The 'Resolved' category archives questions which have been answered since they were added to the site.

As of Sep. 2023, this entry is now moved to the 'Resolved' section.

A recent set of experiments at CERN, which created thousands of 'antihydrogen' atoms (anti-protons with orbiting positrons), and then 'dropped' them down a 3m high column, have proved for the first tiime that the anti-atoms do fall in a gravitational field.

Previously, some theorists had suggested that antimatter may have reacted in the opposite way to 'ordinary' matter.

At present it hasn't been confirmed that the anti-atoms fall at exactly the same rate as 'ordinary' matter does, but this is thought likely to be the case.

See : Nature 621, 716–722 (2023).

For reference, the original text of the Wikenigma article, now superceded, is archived below :

It's currently not known whether antimatter reacts to gravity in the same way as 'conventional' matter.

Most physicists seem to be inclined to think that matter and antimatter must have identical gravitational properties, in the sense that gravity is always attractive. This position is supported by the fact that the physical properties distinguishing matter from antimatter (electric charge, internal quantum numbers, magnetic moment) do not affect the gravitational behavior. The obvious quantity that could make the difference, i.e. the mass, is requested to be positive (and equal) for both particles and antiparticles by several experimental and theoretical arguments.

Source : Europhysics Letters, Volume 94, Number 2

Several experiments - both cosmological and laboratory based - have attempted to determine if antimatter is attracted by, or repulsed by gravity. And also whether large accumulations of antimatter would create a gravitational field as matter does.

So far, the results are unclear - though the majority of cosmologists assume that antimatter behaves gravitationally in the same way as matter does. If it's found that antimatter can create 'repulsive' gravitational fields, it would have huge implications for theories regarding the expansion of the universeplugin-autotooltip__plain plugin-autotooltip_bigExpansion of the universe

unknowable

Current cosmological theory, backed up by many diverse observations, suggests that the universe is not only expanding, but that the speed of expansion is accelerating over time. Thus the limit of the observable universe is not only receding away from us (and from every other location in the universe) but the speed at which it recedes is increasing.. The current majority view is that this is not the case. See : Wikipedia

Also see : The Antimatter Problemplugin-autotooltip__plain plugin-autotooltip_bigThe Antimatter Problem

According to Big Bang Theory, matter and anti-matter should have been created in equal amounts at the 'beginning' of the Universe. And, in experiments with high-energy particle accelerators, that is exactly what happens. Baryons (i.e. 'heavy' particles such as neutrons, protons, and their constituent quarks) and their anti-particle equivalents (anti-baryons) are created in equal numbers.

Importance Rating