What is gravity?

Gravity is one of the fundamental forces of the universe. It makes us fall to the ground when we jump, and makes enormous gas clouds to collapse in order to form stars.

For centuries humanity has tried to understand what is gravity. In spite of this, it wasn’t until Isaac Newton first studied gravity that we started to understand this force of the universe. In 1687 Newton published his Law of Gravitation, using mathematical expressions that precisely described the movement of bodies in a gravitational field. This was one of the major revolutions in the history of physics.

However, the work of Newton wasn’t totally complete. His equations couldn’t explain an anomaly in the orbit of Mercury, which makes it orbit the Sun a little bit faster than his equations predict. Moreover, Newton was incapable of explaining the mechanism through which gravity is transmitted between objects. The fact that this force seemed to act instantly throughout the universe greatly annoyed him.

All these mysteries were finally solved thanks to the theory of general relativity from Einstein, published in 1915.

A revolution of the conception of the universe

For centuries physicists treated space as an empty background over which took place all the events in the universe. Space was absolute, it didn’t change, and didn’t exist in any physical terms. With general relativity, Einstein totally changed this conception, affirming that space and time together form the fabric of the universe, called space-time, and that the latter can be stretched, compressed, and twirled, affecting all the matter around it.

Einstein suggested that the form of space-time gives rise to the force we experience as gravity. According to Einstein’s equations, a body, because of its own mass and energy, deforms space around itself, so that when other bodies approach they follow the curvature of space.

So, gravity is no more than the curvature of space, caused by the presence of mass and energy. This has been experimentally verified, by observing how the light of a star changes its trajectory when approaching the Sun.

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