This article was first published by The Conversation. Space.com's Expert voices: Op-Ed and Insights was contributed by the publication.Gravity is why things with energy or mass attract to one another. This is why apples fall to the ground and planets orbit star-shaped stars.Magnets can attract certain types of metals but also push away other magnets. How can you feel the pull of gravity when there are other magnets?Albert Einstein published his theory on general relativity in 1915. Gravitation pulls you towards the ground because all objects that have mass, such as our Earth, bend and curve the fabric, which is called space-time. This curvature is what gravity feels like.What is space-time?Understanding space-time is essential before you can dive into the complex world of gravity.Space-time refers to the combination of the three dimensions space length, width, and height with the fourth dimension of time. Einstein discovered that the laws and physics of physics worked in a universe where time and space are combined using some brilliant math.This means that space and time are interconnected. If you move fast through space, the time you have to travel will slow down compared with someone who moves slowly. Astronauts who move very fast in space tend to age slightly slower than those on Earth.Earth curves space time so you can fall towards it instead of away. Image credit: MARK Garlick/SCIENCEPHOTO LIBRARY via Getty ImagesGravity wells are made of matter, not gravity hillsGravity is the idea that objects are attracted to one another because space-time bends and curves. General relativity was Einstein's idea. It showed that all things in the universe could curve space-time according to physics. This means that everything is both mass and energy.Your brain is used to thinking about the world in three dimensions. It can be difficult to see the four dimensions of space and time as one idea because it tends not to consider them all. To make it easier to visualize, picture the trampoline's surface. It is flat if there is nothing. If you stand on the trampoline it will wrap around your feet creating a valley with the middle of you. The trampoline would roll towards your feet if there was a ball.This is a 2-dimensional illustration of how space-time works. Your mass stretched the trampoline creating a gravity well where the ball rolls into. This is similar to the way that gravity pulls heavy objects like the Earth towards you and me.This is because space and time are interconnected, so time can also be stretched by heavy objects.The trampoline well's sides will be steeper if you are heavier than you are. This is why very large objects in the universe, such as the Sun and black holes, have stronger gravity than Earth.Hence, gravity pulls you down and does not push you away.Imagine someone pushing up on a trampoline. The ball would then roll away! This would be a gravity hill and not a well. Scientists know that matter and stuff make gravity wells, not gravity hills. Scientists may be able to imagine objects made from exotic energy or matter that could push you into space. However, so far no one has discovered anything that could push you away.This article was republished by The Conversation under Creative Commons. You can read the original article.
