Talk:Antimatter

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Help with this template Comments: edit – history – watch – refresh Antimatter is a very important topic within physics, and one of the major discoveries of the 20th century, so I think it deserves a "top" importance designation. The article itself has lots of good information on physics, history, and speculation, as well as links to a number of other articles. I think it could use a bit of editing for readability and, there are a few broken links and other problems that could benefit from some cleaning up. Wesino 17:58, 30 November 2006 (UTC)

Contents 1 Antiuniverse 2 Just Wondering... 3 Quantities 4 Annihilation burst 5 Backwards in time? 6 Antimatter as fuel 7 Efficiency 8 The Article is right about the fuel energy (i think) 9 Gravitational Repulsion of Antimatter? 10 Quantities needed? 11 odd wording 12 Unfair comparison 13 Antideuterium / Antimatter production 14 What does antimatter look like? 15 Who is this Mr. Beutel? 16 Template:Antimatter 17 Inconsistency of Price 18 Gravitational interaction of antimatter 19 "Interrogation"? 20 Bulk production of antimatter 21 Negative Mass? 22 Geometric? 23 Why collision into energy? 24 question 25 OMGWTFBBQ 26 Added a few things 27 Neutrinos and black hole reference 28 Comment mistakenly added to article 29 Nonsense 30 Question! 31 Antimatter Black Holes? 32 Black holes, White holes and outer-universe 33 Production

[edit] Antiuniverse

Is this page really the right place for a description of the Antiuniverse theory? With the recent reports from ATHENA and ATRAP it is looking less and less likely that an Antiuniverse is plausible. I agree that there should be some mention of it, but I sincerly believe it should have a seperate article and (that article) should be referenced in the 'see also' section.

--Lynch82 08:18, 3 March 2006 (UTC)

"probably wrong" isn't good enough reason to get rid of content. The fact that it's considered unlikely is mentioned right in the page. i kan reed 19:04, 2 October 2006 (UTC)

Ok, but should this universe be full of matter, should it not have the opposite in relativity!!! Could the universe that we live in, and is slowly expanding, could it not be expanding into the antiuniverse. It stands to reason that what we know is not the be all and end all of life and the likes. The existance of antimatter has been proven, therefor the universe must have its opposite, wheather it is in this or an alternate one. So I say could the universe that we live in, could it not be expanding into the antiunivers. Thus giving off the gamma rays that flood our scopes and graphs with no answer??? This is but a speculation and a theroy. Pastry!!!! 11.11.06

[edit] Just Wondering...

Whilst I understand that, an antiparticle and a Particle will Anihelate in contact, What would happen if an Antimatter Counterpart, of, lets say, Uranium(Antiuranium?), would come in Contact with an atom of Hydrogen?, Would there be Anihilation?, Thank you for you'r time.-Maurizio Dikdan

What would happen is that the electron in the hydrogen atom would annihilate with one of the positrons orbiting the anti-uranium nucleus, and the proton in the hydrogen atom would annihilate with either one of the antiprotons or one of the antineutrons in the anti-uranium nucleus. This would cause a particle shower of the type described above, which would dump enough heat into the anti-uranium nucleus to boil it into its constituent components, resulting in a shower of antineutrons and anti-helium nuclei (antimatter alpha particles).

Interestingly, the opposite reaction (dropping an antiproton into a uranium atom) has been proposed as one means of initiating fission in a nuclear-pulse-propulsion rocket (a variant of the AIMStar design, if I recall correctly). The idea is that the pulse of high-energy neutrons from one atom's disintegration would cause fissioning in many other nearby uranium atoms, releasing far more energy than the antiproton annihilation alone gave. This in turn would be used to ignite a fusion reaction in a pellet of frozen deuterium, and the resulting plasma fireball would be contained by a magnetic field and directed out the end of the rocket. Nobody's sure if this would work as intended, but it's an approach towards building an interstellar drive that would be far less massive than a Orion-style nuclear drive or a Project Daedalus-style laser-initiated fusion drive, while requiring far less antimatter than a beamed-core antimatter drive. It's described in more detail at antimatter catalyzed nuclear pulse propulsion. --Christopher Thomas 05:11, 28 April 2006 (UTC)

[edit] Quantities

    No more than a handful of atoms have ever been made.

Hm. A "handful of atoms" is a lot of atoms. It's also a lot of energy, if we're talking antimatter atoms!

Hey, I'm slow, but I think a handful of blah, means five. I would assume they have made more than five and less than the zillions that make up a hand. So how many (at least an order of magnitude) have they made?

