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Antimatter questions

  1. Apr 10, 2004 #1
    I just hava a few questions about antimatter.
    Does it have gravity?
    Can you compress it into a singularity?, and if so what would happen if you were pulled towards it?
    Does it have entropy?
    Could you use it to destroy black holes?
    An isotope of carbon(C-22?) decays and produces antimatter, how does it do that? :confused:

    I've just been wondering about these things... :confused:

    De nice coder
     
  2. jcsd
  3. Apr 10, 2004 #2
    Antimatter has many of the same properties as matter, according to theory. It's a little tough to test, because it's difficult to make macroscopic amounts of it. Some antihydrogen has been made at CERN.

    Lots of elements make positrons when they decay. They have too many protons to be stable, so a proton converts into a neutron, a positron, and a neutrino. The neutrino is a particle, so in a sense it "balances" having produced an antiparticle, and its presence means a lot of conservation laws are not violated (which is how neutrinos were predicted in the first place)

    Also, a photon of sufficient energy can split into an electron-positron pair. (or any other particle-antiparticle pair; "sufficient energy" is the rest mass energy of the particles in question)
     
  4. Apr 13, 2004 #3

    Nereid

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    Does it [anti-matter] have gravity?
    Yes.

    Can you compress it into a singularity?
    To the extent that matter can be "compressed into a singularity", yes.

    [...] what would happen if you were pulled towards it?
    The same as what would happen if you were pulled towards an equal mass of ordinary matter (until you came in contact with it, at which point there would be a huge explosion of gammas, and (most of) you or the antimatter would be gone)


    Could you use it to destroy black holes?
    No.
     
  5. Apr 13, 2004 #4
    These two answers seem to be contradictory. Could you/someone please explain in further detail why it can't be used to destroy black holes?
     
  6. Apr 13, 2004 #5

    Nereid

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    I'll take the 'easy' case - an anti-matter black hole with a mass ~>the Sun. As Pergatory passed the event horizon (and was ripped to atoms by the tidal forces), (s)he fell onto the antimatter BH. The atoms which formerly comprised his body annihilated with anti-atoms, emitting lots of hard gammas. However, the gravitational pull of the remaining mass in the BH is (was?) still ~1 sol (etc) and so the gammas couldn't escape (remember, not even light can escape a BH).

    Of course, we can never know what happened to Pergatory; once passed the event horizon, no communication of any kind is possible.

    The sequence of destruction would be different for a BH of mass ~100kg (not to mention that the 'pulling towards' would be very feeble indeed), but the principle is the same.

    I don't know what would happen if the BH had a mass approx the same as that of a positron.
     
    Last edited: Apr 13, 2004
  7. Apr 13, 2004 #6

    Njorl

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    I would think that there would be a minimum size for a black hole. The rest mass is equivalent to some energy. A gamma ray with that energy must have a wavelength entirely contained within the black hole's event horizon. As the mass decreases, the event horizon shrinks, and the wavelength grows. At some point, the energy can not be contained.

    Njorl
     
  8. Apr 13, 2004 #7
    Even so, isn't gravity a function of rest mass? While the gamma rays are prevented from escaping (unless we've succeeded in destroying the BH), and the BH retains all its original energy plus that of the added (anti-)matter, the overall rest mass still decreases?

    So if we can decrease the rest mass of a black hole, we essentially have a method by which to destroy it. Of course, then we have the problem of such a huge amount of energy (far more than the original BH) being unleashed all at once when the event horizon collapses... but that's another story. :wink:
     
  9. Apr 13, 2004 #8

    Nereid

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    Ah where's that sticky on (rest) mass when you need it!

    Anti-matter isn't 'anti-mass', or 'negative mass', so far as the Newtonian or GR equations are concerned, it's just as much 'm' as your local friendly proton, Fe atom, paramecium, basketball, canus domesticus, Toyota SUV, HMS Ark Royal, Phobos, Sedna, Neptune, Sirius A, Sirius B, ...

    Pergatory, Nereid, an Fe atom, ... whatever falling into the BH merely adds more 'm' to it, no matter ( :frown: ) what's 'there' already ...
     
  10. Apr 13, 2004 #9
    What I'm saying is that upon the mutual annihilation of matter / anti-matter, only gamma rays are emitted correct? Gamma rays have no rest mass, correct? Therefore, by introducing anti-matter to a matter BH (or vice-versa), can we not reduce its rest mass?
     
