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What happens when a particle and an anti particle collide

  1. Jun 8, 2012 #1
    This is from Lisa Randall's Knocking on Heaven's Door:

    So when particles and antiparticles collide they get converted into pure energy. I've always thought of energy as what causes particles to move, for example, a billiard ball with X joules can transfer that kinetic energy to another billiard ball on collision causing it to move. Correct me if I'm wrong. What happens then to the surrounding area when particles and antiparticles collide and annihilate? Does it cause the particles around them to move?
     
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  3. Jun 8, 2012 #2

    Simon Bridge

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    Everything is energy - including matter.
    Randall means that the particle and anti-particle's mass gets converted into a photon.
    That entire passage seems quite confused. eg. particles and antiparticles don't have to be opposite charges - they don't even need to be different particles.
    E=mc² means that energy and matter are just different ways of describing the same thing.
     
  4. Jun 8, 2012 #3

    Bill_K

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    Robert, You're right, there's no such thing as "pure energy", energy must be carried by one or more particles. The point is that after the collision there is plenty of energy available, and what happens is the next step:
    The energy is distributed to the new particles that have been created.
     
  5. Jun 8, 2012 #4
    Good, that clears up a misunderstanding on my part.
     
  6. Jun 15, 2012 #5
    Correct. For that reason, particles other than photons can be formed when a particle and antiparticle collide.

    Particles other than photons can form in a particle-antiparticle annihilation.At high energies, all sorts of particles form in any particle-antiparticle collision.
    Low energy collisions between positrons and electrons form photons only. This is because electrons interact only through their electromagnetic field. Therefore, neutrinos are unlikely even though they require low energy. Nucleons are something else.
    A nucleon and and antinucleon can form almost any type of particle even at low energies when they annihilate. This is because nucleons interact via several types of field. They interact by the electromagnetic field (photons), the strong field (gluons) and the weak field (W-particles). Hence when two nucleons interact, they can form photons, mesons and paired baryon-antibaryon pairs.
    At high kinetic energies, almost any particle can form in particle-antiparticle annihilation.
    Here are some links to nucleon-antinucleon reaction.

    http://iopscience.iop.org/1402-4896/5/3/003
    A Comment on Nucleon-Antinucleon Annihilation and the Possibility to Determine the Spin for Resonances in the Direct Channel of This Process
    by Lars Brink, Physica Scripta Number 1, July 2012 (015001-015801)
    Abstract
    “The process of nucleon-antinucleon annihilation into pions is considered from the point of duality. The possibility of measuring the spin of an intermediate resonance is discussed.”

    http://prola.aps.org/abstract/PR/v119/i4/p1390_1
    “Pion Multiplicity in Nucleon-Antinucleon Annihilation
    Bipin R. Desai
    Phys. Rev. 119, 1390–1394 (1960)
    Abstract
    In the annihilation problem we have considered the influence of the Ball-Chew model, according to which, at low energies, only a few of the eigenstates of the nucleon-antinucleon system need be considered. The effect of the selection rules that forbid certain pion multiplicities is thereby examined. The energies considered are 50 Mev, 140 Mev, and 0 Mev in the case of protonium—the bound system of a proton and an antiproton.”

    http://prola.aps.org/abstract/PR/v135/i5B/pB1186_1
    SU3 Invariance in Nucleon-Antinucleon Annihilation
    by Tanaka, Phys. Rev. 135, B1186–B1190 (1964)
    Abstract
    “The relations among the amplitudes for nucleon-antinucleon annihilation into two mesons, and also those for annihilation into a baryon-antibaryon pair and a decuplet-antidecuplet pair, are obtained on the basis of SU3 invariance.”

    In principle, a positron-electron annihilation may form neutrinos. However, electrons do not interact very strongly via the weak force. They interact through their electromagnetic force. So the formation of neutrinos is predicted to be very rare at low energies. At high energies, mesons form. However, I don't know if you want to call this particle-antiparticle annihilation.

    http://en.wikipedia.org/wiki/Electron–positron_annihilation
    Electron–positron annihilation
    “Since neutrinos also have a smaller mass than electrons, it is also possible—but exceedingly unlikely—for the annihilation to produce one or more neutrino–antineutrino pairs. The same would be true for any other particles, which are as light, as long as they share at least one fundamental interaction with electrons and no conservation laws forbid it.
    f either the electron or positron, or both, have appreciable kinetic energies, other heavier particles can also be produced (such as D mesons), since there is enough kinetic energy in the relative velocities to provide the rest energies of those particles. It is still possible to produce photons and other light particles, but they will emerge with higher energies.”
     
