In 1584 Giordano Bruno, a Dominican monk, published a book, On the Infinite Universe and Worlds Bruno enjoyed a peripatetic European existence. But in 1592 he imprudently returned to Italy – lured, it is thought, by the hope of a professorship at Padua, which instead went to the young Galileo – and fell into the clutches of the Inquisition. He was imprisoned in Rome for his “obstinate and pertinacious heresies”. In February 1600 he was burnt at the stake in the Campo dei Fiori, Rome, where he is now commemorated by a fine bronze statue.Among Bruno’s conjectures was that: “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.” In the last years of the 20th century, his prescient belief was vindicated: there are, assuredly, planetary systems around many other stars.
We now know that our Solar System is just one planetary system among millions. But our Earth, with its intricate biosphere, may still be special: most planets may well be hostile to life.Cosmologists now have a far bolder conjecture – one that is perhaps still as speculative today as Bruno’s thoughts about “other worlds” were 400 years ago.

Some of us suspect that our entire universe, stretching 10 billion light years in all directions, may not be everything there is – there may have been an infinity of Big Bangs, not just the one that led to what we traditionally call “our universe”.Bruno believed that other planets may harbour life – alien creatures fully as advanced as those on Earth. On this issue, we are still in the realm of conjecture: we know too little about life and its origins to be able to say whether advanced life is widespread, or whether (at the other extreme) it in fact exists nowhere else within our galaxy.Nonetheless, it is interesting to speculate on how we could bridge the “culture gap” with aliens if we ever detected signals from them One thing we’d share would be our “cosmic habitat”. We’d all be made of similar atoms; the atoms that make up other stars and planets are governed by the same laws as those here on Earth. If they had eyes, the aliens would gaze out on the same panorama of stars and galaxies as we do.

We’d all trace our origins back to the same “genesis event” – the so-called Big Bang. We’d all share the potentialities of a (perhaps infinite) future.But we are coming to realise that a universe that could harbour any kind of life – what one might call a “biophilic” universe – must be rather special. This realisation triggers some fascinating speculations.We are the outcome of time and chance – 12 billion years of time, and an immensely long chain of “accidents”. The size and shape of our home galaxy are the outcome of quantum fluctuations imprinted when the universe was the size of a golfball.

The gases that ended up in our Sun, a typical star, had been, for billions of years, churned up by the swirling motions within the spiral galaxy – the Milky Way – in which we live, and buffeted by supernova explosions. Our Earth (along with the other inner planets, Mercury, Venus and Mars) is an agglomeration of rocks and asteroids that crashed together soon after the Sun formed; the largest crash scooped out enough molten rock to make the Moon.The Earth’s surface has been moulded by continental drift, by volcanism and by further impacts. These and other terrestrial contingencies have controlled the topography and climate, and determined the emergence and extinction of species. On a more parochial scale, each of us is the outcome of time and chance – the key events in the lives of all our ancestors.