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The Cosmos of Giordano Bruno

Here is the fascinating exchange between Corey S. Powell, writer for Discover magazine and Steve Soter, co-writer of the new Cosmos series, on the contribution of 16th century monk, Giordano Bruno, to cosmology and the inclusion of his story in the opening episode of Cosmos.

March 15, 2014

Steven Soter
Co-writer, COSMOS: A Spacetime Odyssey
Astrophysics Department, American Museum of Natural History, NY (

Your suggestion (below) that Giordano Bruno was not the first to realize that the stars are suns is mistaken. You cited his predecessor Nicolas of Cusa, who referred in one passage to "the earth, the sun, or another star". But Cusa did not mean that the sun is another star as we understand the term. Throughout his book, he used the word "star" indifferently to refer to the earth, the moon, the sun and the planets, as was common in his time. He also distinguished them from the "fixed stars" on the surface of the eighth celestial sphere. His pre-Copernican conception of the solar system was antithetical to any notion of the stars as other suns.

You claimed that "Cosmos confusingly presents Bruno's infinite cosmology as a physical theory of the universe", because Bruno believed the planets and stars had souls. It is true that Bruno's worldview was vitalistic and magical. He imagined that the Earth had a soul like the other planets. But he passionately believed in the physical reality of the planets and suns, all made of the material elements familiar in his time. He wrote:

" . . . every one of those bodies, stars, worlds and eternal lights is composed of that which is named earth, water, air and fire . . . Those in whose composition fire predominates will be called sun, bright in itself. If water predominates, we give the name telluric body, moon or such like which shines by borrowed light . . ." Bruno was the first to recognize this fundamental distinction between stars and planets.

Bruno described a universe of "innumerable globes like this one on which we live and grow . . . In it are an infinity of worlds similar to our own, and of the same kind." He urged his readers to "dissolve the notion that our earth is unique . . . [so that] we may perceive the likeness of our own and of all other stars . . . the substance of the other worlds throughout the ether is even as that of our own world." Bruno made it as clear as he could, using the rudimentary understanding of matter available in his time, that this was a physical theory of the universe.

You said that Bruno took "a big step backward by interpreting the universe more in theological than mathematical terms." Bruno was neither a mathematician nor a scientist, and his mind was not modern by any means. But he was without doubt the first to imagine a universe resembling the one we know today.

Again, you claimed that Bruno's cosmology "was not a correct scientific idea, nor was it even a guess as Cosmos asserts. It was a religious and philosophical statement." However you characterize Bruno's cosmology has no bearing on its essential correctness. Can we expect a philosopher living in a world steeped in mysticism, groping in the dark at the dawn of modern science, to see things in modern terms? Scattered among his many pages of metaphysical nonsense are nuggets of pure gold. We should be grateful for them and not expect more.

Finally you claimed that Thomas Digges, "far more than Bruno, built on the tradition of Copernicus and sought to bring more of the universe into the grasp of math and geometry." Digges made a major contribution by extending the realm of the stars into infinite space, but he described it as "the palace of felicity . . . the very court of celestial angels, devoid of grief and replenished with perfect endless joy." He is talking about the traditional theological heaven, not the material universe. It was Bruno who used the opening made by Copernicus to give us the first glimpse of the modern astrophysical cosmos. And that was no incremental step. It was a giant leap.


March 14, 2013

Corey S. Powell
Writer for Discover magazine(

My recent post questioning the Giordano Bruno segment in the first episode of the new Cosmos has attracted a gratifying amount of attention, both on this site and elsewhere around the web. It has also prompted a heartfelt reply from Steven Soter, a resident research associate at the American Museum of Natural history and co-writer (along with Ann Druyan) of Cosmos.

It is very much in the spirit of Cosmos, and of the scientific process in general, to engage in debate in the search for deeper truths. It is also a powerful tribute to the new series that so many people are now discussing Bruno, Thomas Digges, and the intertwined relationship of science and religion during the early Copernican era. In that spirit, I am pleased to respond here to Soter's contribution below; he in turn, will soon provide some additional closing thoughts.

Corey S. Powell responds:

This may sound strange, but I'm going to start by disagreeing about some of what we disagree about.

You say: The fact that Bruno was a mystic and a difficult person does not discredit his ideas. I completely agree with this, and never argued otherwise. You say: Bruno got his idea of infinite space from Lucretius and the idea of an infinite God from Nicolas of Cusa. I agree on these points as well. The treatment of Bruno's reading of Lucretius is handled beautifully in Cosmos.

Here are the two main areas where I think the Cosmos episode went awry.

First, the depiction of Bruno as a lone wolf (" ... for one man, Copernicus did not go far enough ...") is historically inaccurate and -- more important, to my mind -- it misrepresents the collaborative and cumulative way that science operates. As I noted, the notion of infinite space beyond our solar system originated with Thomas Digges, whom Bruno undoubted read and may have met during his time in England. Even the idea that other stars are suns has possible precedent a century earlier in the work of Nicolas of Cusa, who wrote this remarkable passage [with the emphasis mine]:

... it would always seem to each person (whether he were on the earth, the sun, or another star ) that he was at the "immovable" center, so to speak, and that all other things were moved ... if he were on the sun, he would fix a set of poles in relation to himself; if on the earth, another; on the moon, another; on Mars, another; and so on.

