If you've never heard of John Michell, you're not alone. This 18th-century natural philosopher is described by some as one of the most underappreciated minds of the Scientific Revolution.
Touching on fields like geology and chemistry, Michell has, in more modern times, been given the titles of Father of both seismology and magnetometry, but his accomplishments don't stop there.
Perhaps most incredibly of all, Michell is the first person ever known to make the connection between gravity, escape velocity, and light that leads to the creation of black holes. In fact, Mitchell predicted the existence of black holes more than 130 years before Karl Schwarzschild deduced their existence using Albert Einstein's theory of General Relativity in 1916.
The Little Known Life of John Michell
There isn't much that we can actually say about John Michell's life, sadly. We know that he was born in 1724 in Eakring in Nottinghamshire. We also know that he didn't come from a well-to-do family; his father, Gilbert, was a rector, and all we know of his mother, Obedience, was that she was originally from London.
Michell entered Cambridge University in June 1742 as a pensioner, meaning that he had no scholarship to pay his way and that he was responsible for paying for his tuition, room, and board himself.
There isn't an exact record of his graduation, but he scored 4th overall on the university's mathematics examinations in early 1749 and was likely awarded a B.A. in mathematics in February of that year.
The length of time between his admission and graduation suggests he didn't spend all seven years in residence at Cambridge, which could have been a matter of financing, given his family background.
A condition of being given a fellowship at Queens' College, Cambridge, was taking holy orders in the Anglican Church, which Michell did and was ordained as a deacon in February 1749. He was then elected a Fellow of Queens' College on March 30, 1749.
John Michell's Academic Career
Michell's first major work came the following year, in a paper called "A treatise of artificial magnets," which was the first to correctly identify the inverse square law of magnetic attraction.
It also correctly identified how to measure the proper positions of magnetic poles, but his discoveries garnered little attention at the time, possibly because he did not fully describe his data or methodology in the paper.
Charles-Augustin de Coulomb is typically given credit for identifying the inverse-square law of magnetic action, even though his work was published in the 1780s. It wouldn't be the first time Michell was overlooked.
Michell received an M.A. in 1752, and later a B.D. in 1761, according to Cambridge records. This latter divinity degree was a customary requirement of maintaining a Fellowship, but it came with some perks, such as a lifetime appointment as a Rector in the church, which Michell was given in 1760, at St. Botolph's parish in Cambridge.
Michell was also elected to the Royal Society that same year, and it was from around this time that we get the only real description of Michell in the historical record, from William Cole, who wrote of him:
John Michell, BD is a little short Man, of a black Complexion, and fat; but having no Acquaintance with him, can say little of him. I think he had the Care of St Botolph’s Church, while he continued Fellow of Queen’s College, where he was esteemed a very ingenious Man, and an excellent Philosopher. He has published some Things in that way, on the Magnet and Electricity.
Also in 1760, Michell read a paper to the Royal Society on an analysis of the Lisbon earthquake of 1755. Although his theory of the cause of the quake (a steam explosion) was incorrect, he was the first person to correctly observe that earthquakes propagated as waves and he was able to estimate the location of the epicenter of the earthquake. The paper also discussed various geological strata, taken from his own personal observations, and he noted the existence of fault-lines.
Michell continued to climb the academic ladder at Cambridge for the next several years, during which time he married his first wife and had his only child, Mary. His wife died shortly after their daughter was born in September 1765.
Soon after, in 1767, Michell published what is considered to be one of his most important works, "An Inquiry into the Probable Parallax, and Magnitude of the Fixed Stars, from the Quantity of Light Which They Afford us, and the Particular Circumstances of Their Situation."
In it, Michell points out how many stars appear to have the same luminosity as the planet Saturn, whose rough distance away was known, owing to the initial calculations of the solar parallax made during the Transit of Venus in 1761.
With this information, Michell set out to figure out how far away a star would need to be to appear as bright as Saturn. This was the first real attempt to calculate the distance of the stars in the sky, and his calculation was only off by a factor of 4, which for the time is an incredible feat.
In the second part of this paper, Michell took the then-novel approach of applying statistical analysis to the question of whether double-star or multiple-star systems that had been observed by astronomers were indeed physically close together or just looked that way due to the effect of parallax.
