Geo600 is a very special kind of machine that helps scientists study the universe. Imagine a really, really long stick that is so long it goes from your house to your school and even beyond! Now, imagine that you and your friends want to study how this stick moves when you shake it. That's kind of what Geo600 does, except it does it with lasers!
Geo600 is located in Germany, and it's one of the most sensitive gravitational wave detectors in the world. Gravitational waves are like ripples in space-time that happen when really big things move, like when stars explode or black holes collide. These waves are so tiny that they're really hard to detect, which is why we need machines like Geo600 to help us out.
Geo600 uses lasers to measure small changes in the distance between two mirrors that are located 600 meters apart. When a gravitational wave passes through the machine, it causes the distance between the mirrors to change very slightly. The lasers can detect this change, even though it's millions of times smaller than the width of a human hair!
Scientists use the data from Geo600 to learn more about how the universe works. They can study things like black holes, neutron stars, and even the Big Bang! It's kind of like using a stethoscope to listen to your heart, but instead of your heart, we're listening to the universe. Cool, right?