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Gravity Re-Visualised


Suppose you are standing on top of the Eiffel Tower. You can see the curvature of the Earth and the hundreds of people walking below you. Then you decided to jump. What would you feel?
You would be in a state called weightlessness, i.e you have no weight.
Now suppose you are in a satellite, revolving around the Earth. What would feel?
At a glance, you would say there is no gravity because you are in space and hence you are floating around. What if, I said, that the action of you falling off the Eiffel Tower and you being in the satellite is the same.
In the year 1686, Sir Isaac Newton presented the Universal law of Gravitation in his book Principia Mathematica. It stated that objects attract each other due to their mass and explained as to why planets orbits around the Sun in an elliptical manner.
Fast forward to 1915,  Albert Einstein thought it was actually the curvature of space that actually accounted for the motion of various planetary motion.  Think of it like this. Suppose you have a piece of cloth and along the boundaries of the cloth, you attach it over a hollow ring. Next, put an object with some mass in the middle of the setup. Now take a small marble and release it from the boundary of the ring. You would see that the marble rolls of towards the bigger object in the middle. Do it again, but this time, push the marble sideways as you release it. Now you would see that the marble rotates in an elliptical manner around the heavier object as it slowly and slowly rolls down.

This is what Einstein imagined gravity as. All objects with mass actually rest on a piece of fabric called space-time. Anything with mass cause a depression in the space-time fabric. So when an object falls, it is actually following the depression of the fabric caused by the mass of the heavier object. So matter and energy tells how the space-time fabric to curve and in return, the space-time fabric tells how matter and energy should move. Einstein’s visualized a new theory of gravity which successfully explained the ripples in gravity caused by black holes or the bending of light near stars.
As in the case of falling and floating in space, in both cases, gravity is acting upon you. You are falling towards the Earth but the only difference is that while in space you are actually falling and moving sideways, at a rate which perfectly aligns with the curvature of the Earth.

Regards,

Sanjay Dutta
CSE-C, 2nd year

Image Source: https://masteroftheuniverseweb.files.wordpress.com/2016/08/spacetime.jpg

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