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How is it that Neutrinos are able to Pass through the Earth?

  1. Jun 27, 2006 #1
    Is there that much space in between all the electrons, protons, and neutron that this is likely? The only explanation that I can think of is that the neutrinos are in a different region of n-dimensional space-time and the fact that they pass through the earth is merely a geometric illusion.


    I should have tried wikipedia

    Last edited: Jun 27, 2006
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  3. Jun 27, 2006 #2


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    Your first description (atoms are mostly empty space) is the right explanation.
  4. Jun 27, 2006 #3
    An interesting aside from http://www.discover.com/issues/aug-01/cover/ [Broken]

    Once you create a neutrino, a tiny subatomic particle, it moves at nearly the speed of light, and it doesn't stop. It keeps going in a straight line to the edge of the universe. Straight through any stars, planets, or mountains; straight through any atoms, nuclei, or other particles that happen to lie in its path. Straight through any people too: At this moment— let's say you're reading this at night, somewhere in the United States, relaxed in your living room— every second, 40 billion neutrinos from the sun are rocketing up your left nostril and through your brain's frontal lobe, on their way through the roof of your house and then clear out of the Milky Way galaxy, having already passed through China, Earth's rocky mantle, the seat of your recliner, and your left thigh. Even huger numbers of neutrinos pierce you from above; they come from stars in the night sky, from cosmic rays, and above all from the Big Bang— 15 billion years old, those neutrinos are, and still traveling.
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  5. Jun 27, 2006 #4
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  6. Jun 27, 2006 #5


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    Someone posted one that appeared today:


    Caveat: I have no idea of "valid" this is. So take this with a grain of salt and wait for it to appear in a peer-review journal.

  7. Jun 27, 2006 #6


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    I understood that neutrinos couldn't be dark matter because they are "hot", i.e. fast moving, and various observational constraints seemed to have ruled out hot dark matter.
  8. Jun 27, 2006 #7


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    Doesn't this negate the thrust of your post? They come at us from every direction, and there is really no material difference if they come at us from above or from the other side of the earth, since they so rarely interact with matter, and pretty much all the neutrinos that come at us from the side of the universe under our feet just zip through the Earth and through us too.
  9. Jun 27, 2006 #8
  10. Jun 27, 2006 #9
    Not sure... it wasn't my writing. I think, however, that it was meant as a elementary conceptual(and obviously playful) distinction with regards to neutrinos emitted from our sun versus the totality from the universe in all directions.
    Thus the intro is a "gentle-primer"; not meant for actual scientists which may demand a rigorous intro treatment, rather an intro which may entice the inquisitive "layman" reader to delve further into the article and subject matter. All is good.
  11. Jun 27, 2006 #10
    That's a whole lot of empty space. Does this not happen with electrons because their electrical charge changes the direction of their path?
  12. Jun 28, 2006 #11


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    It's funny, but physics has a whole lot of ways of answering this question that are valid. The reason is that there are many different ways of making the calculation and many different ways of interpreting it.

    One way of describing it is that electric charge is carried by a particle, the photon, that is massless. Since it is massless, it obeys an inverse square law.

    Neutrinos have no electric charge, they can only interact weakly. Now electrons interact weakly too, but it is very weak compared to their electric charge interactions.

    When I say that the interactions are "weak" I really don't mean that, technically, their coupling constants are all that different. Instead, the weak force is weak only because the carrier for it, the W and Z particles are not massless, and in fact have pretty high masses.

    Because they have masses, the weak force is unlikely to travel very far. The reason for it being "unlikely" is because the energy to create such a massive particle has to be borrowed and under the Heisenberg uncertainty principle, a high amount of energy is likely to be be borrowed for only a very short amount of time, and therefore is unlikely to travel very far.

    Now that all said, if it were the case that a neutrino was very energetic, then it would be a lot easier to borrow the energy for that W or Z particle, and then the neutrino would be a lot more likely to interact. Because of this, the neutrino "cross section", or apparent size, increases as the energy of the neutrino increases.

    In fact, with some of the very high energy particle accelerators that are planned, there is a possibility that the neutrinos themselves could cause enough radiation that this radiation would be dangerous to human life. Part of the reason for the high radiation levels is because the higher energy neutrinos are more likely to collide, and part of the reason is because when they do collide, being high energy, they cause a bigger particle shower.

    For this reason, the designers of these bigger particle accelerators are taking this into account in designing these machines:

    The above article also talks about how neutrino cross sections increase with energy.

    Last edited: Jun 28, 2006
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