However, in a natural enviroment and most manmade ones, other factors like magnetic fields, convection and Coriolis forces, air mass movement over an open system, evaporative cooling, and the imperfectly attainable insulation and isolation of a system don't allow a perfect equlibrium state, even in a gas at the molecular level. In other words, there's a plausibly detectable difference in temperature between nearby objects, they're not likely to be exactly the same temperature. The Law of Diminishing Returns, however, prevents most efforts to measure such a slight difference at that miniscule threshold.

Though there's no visible light, invisible to a human eye ultraviolet and infrared light sources might still input heat. Natural background radioactive particles' radioactive decay also inputs heat, geothermal sources, friction from moving glaciers and other ice masses in motion, heat from gravitational forces, etc., input heat.

273 Kelvin, abolute zero, is where any possible heat radiation from a radiating body stops. But absolute zero is an unattainable state, it's an asymptote boundary like the speed of light. Something even slightly warmer next to an object near that temperature would radiate heat into it. But still the difference could plausibly result in seeing them in infrared vision as a darker object and a lighter one.

Natural infrared vision would seem to me to have fantastically evolved with superacute temperature gradient detection. Manmade infrared devices are relatively crude by comparison to that imaginative but plausible premise. So see? Yes, in very microminute gradients of temperature difference. Say on the order of several nano degrees Kelvin difference. Probable, not likely; impossible, no. Ideal, though, for a fantastical science fiction or fantasy premise.

The two complications I can imagine, one, that the heat of the viewer's optical organs might be brighter than its surroundings, therefore all it would see is its own eye heat. The eyes would have to be about the same temperature as the ambient background. Two, that chance encounters with high heat sources would blind it. Infrared light shading membranes or eyelids or irises that are highly responsive might address that.

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If you have natural infrared vision and you're in a very cold place with no heat sources and with other natural light - the sun - unavailable, could you see?

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Other senses might also be in use. Of course, in an arctic condition, they might not be effective, such as cold protection might muffle ears or sensing the air around it.

It might also hunt by smell or taste. Of course, in the arctic conditions, freezing of the smelling tissues could be a serious problem.

Yeah, that’s what I think. So they couldn’t use their sight without a flashlight just like us in this situation. Their vaunted “heatsight” would not be a significant factor.

Extrinsic -- The two complications I can imagine, one, that the heat of the viewer's optical organs might be brighter than its surroundings

Interesting. A complication I hadn’t considered. Neat idea.

Extrinsic -- chance encounters with high heat sources would blind it

I’ve already noted that in the story. And, think very humanoid but not at all human. They’ve got eyelids. They evolved into underground dwellers who go topside to hunt and farm. They’re way more comfortable in spaceships than we will be.

Bent Tree -- example if this creature evolved in a tropical environment then perhaps it would have trouble in a very cold world. if it were not its own.

A spacefaring race. The world this happens on is not where they came from nor is it Earth. The story plays out in the south polar regions. Really cold but endurable without spacesuits.

Rstegman -- Other senses might also be in use. Of course, in an arctic condition, they might not be effective, such as cold protection might muffle ears or sensing the air around it.

Interesting but not what I’m looking for right here. I’ll keep it in mind for other aliens. These aliens do have a sensitivity to magnetic (or maybe it’s moving magnetic) fields but that is toned down. They have almost lost it from living in high tech for so long.

Thanks guys.

By the way...clearing my throat...would one of you be willing to read the story? I've got another 2900 words to cut out (it's just under 20,000 words now) but I've already cut almost 10,000 words out. I need someone unfamiliar with the story to read what I have over and see if it still makes sense. You could read down to the first point where you really lost interest, even that would be a big help.

For example; We never utilized the absolute threshold of our senses because we do not rely on them, well should I say that it is not worthe the energy expenditure required to stretch our perception, but if the need arises then we could advance further towards that absolute.

1)A eletric display which flashes a number on its screen is turned up to a point at which the human eye can no longer distinguish that it is a number on the screen( Lets say 35 pulses per second, which may or may not even be close to the actual number) So it is flashing at a rate in which it cannot be seen.

Now the person jumps from a plane, or bungee jumps or gets into a car accident. suddenly once the brain is triggered in this startled state, a person can read this number.

2) Blindness. It is pretty much common knowledge and there are countless experiments about the sensory perceptions of the blind. Other senses become more accut because they rely on them more.

But if there were something like geothermal heat sources, and perhaps some climactic seasonal heat sources (e.g., warmer winds or rain instead of snow at certain times of the year) a creature could possibly detect terrain via IR "vision" since some thermal gradient would likely exist.