Cosmic pluralism, the plurality of worlds, or simply pluralism, describes the philosophical belief in numerous “worlds” in addition to Earth (possibly an infinite number), which may harbour extraterrestrial life.  

(from Wikipedia article “Cosmic Pluralism“)

In my criticism of Adamson’s initial argument for the existence of God, I pointed out that cosmic pluralism is an idea that has been around since the beginning of Western philosophy about 2,500 years ago (the pre-socratic philosopher Anaxagorus advocated cosmic pluralism, for example), and that cosmic pluralism was advocated in Europe more recently by Giordano Bruno, about 430 years ago.

Furthermore, cosmic pluralism was a view held by many of the leading philosophers that are usually covered in introductions to philosophy and in history of western philosophy courses: Gottfried Leibniz, Rene Descartes, George Berkeley, John Locke, and Immanuel Kant.

Some of the founding fathers of our nation were cosmic pluralists: Thomas Paine, John Adams, Benjamin Franklin, and probably Thomas Jefferson too.  In his Almanack of 1749, Benjamin Franklin wrote:

It is the opionion of all the modern philosophers and mathematicians, that the planets are all habitable worlds.  If so, what sort of constitutions must those people have who live on the planet Mercury? where, says Sir Isaac Newton, the heat of the sun is seven times as great as it is with us; and would make our water boil away.  (III, p.345)  

(quoted in The Extraterrestrial Life Debate, 1750-1900, by Michael Crowe, p.108)

I previously pointed out that science fiction books, stories, movies, and television programs often assume the truth of cosmic pluralism, so even if Adamson was completely ignorant of the history of philosophy and ignorant about the cosmological beliefs of our founding fathers, she ought to have been aware of the idea of cosmic pluralism from science fiction books or movies or television shows.

One might object, at this point, that cosmic pluralism is a matter of speculation.  Anaxagorus was not a scientist, at least not in the modern sense.  He did not use a telescope to observe the planets in our solar system or the stars in our galaxy.  Bruno was not a scientist; he was a philosopher and theologian.  Bruno arrived at his theory of the universe based on abstract philosophical and theological reasoning, not on the basis of empirical science, not on the basis of careful observations and measurements, not on the basis of experiments.  Science-fiction stories and movies might well assume the truth of cosmic pluralism, but that doesn’t mean that we ought to believe that cosmic pluralism is true; fiction can be based on false or unproven assumptions.

It is true that Bruno was not a scientist; however, it is quite possible that he was influenced to adopt cosmic pluralism and the view that the universe was infinite by the English mathematician and astronomer Thomas Digges:

Bruno is often credited with recognizing that the Copernican system allowed an infinite Universe. In truth, the idea that a heliocentric description of the solar system allowed (or at least did not rule out) an infinite Universe was first proposed by Thomas Digges in 1576 in his A Perfit Description of the Caelestial Orbes, in which Digges both presents and extends the Copernican system, suggesting that the Universe was infinite. Nor is the idea of an infinite heavens original to Digges, as there are numerous historical antecedents, specifically Nicholas of Cusa in the 15th Century and atomist Lucretius in the 1st century BC (both of whom Bruno reference, if not always consistently). Bruno’s two works most fully expounding his views of the universe, The Ash Wednesday Supper and On the Infinite Universe and Worlds, were published in 1584, 8 years after Digges, and during the period of Bruno’s exile in England. While we have no record of Digges and Bruno having met, Digges’ work was widely discussed and Bruno would likely have come into contact with the ideas if not the man himself as he spent time within the intellectual circle of Elizabethan England.

(from: “The Folly of Giordano Bruno”, by Richard W. Pogge)

So, the idea of cosmic pluralism might well have come to Bruno from the reflections of the mathematician and astronomer Thomas Digges on Copernicus’s heliocentric theory.

Furthermore, Bruno was burned at the stake (by the brilliant Christian leaders of the Roman Inquisition) in 1600, and just ten years later Galileo published the first scientific work of astronomy based on observations made with a telescope: Sidereal Messenger (or Sidereal Message).  In that publication, Galileo reported that he was able to see many more stars with his telescope than what others had been able to observe with the naked eye:

Galileo reported that he saw at least ten times more stars through the telescope than are visible to the naked eye, and he published star charts of the belt of Orion and the star cluster Pleiades showing some of the newly observed stars. With the naked eye observers could see only six stars in the Taurus constellation; through his telescope, however, Galileo was capable of seeing thirty-five – almost six times as many. When he turned his telescope on Orion, he was capable of seeing eighty stars, rather than the previously observed nine – almost nine times more. … Also, when he observed some of the “nebulous” stars in the Ptolemaic star catalogue, he saw that rather than being cloudy, they were made of many small stars. From this he deduced that the nebulae and the Milky Way were “congeries of innumerable stars grouped together in clusters” too small and distant to be resolved into individual stars by the naked eye.  

(from Wikipedia article “Sidereus Nuncius”)

Galileo’s observations did not prove that the universe was infinite or filled with billions of planets orbiting around billions of stars, but they did show that there were many more stars than what had previously been thought, and that there might well be “innumerable stars” in the nebulae and the Milky Way.  So, Galileo provided emprical evidence that was supportive of Bruno’s view of the universe.

