Negative Mass

So in my post from the other week I alluded to the idea that negative mass is absurdly awesome, and that I may talk about it in the future. Well, folks, the future is now. So let's get to talking about negative mass.

First of all, negative mass falls under the category of exotic matter, which is pretty much filled with stuff, that, while not mathematically impossible, is unlikely to exist and has never been observed anywhere in the universe. This does not stop exotic matter from being the most interesting kind of matter (it may actually be part of the reason it is so cool). So, as we know, all matter seems to have mass, a property intrinsic to matter, and, according to the Standard Model, imparted upon the matter via interaction with the Higgs Field (that's what all the Higgs Boson hullabaloo was about a while back—that was the boson which would act as the "force carrier" for the Higgs Field, and give objects mass (and, by extension, gravity)). Now, all mass in the universe (that we know of) is positive. Now, there is no mathematical rule stating that mass cannot be negative. Air Bud clause aside, it's still rather unlikely, but if it were to exist, it would have some very interesting properties.

First of all, negative mass would behave... entirely predictable in relation to gravitational attraction. Or so it would seem. See, the force of gravity felt on one body by another is governed by the equation

So, if both bodies have a positive (read: normal) mass, the gravitational force is positive. If both bodies are negative, the force is also positive, as the negatives cancel each other out. The cool bit is if one body is negative and the other is positive; then the force becomes negative. In this case, both bodies should be repelled from each other by what is more-or-less anti-gravity, right?

Wrong.

This is where the awesomely weird stuff comes into play. See, the positive mass will indeed be repulsed by the negative one, but, the negative one won't. That's because the actual movement from a force is governed by Newton's Second Law:

So, if our force is negative (from the earlier equation), and our mass is negative, we end up with a positive acceleration. In this case, it means that the body with negative mass will be repulsed by the object with positive mass, but will move in the opposite direction of the force applied by that repulsion. That means that it would be perpetually chasing the body with positive mass, while that same force is pushing the positive mass body away. This would actually apply to all forces. Think about it: if you were to push negative mass one direction, it would react by moving in the exact opposite direction. Which is just ridiculous. And so cool.


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