What goes up, must come down…except maybe antimatter

Gravity is a universally attractive force, at least as far as we can tell. However, some physicists have posited that antimatter behaves the opposite way, as though they have negative mass. Testing that hypothesis is remarkably hard, though: antimatter particles annihilate with their regular matter partners if they encounter each other (at low speeds at least), and gravity is by far the weakest force in the Universe. As a result, we can’t make a big weight out of antimatter and drop it. So, researchers at CERN have proposed another way, using the existing ALPHA experiment designed to trap anti-hydrogen. While preliminary results can’t answer whether antimatter possesses antigravity, the experiment itself is promising.

How deep does the asymmetry between matter and antimatter go? Each type of particle (electrons, protons, etc.) have antimatter partners: positrons, antiprotons, and so forth. These antiparticles have an opposite electric charge (unless they’re neutral), but otherwise behave much like their matter counterparts. But one interesting question remains unanswered: does antimatter possess antigravity, experiencing a repulsive force when matter experiences attraction? And, even if antimatter experiences plain old gravity, does it behave in exactly the same way as matter does?

Researchers from the ALPHA experiment at CERN realized their antihydrogen trap could help answer that question. [Read more…]

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