Talk:Gravitational interaction of antimatter

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[edit] CTP Symmetry

I believe this article should more clearly point out that CTP Symmerty does not excluded antimatter... (if antimatter attracts antimatter, and matter attracts matter, than antimatter attracting matter is not a violation of CTP). The interest in studying antimatter is simply to explore the possibility of a CTP violation; but it is not commonly assumed that one does exist. If it is found that antimatter attracts matter (which is the most widely accepted opinion) then CTP will be upheld (for now). Until a CTP violation is found and proven this article should clearly state that antimatter interacting with matter is the most logical, commonly accepted theory...

The article does explain that most physicists accept that antimatter attracts matter, but I think for the sake of quality it should be explained the reason for this is because that would be the simpliest (and hence most likely) resolution of CTP.

--Lynch82 14:15, 4 March 2006 (UTC)

I also believe there should be more of an explanation of vector theroies, including tying them back to being much more inline with CTP (though still a violation).

(note: I am happy to make edits to the article, but I though it would be rude to just jump in and do it given this page seems to be predominantly maintained by a handful of individuals.)

--Lynch82 14:18, 4 March 2006 (UTC)

Be bold. As long as your edits are competent and NPOV, there shouldn't be a problem. Page ownership is rather antithetical to the wiki ideal.
Also, general practice is to start new talk sections at the bottom of the page. - mako 01:51, 5 March 2006 (UTC)
Thanks for the links and information provided. I am new to Wikipedia and still learning the ropes. From now on I will start new topics at the bottom, and later today I will revise this article. --Lynch82 05:12, 5 March 2006 (UTC)
How is antimatter-matter gravitational repulsion a clear violation of CPT? In the best reference on this subject("The arguments against..."), Nieto and friends state, "CPT only implies that an antiapple falls toward an antiearth in the same way. CPT says nothing about how an antiapple (that is to say an antiproton or a positron) falls toward an earth." It takes additional assumptions about how gravity works(tensor gravity/gravitons) for repulsion to run afoul of CPT. -Intangir 06:27, 3 April 2006 (UTC)
I don't know why exactly it would be a violation of CPT for antimatter and matter to repel. I may be missing something, but the sources I have read seem to say that CPT doesn't even suggest one way or the other. I've not gotten a response for awhile now, so I have removed the sentence suggesting that it would be a 'clear violation'. If anyone knows otherwise, please tell me. -Intangir 15:54, 19 June 2006 (UTC)

[edit] Experiment

Good article. You've avoided all of my concerns on the subject.

It suddenly strikes me that a simple experiment should not be too hard. One creates antihydrogen, using standard techniques. One uses standard cooling techniques to get it as cold as possible within its trap. One then turns off the trap, and observes where the gamma rays are coming from. If they come from below, its falling down. If they come from above, its falling up. Surely this can't be too hard? It would at least resolve the issue of the sign, although clearly not the magnitude. linas 15:39, 13 December 2005 (UTC)

