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My current understanding is that it's generally expected (and has been predicted) that antimatter will fall down and not up in earth's gravity. But I haven't been able to locate any definitive experimental results, much less independent verification.

What is the current status of reported experimental results, and of ongoing experiments? Is there currently one particular aspect of the measurement that is currently the limiting factor? Also, which is the most likely to give unambiguous results - antiprotons, atomic anti-hydrogen, or molecular anti-hydrogen?

edit: Based on the comment, I've looked at these questions:

Has the gravitational interaction of antimatter ever been examined experimentally?,

Do particles and anti-particles attract each other?, and

Why would Antimatter behave differently via Gravity?,

saw this

Description and first application of a new technique to measure the gravitational mass of antihydrogen, and this

The GBAR antimatter gravity experiment paper,

and in this table found websites for the AEGIS experiment and the GBAR experiment as well as this post and video about ALPHA-2.

But I'm a bit overwhelmed by all of this. I get the feeling that there is great interest, but no conclusive measurement of even the sign of the gravitational mass of (atomic?) antihydrogen, much less any independent verification, but I am not sure I'm interpreting this correctly.

The Nature paper is dated January 2013 and includes this figure - the red circles are data - measured decays, while the green dots and both black line are simulations. Thus my question in March, 2016: "What is the Current Status of Measurement of the Gravitational Mass of Antimatter?"

enter image description here

Figure 2 from: "Description and first application of a new technique to measure the gravitational mass of antihydrogen" The ALPHA Collaboration & A. E. Charman, Nature Communications 4, Article number: 1785 doi:10.1038/ncomms2787

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  • $\begingroup$ Related: physics.stackexchange.com/q/139545/2451 $\endgroup$
    – Qmechanic ♦
    Commented Mar 2, 2016 at 20:06
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    $\begingroup$ I'll just add the comment that it would actually be quite unexpected if antimatter fell up, and if this were the case, pair production and annihilation combined with gravitational blueshift could be used to create perpetual motion machines. $\endgroup$
    – Zo the Relativist
    Commented Nov 28, 2021 at 4:36
  • $\begingroup$ A photon is its own antiparticle and it still falls down, as experimentally proved by the deflection of light. So one can say that antiphoton falls down, like electrons do. More generally, that all matter or antimatter falls down is a prediction of the equivalence principle which is experimentally tested to an amazing accuracy. $\endgroup$
    – TwoBs
    Commented Aug 7, 2023 at 18:30
  • $\begingroup$ @TwoBs so shall we just stop testing theories that seem to work well so far? Newtonian mechanics worked to an "amazing accuracy" under all of the original conditions for which it was tested, but that's only because of the limited range of scenarios to which it was applied. "Amazing accuracy" is not equivalent to scope. The first few terms of a Taylor expansion can work to "amazing accuracy" near the origin. $\endgroup$
    – uhoh
    Commented Aug 7, 2023 at 23:58
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    $\begingroup$ @uhoh: I explain the construction here: physics.stackexchange.com/questions/83378/…, but it appears in Schutz and in MTW $\endgroup$
    – Zo the Relativist
    Commented Aug 10, 2023 at 14:31

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The current status of measurement can be found in the list of publications at the document server at CERN by requesting "antihydrogen gravitational mass" in the search. There are proposals with different methods but no announcement of a measurement.

The Aegis experiment is in no position to give any measurement yet so the status is still undefined. Here is their status report for 2014, published in 2015. One has to wait for the 2015 report.

The ALPHA results you show is the most recent announcement on the matter from them dated in 2013.

From their site:

Today,(30 April 2013) the ALPHA Collaboration has published results in Nature Communications placing the first experimental limits on the ratio of the graviational and inertial masses of antihydrogen (the ratio is very close to one for hydrogen). We observed the times and positions at which 434 trapped antihydrogen atoms escaped our magnetic trap, and searched for the influence of a gravitational force. Based on our data, we can exclude the possibility that the gravitiational mass of antihydrogen is more than 110 times its inertial mass, or that it falls upwards with a gravitational mass more than 65 times its inertial mass.

