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Exactly what anti-matter is

  1. Sep 13, 2003 #1
    Before the summerholidays I asked my physics teacher what anti-matter is and like always she didn't know . So now I'm asking you guys if you know exactly what anti-matter is and how we can make it useful.

    I thank you in advance,

  2. jcsd
  3. Sep 13, 2003 #2
    The simple answer is that Anti-Matter is normal matter but with opposite charge. I.E. An anti-electron (positron) has the same mass and spin as an electron but has positive charge. An anti-proton is a proton with negative charge.

    More accurately an anti-particle is comprised of the opposite set generator. Have a read of http://particleadventure.org for more about this.

    The thing that makes anti-matter useful is that you acheive 100% efficiency when creating energy, via E=mc^2, in a matter/anti-matter collision. Nuclear explosions are only about 10% efficient at converting mass-energy.

    The problem is that it currently takes more energy to artificially create anti-matter than you get out of the reaction. We've only made a few grams, under a Kg, of artificial anti-matter to date.
  4. Sep 13, 2003 #3


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    Hello thed, I've been appreciating your clear accurate posts in other threads. Here also. Good concise helpful response etc but could you be a bit clearer as to this 10%?

    When I compare the mass of uranium to the mass of typical fission products I find that much less than 10 % of the mass has dissapeared in the rearrangement of nucleons (protons, neutrons)

    Likewise with Lithium Deuteride. Am i missing something or do you mean something else by efficiency? Could do with some more expl.
  5. Sep 13, 2003 #4


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    Re: Anti-matter

    Thed already gave a good link & description as to the properties of antimatter. I will add the analogy that is used most freauently to explain its existence.

    Similar to general relativity, in which we are asked to imagine space-time as a flat rubber sheet, this analogy requires us to think of space-time as a flat sheet of cookie dough. In order to make a cookie, one must cut out a hole in the dough. If we take the cookie to represent a particle of matter, then antimatter is the hole that is left when we cut the cookie out of the dough. Just as one cannot make a cookie without cutting a hole in the dough, one cannot make a particle without making its corresponding antiparticle.

    This fact can be somewhat troubling to particle physicists, because of what it implies about the early moments of the formation of the universe, when all existing matter first came into being. For each particle of matter that formed, an antiparticle must also have formed. By this reasoning, there should be equal amounts of matter and antimatter in the universe. So the troubling question is, "where it is all the antimatter?".

    Some models have been formulated proposing that equal amounts of matter and antimatter were created, but their unequal rates of decay resulted in the eventual disappearance of most of the antimatter. Another model implies that for some unknown reason, there was a slight inequality in the amounts right from the beginning. Some variations of this model placed the discrepancy as little as one billion and 1 particles of matter for everyone billion particles of antimatter. And the entire universe we see around us is that one-part-per-billion discrepancy.
  6. Sep 13, 2003 #5
    Thanks for the praise but wish I could enlighten you :)

    You are right, much less than ten percent of the mass converts to energy in some reactions. I done a quick shufty on the Net to find some material to back my claim and came across http://nuketesting.enviroweb.org/hew/Nwfaq/Nfaq4-1.html#Nfaq4.1.5. [Broken] Which does not back me.

    10% is a figure I've sure I've come across before but at the moment I am doubting the accuracy of it. Anyone care to add to this while I try and find more info?
    Last edited by a moderator: May 1, 2017
  7. Sep 13, 2003 #6


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    Much much less actually, something like nanograms I believe.
  8. Sep 13, 2003 #7


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    A fission reaction or(explosion) converts about 0.1% of the mass to energy.

    For fusion, it jumps to 0.375%.
    Last edited by a moderator: May 1, 2017
  9. Sep 13, 2003 #8
    Also, and I quote Richard Feynman " They (the particle and the anti) annihilate each other with a great explosion of energy being liberated, with various pi-mesons, gamma rays, and whatnot."
    Last edited: Sep 13, 2003
  10. Sep 14, 2003 #9
    Antimatter IS "useful." Ask anyone who'se had a disease diagnosed with a PET scan.
  11. Sep 14, 2003 #10


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    You're not saying that in a nuclear reaction only 10% of the mass that disappears is converted to energy, are you? That violates the first law of thermo.

    Nuclear reactions may be inefficient in that they only convert a small percentage of their matter to energy (leaving the rest as matter), but the actual matter to energy conversion is always 100% efficient - all matter that disappears becomes energy.
  12. Sep 15, 2003 #11
    what about anti-spin?

    Hi thed,
    Isn't the anti-neutrino different than the neutrino; ie, is the positron spin not -1/2? Classically speaking, the "left hand rule" rules the electromagnetic anti-world. Cheers, jim
  13. Sep 15, 2003 #12
    Another thing that Feynmann came up with, actually he stole it from Wheeler, was that while a normal particle travels forward in time an anti-particle travels backward in time. This is what accounts for the opposite charge. Feynmann used this idea in quantum electrodynamics and it is evident in Feynmann diagrams where you draw electrons with arrows going forward in time and positrons with arrows going backward in time.
    Last edited by a moderator: Sep 15, 2003
  14. Sep 15, 2003 #13


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    there is a slight semantic hazard to watch out for (what you say is right, I am just pointing out a semantic thing)

    an anti-particle proceding forwards in time (just going along like everybody else from day to day :smile: )
    can be described as an ordinary particle but time-reversed
    and in a Feynmann diagram you can show a positron using
    an electron-line with the arrow backwards and it works out

    but this doesnt seem quite the same thing as saying that
    the positron is going backwards in time
    If you talk about him as a positron then he's going forwards and
    it is only if you want to talk about him as an electron that
    he is going backwards

    is this distinction worth making, or is it a case of being overly careful?
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