# Temperature in vacuum?

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1. Jan 2, 2016

### ChloeYip

I have learnt that temperature is defined as the vibration of particles.
However, in vacuum, there is no particles.
In reality, no absolute vacuum can be done, so I can't find answer online.
Do you think the temperature (in Kelvin) is zero or undefined?
Thank you.

2. Jan 2, 2016

### marcus

Light
Heat glow.
Even in a vacuum there is the electromagnetic field. It is everywhere. It vibrates at different frequencies, some are visible light, some are warmth, some are too low-frequency and weak for us to feel with our senses.

Corresponding to any temperature there is a thermal mix of frequencies or mix of energies which you get as a heat glow off the walls of the box that you have your vacuum in. The light (in the general sense of electromagnetic radiation) inside the otherwise empty box has a temperature

Last edited: Jan 2, 2016
3. Jan 3, 2016

### ChloeYip

What if technology get more advanced in the future and block all EM wave? Would there be still temperature?

p.s. I am just a high school student, can you please answer in a more simple way? Thanks.

4. Jan 3, 2016

### vanhees71

The vacuum is the ground state of quantum field theory. For any quantum mechanical system the vacuum is the equilibrium state with temperature $0$ and all chemical potentials $0$.

5. Jan 3, 2016

### Staff: Mentor

Are you familiar with the concepts of heat conduction, convection, and radiation?

6. Jan 7, 2016

### alw34

"Observation indicates that in our universe the grand total vacuum energy is extremely small and quite possibly exactly zero. Many theorists suspect that the total vacuum energy is exactly zero."

http://www.scientificamerican.com/article/follow-up-what-is-the-zer/ [Broken]

Probably not quite, but really really,really close.....there would still be gravitational waves which are many,many times weaker [and which I think have never actually been detected they are so weak....really difficult to measure so far] ...........

Last edited by a moderator: May 7, 2017
7. Jan 7, 2016

### Staff: Mentor

It is not.
The precise definition of temperature is complicated. A vacuum still has a temperature, in the absence of an radiation the temperature is zero. Without matter but with a bit of radiation, like we have it in space far away from stars, the temperature is about 3 K, close to zero but not zero (and we can reach much lower temperatures on Earth).