Hey, I'm slow, but I think a handful of blah, means five. That's precisely the problem. In this context the colliqualism doesn't really make sense, so it shouldn't be used. It's like saying that something "sparked a wave of controversy"--sure those are both commonly used colliqualisms, but you still can't spark a wave.

A silly question: Is there a form of "positive electricity" (positricity? Proticity?) ?--68.49.39.32 04:42, 14 Jan 2005 (UTC)

Electricity isn't the result of electrons specifically, its the result of the flow of charge. Protons, electrons, positrons, even charged atoms can create electricity. If you are significantly charged, you would be creating significant electricity simply by moving. Fresheneesz 09:09, 5 April 2006 (UTC)

For the past 40 years, the World has produced about a microgram of antimatter, but in 1999, NASA announced that they successfully made 9 antihydrogon atoms. If we were to build maybe, 1000 AM facilities in the future (possibly on the Moon), we will be able to make a millionth of a gram a YEAR. But, it would would make better sense to use this large amount for research purposes, instead of fuel and weapons, if we were to use it for that purpose it would be a waste of energy, because were using a large amount of energy to make an equal amount of energy equivalent to the antimatter made, so you would be wasting a perfectly large amount of energy.

The exhaunge rate is 500,000 matter subatomic particles to make 1 anti subatomic particle. —This unsigned comment was added by 70.249.162.69 (talk • contribs) on 23:12, 23 March 2006.

[edit] Annihilation burst

"Annihilation burst gives electromagnetic radiation" is correct for electron-positron annihilation (at least at low energies). It is incorrect for cases like proton-antiproton annihiliation, where you mainly get pions and some kaons. I put in a more general description. -- Thomas

[edit] Backwards in time?

I'm very far from a chemist or physicist or something, but somehow I have doubts about this, "Antiparticles can be considered as normal particles moving backwards in time". I'm assuming it's roughly accepted as truth, seeing as how it's still part of the page... But just double checking. Jimbobbob 02:57, 2004 Oct 27 (UTC)

• Pending confirmation by an expert, I have removed this sentence. I also highly doubt its truth. - Mike Rosoft 11:10, 16 Nov 2004 (UTC)
  • All right, I have re-added it. (It is mentioned in the article on antiparticles.) But I'd still like to see a confirmation from a physicist. - Mike Rosoft 11:55, 16 Nov 2004 (UTC)
    • Yes, this is the standard interpretation of antiparticles in quantum field theory. For example, if we take an interaction between particles and somehow revert the arrow of time, each incoming particle transforms into the outgoing antiparticle, etc. --Itinerant 04:27, 16 Mar 2005 (UTC)
      • This is called the Stückelberg-Feynman interpretation of antimatter, and is essential to how feynman diagrams are drawn. Intangir 00:32, 4 May 2005 (UTC)

Antimatter has nothing to do with time and Feynman diagrams.Is just a solution of Dirac equation of relative electron.The quantum field theory is universal and the arrow of time is described only in thermodynamics.E = + _p2c2 + m2c4 —The preceding unsigned comment was added by 194.63.235.164 (talk • contribs) .

why are u ppl so against traveling back in time? its only possible for small things anyway, not us big things, so no worry of someone killing your parents :) —The preceding unsigned comment was added by Protecter (talk • contribs) .

That's what you say, 194.63.235.164, but I say they're going backwards in time. The "arrow of time" in thermodynamics has nothing to do with this, because when you reverse the flow of time all particles change into their antiparticles but everything still works the same. —Keenan Pepper 12:28, 8 May 2006 (UTC)

What a shame. I used to imagine that if I changed my office to antimatter, it would become more organized automatically ... -- Stiip 00:31, 11 October 2006 (UTC)

[edit] Antimatter as fuel

The article says: "... possible to attain antimatter for $25 billion per gram (roughly 1,000 times more costly than current space shuttle propellants)". This has to be checked and clarified. What exactly is meant by "1,000 times more costly"? Surely it doesn't mean that current space shuttle propellants cost $25 billion per kilogram? Are we comparing antimatter vs. space shuttle fuel in terms of cost per unit of produced energy?

