Chapter Four
ELECTROMAGNETIC FORCES IN ACTION

5. Electromagnetic waves in nature

5-1. Sun rays

“The sticky leaves that bloom in spring are dear to me, the blue sky is dear,” said Ivan Karamazov, one of the heroes born of Dostoevsky’s genius.

Sunlight has always been and remains for a person a symbol of eternal youth, all the best that can be in life. One can feel the excited joy of a man living under the Sun, and in the first poem of a four-year-old boy:

May there always be sunshine
May there always be heaven, May there always be mother,
May it always be me!

And in the quatrains of the wonderful poet Dmitry Kedrin:

You say our fire has gone out.
You say that we have grown old with you,
Look how the blue sky shines!

The dark kingdom, the kingdom of darkness, is not just the absence of light, but a symbol of everything that is heavy and oppressive to the human soul.

Sun worship is the oldest and most beautiful cult of humanity. This is the fabulous god Kon-Tiki of the Peruvians, this is the deity of the ancient Egyptians - Ra. At the very dawn of their existence, people were able to understand that the Sun is life. We have known for a long time that the Sun is not a deity, but a hot ball, but mankind will forever have a reverent attitude towards it.

Even a physicist, accustomed to dealing with the precise recording of phenomena, feels as if he is committing blasphemy when he says that sunlight is electromagnetic waves of a certain length and nothing more. But this is exactly so, and in our book you and I should try to talk only about this.

As light, we perceive electromagnetic waves with a wavelength from 0.4 micrometers to 0.72 micrometers (and if the red light is very bright, then up to 0.8 micrometers or a little more). Other waves do not cause visual impressions.

The wavelength of light is very short. Imagine an average sea wave that increased so much that it occupied the entire Atlantic Ocean from New York in America to Lisbon in Europe. The wavelength of light at the same magnification would only slightly exceed the width of a book page.

5-2. Gas and electromagnetic waves

But we know very well that there are electromagnetic waves of a completely different wavelength. There are kilometer-long waves; There are also shorter ones than visible light: ultraviolet, x-rays, etc. Why did nature make our eyes (as well as the eyes of animals) sensitive to a certain, relatively narrow range of wavelengths?

On the electromagnetic wave scale, visible light occupies a tiny band sandwiched between ultraviolet and infrared rays. Along the edges extend wide bands of radio waves and gamma rays emitted by atomic nuclei.

All these waves carry energy, and, it would seem, could just as well do for us what light does. The eye might be sensitive to them.

Of course, we can immediately say that not all wavelengths are suitable. Gamma rays and X-rays are emitted noticeably only under special circumstances, and they are almost non-existent around us. Yes, this is “thank God.” They (especially gamma rays) cause radiation sickness, so humanity could not long enjoy the picture of the world in gamma rays.

Long radio waves would be extremely inconvenient. They freely bend around meter-sized objects, just as sea waves bend around protruding coastal stones, and we could not examine objects that we vitally need to see clearly. The bending of waves around obstacles (diffraction) would lead to the fact that we would see the world “like a fish in mud.”

But there are also infrared (heat) rays that can heat bodies, but are invisible to us. It would seem that they could successfully replace the wavelengths that the eye perceives. Or, finally, the eye could adapt to ultraviolet light.

Well, the choice of a narrow strip of wavelengths, which we call visible light, precisely in this part of the scale, is completely random? After all, the Sun emits both visible light and ultraviolet and infrared rays.

No and no! This is far from the case here. First of all, the maximum emission of electromagnetic waves by the Sun lies precisely in the yellow-green region of the visible spectrum. But this is not the main thing! The radiation will also be quite intense in neighboring regions of the spectrum.

5-3. "Windows" in the atmosphere

We live at the bottom of the ocean of air. The earth is surrounded by an atmosphere. We consider it transparent or almost transparent. And she

is such in reality, but only for a narrow section of wavelengths (a narrow section of the spectrum, as physicists say in such a case), which our eye perceives.

This is the first optical “window” in the atmosphere. Oxygen strongly absorbs ultraviolet radiation. Water vapor blocks infrared radiation. Long radio waves are thrown back, reflecting from the ionosphere.

There is only one other “radio window”, transparent to waves from 0.25 centimeters to about 30 meters. But these waves, as already mentioned, are poorly suited for the eye, and their intensity in the solar spectrum is very low. It took a big leap in the development of radio technology, caused by the improvement of radars during the Second World War, to learn how to reliably pick up these waves.

Thus, in the process of struggle for existence, living organisms acquired an organ that reacted precisely to those radiations that were the most intense and very well suited for their purpose.

