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Observation of the effect of gravity on the motion of antimatter
- jl6 3y agoFun fact: if you’ve ever had a PET scan, you’ve had antimatter generated and annihilated within your own body, and you most likely survived the process.
- nonameiguess 3y agoNo likely here. Anyone reading this definitely survived the process.
- halfmatthalfcat 3y agoGhosts browsing HN are offended
- tgv 3y agoHow so?
- eigenket 3y agoThe letters PET stand for Positron Emission Tomography. It works by you ingesting a material that emits positrons. Positrons are antimatter electrons, they annihilate with electrons in your body and produce EM radiation which is detected by the scanner machine.
- gpderetta 3y agoMore specifically, the material emits high energy photons, that almost immediately "decay" into positron/electron pairs that travel at almost exactly opposite directions. Then detectors at opposite ends of the machine detect the electron and the positron, match the event pairs and can then reconstruct the line of travel and the emission depth (from the detection timestamp delta). IANAP, but did a bit of work on tomographic image reconstruction. edit: never mind, I got that wrong (it has been a while...): the material does emit a positron that decays into opposite photon pairs.
- eigenket 3y agoI am a physicist and you have it pretty close to correct, except reversed. The atom emits a positron (and in the process turns one of its protons into a neutron), the positron annihilates with an electron and this produces opposite photon pairs which are detected.
- heavyset_go 3y agoWhere does the electron come from, the body? Or is it generated in pairs with the positron or something?
- deleted 3y ago[deleted]
- eigenket 3y agoYeah, the positron hits an ambient electron from somewhere in the environment, in a PET scan this is usually inside the body.
- bonzini 3y ago... which is why it's called ionizing radiation, removing an electron (or adding it in the case of beta decay) turns neutral atoms into ions.
- eigenket 3y agoIn general yes. In this specific case not entirely, because once the radiating nucleus has undergone positron emission it has turned one of its protons into a neutron, which means it now needs one less electron in order to form a neutral atom. The "spare" electron can wander off and replace (eventually, on average) the electron that gets annihilated by the positron.
- platz 3y agoHow does a photon survive going through the body to make it to the detector? Seems like there is a lot of stuff in the way.
- short_sells_poo 3y agoThere's an old saying: "the dose makes the poison" :)
- labster 3y agoFun fact: bananas also produce antimatter, and generate antimatter in your body once consumed.
- sylware 3y agoJust to be really sure.
- myaccount80 3y agoCan anyone explain how do they make the antimatter particles and how do they actually know/analyze that they are making antimatter atoms ?
- Ygg2 3y agoCreate several thousand anti hydrogen atoms. Put them in a magnet trap. Open top and bottom of the trap. Detect collisions with wall. If more down. It's affected by gravity.
- jansan 3y ago> Create several thousand anti hydrogen atoms. The question was how this is done.
- Ygg2 3y agoThe way it's always done. High energy beams + magnetic sieve. Positrons are by-products of high energy collisions. You just need to separate them by mass and charge. Combine them with anti-protons and you get hydrogen atoms. Then make anti-hydrogen traps. Check Wikipedia for clues. https://en.m.wikipedia.org/wiki/Antihydrogen https://en.m.wikipedia.org/wiki/Antihydrogen
- perihelions 3y agoIt's a nitpick but this experiment uses a radioisotope source (Na-22) for positron collection.
- ben_w 3y agoThe answer you gave is like the meme of how to draw an owl in two steps (1. draw a perfect circle, 2. draw the rest of the owl). A more helpful answer might be something like: -- Each particle has a corresponding field over all of space. The substance-like particles obey certain rules, called Fermi statistics, which leads to a model called the Dirac sea; this makes all of space analogous to semiconductors, with electrons and holes, except that because this is just an analogy the holes are actually antiparticles. The analogy is useful, in that it takes a certain minimum energy level to create a particle-antiparticle pair, just as it does an electron-hole pair. For fundamental particles like electrons-positrons, this is fine and works as expected; the only extra step is knowing what has to absorb the energy to create the pair… but it turns out that all normal matter will do. For composite particles like protons and neutrons, this is much harder, as the thing you make this way are quark-antiquark pairs, and to make either an antiproton or antineutron you need a specific combination of three specific "colours" (not real colours) of quark, and we have only extremely limited control in this regard. When you have both positrons and antiprotons, "cool" them from the absurdly high energy states necessary to create them and let them combine just like electrons and normal protons recombining after getting ionised.
