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I am interested in experimental physics and looking for information about the above question.

Qmechanic
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Dirk
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    Sure, if you have enough money....In 1999, NASA gave a figure of $62.5 trillion per gram of antihydrogen but anti oxygen is a long way away yet –  Jul 24 '17 at 14:23
  • Thx for your answer. Are there any theoretical evidences about the property of antiwater? I have not found any studies about it. – Dirk Jul 24 '17 at 14:32
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    Anna knows far more than I do about physics, especially experiments, but in theory, AFAIK, there will be little literature because, with enough money, it's a given that we could do it. But anti hydrogen is important, because we can test, for example, if it feels gravity the same way hydrogen does,(and yes, it acts the same way). There is no need (or money) to check any higher up the periodic table. –  Jul 24 '17 at 14:57
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    @Countto10 It's not really a given. To create anti-oxygen, you'd need a lot of anti-nucleons, that would survive long enough, and you'd need to drive them together. This would require superb trapping, and we've only made anti-helium for a very brief period of time, let alone anti-oxygen. (See Anna's answer below) – Omry Jul 24 '17 at 16:00
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    And note that for a molecule you'd also need antielectrons (positrons). – JimmyB Jul 25 '17 at 09:17
  • I call dibs on "antiwater" as a band name! – Todd Wilcox Jul 25 '17 at 19:19

3 Answers3

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Research has created antihydrogen, and that is about it for the present as far as antimatter in bulk, which one would need for antiwater..

Scientists in the US produced a clutch of antihelium particles, the antimatter equivalents of the helium nucleus, after smashing gold ions together nearly 1bn times at close to the speed of light.

They were gone as soon as they appeared, but for a fleeting moment they were the heaviest particles of antimatter a laboratory has seen.

If you look at the nuclear binding energy plot, oxygen needs a lot of antinucleons to materialize. Present research has just seen antihelium.

anna v
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  • Wasn't there a recent (last year or so?) CERN experiment showing the anti-hydrogen spectrum was the same as hydrogen? – Jon Custer Jul 24 '17 at 15:00
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    (Spectrum of Antimatter)[https://home.cern/about/updates/2016/12/alpha-observes-light-spectrum-antimatter-first-time]. A shame it wasn't different to hydrogen..... –  Jul 24 '17 at 15:08
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    @Countto10 There's no such thing as "shame" in experimental physics results. Nature is what it is. Deal with it. – Emilio Pisanty Jul 24 '17 at 15:51
  • Thanks for the answers. I think everything is connected to another theory. I find it like a bit messey :) General relatitivity theory - Inflation theory - String theory. The experimental results could give more detailed results :) Lean back & watch science :) – Dirk Jul 24 '17 at 19:48
  • Have they tried making antiHelium by pushing two antiHydrogens together in an antiNuclear way? Is it strange that antiHelium was made after hitting a metal made of a different element? – Ben Rawner Jul 12 '18 at 02:24
  • @BenRawner At present the number of antihydrogens produces is small, (80 in the link given in the answer) and as neutral even a beam of antihydrogen would not be easy to control in direction and momentum so as to bring them at rest so the attractive strong forces would work. One might try making an anti -alpha particle by two antiprotons at rest and then dressing it with two positrons , but since they just managed 80 antihydrogens increasing the complexity in this way will decrease the probabilities probably exponentially. – anna v Jul 12 '18 at 05:04
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Anti-matter is a lot less exciting than you probably think. If we could magically change all matter to anti-matter by waving a magic wand then it would make almost no difference. The anti-Dirk could drink an anti-glass of anti-water in exactly the same you drink a glass of water. The anti-water would have the same density, boiling point, ability to dissolve anti-salt and so on. Even looking in greater detail the electronic and indeed nuclear spectra would be identical to water.

We have never made anti-water, or even anti-oxygen, and it will be a long time before we achieve such a feat. However we can be very confident about the behaviour of anti-matter because matter and anti-matter are related by a symmetry called CP-Symmetry that is theoretically well understood and experimentally well tested. There are a few differences due to a phenomenon called CP violation1 but this is only observable in colliders like the LHC, and even then it isn't a large effect. As far as everyday life goes anti-water would interact with other anti-matter in exactly the same way as water interacts with matter.

