General relativity facts for kids
The General Theory of Relativity, or general relativity, is a big idea about gravity. It was created by Albert Einstein in 1915. This was ten years after his special theory of relativity.
Einstein's theory uses the idea of spacetime. Spacetime is like a giant fabric that makes up our universe. It has three dimensions of space (like up/down, left/right, forward/backward). It also has one dimension of time. Every event happens at a certain place and time in this spacetime.
General relativity says that anything with mass (like planets or stars) causes spacetime to bend or curve. Other objects then follow these curves. Think of a bowling ball on a trampoline. It makes a dip. A marble rolled nearby would curve towards the bowling ball. This is how Einstein explained gravity. The more mass something has, the more it bends spacetime.
This theory also explains gravitational lensing. This is when light bends as it passes a very heavy object. Scientists proved this during a solar eclipse. They saw starlight bend around the Sun.
General relativity also helped start cosmology. This is the study of how our universe is built. Einstein first thought the universe was unchanging. He even added a "cosmological constant" to his equations. But later, he called this his "biggest blunder." Today, many scientists think this constant is needed again. It helps explain new things we know about the universe.
A popular idea in cosmology is the Big Bang theory. It says the universe started about 15 billion years ago. It began as a tiny, super hot, and super dense point. All the matter we see today came from this point.
Einstein didn't invent the idea of a "black hole". But later scientists used his theory to describe them. A black hole is an object that bends spacetime so much that nothing, not even light, can escape. Scientists think they form when giant stars die. These stars must be at least three times bigger than our Sun. This can happen after a huge explosion called a supernova. Black holes might create gravitational waves. Scientists are looking for proof of these waves.
Contents
How Gravity Works in Spacetime
Einstein said that time and mass can change when objects move very fast.
Time and Speed
Imagine you are racing a friend in space. You both have identical watches. If you travel much faster, almost at the speed of light, your watch will tick slower than your friend's watch. Your friend would see their watch ticking faster than yours. Scientists call this "time dilation". Your friend would also see you get smaller. You would see your friend get bigger.
These changes in size and time happen at any speed. But they are only noticeable when you move extremely fast. This means speeds close to the speed of light. The speed of light is about 186,000 miles (299,000 km) per second! That's why we don't notice these effects in our daily lives.
Mass and Bending Space
Einstein also explained that objects actually bend the space around them. How does this happen?
Think about throwing a ball near an elephant. The ball's path would curve slightly towards the elephant. This is because the elephant's mass creates "gravity" around it. This gravity bends the space nearby. The more mass something has, the more it bends space. So, an elephant bends space more than you do, because it has much more mass.
All objects bend space around them. Even you bend space! But this bending is only easy to see for very big objects. These include planets and stars.
Related pages
Images for kids
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This shows how light changes color as it escapes from a very heavy object.
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Light bending around a heavy object. The light starts from the blue spot and curves near the gray body.
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Imagine a ring of tiny particles. A gravitational wave passing by would stretch and squeeze them like this.
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This graph shows how the orbits of two special stars changed over 16 years, proving Einstein's theory.
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A picture of a complex shape called a Calabi-Yau manifold. It's used in theories about extra dimensions.
See also
In Spanish: Relatividad general para niños
