Let us suppose that the particles of light are attracted in the same way as all other bodies with which we are familiar, (…) of which there can be no reasonable doubt, gravity being, as far as we know or have reason to believe, a universal law of the nature. Under this assumption, if there were any star whose density was great enough, (…) all light emitted by that body would return to it because of its own gravity. (Letter from John Michell to Henry Cavendish, 1783).

It is therefore possible that the largest luminous bodies in the universe are, for this reason, invisible. (Simon Pierre LaPlace, Le Systeme du Monde, 1796).

Among the men of science in England in the second half of the eighteenth century, there was one especially notable for the wide range of his genius and the originality of his methods of investigation. (…) Although highly respected and esteemed by his contemporaries, he has hardly received from subsequent generations the recognition to which the merit of his work undoubtedly entitles him. (Archibald Geikie, Memoir of John Michell, 1918).

Ideas that were once new seem easier to understand when someone has managed to understand and explain them before. A vehicle with wheels seems to us the most logical way to transport weight along a road, but that logic is only understood once the wheel has already been invented and adopted, something that did not happen at the same time in all places in the world. world. What we consider obvious today because we grew up learning it as an indisputable truth, was not always so obvious, except for a small handful of exceptional minds. A 21st-century person may think that the basic principles for describing reality that Euclid enunciated in his work The Elements are little more than platitudes, and yet ideas such as “a straight line can be drawn using any two points” required a superior talent to be conceived and recognized as fundamental truths. The human mind does not find much problem in assimilating ideas already elaborated, but producing new ideas is such a difficult achievement that some reasoning that now seems very simple to us was barely glimpsed by a few individuals throughout the centuries, until the rest of humanity was finally ready to share them.

In 1914, when World War I broke out, one of the most brilliant German physicists and astronomers of his time, Karl Schwarzschild, enlisted in the army. He had just turned forty, a most unusual age for a recruit. Even worse: by wearing the uniform he was abandoning a fruitful scientific career in which he had encompassed, with admirable versatility, various areas of human knowledge. But not even the harshness of the battles could stop his intellectual production. While serving as an artillery officer, participating in those carnage that would end up frightening history itself – long seasoned in all kinds of horrors – Schwarzschild continued to generate new ideas. He took advantage of the inert times between one combat and the next to change the cannons for pencil and paper, dedicating the hours of his rest to enthusiastically analyze the theory of general relativity that his colleague Albert Einstein had just presented to the world. In late 1915, Einstein himself received a letter from the trenches; in it Schwarzschild offered him the solution to the “field equations” that Einstein, the future Nobel laureate, had not yet unraveled. death.

Schwarzschild’s latest work, developed as we see in the most unusual and harsh circumstances, offered the mathematical support on which to conceive an object whose mass was so great that its “escape velocity” was even higher than the speed of light. Being the escape velocity that which any body must reach to leave a gravitational field, Schwarzschild deduced that not even light, the fastest entity conceived by physics, could run fast enough to escape from the jaws of the hypothetical cosmic monster. A monster whose real existence, by the way, Einstein never believed. Although impressed by the implications offered by the resolution of the field equations, Einstein thought that this supposed spatial Gargantua that swallowed all light was more a beautiful abstract artifact emerged from mathematics than a star present in space. Some colleagues subscribed to his skepticism; others suspected that Einstein might be wrong. The arguments for and against the reality of the unfathomable Schwarzschild gravity wells have been going on for decades. It wasn’t until the 1960s that Irish astrophysicist Jocelyn Bell Burnell discovered the first neutron stars, raising suspicions that the monsters might be real. The American John Wheeler suggested a name, perhaps inaccurate, but undoubtedly very powerful, with which to baptize this class of voracious demons: “black holes”. Today we already know that such creatures are out there.

As can be seen, the concept of black holes seems to be something typical of the 20th century, something derived from Einsteinian physics. However, long ago, in the 18th century, an English scientist named John Michell first suggested its existence. The man who predicted the existence of black holes—in 1783!—should have enjoyed universal posthumous fame, but in addition to his scant interest in promoting his discoveries during his lifetime, the precocity of his conceptions made him pay a price of facing posterity…

John Michell was born on Christmas 1724, the same time his countryman Isaac Newton died. Michell, like Newton, was a very religious man, although it seems that little dogmatic. He worked as a professor at the University of Cambridge and during his thirteen-year stay he gave a good example of the breadth of his talent, teaching a host of subjects always at the highest level (arithmetic, theology, geometry, Greek or Hebrew), while he held other positions administration in the institution and already had the energy to obtain two advanced degrees in Art and Religious Studies. Perhaps the most important of all his academic positions at Cambridge was the chair of Geology, a discipline for which, together with the study of magnetism, he obtained his professional prestige and would be remembered in later times, at least until the scientific community understood the magnitude of his contributions in physics and astronomy. Not much is known about Michell on a personal level; not even his portraits survive, assuming he ever commissioned one. A colleague wrote a brief description which has been preserved in the archives of the British Museum: ‘John Michell is a short, dark complexioned, fat little man. Not being known to him, I can say little about him. (…) He is esteemed as a very ingenious man and an excellent philosopher [scientist]. He has published some things in that sense, about magnetism and electricity». Comments have also come down to us about his constant research activity at Cambridge; Apparently, when he was not teaching or performing administrative tasks, he shut himself up in the laboratory, where he skillfully designed apparatus to carry out experiments on the most diverse subjects. He abandoned his post at the university when he married and against the odds agreed to serve as rector of a rural Anglican church. Once living in the country he showed little interest in getting his works published—which he did very occasionally—and his only concern was to communicate each discovery to his friends by private correspondence. . This did not prevent him from enjoying fame and respect among the scientific community: he traveled to London with some regularity and befriended scholars such as Henry Cavendish, the discoverer of hydrogen, and Joseph Priestley, the discoverer of oxygen. When he did not deign to appear in the capital, it was the famous scientists who went to visit him at his house (for example, the American inventor and politician Benjamin Franklin was one of those who wanted to go and meet him). Despite his reluctance to actively cultivate any kind of fame, Michell enjoyed enormous prestige among the scientists of his time.