Talk:Antimatter

    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?

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

Contents

1 Annihilation burst 2 Backwards in time? 3 Antimatter as fuel 4 The Article is right about the fuel energy (i think) 5 Gravitational Repulsion of Antimatter? 6 Quantities needed? 7 odd wording

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

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 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)

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)

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)

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

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)