  7. Jun 15, 2012 #6
    Yes this is what e=mc2 is , the matter that is equivalent to energy can be turned into energy only if it's collided with an anti-particle.
    However, if the mass of the matter is huge, it can give out lots of energy!!
     
  8. Jun 15, 2012 #7
    Does that energy warp spacetime to the same extent that the former mass once did?
     
  9. Jun 16, 2012 #8
    A boom.
     
  10. Jun 16, 2012 #9

    Simon Bridge

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    Not just for annihilation:
    http://en.wikipedia.org/wiki/Binding_energy#Mass-energy_relation
    ... it shows up all the time.
    Considering the scale factor is of order 1017 this "huge" amount of matter need not be all that huge.
    Releasing the energy of one gram of matter is equivalent to about 22 tons of TNT.
    Consequences of an open-air blast of 1kg of TNT.
    Depends - if all the energy is still in the same space then of course it does: this situation is what mass is. If the energy is more diffuse then it has less effect - just like if you have a more diffuse distribution of matter.
    But what you are trying to ask is answered in this Q&A:
    ... a box of photons will indeed cause as much gravity as a box of coal with the same total energy.
     
    Last edited: Jun 16, 2012
  11. Jun 16, 2012 #10
    Yes Simon , you are right , however considering that it's kinda of hard to get 1 gram of anti-matter, 1 gram can be considered huge by that logic...
     
  12. Jun 16, 2012 #11

    Simon Bridge

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    :) I didn't say anything about antimatter - that's one gram of any matter.
    But you did say "with an antiparticle" so I'll give you that one.

    (That 1g lump annihilated with antimatter would come out as 44T of TNT btw)
     
  13. Jun 16, 2012 #12
    Oh ok :)
    Is it possible for labs to make 1 kg of anti-matter to collide with 1 kg of matter?
     
  14. Jun 16, 2012 #13

    Simon Bridge

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    I think it's possible in principle - just very very difficult.
    I understand that antihydrogen has been made and the difficulty now it to slow it down enough for study.

    Large quantities of antimatter do exist in nature though.
     
  15. Jun 16, 2012 #14
    I know what i am going to say now is irrelevant but my quote button is blocked and i can't quote anybody , how can i use it ...
     
  16. Jun 16, 2012 #15

    Simon Bridge

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    You can quote by cutting and pasting - and just writing in the quote tags.
    You should be able to quote people - if this keeps up, flag a admin.

    (but if you mean the radio-button, in "options", below the quick-reply box, that don't work for me neither.)
     
  17. Jun 16, 2012 #16
  18. Jun 16, 2012 #17
    "I think it's possible in principle - just very very difficult."
    You make perfect sense, thanks ...
     
  19. Jun 17, 2012 #18

    L-x

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    "I think it's possible in principle - just very very difficult."

    very very difficult is an absurd underestimate. Producing and containing 1kg of antimatter is "possible in principle" in the same way that counting every particle in the observable universe is "possible in principle".
     
  20. Jun 17, 2012 #19
    "Producing and containing 1kg of antimatter is "possible in principle" in the same way that counting every particle in the observable universe is "possible in principle""

    Scientists have found ways to calculate the number of atoms in the universe. I am guessing you can do so by finding the average volume of the atom and the volume of all matter in the observable universe(planets, stars....) and then you can divide the volume of that matter by the average volume of the atom to find the number.
    I might be wrong and you must consider a lot of other things.
     
  21. Jun 18, 2012 #20

    L-x

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    Scientists have indeed, and you're thinking along nearly the right lines: cosmological observations allow scientists to make a reasonable estimate of the energy density of matter in the universe, and calculating the volume of the observable universe is straightforward (though interestingly, due to the expansion of the universe, that volume isn't just 4/3 pi (age of universe times c)^3). In fact it's calculations like this which have lead to conclusions that the universe is full of mysterious "dark matter", because when cosmologists predict how much "stuff" we should be able to see, they get an answer that's about 5 times bigger than what we can actually observe through telescopes.

    I didn't say calculate though. I said "count", as in getting the exact number. All I meant (in a slightly silly way, admittedly) is that someone obtaining that much antimatter is not going to happen in the remotely foreseeable future.
     
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