New experiments to test exactly how antimatter reacts to gravity

London, June 12 : Physicists have proposed new experiments to test exactly how antimatter reacts to gravity.

According to a report in New Scientist, physicists have studied antimatter, the mirror version of ordinary matter, for decades.

They know, for example, that antiparticles have the same mass as ordinary particles, but opposite charge. But no one knows what effect gravity will have on such particles.

Now, several groups want to measure exactly how the Earth will pull on antimatter. The tests would create a horizontal beam of the stuff and measure how much gravity deflects it.

Though the complicated ballistic test may show no difference between the way matter and antimatter fall, some experimentalists are holding out hope that they may see something completely unexpected, which could point the way to new gravity-like forces, or perhaps even antigravity.

"If antimatter fell down faster, it would mean the discovery of at least one new force, probably two. If it fell up, it would mean our understanding of general relativity is incorrect," said Thomas Phillips, a physicist at Duke University in Durham, North Carolina, US.

Gravity is largely expected to have the same effect on antimatter as it does on matter. But theories of quantum gravity, which attempt to unite quantum mechanics and general relativity, allow for the possibility of two other gravity-like forces.

In ordinary matter, these forces would oppose each other, cancelling out any effect. For antimatter, these two forces could add together, pulling such particles towards Earth even harder.

As for the possibility of antigravity, it is not ruled out in the standard model of physics. As a result, some researchers have suggested antimatter may be repelled by gravity.

That could explain why so little antimatter is found today, even though theories predict it should have been as plentiful as matter in the early universe.

This possibility of observing strange new physics has led several researchers, including Phillips, to lobby for new accelerator experiments.

Phillips is proposing to test antihydrogen for such behavior at Fermilab in Batavia, Illinois, US.

At least two other proposals are in the works for CERN in Geneva, Switzerland. The more developed proposal is for an experiment called AEGIS, which would be set up at CERN's Antiproton Decelerator and if approved, might be able to return its first data within five years.

Each experiment would test the effect of gravity on antihydrogen, particles which have the same mass as hydrogen but contain antiprotons instead of protons and positrons instead of electrons.

ANI