Interesting article from New Scientist: A Phantom Menace to Dark Matter Theory by Marcus Chown.
In a nutshell, there’s a new theory that tries to explain why stars aren’t chucked out of the galaxy when they are near the edges, like a little kid on the playground merry-go-round. (Hey, it happens.) Newtonian physics say that this is what should happen, but it doesn’t. The most recently accepted idea was that “dark matter” – vast amounts of stuff in space that exudes no light or radiation but still has mass and gravity – countered the opposing force and “held in” the stars. But this makes for an awkward and sloppy theory, as it would require specific amounts of dark matter to be around each and every galaxy performing this service, and that just seems….well, unlikely.
Enter the MOND theory.
An acronym of “MOdified Newtownian Dynamics”, the theory states that gravity changes its tune at different speeds with large-scale things like stars and planets. Things that move slower experience stronger gravitational forces. Hard to prove, considering the subjects and how long they take to move around a galaxy (takes our sun – planets in tow – about 225 million years to make one full trip around the galactic center) but the ends seem to work well with the means.
Interesting thing about this theory is that, if it’s true, there should also be a place within our own solar system that has a “cancellation point” between the gravitational tug from the sun and the pull from the galactic center. According to the article, this could be a region rather than a specific point in space, and thus exert its force on the rest of the planets – Earth included – from several different places at once.
If MOND exists, it will appear as if there is an anomalous, “phantom” mass in that region, exerting a gravitational force on the bodies in our solar system. And because this phantom force originates from a broad zone rather than a defined single point, it would exert a pull on the planets from two directions at the same time – a so-called “quadrupole” effect.
So what does this mean? Well, also according to the MOND theory and one proposed by Einstein, the effect could slowly alter the orbits of the planets, inexorably changing their orientations like a pendulum drawing ovals in the sand. Perhaps not as dramatic, but still a change that has to be caused by something.
Of course, none of it will make a bit of difference to any of us right here and now, it’s all an example of answers just providing us with more questions. But knowledge stacks, and the search for truth in our universe will be a neverending one, assuredly.
And that’s a good thing. 🙂