Our results far from settle the question of antimatter gravity. But they open the way towards higher-precision measurments in the future, using the same technique, but more, and colder trapped antihydrogen atoms, and a better understanding of the systematic effects in our apparatus.

Note the number of antihydrogen used is 434.

From the dates of their last publications (2014) it seems they must be waiting for data, to be given antiproton beams, or working or recent runs.

You have to keep in mind that experiments with accelerators take years and decades. (the Higgs experiments were being designed end of the 90's).Patience.

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  • $\begingroup$ Thank you for your thorough answer! Since these experiments are way more than 10X smaller than ATLAS or CMS by any measure, I thought 3 years would be long enough to wait before asking, rather than 30 :) The status report in your link is excellent reading! $\endgroup$
    – uhoh
    Commented Mar 3, 2016 at 5:40
  • $\begingroup$ They have to be given enough run time on the beams. I am not sure, but it is possible that if the LHC is running no antiproton beams are available, and if there is a pause the PS will also need maintanance, so they will not be getting priority beam time $\endgroup$
    – anna v
    Commented Mar 3, 2016 at 7:10
  • $\begingroup$ I just noticed in the BBC news item about the recent laser-induced optical transitions in anti-hydrogen, they also say: "This machine, called Alpha-g, should be built at Cern by the end of 2017 and is set to perform its first measurements in 2018.." $\endgroup$
    – uhoh
    Commented Dec 20, 2016 at 1:18
  • $\begingroup$ ...and here it is I believe, though now it seems to be called Alpha-2 nature.com/articles/s41586-018-0017-2 There is also this teaser in LiveScience: "And Hangst thinks that mystery could be solved before the end of 2018, when CERN will shut down for two years for upgrades. 'We have other tricks up our sleeve,' he said. 'Stay tuned.'" $\endgroup$
    – uhoh
    Commented Apr 5, 2018 at 4:30
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    $\begingroup$ I checked Alpha-g and Gbar for status, they are still working on the beams gbar.web.cern.ch/results/publications.php , alpha.web.cern.ch/news $\endgroup$
    – anna v
    Commented Aug 8, 2023 at 5:39
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Atomic. Synthesis of molecular antihydrogen is beyond the current state of the art.

Other ideas how to test whether antimatter gravity is repulsive are to study positronium gravity and muonium gravity. These are discussed in recent posts on arxiv.org: https://arxiv.org/find/all/1/all:+AND+antimatter+gravity/0/1/0/all/0/1

There's also coverage of this topic at theguardian.com.

Dan Kaplan

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  • $\begingroup$ Thanks! That link is returning 84 hits, are there a few in particular (or even any at all) that adds something to what's discussed and linked here already, or that you'd like to highlight in particular? $\endgroup$
    – uhoh
    Commented Jan 2, 2017 at 8:10
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Anti-hydrogen is the preferred material, as it is electrically neutral. This is currently under active investigation at CERN; you can discover the current status via their websites.

The following links to a summary of their recent results: http://home.cern/about/updates/2014/01/antimatter-experiment-produces-first-beam-antihydrogen

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  • $\begingroup$ Atomic or molecular? Is that post 2 years old, updated a year ago - there is nothing newer? There are currently no other experiments besides this one? Actually I don't even find the word "gravity" anywhere on that page! $\endgroup$
    – uhoh
    Commented Mar 2, 2016 at 16:20
  • $\begingroup$ @uhoh: there are additional links provided on the referenced page, you will find this to be a good starting point to find the status of this ongoing research. The results are for anti-hydrogen; nothing definitive on gravity has been reported yet, but the expectation is as you said. $\endgroup$
    – Peter Diehr
    Commented Mar 2, 2016 at 16:36
  • $\begingroup$ If you are certain that one of the links on that page will lead me to information about "the Current Status of Measurement of the Gravitational Mass of Antimatter?" could you tell me which link it is? $\endgroup$
    – uhoh
    Commented Mar 2, 2016 at 16:53

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