Imagine you are playing with a toy car that you can push and pull to make it move. The car moves because you are pushing or pulling it, right?
Now, imagine that there are really tiny things called particles that are all around us. These particles are so small that we can't see them! But they are there, and they are moving all the time.
Sometimes, when really big things move in space, it creates waves in these particles that we can't see. These waves are called gravitational waves.
Scientists want to study these gravitational waves, so they built a very special machine called a deci-hertz interferometer gravitational wave observatory. It's like a really, really big toy car that they can use to "listen" to the waves in the particles.
The machine is so big that it takes up a lot of space! It has two really long arms that are 3 kilometers long each. Inside the machine, there is a special way of measuring the waves in the particles.
When a big thing, like two black holes colliding, creates gravitational waves, the waves will reach the machine and cause the arms to move just a tiny bit. The machine can detect this movement and tell scientists that there were some gravitational waves happening!
So, just like pushing and pulling your toy car makes it move, the gravitational waves from space can make the machine's arms move, and that helps scientists study and learn more about the universe!