Gravity

Have you ever wondered why you don’t just float out of your bed at night and bump into the ceiling. Or why, when you drop your pencil, it clatters to the floor instead of zooming off toward the sky. Can you imagine a world where raindrops fell up instead of down. It would be a very silly place. The reason for all this order, this wonderful predictability, is me. I am a secret force, an invisible hug that the Earth gives to everything and everyone on it. I’m the reason you stay on the merry-go-round when it spins and why a kicked soccer ball always comes back down. I am like cosmic glue, holding our world together so it doesn't fly apart. You can’t see me or touch me, but you can feel me every second of every day. I keep your feet planted firmly on the ground when you run and jump. I am the silent, steady power that keeps the world as you know it in one piece. Who am I. I am Gravity.

For thousands of years, people felt my presence but didn't truly understand me. They knew that things fell down, but they couldn't explain the grand secret behind it. That all started to change in England, around the year 1666, thanks to a very curious man named Isaac Newton. One day, he was sitting in a garden, thinking deeply, when he saw an apple fall from a tree. Plonk. It landed on the ground. Now, many people had seen apples fall, but Isaac asked a brilliant question. He wondered if the same force that pulled the apple to the ground was also reaching much, much higher. He looked up at the sky and saw the Moon. He had a magnificent idea. What if I was the one pulling on the Moon, too. He realized that I was the invisible string keeping the Moon from flying away, making it circle the Earth month after month. Isaac figured out my secret rule: everything in the universe that is made of 'stuff'—what scientists call mass—has a pulling power. The more stuff something has, the stronger its pull. That’s why you don’t notice the pull from a book or a chair, but you definitely feel the pull from the gigantic Earth. It was a revolutionary idea that I wasn't just an earthly force, but a universal one that governed the stars and planets.

My story got even more interesting much later. About 250 years after Isaac and his apple, another super-smart person named Albert Einstein came along. Around 1915, he imagined me in a completely new way. He didn't see me as an invisible rope, but as a shape in the very fabric of the universe. Imagine that space is a giant, stretchy trampoline. Albert said that a huge object, like our Sun, is like a heavy bowling ball placed in the middle. It creates a deep curve, a dip in the trampoline. Smaller objects, like the Earth, are like marbles rolling along the edge of that curve. They aren't being pulled so much as they are following the bend in space created by the Sun. That bend is me. This amazing idea helps explain how I gather dust and gas together to form sparkling new stars, how I group those stars into magnificent galaxies, and how I keep all the planets swirling in a beautiful, cosmic dance. Because humans like Isaac and Albert worked so hard to understand me, you can do incredible things today. You can send satellites into orbit that let you talk to friends across the world and explore the farthest reaches of our solar system. I am more than just what keeps you on the ground; I am the architect of the cosmos, reminding you that everything, from you to the most distant star, is connected.