The fact that the maximum radiation from the Sun exactly falls in the middle of the “optical window” should probably be considered an additional gift from nature. (Nature in general turned out to be extremely generous towards our planet. We can say that she did everything, or almost everything in her power, so that we could be born and live happily. She, of course, could not “foresee” all the consequences of her generosity, but she gave us reason and thereby made us responsible for our future fate.) It would probably be possible to do without the striking coincidence of the maximum radiation of the Sun with the maximum transparency of the atmosphere. The rays of the Sun, sooner or later, would still awaken life on Earth and would be able to support it in the future.

5-4. Blue sky

If you are reading this book not as a manual for self-education, which it would be a pity to throw away, since time and money have already been spent, but “with feeling, sense, arrangement,” then you should pay attention to the seemingly obvious contradiction. The maximum radiation from the Sun falls on the yellow-green part of the spectrum, and we see it as yellow.

The atmosphere is to blame. It transmits better the long-wave part of the spectrum (yellow) and worse transmits the short-wave part. Therefore, the green light appears to be greatly weakened.

Short wavelengths are generally scattered by the atmosphere in all directions especially intensely. That’s why “the blue sky shines above us,” and not yellow or red. If there were no atmosphere at all, there would be no familiar sky above us. Instead there is a black abyss with a dazzling Sun. So far only astronauts have seen this.

Such a Sun without protective clothing is destructive. High in the mountains, when there is still something to breathe, the Sun becomes unbearably burning *): you cannot remain without clothes, and in the snow - without dark glasses. You can burn your skin and retina.

*) Ultraviolet radiation is not sufficiently absorbed by the upper layers of the atmosphere.

SuperCook Note. The main source of the blueness of the earth's sky is atmospheric oxygen (nitrogen is colorless). Dust in the air dissipates this blueness of oxygen, making it whitish. The cleaner the air, the brighter and bluer the earth's sky. If the Earth had an atmosphere of chlorine, the sky would be green.

5-5. Gifts of the Sun

Light waves falling on the Earth are a priceless gift of nature. First of all, they provide warmth, and with it life. Without them, the cosmic cold would have shackled the Earth. If the amount of all the energy consumed by humanity (fuel, falling water and wind) were increased by 30 times, then even then this would amount to only a thousandth of the energy that the Sun supplies us free of charge and without any hassle.

In addition, the main types of fuel - coal and oil - are nothing more than “canned rays of the sun.” These are the remains of vegetation that once lushly covered our planet, and perhaps, partly, the animal world.

The water in the turbines of power plants was once raised upward in the form of steam by the energy of the sun's rays. It is the sun's rays that move the air masses in our atmosphere.

But that is not all. Light waves do more than just heat. They awaken chemical activity in the substance that simple heating cannot cause. Fabric fading and tanning are the result of chemical reactions.

The most important reactions take place in “sticky spring leaves,” as well as in pine needles, leaves of grass, trees, and many microorganisms. In a green leaf under the Sun, processes necessary for all life on Earth occur. They give us food, they also give us oxygen to breathe.

Our body, like the organisms of other higher animals, is not capable of combining pure chemical elements into complex chains of atoms - molecules of organic substances. Our breath continuously poisons the atmosphere. By consuming vital oxygen, we exhale carbon dioxide (CO2), binding oxygen and making the air unfit for breathing. It needs to be continuously cleaned. Plants on land and microorganisms in the oceans do this for us.

Leaves absorb carbon dioxide from the air and break down its molecules into their component parts: carbon and oxygen. Carbon is used to build living plant tissues, and pure oxygen is returned to the air. By attaching atoms of other elements extracted from the earth by their roots to the carbon chain, plants build molecules of proteins, fats and carbohydrates: food for us and for animals.

All this happens due to the energy of the sun's rays. Moreover, what is especially important here is not only the energy itself, but the form in which it comes. Photosynthesis (as scientists call this process) can only occur under the influence of electromagnetic waves in a certain range of the spectrum.

We will not attempt to talk about the mechanism of photosynthesis. It has not yet been fully clarified. When this happens, a new era will likely dawn for humanity. Proteins and other organic matter can be grown directly in retorts under the blue sky.

5-6. Light pressure

The finest chemical reactions are generated by light. At the same time, he turns out to be capable of simple mechanical actions. It puts pressure on surrounding bodies. True, here too the light shows a certain delicacy. Light pressure is very low. The force per square meter of the earth's surface on a clear sunny day is only about half a milligram.

A fairly significant force acts on the entire globe, about 60,000 tons, but it is negligible compared to the gravitational force (1014 times less).

Therefore, the enormous talent of P. N. Lebedev was needed to detect light pressure. At the beginning of our century, he measured the pressure not only on solids, but also on gases.

Despite the fact that the light pressure is very low, its effect can sometimes be observed directly with the naked eye. To do this you need to see a comet.

It has long been noticed that the tail of a comet, consisting of tiny particles, when moving around the Sun, is always directed in the direction opposite to the Sun.

The particles of the comet's tail are so small that the forces of light pressure turn out to be comparable or even superior to the forces of their attraction to the Sun. That's why comet tails are pushed away from the Sun.

