# What Is Gravity? The Things You Need To Know About Gravity

We all know the fact that Gravity is responsible for why objects attract to each other, why we stick to the surface of the earth and why planets orbit around the sun.

There are four fundamental forces that exist in our universe: Electromagnetic force, gravitational force followed by the strong and weak nuclear force. These four are the fundamental forces responsible for any force taking place in the universe.

But the real question is,

Is gravity a force?

Let us go into the depth of this and first understand its history of discovery.

# Discovery Of Gravity

Starting from the very start, in the 4th century BC, Aristotle, a Greek philosopher said each and every object in the universe has a natural tendency to fall to the center of the universe.

He said, there is no effect or motion without any cause taking place.

Also at that time the Geocentric model was known to be correct, so his idea was widely accepted.

But after Nicolas Copernicus found and concluded that it would make sense if the Sun would be at the center of the planets.

“Earth is not the center of the universe but planets revolve around the sun,”

as per Nicolas Copernicus.

He introduced the heliocentric model to the world.

At first, many people were against this idea. His ideas were fiercely opposed by the Roman Catholic Church because they displaced Earth from the center, and that was seen as both a demotion for human beings and contrary to the teachings of Aristotle.

But then, after his death people tend to believe his proposed ideas as many great scholars supported the heliocentric model.

But yet no one explained the phenomena of gravity.

In 1687, Sir Issac Newton published the theory of gravity in a treatise, Philosophiæ Naturalis Principia Mathematica.

He explained that every object in the universe attracts others with a force, that is nothing but gravitational force.

He also formulated a mathematical expression of gravity in the book.

F= GMm/ r^2

where,

F is the gravitational force

G is gravitational constant

M is the mass of Earth

m is the mass of object and

r is the distance between two objects

# Gravitational Constant

Although Newton gave the gravitational formula. He theorized the law and gave mathematical equations. But he did not calculate the universal gravitational constant.

Between 1797–1798, a scientist named Henry Cavendish was the one who experimented for the first time and calculated the value of gravitational constant through an experiment in the laboratory.

The gravitational constant was found to have a value of

But soon, it was realized that there was something which was missing in gravitational law given by Sir Issac Newton. The law may explain many things in our solar system but there were few problems it was not able to explain.

One of them was the mercury orbit problem. If a law or a theory is not able to explain a thing then it is not directly discarded, but needs some modification or a new theory is required.

This was the case in Newton’s law of gravitation.

# Problem With The Newton’s Law Of Gravitation

The law of gravitation is able to give an explanation why two objects attract each other.

It is able to give numerical value to the force that object is getting attracted to any other body.

With the help of this law, we were successful in discovering a planet, Uranus.

But it is unable to explain many other problems. One of the problems it could not explain is the orbit of Mercury. The calculation predicted to that of actually calculated didn’t match.

It also failed to explain the basic principle behind acceleration and gravity.

Newton proposed how gravity works and how we can calculate it but he couldn’t explain the reason behind gravity.

# Einstein’s General Theory Of Relativity

In 1916, Albert Einstein published a paper on the General theory of relativity which explained the very basic idea of space, time, gravity and acceleration.

His discovery abolished the established notions about space and time replacing Newton’s law of gravitation.

According to Einstein, Gravity is the result of space-time curvature.

He explained gravity through space-time.

# Understanding The Space And Time

Einstein proposed in his paper that space and time are not absolute. They are relative to each other.

Space cannot be explained without the time and vice-versa.

Let us take an example to understand what space-time means and how it gives rise to gravity.

Imagine a fabric several to be stretched from all sides as shown above. If you put a metallic ball from above it would bend the central part of the fabric. Right?

But just think why would it bend?

It would bend due to its heavy mass.

Now imagine if you drop other balls but this time these were to be smaller and lighter than the one initially dropped. What would you think would happen?

You would see the lighter and smaller balls revolving around the heavy metallic ball.

Here is a small illustration to understand how space-time works.

This is how our universe also works. Every object is inside this space-time. And for every object, it behaves like a stretched fabric.

This is the reason why planets revolve around the Sun. And why the moon revolves around the planet. Because the Sun is heavy it makes a curve around it. Due to which planets around it revolve, the same way as you just see in the above diagram.

# Warping Of Space-Time

The bending of fabric which is made due to the heavy mass of an object is the curvature through which other lighter objects revolve around it. In more scientific terms, we call this curvature as warping of space-time.

And this warping of space-time is responsible for gravity.

That is why Einstein described gravity to be a geometry, not a force.

# Gravity Is Not A Force!

Aforesaid, gravity is a consequence of curvature made in space-time. At first, it was hard to believe that it is not a force but a phenomenon. But when the general theory of relativity got verified by many experiments, it is then believed that gravity is not fundamental, it is a consequence.

# Conclusion

Gravity has been an interesting topic that has been a topic of study from Aristotle time to now.

The search for what is gravity was already started in 4th century BC but in the mid 16 th century, Newton was the first who mentioned the term gravity in his treatise giving out a mathematical expression explaining it. He gave out the law of gravitation.

But soon it was realized that his law was unable to explain some problems in our solar system. The Mercury orbit problem was one of them.

It was even not able to explain the cause behind gravity.

Albert Einstein with his general theory of relativity was the one who explained gravity through space and time. He concluded his idea by stating that gravity is not a force but a geometry made due to the warping of space-time.

His idea was hard to believe at first but then it got verified several times through experiments.

GPS(Global-positioning-system) is a real-life example of that theory, which itself is proof that Einstein was not wrong.