General, Research, Technology

Let's see: what is light?

He is around us and allows us to see the world. But ask any of us, and most will not be able to explain what this light really is. Light helps us understand the world in which we live. This language reflects our language: in darkness we move to the touch, we begin to see light with the onset of dawn. And yet we are far from a complete understanding of the world. If you bring a ray of light closer, what will be in it? Yes, the light moves incredibly fast, but can't it be used for travel? And so on and so forth.


But not all forms of radiation are the same. At the end of the 19th century, scientists were able to determine the exact essence of light radiation. And the strangest thing is, this discovery did not come in the process of studying light, but came out of decades of work on the nature of electricity and magnetism.

Electricity and magnetism seem perfectdifferent things. But scientists like Hans Christian Oersted and Michael Faraday have found that they are deeply intertwined. Oersted found that the electric current passing through the wire deflected the needle of the magnetic compass. Meanwhile, Faraday discovered that moving a magnet near a wire could generate an electric current in the wire.

The mathematicians of that day used these observationsto create a theory that describes this strange new phenomenon, which they called "electromagnetism." But only James Clerk Maxwell could describe the whole picture.

It is hard to overestimate Maxwell's contribution to science. Albert Einstein, who was inspired by Maxwell, said that he changed the world forever. Among other things, his calculations helped us understand what light is.

The very phrase that light is a formelectromagnetic radiation does not say much. But it helps to describe what we all understand: light is a spectrum of colors. This observation dates back to the work of Isaac Newton. We see the color spectrum in all its glory when a rainbow rises in the sky - and these colors are directly related to Maxwell's concept of electromagnetic waves.

The red light at one end of the rainbow iselectromagnetic radiation with a wavelength of 620 to 750 nanometers; the violet color at the other end is radiation with a wavelength of 380 to 450 nm. But there is more to electromagnetic radiation than visible colors. Light with a wavelength longer than red we call infrared. Light with a wavelength shorter than purple is called ultraviolet. Many animals can see in the ultraviolet, some people too, says Eleftherios Gulilmakis of the Max Planck Institute for Quantum Optics in Garching, Germany. In some cases, people see even infrared. Perhaps that is why it does not surprise us that we call ultraviolet and infrared forms of light.

Curiously, however, if the wavelengths becomeeven shorter or longer, we stop calling them "light." Outside of ultraviolet, electromagnetic waves can be shorter than 100 nm. This is the realm of x-rays and gamma rays. Have you ever heard x-rays be called the form of light?

Maxwell's work in the field of electromagnetismled us further and showed that visible light was part of a wide spectrum of radiation. The true nature of the light also became clear. For centuries, scientists have been trying to understand what form light actually takes on a fundamental scale as it moves from a light source to our eyes.

Some believed that light moves in the form of waves.or ripples, through the air or the mysterious "ether". Others thought this wave model was erroneous, and considered light to be a stream of tiny particles. Newton was inclined to a second opinion, especially after a series of experiments that he conducted with light and mirrors.

When light passes through thin slits, it behaves like water waves that pass through a narrow hole: they scatter and propagate in the form of a hemispherical ripple.

When this light passes through two slits, eachthe wave extinguishes another, forming dark patches. When the ripples converge, it is supplemented, forming bright vertical lines. Jung’s experiment literally confirmed the wave model, so Maxwell put this idea into a solid mathematical form. Light is a wave.

Usually you change the amount of energy in a wave,making it higher - imagine a high tsunami of destructive power - and not longer or shorter. In a broader sense, the best way to increase the energy that light transfers to electrons is to make the wave of light higher: that is, to make the light brighter. Changing the wavelength, and hence the light, should not have made much difference.

Einstein realized that the photoelectric effect is easier to understand if you imagine light in the terminology of Planck quanta.

He suggested that the light is carried by tinyquantum portions. Each quantum carries a portion of discrete energy associated with the wavelength: the shorter the wavelength, the denser the energy. This might explain why portions of violet light with a relatively short wavelength carry more energy than portions of red light with a relatively long wavelength.

It would also explain why a simple increase in light brightness does not really affect the result.

Light Brighter Delivers More Portions of Light tometal, but this does not change the amount of energy carried by each portion. Roughly speaking, one serving of violet light can transfer more energy to one electron than many servings of red light.

Einstein called these portions of energy photons and inthey are now recognized as fundamental particles. Visible light is transported by photons, and other types of electromagnetic radiation like x-ray, microwave and radio wave - too. In other words, light is a particle.

Watching these individual waves of lightwas the first step toward controlling and changing the light, he says, just as we change the radio waves to carry radio and television signals.

One hundred years ago, the photoelectric effect showedthat visible light affects electrons in a metal. Gulilmakis says that it should be possible to precisely control these electrons using visible light waves modified in such a way as to interact with the metal in a well-defined way. “We can control the light and use it to control matter,” he says.

It can revolutionize electronics,lead to a new generation of optical computers that will be smaller and faster than ours. "We can move electrons as we please, creating electric currents inside solids with the help of light, and not like in ordinary electronics."

Here is another way to describe the light: it is a tool.

However, nothing new. Life has used light ever since the first primitive organisms developed photosensitive tissues. The eyes of people are caught by photons of visible light, we use them to study the world around us. Modern technology takes this idea even further. In 2014, the Nobel Prize in Chemistry was awarded to researchers who built such a powerful light microscope that it was considered physically impossible. It turned out that if you try, the light can show us things that we thought we would never see.