It's not hard to understand why this happens. The force of gravity is proportional to the mass and, therefore, to the cube of the linear dimensions of the body. Solar pressure is proportional to the size of the surface and, therefore, to the square of the linear dimensions. As the particles become smaller, the gravitational forces consequently decrease faster than the pressure, and with sufficiently small particle sizes they become less than the forces of light pressure.

An interesting incident occurred with the American satellite Echo. After the satellite entered orbit, a large polyethylene shell was filled with compressed gas. A light ball with a diameter of about 30 meters was formed. Unexpectedly, it turned out that during one revolution the pressure of the sun's rays displaces it from orbit by 5 meters. As a result, instead of 20 years, as planned, the satellite stayed in orbit for less than a year.

Inside stars, at temperatures of several million degrees, the pressure of electromagnetic waves should reach enormous values. It must be assumed that, along with gravitational forces and ordinary pressure, it plays a significant role in intrastellar processes.

The mechanism for the occurrence of light pressure is relatively simple, and we can say a few words about it. The electric field of an electromagnetic wave incident on a substance rocks the electrons. They begin to oscillate transversely to the direction of wave propagation. But this in itself does not cause pressure.

The magnetic field of the wave begins to act on the electrons that have come into motion. It is precisely this that pushes the electrons along the light beam, which ultimately leads to the appearance of pressure on the piece of matter as a whole.

5-7. Messengers of distant worlds

We know how large the boundless expanses of the Universe are, in which our Galaxy is an ordinary cluster of stars, and the Sun is a typical star belonging to the yellow dwarfs. Only within the solar system is the privileged position of the globe revealed. Earth is the most suitable for life among all the planets in the solar system.

We know not only the location of countless stellar worlds, but also their composition. They are built from the same atoms as our Earth. The world is one.

Light is a messenger of distant worlds. He is the source of life, he is also the source of our knowledge about the Universe. “How great and beautiful the world is,” electromagnetic waves coming to Earth tell us. Only electromagnetic waves “speak”—gravitational fields do not provide any equivalent information about the Universe.

Stars and star clusters can be seen with the naked eye or through a telescope. But how do we know what they are made of? Here a spectral apparatus comes to the aid of the eye, “sorting” light waves by length and sending them out in different directions.

Heated solids or liquids emit a continuous spectrum, that is, all possible wavelengths, ranging from long infrared to short ultraviolet.

Isolated or almost isolated atoms of hot vapors of a substance are a completely different matter. Their spectrum is a palisade of colored lines of varying brightness, separated by wide dark stripes. Each colored line corresponds to an electromagnetic wave of a certain length *).

*) Let us note, by the way, that outside of us there are no colors in nature, there are only waves of different lengths.

The most important thing: the atoms of any chemical element give their own spectrum, unlike the spectra of atoms of other elements. Like human fingerprints, the line spectra of atoms have a unique personality. The uniqueness of the patterns on the skin of the finger helps to find the criminal. In the same way, the individuality of the spectrum gives physicists the opportunity to determine the chemical composition of a body without touching it, and not only when it lies nearby, but also when it is removed at distances that even light travels over millions of years. It is only necessary that the body glows brightly **).

**) The chemical composition of the Sun and stars is determined, strictly speaking, not from emission spectra, since this is a continuous spectrum of the dense photosphere, but from absorption spectra by the solar atmosphere. Vapors of a substance absorb most intensely precisely those wavelengths that they emit in a hot state. Dark absorption lines against the background of a continuous spectrum make it possible to determine the composition of celestial bodies.

Those elements that are on Earth were also “found” in the Sun and stars. Helium was even earlier discovered on the Sun and only then found on Earth.

If emitting atoms are in a magnetic field, then their spectrum changes significantly. Individual colored stripes are split into several lines. This is what makes it possible to detect the magnetic field of stars and estimate its magnitude.

The stars are so far away that we cannot directly notice whether they are moving or not. But the light waves coming from them bring us this information. The dependence of the wavelength on the speed of the source (the Doppler effect, which was already mentioned earlier) makes it possible to judge not only the speeds of stars, but also their rotation.

Basic information about the universe comes to us through an “optical window” in the atmosphere. With the development of radio astronomy, more and more new information about the Galaxy is coming through the “radio window”.

5-8. Where do electromagnetic waves come from?

SuperCook Note: The only source of electromagnetic waves is the acceleration of charged particles. And such accelerations can occur for completely different reasons.

We know, or think we know, how radio waves are created in the universe. One of the sources of radiation was mentioned earlier in passing: thermal radiation arising from the deceleration of colliding charged particles. Of greater interest is non-thermal radio emission.

Visible light, infrared and ultraviolet rays are almost exclusively of thermal origin. The high temperature of the Sun and other stars is the main reason for the birth of electromagnetic waves. Stars also emit radio waves and X-rays, but their intensity is very low.

