Up or down? Antimatter is matter's opposite, so wouldn't it make sense that if matter falls down then antimatter would "fall" up? Researchers have debated this question and whether or not antigravity exists for years. Now, physicists have taken a closer look at the possibility of antigravity and have made some surprising discoveries.

So far, all of the evidence that gravity is the same for matter and antimatter is indirect. In order to directly tackle the question, researchers decided to use their ongoing antihydrogen research with CERN's international ALPHA experiment. If gravity's interaction with anti-atoms is unexpectedly strong, then the anomaly would be noticed in ALPHA's existing data on 434 anti-atoms.

ALPHA creates antihydrogen atoms by uniting single antiprotons with single positrons (antielectrons) by holding them in a strong magnetic trap. When the magnets are turned off, the anti-atoms soon touch the ordinary matter of the trap's walls and annihilate in flashes of energy. If the researchers knew an anti-atoms precise location and velocity when the trap was turned off, all they would have to do would be to measure how long it takes to fall to the wall.

Unfortunately, ALPHA's magnetic fields don't turn off instantly, and flashes occur all over the trap walls at times and places that depend on the anti-atoms detailed but unknown initial locations, velocities and energies. This, in turn, makes it difficult for researchers to find out anything about them.

The first results measured the ratio of antihydrogen's unknown gravitational mass to its known inertial mass. Unfortunately, the findings didn't settle the matter of antigravity. If an antihydrogen atom falls downward, its gravitational mass is no more than 110 times greater than its inertial mass. If it falls upward, its gravitational mass is at most 65 times greater.

So if it didn't solve the question, then what good was the experiment? It did show that measure antimatter gravity is actually possible. This could potentially lead to an experimental method that would lead to much greater precision in the future.

So is it up or down? It turns out that researchers will have to experiment a bit more to answer that question.

The findings are published in the journal Nature Communications.