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Particle creation

  1. Mar 12, 2009 #1
    I understand that it is said that the universe is expanding and all that but where did all the matter come from that exists, did it all come from a single point particle or is there another theory for this. It seems like one of those questions that it is still under investigation heavily by cosmologists.
     
  2. jcsd
  3. Mar 12, 2009 #2
    BB theory does not address where it came from, only the results since that initial expansion. the matter was generated from the extremely high energy content of the photons released during that expansion. any photon of sufficient energy will spontaneously generate a matter particle and corresponding anti-matter particle. perhaps a more compelling question is where did all the antimatter go, and why is there an inherent (apparent) imbalance of matter and antimatter in the universe we observe today.
     
  4. Mar 12, 2009 #3
    yeah, what are the mainstream theories for the massive inbalance of matter and antimatter.
     
  5. Mar 12, 2009 #4
    How much imbalance between matter ans anti is assumed ?
     
  6. Mar 13, 2009 #5

    Chalnoth

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    Well, basically all of the particles in the visible universe came from the end of inflation. During inflation, the universe was dominated by a form of matter that acted rather like a cosmological constant due to its properties. Everything that we see in our current universe started from a patch of this inflating stuff that was much, much smaller than the nucleus of an atom.

    Now, because this inflating stuff acts rather like a cosmological constant with a large energy density, it caused the universe to expand at an accelerated rate, going from smaller than the radius of an atom to many light years across in the blink of an eye (side note: we don't know how big the universe as a whole is, here I'm just talking about the portion of it that led to what we can directly see).

    This inflating stuff also wasn't exactly like a cosmological constant (if it were, it would never have stopped). The energy density was slowly diluting with the expansion, and when there was no kinetic energy left in the field, it started to decay. Now this massive energy density that was driving an extraordinarily rapid accelerated expansion was dumped into the normal matter fields that we know and love. This is where all of the particles in our universe came from, and it's an event known as reheating.

    Now, we are still investigating the specific properties of inflation, and perhaps once we learn about what inflation was, we will be able to say something definitive about how it started. But until then inflation offers a very nice explanation for how all the matter around us came to be.

    Granted, this ignores other issues like baryogenesis, nucleosynthesis, and the like. The universe is quite complex, after all. But if you're asking why there's stuff instead of no stuff, this is why. It's all down to inflation.
     
  7. Mar 13, 2009 #6
    so basically extremely high energy photons will turn into fundamental particles?
     
  8. Mar 13, 2009 #7

    Chalnoth

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    Well, right. When you smack two photons together that have a center-of-momentum energy greater than twice the mass of the electron, they'll annihilate with one another to produce an electron-positron pair. If they have still more energy, they can produce heavier particle/anti-particle pairs.
     
  9. Mar 13, 2009 #8
    How can we smack photons ? photon accelerator ? And could they be gamma rays ?
     
  10. Mar 13, 2009 #9
    technically you can't accelerate a photon since its speed is constant.
     
  11. Mar 14, 2009 #10

    Chalnoth

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    Well, you certainly can't accelerate a photon in the same way you can accelerate charged particles. But you can add energy to an electromagnetic field, so much so that, on occasion, you get pair production. This will happen, for instance, if you charge up a capacitor to extreme levels so that the electric field between the plates is so large that some of the photons occasionally have energies high enough to produce electron/positron pairs.
     
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