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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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uhoh
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  • Related: http://physics.stackexchange.com/q/139545/2451 – Qmechanic Mar 02 '16 at 20:06
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    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. – Zo the Relativist Nov 28 '21 at 04:36
  • 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. – TwoBs Aug 07 '23 at 18:30
  • @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. – uhoh Aug 07 '23 at 23:58
  • @ZotheRelativist agreed, you can write to the PIs of all these experiments and let them know they should not have started these projects and can just stop now. – uhoh Aug 08 '23 at 00:00
  • @uhoh My point was twofold: (a) photons are their own antiparticle, so one knows already how an antiparticle falls up or down; (b) sure we should test theories that seems working but testing whether anti-particle falls up is among the worst choice of testing, in my opinion, because it is degenerate with other tests (or theory considerations) that are much more stringent already. I would like to add that if anti-particle falls down almost everyone would assign this to another force sourced by matter, not to gravity, in my opinion. – TwoBs Aug 08 '23 at 13:34
  • sorry, a misprint: ''...if anti-particle falls down...'''---> ...falls up... Just to reiterate the last part of my comment: these experiments are better thought, in my opinion, as tests on the existence of a fifth force, and place bound on those, not on gravity. – TwoBs Aug 08 '23 at 15:35
  • @uhoh: did I say people shouldn't run an experiment? If a result is "unexpected", that means finding it would be a major discovery. Again, though, you could build a perpetual motion machine if antimatter fell up. – Zo the Relativist Aug 09 '23 at 15:09
  • @ZotheRelativist those need to produce more energy than you put in. Considering the amount of energy spent in the production of antiprotons (the local universe doesn't just leave them lying around or growing on trees) has a viable perpetual motion machine design actually been proposed? How does it actually make more energy than it uses? Is there a credible source that can be cited? I'm happy to ask that as a new question if you think you have a Stack Exchange-worthy supported answer! – uhoh Aug 09 '23 at 18:19
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    @uhoh: I explain the construction here: https://physics.stackexchange.com/questions/83378/are-there-models-simulations-of-antigravitational-antimatter-galaxies/134888#134888, but it appears in Schutz and in MTW – Zo the Relativist Aug 10 '23 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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anna v
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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

Dan Kaplan
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  • 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? – uhoh Jan 02 '17 at 08:10
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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

Peter Diehr
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  • 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! – uhoh Mar 02 '16 at 16:20
  • @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. – Peter Diehr Mar 02 '16 at 16:36
  • 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? – uhoh Mar 02 '16 at 16:53