of metastable He (23S1) atoms at ultra low temperatures close to the BEC phase t... more Photoassociation of metastable He (23S1) atoms at ultra low temperatures close to the BEC phase transition is studied, which was achieved previously in an Ioffe-Pritchard magnetic trap and detected optically through absorption imaging of the optical density profile. In the present experiment, the cloud is brought close to the BEC transition by evaporation and then illuminated by laser pulse tunable around the three (23S1-23P0,1,2) resonance lines at 1083 nm. A subsequent optical density measurement is used to detect any increases in the trap loss rate that may have been caused by the pulse. The experiment is particularly interested in detecting losses due to the production of ultracold molecules by photoassociation (PA), and in finding several weakly bound S-P states that have not previously been detected.

Gravito-Electromagnetism: Glimpses of Unexplored Deep Connections

International Journal of Modern Physics D, 2004

Any attempt at unification of the fundamental interactions will recognize its 'right path&#39... more Any attempt at unification of the fundamental interactions will recognize its 'right path' when electromagnetism and gravity are seen together as manifestations of the same interaction. First excitement along this direction was the Kaluza–Klein program, and the unsuccessful attempt was Einstein's unified field theory. Over the years, the program has changed much, but the basic idea that there are links between gravity and electromagnetism, perhaps in a higher dimensional world, has not changed. There are several interesting and important phenomenological aspects related to this issue, to be experimentally explored at the classical level, which may reveal some of the deep connections between the two long range interactions. In this essay, we discuss a program to experimentally explore some connections between gravity and electromagnetism, not yet adequately studied. Some of the key issues we address are the complete absence of gravity for electrons inside a metal drift tu...

Photon Correlations and Entanglement: Foundational Issues and Some Applications

International Conference on Fibre Optics and Photonics, 2012

I briefly review second order or two-photon correlations starting from the Hanbury Brown-Twiss co... more I briefly review second order or two-photon correlations starting from the Hanbury Brown-Twiss correlations to its modern versions in quantum optics studies. With this background, I address some foundational issues in the physics of quantum correlations and quantum entanglement and argue in favour of the validity of Einstein locality, to settle a long-standing debate. Understanding entanglement from this perspective has applications in quantum information theory, especially in gaining intuition about the relation between different measures of entanglement and its time evolution. Some examples are highlighted. I discuss how ideas on photon correlations applied to squeezing fluctuations in coherent light have become important in metrology, and perhaps crucial, in the successful operation of high sensitivity gravitational wave detectors.

Search for a fifth force

Pramana, 1993

Page 1. PRAMANA 9 Printed in India Supplement to Vol. 41 __ journal of December 1993 physics pp. ... more

The incompatibility between local hidden variable theories and the fundamental conservation laws

Pramana, 2005

I discuss in detail the result that the Bell’s inequalities derived in the context of local hidde... more I discuss in detail the result that the Bell’s inequalities derived in the context of local hidden variable theories for discrete quantized observables can be satisfied only if a fundamental conservation law is violated on the average. This result shows that such theories are physically nonviable, and makes the demarcating criteria of the Bell’s inequalities redundant. I show that a unique correlation function can be derived from the validity of the conservation law alone and this coincides with the quantum mechanical correlation function. Thus, any theory with a different correlation function, like any local hidden variable theory, is incompatible with the fundamental conservation laws and space-time symmetries. The results are discussed in the context of two-particle singlet and triplet states, GHZ states, and two-particle double slit interferometry. Some observations on quantum entropy, entanglement, and nonlocality are also discussed.

Do leptons generate gravity? First laboratory constraints obtained from some G experiments and possibility of a new decisive constraint

Physics Letters A, 2001

The equivalence of the active and passive gravitational masses has been tested in the laboratory ... more The equivalence of the active and passive gravitational masses has been tested in the laboratory to an accuracy of about 5 parts in 10 5. However, this level of sensitivity is not enough to answer the important question whether leptons generate gravity. We point out that some of the contemporary experiments aimed at re-determining the Newtonian gravitational constant, G, have reached the level of sensitivity required to provide the first meaningful result from a direct experiment on this important issue. Stronger constraints on the hypothesis that leptons do not generate gravity could be more decisively provided by still other G experiments if their aimed sensitivities are maintained in experiments with different sets of source masses.

