AMO
In the literature: open
Does antihydrogen fall with g to within 1 percent?
In plain words
In 2023 the first direct experiment showed that antihydrogen falls down, not up, but only to about 20% precision. A 1% measurement would test whether antimatter feels gravity exactly like matter.
Precise statement
ALPHA-g measured the vertical acceleration of antihydrogen as a_g = (0.75 +- 0.13 stat+sys +- 0.16 simulation) g (2023). Determine $a_g/g$ with total uncertainty below 0.01 and test whether it differs from 1.
What would settle it
A laser-cooled antihydrogen release or interferometric measurement (ALPHA-g, GBAR or AEgIS) reaching $1\%$ uncertainty on $a_g$.
Status in the literature
Unverified note
No measurement of $a_g$ more precise than the 2023 ALPHA-g result has been published as of 2026; antihydrogen laser cooling (2021) is the stated prerequisite for the next step.