Why does gravity pull us down and not up?

Why does gravity pull us down and not up?

Gravity is the reason why objects with mass or energy are attracted to each other. This is why apples fall to Earth and planets revolve around stars.

Magnets attract some types of metals, but they can also push away others. So how do you just feel the pull of gravity?

In 1915, Albert Einstein discovered the answer when he published his theory of general relativity. The reason why gravity is pulling you toward Earth is because all objects with mass, like our Earth, actually bend and bend the fabric of the universe, called space-time. This bend is what gravity feels like.

What is spacetime?

Before entering the complex world of gravity, you need to understand space-time.

Space-time is exactly what it sounds like: the three dimensions of space – length, width and height – combined with the fourth dimension – time. Using some brilliant mathematics, Einstein was the first person to realize that the laws of physics operate in the universe Space and time are merged together.

What this means is that space and time are related – if you move very quickly through space, time slows down for you compared to someone moving slowly. This is why astronauts – who move very quickly in space – They age a little slower than people on Earth.

The Earth bends space-time so that it falls toward the Earth rather than away from it. Credit: Tokamak / Wikimedia Commons, CC BY-SA

Material is what makes gravity wells, not gravity hills

Remember, gravity is the idea that objects in the universe are attracted to each other because space-time is curved and curved. When Einstein came up with general relativity, he showed that all objects in the universe can bend spacetime – in physics terms objects are both mass and energy.

Since your mind usually thinks of the world in three dimensions, it is really difficult to think of the four dimensions of space-time as a single idea. So, to make it easier to visualize, imagine the surface of a trampoline. If there's nothing on it, it's flat. But if you stand on the trampoline, it extends around your feet and forms a valley when you are in the center. If there is a ball on the trampoline, it will roll toward your feet.

Gravity works similar to how objects roll toward your feet if you are standing on a trampoline.

This is a two-dimensional example of how space-time works. Your mass stretches the trampoline, creating what is called a gravity well in which the ball rolls. This is very similar to how the gravity of a heavy object – such as the Earth – pulls objects like you and me toward it.

And to make things even stranger, since space and time are connected, Time is also extended due to heavy objects!

In the movie Interstellar, the characters go to a nearby planet Black holeWhile they are there, they age more slowly than everyone else.

The heavier you are, the steeper the sides of the trampoline will be. That's why really massive objects in the universe — like the Sun or black holes — have a stronger gravitational pull than Earth's.

So why does gravity pull you down and not push you away?

Imagine that someone went under a trampoline and pushed it up. The ball will roll away! This will be a gravity hill, not a gravity well. As far as scientists know, matter – or objects – always make gravity wells, not gravity hills. Scientists can imagine objects made of exotic matter or energy that would cause gravity to push you into space, but so far, no one has found anything that could cause gravity to push you away from Earth.

Written by Mario Boronda, Associate Professor of Physics, Oklahoma State University.

Adapted from an article originally published in Conversation.