The Theory of Relativity: The greatest discovery of all times

The Theory of Relativity: The greatest discovery of all times

Introduction

The Theory of Relativity is one of the most successful theories until now that is the basis of most of the discoveries. Published between 1905 and 1916, this theory has proven itself to be the most true concept throughout history.

The famous equation which is the basis of all relativity, 'E = mc²'

History and Creation

When Isaac Newton published his Philosophiæ Naturalis Principia Mathematica or the Mathematical Principles of Natural Philosophy, he described the Law of Gravity as one that says that every object that has mass attracts things towards itself through its individual gravity. The problem here was that he didn’t know the source of Gravity, like, where did it come from? This problem remained unanswered until 1905 when Einstein published a book titled Zur Elektrodynamik bewegter Körper in which he showed his theory of Special Relativity. This theory dealt well when the objects were not in motion and when Gravity was not there. But it didn’t stop there, he wanted to go further. He did a thought experiment. One day, he saw some window washers high on the stairs. He imagined what would happen if one of them would fall. Of course, it would not be good. But Einstein took it differently. He said that if he were in the place of the washer and would be falling at a speed of 8.2 m/s. Gravity would be the only force acting upon him and the ground would not be pushing on him so he would feel weightless resulting in a freefall. This is the same as being weightless in space. Now, imagine being on earth in a room and measuring your weight. You would weigh the same amount as much as you weigh (say, 51 kg). But now if you were in a spaceship that was moving upward with a speed of 8.2 m/s which is the exact amount of the gravitational acceleration on earth, you would weigh 51 kg again. So it would be indistinguishable for him between being attracted by gravity or being pushed down by acceleration. This is the Principle of Equivalence.

Discovering the curvature in space

Let’s take that spaceship again. Now suppose that the man on the spaceship shines a torch from one side to the other. He would see that the centre of the beam at the source is higher than the middle of the beam at the end as the acceleration pushes it down. Now, do the same thing on Earth. We would expect the centre of the beam to be at the same height at both points but that would violate the Principle of Equivalence. So the light beam would bend. This meant that light must bend in a gravitational field. But light always takes the shortest part, why would it bend? But now, take it differently. Maybe the light is taking the shortest path. Maybe the shortest path is not a straight line. Just imagine, Isn’t the shortest part from the North Pole to the South Pole curved provided that you are bound to the surface. So maybe Gravity bends space in a way that because space gets curved, the shortest path itself gets curved. Instead, every path is curved there in a way that no straight line can exist relative to the person who is in a place where space is not curved. Now, this had to be proven by mathematics. But it was so complex that einstein had to contact his old buddy, Mathematician Marcel Grossman. He had just done his PhD in the topic of ‘Geometry of Curved Spaces called Riemannian Geometry’. A perfect man for this job! They both figured out the mathematics of curved Space-Time. Actually, Curved Geometry is the basis of General Relativity.

Image Source - Google | Image by - Understanding Science | Light curving when passed through curved space-time

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