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Less than 0 kelvin? Meaning of temperature

  1. Mar 22, 2007 #1
    If tempertaure means the movement of particles, Can tempertaure be below 0 Kelvin? I mean no movement, vacumm
  2. jcsd
  3. Mar 22, 2007 #2
  4. Mar 22, 2007 #3
    If absolute 0 means no movement of particles

    Can Absense of any particle (vacuum) be regarded as 0k

    what is heat energy in vacuum?
  5. Mar 22, 2007 #4
    I think there's no concept of vacuum's temperature at least for classical physics. Because temperature measures the movement and/or oscillation of particles, so no particles mean no temperature. It is like you say of the speed of a car, but if there's no car, the speed of nothing is meaningless.
    I am not sure if in modern physics when they say the vacuum is not nothing, but somethingl, the temperature concept can be applied.
  6. Mar 22, 2007 #5
    Quantum mechanics predicts that the lowest energy state of a vibrator has finite energy - the zero point energy. So atoms are predicted to continue to vibrate about their equilibrium position even at 0k. This is separate from the electronic energy - the total interaction energy of the electrons and nuclei at a fixed equilibrium geometry.
  7. Mar 22, 2007 #6


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    There is a well-described answer to this FAQ that everyone might want to check out.

    http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/negativeTemperature.html [Broken]

    Last edited by a moderator: May 2, 2017
  8. Mar 22, 2007 #7
    Temperature does not measure motion or kinetic energy of particles, although in almost all cases it coincides with a measure of these things.

    A difference in temperature measures the potential for thermal energy exchange/heat.

    A system such as the earth orbiting the sun has a negative temperature.
  9. Mar 25, 2007 #8
    What will happen if we put a heated (suppose) metal in vacuum? Will it lose its heat? But how can this be possible, since there are no particles in the sorruonding vacuum?
  10. Mar 25, 2007 #9

    Heat transfers through 3 ways : conduction, radiation and convection. In your case, only radiation takes place which imits IR
  11. Mar 25, 2007 #10
    If heat means the movement for patricles, plase clarify how this movemnt subsides by loss of heat as radiation, how can IR radiation be responsible?
  12. Mar 25, 2007 #11
    Particles have kinetic energy, and non-zero momenta even at 0 K. It's an interesting question as to whether they can be said to move or not.

    What we can say, is that at 0 K, the probability density from the wave-function is stationary and the wave-function is in its ground state.

    It's possible to define a time correlation function for a system in its ground state. That leads me to suspect that it is meaningful to talk about atomic motion at 0K.
  13. Mar 25, 2007 #12
    Heat is one kind of energy which is the kinetic energy of the particles. In this case, this kind of energy is converted to radiation, the IR which is also another kind of energy.
    The energy from the sun to reach earth is transfered by this way as well.
  14. Mar 25, 2007 #13
    Slightly OT, but kinetic energy is actually part of the internal energy of the system. Heat is the energy transfer that goes into raising the temperature of the system.

    Edit: Even that's wrong. Heat flow acts to change the internal energy of a body, which may or may not result in a temperature increase. However, heat flow can only take place between bodies of different temperatures.
    Last edited: Mar 25, 2007
  15. Mar 25, 2007 #14
    Arent Infra-red eletromagnetic waves? If that is so, can over wavelngth em waves also be considered to carry heat energY?
  16. Mar 25, 2007 #15


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    Say what? What is "over wavelength"?

    What we call "radiant heat" is defined as the IR spectrum. This is because this is the range of the em spectrum that many of our common molecules (such as water and our skin) can receive the energy efficiently and convert to what we call "heat".

    ALL em waves carry energy, but not all of this energy are converted efficiently to what we normally call heat. UV spectrum can heat up ordinary glass because it absorbs that spectrum efficiently, yet visible light has no affect on it.

    This thread has become rather confusing and unfocused.

  17. Mar 25, 2007 #16
    Sorry, I meant 'other' wavlenght, I apologise if it caused any misconfusion

    How can you hypothesize that enrgy can be Absorbed

    As Energy is indirectly proportional to Wavelngth, shorter wavelngth Electromagnetic waves SHOULD also be considered to cause Heat

    By the way, Can you please clarify what you mean by Heat in the above context

    Also, I thnik that heat has to be related to movement of molecules since tempertaure is responsible for the physical state of matter (gas, liquid, solid)

    Thank you.

  18. Mar 25, 2007 #17


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    Because that is what happens when light "disappears" when it hits objects. Do you have an alternative explanation for the blackbody radiation?

    Not it doesn't. You are forgetting one half of this important equation - THE NATURE OF THE RECEIVER. You may want to read our FAQ on photon transmission through a solid, especially on the PHONON spectrum of a material. The TYPE of material can also dictate if em radiation of a certain wavelength can be absorbed. No material has an infinite bandwidth of absorption. Your skin is obviously transparent to x-ray, which has a higher energy than visible light which is absorbed by the skin and turned into heat. So just because something has a higher energy doesn't mean it can "cause heat". Besides, you are ignoring the possibility that a certain range of wavelength can cause other phenomena such as molecular energy transition, photoemission, etc... Here, the absorbed energy does not go into heat.

    Atomic or molecular KE or lattice vibrations, the SAME way it is defined in thermodynamics!

  19. Mar 25, 2007 #18
    due to the definition of temperature, its impossible to have negative movement, so by soemhow going below 0 Kelvin would actually be going warmer
  20. Mar 25, 2007 #19
    Zero point motion is predicted to persist to 0K. This energy cannot be radiated or lost any other way because there are no lower vibrational states available. But, the remaining motion occurs on a scale that is relatively small with respect to atomic sizes. The time-averaged atomic position remains fixed. The Lewis and Randall definition of 0K is that the entropy also be 0 and the substance be in a pure, perfect, crystalline state. As you get close to 0K, unpaired electron spin or nuclear spin can complicate matters, because mixtures of spin states can be obtained in the absence of a perturbing applied field.
  21. Mar 26, 2007 #20
    If you say all the EM radiations carry energy. How can the energy 'dissapper'? Isnt that violation of Enery-Mass equivalence

    All matter is supposed to be made of same material. And What do you mean by 'nature' in atomic terms.

    Well, this is purely hypothetical. X-rays are not absorbed by skin neither by bones. I recently postulated the reason for reflection of light

    Size of wavelength of Visible radiation = of order of [tex]10^{-7}[/tex]
    and size of whole atom = [tex]10^{-10}[/tex]
    Size of nucleas = [tex]10^{-15}[/tex]
    Empty space = [tex]10^(-5}[/tex]

    Hence the EM wave will not penetrate through the atom, and the photon will be reflected as such.

    You can apply tjhis to the above scenario, X-rays can penetrate through the skin cells but not bonemarrow.

    Fine that Heat is considered to be molecular Kinetic Energy, But how can it be 'lost' as radiations?

    Zzzz. (sleeping)
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