Writing is like T20 batting. If you block, you might as well retire to the pavilion! -- Pete Langman
Expat in Germany

Wednesday, February 17, 2016

From Mukhi to Talkie - Gravitational Waves

We have seen in the James Bond movie, Golden Eye when Sean Bean falls to death on the huge antenna in Puerto Rico. 'For England!' He fell onto the largest dish antenna in the world. It is a radio wave detector and works exactly like the Direct to Home dish antennas that we have at home. This type of an antenna is very powerful over the traditional rod antennae in that the gain is quite high due to its parabolic shape. To detect electromagnetic waves, fractal antennas are used (open up your phones, you will find one) and are efficient apart from being space efficient. But these are not the only waves that are discovered. Scientists in the future are going to face a crisis, for the amount of knowledge one should possess about a subject is increasing enormously. Exactly a hundred years ago, one of the greatest men to have ever lived, Albert Einstein predicted the existence of a new set of waves called the Gravitational waves and the doubts were confirmed in 1993.

Celestial bodies in space-time
 The universe is so huge and old that time and space are certain dimensions (to know more, do not contact the author, contact your nearest library). The best illustration for this is the famous stretched plastic sheet on which heavy objects when placed, create a curvature. However, the universe is not just a plane and this sheet or the space-time is everywhere, say. Now if there is a disturbance, just like ripples in water, there would waves created, called Gravitational waves. The mathematics behind it is much more than just four lines in English as above. It is quite easy to visualize this in terms of ripples in water when two bodies revolving around each other merge to form a single mass. Gravitational waves were first asserted to a binary pulsar (basically two star collision). This was 1.3 billion years ago, roughly when the Earth was learning to form continents. It is exciting enough to know what happened to Netaji Subhash Bose not more than hundred years ago. Now imagine if you could know what happened much before San Jose formed!

LIGO confirms G-wave
To understand optical interferometry, one should understand light (of course, no one did completely). What we all know about light till now should be revisited, forgotten and changed. Light can be defined using two things: phase and polarisation. Phase would be enough for now. When two light waves of same wavelength with a constant phase difference meet, they interfere constructively or destructively. This is the principle essentially used by a Michelson interferometer. The two arms in a Michelson interferometer are not of the same length. This extra length in one arm provides extra distance for light to travel through it and when it hits a mirror, it goes back 'later' than light from the other arm. This gives rise to temporal coherence, i.e phase difference due to time. The Laser Interferometer Gravitational Wave Observatory (LIGO) is a huge Michelson interferometer. The gravitational wave when it reaches the interferometer, distorts the space dimension, thereby changing the relative length of both the arms. This gives rise to temporal coherence which is observed when laser is passed through both the arms and thus the distortion in the arm length can be found out which gives all the information one needs to know about the gravitational wave. Indeed it would be like un-muting a talkie movie. From a silent movie (mukhi) to a talkie movie! 
Ironically, one can call this an achievement of the optics community.

LIGO Livingston interferometer. Each arm is so long that both dont fit into the same frame 

Actually, more than the gravitational waves, the interferometer is a scientific and engineering wonder. The mirrors literally are suspended in thin air. The up-gradation to the present LIGO is like replacing a two gear system with five gear system, it dramatically increases efficiency. Same thing with the mirrors, they were improvised from a single pendulum to four pendulum. The arms are as long as 4 Km because the distortion created would be so small that it is tough to identify it. Even the laser used has a high coherence length. To avoid noise from Earthly things like traffic, dogs barking and men sneezing, two non local interferometers are built to corroborate the data which happened recently. Both the interferometers in Hanford and Livingston gave the same readings. There are similar projects VIRGO in Europe and IndIGO in India(coming soon, say in just eight years by which the entire universe could possibly be mapped).

The confirmation of gravitational waves not only proves Einstein to be a super human, it also helps mankind in its understanding of the universe and encourages generations to come to be curious without consequence.
For Curiosity!