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B Fastest particle

  1. Feb 6, 2017 #1
    How fast does the fastest subatomic particle travel at?
    When left at a temperature or zero degress Celsius.
  2. jcsd
  3. Feb 6, 2017 #2


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    Staff: Mentor

    Your question is not clear. Do you mean what is the fastest speed ever measured, or the fastest we have accelerated a particle?

    In nay case, I do not think that it helps to discuss it in terms of thermodynamic equilibrium, so forget about temperature for now.

    (By the way, I have changed the thread level from "A" to "B" (high school). Tell me if you would prefer an answer at the undergraduate "I" level.)
  4. Feb 6, 2017 #3


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    2017 Award

    Staff: Mentor

    In which reference frame? For every particle and for every speed below the speed of light, you can find a reference frame were it travels at this speed. With the exception of massless particles, they always travel at the speed of light.

    Relative to Earth, the fastest particles accelerated by humans were electrons in LEP at CERN, at 0.99999999999 times the speed of light (the 9s are counted). The fastest particle observed came via cosmic rays at 0.999999999999999999999995 times the speed of light.

    If you are interested in thermal motion: This is just a matter of finding the lightest particles. Hydrogen atoms at room temperature have a speed of the order of 1 kilometer per second, or 0.000003 times the speed of light. Free thermal electrons would be faster, but having them at room temperature requires very odd conditions. Free thermal neutrons would be even faster, but there is no realistic way to produce that now.
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