Antihydrogen atoms are created in a trap because the trap is needed to slow the positrons and antiprotons. The trap is not effective on antihyrdogen as antihydrogen is electrically neutral. ATHENA and ATRAP use this exact method to cofirm the existance of antihydrogen, as it leaves the trap once create (wether the trap is on or off). Now even when observing an antihydrogen atom, it is still difficult to determine the effect of gravity... due to magnetic moments causing deflection, and due to the short livedness of the atoms. --Lynch82 13:22, 4 March 2006 (UTC)
The physicists also do not know where the antihydrogen is created, they could be created anywhere in the central well of the trap... so 'above and below' is hard to determine. The antihydrogen can also only be detected when it is annihilated, and due to deflection and energetic potential it is not exactly 'simple' to determine wether the atom reached annihilation by gravity or simply energy. --Lynch82 13:28, 4 March 2006 (UTC)
I guess turning off the trap might be really really hard, without imparting momentum to the atom. linas 15:40, 13 December 2005 (UTC)
I have no idea why they haven't done an antihydrogen experiment yet. There are a huge number of proposed experiments for measuring the acceleration of antihydrogen. It seems as though there are far more experimental proposals than theoretical articles on this matter! Of course, there might be lots of weird effects that they are worried about. For example, Fairbank's experiment seemed like it would work. In the current revision I blame the charge mass ratio for the problem. Nieto talks about how, in reality, the experimental set up was most ruined by some kind of 'sagging' of the electrons which somehow canceled any gravitational effect. Fairbank ended up measuring something like ~0.06 for electron gravitational acceleration.
Also, thanks for your support! Once I finish this, I think I'll do antiphotons next. Hehe, maybe I'll make writing this kind of article a habit. -- Intangir 20:21, 13 December 2005 (UTC)
Yeah, well, be careful. The reason that there's little in the way of theoy is that there's "nothing to do" on the theory side, until someone does the experiment first, and gets a non-null result. This is for the same reason that no one is working on the "theory" of the Eotvos experiment (see weak equivalence principle). Its a waste of time until someone observes a non-null result. Ergo the interest in te Pioneer anomaly. linas 21:20, 13 December 2005 (UTC)
BTW you might enjoy the mirror universe: TeV scale gravity, mirror universe, and ... dinosaurs Article from Acta Physica Polonica B by Z.K. Silagadze.
How about ATHENA? They mention the antimatter/gravity subject on their "why" page. (Seems our ATHENA article needs work.) - mako 06:27, 21 December 2005 (UTC)
LOL, great point! I've forgotten to reference them entirely! -- Intangir 06:56, 21 December 2005 (UTC)
I know it's been a year since there has been any posts on here but here I go anyway...In response to the original point made by Linas about carrying out an antimatter experiment I raise the following issue. The 'trap' as far as I'm aware, in which antimatter and matter is stored, is a loop which keeps the particles moving/spinning by way of huge magnetic fields. If these fields were switched off, I'm pretty sure (but not 100% sure) that the antimatter would *poof* and be gone. Therefore the the huge magnetic fields would still more than dominate any gravitational effects. Then again, there may be a way to store antimatter other than this of which I'm not aware. Is there? I'd be interested to hear your thoughts on this. Now this next bit I'm very unsure about, but in the spirit of the wiki here I go again...assuming that the antimatter requires these magnetic fields to keep it stored then...and this is very high-school...seeing as heat 'is' motion perhaps we couldn't cool it very low while it is moving as such in these fields. The obvious issue with this is that we can supercool liquid helium to less than 1K on Earth, while the Earth is moving very quickly around the sun - it seems to be a relativity problem. Where does relative motion define the heat of things? Is it relative to the particles nearby, the planet, the supercooling chamber? Yet another possibility is that heat isn't actually defined by motion any more and I am slightly out of date. Again, your thoughts? --Lorddoig 14:45, 27 November 2006 (UTC)
I've just been under the assumption that they couldn't easily measure any gravitational effects of the particles while they were still in the trap. I suppose they would cool them down in the trap and then shuttle them off to some evacuated chamber to perform the experiment. They need the antihydrogen cold so their initial motion doesn't swamp out the effect of gravity. It would be hard to see the effect of gravity if your particles are moving so fast they collide with the walls and annihilate before you can blink. BTW, heat sort of corresponds to the average kinetic energy of the particles relative to each other, not to some shared fixed body like the Earth. Intangir 15:27, 20 March 2007 (UTC)

[edit] Author needs to clarify a nonsensical remark

Negative values of the Kerr-Newman solution? That doesn't even make sense as written. Maybe the author meant negative values of the mass parameter, but in that case, what is so special about Kerr-Newman? Please note that physical interpretation of parameters of exact solutions in gtr is notoriously tricky, and considerable expertise is often required to even partially justify a given interpretation (partial justification is usually about all that can be attained).

Whoever wrote this (Intangir?), clarify it, explain it, or delete it, please. ---CH 23:33, 19 December 2005 (UTC)

I'll try to explain it in my next revision(maybe tomorrow) if I can figure out what the author of the paper meant by it(if I can't I'll reword it). He (Chardin 1997) related it to crazy wormhole ideas or something; that was the context that it had been studied before. I'm no expert. If you think you can make more sense of it, I encourage you to download the paper if you are lucky enough to have electronic access. I just had finals and such so I haven't been able to clean everything up yet. -- Intangir 01:53, 20 December 2005 (UTC)
I take it you have seen the paper you have in mind, or at least know the title. Is it perhance one of these eprints? I tend to avoid crazy papers on any subject :-/ but I guess I could make an exception and take a quick look to settle this terminology question.---CH 22:58, 20 December 2005 (UTC)
No, I don't think there was an arxiv preprint for it. It is this article:
G. Chardin, Motivations for antigravity in General Relativity, Hyperfine Interactions, Volume 109, Issue 1 - 4, Mar 1997, Pages 83 - 94
Now that I have time to reread it, I see that it is talking about negative mass. I have time now, so I'm about to revise the article. --Intangir 01:29, 21 December 2005 (UTC)
A general comment: be careful about citing published papers here at WP unless you are confident that they are correct (ideally, one would be competent to review a similar draft for a high quality journal, although this might be taking the WP "expert" term too literally.). Some published articles may be authored by persons with little knowledge of gtr (or poor scientific judgement). Papers dealing wiht gtr which have been published in journals like Class. Quant. Grav., General relativity, and PRD are more likely to have been reviewed by experts in classical gravitation than papers published in some other journals I could name. In fact, there are a number of outright crank journals out there. And even CQG has had its problems (see Bogdanov affair), so you can never be too careful about accepting a paper simply on the basis of author or journal reputation! ---CH 20:37, 5 February 2006 (UTC)

