We can feel infrared as heat but cannot see it and this affects our attitudes toward it. Infrared radiation is one of the three ways that heat can travel; conduction, convection and radiation. Infrared seems to us to be so monolithic but actually has many different frequencies just as visible light does. We have a vast amount to gain with some new thinking about this section of the spectrum.
Infrared can be easily sensed to measure the temperature of an object. Astronomers have long used data from infrared radiation to study the universe. There are night-vision goggles that reveal enemy soldiers hiding in vegetation by the difference between their body temperature and that of the background.
I would like to point out that even if the temperature of two objects is the same, they will radiate different frequencies of infrared, or IR, according to their atomic or molecular composition and structure. Each atom and molecule has a natural vibrational rythm like a pendulum. Objects typically absorb IR and re-radiate it at different frequencies. The amount and frequency of the re-radiated IR can tell us a lot about the inside of an object.
This concept of gaining information from heat that would otherwise be inaccessible is made possible by the fact that different objects absorb and re-radiate IR at different frequencies according to their internal composition. Smaller molecules will vibrate faster with heat energy and will thus radiate IR at a higher frequency, although with less energy, than larger molecules.
There are tremendous advantages to this new way of thinking about IR in order to get information about the composition of an object from the heat it radiates. Visible light cannot tell us what is inside an object, IR can. All objects above a temperature of absolute zero radiate IR.
The technique of using X-rays to see through an object is similar in concept but use of IR does not require the object to be brought into a laboratory. IR can be a very effective form of passive X-rays. Everything about the structure of an object could be discerned by it's IR signature if we could prefect this technique.
We consider heat, or infrared radiation, as a very simple entity that we tend to measure only in quantity. We can feel heat but cannot see it and usually only recognize it when the temperature is above what we consider as room temperature. But I recognize heat as far more complex than that and the idea of getting information from heat has a vast amount of unrealized potential.
The everyday radiation of heat around the environment is far more complex than is generally supposed. Keep in mind that heat moves in three ways. Conduction, convection and, radiation. The conduction and convection of heat is relatively simple. It is the radiation of heat by infrared electromagnetic radiation that requires much more understanding. The simplicity of conduction and convection movement of heat hides the complexity of radiant heat.
As we know, objects tend to absorb heat and then radiate it at a different frequency. Every atom and molecule radiates heat at a it's own frequency of infrared. This is the section of the electromagnetic spectrum longer than radio waves but shorter in wavelength than visible light.
Radiant heat is absorbed or passes through a material it encounters according to how the frequency of the infrared radiation matches the resonant frequency of the atoms. More infrared radiation is reflected or passes through a material whose atoms do not vibrate at or near the frequency of the IR coming in. This operates much like the tuned circuit in a radio receiver but in the case of radiant heat, the atoms themselves are the receivers.
Suppose we heat a lump of iron. Now if we take two lumps of identical size and shape, one of iron and one of another metal and put both at exactly the same distance from the hot lump of iron. The cold lump of iron will absorb more radiant heat from the hot iron than will the cold lump of the other metal. This is because the atoms of the hot iron will radiate a frequency of infrared that the cold lump of iron is more naturally tuned into than the other lump of metal.
Water is slow to absorb radiant heat because it is not at the resonant frequency of the water molecules. Water does however, hold onto heat once it has it because it's molecules are so mobile that it transmits heat to neighboring molecules by conduction instead of radiating it away. This gives water it's tremendous heat capacity. Land and rock absorb heat from the sun faster than water because the natural vibrational period of it's molecules are closer to the predominant frequencies of IR coming in.
What all of this means to us is that each object must have a unique heat spectrum signature. We could develop sensitive receivers that are tuned into the IR frequency radiated out by gold atoms. For that matter, every person and animal has different DNA atoms that radiate out slightly different frequencies of IR. Every different atom and molecule radiates heat at a different frequency regardless of the frequencies it absorbed to gain the heat. I believe that a heat spectrum scan of the body can tell us far more than X-rays can.
This is an idea with mind-boggling potential. We recognize that radio waves consist of many different frequencies and light of many shades and colors (colours), why don't we see heat in the same way?
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