I wrote some stuff about production of macroscopic quantities of antimatter in the article about antimatter weapons. Now I think that it probably belongs in the same place as the information about antimatter as fuel from this article. If someone wants to move or edit it, be my guest. --Itinerant 04:27, 16 Mar 2005 (UTC)

Antimatter has nothing to do with time and Feynman diagrams.Is just a solution of Dirac equation of relative electron.

why does anti-matter have to be so annoyingly stubborn? why can't it just be nice to matter? MAKE TEA NOT WAR. Bartimaeus 16:56, 22 November 2006 (UTC)

[edit] Efficiency

The "Antimatter as fuel" section states: 'Counterbalancing this, when antimatter annihilates with ordinary matter, energy equal to twice the mass of the antimatter is liberated—so energy storage in the form of antimatter could (in theory) be 100% efficient.'

I don't know enough physics to be sure, but I read (on Antimatter weapon and somewhere else I don't recall) that about 60% of the energy is released as neutrinos. Since those almost don't interact with matter, I don't see how the efficiency could be 100%.

It's been proven by scientists at C.E.R.N, http://livefromcern.web.cern.ch/livefromcern/antimatter --Dansanman 06:33, 3 February 2006 (UTC)}

Your link does not appear to contain information about the question of annihilation products. My understanding of what actually happens is that proton/antiproton annihilation (the reaction producing most of the energy in an antimatter drive or bomb) produces one quark/antiquark annihilation, expelling the remaining quarks bound as pions. The initial annihilation produces gamma rays, mostly (as it would be a quark annihilating with its antimatter counterpart, just as with the decay of a π⁰ meson). The expelled pions are either two π⁰ mesons, which almost immediately decay into gamma rays, or a π ⁺ and π ⁻ meson, which decay into antimuons or muons (respectively) after a few metres of travel, which in turn decay after travelling hundreds of metres. During this time, π ⁺ , π ⁻ , μ ⁻ , and μ ⁺ can be deflected to provide thrust for a space drive, or can interact with electrons and nuclei in matter to provide heat for power or a different type of space drive. The main mode of energy loss if I understand correctly is with gamma ray emission during the first annihilation and for π⁰ annihilations (as the gamma rays carry away most of their energy or dump it as difficult-to-use heat in reactor shielding). Neutrinos carry away some of the energy when charged pions decay into muons, but quite a bit of it stays with the muons. I don't have exact efficiency numbers, but an upper limit for a space drive would be about 450 MeV of kinetic energy in two charged pions of mass 135 MeV/C^2, from a proton/antiproton pair with a mass of about 1880 MeV/C^2, for an efficiency of around 50%. Actual efficiency will be less due to neutral pion production. Efficiency of a power plant would be much less, because your final stage is a heat engine with a maximum efficiency of around 30%-50%. --Christopher Thomas 03:08, 13 February 2006 (UTC)

[edit] The Article is right about the fuel energy (i think)

The article said: "The reaction of 1 kg of antimatter with 1 kg of matter would produce 1.8×10²¹ J of energy (by the equation E=mc²)." Based on my calculations, 1 kg × (300000 km/s)² = 1.8×10¹⁷ J. Several other websites also say 10¹⁷, no one said 10²¹. - Wilfried Klaebe, 2004-12-24 14:50 +0100

The last person that posted saying that the quantity of energy is wrong, if he used the equation he described, he commited several mistakes. First, it's 2kg of matter being turned into energy, and second , if you analyze the units, he should have transformed the speed of light into meters por second and not leave it in kilometers (remember a joule equals kilogram times meter square over second square), that is why he is getting a different result.

1.8*10¹⁷ is indeed the correct amount. Speed of light is 300000 km/s = 3*10⁸ m/s, 2mc^2 = 2*9*10¹⁶ J = 1.8*10¹⁷ J. --Itinerant 04:27, 16 Mar 2005 (UTC)

No,1 kg corresponds to 25,000,000,000 kWh of energy, here, http://livefromcern.web.cern.ch/livefromcern/antimatter/academy/AM-travel01.html --Dansanman 06:38, 3 February 2006 (UTC)}

1 kilowatt-hour = (1000 J/s)(60*60 s) = 3,600,000 J. Different units; both calculations are correct. CERN did the calculation for 1kg of matter, but we're interested in 1kg antimatter annihilating with 1kg matter, so we used 2kg. - mako 22:31, 3 February 2006 (UTC)

[edit] Gravitational Repulsion of Antimatter?