[edit] Outstanding Issues

With the new revision everything is a little cleaner and all the necessary citations are accounted for. It is now reasonable, so I'm adding links to this article in all the related articles. However, there are still plenty of outstanding issues:

  • It seems biased in favor of antigravity. Naturally, this is because I am also biased! No really good theoretical argument against antigravity is presented. I simply don't know of one which hasn't been refuted.
  • The article only briefly mentions that antigravity was said to violate the CPT symmetry and cause vacuum instability. A full discussion of these arguments is needed. I know Chardin argues that any instability would be no worse than hawking radiation, and that antigravity could be a mechanism for that.
  • No discussion of gravivector stuff. I think this may be favored over antigravity ideas. Anyone interested in writing a gravivector article? A relevant, easy-to-read Scientific American article is cited here, hint hint.
  • The <10% probability cited in the SN1987A section isn't really asking the correct question. The relevant question which should be asked is 'What is the probability that both neutrinos and antineutrinos eminating from the supernova were detected?'. If a neutrino was detected, it may have been from a different source. It'd be nice to find out that probability. Also, 10% is probably an overly conservative estimate.
  • Morrison only argued against a straw man. Morrison failed to realize that if antimatter reacted oppositely then antiphotons would no longer be theoretically identical to photons. They would redshift where normal photons would blueshift and vice versa. I haven't added this because I haven't found any journal articles on this yet, but I intend to research some for a future antiphoton article.
  • I don't like referencing the USENET FAQ. I think it is unfairly biased against antigravity. It doesn't mention the small, but not insignificant, probability that SN1987A might not have detected any normal neutrinos. It doesn't seem to realize the straw man nature of Morrison's conservation of energy argument. It doesn't recognize that the second law would still not be violated. Worst of all, it doesn't mention any of the arguments in favor of antigravity. My dislike of the USENET FAQ's treatment of this issue was one of the factors which led me to write this article. It simply isn't a very good source, but everyone (on the internet at least) cites it anyway.
  • My description of the Morrison argument sucks. Also, a diagram would help explain it wonderfully.
  • Arrow of time (or the lack thereof) implications should be discussed.
  • More stuff(added later)
*What!? No mention of ATHENA or ATRAP?!
*Clarification of what is meant by repulsion. Consider Newtonian, GR, and Quantum Gravity.

--Intangir 04:59, 21 December 2005 (UTC)

[edit] Potentially serious problems with this article

Three things stand out on a first reading of this article:

  • This article does indeed come across as having a very pro-antigravity slant. My understanding is that this does not reflect the consensus of the scientific community at present (which is, as stated in the first paragraph, that matter and antimatter react to gravity in the same way).
-I agree, this is definitely fringe science. The scientific consensus needs more emphasis in the article. Intangir
  • The statement that the idea of antimatter being repelled by matter gravitationally "has gained considerable theoretical ground" isn't supported in the article. The more serious-looking references cited are from the 1950s and 1960s.
-The classic arguments against repulsion were all put forward back then. In 1991, Nieto and Goldman wrote a paper which was very critical of them, refuting some of them outright. They cited Chardin as reversing the Good argument to be in favor of repulsion, and Chardin has continued to improve the theory. Intangir
  • The statement that antimatter may have negative mass is completely inconsistent with observations. All indications to date have been for positive rest energy, identical to that of their matter counterparts, unless you're proposing that conservation of energy doesn't hold.

