# How can there be heat in a vacuum?

I keep reading in the Physics World focus issue on vacuum technology about scientists creating high temperatures in the vacuums etc.

If heat is caused by thermal energy being radiated from particles due to their energy, then how can there be heat in a vacuum, as there are no particles present?

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it would be nice if you provided the link to the article/its abtract –  Yrogirg Aug 14 '12 at 18:17
Why would that be necessary? –  Olly Price Aug 15 '12 at 14:04
so we could see what do they mean by "high temperatures in the vacuums" –  Yrogirg Aug 15 '12 at 14:08
Obviously they just said a high temperature... e.g. "setting the vacuum to temperatures of 900K" or something. Clearly. –  Olly Price Aug 15 '12 at 14:10
"Obviously they just said a high temperature... e.g. "setting the vacuum to temperatures of 900K" or something." I bet that's exactly what they said in their published work. "We set vacuum to temperature 900K", and nothing more, that's certainly how does science works. –  Yrogirg Aug 15 '12 at 17:30

Heat is not

caused by thermal energy being radiated from particles due to their energy

heat is the ramdomized (i.e. neglecting bulk flows) energy of motion in any material (including, for instance, photon gases).

Any vacuum that we can make or have access too includes a small amount of matter, and the temperature of that stuff can be measured. Not that because there is very little stuff even high temperatures do not imply a lot of heat.

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Think you've confused heat with internal energy –  Benjamin Hodgson Aug 14 '12 at 22:33

Vacuum is often defined as "space entirely devoid of matter". On the other hand, in physics, we often discern matter and radiation. So there can be radiation in vacuum, and it can have a certain temperature. Of course, this depends on the definitions, and I don't think this is what was meant in the article.

By the way, you do need to give a reference - this is standard practice in science, and it makes a lot of sense - with all due respect, we can never be sure your citation is accurate, unless we have a reference. We generally do not believe each other without proof in science :-)

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In the case of vacuum that you are referring to the scientists are loosely referring to the kinetic energy of the particles as their temperature: $(1/2) m v^2 = (3/2) kT$.

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