I have often wondered why we so quickly assume that the weight (not mass) of anti-matter is positive. If a hole in a silicon lattice is a good analogy of a positron in free space, then it is natural to think that positrons are repulsed by the gravitational force of a normal matter, since holes are. This could also help explain other problems. First, where is all the anti-matter? Perhaps in super-clusters of galaxy clusters. Why is the expansion of the universe accelerating? Imagine only two stars exist, one normal and one anti matter. They not only repel each other, they accelerate as they separate. The same may be true for large groups of super galaxy clusters mixed with anti super galaxy clusters. How do we know the weight of anti-matter? - Bill Cox; Feb 4, 2005; bill@viasic.com

• If antimatter had negative mass, it would have negative mass-energy (e=mc^2) and so a particle-antiparticle collision would result in the two disappearing, and the leftover kinetic energy being used to create products. However, the observed enery totals after annihiations have far higher mass-energy than could be accounted for if only the kinetic energy was left to create products. -9/4/2005 smangham@hotmail.com: Badly expressed my objection origonally, reworded it to make more sense

• • Actually, the full equation is more like e^2=m^2c^4+p^2c^2, where p is momentum. Assuming no momentum gives us e^2=m^2c^4 . It doesn't seem obvious from there that it should have negative energy. Intangir 00:47, 4 May 2005 (UTC)

• For the moment, the discussion about the possible gravitational repulsion of antimatter is on the negative mass page. Intangir 00:38, 4 May 2005 (UTC)

Do black holes not give off gamma radiation?????? So does it not stand to reason that this could be the universes natural antimatter lab?????? This therefor could explain the absense of antimatter in our known universe. The gravitational pull of a said black hole draws even the smallest particals and the fastest into its centre. Could it be that the centre is just a compounded sphere of antimatter rotating at such a high speed that none are relesed and the matter that is drawn in is crushed and colide with the antimatter giving off gamma radiation in the process. One chefs view. Pastry 11.11.06

[edit] Quantities needed?

Scientists in 1995 succeeded in producing anti-atoms of hydrogen, and also anti-deuteron nuclei, made out of an antiproton and an antineutron, but not yet more complex antimatter. In principle, sufficiently large quantities of antimatter could produce anti-nuclei of other elements, which would have exactly the same properties as their positive-matter counterparts. However, such a "periodic table of anti-elements" is thought to be, at best, highly unlikely, as the quantities of antimatter required would be, quite literally, astronomical.

I'm far from knowledgable about antimatter, but why would it take "astronomical quantities" of antimatter to produce a more complex element than hydrogen? For a single atom of anti-helium, you'd need two positrons, two anti-protons, and two neutrons, no? jdb ❋ (talk) 06:03, 26 Feb 2005 (UTC)

Probably the chance that the reaction work occur...Joe Normal

I'm surprised they produced antideuterium at all. Protons can be produced at high energy and slowed down, but neutrons can't be trapped, so you'd have to either try to produce a bound antineutron/antiproton pair out of thin air (good luck), or try to get antiproton/antiproton fusion happening (could be done, but would take a very long time, due to the small interaction cross-section; this is why fusion of light hydrogen for power isn't feasible). Making anything heavier would involve producing large quantities of antideuterium and fusing that, which would be horrifically expensive and time-consuming. --Christopher Thomas 03:13, 13 February 2006 (UTC)

[edit] odd wording

I just removed a rather odd sentence in the body of the article: "Just imagine if humanity used it as a weapon" since it dosent seem to fit in with a factual article 61.68.242.104 06:05, 24 Mar 2005 (UTC)

[edit] Unfair comparison

The reaction of 1 kg of antimatter with 1 kg of matter would produce 1.8×1017 J of energy (by the equation E=mc²). In contrast, burning a kilogram of gasoline produces 4.2×107 J, and nuclear fusion of a kilogram of hydrogen would produce 2.6×1015 J.

Surely that's comparing 2kg of antimatter/matter fuel with 1kg of other types of fuel. That seems a little unfair.--Malcohol 12:37, 31 August 2005 (UTC)

Well, in the case of the gasoline there's also a substantial quantity of oxygen involved in the combustion (dunno exactly how much, I haven't done any chem in over a decade) not accounted for in that comparison either. It's an illustrative comparison. Look at the orders of magnitude involved; the factor of 2 in the mass is dwarfed by the factor of about 70 between the energy in the fusion and matter/antimatter reactions.--Robert Merkel 14:17, 31 August 2005 (UTC)

Robert's right about the gasoline, just doing a quick calculation using octane- C8H18 (nothing to do with the octane rating) nearly 4 kg of oxygen is needed to combust 1 kg of octane. I may be wrong so here is the equation I used- C8H18 + 12.5 O2 = 8 CO2 + 9 H2O Afn 16:31, 1 September 2005 (UTC)

These are interesting observations. Perhaps it would be useful if, somewhere on the wiki, there was a table of 1k-of-total-mass-of-certain-materials produces this-many-joules. This is just a thought, as I don't have the know-how myself. --Malcohol 08:55, 7 September 2005 (UTC)

[edit] Antideuterium / Antimatter production

Scientists in 1995 succeeded in producing antiatoms of hydrogen, and also antideuteron nuclei, made out of an 
antiproton and an antineutron, but no antiatom more complex than _antideuterium_ has been created yet.

