General Theory of Relativity

Imagine the whole universe is a giant, invisible, stretchy sheet, like a huge trampoline. Now, imagine putting a giant bowling ball right in the middle. It would make a big dip, wouldn't it. Well, that's what huge things like our sun do. They make big dips and curves in the stretchy sheet of space and time. I make planets, like our Earth, roll along the curves made by the sun. That's why Earth goes around and around it. I even play with time, making clocks tick just a tiny bit slower near very heavy things. It’s a big secret of the universe, and it is me. I am the General Theory of Relativity.

For a very long time, people had a different idea about how things moved. A brilliant scientist named Isaac Newton thought of gravity as a mysterious, invisible rope that pulled things, like an apple, down to the ground. But then, a very curious man with famously wild and messy hair came along. His name was Albert Einstein, and he loved to think about the universe in new ways. Around the year 1907, he had what he called his 'happiest thought'. He imagined a person falling from a roof and realized they wouldn't feel their own weight. To them, it would feel just like floating in space. He realized that gravity wasn't a pull at all. He worked on this amazing puzzle for many years, doing lots of math and thinking very hard. Finally, on November 25th, 1915, he was ready. He shared his complete idea with everyone, explaining that gravity is simply the shape of the universe, the bends and curves in that giant, stretchy sheet.

Even a wonderful idea from a man with wild hair needs proof to show everyone it's true. So, scientists waited for the perfect chance to test me. That chance came during a total solar eclipse on May 29th, 1919. During an eclipse, the moon blocks the sun's bright light for a few minutes, making the stars nearby visible even in the daytime. An astronomer named Sir Arthur Eddington traveled a long way to an island in Africa to see it. He took special pictures of the stars that appeared next to the hidden sun. When he looked at the pictures, he saw that the light from the distant stars had bent as it passed by the sun's big dip in spacetime, just as I predicted it would. This was the proof. I wasn't just a cool story; I was a real description of how our universe works.

You might think I am just an old idea about stars and planets, but I am still very busy today, helping you in ways you might not even notice. If you've ever used a map on a phone or in a car to find your way, you've used me. The special satellites that fly high above Earth make that GPS work, and they have to use my rules. Their clocks tick just a little faster up there, so they have to adjust their time to be accurate for everyone on the ground. I help us understand some of the universe's biggest mysteries, like giant black holes where my curves are super deep, and I help us imagine all the way back to the beginning of everything. I am a reminder to always stay curious, ask big questions, and never stop imagining.