When charged particles of cosmic rays collide with atoms of the earth's atmosphere, short-wave radiation is generated: gamma and x-rays. True, being born in the upper layers of the atmosphere, they are almost completely absorbed, passing through its thickness, and do not reach the surface of the Earth.

The radioactive decay of atomic nuclei is the main source of gamma rays at the Earth's surface. Here, energy is drawn from the richest “energy storehouse” of nature - the atomic nucleus.

All living beings emit electromagnetic waves. First of all, like any heated body, infrared rays. Some insects (such as fireflies) and deep-sea fish emit visible light. Here it is born due to chemical reactions in luminous organs (cold light).

Finally, during chemical reactions associated with cell division in plant and animal tissues, ultraviolet light is emitted. These are the so-called mitogenetic rays, discovered by the Soviet scientist Gurvich. At one time it seemed that they were of great importance in the life of cells, but later more accurate experiments, as far as one can judge, gave rise to a number of doubts here.

5-9. Olfaction and electromagnetic waves

It cannot be said that only visible light affects the senses. If you raise your hand to a hot kettle or stove, you will feel the warmth from a distance; our body is able to perceive fairly intense streams of infrared rays. True, the sensitive elements located in the skin do not react directly to radiation, but to the heating caused by it. It may be that infrared rays do not produce any other effect on the body, but perhaps this is not so. The final answer will be obtained after solving the riddle of smell.

How do humans, and even more animals and insects, smell the presence of certain substances at a considerable distance? A simple answer suggests itself: penetrating into the olfactory organs, the molecules of the substance cause their specific irritation of these organs, which we perceive as a certain smell.

But how can we explain this fact: bees flock to honey even when it is hermetically sealed in a glass jar? Or another fact: some insects smell at such a low concentration of the substance that on average there is less than one molecule per individual.

In this regard, a hypothesis has been put forward and is being developed according to which the sense of smell is caused by electromagnetic waves more than 10 times longer than the wavelength of visible light. These waves are emitted by low-frequency vibrations of molecules and affect the olfactory organs. It is curious that this theory brings our eyes and nose closer together in an unexpected way. Both are different types of receivers and analyzers of electromagnetic waves. It is still quite difficult to say whether all this is actually true.

5-10. Significant "cloud"

The reader, who throughout this long chapter has probably become tired of being amazed at the endless variety of manifestations of electromagnetism, penetrating even into such a delicate area as perfumery, might come to the conclusion that there is no more favorable theory in the world than this. True, there was some confusion when talking about the structure of the atom. Otherwise, electrodynamics seems flawless and invulnerable.

This feeling of enormous well-being arose among physicists at the end of the last century, when the structure of the atom was not yet known. This feeling was so complete that the famous English physicist Thomson, at the turn of two centuries, seemed to have reason to talk about a cloudless scientific horizon, on which his gaze saw only two “small clouds.” The talk was about Michelson's experiments on measuring the speed of light and the problem of thermal radiation. The results of Michelson's experiments formed the basis of the theory of relativity. Let's talk about thermal radiation in detail.

Physicists were not surprised that all heated bodies emit electromagnetic waves. It was only necessary to learn how to quantitatively describe this phenomenon, relying on a harmonious system of Maxwellian equations and Newton’s laws of mechanics. While solving this problem, Rayleigh and Genet obtained an amazing and paradoxical result. From the theory it followed with complete immutability, for example, that even a human body with a temperature of 36.6 ° C would have to sparkle dazzlingly, inevitably losing energy and quickly cooling to almost absolute zero.

No subtle experiments are needed here to verify the obvious conflict between theory and reality. And at the same time, we repeat, the calculations of Rayleigh and Jeans did not raise any doubts. They were a direct consequence of the most general statements of the theory. No amount of trickery could save the situation.

The fact that the many times tested laws of electromagnetism went on strike as soon as they tried to apply them to the problem of radiation of short electromagnetic waves so stunned physicists that they began to talk about the “ultraviolet catastrophe” *). This is what Thomson had in mind when talking about one of the “clouds”. Why only a “cloud”? Yes, because it seemed to physicists at that time that the problem of thermal radiation was a small private issue, not significant against the backdrop of the overall gigantic achievements.

*) The “catastrophe” was called ultraviolet, since the troubles were associated with radiation of very short waves.

However, this “cloud” was destined to grow and, turning into a giant cloud, obscure the entire scientific horizon, pouring down with an unprecedented downpour, which eroded the entire foundation of classical physics. But at the same time, he also brought to life a new physical understanding of the world, which we now briefly denote in two words - “quantum theory.”

Before talking about something new that has significantly revolutionized our ideas about both electromagnetic forces and forces in general, let’s turn our gaze back and try, from the height to which we have risen, to clearly imagine why electromagnetic forces play nature has such a prominent role.

