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What is the Temperature of an atom moving at the speed of light?

  1. Jan 12, 2012 #1
    What is the Temperature of an atom moving at the speed of light?

    Since absolute zero is the lack of activity and energy and

    since no physical object can move faster than the speed of light

    What is the temperature of an atom moving at the speed of light?

    Light is either a particle or a wave or both or neither .. the temperature of light would not be the temperature of an atom moving at the speed of light.

  2. jcsd
  3. Jan 12, 2012 #2


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    Massive particles can not travel at the speed of light, so most of your question is meaningless.

    A gas of photons can have a temperature, but a single photon can not. Temperature is a property of large collections of objects and a single object can not have a temperature.
  4. Jan 12, 2012 #3
    ok so therefore there is no answer since massive particles cannot travel at the speed of light .. interesting

    which brings up the question .. why?

    ok I said one atom .. please excuse my ignorance

    a group of atoms moving at the speed of light

    but since a massive atom cannot move at the speed of light .. that is really going to slow down space travel.
    Last edited: Jan 12, 2012
  5. Jan 12, 2012 #4


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    Because it would take infinite energy and we don't have that much.
  6. Jan 12, 2012 #5
    See "special relativity"

    Also the temperature of a gas moving near the speed of light is given by the same equation as a gas moving much less than the speed of light, the ideal gas law (PV=nRT)
  7. Jan 13, 2012 #6
    It won't slow down space travel.
    With a ship speed close to the speed of light, the travel time would be quite short for the passengers of the ship, due to relativistic effects.
    So for example travelling a 100 light years distance could take only a few years for the passengers inside the ship. It would still take 100+ years for everyone outside the ship, not travelling with relativistic speed.

    And if a ship could travel with the speed of light (not possible, but nice to imagine), the travel time for its passengers would be instant, no matter the distance.
  8. Jan 13, 2012 #7
    Ok .. It would take infinite energy .. agreed

    the object would have infinite mass

    no single atom can have temperature but two can .. silly notion

    and yes it wouldn't slow down space travel since speed is relative to the point you are observing it from.

    however I didnt ask if it was possible .. I just asked what would be the temperature of an atom moving at the speed of light. Would this value be the absolute hottest temperature and the equivalent of absolute zero on the temperature scale.

    moving does not need to mean traveling it could also mean vibrating as atoms which are hot do.
  9. Jan 13, 2012 #8
    There is something called Planck Temperature, which is supposed to be the absulate limit to temperature. I'm not sure, but I suspect it has something to do with this temperature requiring the atoms to vibrate at the speed of light?
  10. Jan 13, 2012 #9
    You mean what do the laws of physics say would happen in a situation which breaks the laws of physics? Do you see the problem here? Unicorns, leprechauns and pixie dust happen.
  11. Jan 13, 2012 #10
    This is wrong. A single atom can and does have a temperature. Pengwuino said a single PHOTON can't have a temperature, not a single ATOM, which definitely can have a temperature.
  12. Jan 13, 2012 #11
    The point I think you're missing is that temperature is related to the energy of [a collection of] particles, and the energy of a particle can increase without bound, even though its speed must be less than c. There is no maximum temperature.

  13. Jan 13, 2012 #12
    Ok so these people are wasting time and money

    Google: Absolute hot :NOVA

    or click this link

    But you are right in that definition

    however temperature by definition is not what I asked

    interesting that there is no way to assess the temperature of a single atom.
  14. Jan 13, 2012 #13
    A single atom does not have a temperature. The temperature is defined as the derivative of the energy with respect to entropy keeping volume and particle number constant. Say I have a hydrogen atom in its ground state, degeneracy is 2 (one state which can be up state or down state) the next energy level is 6 degenerate (the p-orbitals), it's a finite jump and there's no continuum approximation. Temperature is not defined. In general temperature is only defined relative to the notion of a heat bath (canonical ensemble), in the microcanonical ensemble (isolated system) it is simply a Lagrange multiplier, it doesn't carry the same meaning.
  15. Jan 13, 2012 #14
    Well even intuitively the temperature is the average energy per particle, if you only have one particle...
  16. Jan 13, 2012 #15
    so taken as individual atoms they have no temperature but if there is a crowd of them they do have temperature.

    so what is the minimum number of atoms that you have to have to say that there is temperature?

    what would be the temperature of this minimum crowd of atoms if they were moving/vibrating at the speed of light?

    Of course assuming that they are moving/vibrating at the speed of light no matter how impossible that may be to achieve.
  17. Jan 13, 2012 #16
    The basic answer was given in the first post, you cannot have atoms moving at the speed of light. You are asking "what happens when I walk through this wall?" You can't walk through a wall so there is no answer. I don't know what else can be said here.

    The minimum number of atoms? Lots. Again if I tell you "the minimum number is thirteen trillion" what can you use this for? You can research what constitutes a statistical ensemble and where the limits of the continuum model of a fluid breaks down, but the heart of your question still assumes that an impossibility is possible.
  18. Jan 13, 2012 #17
    Your question is moot because our current models for physics suggest that the energy required would be, literally, infinite.
  19. Jan 13, 2012 #18
    Ok it is infinitely impossible for this to be but

    If it did happen

    What would be the temperature of an atom or bunch of atoms moving/vibrating at the speed of light?

    It should be a simple calculation .. just like they extended to absolute zero as the lack of energy and motion ... what would be the temperature extended the other way to infinite energy and motion at the speed of light.
    Last edited: Jan 13, 2012
  20. Jan 13, 2012 #19


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    Hm ... this is not going well. It's been stated a couple of times that you are asking for an answer to the question of what happens if the impossible happens.

    Just make up your own answer. It will be just as good as anything anyone else can tell you.
  21. Jan 13, 2012 #20
    Yup figured that out a few answers ago

    no one knows ..

    thank you for your time and patience.
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