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Does Antimatter Fall Up Or Down?
KentuckyFC writes "There are enough loopholes in the general theory of relativity to allow antimatter to fall up rather than down in a gravitational field. We've never been able to make enough of the stuff to do the experiment. But at the European particle physics laboratory at CERN, where scientists have been refining the technique for making antihydrogen, researchers are designing an experiment called AEGIS that will finally settle the matter. The idea is simple — fire a beam of antihydrogen atoms and watch which way they fall — but the details are fiendish (abstract). The answer should help solve a number of important conundrums such as why there is so little antimatter in our part of the universe and what the value of the cosmological constant is."
According to GR, gravity is the curvature of Space-Time. As the anti-matter moves through space it has to follow this curvature. If it does not, that means GR is wrong (which may be the case, but I doubt this experiment will disprove GR).
Government cannot make man richer, but it can make him poorer. - Ludwig von Mises
An experiment that reduces doubt. Does that work for you?
There are enough loopholes in the general theory of relativity to allow antimatter to fall up rather than down in a gravitational field.
Uh, no there are not. Gravity (or geometry, same thing in the theory) depends on mass energy in General Relativity. Stuff (with mass energy) follows the metric (the local geodesic). Even photons (which are their own anti-particles) follow the geodesic - and that has certainly been tested. Equivalence principle tests also show that different sorts of nuclear matter (including neutrons) individually follow the geodesic. Anti-matter certainly has mass energy, and (with matter) can be converted to photons and is no different in the theory. In other words "there is only one type of geodesics and there are no antigeodesics for antimatter."
The original article talks about "flavors" of General Relativity. Ain't so such beasties. Period. If you go to the real original article, you find a proposal for a 1% test of the equivalence principle for antimatter, and no such claims of flavors. Now, the equivalence principle has been tested to better than parts per trillion, and part of the mass energy in ordinary matter is made up of antimatter (in virtual particle pairs), so (based on the experimental evidence) I would claim that this test will be negative and is not actually that interesting as new physics. (The articles say that these older tests are "model dependent," but they are not model dependent enough to matter for this.)
That doesn't mean that this shouldn't be done (everything should be tested in physics, and different tests are always useful), but the prediction of General Relativity is clear : if anti-matter has anti-gravity, then General Relativity is wrong. The experimental evidence is also clear : this isn't going to be accurate enough to matter. Will make for some good public relations, though.
I think that the parent means that neutral bosons have no antiparticles. While neutron is a barion and thus has an antiparticle composed of (~u ~u ~d) quarks, neutral bosons (such as photon and Z0) do not have corresponding antiparticles.
Holes are a virtual particle with no mass, whereas anti-matter has mass. Electrons actually exist, but holes are simply a place where an electron can fit. Take the example of a helium balloon in a car: if you slam on the breaks, it flies to the back of the car because all the air is rushing forward, and the balloon's relative vacuum gets pushed backward. A hole behaves similarly. Antimatter, on the other hand, has mass just like its matter counterpart and therefore isn't directly comparable to a hole.
Uh, no, actually, they don't. Because F=Gmm'/r (m being the mass of one object, and m' the other, G being the gravitational constant and r being the distance between them), and a=F/m (acceleration equals force divided by mass). When you substitute one for the other, you get a=Gm'/r - which is completely independent of the mass of the object being observed. Now, you could argue that (as you seem to) that the earth is also accelerating towards the other mass, leading to what seems to be a higher rate of falling - but (contrary beliefs about relativity aside), you can't really treat all of the acceleration as relative in that manner - that simplification of relativity only works for uniform motion - it is possible to detect acceleration (although you can also replace it with a gravitational field, but that would then invalidate our original formulas - can't change horses in mid-stream like that).
Sorry, this is all silly.
"Anti-matter" is not the opposite of matter. It is matter with opposite charge or other opposite properties. Mass has no opposite. It is there, or it isn't. (Or it is and then it isn't and then it is and then it isn't, on the level of quantum fluctuations of the gravitational field.)
And no, a hole isn't "anti-matter". It's merely a void in the surrounding matter. It rises because of a principle known as "buoyancy" which is really the gross action of the matter surrounding it causing pressure differentials as a function of distance from the CM. As long as the surrounding matter can flow, it can fill any displacement of the void, and the mass will tend to move down rather than up, and the void will therefore appear to tend to move up rather than down.
And no, hot-air balloons don't rise because of the heat, they rise because they make the air in the balloon less dense than the air outside the balloon. How they do it is not relevant. A rigid balloon and a vacuum pump would work, too.