Gravity - force or effect

 

Image taken from pixabay.

We can feel the effect of gravity all the time and have been doing so from the beginning. Most of our lives we hate it too because we dream of flying but earth's gravity does not allow us to do that. But it is very important as it has contributed in shaping the world and every living and non-living thing on it, either direcly or indirectly. If the gravity of earth was even slightly different then everything might have been different. Even the working of our internal organs is linked to the earth's gravity.

What is gravity?

The early humans didn't know about gravity but they did know that it was not good to fall down. Over time humans tried to understand it, from ancient greek philosophers to the famous story of Isaac Newton watching an apple fall from a tree which lead to his universal law of gravitation. According to this law 2 objects will exert force on each other called the gravitational force. This gravitational force is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

But a more accurate description was given by Albert Einstein's theory of relativity. According to Einstein's theory gravity is not a force and it is caused by the warping of spacetime due to the mass of an object. The greater the mass the more it will warp the fabric of spacetime and the stronger the gravity. We can even see the effects of these warping in space, for example if we are looking at a galaxy through a powerful telescope and a massive object like a black hole or another galaxy passes in front of it the light of the galaxy in the background is warped, this is called gravitational lensing.

Speed of gravity.

When we think about gravity we might not associate speed with it because of how we experience it on earth. But it does have a speed and that speed is equal to the speed of light. Einstein's theory of general relativity also predicted gravitational waves that were detected about a century later. The speed of these gravity waves is equal to the speed of light. That does not mean that gravity is some object moving here and there at the speed of light, it means that the effect of gravity is felt at this speed. As an example, the sun is about 8.3 light minutes away from us. If it disappeared at this very moment we will keep seeing it in the sky and feeling it's heat for 8.3 minutes after its actually gone and we will also keep feeling it's gravitational pull for the same amount of time.

Extreme case.

All objects in the universe, no matter how small or large, exert their gravitational pull on each other. The trees, rocks, animals and even us, we all have our own gravity. We just don't feel it because we are all standing on earth and compared to the gravitational pull of the earth our's is negligible. As mentioned above the more mass an object has the stronger it's gravity is going to be. If that mass is large enough and concentrated enough it can warp spacetime so much that even light, the fastest thing in the universe, cannot escape it's gravitational pull. Yes you guesed right, I'm talking about a black hole the ultimate victory of gravity.

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