Does Antimatter Fall Up? 255
New submitter Doug Otto sends word that researchers working on the ALPHA experiment at CERN are trying to figure out whether antimatter interacts with gravity in the same way that normal matter does. The ALPHA experiment wasn't designed to test for this, but they realized part of it — an antihydrogen trap — is suitable to collect some data. Their preliminary results: uncertain, but they can't rule it out. From the article:
"Antihydrogen provides a particularly useful means of testing gravitational effects on antimatter, as it's electrically neutral. Gravity is by far the weakest force in nature, so it's very easy for its effects to be swamped by other interactions. Even with neutral particles or atoms, the antimatter must be moving slowly enough to perform measurements. And slow rates of motion increase the likelihood of encountering matter particles, leading to mutual annihilation and an end to the experiment. However, it's a challenge to maintain any antihydrogen long enough to perform meaningful experiments on it, regardless of its speed. ... The authors of the current study realized that [antiatoms trapped in ALPHA] eventually escaped or were released from this magnetic trap. At that point, they were momentarily in free-fall, experiencing no force other than gravity. The detectors on the outside of ALPHA could then determine if the antihydrogen was rising or falling under gravity's influence, and whether the magnitude of the force was equivalent to the effect on matter."
Re:I must be stupid (Score:5, Insightful)
Obviously there must be some credence to this idea for such an experiment to take place, but since my understanding is that gravity is an inherent effect of mass warping space, wouldn't anti-matter possess mass in the same way that matter does, so why would gravity act differently?
Just asking. Not trying to claim anything.
Inertial mass and gravitational mass are observed - for normal matter - to be exactly equivalent. There's no actual reason they should be though, since they're the product of very different interactions - it's perfectly logical to have something which "weighs" a 1000kg when experiencing electromagnetic acceleration, and only 10kg when experiencing gravitational acceleration.
For normal matter, this is the case. For antimatter it's presumed but not actually tested, and therein lies the rub. Even a slight deviation would be huge - and have big implications for the question of why the universe has so much matter in the first place.
Re: What am I missing? (Score:5, Insightful)
Scientists like upsets. They wouldn't BE upset, it would be an upset.
Re:What am I missing? (Score:5, Insightful)
Because these are individual atoms. Very hard to detect unless they are clumped together as a mass... as in the millions. The only way to know their position is to force them to be where you want them via a magnetic field... etc... which ruins your chances of measuring any gravitational effect which is unfathomably tiny at atomic scales. You could make a whole pile of them (very difficult indeed) so it would act more like classical matter... the problem there is that by the time you had that much, when it hit the bottom of your container you'd find out just exactly what e=mc2 is all about and likely need to start looking for a new research facility.
Re:The Path To Faster-Than-Light Travel (Score:5, Insightful)
Anti-matter still has a positive mass. Otherwise when a positron meets an electron it wouldn't release any energy. Personally, I highly doubt it "falls up", as that would be inconsistent with general relativity because anti-particles would not follow a curved space. What would be really cool is if it was found that anti-matter curved space in the opposite direction as matter, making gravity repulsive. I highly doubt that's the case, but it would certainly be a cool discovery.
Re:Maybe our universe is a 'matter bubble' (Score:3, Insightful)
You are in that strange paradox of a state in which you know too much, but also too little about physics.