Is this statement a little bit wrong? Because the Antideuteron article clearly states that no antiatom even _as_ complex as antideuterium has been created to this day.

Antideuteron has been created, therefore the statement is correct.

Yes, but not antideuterium. Read the whole sentence before you answer will you?

[edit] What does antimatter look like?

I've always wondered, if you had enough antimatter to be visible with the naked eye, what would it look like? Would it look any different from normal matter, or would it be visible at all? — JIP | Talk 05:14, 19 September 2005 (UTC)

It should look just like normal matter, as the energy levels for positron orbitals would be the same. It should also act the same chemically (with itself, that is).--Christopher Thomas 03:15, 13 February 2006 (UTC)

Ok call me stupid but i was thinking that if antimatter is onthe opposite of matter, as in rotation and i think gravitation, or could it be magnatism. Could it not be that antimatter and dark matter or dark energy is of the same idea. Both are unknown and both have some very similar qualities that lead me to think that they could be one in the same. Just a thought. Try me here!!!!!!!! Pastry 11.11.06

Can you be certain that antimatter can be seen if you were able to produce enough of it??? Would light be absorbed or would other particals be attracted to it??

[edit] Who is this Mr. Beutel?

... "Mr. Beutel's class info here", eh? Someone got it before I had a chance to, anyway..

[edit] Template:Antimatter

I found this template and it looks to me it's not used anywhere? Would it be appropriate to add it on this page? Skydiver 17:09, 7 December 2005 (UTC)

I've added the template since no-one objected. Skydiver 09:47, 9 December 2005 (UTC)

I am adding it to any articles linked to the template. Chad 08:16, 6 February 2006 (UTC)

[edit] Inconsistency of Price

Uh, yeah...on this page, it lists antimatter as costing $25 million per gram, but the page for antimatter weapons appears to list it as $25 billion. I don't know which is correct, but someone who knows should do something about it. Nick 02:33, 19 December 2005 (UTC)

I'd go with the $25 billion per gram value. A back of the envelope estimate can be obtained by assuming $0.05 per kWh (3.6 MJ), C^2 J/kg, and an efficiency of at best 1 part in 10^4 (for a facility optimized for antiproton bulk production; current facilities are about 1 part in 10^-6). This gives about $1.2 billion per gram at 1 part in 10^4 efficiency (not currently obtained). Positrons are much easier to produce, but aren't very useful (you can't make neutral antimatter atoms to trap and store without antiprotons). --Christopher Thomas 07:54, 12 February 2006 (UTC)

Uh.. you can't "trap and store" neutral atoms anyway. Why would you want antimatter atoms? Fresheneesz 03:40, 6 April 2006 (UTC)

Sure you can. This is done all the time for producing Bose-Einstein condensates. You cool them and use photon pressure and a strong magnetic field. As for _why_ you'd want to do it, most thought-experiments along these lines that involve large amounts of antimatter have been for the construction of an interstellar probe powered by antimatter-catalyzed fission or fusion. On a laboratory scale, you'd do it so that you could probe antihydrogen's properties in detail to see if it matches predictions. The missing link for lab-scale experiments is a means of cooling antihydrogen from temperatures on the order of eV (what you get in the "cooled" antiproton traps) to temperatures on the order of micro-eV or lower (what you need for laser cooling and long-term neutral atom confinement). --Christopher Thomas 04:19, 6 April 2006 (UTC)

Also check out the ATHENA experiment for 'why'. - mako 08:28, 6 April 2006 (UTC)

Hmm, allright, my mistake. But how does a large magnetic field help confine a neutral body? Fresheneesz 08:43, 7 April 2006 (UTC)

Many atoms, including hydrogen, have a substantial magnetic moment, and so are influenced by magnetic fields. --Christopher Thomas 15:58, 7 April 2006 (UTC)

[edit] Gravitational interaction of antimatter

I added a see also link to the fringe science article on the Gravitational interaction of antimatter. -- Intangir 05:08, 21 December 2005 (UTC)

[edit] "Interrogation"?

"(...)confine the antiatoms in an inhomogenous magnetic field (...) and interrogate them with lasers."