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“The sticky leaves that bloom in spring are dear to me, the blue sky is dear,” said Ivan Karamazov, one of the heroes born of Dostoevsky’s genius.

Sunlight has always been and remains for a person a symbol of eternal youth, all the best that can be in life. One can feel the excited joy of a man living under the Sun, and in the first poem of a four-year-old boy:

May there always be Sun, May there always be sky, May there always be mother, May there always be me!

and in the quatrains of the wonderful poet Dmitry Kedrin:

You say our fire has gone out. You say that you and I have grown old, Look how the blue sky shines! But it is much older than us...

The dark kingdom, the kingdom of darkness, is not just the absence of light, but a symbol of everything that is heavy and oppressive to a person’s soul.

Sun worship is the oldest and most beautiful cult of humanity. This is the fabulous god Kon-Tiki of the Peruvians, this is the deity of the ancient Egyptians - Ra. At the very dawn of their existence, people were able to understand that the Sun is life. We have known for a long time that the Sun is not a deity, but a hot ball, but mankind will forever have a reverent attitude towards it.

Even a physicist, accustomed to dealing with the precise recording of phenomena, feels as if he is committing blasphemy when he says that sunlight is electromagnetic waves of a certain length and nothing more. But this is exactly so, and in our book you and I should try to talk only about this.

As light, we perceive electromagnetic waves with a wavelength from 0.00004 centimeters to 0.000072 centimeters. Other waves do not cause visual impressions.

The wavelength of light is very short. Imagine an average sea wave that increased so much that it occupied the entire Atlantic Ocean from New York in America to Lisbon in Europe. The wavelength of light at the same magnification would be only slightly longer than the width of this page.

The eye and electromagnetic waves

But we know very well that there are electromagnetic waves of a completely different wavelength. There are kilometer-long waves; There are also shorter ones than visible light: ultraviolet, x-rays, etc. Why did nature make our eyes (as well as the eyes of animals) sensitive to a certain, relatively narrow range of wavelengths?

On the electromagnetic wave scale, visible light occupies a tiny band sandwiched between ultraviolet and infrared rays. Along the edges extend wide bands of radio waves and gamma rays emitted by atomic nuclei.

All these waves carry energy, and, it would seem, could just as well do for us what light does. The eye might be sensitive to them.

Of course, we can immediately say that not all wavelengths are suitable. Gamma rays and X-rays are emitted noticeably only under special circumstances, and they are almost non-existent around us. Yes, this is “thank God.” They (especially gamma rays) cause radiation sickness, so humanity would not be able to enjoy the picture of the world in gamma rays for long.

Long radio waves would be extremely inconvenient. They freely bend around meter-sized objects, just as sea waves bend around protruding coastal stones, and we could not examine objects that we vitally need to see clearly. The bending of waves around obstacles (diffraction) would lead to the fact that we would see the world “like a fish in mud.”

But there are also infrared (heat) rays that can heat bodies, but are invisible to us. It would seem that they could successfully replace the wavelengths that the eye perceives. Or, finally, the eye could adapt to ultraviolet light.

Well, the choice of a narrow strip of wavelengths, which we call visible light, precisely in this part of the scale, is completely random? After all, the Sun emits both visible light and ultraviolet and infrared rays.

No and no! This is far from the case here. First of all, the maximum emission of electromagnetic waves by the Sun lies precisely in the yellow-green region of the visible spectrum. But this is not the main thing! The radiation will also be quite intense in neighboring regions of the spectrum.

"Windows" in the atmosphere

We live at the bottom of the ocean of air. The earth is surrounded by an atmosphere. We consider it transparent or almost transparent. And it is such in reality, but only for a narrow section of wavelengths (a narrow section of the spectrum, as physicists say in such a case), which our eye perceives.

This is the first optical “window” in the atmosphere. Oxygen strongly absorbs ultraviolet radiation. Water vapor blocks infrared radiation. Long radio waves are thrown back, reflecting from the ionosphere.

There is only one other “radio window”, transparent to waves from 0.25 centimeters to about 30 meters. But these waves, as already mentioned, are poorly suited for the eye, and their intensity in the solar spectrum is very low. It took a big leap in the development of radio technology, caused by the improvement of radars during the Second World War, to learn how to reliably pick up these waves.

Thus, in the process of struggle for existence, living organisms acquired an organ that reacted precisely to those radiations that were the most intense and very well suited for their purpose.

The fact that the maximum radiation from the Sun exactly falls in the middle of the “optical window” should probably be considered an additional gift from nature. (Nature in general turned out to be extremely generous towards our planet. We can say that she did everything, or almost everything in her power, so that we could be born and live happily. She, of course, could not “foresee” all the consequences of her generosity, but she gave us reason and thereby made us responsible for our future fate.) It would probably be possible to do without the striking coincidence of the maximum radiation of the Sun with the maximum transparency of the atmosphere. The rays of the Sun, sooner or later, would still awaken life on Earth and would be able to support it in the future.

