The Copernicus Complex by Caleb Scharf review – a cosmic quest

The Copernican principle changed everything. It was not formulated by Copernicus, who in 1543 proposed only that the Earth was not the centre of the universe, and that the motion of the Earth around the sun could explain the irregularities in the heavens. At the time, ideas like that could get people condemned to the stake. But it was the start of a revolution. The modern working hypothesis known as the Copernican principle states that there is nothing special about our planet, our solar system, our galaxy, our place in the universe.

Nor is there anything special about now. The laws of physics have not changed in 13.8bn years. In some unimaginable cosmic future, the speed of light in a vacuum will be the same, and the mechanics of waves – water, seismic and light – will be as they were in the beginning. The properties of hydrogen and helium are the same, and the gravitational forces that shaped the solar system would be no different in Andromeda, or the Orion Nebula. The peculiar ways that different atoms and molecules absorb and radiate light at predictable wavelengths are the same in the corona of the sun as in intergalactic space 1bn light years away.

This assumption of cosmic mediocrity has had consequences for which words such as "marvellous" and "awesome" are understatements. You can analyse light from a galaxy on the edge of the visible universe and calculate that it is accelerating away from us. So are all the faraway galaxies. If they are rushing away, then they must have once been very close together, in a universe unimaginably dense and hot. If so, then the remnant heat of this Big Bang must still be detectable, even in the spaces between the stars.

If you can predict this temperature, and then detect it (and both these things happened in 1965) you have confirmed two things. One is that the cosmos had a beginning, a "let there be light" moment and a subsequent history that can be pieced together with precision. The other is that the Copernican principle delivers.

At this point the difficulties begin. The same reasoning leaves open another couple of ideas. Because the spectral signatures – the little absorption lines in light that shine through elements and compounds – are assumed to be the same everywhere, astronomers have recognised alcohol and water and formic acid and vinegar and hydrogen cyanide and all sorts of organic chemistry everywhere in the galaxy. The other is that the values of physical forces seem to be exquisitely tuned, and if the ratios or constants of these forces had been even very slightly different there would have been no stars, no planets, no carbon and no carbon-based life-forms. This cosmic coincidence is known as the anthropic principle and strikes some people as so eerie that the great physicist Freeman Dyson observed: "I find that in some sense, the universe must have known we were coming."

Awkwardly, the same observations suggest that the universe should be fizzing with life, but as far as we know, life bubbled up in only one place. So for the only sentient observers we know about, the Earth is a pretty special place: the centre of the universe, in fact. It gets more awkward. The sun turns out to be in a minority of stars. Since 1995, astronomers have been able, indirectly, to confirm the existence of thousands of other planetary systems orbiting distant stars and hardly any of them are like the solar system. So there could be something special about the size, the orbits and the order of planets in the solar system after all.

Furthermore, the star-making, planet-forming opportunities are beginning to dwindle. From now on, fewer and fewer stars will be forged. Earth, too, turns out to have the right geochemistry, and to be in the right orbit, at the right distance, with a moon conveniently placed to keep its orbital axis stable for long enough for life to evolve. As far as anybody knows, there is no place like our home. We could well be extraordinary, even if we are insignificant.

If the Copernican principle were scientific dogma – instead of a vital working assumption – then Caleb Scharf would be propagating scientific heresy in questioning it. However, there have always been limits to the assumption. If matter dropped out of the Big Bang as hydrogen, helium and a dash of lithium, and all the other 89 elements were forged in the thermonuclear furnaces of the stars, then scattered across space by supernovae, perhaps 10bn years had to elapse before any new star systems could condense and rocky planets with iron cores could begin to form, and offer hospitable places for biochemistry to begin. So there is something special about this phase of creation.

A universe that expands from a single point would also look very different at different times: no stars would be visible in the beginning, because there would be no stars. Right now we can see other galaxies in every direction but in some future phase they will all have crossed a cosmic horizon and any observers on some forlorn planet will be alone in a cold, dark, universe: they will have no evidence that there had ever been a beginning.

There are peculiar local details of science history: the geocentric cosmology worked out by Aristotle and Ptolemy and adopted gratefully by Christian authorities was only in question because Mars and the other planets could not be fitted into the big picture without some complicated fudges. But elliptical orbits are not fixed: they become more eccentric or more circular with time. In a different era, Mars might have fitted the model better, or the movement would have been so obvious that only a sun-centred cosmos would have suggested itself.

The future, too, could tell us a new story. With optical super-telescopes we might soon see not just distant, Earthlike planets but even the signature of life in their atmospheres. At any moment, a radiotelescope might start to pick up a message from a civilisation far away and long ago in the galaxy. In either case, humans would no longer be alone, and the Earth not such a special place. In either case, there would still be questions about the conditions that make life possible.

To resolve some of these questions, Scharf, an astrophysicist and astrobiologist, proposes a new "cosmo-chaotic" principle that might explain here and now, and us and the "them" that we think must exist, somewhere. Life, he argues, may perhaps only be possible at the borders of calm and chaos, where the accidents of matter and motion dictate change and variation without overwhelming the emerging entities, and this in turn might make sentient life a natural but very rare event.

Scharf does not have the answers. His book is an intoxicating collection of questions answered with other questions, and startling discoveries that make creation even more mysterious. A couple of decades ago, physicists spoke confidently of a "theory of everything" and one or two even proposed an "end to science". All has now changed. The mysteries have multiplied.

Forget the tricksy parenthesis in the subtitle. Skip past an early tendency to label scientists as budding, and science as cutting-edge. This book expands, like spacetime itself, from a very small point. It begins with the microscope pioneer Antony van Leeuwenhoek's famous discovery in Delft in 1674 of a microcosm in a drop of lake water, and it ends with speculation about a lonely civilisation, 100bn years on, in a freezing vacuum that no longer contains information about anything. Books such as these remind us that we are lucky to be here at all, and even luckier to be here now.

• Tim Radford's The Address Book: Our Place in the Scheme of Things is published by 4th Estate. To order The Copernicus Complex: The Quest for Our Cosmic (In)Significance by Caleb Scharf for £14.99 with free UK p&p call Guardian book service on 0330 333 6846 or go to guardianbookshop.co.uk.