- rapjr9 3y agoSo this seems to mean that antimatter is not negative matter, it is normal matter with different characteristics. Seems like a huge clue as to what matter actually is made of and what holds it together.
- Jensson 3y agoThis is what physicists expected. Both part of gravity as warping space expects this, and that gravity fields are based on energy content. Anti particles still have positive energy, so should generate and interact with gravity like normal.
- pragnesh 3y agorelated video tweet from CERN https://twitter.com/CERN/status/1707054178625864177 https://twitter.com/CERN/status/1707054178625864177
- jansan 3y agoThat guy looks exactly like someone who would use Comic Sans in a Powerpoint presentation of a Nobel price worthy discovery.
- dudeinjapan 3y agoWhy does everyone hate Comic Sans? Its my go-to font for making technical illustrations its pretty easy to read.
- jansan 3y agoNo hatred involved here. This was supposed to be a light joke referring to the use of Comic Sans in the Higgs boson presentation by CERN scientists (that later led to a Nobel Prize). No matter how you see it, Comic Sans was an unusual choice. I thought is was simply hilarious and I actually hope someone will do it again.
- YurgenJurgensen 3y agoI believe that it’s not even very good at what it’s intended for. There are better comic lettering fonts available now even for free.
- dudeinjapan 3y agoBut how many are bundled with Windows???
- amelius 3y agoDoes that mean that any anti-matter out there will eventually find us?
- labster 3y ago[flagged]
- WJW 3y agoNot anymore than any other type of matter out there.
- nonameiguess 3y agoAs far as we know, there likely isn't any, at least not in a persistent large-volume amount. Antimatter particles are continually created by high-energy collisions of regular matter particles, but annihilate quickly. Cosmology speculates some miniscule imbalance in the ratio of baryons to antibaryons shortly after the Big Bang, the cause of which we don't know, is the only reason anything material exists in the modern universe at all. Most particles annihilated with their corresponding antiparticles, but there were somewhat more baryons that survived because no antibaryons remained to annihilate with, and those became all of the galactic structure we're familiar with, see, and are made of. No antimatter should have remained. More is always produced, but it annihilates well before having any opportunity to become macro-scale structure of its own.
- anodari 3y agoA friend in college believed in the concept of a matter-repelling antimatter drive that generates propulsion by one repelling another. However, this experiment demonstrates that it may not be possible. Could this experiment enforce theories that propose gravity operates differently from quantum theory?
- Ygg2 3y agoWdym. Standard model suggest anti matter will behave like regular matter.
- phkahler 3y agoThe Standard model doesn't include gravity.
- rob74 3y agoThat was my first thought too: all those sleek (or less sleek, as in The Fifth Element) anti-gravity flying cars from sci-fi films just became a little less probable...
- thfuran 3y agoDid they? If you can stick a nontrivial amount of antimatter in a car, surely you have the energy budget to lift the thing off the ground.
- WJW 3y agoNot really, as the current dominant theory already predicted that gravity affected antimatter in the same way as normal matter. This experiment affirms the standard model rather than disproving it.
- rnhmjoj 3y agoYou're probably thinking of exotic matter with negative mass, not antimatter. Antimatter is matter made of (elementary) antiparticles, which are identical to the usual particles expect they have opposite electric charge. So, we didn't expect there would be any difference as far as gravity is concerned.
- Sporktacular 3y agoI couldn't understand this headline. Antimatter only differs in charge so of course it's affected the same way by gravity. So this is just a confirmation?
- dan_mctree 3y agoThat's right, it's usually been theorized that gravity would affect antimatter the same way as regular matter, but it's been hard to confirm as it's a serious challenge to obtain a significant mass of antimatter
- chriswarbo 3y agoScience is not theology: ideas must be tested against reality. We thought antimatter would fall down, but it's been very hard to test (since gravity is so weak). In particular, antimatter tends to form as fast-moving charged particles, whose gravitational behaviour is drowned-out by other forces like electromagnetism. Hence we need to form neutral particles, like atoms of anti-hydrogen; and that requires slowing the particles down. Even then, measuring the gravitational effect on such tiny scales requires incredible precision!