1 though CP violation is possibly the reason matter exists at all, though that's a question for another day

Johnathan Gross
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John Rennie
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  • So... is there any experimental evidence that antimatter falls downwards? Given that there isn't any working quantum theory of gravity, I tend to think it's worth checking ;-). Similarly, given that there are small imbalances in the presence of matter vs antimatter in the universe, I'd also say that any possible source of C asymmetry, no matter how implausible, is definitely worth looking into. – Emilio Pisanty Jul 24 '17 at 15:53
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    @EmilioPisanty Gravity's effects on antihydrogen are being checked. We've yet to reach a well-defined answer, see https://www.nature.com/articles/ncomms2787 I must say, however, that since the labeling of particles versus anti-particles is arbitrary, it seems unlikely that the ratio of the gravitational masses would be far from one. – Omry Jul 24 '17 at 15:58
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    @Omry the CERN expt is to check the motion of anti-hydrogen in the gravitational field created by the Earth i.e. normal matter. Checking the motion of anti-hydrogen in the gravitational field created by an Earth mass of anti-matter is a little more difficult. – John Rennie Jul 24 '17 at 16:03
  • @JohnRennie I interpreted his question as anti-particles in a normal gravitational field. Now I'm not sure if he meant anti-particles in gravity, or anti-particles in "anti-gravity". – Omry Jul 24 '17 at 16:04
  • @EmilioPisanty I may be wrong but it would mean that GTR is false as such particles would not move in straight lines in curved space-time (See also: https://en.wikipedia.org/wiki/Negative_mass). That would be an interesting result but I wouldn't bet my house on it... – Maja Piechotka Jul 24 '17 at 21:30
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    @Maciej Yes, and for that reason antimatter is unlikely to fall upwards, but we still need to check. The point of that comment is that the answer is rather overconfident in the symmetry between matter and antimatter, given that there are deep asymmetries between them that are complete mysteries (which asymmetries? well, when's the last time you saw matter, and when's the last time you saw antimatter?). So, the answer could well read "apart from that big gaping hole in physics that we don't understand at all, no, there are no known differences between matter and antimatter". – Emilio Pisanty Jul 24 '17 at 21:59
  • Very nice answer and perspective. Related; What is the Current Status of Measurement of the Gravitational Mass of Antimatter? – uhoh Jul 25 '17 at 05:32
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    @EmilioPisanty We do have a lot of indirect evidence as well, though; for example, the success of QCD at describing what happens at the LHC suggests that hadrons really are a huge mess of quarks and anti-quarks, which in turn suggests that almost all of normal matter in the universe ("by weight") has mass derived from the binding energy of quarks and anti-quarks, and thus shouldn't be substantially different (if at all) if the unpaired quarks were anti-quarks instead. John does address your mysterious asymmetries in his answer, he just doesn't consider them important for human-scale stuff. – Luaan Jul 25 '17 at 12:21
  • @Luaan Yes, the Standard Model does have a habit of taking the parts of physics it cannot explain and decreeing them to be "unimportant edge cases". People with a more open mindset might disagree and call "edge cases" like baryogenesis things like "the most important open problem in particle physics". But then, yes, I agree, it's a matter of opinion, and it's anyone's right to just focus on the standard model and ignore any hints of new physics, however obvious. – Emilio Pisanty Jul 25 '17 at 14:44
  • @EmilioPisanty Oh, I certainly do consider baryogenesis one of the most important open problems in particle physics. That doesn't mean it's not an edge case, just like SR/GR was. And if we ever discover that the hints do actually point to a whole new area of physics, awesome :) If it leads to a fundamental rethinking of some daily-reality physics, like GR or QFT, even better. But there's so many problems with explanations that seem very likely, but aren't accepted (yet)... An interesting topic for study, certainly. But do you really expect a ground-breaking discovery? A large-scale deviation? – Luaan Jul 25 '17 at 14:56
  • now that does bring a really interesting question, why does the majority of the universe composed of matter rather than antimatter – PirateApp May 25 '23 at 12:35
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    @PirateApp No-one knows. It is one of the open questions in physics. – John Rennie May 25 '23 at 12:39
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Actually, CERN has announced that they have observed anti helium atom in outer space in 2016,

The AMS Collaboration could have another huge surprise is stock: discovering the first antiatoms of helium in outer space. Given that anything more complex than an antiproton is much more difficult to produce, they will need to analyze huge amounts of data and further reduce all their experimental errors before such a discovery could be established.

It is not mentioned in here, but one of my professors working on AMS had told me that they have just observed 4 anti-helium atoms.

Our
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