# Thermodynamics - Possibility of Cold radiation

I am no physicist, let’s just get that out in the open, I'm just a guy with an interest in this area. One thing I have learned in my limited examination of the natural world is that things tend to exist in states of polar opposites, but of the same type, ie male and female, but both human; north and south (pole) in magnetics; positive and negative in electricity; the cycles of a sine wave etc. So why can't the same be said of heat and cold?

I have read the answers on this question that state that cold is merely the absence of heat. But to me this doesn’t adequately explain the phenomenon of feeling coldness radiate off of a cold body. Now before you just say, “this guy hasn’t read anything” I realize that the immediate answer will likely be that my hand feels the heat radiating from the external surroundings and the air temperature around it combined with the heat from my hand being reflected back to it from the same molecules of air around it, and when a cold object is placed near my hand, what I am feeling is the lack of heat being reflected from my hand and from the surrounding air and that the temperature difference I am feeling is the reflection of my hands heat and the air being cooled by the cold object. Basically like the heat from my hand (and the surrounding air temperature) is moving to try and raise the temperature of the cold object to an equilibrium.

Or maybe I butchered that explanation. But my question is: How does the current idea of radiant heat and the apparent improbability of radiant cold fare against Pictet’s Experiment? And has anyone tried to recreate the experiment under different conditions? In the original experiment, a reflective surface was placed behind the cold object, but what if the reflective surface was simply a flat surface? If a flat reflective surface was placed behind the object and then replaced with a parabolic reflective surface of the same size and comparable dimension/density, would a further decrease in temperature be recorded?

Here is a link to a previous discussion on the topic from another thread on this board

• What do you mean by "radiant heat" and "radiant cold"? "Heat", as used in physics, is transport of energy from one system to another (it even has units of energy), thus your definitions of "heat" and "cold" are merely the direction of energy transportation - from the system to your fingertips (heat) or the other way around (cold)."Heat" and "Cold" are not properties of any system, temperature is (but in everyday life we rarely encounter temperature "directly"). Temperature, roughly speaking, is a measure of mean energy per degree of freedom in the system. Commented Jul 8, 2015 at 3:56
• On another issue, there are many things that not tend to exist in pairs, such as mass (there is no "negative mass") and quarks (which have 2 "counter particles"). Commented Jul 8, 2015 at 3:56
• Chris, I won't say that you haven't read anything, but I will say that if you want to understand physics then you have to read textbooks on physics, and not only do you have to read them, but you also have to read them with an open mind, i.e. you can't bring philosophical concepts like yin-yang with you. They have no use in physics and science in general. Just leave them at home. Temperature is that which makes heat flow from hot (temperature) to cold (temperature). That's it. Male-female, by the way, doesn't even exist in biology, but I will let a biologist set you straight on that. Commented Jul 8, 2015 at 4:29
• I'm not sure physics wouldn't benefit from a little more philosophy. In fact that was the basis for much of our scientific discovery, the great question of "why". And it isn't about "yin and yang" but about balance, which as I understand it is the basic idea behind the second law of thermodynamics - systemic entropy whereby the energy of a certain part of a system equals that of the rest of the system resulting on a zero sum, yes? Commented Jul 8, 2015 at 5:02
• Alexander, I have a question. I can see there is no 'anti-mass' but I thought a law of physics stated that matter can neither be created or destroyed, yet the introduction of matter and antimatter seem to lead to an annihilation of both. If this is a true destruction of mass and not a translation of mass into something else and therefore calls this law of physics into question doesn't that mean other aspects of physics could be off? After all we are still trying to find that unified field theory. Commented Jul 8, 2015 at 5:19

## 2 Answers

1) You might find this discussion of Pictet's experiment interesting, and it specifically answers your question about non-planar mirrors.

2) If cold radiation is physically real, then it ought to be possible to produce temperatures below 0 Kelvin (absolute zero), simply by focusing enough of them, just as a solar furnace can produce extremely high temperatures by use of a mirror. The fact that this does not happen ought to be a clue.

Thermodynamics - Possibility of Cold radiation

already shows a confusion on terms.

Cold ( and Hot) are connected with the energy content of the body under discussion, temperature measured with a thermometer.

Radiation is connected with transfer of energy from the body to the environment . The environment into which energy is radiated can be the vacuum, or air ( intervening and maybe then another body).

So heat or cold is not radiated, the electromagnetic radiation is the phenomenon through which heat and cold, i.e. energy, can be added or removed from a body.

Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D animation shows a plane linearly polarized wave propagating from left to right. Note that the electric and magnetic fields in such a wave are in-phase with each other, reaching minima and maxima together .

All bodies radiate away energy, (which is loss of heat/energy) in the form of electromagnetic waves depending on their temperature. Hot ones a lot of radiation , cold ones much less, but all radiate to the environment, and it is called black body radiation.. Thus all bodies radiate against each other. The ones with lower temperature absorb radiation increasing their energy content and thus temperature , the ones at higher lose energy and get colder. They reach what is called thermodynamic equilibrium if no extra energy comes in, i.e. the same temperature.

There does not exist a possibility of "cold radiation" , it is the effect of adding or removing energy from the bodies that changes temperatures. (adding/removing is your + and - in this sense).

The "feeling" of cold is just that "feeling", a complicated biological reaction to the environment. The hand , the human body, can sense if it is gaining or losing energy and the rate of gaining and loosing energy. It gets hot in the sun ( the sun radiates to the human body and overwhelms the radiation of the body to the sun) , and cold on ice ( where the radiation of the human body to the ice overwhelms the radiation of the ice to the human body) . In one case the human body is the receptor of summed energy transfer in the other the generator of summed energy transfer.

• So, if I'm reading your response right, and please forgive me if I'm not, all bodies - even cold ones - radiate heat? But cold bodies radiate it much much less than warm bodies (say the surrounding area) and this results in a transfer of the energy from the 'warm' or high energy body to the 'cold' body? I can understand the concept of thermodynamic entropy but how does a cold body still radiate heat? Commented Jul 8, 2015 at 5:09
• I am correcting the radiate heat. Commented Jul 8, 2015 at 5:29
• All bodies are composed of atoms and molecules. These vibrate in place and their vibrations are the energy that is called heat. The hotter the more they vibrate. BUT vibrations in each others electric and magnetic fields generate electromagnetic waves, these are the waves that leave as black body radiation, as they move through the body (not all, some are re-scattered etc but that is another story, enough leave), As energy is radiated away the heat content falls and temperature falls. Commented Jul 8, 2015 at 5:34
• @ChrisJohnson - "how does a cold body still radiate heat?" A cold body is not qualitatively cold (forget the philosophical concept for now), it is merely less hot than a hot body. Just like a hot body, a cold body radiates energy at a rate proportional to the fourth power of its temperature (referenced to absolute zero), so it does it much more slowly. If it is near one or more warm bodies it will absorb some of what they emit, and so experience a rise in temperature (become warmer or less cold). Commented Jul 8, 2015 at 13:18
• Will try to keep it as simple and innocent as the question was. Coldness or Hotness you and I know actually is our way of discussing temperature that we can feel using any available means and/or senses. Moving backwards from 50 degrees Celsius to 0 degree Celsius gives you a feeling of that transition. Going further down to few more degrees will again give you a hint Commented Jan 10, 2019 at 4:59