If you are reading this book not as a manual for self-education, which it would be a pity to throw away, since time and money have already been spent, but “with feeling, sense, arrangement,” then you should pay attention to the seemingly obvious contradiction. The maximum radiation from the Sun falls on the yellow-green part of the spectrum, and we see it as yellow.

The atmosphere is to blame. It transmits better the long-wave part of the spectrum (yellow) and worse transmits the short-wave part. Therefore, the green light appears to be greatly weakened.

Short wavelengths are generally scattered by the atmosphere in all directions especially intensely. That's why the blue sky shines above us, not yellow or red. If there were no atmosphere at all, there would be no familiar sky above us. Instead of it there is a black abyss with a dazzling Sun. So far only astronauts have seen this.

Such a Sun without protective clothing is destructive. High in the mountains, when there is still something to breathe, the Sun becomes unbearably burning *: you cannot remain without clothes, and in the snow - without dark glasses. You can burn your skin and retina.

* (Ultraviolet radiation is not sufficiently absorbed by the upper layers of the atmosphere.)

Light waves falling on the Earth are a priceless gift of nature. First of all, they provide warmth, and with it life. Without them, the cosmic cold would have shackled the Earth. If the amount of all the energy consumed by humanity (fuel, falling water and wind) were increased by 30 times, then even then this would amount to only a thousandth of the energy that the Sun supplies us free of charge and without any hassle.

In addition, the main types of fuel - coal and oil - are nothing more than "canned rays of the sun." These are the remains of vegetation that once lushly covered our planet, and perhaps, partly, the animal world.

The water in the turbines of power plants was once raised upward in the form of steam by the energy of the sun's rays. It is the sun's rays that move the air masses in our atmosphere.

But that is not all. Light waves do more than just heat. They awaken chemical activity in the substance that simple heating cannot cause. Fabric fading and tanning are the result of chemical reactions.

The most important reactions take place in “sticky spring leaves,” as well as in pine needles, leaves of grass, trees, and in many microorganisms. In a green leaf under the Sun, processes necessary for all life on Earth occur. They give us food, they also give us oxygen to breathe.

Our body, like the organisms of other higher animals, is not capable of combining pure chemical elements into complex chains of atoms - molecules of organic substances. Our breath continuously poisons the atmosphere. By consuming vital oxygen, we exhale carbon dioxide (CO 2), binding oxygen and making the air unsuitable for breathing. It needs to be continuously cleaned. Plants on land and microorganisms in the oceans do this for us.

Leaves absorb carbon dioxide from the air and break down its molecules into their component parts: carbon and oxygen. Carbon is used to build living plant tissues, and pure oxygen is returned to the air. By attaching atoms of other elements extracted from the earth by their roots to the carbon chain, plants build molecules of proteins, fats and carbohydrates: food for us and for animals.

All this happens due to the energy of the sun's rays. Moreover, what is especially important here is not only the energy itself, but the form in which it comes. Photosynthesis (as scientists call this process) can only occur under the influence of electromagnetic waves in a certain range of the spectrum.

We will not attempt to talk about the mechanism of photosynthesis. It has not yet been fully clarified. When this happens, a new era will likely dawn for humanity. Proteins and other organic matter can be grown directly in retorts under the blue sky.

Light pressure

The finest chemical reactions are generated by light. At the same time, he turns out to be capable of simple mechanical actions. It puts pressure on surrounding bodies. True, here too the light shows a certain delicacy. Light pressure is very low. The force per square meter of the earth's surface on a clear sunny day is only about half a milligram.

A fairly significant force acts on the entire globe, about 60,000 tons, but it is negligible compared to the gravitational force (1014 times less).

Therefore, the enormous talent of P. N. Lebedev was needed to detect light pressure. At the beginning of our century, he measured the pressure not only on solids, but also on gases.

Despite the fact that the light pressure is very low, its effect can sometimes be observed directly with the naked eye. To do this you need to see a comet.

It has long been noticed that the tail of a comet, consisting of tiny particles, when moving around the Sun, is always directed in the direction opposite to the Sun.

The particles of the comet's tail are so small that the forces of light pressure turn out to be comparable or even superior to the forces of their attraction to the Sun. That's why comet tails are pushed away from the Sun.

It's not hard to understand why this happens. The force of gravity is proportional to the mass and, therefore, to the cube of the linear dimensions of the body. Solar pressure is proportional to the size of the surface and, therefore, to the square of the linear dimensions. As particles decrease, gravitational forces decrease as a result faster, than pressure, and at sufficiently small particle sizes the light pressure forces become smaller.

An interesting incident occurred with the American satellite Echo. After the satellite entered orbit, a large polyethylene shell was filled with compressed gas. A light ball with a diameter of about 30 meters was formed. Unexpectedly, it turned out that during one revolution the pressure of the sun's rays displaces it from orbit by 5 meters. As a result, instead of 20 years, as planned, the satellite stayed in orbit for less than a year.

