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Thread: Matter-antimatter

  1. #1 Matter-antimatter 
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    They say that at the beginning of the universe there were nearly equal parts of matter and antimatter but they annihilated and because there was just a bit more matter the matter survived and became our universe. If this is so where did all the energy go?


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  3. #2 Re: Matter-antimatter 
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    Quote Originally Posted by Wildstar
    They say that at the beginning of the universe there were nearly equal parts of matter and antimatter but they annihilated and because there was just a bit more matter the matter survived and became our universe. If this is so where did all the energy go?
    It is all around you, in mass, in the CMBR, in the energy that somes from the sun and the stars, etc.


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  4. #3  
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    okay. it's just that i thought that when antimatter and matter combined they released gamma rays. So i didn't know if you could see them or not. But I can see if the energy was converted to particles
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  5. #4  
    Forum Radioactive Isotope MagiMaster's Avatar
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    It may have been gamma rays when the annihilation took place, but it's been shifted down to microwaves now.
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  6. #5  
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    I see. Okay Thanks
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  7. #6  
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    Quote Originally Posted by MagiMaster
    It may have been gamma rays when the annihilation took place, but it's been shifted down to microwaves now.
    No, the immediate result - the gamma rays - again underwent pair production as a part of a cascade of annihilation and matter production down to least massive particles, where the resulting energy of annihilation was small. Remember that during pair production, not all photon energy necessarily is spent on producing mass. Some of it can be transformed into kinetic energy of the resulting particles.

    The cosmic microwave background is something entirely different and does not relate to this process. The annihilation-production cycle had already ended a while ago. It dates back to a time, where the universe was a few thousand degrees hot and after expansion and cooling became suddenly transparent. The so called plasma consisted of ionised matter and photons. Photons were travelling around. Their mean free path was very small - similar to stars nowadays - leading to the ionisation of an atom. The free electrons also interacted with the photons leading to scattering effects. Some ions were able to re-capture an electron to become a neutral atom again. This produces a dynamical equilibrium that depends on the temperature and/or density of the matter. After expansion and cooling, temperature was too low to sustain efficient ionisation and the mean free path of photons increased so that the universe became transparent.

    What we see now as the cosmic microwave background is the Black Body radiation of that opaque gas plasma just before it became transparent.
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  8. #7  
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    Quote Originally Posted by Dishmaster
    Quote Originally Posted by MagiMaster
    It may have been gamma rays when the annihilation took place, but it's been shifted down to microwaves now.
    No, the immediate result - the gamma rays - again underwent pair production as a part of a cascade of annihilation and matter production down to least massive particles, where the resulting energy of annihilation was small. Remember that during pair production, not all photon energy necessarily is spent on producing mass. Some of it can be transformed into kinetic energy of the resulting particles.

    The cosmic microwave background is something entirely different and does not relate to this process. The annihilation-production cycle had already ended a while ago. It dates back to a time, where the universe was a few thousand degrees hot and after expansion and cooling became suddenly transparent. The so called plasma consisted of ionised matter and photons. Photons were travelling around. Their mean free path was very small - similar to stars nowadays - leading to the ionisation of an atom. The free electrons also interacted with the photons leading to scattering effects. Some ions were able to re-capture an electron to become a neutral atom again. This produces a dynamical equilibrium that depends on the temperature and/or density of the matter. After expansion and cooling, temperature was too low to sustain efficient ionisation and the mean free path of photons increased so that the universe became transparent.

    What we see now as the cosmic microwave background is the Black Body radiation of that opaque gas plasma just before it became transparent.
    Right.

    For more detail at an accessible level see The First Three Minutes by Steven Weinberg. (Note: This book was written prior to the experimental evidence for the accelerating expansion of the universe, so some statements need to be understood in that light.)
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  9. #8  
    Forum Radioactive Isotope MagiMaster's Avatar
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    @Wildstar, go with what they said then.
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