Michell showed that the odds of all the stars in the sky being single star systems was so remote as to be dismissable. He also predicted that there would be many more multi-star systems in the sky than had even been observed up to that point, based on his calculations.
This predated William Herschel's publication of observations of binary star systems by more than a decade and, while Herschel's work was important in its own right, his publications of actual binary star observations has also entirely overshadowed Michell's earlier work.
But Michell's most incredible prediction, one that would languish unacknowledged for more than a century, was still to come.
Newton's Laws of Gravitation
When Isaac Newton published his Naturalis Principia Mathematica in 1687, it literally set off a revolution in the study of astronomy, as well as many other physical sciences.
Classical mechanics stood for just over two centuries as the dominant model for the order of the universe until Einstein's Relativity supplanted it in 1916, and even then, not entirely.
One of the basic discoveries of Newton was that an object's gravitational pull was directly tied to its mass, and that this measure of gravitational pull could be expressed in terms of known measures of speed (e.g. meters per second).
Specifically, Newton discovered that the gravitational pull of an object like the Earth could be expressed as an escape velocity, which a second object, like a cannonball, would have to achieve in order to escape its gravitational pull.
By 1676, the question of the speed of light had been sufficiently settled by the work of Ole Rømer, who made the first quantitative measurements of the speed of light. He demonstrated that light propagated at a finite, measurable speed, then calculated as 131,000 miles per second (the true speed is 186,000 miles per second, but Rømer was working with imperfect data when making his calculation (131,000 mi/s = 210,800 km/s and 186,000 mi = ~300,000 km/s)).
Given what was known at the time, it's somewhat surprising that it would take as long as it did before someone made the connection between the speed of light and the escape velocity of a sufficiently massive object in space. But when that connection was made, it wasn't made by Einstein or Schwarzschild, but rather the lowly country rector, Michell, in 1787.
Coming up in the generation after the death of Newton, John Michell and his contemporaries were more immersed in the great genius's work than anyone.
Newton gave the world an entirely new way to make sense of the universe, so a lot of scientists of the era were understandably looking for areas where they could apply this new understanding and make new discoveries.
Michell, for his part, was interested in knowing whether you could use the light from a star to determine its mass. He was particularly interested in Newton's corpuscular theory of light, the idea that light was composed of corpuscles ("little particles") traveling at a finite speed and that had momentum.
This latter feature implied that light should be affected by the gravitational pull of an object as readily as a planet, which Michell thought he could use to devise a way to calculate a star's mass by measuring how much it slowed the light emanating from it.
Mitchell explored this idea in his paper, "On the Means of discovering the Distance, Magnitude, &c. of the Fixed Stars, in consequence of the Diminution of the Velocity of their Light", which was read to the Royal Society in 1783.
And while the idea that a sufficiently massive star slows light down isn't accurate (more on that in a bit), a more radical implication of his idea turns out to be far more prescient.
In his paper, Michell described a body whose mass was so great, and thus its gravitational pull was so extreme, that its escape velocity exceeded the speed of light itself.
"If the semi-diameter of a sphere of the same density as the Sun in the proportion of five hundred to one," Michell wrote, "and by supposing light to be attracted by the same force in proportion to its [mass] with other bodies, all light emitted from such a body would be made to return towards it, by its own proper gravity."
Michell realized that such a "dark star" (Michell never actually names the object he was describing, the term "dark star" would be applied to it by later writers), would be impossible for any astronomer to see directly since the light it emitted could never escape its gravitational pull.
If all of this sounds familiar, it's because Michell is talking about the defining feature of a black hole.
Even more remarkably, Michell went on to describe how astronomers might be able to detect such objects in space by looking for single stars that behaved as if they were part of a binary star system.
"If any other luminous bodies should happen to revolve about them," Michell wrote, "we might still perhaps from the motions of these revolving bodies infer the existence of the central ones with some degree of probability, as this might afford a clue to some of the apparent irregularities of the revolving bodies, which would not be easily explicable on any other hypothesis."
This prediction also proved to be far ahead of its time, as this remains a key technique astronomers use when they go looking for black holes today.
Why didn't Dark Stars catch on?
While John Michell might have accurately predicted black holes, the means he used to get there would prove detrimental. Newton's corpuscular theory of light was displaced by the wave theory of light, proposed by Dutch physicist Christiaan Huygens in 1799, which held that light did not interact with a gravitational field.