In 1750, the English astronomer and mathematician Thomas Wright published a book which suggested that observed faint nebulae indicate that the universe includes far distant galaxies:

Wright is best known for his publication An original theory or new hypothesis of the Universe(1750), in which he explains the appearance of the Milky Way as “an optical effect due to our immersion in what locally approximates to a flat layer of stars.” This idea was taken up and elaborated by Immanuel Kant in his Universal Natural History and Theory of Heaven.  Another of Thomas Wright’s ideas, which is also often attributed to Kant, was that many faint nebulae are actually incredibly distant galaxies. (from Wikipedia article “Thomas Wright”)

Wright also suggested that the Milky Way galaxy “might be a rotating body of a huge number of stars held together by gravitational forces, akin to the Solar System but on a much larger scale.” (from Wikipedia article “Galaxy”).

As astronomy continued to advance, the population of the universe continued to grow:

Toward the end of the 18th century, Charles Messier compiled a catalog containing the 109 brightest celestial objects having nebulous appearance. Subsequently, William Herschel assembled a catalog of 5,000 nebulae.

(from Wikipedia article “Galaxy”).

I found a copy of an astronomy textbook published near the end of the 19th century, and it gives an estimate of the number of stars that were observable at that time with the telescopes that were then available:

Number of the Stars. –Besides twenty stars of the first magnitude, not only are there nearly six thousand of lesser magnitude visible to the naked eye, likewise many hundreds of thousands visible in telescopes of medium size, but also millions of stars revealed by the largest telescopes. …

… But in order to discern all the uncounted millions of yet fainter stars, we need the largest instruments, like the Lick and the Yerkes telescopes. Their approximate number has been ascertained not by actual count, but by estimates based on counts of typical areas scattered in different parts of the heavens. The number of stars within reach of our present telescopes perhaps exceeds 125 millions. … (A New Astronomy, p. 368-369, by David Todd, M.A., PH.D. Professor of Astronomy and Navigation and Director of the Observatory, Amherst College. Copyright, 1897 and 1906.)

So, at the beginning of the 20th century, astronomers were able to observe over 100 million stars by means of modern telescopes.  This did not show that the universe was infinite like Bruno had claimed, but scientific astronomy had established that there was an incredible number of stars in the universe, thus providing significant empirical support for cosmic pluralism.

In 1920, there was the “Great Debate” in astronomy over whether the universe includes far distant galaxies beyond out own galaxy (as Thomas Wright had proposed back in 1750):

In astronomy, the Great Debate, also called the Shapley–Curtis Debate, was an influential debate between the astronomers Harlow Shapley and Heber Curtis which concerned the nature of so-called spiral nebulae and the size of the universe. The basic issue under debate was whether distant nebulae were relatively small and lay within the outskirts of our home galaxy or whether they were in fact independent galaxies, implying that they were exceedingly large and distant. The debate took place on 26 April 1920, in the Baird auditorium of the Smithsonian Museum of Natural History.  …

Shapley was arguing in favor of the Milky Way as the entirety of the universe. He believed that “spiral nebulae” such as Andromeda were simply part of the Milky Way. He could back up this claim by citing relative sizes—if Andromeda were not part of the Milky Way, then its distance must have been on the order of 10⁸ light years—a span most astronomers would not accept. …

Curtis on the other side contended that Andromeda and other such “nebulae” were separate galaxies, or “island universes” (a term invented by the 18th-century philosopher Immanuel Kant, who also believed that the “spiral nebulae” were extragalactic). He showed that there were more novae in Andromeda than in the Milky Way. From this he could ask why there were more novae in one small section of the galaxy than the other sections of the galaxy, if Andromeda was not a separate galaxy but simply a nebula within our galaxy. …

(from the Wikipedia article “Great Debate (astronomy)”)

In 1925, the astronomer Edwin Hubble presented a scientific paper that provided powerful evidence supporting Curtis’ view that the universe included far distant galaxies:

Due to the work of Edwin Hubble, it is now known that the Milky Way is only one of as many as an estimated 200 billion galaxies in the observable universe, proving Curtis the more accurate party in the debate.  

(from the Wikipedia article “Great Debate (astronomy)”)

Edwin Hubble’s arrival at Mount Wilson Observatory, California in 1919 coincided roughly with the completion of the 100-inch (2.5 m) Hooker Telescope, then the world’s largest. At that time, the prevailing view of the cosmos was that the universe consisted entirely of the Milky Way Galaxy. Using the Hooker Telescope at Mt. Wilson, Hubble identified Cepheid variables (a kind of star that is used as a means to determine the distance from the galaxy… in several spiral nebulae, including the Andromeda Nebula and Triangulum. His observations, made in 1922–1923, proved conclusively that these nebulae were much too distant to be part of the Milky Way and were, in fact, entire galaxies outside our own, suspected by researchers at least as early as 1755 when Immanuel Kant’s General History of Nature and Theory of the Heavens appeared. This idea had been opposed by many in the astronomy establishment of the time, in particular by the Harvard University-based Harlow Shapley. Despite the opposition, Hubble, then a thirty-five-year-old scientist, had his findings first published in The New York Times on November 23, 1924, and then more formally presented in the form of a paper at the January 1, 1925 meeting of the American Astronomical Society.

(from the Wikipedia article “Edwin Hubble”)

Thus, in the 1920s the astronomers Heber Curtis and Edwin Hubble showed us that the universe was much larger than most other astronomers supposed and that the universe contained a fantastically huge number of stars, well beyond the 125 million stars that were observable at the beginning of the 20th century.

To be continued…