# What is gravity? Who Discovered the Gravity?

The search for a scientific law that would adequately explain gravitation, or the force of gravity, began more than two thousand years ago, and although much progress has been made in all those years, scientists still have much to learn about the true nature of gravity. Maybe one of today’s young scientists will be the one to solve the remaining mysteries surrounding this force of nature.

## Gravity – How Does It Work?

An object is anything made of matter. The total amount of an object’s matter is called its mass. Gravitation is a force of attraction between objects in relation to their mass.

An object that is near the Earth is attracted toward the surface of the planet, or toward the larger mass. Objects that are already on the Earth’s surface experience a downward force. We humans experience this force on our bodies as what we call our “weight.”

The planets in our solar system also experience the force of gravity; gravitation is what keeps the planets safely in their orbits around our giant Sun.

## Sir Isaac Newton and His Famous Apple

In Famous Experiments You Can Do, Robert Gardner writes: “Newton is regarded by many as the most brilliant scientist and mathematician who ever lived.” Amazingly, Isaac Newton (1642-1727) was not an exceptional student, but he was extremely curious about how nature worked, and his uncle persuaded Newton’s mother that he should be sent to Cambridge University to pursue his studies.

During his early years at Cambridge, Newton became convinced that scientists need to rely on experiments in order to understand the nature of the universe, rather than simply trusting what they can observe with their senses.

From the summer of 1665 to the spring of 1667, Newton left Cambridge in order to avoid the plague that was sweeping through England. During that time, he stayed at his mother’s home in Woolsthorpe and enjoyed some of the most productive months of his life. Not only did he lay the foundation for calculus, but he also began formulating his theory of universal gravitation. According to the popular tale, Newton saw an apple fall from a tree in an orchard next to his mother’s house. This simple observation led him to wonder if the same gravitational rules that applied to the motion of bodies on Earth also applied to the motion of the moon and other celestial bodies.

Newton would later write: “I thereby compared the force requisite to keep the moon in her orb with the gravitational force at the surface of the earth and found them to agree pretty nearly.”

## Einstein’s General Theory of Relativity

In 1915, German-born physicist Albert Einstein (1879-1955) presented a very important theory to the scientific community: a theory of space, time, and gravitation, which became known as the general theory of relativity.

Einstein’s general theory of relativity sees gravity as the result of distortion in the four-dimensional space-time continuum. As Prabhakar Gondhalekar explains in The Grip of Gravity: “For example, an apple falling to Earth is no longer considered to be attracted by some mysterious force acting at a distance through space but instead rolls into the local space-time ‘well’ created by Earth.”

This gravity well or curvature is determined by the distribution of matter. According to Einstein’s theory, the greater the density of matter in a given area, the greater the curvature of space-time in that area. An easy way to visualize a gravity well is to picture space-time as a stretched sheet of rubber. If a heavy object is placed on the sheet of rubber, the area around it is stretched or distorted. The amount of distortion depends on the mass of the object.

Following is Gondhalekar’s description of the gravity well of our solar system: “The Sun, being the most massive object of the solar system, causes the largest distortion of the space-time in its immediate vicinity. That curvature curves space further out, and so on. The planets are trapped in this well surrounding the Sun.”

## Finding the Pieces of the Gravity Puzzle

Newton and Einstein have dominated the field of gravitational theory. Other scientists who have made contributions in the quest to understand gravity include Aristotle (384-322 BC), Nicolaus Copernicus (1474-1543), Tycho Brahe (1546-1601), Galileo Galilei (1564-1642), Johannes Kepler (1571-1630), Edwin Powell Hubble (1889-1953), and Robert Henry Dicke (1916-1997). Who will be the next person to find a piece of the gravity puzzle? How about you?