Crazy photons vs. reflective photons | Cosmic Void


We hardly remember the summer or those days when we put on some sunglasses, sat on the seashore, and relaxed. Many of our readers will know that it is much better to approach that contemplative activity of the vast ocean with polarized sunglasses. Well, that is what astrophysicists sometimes do to better study the cosmos: put polarized glasses on the telescope. We explain what polarization is (in physics, not politics).

Everything in the universe, by virtue of being at a certain temperature, emits light, photons. Very hot stars, such as the Sun, or incandescent bulbs, emit photons in the optical range of the electromagnetic spectrum; our bodies, on the other hand, are machines for creating less energetic photons, in the infrared.

The mechanism that creates these photons is the result of particles such as electrons, or atoms and molecules themselves, changing energy, which quantum physics tells us cannot be just anyone. When the electrons in an atom go from a higher energy level to a lower one, they emit that difference in energy in the form of electromagnetic radiation, photons. As an analogy, in a staircase we can only be at certain heights, those of the steps; if we want to go up, we need energy, from our legs; if we go down, just the opposite, we lose it. This loss of energy between quantum levels, which would be the steps for electrons, is translated into the emission of photons. Something similar happens with molecules, which tend to vibrate with specific characteristics (quantized, it is said), each with its own characteristic energy. In the process of vibration they emit photons. In this case, the molecules are like a tuning fork, but emitting electromagnetic waves, which is the same as photons, instead of sound waves.

Electromagnetic radiation is a wave in which an electric field oscillates between 2 values ​​periodically, coupled with another wave formed by a magnetic field, and both fields are always perpendicular. What is the electric field? Well, it is nothing more than something that tells you how to move an electric charge, for example, an electron. It is like a conveyor belt, which tells us at the airport in which direction to move (we could go the other way, but it would cost us a lot of energy).

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Let’s imagine an electromagnetic wave created on a table, in such a way that the electric field is always perpendicular to the surface. An electron at a certain point on the table will be forced to move perpendicularly, upward, away from the table, or downward into it, by the action of the electric field. Since we are talking about a wave, sometimes the field tells it to move upward and sometimes downward, it oscillates periodically. The light we see drives our electron in the example pretty crazy, sending it up and down on the order of 600 billion times per second. As the wave is also transmitted at the speed of light, in the end the electron stays more or less in the same place. The same happens with the magnetic field, which would be oscillating and pointing to one side or the other in the plane of the table, coordinated with the electric one.

In short, a photon is an electromagnetic wave oscillating in a certain direction. Returning to the creators of light, bodies do not create a single photon, they create a multitude of them, each with properties that depend on how the quadrillion particles in it were vibrating (in what plane, direction, or with what intensity). the smallest part of a body that we can imagine. Normally, not all molecules in a body vibrate in the same way, the properties of each of these oscillators are quite random, so the photons created are waves whose plane of oscillation is also random. Light is said to be unpolarized when the fields are not oriented in any specific direction. Each photon goes to its own ball, with a crazy combination of oscillation directions, that is, polarizations. In our example, the electric field sometimes points perpendicular to the table, sometimes at a different angle, the direction and intensity at each moment are continuously varying without any pattern.

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If the normal thing is that the light created by the bodies, as is the case of the Sun, does not have any preferred plane, why wear polarized glasses? Let’s go back to the sea. The water molecules on the surface of the water vibrate in one plane, the one that separates the water from the air. So the nonpolarized radiation that comes from the Sun hits the water molecules and they absorb part, vibrate and emit another part of the incident radiation in the form of reflected light. The radiation reflected from the sea surface is therefore partly horizontally polarized (which is the direction of the water surface), the more the greater the angle of incidence of the sunlight or the smoother the angle. water surface. This polarized light is what we see as flashes in the sea that normally do not allow us to distinguish what is under the water. Sunglasses made up of a material whose molecules only oscillate in a certain direction, vertically, only allow the photons associated with a vertically oscillating field to pass through, with which we can filter that horizontally polarized light, get rid of many flashes, not be dazzled and see much better what is under water. A normal sunglasses would not do the same job, the key is that they are polarized. Something similar also happens with light that is not reflected but refracted by a gaseous medium such as air in the atmosphere, but with a much less marked effect.

Making “polarized glasses” for a professional telescope is not that easy, normally less than one percent or even less than just one per thousand of the radiation that comes to us from an astronomical source can have some type of polarization. But the potential is immense. We could study the atmospheres of distant planets, perhaps some not very different from Earth, avoiding being dazzled by the light of the star; or even exo-oceans, seas on extrasolar planets could be discovered. We will tell more in detail in future installments, for today we have already talked a lot about physics.

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Pablo G. Pérez González He is a researcher at the Astrobiology Center, dependent on the Higher Council for Scientific Research and the National Institute of Aerospace Technology (CAB / CSIC-INTA)

Cosmic Void It is a section in which our knowledge about the universe is presented in a qualitative and quantitative way. It is intended to explain the importance of understanding the cosmos not only from a scientific point of view but also from a philosophical, social and economic point of view. The name “cosmic vacuum” refers to the fact that the universe is and is, for the most part, empty, with less than 1 atom per cubic meter, despite the fact that in our environment, paradoxically, there are quintillion atoms per meter cubic, which invites us to reflect on our existence and the presence of life in the universe. The section is made up of Pablo G. Pérez González, researcher at the Center for Astrobiology; Patricia Sánchez Blázquez, Associate Professor at the Complutense University of Madrid (UCM); and Eva Villaver, researcher at the Center for Astrobiology.

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George Holan

George Holan is chief editor at Plainsmen Post and has articles published in many notable publications in the last decade.

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