Inside stars, at temperatures of several million degrees, the pressure of electromagnetic waves should reach enormous values. It must be assumed that, along with gravitational forces and ordinary pressure, it plays a significant role in intrastellar processes.

The mechanism for the occurrence of light pressure is relatively simple, and we can say a few words about it. The electric field of an electromagnetic wave incident on a substance rocks the electrons. They begin to oscillate transversely to the direction of wave propagation. But this in itself does not cause pressure.

The magnetic field of the wave begins to act on the electrons that have come into motion. It is precisely this that pushes the electrons along the light beam, which ultimately leads to the appearance of pressure on the piece of matter as a whole.

Messengers of distant worlds

We know how large the boundless expanses of the Universe are, in which our Galaxy is an ordinary cluster of stars, and the Sun is a typical star belonging to the number of yellow dwarfs. Only within the solar system is the privileged position of the globe revealed. Earth is the most suitable for life among all the planets in the solar system.

We know not only the location of countless stellar worlds, but also their composition. They are built from the same atoms as our Earth. The world is one.

Light is a messenger of distant worlds. He is the source of life, he is also the source of our knowledge about the Universe. “How great and beautiful the world is,” electromagnetic waves coming to Earth tell us. Only electromagnetic waves “speak” - gravitational fields do not provide any equivalent information about the Universe.

Stars and star clusters can be seen with the naked eye or through a telescope. But how do we know what they are made of? Here a spectral apparatus comes to the aid of the eye, “sorting” light waves by length and sending them out in different directions.

Heated solids or liquids emit a continuous spectrum, that is, all possible wavelengths, ranging from long infrared to short ultraviolet.

Isolated or almost isolated atoms of hot vapors of a substance are a completely different matter. Their spectrum is a palisade of colored lines of varying brightness, separated by wide dark stripes. Each colored line corresponds to an electromagnetic wave of a certain length *.

* (Let us note, by the way, that outside of us there are no colors in nature, there are only waves of different lengths.)

The most important thing: the atoms of any chemical element give their own spectrum, unlike the spectra of atoms of other elements. Like human fingerprints, the line spectra of atoms have a unique personality. The uniqueness of the patterns on the skin of the finger helps to find the criminal. In the same way, the individuality of the spectrum gives physicists the opportunity to determine the chemical composition of a body without touching it, and not only when it lies nearby, but also when it is removed at distances that even light travels over millions of years. It is only necessary that the body glows brightly *.

* (The chemical composition of the Sun and stars is determined, strictly speaking, not from emission spectra, since this is a continuous spectrum of the dense photosphere, but from absorption spectra by the solar atmosphere. Vapors of a substance absorb most intensely precisely those wavelengths that they emit in a hot state. Dark absorption lines against the background of a continuous spectrum make it possible to determine the composition of celestial bodies.)

Those elements that are on Earth were also “found” in the Sun and stars. Helium was even earlier discovered on the Sun and only then found on Earth.

If emitting atoms are in a magnetic field, then their spectrum changes significantly. Individual colored stripes are split into several lines. This is what makes it possible to detect the magnetic field of stars and estimate its magnitude.

The stars are so far away that we cannot directly notice whether they are moving or not. But the light waves coming from them bring us this information. The dependence of the wavelength on the speed of the source (the Doppler effect, which was already mentioned earlier) makes it possible to judge not only the speeds of stars, but also their rotation.

Basic information about the universe comes to us through an "optical window" in the atmosphere. With the development of radio astronomy, more and more new information about the Galaxy is coming through the “radio window”.

Where do electromagnetic waves come from?

We know, or think we know, how radio waves are created in the universe. One of the sources of radiation was mentioned earlier in passing: thermal radiation arising from the deceleration of colliding charged particles. Of greater interest is non-thermal radio emission.

Visible light, infrared and ultraviolet rays are almost exclusively of thermal origin. The high temperature of the Sun and other stars is the main reason for the birth of electromagnetic waves. Stars also emit radio waves and X-rays, but their intensity is very low.

When charged particles of cosmic rays collide with atoms of the earth's atmosphere, short-wave radiation is generated: gamma and x-rays. True, being born in the upper layers of the atmosphere, they are almost completely absorbed, passing through its thickness, and do not reach the surface of the Earth.

The radioactive decay of atomic nuclei is the main source of gamma rays at the Earth's surface. Here energy is drawn from the richest “energy storehouse” of nature - the atomic nucleus.

All living beings emit electromagnetic waves. First of all, like any heated body, infrared rays. Some insects (such as fireflies) and deep-sea fish emit visible light. Here it is born due to chemical reactions in luminous organs (cold light).

