BOOK OF THE MONTH: MARCH 2016

                                                                        

Title         : Ripples on a Cosmic Sea: 
                 The Search For Gravitational Waves  
Authors   : David Blair and Geoff McNamara 
Pages       : 224  
Publisher : Helix Books / Perseus Books  
ISBN        : 10:0738201375

In physics, gravitational waves are ripples in the curvature of spacetime which propagate as waves, travelling outward from the source. Predicted in 1916 by Albert Einstein on the basis of his theory of general relativity, gravitational waves transport energy as gravitational radiation. The existence of gravitational waves is a consequence of the Lorentz invariance of general relativity since it brings the concept of a finite speed of propagation of the physical interactions with it. By contrast, gravitational waves cannot exist in the Newtonian theory of gravitation, since Newtonian theory postulates that physical interactions propagate at infinite speed.

Various gravitational-wave observatories (detectors) are under construction or in operation, such as Advanced LIGO which began observations in September 2015. Potential sources of detectable gravitational waves include binary star systems composed of white dwarfs, neutron stars, or black holes. On February 11, 2016, the LIGO Scientific Collaboration and Virgo Collaboration teams announced that they had first observation of gravitational waves from a pair of merging black holes using the Advanced LIGO detectors.

As per Einstein's theory of general relativity, gravity is treated as a phenomenon resulting from the curvature of spacetime. This curvature is caused by the presence of mass. Generally, the more mass that is contained within a given volume of space, the greater the curvature of spacetime will be at the boundary of its volume. As objects with mass move around in spacetime, the curvature changes to reflect the changed locations of those objects. In certain circumstances, accelerating objects generate changes in this curvature, which propagate outwards at the speed of light in a wave-like manner. These propagating phenomena are known as gravitational waves.

Gravitational waves should penetrate regions of space that electromagnetic waves cannot. It is hypothesized that they will be able to provide observers on Earth with information about black holes and other exotic objects in the distant Universe. Such systems cannot be observed with more traditional means such as optical telescopes or radio telescopes, and so gravitational-wave astronomy gives new insights into the working of the Universe. In particular, gravitational waves could be of interest to cosmologists as they offer a possible way of observing the very early Universe. This is not possible with conventional astronomy, since before recombination the Universe was opaque to electromagnetic radiation. Precise measurements of gravitational waves will also allow scientists to more thoroughly test the general theory of relativity.

Gravitational waves have two important and unique properties. First, there is no need for any type of matter to be present nearby in order for the waves to be generated by a binary system of uncharged black holes, which would emit no electromagnetic radiation. Second, gravitational waves can pass through any intervening matter without being scattered significantly. Whereas light from distant stars may be blocked out by interstellar dust, for example, gravitational waves will pass through essentially unimpeded. These two features allow gravitational waves to carry information about astronomical phenomena never before observed by humans.

Most people live and work entirely oblivious to the fact that a myriad of ghostly ripples are passing through them all the time. Generated in the depths of space by colliding stars and black holes, exploding supernovas and quasars, these so-called gravitational waves are literally ripples in the fabric of space itself. Sweeping across the cosmos at the speed of light, they encode vital clues about the exotic systems that produced them. Predicted by Einstein over eighty years ago, but never detected in the laboratory, gravitational waves have proven elusive to scientists.

In the first book for a general reader on these amazing waves, Blair and McNamara weave a thrilling tale about the race to build the first gravitational wave antenna—a challenge that has prompted physicists and astronomers to devise some of the most breathtaking technology the world has ever seen. What these scientists find will allow us to listen to the explosion of stars, the creation of black holes, even the sound of the Big Bang itself, and will undoubtedly chart a new course for astronomy in the coming millennium.

Review Courtesy: www.amazon.com, www.wikipedia.com