My Advanced Dynamics class will be pretty challenging. The difficulty will be worth it though just to hear my professor get super excited about Newton and Physics.
Let’s get geeky.
One thing the professor mentioned was Modified Newtonian Dynamics (MOND), something I had known nothing about. I decided to do a little extra research on the matter and share it with the world.
We’ve all heard of Dark Matter. The big reason Dark Matter is believed to exist is because galaxies act a little funny. Let’s first look at things that aren’t galaxies… take for example our solar system.
Mercury is close to the sun. Because of this, the sun’s gravity influences this little planet more than the sun influences… say… Neptune. As a results, Mercury rotates much faster around the sun than the rest of the planets. Not only does it follow Newton’s law F=ma, it just makes sense.
Unlike our solar system however, all bodies in a galaxy move around the center at about the same speed. This doesn’t make ANY sense. If gravity is huge and imposing at the center of the galaxy, it should be weak and pathetic at the edge of the galaxy. Until 1981, everyone had assumed that the only explanation of this would be if there was some mass that we didn’t know about that was adding some muscle to the weak edges. And thus DARK MATTER was born.
Dark matter, as Newton followers believe, forms a ring around the galaxy that equalizes the gravitational forces. The result is that all bodies in a galaxy would rotate at the same speed. ta-da! problem solved!!
Mordehai Milgrom, an Israeli physicist, was NOT COOL WITH THIS.
Milgrom suggested that perhaps when the acceleration of F=ma is really tiny, things get funky.
Tiny is relative of course… but when we’re looking at galaxies, tiny accelerations could be pretty substantial by our standards. So Milgrom suggested F=ma be changed to:
F= m u(a/a0)a
There’s plenty of data on that equation on the internet, so if you’re interested I would recommend checking out this site.
The problem with MOND, is that it’s extremely hard to TEST. This is because we can’t really deal with a scale big enough to make accelerations really tiny. So far all scientists seem to be able to do is observe OTHER galaxies and say “hey… that one has constant speeds too.”