  11. Apr 13, 2004 #10

    JJ

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    Gammas don't have rest mass, but they do have lots of energy. Remember that E=mc^2. I'm not sure is you noticed someone mentionned electron-positron pair production; that's when a gamma ray of sufficient energy (more than double the masses of the electron and positron times c squared) splits and creates an electron and a positron. Same thing happens with matter-antimatter reactions, except in the opposite direction: all of the mass is converted into two perpendicular (if I remember right) high energy gamma rays (just high energy photons, in case you don't know). Since the gamma rays (light) can't escape the event horizon of a black hole, they fly right back in. There, you've just succeeded making the beast bigger and badder.
     
  12. Apr 14, 2004 #11
    If antimatter has gravity, then it can collapse into an anti-black hole.
    If an anti-black hole and a black hole collide (assuming equal mass), would they neutralize each other, neutralize part of their mass giving the rest of the mass enough energy to escape the gravity well, or ?

    If there was more anti-matter then matter, would the black hole still exist?
    or would you just end up with a large chunk of anti-matter?). assuming the anti-black-hole has double the mass of the black-hole then, wouldn't the energy produced, fall back into the anti-black hole (or whats left of it) and increase its mass?
     
  13. Apr 15, 2004 #12

    JJ

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    First, an anti-matter black hole would never exist in our neck of the woods, since there's a preference towards matter. All of it would have flown over to matter and innihilated itself. I'm not sure, but I also believe that there is no such thing as an anti-neutron; therefore, when the star reaches the neutron star phase, it may at most conserve a relatively moderate charge.

    But I now wonder about something, if anti-matter black holes existed: since the electro force is much stronger than the gravitational, could the matter and antimatter collide in front of the event horizon in an extreme case?
     
  14. Apr 15, 2004 #13

    Nereid

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    Anti-matter is, from the POV of gravity, just mass, so there's no difference between an 'anti-black hole' and a black hole - they're both just black holes (see my earlier post in this thread).
    Every particle has a corresponding anti-particle, at least in the Standard Model, and there are (AFAIK) no observational or experimental results inconsistent with this model.
     
  15. Apr 15, 2004 #14
    Wouldn't that only apply to fundamental particles (of which the neutron is not), or is it possible to combine the right anti-quarks into in anti-neutron?
     
  16. Apr 15, 2004 #15

    JJ

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    Matter and anti-matter collide because of usually opposite charges, right? What happens with neutrons and anti-neutrons (which I now believe in)?
     
  17. Apr 15, 2004 #16

    chroot

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    Matt,

    You can certainly make antineutrons. You can even make entire anti-atoms, and, in principle, anti-cats and anti-Toyotas out of them.

    In fact, many of the big particle accelerators use beams of counter-rotating protons and antiprotons for their collisions.

    - Warren
     
  18. Apr 15, 2004 #17

    chroot

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    JJ,

    They won't feel any coulomb attraction at a distance, but they will still feel coulomb attraction if they get too close to each other. Remember that while the neutron (and antineutron) are overall neutral particles, they are composed of internal charged quarks. If you get close enough to a neutron, you can "feel" its individual quarks inside.

    And both neutrons and antineutrons continue to feel the strong force as usual.

    - Warren
     
  19. Apr 16, 2004 #18
    Here's a question. From what I recall reading or seeing, scientists believe that generally quarks can't exist by themselves. What if you put an anti-neutron and a proton in a vacuum and collided them? In that case, you'd be hitting a uud with a udd (yeah, that should be an overline, oh well). Would the anti-quark pairs annihilate each other, leaving you with lone u and d particles?
     
  20. Apr 16, 2004 #19

    Nereid

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    Welcome to Physics Forums Matt-235.

    Exactly!

    Well, almost; the u and anti-d form ... a pi meson! (since quarks hate being alone)

    So a collision between an anti-neutron and a proton could yield some gammas (how many?) and a positive pion. The gammas would quickly 'decay' into particle-antiparticle pairs (which ones?)
     
  21. Apr 16, 2004 #20

    JJ

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    Yes, what causes a gamma to suddenly decay into a matter-antimatter pair?
     
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