Download

Contemplations on Our Physical Links to the Universe: Searching for and Finding the Hidden Harmony

Leonardo, 2006

The author discusses the evidence and consequences of our indissoluble physical links to the enti... more The author discusses the evidence and consequences of our indissoluble physical links to the entire universe. He finds that the apparent conflicts in fundamental physical theories regarding issues of causality and locality are not real conflicts based in the physical world. He presents an emergent worldview interpreted in the context of a cultural, philosophical and linguistic background in which a strong tension between inseparability of the whole and the local causal flow of events seems not to exist. The existence of the whole can be felt in the parts, as something real, measurable and undeniable. Its simplicity and harmony are spiritually enriching and emotionally moving.

Download

Naked singularities in spherically symmetric gravitational collapse: A critique

General Relativity and Gravitation, 1994

One of the most important questions in the physics of gravitation phenomena is whether gravitatio... more One of the most important questions in the physics of gravitation phenomena is whether gravitational collapse can lead to the formation of singularities which are not hidden by an event horizon. The Cosmic Censorship Conjecture (CCC) represents the hope that such a drastic event cannot happen in realistic physical situations. However, in the recent past several counter examples to the CCC were demonstrated by several researchers in situations of spherically symmetric gravitational collapse. The disturbing aspect about these counter examples is that they are strong naked singularities—they can crush matter to zero volume and can have a disastrous influence on causal physics. We examine these counter examples for their physical content by working through the dynamical collapse of inhomogeneous dust and argue that these are not physically acceptable counter examples. Our main result is that the singularities when naked are weak and when strong, strongly censored. The strong naked singularities in the counter examples do not arise from dynamical collapse; they result from the intrinsically singular nature of the initial density distributions chosen. The CCC seems to remain robust as far as spherically symmetric collapse is concerned.

Correlation functions, Bell's inequalities and the fundamental conservation laws

Europhysics Letters (EPL), 2005

I derive the correlation function for a general theory of two-valued spin variables that satisfy ... more I derive the correlation function for a general theory of two-valued spin variables that satisfy the fundamental conservation law of angular momentum. The unique theory-independent correlation function is identical to the quantum mechanical correlation function. I prove that any theory of correlations of such discrete variables satisfying the fundamental conservation law of angular momentum violates the Bell's inequalities. Taken together with the Bell's theorem, this result has far reaching implications. No theory satisfying Einstein locality, reality in the EPR-Bell sense, and the validity of the conservation law can be constructed. Therefore, all local hidden variable theories are incompatible with fundamental symmetries and conservation laws. Bell's inequalities can be obeyed only by violating a conservation law. The implications for experiments on Bell's inequalities are obvious. The result provides new insight regarding entanglement, and its measures.

Download

Renewed relevance of new tests of the equivalence principle involving intrinsic properties of particles and antiparticles

Classical and Quantum Gravity, 2012

The equivalence of the Shapiro delay for photons and (anti)neutrinos is the currently accepted lo... more The equivalence of the Shapiro delay for photons and (anti)neutrinos is the currently accepted lone test of the equivalence principle concerning intrinsic properties and quantum numbers of relativistic particles and seemingly constitute the only direct test for antiparticles. We show that due to the overwhelming contribution of the kinetic energy to the effective passive gravitational mass, Shapiro delay neither tests the equivalence principle nor anomalous long-range couplings related to the intrinsic properties and quantum numbers of the particles. In effect, the internal properties of the test particle are irrelevant in the context of weak equivalence principle (WEP) due to the relativistic suppression factor. The general result, independent of the nature of the long-range WEP-violating interaction assumed, underlines the potential significance of new tests.