I'm going to link this article from WP:PNA/Physics, as it could use vetting by more people versed in the field (I'm not a researcher in relativity or particle physics). --Christopher Thomas 06:19, 21 December 2005 (UTC)

-Hmmm... I think it is really just negative gravitational mass that Chardin is suggesting, of which we have no observations. Anyways, expert attention would be awesome. -- Intangir 06:56, 21 December 2005 (UTC)
Unfortunately, I cannot obtain the article in question. I am not familiar with the journal either, and I can't find anything relevant in Citebase. It seems to be a Springer journal devoted to "border areas", which could be an alarming turn of phrase in this context :-/ Classical and Quantum Gravity and General Relativity and Gravitation are probably the two mainstream journals most directly aimed at physicists interested in gtr, although Phys. Lett and some others publish speculative essays.
I did get the abstract of this paper from Google scholar. Based on that, Intangir, I think you might still be misinterpreting negative mass part of the Kerr solution. Without seeing the paper I am only guessing, but I guess that does not mean simply setting the mass parameter in the usual Kerr solution to a negative real value. All I can suggest is that you post a query in the moderated newsgroup sci.physics.research addressed to Steve Carlip, John Baez, etc. ---CH 13:09, 21 December 2005 (UTC)

[edit] Explanation of dispute flag

This article needs to be completely rewritten by someone with expert knowledge, but a sufficiently NPOV expert might be hard to find, since the question of which way antiparticles should fall in a uniform gravitational field is vexed. Some brief comments:

  1. The introduction and particularly the link to antigravity is quite misleading, and should either be removed or else that article should also be extensively rewritten to clearly distinguish between this controversy and speculations which tend to constitute outright crackpottery. The key point is that "antigravity" is a term which like "Mach principle" can mean zillions of quite different notions, and while it might be amusing to call some phenomenon "antigravity" this can also confuse anyone not in on the joke.
  2. All encyclopedia articles should pass from the general to the specific, and should generally follow chronological order when explaining how ideas have developed. For instance, detailed discussion could begin with 1932. Cranky stuff should be mentioned briefly at the end, if at all (with links to both cranky and debunking sites if mentioned).
  3. The best experimental evidence is left dangling. Evidence of what? Who thinks this is relevant and why?
  4. The mention of gtr is completely munged. Unfortunately there are several things to explain here, all requiring their own articles, and all, unfortunately, almost certain to be misunderstood by anyone lacking considerable experience with computations with Lorentzian manifolds. In particular, the issue of whether one can "legimately" adopt arbitrary real values for parameters (perhaps called a "mass") appearing in some solution written in some chart is distinct from the rather difficult notion that in a sense the mass of an object in gtr can be position dependent and even reverse sign. In the Kerr vacuum there is a third phenomenon which some have called "antigravity", having to do with "centrifugal forces" felt by certain observers. All of these are rather difficult to explain and I have seen many trained physicists get terribly confused by them (e.g. in arXiv eprints). Hence my injunction against anyone who is a gtr Ph.D. and also wise/thoughtful/experienced and also mindful of NPOV trying to add more explanatory material to the article.

All in all, I suggest reducing the article to a stub until such an expert can be found.

Suggestion: blank the current article, start with the unsolved problem template, write a very brief very NPOV description in that, and slightly elaborate in an introduction, pointing out what I just said, that this controversy should be distinguished from the imprecise term "antigravity" (which often functions as a weasel word here at WP), briefly mention that this was worked on by various investigators who have reached a variety of sometimes contradictory conclusions. Then add back a few of the citations, but only to papers published in reputable journals. ---CH 18:18, 21 December 2005 (UTC)

You want to blank the article because the two GTR sentences at the end are mungy? At the moment it is just a stubby little section begging for some one knowledgeable to expand on. While the relativity stuff might need to be written by experts, the rest is not nearly as complicated. There is no "variety of contradictory conclusions". No one has defended Schiff's or Good's flawed arguments since Nieto and Goldman refuted them. As for who thinks the supernova evidence is relevent... everyone does! Nieto, Baez, Chardin all mention it. I've attempted to reflect the historical nature of the debate. I've mentioned the three arguments which led physicists to believe that antimatter falls down. It happens that these were (uncontroversially as far as I can tell) refuted in the early 90's. This article is not cranky(except for the GR sentences), it is mostly just giving the scientific consensus on the quality of the old arguments. And yes it is yet another phenomena called antigravity, big deal- just another thing to clarify. I see no reason to start from scratch. -- Intangir 19:13, 21 December 2005 (UTC)
I have revised the article in an attempt to address each of your four bulleted points. In doing this, I voluntarily removed the disputed GTR section. I think that all the cited, journaled sources now come from reputable journals. However, the two articles which talk about the apparent cosmological constant have not been peer previewed, I think. To ameliorate this, I have worded the article to merely state that their authors suggest antigravity predicts a flat-on-the-largest-scale spacetime. Whether or not antigravity predicts this, I think this is the good NPOV way of representing this. Anyways, is there anything in the article which is still disputed? -- Intangir 20:44, 24 December 2005 (UTC)
Intangir, I am quite disappointed. You need to discuss the expected physical properties of say an antiproton, compare with a proton, explain what precisely you mean by "repulsion" (possibly first in a Newtonian context, then a classical gravitation context, finally perhaps in speculative quantum graviy context), etc., etc. I don't even know where to begin. I hope you will blank and start over as I suggested. ---CH 23:47, 24 December 2005 (UTC)
Ok, I'll work on adding that in. However, my question is whether or not there are any particular facts in the article which you are disputing? -- Intangir 00:00, 25 December 2005 (UTC)

