Quantum

Title: Quantum – Einstein, Bohr and the Great Debate About the Nature of Reality
Author: Manjit Kumar
Publisher: Hachette India 2009 (First published 2008)
ISBN: 978-93-80143-10-1
Pages: 386

This is a definitive book on what quantum mechanics is and how it came about. Manjit Kumar, who lives in the U.K was the founding editor of Prometheus, an interdisciplinary journal that covered the arts and sciences. He has written for a variety of newspapers and periodicals, as well as co-authoring Science and the Retreat from Reason. His style is impeccable and lucid. Like a master dissecting the innards of an object worth studying, he lays out the bits and pieces on the table for everyone to see and appreciate clearly and then goes on to the details in a majestic way – an act which can be performed only by a well accomplished scholar, who means what he says. This book surpasses all others on quantum mechanics and is definitely not for those who fret over equations and graphs. Otherwise, for a genuine student of popular science, who wants to know how the most accurate description of reality so far, has come about to grab its place in modern science. The illustrated graphs and diagrams succinctly personify the ideas presented and the equations are presented only where it is absolutely required without which the argument can’t proceed beyond. A person with a secondary-school level exposure to physics won’t find the mathematical abstractions daunting. The book is well endowed with a timeline of the important events and an excellent glossary. Some photographic plates of the protagonists ensure added interest. Especially appealing was a group photograph of the 5^th Solvay conference in 1927. Of the 27 scientists pictured, 19 became Nobel laureates.

The origins of quantum mechanics lay in the intellectual curiosity of 19^th century of why a hot metallic body emits light of different colours when it was heated. The problem was extended to blackbody radiation and Wilhem Wien discovered the relation between energy and temperature of blackbody. The body, when heated up would start emitting light with higher energy as the temperature is increased. However, Wien’s formula was found to be incorrect in the infrared region. The theory and experiments seemed to differ. Max Planck made the apt discovery that energy is emitted or absorbed in small, discrete packets called quanta. He is regarded as the father of quantum physics. He found the theory difficult to reconcile with classical theory where energy is dissipated or absorbed in a continuous form. The next breakthrough for quantum came in 1905 from Albert Einstein who was a Swiss patent clerk at that time. He postulated that light also comes in discrete quantum packets and explained how the photo-electric effect takes place. It was for this theoretical explanation of the well known effect that he was awarded the Nobel Prize. The incredulous scientific community had to accept his theory as it was able to account for the observed paradox in specific heat capacities of elements.

The world of physics was shaping up crudely in this period and the many theories we study quite early in our academic curricula and take for granted had not even been postulated. The world was quite reticent to accept the atomic theory, the idea that everything is made of tiny atoms! Once it was established beyond doubt, the next question was how to account for atomic structure. Ernest Rutherford suggested that it consists of a central core called the nucleus, around which electrons orbit in a three dimensional space. Niels Bohr found this postulate to be riddled with inconsistencies. Any such being circling about a centre would radiate its energy and would collapse to the centre, unless some other force is acting upon them. The earth goes around the sun in a stabilized orbit because of the gravitational force between these bodies. But for atom, no such force existed and the stability seemed to be a mystery. Then Bohr came out with his world-famous atomic model in which electrons circle around the nucleus only at well defined and discrete distances from the central core. If the electrons follow these paths, they won’t radiate energy away. They can absorb energy from the outside and move to outer levels with higher energy and also can dissipate energy to move from outer levels to inner levels. This explained the reason behind the existence of bright lines in the emission spectrum of hydrogen. When an electron in a higher orbit in the hydrogen atom emits a quantum of radiation and moves to an inner orbit, that energy comes out with a specific wavelength (colour) which is expressed as a function of the orbits. It was later discovered that each line is not in fact one, but two separate lines. Along with Sommerfeld, he modified the model to accommodate elliptical, instead of circular orbits which solved the spliiting of lines problem.

Even though the pioneers of science in the first quarter of 20^th century, Bohr and Einstein differed on the theoretical implications of their work, the former thoroughly espousing quantum mechanics while the latter latching on to the classical interpretation of reality and causality. Some times, we feel that the animosity extended to the personal level and we see in many places that even the great luminaries quarrelled among each other when their firmly held ideas were challenged by others. Bohr opposed the light-quanta of Einstein, rechristened photons. When Arthur Compton experimentally proved that radiation acted in quanta in one of his x-ray scattering studies, Bohr confronted it with a theory that the conservation of energy doesn’t act in sub-atomic levels. However, this was proved wrong and Einstein’s postulate was proved right. Later, Louis De Broglie postulated that all matter, including electrons acted like waves, putting forward his wave-particle duality. Electrons were proposed to be like standing waves generated in a tightly tied string, when it was mechanically vibrated. The number of waves in a string will be depend upon the half-wave lengths. This theory explained why only specific orbits exist inside the atom. As per de Broglie’s postulate, only those orbits will be available in which the circumference equals an interger multiplier of the half-wave lengths of the electron. This neatly explained the unscrutable issue.

