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Antiparticles crash course

  1. Aug 24, 2004 #1
    I've been reading a lot lately, stephen hawkings mostly, a few others as well, but its difficult. The more things i read on the same subjects the better i understand the fundemental ideas, but its still difficult. One thing i have trouble grasping is anti particles. I've never been introduced to them really except in passing when my physics teacher's rambling a little, so i really don't know much of what to think of them. Could anyone just give a basic introduction to what they are, how we know they exist, or anything that helps to understand them or their role in our universe? that be great!

    ~abigale~
     
  2. jcsd
  3. Aug 24, 2004 #2

    chroot

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    Antimatter particles are just like normal particles in most ways. The most marked difference is that they have opposite electrical charge. They have the same masses, however, and generally behave the same way the normal particle behaves -- they undergo the same sorts of decay mechanisms, for example.

    They also annihilate normal matter particles. When an electron and an anti-electron (a positron) collide, they both disappear in a flash of gamma rays. Their entire rest-masses are converted directly into high-energy radiation.

    Antimatter occurs all over. When cosmic rays hit the atmosphere, they can stimulate the production of pairs of particles, one of which is antimatter. Antimatter particles occur all the time in particle accelerators. We know antimatter exists because we can see it with the detectors in particle physics experiments.

    The early universe was full of both matter and antimatter particles in nearly equal amounts. There happened to be about a billion and one matter particles for every billion antimatter particles, so the universe wound up a slight excess of matter that has since turned into galaxies and people.

    - Warren
     
  4. Aug 24, 2004 #3
    can we see antimatter? like, suppose enough particles came together to form a big thing the size of a basketball, would we be able to see that? is it possible for that even to happen? and are there any common effects witnessed in normal life caused by them?
     
  5. Aug 24, 2004 #4

    chroot

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    It's possible, in principle, to have a big hunk of antimatter the size of a baseball. It'd be very difficult to work with though, because it would annihilate anything it touched. You'd have to keep it safely inside an evacuated magnetic confinement chamber. It is beyond our current technology to either create or control such a hunk of antimatter, but it is possible, in principle.

    You can "see" antimatter quite easily by using a photographic plate and a magnet, preferably up in a balloon in the upper atmosphere. Cosmic rays zip across the photographic plate; some are electrons, for example, and others are anti-electrons. The magnet makes the electrons bend one way, and the anti-electrons the other. You can measure the radius of curvature to determine the energies of the particles, and, with a little deductive reasoning, the masses.

    - Warren
     
  6. Aug 27, 2004 #5
    Yes, antimatter would look just like ordinary matter.
     
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