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BLACK HOLES AND TIME WARPS: EINSTEIN’S OUTRAGEOUS LEGACY·Kip S Thorne Papermac·1994·Price Rs 330

 
By Shobhit Mahajan
Last Updated: Saturday 04 July 2015

einstein's theory of general relativity, formulated in 1915, is widely acknowledged as one of the most elegant theories in physics. Einstein's special theory of relativity, formulated in 1905, replaced the Newtonian concept of space and time as absolute entities by a world-view where space and time depended on the observer. This theory was applicable only to observers at rest or in uniform motion. The general theory was an extension of the special theory to include the effects of gravitation and physics as seen by accelerated observers. The novel aspect of the general theory was the idea that gravity is a 'curved spacetime' phenomenon which produces effects identical to those produced by the gravitational field of a body.

The general theory of relativity had an enormous influence on scientific thought in its early years. The whole perspective with which we viewed the universe underwent a radical change.Sadly, however, with the advent of quantum mechanics, the theory of relativity was cutoff from the mainstream of physics, which was almost exclusively focused on solving the problems of the microscopic domain. Since experimental verification was difficult to come by, the theory became a formalistic, stagnant subject, primarily of interest to mathematicians.

Things began to change in the '50s. With the development of new technologies in the Second World War, there was tremendous advance in experiments. Thus began the 'renaissance of general relativity' and, by the '70s, the legacy of Einstein's general theory of relativity was occupying some of the world's most brilliant minds.

Kip Thorne has introduced us to the history of this legacy in his book. One of the best known relativists and astrophysicists, Thorne is eminently suited to do the job.

"Of all the conceptions of the human mind, from unicorns... to the hydrogen bomb, the most fantastic perhaps, is the black hole: a hole in space with a definite edge into which anything can fall and out of which nothing can escape; a hole with a gravitational force so strong that even light is caught and held in its grip; a hole that curves space and warps time." Thus begins the book's prologue, which is in the form of a science fiction story about a space ship near a black hole. Complete with all the trappings of a Star Trek episode, the prologue gives us a fascinating preview of what is in the book.

The book then moves on to describe the revolution brought about by Einstein through his theory of relativity. Given that the ideas of relativity do not appear to be commonsensical, Thorne has done a marvellous job of making them accessible to the non-specialist reader. The mathematics is kept at a minimum and accurate analogies are used to give us a flavour of the physical ideas behind these otherwise highly mathematical theories.

In 1915, Schwarzschild, a distinguished astrophysicist, worked out the predictions that the new theory of gravitation made about stars. According to his calculations, which were valid only under a particular set of conditions, if a non-spinning star was massive enough, not only would space around it be curved but time would also behave differently. Time would flow more slowly near the star's surface than away from it and would come to a standstill if the mass of the star exceeded a critical mass! However, his arguments failed to convince Einstein and other contemporary cosmologists, and the idea of a 'black hole' died a premature death.

The next few chapters of the book are devoted to dif ferent kinds of stellar corpses, namely white dwarfs, neutron stars and black holes. It is now accepted that neutron stars, which are slightly more massive than our sun, but are only about 100-1000 km in radius, are responsible for pulsars objects in the sky which emit radio pulses with eerie regularity.Thorne explains the physics of neutron stars and the story of the genesis of the idea in a masterful way. Here, history is woven in with physics and sociology of science finds place with personal insights into the temperaments of various scientists.

The whole field of black hole physics, which was revived in the '60s, is covered in a few chapters. This introduction to the subject, which is one of the most perplexing and fascinating in physics, is certainly the best one I have read. Thorne brings this highly mathematical subject to life with the help of excellent analogies and diagrams. Classical black holes, their observational evidence in the form of x -ray sources like Cygnus x -1 and singularities in general relativity are very well summarised. He also devotes a chapter to gravitational radiation, which is supposed to be emitted by matter.

In 1975, Stephen Hawking shocked the world by showing that black holes, contrary to what was believed, actually emit radiation. This was a result of quantum effects in the neighbourhood of a black hole. This discovery led to a whole new hitherto unexplored field of black hole physics with quantum mechanics. Thorne relates the history of the work leading to and consequent to this result. Here again he weaves a narrative that interlocks history and physics with personal observations.

The last few chapters of the book are more speculative and are based on work which is very recent. This includes topics like the possibility of time travel. Thorne is very categorical in pointing out which part is well established and what is still just speculation. Of course, he has his biases which he points out candidly.

Kip Thorne has indeed written an excellent book. It has a wonderful glossary and an extensive bibliography. It is extremely reader-friendly and accessible, comprehensive and balanced. This is certainly one of the best popular science books to come out in a long time. One just hopes that it enjoys the success of A Brief History of Time , which was certainly a mediocre book compared to this one.

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