Gravity is the reason that things with mass or energy attract each other; therefore apples fall to the ground and planets revolve around stars.
Magnets attract some types of metals, but can drive away other magnets as well. How is it that you only feel the pull of gravity?
In 1915 Albert Einstein discovered the answer when he published his general theory of relativity. The reason gravity pulls it towards the ground is because all massive objects, like our earth, actually bend and curve the structure of the universe called spacetime. That curvature is what you feel as gravity.
What Is Spacetime?
Before entering the complicated world of gravity, you must understand spacetime. Spacetime is exactly what it sounds like: the three dimensions of space (length, width and height) combined with the fourth dimension, time. With the help of very brilliant mathematics, Einstein was the first to realize that the laws of physics work in a universe where space and time merge with each other.
This means that space and time are linked – if you move through space very fast, time will slow down for you compared to someone who moves slowly. Because of this, astronauts who move very fast in space age a little more slowly than humans on Earth.
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Matter Makes Gravity Wells, Not Gravity Hills
Remember, gravity is the idea that objects in the universe attract each other because space-time is bent and curved. When Einstein invented general relativity, he showed that all things in the universe can bend space-time. From a physis point of view, this matter is mass and energy.
Since your brain generally imagines the world in three dimensions, it is really difficult to think of the four dimensions of spacetime as a single idea. So for easier visualization, imagine the surface of a trampoline. If there is nothing on-it, it is flat, but when you stand on the trampoline it spreads around your feet and forms a valley with you in the middle; When a ball is on the trampoline, it will roll at your feet.
This is a two-dimensional example of how spacetime works. Its mass stretched the trampoline, creating a so-called gravity well in which the ball rolls. This is very much like the g-ravity of a heavy object, like the earth, attracts things like you. and me to him.
To make things even stranger since space and time are connected, time is also stretched with heavy objects!
The heavier you are, the steeper the sides of the trampoline will be. For this reason, really massive things in the universe, like the sun or black holes, have a stronger gravity than the earth.
Why Does Gravity Push Us Down Instead Of Up?
Imagine someone went under the trampoline and pushing themselves up, the ball would roll away! This would be a gravity hill, not a gravity well. As far as scientists know, matter or something always creates gravitational wells, not gravitational hills. Imagine things made of exotic matter or energy that would cause gravity to push you into space, but so far no one has found anything that can cause gravity to push you away from Earth.