This seems to be a usage of "interrogate" with which I am not familiar. Can someone expand on this? DS 13:47, 17 January 2006 (UTC)

Yes, it means to investigate or probe them, as you can understand through context. I'm convinced that this is proper use of the word. FFLaguna

[edit] Bulk production of antimatter

The article states that "There is, however, no known practical or theoretical method by which antielements could ever be produced in bulk quantities.". While I don't know of any method of production that would be _practical_, you could in principle produce large amounts of antimatter by dumping matter into a small black hole and separating particles and antiparticles out of the polar jets using a magnetic field (charge-to-mass ratio has the opposite sign for particles and their antimatter counterparts). Good luck finding paper references for using that as an industrial process, though. --Christopher Thomas 05:55, 15 February 2006 (UTC)

Gravitaional forces???? Ouch it hurts, sorry. Would you not be drawn in and crushed also. This is not a fesable idea! Pastry 11.11.06

[edit] Negative Mass?

The positron emission article says that "a proton is converted to a neutron...and a beta plus particle (a positron)...are emitted." A neutron has more mass than a proton, so this logically means a positron has negative mass. So if a large quantity of antimatter were placed on Earth, it would it move up because of "antigravity"?

Positron emission can't happen without an external source of energy, which is converted into the positive mass of the positron. See Gravitational interaction of antimatter. —Keenan Pepper 03:20, 15 March 2006 (UTC)

[edit] Geometric?

"Antimatter production is currently very limited, but has been growing at a nearly geometric rate since the discovery of the first antiproton in 1955."

I'm just curious as to what a "geometric" increase actually means? It increases by circles and squares?

Circles, no; squares, sorta. It's probably alluding to the geometric progression. - mako 08:37, 10 April 2006 (UTC)

The area of a circle is proportional to the radius squared too. —Keenan Pepper 12:01, 10 April 2006 (UTC)

lol -NOOBLET

[edit] Why collision into energy?

Why do a particle and its anti-particle convert into energy upon collision? What is the mechanism for this interaction, and should it be included in this article? FFLaguna

"Convert into energy" is a poor description, as "energy" is a bookkeeping number, not a tangible "thing". When a particle and antiparticle (or indeed, any other two particles) interact, the result of the interaction can be any other configuration of particles with the same energy, momentum, and other conserved values ("quantum numbers") that the original system had.

For ordinary, stable particles like protons or electrons bumping into each other at low energies, what you normally get out is the same particles that came in, with an exchange of energy and momentum, because these are the only allowed states within the energy limits. In high-energy collisions, you can get more exotic particles created, or particle/antiparticle pairs, as long as the total system energy (including rest energy of the new particles) remains the same, and all other values are conserved.

A particle/antiparticle collision is special, because all of the conserved values (quantum numbers) besides energy and momentum cancel out. That's actually one way of describing what antimatter is (matter with reversed charge, parity, baryon/lepton number, strangeness, etc). Because these values sum to zero, the outcome can be any other particle/antiparticle pair, or a pair of photons, or a combination of the above, or odder variations. What usually happens is that you get a shower of light-weight particles (like electron/positron pairs and mesons) and high-energy gamma rays resulting. Not all of the energy has to go into the rest mass of particles, so when particles are created, they'll typically have quite a bit of kinetic energy as well, representing the difference between the rest mass of the products and the original particle/antiparticle pair's energy.

For specific examples, a low-energy interaction between an electron and positron (mass of about 500 keV) will give you two 500 keV gamma rays going in opposite directions, and the annihilation of a proton and antiproton will generally give you gamma rays in the hundreds-of-keV range and pi mesons, though other combinations are possible (you can think of this one as resulting from one quark from the proton and one antiquark from the antiproton annihilating, but that's not strictly correct). High-energy collisions typically produce "jets" of particles, which represent heavy, unstable particles that are created and then immediately decay into showers of secondary products going in the directions of the originally-created particles. As long as the kinetic energy supplied is large, the interacting particles can be just about anything (not necessarily particle/antiparticle pairs, though they're often used).

The "particle/antiparticles annihilate to produce energy" line, as far as I can tell, comes from a bad habit popular literature has of confusing light with energy. It _has_ energy, but the light is composed of particles (photons).

