If a hot object is totally insulated from the outside world..?

Question

If a hot object is totally insulated from the outside world (totally unable to interact with anything else), will its temperature ever be able to change? why or why not?

Answer 1

No, its temperature would reach an equilibrium constant value and stay there. You're describing a "closed system". That means no energy can enter or leave by any means, including work, radiation, conduction, or convection. Energy is therefore internally conserved. Temperature is a statistical concept defined in terms of how many quantum states are *accessible* given such constraints. For such a system, uniform temperature is the equilibrium state because that is the most probable. The quantitative value that it achieves depends on the systems total energy and heat capacity.

To understand that explanation in more detail requires learning about entropy, the definition of temperature in terms of it and energy, and statistical mechanics in general.

Answer 2

Yes, it will get cooler because all objects with heat radiate energy as a black body. This is the reason hot things glow, like lightbulbs, or the sun. At cooler temperatures they still radiate, but you just can't see it with your eyes because the wavelength is too long. So unless you collect all the energy the object radiates and put it back into the object somehow (which would require interaction with something other than itself) the object will lose temperature over time.

followup: Dr. R's answer and mine are different because we interpreted your question differently. I did not read a forbidding of radiative heat loss in your description, while he did. If you are in fact describing a "closed system" where no energy can leave or enter under any conditions, then no the temperature could not change. However if you merely forbid conductive heat loss, by say, putting the object in hard vacuum, then the temerature will indeed drop as I described.