2015 marks 100 years since The General Theory of Relativity was dropped onto the world by Albert Einstein. The General Theory of Relativity came in a decade after the Special Theory of Relativity in 1905. Aside from it’s groundbreaking implications, the theory also happened to be a very emotional one for Einstein. So far, the General Theory of Relativity continues to dominate our understanding of the universe by far, and has found itself applications in all sorts of crazily important industries.

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Why Relativity?

Newton did change the world with his theory of Gravity back in 1687. For the first time, man had found a common law that unified the Earth and the Heavens. While it worked beautifully, and had a much larger inspirational effect, there were certain anomalies found in Newtonian classical mechanics. Some observations didn’t match predictions. This was when Einstein came up with a theory that stated that the fabric of space-time itself is curved. There have been various consequences that adhere to the theory of general relativity such as light rays bending in a gravitational field. There are many other instances to which we could relate this theory into our day to day lives. Essentially, the major implications of the theory of Relativity were:

Space and Time aren’t separate. They’re both part of a 4 dimensional fabric called space-time. It is possible to alter our movement through the three dimensions, AND through time.

The only constant in the universe is the speed of light. The more you accelerate to this cosmic speed limit, the slower time will pass for you. This allows for ‘trips’ to the future by simply doing a roundtrip to your location at a high enough speed.

Along with velocity, the passage of time is also affected by gravity.

These implications have had an immeasurable impact on the industries of today. A century later, the General Theory of Relativity is more relevant than ever.

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The Relevance of General Relativity

Clocks run slower in regions of greater gravitational fields.

Gravity slows down time. The closer you are to a gravitional source, the slower time will pass for you relative to someone in a lower gravitational region. This implication has been proved with an experiment, carried out using atomic clocks placed at varying altitudes. These insanely accurate clocks eventually showed a difference in time, even though it was in the order of a few milliseconds. What does it mean for us? Well, if it’s important for you – your head is younger than your hands which are younger than your foot because of varying distances from the earth’s gravitational field. The parts of your body closer to the Earth age slower.

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“A straight line is the shortest distance between any two points’’, might not always work out to be true. It is a curved path in a few cases. Let us consider two huge bodies in the universe in a straight light, but when we view them the bodies appear to be side by side with their edges touching. This is because the light takes up the geodesic path which the shortest distance, considering all the forces at play. This is because the light rays bend about the enormous gravitational field exerted by the bodies.

Mercury’s paradoxical orbit

This explanation answered one of the mystifying questions about Mercury changing its orbital orientation when closest to Sun. Precession of orbits is common to all the planets but for Mercury it was at a greater rate as predicted by Newtonian mechanics and Kepler’s laws. There was a 43 arc second discrepancy that remained unexplained for about two centuries. The mass of Sun warps the gravitational fabric and Mercury being very close to the Sun comes within the distorted space which causes an increase in precession angle.

GPS Satellites

The GPS wouldn’t have been possible without Relativity. Every satellite we send into space needs to be time-corrected to allow for the effects of Relativity. Our entire space program depends on Einstein’s theory! The time dilation is accurately calculated for these satellites traveling at a height of about 36,000 kilometers (geo stationary satellites have to be at this altitude) from the earth’s surface. Even a 15 nanosecond time difference may change the position by about 50 meters.

Relativity still remains one of the most revolutionary theories to explain the universe. It’s helped us understand the black hole, the expanding universe and a host of other aspects about the universe that had baffled us. This one theory has paved way for enormous number of clarifications, discoveries and applications.

Also read: 50 billion Neutrinos pass through your body every second

These are just a few implications of this theory. Einstein’s journals indicate that this discovery had impacted him emotionally in significant ways, to the point that he thought Nature had truly spoken to him. This theory now drives the modern world as we know it today. 2015 was justifiably called the International Year of Light – Einstein’s Centenary.