Some particles serve as building blocks, but there are also others, such as the neutrino, which are primarily end-time particles. No, I’m not talking about the Christian apocalypse: I mean that it is literally a product of the general decay in the universe. In fact, in 1931, Wolfgang Pauli hypothesized that neutrinos existed because the reports of certain radioactive decays didn’t add up, and a good way to justify the missing energy was to assume that the person responsible for the deprivation a particle that had not done this had not yet been discovered. Shortly after Pauli’s suggestion, Enrico Fermi developed a theory of radioactive decay that incorporated these particles and gave them the name “neutrinos,” which means “little neutron” in Italian. Almost thirty years after this initial hypothesis, Clyde L. Cowan and Frederick Reines observed them for the first time in the so-called Cowan and Reines neutrino experiment, carried out at the Savannah River nuclear reactor (South Carolina). The experiments tested the theory that when an antineutrino, such as that produced in a nuclear reactor, interacts with a proton, a neutron and a positron are formed. The positron, the electron’s antiparticle, then came into contact with it and was destroyed, emitting two high-energy light particles: gamma rays. The experiments they conducted on the Savannah River were intended to detect these gamma rays and the resulting neutrons. The unique combination of two gamma rays and a neutron made it clear that the reactor had produced an antineutrino, setting the entire sequence of events in motion.
Neutrinos are not only difficult to detect, but also something fabulous. They are uncharged, but each type is associated with a charged lepton partner. This means that they come in three variants: the electron neutrino, the muon neutrino and the tauon neutrino. It took us almost fifty years to figure out that neutrinos have mass. I was in my senior year of high school when the revelation was made public. Because their mass is so small, they are always what we call “relativistic particles.” They can travel at speeds close to the universal limit – the speed of light – and are therefore very effective at generating energy, for example in a nuclear decay scenario. It is this property that makes neutrinos of enormous interest not only from the perspective of particle physics, but also from astrophysics. One of the places where neutrinos are created is in stars, which produce them in large quantities when they explode; a phenomenon known as a supernova. Therefore, we turn to neutrinos as well as photons – light particles – and ripples in spacetime – gravitational waves – to study the universe. We are still not sure what the mass of the neutrino is, nor can we explain why its mass is extremely small but still greater than zero. Based on all our knowledge of physics, we assume that the mass is either zero or a significant quantity. So because we didn’t know anything about their mass or whether they had any mass at all, we thought for a while that neutrinos were something called dark neutrinos. It’s only been about a decade since we’re sure they’re not heavy enough, and that leaves us with one question: What the hell is dark matter?
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Let’s start here: Dark matter doesn’t have to be real. The term was coined in 1906 by Henri Poincaré, who christened it “matière obscure”. Twenty-two years earlier, in 1884, the English astronomer Lord Kelvin had theorized that “many, perhaps the vast majority, of our stars are dark bodies.” In the 1920s, Dutch astronomers Jacobus Kapteyn and Jan Oort also postulated the presence of something similar to Matière Obscure, which came from their observations of the stars of the Milky Way and other galactic neighbors. In 1933, Swiss astrophysicist Fritz Zwicky claimed that there was evidence of what he called “dark matter” in German, this time based on observations of star clusters. Further evidence was provided by American astronomer Horace Babcock in 1939, and by that time the name “dark matter” had already become established; Even if it didn’t make sense, because the problem wasn’t that it was dark, but that it was imperceptible and invisible.
The distinction is relevant when we consider the first truly significant evidence for the existence of Matière Obscure, which came in the 1960s and 1970s, thanks in large part to Vera Rubin’s creative use of a new spectrograph developed by Kent Ford. This spectrograph breaks light into different colors, and Dr. Rubin was the first scientist to realize that it could be used to measure the speed of galactic stars with unprecedented accuracy. The results showed that there was a clear mismatch between the speed at which the stars should be rotating around the center of the galaxy (if the stars were the only matter in the galaxy) and the speed at which they were actually moving. If all of a galaxy’s mass is contained in stars and dust, we can calculate the size of that galaxy by looking at how much radiation we collect from both. There is a beautiful physics equation that gives us the connection between luminosity – brightness – and mass; and another that gives us the connection between the mass of a galaxy and the speed at which stars orbit its center. It is one of Newton’s laws and is taught in high school. But in the case of galaxies we run into a problem. The mass resulting from all the stars together, from their orbital speeds, does not match the mass calculated from luminosity measurements. The orbital speed suggests that there should be a much larger mass.