A dark star can't exist if light doesn't interact with a gravitational field, so had Michell's work had gotten any real attention by the 19th century, he would have been written off.
By then, however, a French astronomer named Pierre-Simon de Laplace had also published a theory about such "invisible stars" in 1796, also based on the classical mechanics of Newton.
As a particularly prestigious astronomer in France, his work would overshadow Michell's, no surprise, but at least when people rejected the idea of dark stars, they dismissed Laplace's work instead.
Michell's work also suffered from his disinterest in promoting it or defending his claims to the discoveries he did make. The history of science is a shockingly nasty business full of bitter feuds and rivalries.
Most of these sprang directly from competing claims of first discovery, so one might be forgiving of Michell's disinterest in picking fights with fellow scientists. Still, history remembers the victors of those fights and tends to forget those who choose not to fight at all.
John Michell's Dark Star Vindicated?
The wave theory of light might have put a damper on dark stars during the 19th century, but Einstein upended all of that when he published his work on General Relativity.
The discovery that gravity wasn't a force but rather a result of matter and energy interacting with the curvature in the fabric of spacetime created by mass was revolutionary for a lot of reasons, one being that it put an end to the wave theory of light.
The speed of light might be constant regardless of a gravitational field, but it is still absolutely affected by the curvature of spacetime.
And Swartzchild deduced in 1916 that if an object of extreme density curved spacetime enough, then the escape velocity needed to climb out of its gravity well could exceed the speed of light. So, even if light is traveling at a constant speed, the space around these black holes would still bend that light inward, drawing it down like water circling a drain.
While Schwarzschild is credited with first describing a black hole, he effectively came to the same natural conclusion that Michell had come to more than a century earlier, but using the more accurate model of the universe provided by General Relativity.
Michell's dark star does differ from Schwarzschild's black holes in one key way, however. Whereas black holes are massive objects compressed to an infinitely dense point, Michell's dark stars are incredibly large — about 500 times the mass of the sun or greater, assuming they both have the same average density.
No such star is known to exist, and even if it did, it still would not develop an event horizon that would trap light forever. In order to form an event horizon, a mass would have to be compressed below what is called the Schwarzschild radius, which isn't a feature of Michell's dark stars as he described them.
Ultimately, the dark stars Michell described could only exist if Newton's theories were accurate, which they ultimately were not, but Michell's reasoning is still sound.
More recently, the idea of a "dark star" has seen something of a revival. Some physicists argue that the idea of a singularity at the center of a black hole — a place where its density, and thus the curvature of spacetime around it, becomes infinite — is impossible.
Instead, they believe that matter in a black hole is compressed to a "Planck core", named for the Planck length, which is thought to be the smallest measurable unit of length possible.
In this model of a singularity-less black hole, the entire mass of a star might be compressed to about a trillionth of the size of a proton, but this still gives you a measurable density, not an infinite one.
This model, then, implies that there is a mathematical "bottom" to a black hole, and at the center of it sits a dark star. Since we know of no way to peek behind an event horizon of a black hole (or a dark star, if that be the case), we'll probably never have a definitive answer either way.
While this isn't exactly what John Michell was proposing in 1783, it isn't all that different either. Instead of mass and corpuscles, you're dealing with density and curvature to come to the same practical condition of an escape velocity that exceeds the speed of light.
For this, John Michell is starting to receive some recognition for his work. His work was rediscovered in the 1970s and now he is much more widely credited as the first to anticipate the existence of black holes, and is more widely considered one of the great minds of the 18th century.
"When John Michell conceived of black holes in 1783, very few scientists in the world were mentally equipped to understand what he was talking about," the American Museum of Natural History wrote as part of its Cosmic Horizons collection.
Similarly, the American Physical Society wrote that John Michell was "a man so far ahead of his scientific contemporaries that his ideas languished in obscurity, until they were re-invented more than a century later."
Michell was also recognized by his peers as a brilliant scientist during his life, and while he left Cambridge in 1767 to take up full-time duties as the rector of a parish in Yorkshire in the north of England, he continued his scientific studies and was visited regularly by some of the preeminent scientists of the age, like Joseph Priestly, Henry Cavendish, and even Benjamin Franklin.
Michell died on April 21, 1793, and though his friends and parishioners recognized the genius he possessed, it would take more than a century before the rest of the world managed to catch up.