What is Modified Newtonian dynamics (MOND)?

Modified Newtonian dynamics, or MOND, is like giving gravity a new trick to help it explain why things move the way they do in space.

Imagine you're playing with your toy car on a very smooth floor. Normally, when you push it, it rolls straight and stops when there’s nothing pushing it anymore, just like how we think gravity works. But sometimes, far away from everything else, your toy car keeps rolling longer than it should. That's kind of what happens in space with stars and galaxies, and that’s where MOND comes in.

Normally, scientists thought the extra movement was caused by dark matter, something we can't see but that pushes on things in space. But MOND says gravity just changes its behavior when it's very weak, like your toy car suddenly getting a little extra push when no one is pushing it.

It’s like saying gravity has a secret rule: "When you're far away, I’m not as strong, but I still help things move, just in a different way."

So MOND helps explain why stars and galaxies act the way they do without needing that invisible helper called dark matter.