This again suggests that an enormous amount of matter is missing; or in other words, the existence of an invisible matter. There are other possible solutions, such as that our theory of gravity is incorrect (I’ll get into that later), but for now I’ll focus on the more popular idea that we need to know where the missing matter is or else Therefore, our two carefully collected data do not agree. By observing the movements in galaxies, scientists realized for the first time that the problem of missing matter was a real and major problem. But that wasn’t the only clue, and there are several discrepancies today that cannot be explained by including “dark matter” in the equation.
Everything we don’t know
Dark matter is essentially a reminder of how much we don’t know about the universe. The Standard Model of particle physics cannot understand everything. Thanks to a range of astronomical measurements, we believe – that is, most cosmologists and particle physicists believe – that 80 percent of the matter in the universe is what is now called dark matter. Our current understanding of the universe suggests that the components of everything we have seen so far – the matter that makes us up – only makes up about 20 percent of the entire universe. The rest is dark matter. And if, as Einstein taught us, we expand our definition of matter to include energy, the breakdown is even murkier: 5 percent would be matter in the Standard Model, 5 percent of that would be matter covered in the Standard Model; 25 percent dark matter (whatever that is); and 70 percent dark energy. It turns out that the standard model isn’t everything after all. In fact, it may only explain 5 percent of the matter-energy content of the universe. In other words: baryons, the standard model, everyday matter… us? We are very strange, a complete abnormality. And I’m not just talking about physicists, I’m talking about all of us, including the redwoods, our planet, our entire solar system. Most of space is empty, and the parts that are not empty appear to be practically filled with a type of matter invisible to us. We haven’t yet figured out if there’s a way for our scientific instruments to get close to it. We don’t know if it’s one type of particle or if there are more than a thousand. (…) The only thing we know is that this invisible matter is responsible for holding our galaxies together and that it plays a fundamental role in the creation of the matter we can see.
The most obvious question that could be asked here is simply why the Standard Model does not account for a dark matter particle. The answer: The structure of the Standard Model is not our decision. We are subject to the limitations of the mathematical structures of our theories and experimental data. The problem with dark matter is that we have never seen it before and there is no room for it in the Standard Model based on what we have observed. Plus, his bad reputation literally doesn’t help with public relations. We should rather call it “invisible matter,” “transparent matter,” or “clear matter.” I vote for invisible or transparent matter because clear matter reminds me of a particularly bad period in Pepsi’s product management (for millennials and subsequent generations, suffice it to say that Crystal Pepsi, also marketed as Pepsi Clear, arrived with a monstrous marketing campaign – including a vaunted SuperBowl ad — which ended in disaster for both Pepsi and a popular Van Halen song.
The first question asked, of course, was whether an explanation using Standard Model particles was possible, and for a long time, even until recently, neutrinos were strong candidates. Neutrinos are not completely invisible: they produce some interaction with electromagnetic forces and thereby emit light; However, the interaction is so small that it is practically imperceptible. However, what I’ve learned about neutrinos over the last decade shows that they can’t possibly represent most of the invisible matter we’re looking for, for the simple reason that they don’t have enough mass. To properly account for all the missing matter, each neutrino would have to have a mass hundreds or even thousands of times greater than its own mass. It is currently assumed that the study of dark matter “goes beyond the physics of the Standard Model”. This invisible matter is believed to consist of a particle that we have not yet observed. It’s again one of those crucial problems for a physicist: you can end up drowning so much that you devote your whole life to this topic.
The disordered cosmos
Title: The disordered cosmos. A journey into dark matter, space-time and displaced dreams
Author: Chanda Prescod-Weinstein
On sale: November 6th
Price: €24
Pages: 328 pages
Publisher: Captain Swing
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