Let's say that a hot gas is trapped in a metal box. This metal box is magnetically suspended in another structure with a low temperature. The inner box does not touch anything. And there is a void in the structure. To me there seems to be no way for heat transfer to occur. Will the gas change its temperature with time?
I can't make this a comment since I don't have enough reputation.
The metal box itself can absorb some of the heat (by conduction) and then give out energy in the form of electromagnetic radiation. If you want to do some real physics with such a system, you could idealize the box as a black body and continue.