# Less than 0 kelvin? Meaning of temperature

by .ultimate
Tags: kelvin, meaning, temperature
 P: 45 If tempertaure means the movement of particles, Can tempertaure be below 0 Kelvin? I mean no movement, vacumm
 P: 12 I dont understand the last part. 0 Kelvin is absolute zero. Particles don't move in 0 Kelvin. http://en.wikipedia.org/wiki/Kelvin
 P: 45 If absolute 0 means no movement of particles Can Absense of any particle (vacuum) be regarded as 0k what is heat energy in vacuum?
P: 137

## Less than 0 kelvin? Meaning of temperature

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.
 P: 41 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. -Jim
 Mentor P: 27,565 There is a well-described answer to this FAQ that everyone might want to check out. http://math.ucr.edu/home/baez/physic...mperature.html Zz.
 P: 1,295 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.
 P: 45 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?
P: 691
 Quote by .ultimate 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?

Heat transfers through 3 ways : conduction, radiation and convection. In your case, only radiation takes place which imits IR
 P: 45 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?
P: 530
 Quote by Kanse I dont understand the last part. 0 Kelvin is absolute zero. Particles don't move in 0 Kelvin. http://en.wikipedia.org/wiki/Kelvin
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.
P: 691
 Quote by .ultimate 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?
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.
P: 530
 Quote by pixel01 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.
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.
 P: 45 Arent Infra-red eletromagnetic waves? If that is so, can over wavelngth em waves also be considered to carry heat energY?
Mentor
P: 27,565
 Quote by .ultimate Arent Infra-red eletromagnetic waves? If that is so, can over wavelngth em waves also be considered to carry heat energY?
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.

Zz.
P: 45
 Quote by ZapperZ 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. Zz.
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.

Uu.
Mentor
P: 27,565
 Quote by .ultimate Sorry, I meant 'other' wavlenght, I apologise if it caused any misconfusion How can you hypothesize that enrgy can be Absorbed
Because that is what happens when light "disappears" when it hits objects. Do you have an alternative explanation for the blackbody radiation?

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

 By the way, Can you please clarify what you mean by Heat in the above context
Atomic or molecular KE or lattice vibrations, the SAME way it is defined in thermodynamics!

Zz.
 P: 555 due to the definition of temperature, its impossible to have negative movement, so by soemhow going below 0 Kelvin would actually be going warmer

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