Our minds have a special admiration for the invisible. We know that there are things that escape our eyes and remain hidden, which also leads us to other feelings such as curiosity, imagination and even (dis)belief or terror. If I do not see it with my eyes, if I do not touch it with my fingers like Saint Thomas, it cannot exist, I do not believe it. There is not much room for belief in science; doubts about the certainty of something must also be supported by evidence. But in any case, there are many things around us that are invisible.
Being invisible means that something cannot be perceived by the eye. But invisible is something different from imperceptible, also from transparent and of course does not mean non-existent. What perhaps accounts for part of its meaning is the strangeness caused by the invisible. We have mentioned many concepts together and they are very similar and therefore very related. So let’s start with one thing: there are many things that we sometimes cannot see, that are transparent, but still recognizable under certain circumstances. This means that its existence can be proven.
Air, for example, is something invisible, simple and everyday. Air is a medium made up of molecules of nitrogen, oxygen, carbon dioxide, water and more in small amounts. The mixture has a relatively low density. Consider that almost all of the molecules I mentioned are heavier than the water molecule, and while a liter of water has a mass of one kilogram, a liter of air weighs only one gram. If we consider the number of particles in a given volume, is The comparison is similar: water has about a thousand times more particles per unit volume than air. Because of its low density and the type of particles it is composed of, we would say that the air in our atmosphere is invisible. But this only applies in certain circumstances and in a certain sense. Let’s give two examples that show us that air is neither invisible nor transparent as we assume.
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The air in our atmosphere is quite transparent to red light, but not so much to blue light, for which it is like a conglomerate of small mirrors that reflect it (rather, it is said to scatter it), which is the explanation for this In reality, we can “see” the large amount of air that makes up the sky as a bluish color. On the other hand, the air in our atmosphere is opaque to ultraviolet light and also to certain infrared light, electromagnetic wavelengths (of light to understand ourselves) that are “foreign” to humans since only with technology have we been able to access its discovery over the last 200 years. So the concept of the invisibility of air is not so simple: depending on which “eyes” (if we had eyes sensitive to many types of photons) you look at it with, it is translucent, sometimes it is opaque.
But that’s not the whole story with air. Under certain circumstances, air is even visible to the human eye. I could talk about indirect ways of “seeing” the air, such as the effect of turbulence near hot surfaces, for example asphalt in summer, a circumstance in which distorted images can be seen that reveal the presence of air . But I want to focus on a more direct view of the air. When particles from the so-called solar wind interact with the Earth’s magnetic field, they are directed toward the poles. We are referring to the magnetic poles that are close to the poles defined by the Earth’s rotation axis, which in turn are called geographic poles (although none of the three things are exactly the same). These solar wind particles collide with air molecules in the highest regions of the atmosphere, which can cause the nitrogen atoms to lose an electron, they are said to be ionized until the oxygen atoms lose an electron. Increase in energy, it is said to be excited. But just as the goat goes up the mountain and I go to the couch, the electron tries to be as rested as possible at the lowest energy level. This implies that the nitrogen atoms tend to capture the electron stolen from them by a collision with the solar wind and that the oxygen electrons tend to transition to their initial state, i.e. they become de-energized. The result is a loss of energy that cannot be lost, but is released in the form of light, and then we can see the air (that’s what we wanted!) directly through the Northern Lights. Green or orange and red aurora means we see oxygen; Blue auroras, including red ones, mean that we see nitrogen. The air is no longer invisible.
Now that I’ve accomplished my first goal for this section of Cosmic Void, which is to teach physics, let’s move on to the second: describe how amazing the universe is. We have seen auroras on planets like Saturn and Jupiter, which are themselves large gas planets whose “air” we see in different ways. Auroras can also be seen on Venus or Mars itself, the latter with an extremely thin “air” (not very dense) and a very different composition than our air (almost all of it is carbon dioxide, 95%, compared to at least 0 ,1 %). % terrestrial).
But the invisible shows us the unknown far beyond and reveals a strange universe. An emission from gas clouds, which should be invisible to us due to their density, which is normally a billion times less than that of our Earth’s air, allows us to see and confirm the existence of distant galaxies that already existed when Universe 2 % of its flow was age, a distance record recently broken by the James Webb Telescope. These galaxies already have large amounts of excited, even ionized, oxygen, which emits light in so-called aurora lines, like those we described earlier, and in forbidden, slightly stranger lines, also made of carbon or silicon. If there is oxygen and considering that in the universe 91% of the atoms are hydrogen (since hydrogen weighs little compared to others, hydrogen accounts for 71% of the mass of all atoms in the universe), there may be water. In fact, we have it in Gas clouds discovered that were present in galaxies when the universe was 5% of its current age. And carbon compounds.
The invisible, which is not so invisible when you know it and can look at it, is extremely strange. It reveals to us a fantastic universe that is incredible from the start, and I don’t want to say frightening, but it is dizzying when you look at it and understand how big it is and how limited. This is our idea of its nature. We leave ourselves in disbelief, perhaps out of innocence, when we talk about things that cannot really be perceived with photons.
Pablo G. Pérez González He is a researcher at the Astrobiology Center, which is under the Higher Council for Scientific Research and the National Institute of Aerospace Technology (CAB/CSIC-INTA).
Cosmic emptiness It is a section in which our knowledge of the universe is presented qualitatively and quantitatively. The aim is to explain the importance of understanding the cosmos not only from a scientific perspective, but also from a philosophical, social and economic perspective. The name “cosmic vacuum” refers to the fact that the universe is mostly empty, containing less than 1 atom per cubic meter, although paradoxically in our environment there are trillions of atoms per meter cubic, which invites us to wonder about our existence and the to reflect on the presence of life in the universe.
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