Gravity is the force by which a planet or other body draws objects toward its center. The force of gravity keeps all of the planets in orbit around the sun. Link
Gravity is simply put, the center of attraction.
I'm not very good with physics, and it's terms of probably concepts too. But I know that gravity is a significant part in making the world what it is, I would say it holds the world together as a phenomenon for nature.
Without gravity in place, a lot of things will go wrong. People will take advantage of this fact and they will surely involve themselves in something really nasty.
So, there is always a need for a check, there's always a need for gravity.
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