The World Is Quantum


In his preface to the Indian edition of the celebrated Feynman Lectures on Physics, Prof. Balakrishnan of our Physics department poses the whimsical Indian-university-exam-question, What are the applications of quantum mechanics?, and gives the answer: All of nature! This fact, that quantum mechanics is everywhere, was the theme of the first lecture of the IISc Alumni Association Distinguished Lecture Series held here on Wednesday the 18th, given by Prof. Ganapathy Baskaran, Emeritus Professor and Raja Ramanna Fellow at the Institute of Mathematical Sciences, Chennai.

Prof. Baskaran, a distinguished alumnus of the Indian Institute of Science, gave a whirlwind tour of the quantum world to a fascinated audience. And as well he might – he has made many major contributions in condensed matter physics. He also holds the Distinguished Visiting Research Chair at the pioneering Perimeter Institute for Theoretical Physics in Waterloo, Canada, an institute initially funded by the founder of BlackBerry, Mike Lazaridis. Prof. Baskaran is also the recipient of the Shanti Swarup Bhatnagar award – the highest honour given to Indian scientists – as well as other awards too numerous to mention.

There is a perception, often heightened whenever people hear of, say, the confounding Higgs boson: of what possible use of this? “Science, which unfolds the secrets of nature, helps society in unforeseen ways,” was how Prof. Baskaran gently rejected this shortsighted thinking, giving the example of how the World Wide Web was developed, initially so that scientists could share data, at CERN, the particle physics laboratory on the France–Switzerland border. The developers of quantum mechanics – our best description of the physical theory that describes matter at atomic scales – was not developed with the aim of inventing the transistor and other semiconductor devices, the fundamental components of modern electronic gadgets. Much of the world economy now depends, indirectly, on inherently quantum phenomena.

It was in 1900 that the quantum era began, when the German physicist Max Planck had to resort to a “desperate hypothesis” to explain something that had troubled physicists for long: the spectral distribution of radiation – or the relative intensities of light emitted at different wavelengths – from a perfectly black body. This blackbody radiation spectrum varies with the temperature of the body, which could not be explained with the physics known at the time. Planck managed to fit his theory to the experimentally-obtained spectrum by imagining light to be emitted and absorbed in discrete packets, called quanta.

“This led to a collective effort unique in human history, a forerunner to the collective character of modern science,” observed Prof. Baskaran. The resultant theory of nature, quantum mechanics, “has prompted a revolution in our thinking of nature for the last one hundred years, and is one of the greatest creative acts of humankind,” he went on to add. This revolution has seen the toppling of Einstein’s cherished notion of determinism, and introduced uncertainty as a fundamental aspect of the quantum world. Explaining that this is one of several facts about quantum mechanics which defy our common sense, based as it is on our intuition which has evolved in a world governed by classical physics, Prof. Baskaran said, “We don’t directly experience the quantum nature of the world because mass plays a fundamental role.” The electron, for instance, defies our classical intuition because its mass is so small. He gave examples of various exotic quantum phenomena, such as tunnelling (the fact that a subatomic particle like the electron can go through a barrier), and the apparent presence of a particle at many locations simultaneously.

The story of this blackbody radiation curve, however, does not end there. Two radio astronomers, in 1964, accidentally detected feeble radiation at microwave wavelength coming from all directions in the sky, which, they soon realized, didn’t have the usual suspects of galaxies and nebulae as their source. Instead, this was the theoretically-predicted leftover radiation from the Big Bang – our theory of how the universe began. Remarkably, this radiation has a perfect blackbody spectrum corresponding to a temperature of three degrees above absolute zero. In other words, Planck’s quantum hypothesis not only led to a rich and deep understanding of molecules, atoms, and subatomic phenomena, it has also made its presence felt in the night sky. Without the quantum, there is no way to explain the observed cosmic microwave background.

“Quantum mechanics is at work in the nuclear fusion lab at the core of the Sun,” added Prof. Baskaran, “and it is the reason plants are able to photosynthesize and we are able to see with our eyes.” Because we know this “quantum secret of nature”, scientists have been able to construct the Standard Model of particle physics, so called because it explains all of the varied interactions and processes in the subatomic world to great precision, as has been verified repeatedly by experiments – including the discovery of the long-predicted Higgs boson last year.

Closer home, Satyendranath Bose – after whom the class of particles, boson, is named – made fundamental contributions to quantum mechanics. Subrahmanyan Chandrasekhar, while on a ship voyage to England, applied quantum mechanics to the question of the stability of stars and arrived at his eponymous mass limit. Thus, “the beginning of modern astrophysics also lies in quantum mechanics”, exclaimed Prof. Baskaran. “Even the light-sensors used in digital cameras – the charge-coupled device – is based on an inherently quantum phenomenon, the photoelectric effect for which Einstein won the Nobel Prize,” he said with a smile.

Giving examples of such varied techniques as the Magnetic Resonance Imaging, or MRI, used in hospitals, and the electron microscope, extensively used for research in the life sciences, he said that “Many key developments in other fields of science and medicine can also be traced to the quantum hypothesis.” He went on to single out quantum computers as one of the most exciting and promising future applications of quantum mechanics.

The lecture also had its lighter moments: the recent news that the spacecraft Voyager 1 had left the solar system prompted Prof. Baskaran to point out that it derived its power from a radioactive source, which, once again, couldn’t have been harnessed without the predictive power of quantum mechanics. “NASA has spent a few hundred million dollars on this mission. If you convert that to rupees, that’s just the amount our politicians make in one scam!” he joked.

Prof. Baskaran also talked about the place of science in society. “Science is very broad and while it reminds us of our smallness in the universe, it also promises us unlimited potential for human benefit.” He lamented the fact that science in India was confined to a few centres of excellence, while smaller countries such as Singapore devote a much larger amount of money for research in the basic sciences.

The talk, the first of a planned monthly lecture series by the IISc Alumni Association, ended with the presentation of a memento to Prof. Baskaran.

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