Question about antiparticles and gravity

[jfribrg]

Recently I was reading the book Thirty Years that Shook Physics by George Gamow. In it was a discussion of the open question (as of 1966 when the book was written) of whether anti-particles have anti-gravity. There is also the discussion of how at the time there was no experimental way of testing this because the accuracy required for the experiment far exceeded anything conceivable. I'm curious about whether this question has ever been experimentally tested. The notion of anti-gravity sounds vaguely familiar to the notions of dark energy, so I'm wondering if it is really the same thing.

[Grey]

We've discussed this before several times (here, here, and here, for example). The direct experiment (making some anti-hydrogen so that you've got electrically neutral anti-matter, but still keeping it contained and then watching to see how quickly it falls) hasn't been done yet, although I think at this point the AEGIS group at CERN are only a couple years away from being able to do it. However, there are some pretty sound theoretical arguments, based on some fairly straightforward observations and measurements, that antimatter should respond the same as normal matter in a gravitational field.

[Jeff Root]

I was told by someone at CERN that the experiment to measure
the fall or possible rise of neutral antihydrogen atoms in Earth's
gravity will probably be done no earlier than 2015. Before that,
the easier experiment of obtaining spectra will be done.

I've been coddling the idea that antimatter might have antigravity
relative to ordinary matter since the mid-1970's. So far, the only
objections to it which have not fallen under further study were
raised here on BAUT. The Pound-Rebka experiment seems to
conflict with the possibility, as does the apparent observation of
antineutrinos from Supernova 1987A. Pound-Rebka is a rather
indirect measurement, so I think its interpretation regarding this
specific implication may be open to question. The antineutrino
observation is of two dozen neutrinos or fewer, out of the vast
number of neutrinos passing through the detectors at that time,
and it isn't yet clear how "flavor" changes affect which neutrinos
become detectible at what times and under what conditions.

-- Jeff, in Minneapolis