Second, Cosmos confusingly depicts Bruno's infinite cosmology as a physical theory of the universe (in praise of God, yes, but physical all the same). Reading Bruno's most relevant works -- On the Infinite Universe and Worlds and The Ash Wednesday Supper -- is eye-opening. Thank you for inspiring me to do it. Bruno's vision of an infinite space, containing infinite populated worlds, is thrilling and beautiful. Interpreting it primarily in physical terms is anachronistic, however.

Bruno imagines all planets and stars having souls (part of what he means by them all having the same "composition"), and he uses his cosmology as a tool for advancing an animist or Pandeist theology. See historian Stanley Jaki's translation of Ash Wednesday, with highly critical commentary.

True, Bruno takes a big step forward from Copernicus in speaking explicitly about the infinite, and about the existence of other planets and suns; but he takes a big step backward by interpreting the universe more in theological than mathematical terms. You justly write, "It does not matter in the least where correct scientific ideas come from," but my point is that Bruno's cosmology was not a correct scientific idea, nor was it even a "guess" as Cosmos asserts. It was a religious and philosophical statement, one that sparked a great deal of stimulating debate in the 17th century but not one that advanced the broader cause of rationalism.

That is why I say that religion, not science, caused Bruno's deadly clash with the Church. And that is why I spoke up on behalf of the forgotten British astronomer Thomas Digges. Digges, far more than Bruno, built on the tradition of Copernicus and sought to bring more of the universe into the grasp of math and geometry; far more than Bruno, he sought to create a whole community of Copernicans who could keep that process going. Digges at least banished the angels to the distant, starry realm. Interestingly, he was also the first to consider how the night sky can be dark in an infinite universe (a question now known as Olbers' Paradox).

Back to where we agree: "Freedom of thought is the life blood of science." I admire the way Cosmos tells this aspect of the Bruno story, and just to be clear, I greatly admire the entire Cosmos project, which is why I am being so critical here.

I just wish that, with this rare opportunity to present the history of science to a broad audience, Cosmos could have gone further in showing Bruno not just as a victim of the "thought police" but as a complex, inspired, paradoxical participant in the grand struggle to create our modern view of the universe.


March 13, 2014

Steven Soter
Co-writer, COSMOS: A Spacetime Odyssey
Astrophysics Department, American Museum of Natural History, NY (

  Corey S. Powell, writing for Discover magazine, takes the new Cosmos series to task for telling the story of Giordano Bruno in the opening episode. Bruno was burned at the stake in Rome in 1600 for various heresies, including his belief in other worlds.

Powell's critique dwells on the well-known facts that Bruno was a mystic and an extremely difficult person. Well, so was Isaac Newton, who devoted as much time to alchemy and biblical numerology as to physics. But that has no bearing whatever on the value of his good ideas.

Powell writes that the new Cosmos is "downright wrong" because "Bruno was not the first to link the idea of infinite space with the infinite glory of God." But the script never says that. Bruno got the idea of infinite space from Lucretius, but he also read Nicolas of Cusa, who related the concept to an infinite God.

Bruno's originality lay elsewhere. He was indisputably the first person to grasp that the Sun is a star and the stars are other suns with their own planets. That is arguably the greatest idea in the history of astronomy. Before Bruno, none of the other Copernicans ever imagined it.

Powell suggests that Cosmos should have featured the English astronomer Thomas Digges instead of Bruno. The great contribution of Digges was to realize that the Copernican system allowed the stars to extend out to infinite distances, because they no longer had to make a daily revolution around the Earth. But Digges regarded the stars as "the court of the celestial angels", not as the suns of other material earths. And that was a big step backward. In contrast, Bruno wrote, "the composition of our own star and world is the same as that of as many other stars and worlds as we can see." His profound intuition had to wait three centuries to be verified by the spectroscope.

Powell writes that neither Kepler nor Galileo thought much of Bruno. It is true that Kepler recoiled from Bruno's infinite universe of worlds and found it frightful, but his reasoning was based in part on a mystical obsession. He rejected the existence of any planets beyond the six allowed by his notion of a perfect Pythagorean solar system. The naming of the Kepler space telescope, dedicated to the discovery of planets around other stars, is perhaps somewhat ironic.

Here is what Kepler wrote (in De Stella Nova, 1604) about Bruno's infinite universe: "This very cogitation carries with it I don't know what secret hidden horror . . . Well, let us seek the remedy in Astronomy herself, so that by her arts and soothing blandishments this madness of the philosophers . . . might be led back within the bounds of the world and its prisons. Surely, it is not good to wander through that infinity." Kepler was a very great man, but not for this.

While Kepler rejected an infinite universe, he was a good enough scientist to recognize that Galileo's discoveries with the telescope lent support to some of Bruno's ideas. Writing to Galileo in 1610, Kepler was impressed by the observation that stars seen through the telescope still sparkled, in contrast to the circular appearance of planets. He asked:

"What other conclusion shall we draw from this difference, Galileo, than that the fixed stars generate their light from within, whereas the planets, being opaque, are illuminated from without; that is, to use Bruno's terms, the former are suns, the latter, moons, or earths?"

Galileo never once mentioned Bruno's name. Of course in the land of the Inquisition he had good reason. But in his Dialogue on the Two Chief World Systems (the book that got him into deep trouble), he discretely accepted Bruno's greatest idea, writing that the fixed stars are other suns.

It does not matter in the least where correct scientific ideas come from. Once out there, they can be tested. The important thing is not to suppress ideas. Freedom of thought is the life blood of science. That's why Bruno's story is important.