- Grimburger 3y ago> it's been very hard to test (since gravity is so weak) Surely antimatter containment is the bottleneck here?
- Sporktacular 3y agoSure. It's just not really much of a headline, or an idea. There are lots of interactions between combinations of things that haven't been studied. But fine, I guess it's not exactly on the Guardian's front-page.
- caturopath 3y agoThe reason you're reading this on some nerd website and not every single news outlet is that this was the strongly expected result - we see photons affected normally by gravity all over the place, we see CPT symmetry hold up everywhere we look, and negative gravity would be hard to square in with a general relativity way of thinking. That all said, the opposite result would have been huge. We know our understanding of gravity is flawed to a degree we don't know about flaws to the theories of (at a low level) literally everything else we're aware of in the universe.
- samhuk 3y agoKey take aways (for layman): * Previous studies have used charged antimatter like positrons and antiprotons, which they imply is kind of silly because the electromagnetic force is 10^42 times stronger than gravity, so you have to set up absolutely impossibly precise electromagnetic confinement apparatus to measure the relatively tiny gravitational force * So instead, they formed anti-hydrogen (which is neutral), and shot them (10^6 at a time, as my understanding of the text goes?) into a vertical magnetic trap * They waited for the anti-hydrogen to either "rise up" or "sink down" to the top or bottom walls of the apparatus and measured the frequency of annihilations * They biased the vertical magnetic field to various values, to see, at what magnetic field bias, the "top" and "bottom" annihilations were exactly 50/50. * If anti-matter is repulsive, they would expect to need a magnetic field bias that would "help the atoms stay down" to get to the 50/50 "top" and "bottom" rate. * They measured that they needed a magnetic field bias applied to the anti-hydrogen equivalent to "pushing them up" with 0.75g (+/- 0.25g or so), so anti-matter is attractive. No new physics. * 10^-13 % chance that anti-matter is repulsive * Rules out quite a lot of cosmological work that used repulsive antimatter to explain various troublesome cosmology roadblocks (dark energy, etc.)
- phkahler 3y ago>> They measured that they needed a magnetic field bias applied to the anti-hydrogen equivalent to "pushing them up" with 0.75g (+/- 0.25g or so), so anti-matter is attractive. No new physics. Antimatter is attracted to matter. Isn't it still an open question if matter is attracted to antimatter, and if antimatter is attracted to antimatter? What if antimatter is gravitationally repulsive? This experiment wouldn't show that. Not that I think it's likely, but it hasn't been ruled out by this experiment has it?
- sambeau 3y agoFor those of you, like myself, who only know about antimatter from science fiction and space opera, here's the key statement: Here we show that antihydrogen atoms, released from magnetic confinement in the ALPHA-g apparatus, behave in a way consistent with gravitational attraction to the Earth. Repulsive ‘antigravity’ is ruled out in this case. Not being a physicist, I am somewhat saddened by this :'-)
- mannykannot 3y agoI think it is fair to say that physicists in general are eager for results that are counter to expectations, though not so much if they rule out a hypothesis they personally have been pursuing for some time.
- ISL 3y agoThe experiment is very cool and it is satisfying to see a clear demonstration of the effect. Experimentally, however, the effect itself, that antimatter falls, has been demonstrated at much higher precision by weak equivalence principle tests for decades. See, for example, this 1991 paper from Adelberger et al. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.66.850 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.66... I have worked closely with the authors of that paper. I think the reasoning in that and subsequent papers is correct.
- asimpleusecase 3y agoThis is so strange. I took a tour of CERN more than a decade ago, and during the tour we were told about an experiment done there to prove antimatter responded to gravity. They described building and antimatter “fountain” where antimatter was released from an upward directed device and a detector was placed on the floor. They detected annihilations when the particles hit the detector. It sounded like a really elegant setup. I would assume the energy profile of antimatter annihilation would be quite specific and mitigate detecting other random particles. So did I dream this very detailed discovery or is this really old news?