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Layman's question on Cosmic Microwave Background

  1. Jan 19, 2012 #1
    Hi everyone, I'm a lowly computer programmer who has been interested in the CMB lately and recently became curious about one thing...

    As I understand it, the CMB is the left-over radiation from the Big Bang spread uniformly throughout the universe.

    Does this mean that this radiation is also touching my body and everything I see right now?
    Does the Earth's atmosphere somehow prevent it from reaching the surface?

    If it is touching me, then does that also mean that the CMB is also occupying the empty space in my atoms?
    Or does my body keep it out?

    Thanks to anyone who sacrifices their time!
  2. jcsd
  3. Jan 19, 2012 #2


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    Dearly Missed

    Yes it surrounds your body and must go a little ways in. But it's harmless

    The peak wavelength is 1.1 millimeter

    Out of curiosity I looked at http://en.wikipedia.org/wiki/Microwave_oven and learned that CMB is 100 times higher frequency than microwave oven radiation. The shorter wavelength probably means it is less penetrating so I would imagine that most common liquid or solid material would block it. Your skin probably stops all but a tiny fraction of it.

    But atmosphere is not a good shield. The CMB was originally detected by an antenna on the ground.
    Last edited: Jan 19, 2012
  4. Jan 20, 2012 #3


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    Just to reiterate Marcus' point, the temperature of the CMB is just 2.7K, or 2.7C above above absolute zero. So it basically would have no impact on your body. Also, the vast majority of it is blocked by our atmosphere anyway (this is why we have satellites to observe the CMB).
  5. Jan 20, 2012 #4
    I believe I've seen a figure of 400 million photons of the CBMR per cubic meter.

    So at a guess, you've got about that many in you at any moment.
  6. Jan 20, 2012 #5
    How does this compare to the number of photons of sunlight per cubic meter?
  7. Jan 20, 2012 #6


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    Not quite, because as I mentioned above, most of those are blocked by the atmosphere!

    But yes, in the older-style analog TV sets, some fraction of the static in the TV is due to CMB.
  8. Jan 20, 2012 #7


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    About 1% of RF static can be attributed to the CMB. It is stll pretty pathetic. To put this into perspective, a 100 watt light light source emits about 2.5E+20 photons per second - which is a lot more than 400 million [4E+08] photons.
  9. Jan 20, 2012 #8


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    Although to be fair to the CMB, it contains something like 98% of all the light ever emitted in the history of the universe. It's just that the universe is quite big now and that light is spread over the vast emptiness of space.
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