I hope this answer is useful to you. --Christopher Thomas 03:37, 24 April 2006 (UTC)

And much later, I realize that should have read "hundreds of MeV" instead of "hundreds of keV" for proton/antiproton annihilation. --Christopher Thomas 01:20, 25 May 2006 (UTC)

[edit] question

ppl, are antimatter just matter traveling backwards in time? so ive heard... lol like in this diagram

|     |                                           
|W-   |
|\    |
| \-ne|
| |\\ |<----------thats an arrow there 
|   \ |W+ from now on                              
|    \|
|     |
|e-   |e+
|     |

time go up (i cant draw the arrow it screws up)

i cant make it look good uve have to do ur best

actually its best for u not to look at the diagram

cant u say a ne (ele neutrino) was emitted by e- then go backwards in time and getting eaten by W+ then it changes to e+?

btw i think this interaction is impossible im just giving an example forgot other 1s —The preceding unsigned comment was added by Protecter (talk • contribs) on 14:23, 1 May 2006.

Our current understanding is that the laws of the universe obey CPT symmetry, which means that if you looked at the universe with time reversed, matter would look like antimatter (reversed charge and parity). From this point of view, you could argue that in some sense antimatter seems to be matter moving backwards in time, but in practice you can't explain all antimatter-related interactions that way. For example, beta decay and inverse beta decay causes production and consumption of an electron without a positron being involved, and positron emission likewise produces a positron without an electron emitted at the same time. --Christopher Thomas 21:47, 2 May 2006 (UTC)

[edit] OMGWTFBBQ

omg i read from somewhere antimatter has negative gravitational mass lolz i say no some1 plz tell me y they said that in first place? negative grav mass either means neg energy or neg pressure but u no antimatter cant have neg mass so its got neg pressure? -NOOBLET

You waffle nooblet pastry 11.11.06

[edit] Added a few things

I've found that several online role-playing communities have used anti-matter in the past. It's not massively common, but it's apparently done enough for some of them to have conversations about it. So, I did a little research, and found two message boards that have entries into wikipedia, and have used anti-matter in the past, with some sort of explaination.

~ Rhysis 08:53, 31 May 2006 (UTC)

You do realize that "negatron" means "electron", not "antiproton" as you've assumed in your edits, right? --Christopher Thomas 13:33, 31 May 2006 (UTC)

These edits are factually incorrect. Now reverted. -- Xerxes 14:44, 31 May 2006 (UTC)

[edit] Neutrinos and black hole reference

I have two concerns regarding this edit, which was otherwise good:

• Neutrinos have nonzero spin. This would prevent them from being their own antiparticles in the conventional sense, though I understand that neutrinos and antineutrinos are considered different manifestations of one particle in some Grand Unified Theory candidates, making this statement not completely incorrect (just misleading).
• I dispute the removal of the black hole reference, as near a black hole's event horizon is one of three places you'll find temperatures sufficient for pair production (the other two being the primordial universe, and the shock front where a relativistic jet encounters the interstellar medium). How is this not relevant in a paragraph about pair production in very hot environments?

--Christopher Thomas 20:12, 12 June 2006 (UTC)

The neutrino may be its own antiparticle if it has a Majorana-type mass (as opposed to a standard Dirac-type mass). There are searches currently underway to detect neutrinoless double beta decay, which can only occur if this is the case.

Black hole jets are certainly one place to find antimatter. This is not what was said in the article, which went on about black hole horizons and Hawking radiation. While Hawking radiation certainly might include antimatter, antimatter is not particularly important to the effect, which merely includes all possible particles. Further, there is no observation of Hawking radiation, much less antimatter in any such radiation. I would certainly support the addition of a sentence about antimatter from black hole jets, or particularly something about the positronic "fountain" of the Milky Way. -- Xerxes 20:35, 12 June 2006 (UTC)

I already referred to the Majorana mass interpretation of the neutrino. I think that this is sufficiently removed from conventional (Dirac) notions of "particle" and "antiparticle" that it should be flagged as such.

Regarding black holes, in my previous response, I list "near an event horizon" and "relativistic jet" separately for a reason, as these are completely different phenomena. If the horizon is described in terms of the Unruh effect, pair production in a high temperature environment is the _mechanism_ by which antimatter is produced, making it an extremely relevant part of any description of Hawking radiation that takes this form. If you're claiming that Hawking radiation shouldn't be an example because it hasn't been observed, that's one thing, but claiming that pair production isn't a significant part of a description of Hawking radiation if it _does_ exist is quite another. Which argument are you using for the removal? --Christopher Thomas 21:46, 12 June 2006 (UTC)

Both. If Hawking radiation exists (which has not been shown) and if microscopic black holes exist (which observational evidence is against), then antimatter makes up less than half the resulting radiation. Given the number of caveats necessary to link this to antimatter, I just don't see how it's relevant enough to include when so many other real-life antimatter sources are being left out. -- Xerxes 03:12, 13 June 2006 (UTC)

[edit] Comment mistakenly added to article

I also read something alluding to the fact that is very very hard to countain a large quantity of antimatter due to the repulsion between antiparticles (if someone could expend on this). In other words antimatter fuel belongs to science fiction. —The preceding unsigned comment was added by 70.81.162.66 (talk • contribs) .

