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The nature of particles in the Standard Model vs String Theory

  1. Nov 16, 2008 #1
    Neutrinos are elementary particles that have the ability to pass through any matter. Billions of them pass through our bodies every second. Billions of them pass through the Earth and exit on the other side unaffected. They can pass through stars and travel to the other side of the universe. This is so mostly because they don't have an electrical charge and because atoms are 99.9999% empty space. Neutrinos have even the ability to pass through the nucleus of the atom or that 0.0001% that most physicists consider as the physical matter constituent of the atom, where more than 99% of atom's mass is concentrated. So, the ability of neutrinos to pass through 1 light year of lead belt is possible because the Standard model says the atom is not composed of particles with physical dimensions(quarks and electrons), but of zero-dimensional particles held together by subatomic nuclear forces - the strong force and electromagnetism, mediated by gluons and photons.

    On the other hand, String theory assumes that the zero-dimensional particles of the Standard model are not zero-dimensional entities but have a distinct size, although it's the smallest size that has any meaning - the Planck length - 1.6*10^-33cm.

    So my question is this - if String Theory were correct and strings had this almost physical size, how would at least some of the neutrinos passing through the Earth NOT collide at some point during their journey with the strings that compose matter(electrons, quarks, etc.)? If strings are energy/charge that allows neutrinos to pass through them, how can energy/charge have a physical size? Isn't that the reason why the Standard model "fell apart" at certain questions and couldn't give meaningful explanations?
  2. jcsd
  3. Nov 16, 2008 #2


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    Er.. I think you missed a very important point. Neutrinos interact with matter via the weak interactions and, to some extent, via gravitational interactions. But because such interactions are VERY weak (an electron neutrino barely has any mass, and therefore this interactions is, for all practical purposes, non-existent for neutrinos), this is why neutrinos do not interact with matter most of the time.

    It has nothing to with with matter being mostly empty spaces. If that is true, then there would have been NO interaction of ANY kind, since everything is "empty spaces". What is more important is the nature of interactions that an elementary particle can have with other elementary particles.

  4. Nov 16, 2008 #3


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    you also have a classical picture of how particles interact, they don't interact as two tiny balls colliding (such as a micrscopic game of pool), the they interact over certain distances aswell (just as celestial bodies interact over distance).

    So before even thinking about comparing the standard model and string theory, you should get what elementary particle physics is and how particles and interactions are described in quantum physics.
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