Gravity is one of the Four Fundamental Forces of the universe. However, gravity is different than the other three forces. The other three all have to do with energy while gravity is more about space. Gravity works mainly with particles that have the attribute that we call mass.
Gravity causes mass to warp space, larger mass means greater warping. This is very hard to conceptualize, even our most accurate model needs to use gravity so our brains can understand it.
I want you to imagine a huge trampoline. If you were to place a tennis ball and a bowling ball on the trampoline, they will move toward each other. You might say to me, “They both move toward the center because of gravity, how can gravity explain gravity?” Like I said before, our brains did not adapt to be able to perceive such a complex concept. We need to use approximations that our brains are more comfortable with in order to portray these ideas. The more massive object will sink deeper into the trampoline and objects that get near enough to the warped region will be pulled closer.
All mass warps space and all mass is attracted to all other mass. You are attracted to your computer screen right now, the atoms in your eyelash are attracted to the atoms in your eye. However, you don’t feel these attractions because there is a much more massive object pulling you towards it: the Earth.
We used to think of gravity as a downward force. Now that we have a greater perspective of ourselves and our planet, we see that gravity is an inward force. We are just standing on the surface so it appears to be downward relative to us.
Gravity is not only responsible for keeping you and all your stuff on the ground, it also formed all the stars, planets and galaxies and keeps them together and in an orbit. Planets formed at specific distances from their star based on their mass and forward momentum. Our planet is currently in a balance between the inward force of gravity keeping us from drifting away and the forward motion keeping us from falling into the sun.
If you have ever swung a Yo-Yo or another object attached to a string, you have witnessed this effect. The string provides what we call a centripetal force. That force pulls inward while your spinning keeps the Yo-Yo from being sucked toward the middle. If the string breaks, the centripetal force can no longer prevent the Yo-Yo from flying off in the direction of its motion: a right angle to the string at the point of the break. Your hand is the sun, the Yo-Yo is the Earth and the string represents the force of gravity.
We still do not fully understand gravity, but we are able to use what we know from Newton and Einstein to make very close approximations. Personally, I find it exciting that we don’t know everything there is about one of the Fundamental Forces of our universe. There is always more to discover. We’ve already come so far and it’s nice to have a clear path of what more we need to learn.