Even with all these discoveries, it was not possible to explain the fine splitting of hydrogen’s spectral lines. George Uhlenbeck and Samuel Goudsmit proposed a quantum entity, spin, to the electron which would account for the phenomenon. The new parameter helped Wolfgang Pauli to come out with his exclusion principle. Up to then, the developments in the new field were purely piecemeal, without any effort to describe the underlying physical phenomena on the basis of a sound theory. Werner Heisenberg put forward the basics of quantum mechanics while working under the watchful eye of Niels Bohr at his institute in Copenhagen. Heisenberg’s formulae were stressed on the discontinuous, particular nature of quantum entities and used a matrix approach. Meanwhile, Erwin Schrodinger proposed a theory more at ease with the wave nature and which was mathematically simpler and more familiar with the physicists at that time. Naturally, animosity aroused between these two stalwarts and both exercised their influence on their fellows to stick to their own camp. Further studies in this area prompted Heisenberg to come out with his Uncertainty principle, which stated that the momentum and position of a sub-atomic particle, or energy and time of a wave, cannot be accurately determined. This was not due to any physical problem with the measuring instrument or method, but nature, in such microscopic levels doesn’t behave in a way which we expect her to be. This formally put an end to causality. The official stand based on these principles came to be known as the Copenhager interpretation with Bohr, Pauli and Heisenberg as its titans. Bohr announced the quantum mechanical theory as complete during a conference in Como, Italy in 1927. This gradually consolidated into a dogma among physicists.

Einstein, who was the greatest living scientist at that time opposed this conclusion tooth and nail. While he admitted that quantum mechanics was true, because it tallied with every experiment conducted till date. What he couldn’t digest was the assertion that it was complete. Einstein firmly believed that the quantum events have real, physical basis and the Bohr’s team asserted that such an event will be undecided until an observation is made which will make its wave function collapse. He challenged the quantum mechanics team with thought experiments during the Solvay conference in Belgium in 1927, but Bohr could counter all arguments effectively. Einstein came back with a bang during the 6^th Solvay conference in 1930 with his famous light box thought experiment. He proposed that a box full of light is made with a clock in it synchronised with another clock outside. At a predefined time, its shutter opened and a single photon went out. Thus, the moment or time of the wave can be determined. If the box is weighed again after the ejection of photon, the mass of the emitted photon can be determined, from which its energy can be found out by using his famous equation. Thus, Einstein argued that the energy and time can be accurately determined at the same time, making the uncertainty principle and quantum mechanics erroneous. Bohr was dumbfounded at first by the brilliancy of the argument at first. After a sleepless night and endless deliberations with his assistants who included Heisenberg and Pauli, he responded with a flaw in Einstein’s scheme. In order to weigh the box again, it have to be moved up and down to balance it. Since the clock is then moving under earth’s gravity, time will be dilated and clock affected according to Einstein’s own general theory of relativity! In a moment of rush, Einstein had himself forgot about his own theory! Even though he accepted the flaw in his argument, he was not convinced that quantum mechanics was a complete theory. He migrated to the U.S.A when Hitler ascended in Germany and continued to attack the Copenhagen interpretation from time to time, but the world physics community had come to the conclusion that senile decay was affecting his judgement and his arguments didn’t carry the weight which it once did.

Nazi accession in Germany was a violent affair who were bent upon the extermination of Jews in Germany and those countries which came under their yoke. Scientists were expelled from there under the new rule that public servants should be of the Aryan race. Hundreds of scientists, of which about 20 who’d go on to win Nobel Prizes in future fled Germany. Einstein settled in the Institute of Advanced Study at Princeton. After 1930, no major breakthroughs in quantum mechanics came about, vindicating Bohr’s claim that it was complete. However, Einstein continued his tirades against it till he died in 1955, aged 76 and Bohr defended his position till his death came in 1962, aged 77.

This is the synopsis of the book, which in no way conveys the pleasant and erudite style of writing by Manjit Kumar. In fact, there seems to be no points which can be shown against the work. The last two chapters, which summarised the ongoing work in the field after Einstein and Bohr died were a little off the mark as it was somewhat difficult to understand. Except this, nothing can be held out against this fine piece of writing of popular science. The author’s consistent use of the symbol ω (omega) for π (pi) was and is confusing. Some interesting facts can be discerned from the general body of the book. For example, George Thomson was awarded the Nobel Prize in 1937 for discovering that the electron was a wave, while his father, Sir J J Thomson, had been awarded the same prize in 1906 for discovering the electron was a particle! Also, it was curious to learn that there were only three portraits in Einstein’s study, those of Faraday, Maxwell and Gandhi.

This book is highly recommended.

Rating: 5 Star