On Thursday, August 6, 2015 at 10:52:09 AM UTC-4, Alastair wrote:
Dawlish,

On Page 576 of University Physics with Modern Physics, Technology Update, Thirteenth Edition (2010), which continues to set the benchmark for clarity and rigor combined with effective teaching and research-based innovation, they write:

"Radiation. Heat transfer by radiation is important in some surprising places. A premature baby in an incubator can be cooled dangerously by radiation if the walls of the incubator happened to be cold, even when the air in the incubator is warm. Some incubators regulate the temperature measuring the baby's skin ..."

Hot objects radiate heat which warms adjacent objects. Cold objects radiate cold which cools adjects objects. The latter is difficult to demonstrate because it is more difficult to maintain a constant cold temperature than a high temperture. The latter is easy using electrical heating. However, holding a thermnometer over an object taken from a freezer will cause the temperature shown to drop.

I hope you will now realise that you are wrong, will apologise and admit your mistake. Cold radiation does exist.

==========

It does not and cannot, in the sense that I think you are representing it. But you need to define what you mean by "cold" (see RedAcer's reply). Ypu seem just to be citing relative temperatures.

In your example of the incubator, the hypothetical baby is not cooled by cold "radiating" from the incubator wall. Instead, in a properly working incubator the baby is radiating energy and steadily emitting warmth which is radiated back equally by the incubator and the air therein.

All objects above absolute zero emit energy. But the baby may cool if an incubator wall is colder than it should be, not because the wall is "radiating cold" but because it is radiating less energy back to the baby than the baby is emitting. There is net radiation from the baby to its surroundings, and thus it cools (absent any biological processes). "A premature baby in an incubator can be cooled dangerously by radiation...": yes, by radiation *from* the baby (being greater than that towards it) is what this means - not "cold radiation" in the other direction.

And of course a thermometer will measure a lower temperature adjacent to an object that is emitting less radiation.

Stephen