[edit] Gravitational effects of antimatter has been defined

The gravitational effects of antimatter have indeed been defined - antimatter has been, on numerous occasions, observed and calculated to have a mass (As observed in the Standard Model, antimatter particles reverse all additive quantum numbers.). Thus, due to all bosons having an integral spin, these numbers are 1 and -1, so the total spin is 0 (See the definition of Boson and Spin quantum number). Therefore, in theory, a gauge boson is its own antiparticle and can only exhibit one group of properties, meaning that antimatter must have a positive mass and would thus be affected by gravity normally.Xander T. 04:35, 18 March 2007 (UTC)

There is no doubt that the standard model supposes(defines?) antimatter will fall normally. However, the scientific consensus appears to be that this remains untested. I do think it is a good idea to include information on the theoretical difficulties presented by photons and other gauge bosons in the article, as someone seems to have recently done. However, this is essentially the same issue that Morrison brought up; it leads to a violation of the conservation of energy. Intangir 15:04, 20 March 2007 (UTC)
What is this violation of conservation of energy? I am sure that it could be easily explained. - Xander T. 22:13, 30 March 2007 (UTC)
You can create an antiparticle-particle pair with photons and vice-versa. Presumably these photons will behave like any other and gain kinetic energy as they move down in a gravitational field. However, if antiparticles were repelled by gravity where regular particles were attracted, then you would expect that an antiparticle-particle pair would overall gain no kinetic energy when moving through a gravitational field. This would let you 'manufacture' energy by producing antimatter at one height and annihilating it higher up. All of this speculating of course that antimatter 'falls up' but also that there is nothing special about the photons used in pair-production. ie no such thing as 'antiphotons' which would lose kinetic energy as they moved down in a gravitational field(of which there is no evidence, though I doubt anyone has ever really looked. Google scholar hasn't found me any experimental tests of Morrison's argument. I've never heard of something like the Pound-Rebka experiment but for photons yielded by annihilation. Intangir 08:15, 4 April 2007 (UTC)
The phenomenon you explained above describes the energy that would be created if antimatter was repelled by gravity - I am presenting an arguement that antimatter is affected normally by gravity. Additionally, a photon has no mass, and so cannot gain or lose potential energy by moving up and down within a gravitational field - The theory of relativity is not to prove that gravity acts upon photons (Rather, it bends space.), but to be used as a ratio for direct mass to energy conversions and vice-versa, as used in antimatter collisions. Xander T. 05:48, 13 April 2007 (UTC)
Photons have no rest mass, they have effective mass. RJFJR 17:05, 29 October 2007 (UTC)
Um, no, they don't. So shut the fuck up. Because mass is an Lorentz invariant quantity. Do you even know what a four-vector is? How about a Minkowski norm? I'm guessing no. And therefore you don't know what mass is. And therefore you're an idiot for commenting. --70.131.60.191 (talk) 02:30, 1 January 2008 (UTC)

[edit] This entire article is complete bullshit.

Anyone who actually knows what an antiparticle is is laughing at this article right now. Mass is not an additive quantum number. It is not a charge. It is not a flavor. It is not different between a particle and its antiparticle. Given that gravitational interaction depends only on mass, and nothing else, this article is not scientifically valid, never has been, never will be, and is essentially idiotic physically impossible pseudoscientific masturbation. It should be deleted. Immediately. --70.131.60.191 (talk) 02:28, 1 January 2008 (UTC)

[edit] Liao's argument

If antimatter matter repelled normal matter, then there must also be an antiphoton which gets blueshifted climbing out of a normal gravity well (and similarly, a photon would be blueshifted coming from an antigravity well). I don't think we've seen any of these blueshifted spectra, so they probably don't exist. 24.153.142.66 (talk) 21:54, 19 April 2008 (UTC)