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The GPS in your smart phone and the General Theory of Relativity

 

Everyone knows that Albert Einstein was one of the greatest physicists of the early twentieth century. 2015 marks 100 years since he published his theory of gravitation, which keeps us on the floor and keeps the earth in its orbit around the Sun. He called this the general theory of relativity and we call it GR for short.

 

In 1915, Newton's laws of gravity had stood unchallenged for 250 years, and had explained the motion of the planets with great accuracy. Einstein's reason for wanting to replace it was his own discovery in 1905 that nothing could travel faster than light. In Newton's theory the effect of gravitation was instantaneous. Einstein replaced the force of gravity with a geometrical idea of curvature of space and time. The geometric  explained something that Newton had to postulate - particles of different masses move in the same way in the gravitational field of the earth, or the Sun.  In spite of being completely different from Newton's view of gravity, Einstein's theory was able to take over all its triumphs

 

But this was no mere rewriting of an old idea. GR explained the discrepancy in the motion of the planet Mercury and predicted that light rays passing near the Sun would be bent by a small angle. This experiment was carried out in 1919 by English astronomers, and proved Einstein right.  Friedmann, in Russia, showed that the theory could describe an expanding universe. This was confirmed a few years later by astronomical observations which showed distant galaxies moving away at speeds proportional to their distance from us.  

 

Fifty years after Einstein, Hawking and Penrose, were able to put the existence of black holes on a firm mathematical basis. A black hole is a sphere whose boundary is a one way membrane - anything entering it can never come out - not even light.  It results as the final stage of an object collapsing under its own gravity. Soon after this, astronomers found rapid motions and high energy radiation near the centres of galaxies.   The properties of these objects are best explained by the presence of black holes. Today, thousands of black holes are known and studied in great detail. GR is routinely used to understand the light, X-rays, and radio waves which astronomers receive from the centres of galaxies - these do not come from within the black hole, of course, but from material heated up while falling in. Currently, astronomers are poised to measure one more prediction of GR- waves in the gravitational field, traveling at the speed of light.

 

The effects of GR near the earth are very small - a few parts per billion, but very important practically. The GPS receiver in every smartphone has to use formulae based on GR, to locate you to within a few metres accuracy, with respect to satellites tens of thousands of kilometres away moving at tens of thousands of kilometres per hour.

 

GR is in your pocket today. What we celebrate is a milestone in human thought which has changed forever our view of space, time, gravity, and the universe.



Comments

Special theory of relativity is invalid beyond the speed of light for particles of masses greater than 1 kg or time events greater than 1 second.The link of the same is attached below.When contacted the expert professors,in the college they opined such a theory to be backed or nominated for the INFOSYS SCIENCE PRIZE 2016, no college in India is competent in this regard.In this circumstances,whom can I rely and what should I do. The link is https://www.researchgate.net/post/Spooky_action_at_a_distanceWas_Einstein_wrong

Thank you for your comment! These are exciting times. The recent discovery of the existence of gravitational waves by the advanced Laser Interferometer Gravitational Wave Observatory has unveiled new possibilities for us to study of the Universe and its origin. Indian scientists have contributed significantly to this discovery. The Infosys Science Foundation continues to stay committed towards encouraging the quest of the unknown through scientific excellence.

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