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What is the smallest thing discovered in our universe?

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  1. Mar 3, 2015 #1
    I heard quarks could be the smallest things of the universe. How are they measured? What units of measure are associated with quarks?
     
  2. jcsd
  3. Mar 3, 2015 #2
    And to add.

    Could there be something smaller than a quark?
    If there was a multiverse, how would scientists know?
     
  4. Mar 4, 2015 #3

    Drakkith

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    Quarks are probably the smallest objects ever discovered, but the issue of size when you get down to the quantum level becomes a little fuzzy, especially when you also have to think about gluons, photons, and other bosons. It's certainly possible that there are other particles smaller than quarks, but we haven't found any yet.

    Typically one uses electronvolts, eV, as a unit of measurement for the mass of a subatomic particle. For size they are somewhere around an attometer, or 10-18 meters, though, again, the size of subatomic particles is difficult to talk about thanks to quantum effects.

    Measuring the size is difficult as well. The best measurements come from collision events within particle colliders I believe. The entire process is very complicated.

    Unless there was some sort of observable interaction between universes, we wouldn't.
     
  5. Mar 4, 2015 #4

    phinds

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    And just to add to Drakkith's answer, there is no evidence at all that there is such a thing as a multiverse. Some serious scientists believe in the multiverse, but without evidence.
     
  6. Mar 4, 2015 #5
    Thank you so much. Your info helps a lot. (Gave you a 'like':)
     
  7. Mar 4, 2015 #6

    DrClaude

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    The electron is thought to be a point particle. Hard to get smaller than that :wink:
     
  8. Mar 4, 2015 #7
    Neutrinos would be my guess.
     
  9. Mar 4, 2015 #8

    Drakkith

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    All elementary particles are considered to be point particles. That's one reason it's so hard to talk about size when we get down to objects at the subatomic scale!
     
  10. Mar 4, 2015 #9

    mathman

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    At this level the only way to talk about size is by using mass. Electron neutrinos are the smallest.
     
  11. Mar 4, 2015 #10
    So between the electron neutrino and quark, an electron neutrino is the smallest? Why is it so difficult to measure these things? Is it because scientists don't have the tools to measure them properly or perhaps some other reason that I don't know about? Would human comprehension of the activities of the universe be an element of this complication?

    And a separate set of questions.

    Does everything in the universe absorb, reflect, and transmit light? Could the absorption, reflection and transmission be manipulated by some type of advanced technology? And is there a general term that describes the absorption, reflection, and transmission of light?
     
  12. Mar 4, 2015 #11

    Drakkith

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    A decent explanation here: http://en.wikipedia.org/wiki/Point_particle#In_quantum_mechanics

    In quantum mechanics, there is a distinction between an elementary particle (also called "point particle") and a composite particle. An elementary particle, such as an electron, quark, or photon, is a particle with no internal structure, whereas a composite particle, such as a proton or neutron, has an internal structure (see figure). However, neither elementary nor composite particles are spatially localized, because of the Heisenberg uncertainty principle. The particle wavepacket always occupies a nonzero volume. For example, see atomic orbital: The electron is an elementary particle, but its quantum states form three-dimensional patterns.

    Nevertheless, there is good reason that an elementary particle is often called a point particle. Even if an elementary particle has a delocalized wavepacket, the wavepacket is in fact a quantum superposition of quantum states wherein the particle is exactly localized. This is not true for a composite particle, which can never be represented as a superposition of exactly-localized quantum states. It is in this sense that physicists can discuss the intrinsic "size" of a particle: The size of its internal structure, not the size of its wavepacket. The "size" of an elementary particle, in this sense, is exactly zero.

    For example, for the electron, experimental evidence shows that the size of an electron is less than 10−18 m.[6] This is consistent with the expected value of exactly zero. (This should not be confused with the classical electron radius, which, despite the name, is unrelated to the actual size of an electron.)


    Please start a new thread for questions unrelated to the original topic.
     
  13. Mar 8, 2015 #12
    A serious scientist does not believe something to be true without evidence.

    The evidence goes like this...

    Hypothesis X predicts A, B, C, and a multiverse.
    A, B, and C can be experimentally verified to be true, therefore, it is reasonable to believe that the multiverse is also true.

    Note that this is circumstantial evidence, but evidence none-the-less.
     
  14. Mar 8, 2015 #13

    DrGreg

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    And what if, as well, Hypothesis Y predicts A, B, C, and no multiverse?
     
  15. Mar 8, 2015 #14
    Then work needs to be done to find some testable difference in the predictions of hypotheses X and Y.
    It is finding that difference that justifies extensive research into both multi and single universe hypotheses.
     
  16. Mar 8, 2015 #15
    ...isn't it also true electrons disappear into the 'elsewhere' region outside of the past/now/future light cones, then arbitrarily re-appear into material reality at a lower energy level/shell ... if so, doesn't this speak to the possibility of this 'elsewhere' as the progenitor 'fabric layer' of material origination?
     
  17. Mar 8, 2015 #16

    Vanadium 50

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    No.

    No.

    No.
     
  18. Mar 8, 2015 #17

    Drakkith

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    Or you apply Occam's razor and nix the theory that predicts the multiverse.
     
  19. Mar 8, 2015 #18
    The universe contains everything including multiverse. The universe has no center or edge. If you could find the smallest particle someone would later find the particles it is made of.
     
  20. Mar 8, 2015 #19

    Drakkith

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    Not true. Multiverse is the name for multiple universes. The universe currently contains everything known to exist, but it wouldn't contain a multiverse, it would be contained in a multiverse.

    Again, not necessarily true. Elementary particles have no known substructure. In other words, they are not made up of other particles as far as we can tell. (And we have very good reasons for thinking of them as elementary and not composite)
     
  21. Mar 9, 2015 #20
    Perhaps there is a name for the condition that encompasses all things then. You can coin it.

    Elementary particles - no known substructure..... currently. There was a time when the atom was unknown.
     
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