The capabilities of human senses are limited, and yet, thanks to technological advances, we can look beyond the visible world, see the invisible, such as heat rays. Thermal imaging as a way of information about the world around it is gaining new fields of application in technology, biology and medicine. The article is based on a lecture by Genrikh Romanovich Ivanitsky, Director of the Institute of Theoretical and Experimental Biophysics of the Russian Academy of Sciences, delivered at the IX International School-Conference "Biology - Science of the XXI Century" in the city of Pushchino in the spring of 2005.

Beyond the threshold of the visible
Almost 7/8 of all information from the world around a person receives thanks to visual impressions. Many everyday expressions of speech have their etymological roots in visual sensations. For example, cases for us are "clear", "obvious"; it happens that we "suspect" someone of something, "mean" something, finally, each of us has a certain "worldview". And if we say "attitude", then we mean more often just "worldview". No one would ever think of such an absurd interpretation of this term as "the sense of the world." And why, in fact, ridiculous? Is it completely excluded a meeting with intelligent beings in whom a different feeling is most strongly developed? Let's say the sense of smell and hearing are like those of a dog. By the way, the eyesight in dogs is really much weaker than in humans, and, in addition, the dog does not distinguish colors well. But in the earthworm, although it senses the direction of light, the main role in the processes of perception is the sense of touch. The ant has a special topochemical sense, in which the sense of smell is combined with the touch.

So, the main support in the human "perception of the world" is vision. Meanwhile, the possibilities of the eye are far from unlimited. Considering that the length scale of known electromagnetic waves extends from millionths of a nanometer to hundreds of kilometers, the visible range looks like a drop in the sea - a boundless sea of ​​electromagnetic waves. But it would be interesting and very useful for a person to receive information about the most diverse processes that lie beyond the threshold of immediate sensations. The task arises - to see the invisible. And not just to see, but to study in detail the invisible phenomena, using the richness of the capabilities of the human eye and brain, for example, to distinguish "colors", to recognize and classify various objects.

We are talking about infrared radiation, the wavelength range of which lies outside the range of visible light in the micron region. Thermal imaging technology (otherwise it is called thermal imaging, thermal imaging or infrared vision) appeared in the last century, but 20-30 years ago it was used mainly for military purposes - aiming high-precision weapons at objects that emit heat. Today it has every reason to become one of the main information technologies with a wide range of applications. In biology, this is the study of the heat production of living organisms and individual organs, depending on the diurnal and seasonal cycles. In medicine - diagnostics of vascular, inflammatory and tumor diseases, monitoring the effectiveness of treatment, express control during quarantine measures. Thermal imaging equipment makes it possible to conduct fire monitoring of forests and peatlands, monitor the state of volcanoes, observe from the air the displacement of permafrost zones, steppes and deserts, and the migration of animals. In technology, thermal imagers are needed to monitor the operation of machines and mechanisms, energy transport, and thermal insulation of buildings and structures.

With a thermal imager, you can measure the temperature at every point of the object under consideration, but the key part of the term "thermal imaging" is "seeing" (in this case, it is synonymous with sight). Vision is an informational process that allows you to view an object as a whole, to highlight its essential features, to recognize and classify. The principle of operation of thermal imaging devices is based on the conversion of natural thermal radiation from objects into a visible and even color image. A color picture can be created on the screen, where the color of the image elements is determined by the temperature difference between the corresponding areas of the observed object. Of course, the color is conditional, but it reflects the temperature relief of the object. True, not all researchers like to deal with conventionally colored portraits. Some people prefer black and white - this is a matter of taste and habit.

A prerequisite for image formation is the temperature contrast between the object and the background, and within the boundaries of the object's contour, between its individual elements. In the modern generation of thermal imagers, there are no optical-mechanical image scans, therefore they have high speed, small dimensions and power consumption, in addition, they are distinguished by their silent operation with a high signal-to-noise ratio and allow digital image processing in real time.

In infrared rays
Almost all electromagnetic waves are present in sunlight, but not all reach the Earth. On the way to Earth, a band of wavelengths with 

The solar spectrum is narrowed. The atmosphere protects all living things from death. Short waves are absorbed by the ozone layer, while long waves are absorbed by carbon dioxide molecules and water vapor. Three-quarters of the solar energy that hits the Earth's surface occurs in the wavelength range from 0.3 to 0.11 microns. Photobiological processes on Earth occur mainly in the wavelength range from 0.3 to 0.9 microns. It is natural to ask the question: why are shorter and longer wavelengths not available for vision? The answer lies in the amount of their energy. This energy is determined by the classical formula, which is known today even to schoolchildren: E = hc / λ

where E is the energy of a photon (quantum), h is Planck's constant (1.58.10-34 cal.sec; 1cal = 4.2 J), s is the speed of light (3.1010 cm / sec), λ is the wavelength of light.

It can be seen from this formula that the shorter the wavelength of the light, the higher the energy. For waves shorter than 0.3 microns, the specific energy exceeds 95 kcal / mol. With this energy, damage to protein molecules and nucleic acids occurs. On the other hand, at waves longer than 1.8 μm (infrared radiation), the energy is insufficient to cause a photochemical process in the photosensitive pigment (rhodopsin). The permissible energy of light perception for most living beings is in the range from 15 to 65 kcal / mol, which corresponds to the wavelength range from 0.44 to 1.9 microns. The vision of humans and many living organisms is realized in a narrower range: 0.38 to 0.75 microns (from violet to red). Rays, the wavelength of which falls outside this range, although they affect living things (sometimes very harmful), are invisible to us. We do not feel short waves, but we feel infrared rays, but not with our eyes.

In humans, there are two types of infrared receptors scattered throughout the body. About 150,000 receptors tell us about the possibility of losing heat when in contact with cold objects. These are cold receptors. Approximately 16,000 receptors inform us about the receipt of heat from hot objects (heat receptors). Most of the heat receptors are found in the skin: at the tips of the fingers, nose and at the bend of the elbow. Cold receptors are mainly located in the skin of the upper lip, nose, chin, chest, forehead and fingers.

Heat receptors are highly sensitive, but they are isolated from small external temperature fluctuations. If the surface of the skin is damaged, then touching this area even with mildly heated objects causes a sensation bordering on pain.