Finally, during chemical reactions associated with cell division in plant and animal tissues, ultraviolet light is emitted. These are the so-called mitogenetic rays, discovered by the Soviet scientist Gurvich. At one time it seemed that they were of great importance in the life of cells, but later more accurate experiments, as far as one can judge, gave rise to a number of doubts here.

Olfaction and electromagnetic waves

It cannot be said that only visible light affects the senses. If you put your hand near a hot kettle or stove, you will feel the warmth from a distance. Our body is able to perceive fairly intense streams of infrared rays. True, the sensitive elements located in the skin do not react directly to radiation, but to the heating caused by it. It may be that infrared rays do not produce any other effect on the body, but perhaps this is not so. The final answer will be obtained after solving the riddle of smell.

How do humans, and even more animals and insects, smell the presence of certain substances at a considerable distance? A simple answer suggests itself: penetrating into the olfactory organs, the molecules of the substance cause their specific irritation of these organs, which we perceive as a certain smell.

But how can we explain this fact: bees flock to honey even when it is hermetically sealed in a glass jar? Or another fact: some insects smell at such a low concentration of the substance that on average there is less than one molecule per individual.

In this regard, a hypothesis has been put forward and is being developed according to which the sense of smell is caused by electromagnetic waves more than 10 times longer than the wavelength of visible light. These waves are emitted by low-frequency vibrations of molecules and affect the olfactory organs. It is curious that this theory brings our eyes and nose closer together in an unexpected way. Both are different types of receivers and analyzers of electromagnetic waves. It is still quite difficult to say whether all this is actually true.

Significant "cloud"

The reader, who throughout this long chapter has probably become tired of being amazed at the endless variety of manifestations of electromagnetism, penetrating even into such a delicate area as perfumery, might come to the conclusion that there is no more favorable theory in the world than this. True, there was some confusion when talking about the structure of the atom. Otherwise, electrodynamics seems flawless and invulnerable.

This feeling of enormous well-being arose among physicists at the end of the last century, when the structure of the atom was not yet known. This feeling was so complete that the famous English physicist Thomson, at the turn of two centuries, seemed to have reason to speak of a cloudless scientific horizon, on which his gaze saw only two “small clouds.” The talk was about Michelson's experiments on measuring the speed of light and the problem of thermal radiation. The results of Michelson's experiments formed the basis of the theory of relativity. Let's talk about thermal radiation in detail.

Physicists were not surprised that all heated bodies emit electromagnetic waves. It was only necessary to learn how to quantitatively describe this phenomenon, relying on a harmonious system of Maxwellian equations and Newton’s laws of mechanics. While solving this problem, Rayleigh and Genet obtained an amazing and paradoxical result. From the theory it followed with complete immutability, for example, that even a human body with a temperature of 36.6 ° C would have to sparkle dazzlingly, inevitably losing energy and quickly cooling to almost absolute zero.

No subtle experiments are needed here to verify the obvious conflict between theory and reality. And at the same time, we repeat, the calculations of Rayleigh and Jeans did not raise any doubts. They were a direct consequence of the most general statements of the theory. No amount of trickery could save the situation.

The fact that the repeatedly tested laws of electromagnetism went on strike as soon as they were tried to be applied to the problem of radiation of short electromagnetic waves so stunned physicists that they began to talk about an “ultraviolet catastrophe” *. This is what Thomson had in mind when speaking about one of the “clouds”. Why only "cloud"? Yes, because it seemed to physicists at that time that the problem of thermal radiation was a small private issue, not significant against the backdrop of general gigantic achievements.

* (The "catastrophe" was called ultraviolet, since the troubles were associated with very short wavelength radiation.)

However, this “cloud” was destined to grow and, turning into a giant cloud, obscure the entire scientific horizon, pouring down with an unprecedented downpour, which eroded the entire foundation of classical physics. But at the same time, he also brought to life a new physical understanding of the world, which we now briefly denote in two words - “quantum theory.”

Before talking about something new that has significantly revolutionized our ideas about both electromagnetic forces and forces in general, let’s turn our gaze back and try, from the height to which we have risen, to clearly imagine why electromagnetic forces play nature has such a prominent role.

), describing the electromagnetic field, theoretically showed that the electromagnetic field in a vacuum can exist in the absence of sources - charges and currents. A field without sources has the form of waves propagating at a finite speed, which in a vacuum is equal to the speed of light: With= 299792458±1.2 m/s. The coincidence of the speed of propagation of electromagnetic waves in vacuum with the previously measured speed of light allowed Maxwell to conclude that light is electromagnetic waves. A similar conclusion later formed the basis of the electromagnetic theory of light.

In 1888, the theory of electromagnetic waves received experimental confirmation in the experiments of G. Hertz. Using a high voltage source and vibrators (see Hertz vibrator), Hertz was able to perform subtle experiments to determine the speed of propagation of an electromagnetic wave and its length. It was experimentally confirmed that the speed of propagation of an electromagnetic wave is equal to the speed of light, which proved the electromagnetic nature of light.