Antiprotons repel each other, just like protons, but neutral atoms of antimatter attract each other, just like atoms of matter. —Keenan Pepper 21:41, 2 August 2006 (UTC)

[edit] Nonsense

I removed this comment from the medical uses section: "Also, cultured hamster tissues have been tested with antimatter to determine whether or not antimatter is effective at killing sausage." Some people have a weird sense of humour... --Cfslattery1 23:35 (GMT), 22 August, 2006

Yeah, that's not even WP:BJAODN-worthy. —Keenan Pepper 01:42, 23 August 2006 (UTC)

That was the result of a botched revert. The original text read "...at killing cancer cells". I rolled back further to repair this and other damage. I can see enough arguments for using a positron or antiproton source for radiation treatment to believe someone's tried it, though a citation would be nice. --Christopher Thomas 03:15, 23 August 2006 (UTC)

Oh. That makes much more sense. =P —Keenan Pepper 03:26, 23 August 2006 (UTC)

[edit] Question!

Ok, the "antimatter universe" section answered one question, but created a couple more. My original question was going to be "can antiparticles join together as sub units to create antiatoms and then to molecules." Well, obviously, if there were enough, then yes, due to the theory of antigalaxies and such. However, what about the little known dark matter. I'm not entirely sure what it is but seeing as how is seems to be classified as matter, and seems to be causing the universe to accelerate(or at least that is one theory as to why we are not deccelerating) that it must be numerous. Well, first question that comes to mind: "Is there anti-dark matter?" second question: "what if the normal dark matter comes into contact with what would have to be the anti-dark matter around an "anti-matter galaxy?" I know, this is all extraneous speculation, but, if you have an answer(or even, any idea) then please respond. —The preceding unsigned comment was added by Ahnung (talk • contribs) .

Dark energy makes the universe expand, not dark matter. Dark matter has normal gravity, so it tends to pull things together. Dark energy has some weird negative gravity that pushes things apart. Also, there's no reason to assume dark matter even has antiparticles, and even if it does, there's no reason they would interact with matter any differently. So basically, no one knows. —Keenan Pepper 14:09, 11 September 2006 (UTC)

[edit] Antimatter Black Holes?

Forgive me if I'm unable to articulate this adequately but I was wondering... If matter in the Universe obtains sufficient mass you can get a black hole (I know that's rather a simplistic explanation) but what about Antimatter? Does the same apply or would different rules produce an altogether different effect? RawPhoenix 00:01, 23 September 2006 (UTC)

You can't tell the difference between a black hole made of matter, a black hole made of antimatter, and a black hole made of pure energy. The no hair theorem says black holes only have three properties: mass, angular momentum, and electric charge. Baryon number isn't one of those. —Keenan Pepper 00:45, 23 September 2006 (UTC)

[edit] Black holes, White holes and outer-universe

What is the affect of matter and antimatter on the above headline?? Should either, all or just one be made of or start from antimatter?? I have no history in there areas but do have some extensive self knolage of this. Please excuss the typing. If you have any input on this i would be very interested. Thank you, and keep it simple thank you. Pastry 11.11.06

A black hole made of antimatter would act exactly the same as a black hole made of normal matter. The no hair theorem says only mass, angular momentum, and electric charge make a difference. Baryon number is not one of those, so black holes with positive baryon number (normal matter), negative baryon number (antimatter), and zero baryon number (pure energy) would act exactly the same. White holes probably don't exist, but if they did, the situtation would probably be the same as for black holes. —Keenan Pepper 21:11, 11 November 2006 (UTC)

Thank you Keenan! Pastry 17.11.06

As the universe that we live in is made of matter, could the outer of our universe be antimatter?? or is it that the centre of our universe be made of antimatter and the matter that is attracted causes the expantion of ours to what it is now?? Pastry 17.11.06

[edit] Production

A couple of production statistics for Fermilab, if someone wants to work them into the article. [1] gives a total storage record of 246 x 10^10 antiprotons, and a current production rate of 20x10^10 per hour. (The total energy the storage record represents, incidentally, appears to be "enough energy to boil a cold Batavia raindrop". [2]) Shimgray | talk | 23:38, 10 December 2006 (UTC)