What Giordano Bruno did (not) say

I have recently come across the following quote, which is attributed to Giordano Bruno (1548–1600):

In space there are countless constellations, suns and planets; we see only the suns because they give light; the planets remain invisible, for they are small and dark. There are also numberless earths circling around their suns, no worse and no less than this globe of ours.

Isn’t it fantastic? In a time when the prevailing opinion was still that the Earth was at the center of the Universe, and where people—including Giordano Bruno himself—were burned at the stake for daring to challenge this view, Bruno predicted the existence of exoplanets.

Of course, what happened next is that I got curious and inevitably fell into a rabbit hole trying to find the original source of this quote. (This is far from the first time something like this happens to me.) This post is a collection of the things that I managed to dig up.

If I recall correctly, the story began on the Wikipedia page about exoplanets, which in the subsection on early speculations cites Giordano Bruno as:

This space we declare to be infinite… In it are an infinity of worlds of the same kind as our own.

The source that is given for this is Maor (1987); see below for the full reference. Following the archive.org link in the source proves that this book does indeed contain this quote and names Bruno’s 1584 book De l’infinito universo et mondi as the original source.

What happened next is that I googled this quote, hoping to find the original Italian version. Instead, however, I ended up the Wikiquote page for “planet”, which contains precisely the first quote above. There, the source that is given is Rees (2000). I managed to get my hands on this this book to check it, and it does indeed contain this very quote (albeit on page 19). Unfortunately, however, the author does not give a source for it; he merely prefaces the quote with “The concept of a ‘plurality of inhabited worlds’ is still the province of speculative thinkers, as it has been through the ages. The year 2000 marks the fourth centenary of the death of Giordano Bruno, burnt at the stake in Rome. He believed that: (…)”.

The Wikiquote page for Giordano Bruno seemed like a logical next stop, and indeed, it contains a very similar quote to the one in question:

There are countless suns and countless earths all rotating round their suns in exactly the same way as the seven planets of our system. We see only the suns because they are the largest bodies and are luminous, but their planets remain invisible to us because they are smaller and non-luminous. The countless worlds in the universe are no worse and no less inhabited than our earth.

Wikiquote states that the quote is taken from Bettex (1965), which luckily is available again through archive.org, and indeed the quote can be found on page 341f. However, there is again no sign of a source to be found. This is when my bullshit detector started to go off.

It was time to check for myself what Bruno did or did not write. The most reasonable place to start seemed to be his 1584 book On the Infinity of the Universe and the Worlds, because that is the one thing that kept popping up everywhere as I was googling around for the source of the quote. I must say that for a book that is over 400 years old, it is surprisingly hard to get the full original text! Here is one version that I managed to find. In case your renaissance-age Italian, like mine, is a bit rusty, there is also an English translation available here.

Simply searching for the full quote does not yield any results, but that is not surprising. Instead, it seems more promising to search for phrases from the quote that will not vary much in different translations or versions; for example, “constellation” (or “costellazione”) or “dark” (or “obscur*”) seem like good candidates to start with.

The relevant parts are then found in Dialogo terzo (third dialogue). There, Elpino says:

Sono dumque soli innumerabili, sono terre infinite che similmente circuiscono que’ soli; come veggiamo questi sette circuire questo sole a noi vicino.

There are then innumerable suns, and an infinite number of earths revolve around those suns, just as the seven¹ we can observe revolve around this sun which is close to us.

Three lines further in the text, Philotheo continues:

La raggione è, perché noi veggiamo gli soli, che son gli più grandi, anzi grandissimi corpi: ma non veggiamo le terre, le quali per esserno corpi molto minori, sono invisibili.

The reason is that we discern only the largest suns, immense bodies. But we do not discern the earths because, being much smaller, they are invisible to us.

The final piece is the exchance between Burchio and Fracastorio:

Cossì dumque gli altri mondi sono abitati come questo? — Se non cossì e se non megliori, niente meno e niente peggio.

Then the other worlds are inhabited like our own? — If not exactly as our own, and if not more nobly, at least no less inhabited and no less nobly.

After spending more time than I care to admit on this whole exercise, I think the bottom line of is that the quote(s) are not exactly made up, but also not a particularly verbatim rendition of what Giordano Bruno wrote. Instead, it seems more like a deliberately more pointed rewording of the original. Well, either that, or they are taken from some other work of Bruno that nobody ever cared to cite as the source. If that is the case, and you know more, please don’t hesitate to get in touch.

References

Note: I have decided not to unify the cite style of the reference but to keep everything in its original format.

• Eli Maor (1987). “Chapter 24: The New Cosmology”. To Infinity and Beyond: A Cultural History of the Infinite. Originally in De l’infinito universo et mondi [On the Infinite Universe and Worlds] by Giordano Bruno (1584). Boston, MA: Birkhäuser. p. 198.
• Martin J. Rees: Just Six Numbers: The Deep Forces that Shape the Universe, Basic Books, 2000, p. 22.
• The Discovery of Nature (1965), by Albert W. Bettex