Human Universe (2 page)

This sounds like a return to the anthropocentric vision we held for so long, and which science has done so much to destroy in a million humble cuts. Perhaps. But let me offer an alternative view. There is only one corner of the universe where we know for sure that the laws of nature have conspired to produce a species capable of transcending the physical bounds of a single life and developing a library of knowledge beyond the capacity of a million individual brains which contains a precise description of our location in space and time. We know our place, and that makes us valuable and, at least in our local cosmic neighbourhood, unique. We don’t know how far we would have to travel to find another such island of understanding, but it is surely a long long way. This makes the human race worth celebrating, our library worth nurturing, and our existence worth protecting.

Building on these ideas, my view is that we humans represent an isolated island of meaning in a meaningless universe, and I should immediately clarify what I mean by meaningless. I see no reason for the existence of the universe in a teleological sense; there is surely no final cause or purpose. Rather, I think that meaning is an emergent property; it appeared on Earth when the brains of our ancestors became large enough to allow for primitive culture – probably between 3 and 4 million years ago with the emergence of
Australopithecus
in the Rift Valley. There are surely other intelligent beings in the billions of galaxies beyond the Milky Way, and if the modern theory of eternal inflation is correct, then there is an infinite number of inhabited worlds in the multiverse beyond the horizon. I am much less certain that there are large numbers of civilisations sharing our galaxy, however, which is why I use the term ‘isolated’. If we are currently alone in the Milky Way, then the vast distances between the galaxies probably mean that we will never get to discuss our situation with anyone else.

We will encounter all these ideas and arguments later in this book, and I will carefully separate my opinion from that of science – or rather what we know with a level of certainty. But it is worth noting that the modern picture of a vast and possibly infinite cosmos, populated with uncountable worlds, has a long and violent history, and the often visceral reaction to the physical demotion of humanity lays bare deeply held prejudices and comfortable assumptions that sit, perhaps, at the core of our being. It seems appropriate, therefore, to begin this tour of the human universe with a controversial figure whose life and death resonates with many of these intellectual and emotional challenges.

Giordano Bruno is as famous for his death as for his life and work. On 17 February 1600, his tongue pinioned to prevent him from repeating his heresy (which recalls the stoning scene in Monty Python’s
Life of Brian
when the admonishment ‘you’re only making it worse for yourself’ is correctly observed to be an empty threat), Bruno was burned at the stake in the Campo de’ Fiori in Rome and his ashes thrown into the Tiber. His crimes were numerous and included heretical ideas such as denying the divinity of Jesus. It is also the opinion of many historians that Bruno was irritating, argumentative and, not to put too fine a point on it, an all-round pain in the arse, so many powerful people were simply glad to see the back of him. But it is also true that Bruno embraced and promoted a wonderful idea that raises important and challenging questions. Bruno believed that the universe is infinite and filled with an infinite number of habitable worlds. He also believed that although each world exists for a brief moment when compared to the life of the universe, space itself is neither created nor destroyed; the universe is eternal.

Although the precise reasons for Bruno’s death sentence are still debated amongst historians, the idea of an infinite and eternal universe seems to have been central to his fate, because it clearly raises questions about the role of a creator. Bruno knew this, of course, which is why his return to Italy in 1591 after a safe, successful existence in the more tolerant atmosphere of northern Europe remains a mystery. During the 1580s Bruno enjoyed the patronage of both King Henry III of France and Queen Elizabeth I of England, loudly promoting the Copernican ideal of a Sun-centred solar system. Whilst it’s often assumed that the very idea of removing the Earth from the centre of the solar system was enough to elicit a violent response from the Church, Copernicanism itself was not considered heretical in 1600, and the infamous tussles with Galileo lay 30 years in the future. Rather, it was Bruno’s philosophical idea of an eternal universe, requiring no point of creation, which unsettled the Church authorities, and perhaps paved the way for their later battles with astronomy and science. As we shall see, the idea of a universe that existed before the Big Bang is now central to modern cosmology and falls very much within the realm of observational and theoretical science. In my view this presents as great a challenge to modern-day theologians as it did in Bruno’s time, so it’s perhaps no wonder that he was dispensed with.

Bruno, then, was a complex figure, and his contributions to science are questionable. He was more belligerent free-thinker than proto-scientist, and whilst there is no shame in that, the intellectual origins of our ascent into insignificance lie elsewhere. Bruno was a brash, if portentous, messenger who would likely not have reached his heretical conclusions about an infinite and eternal universe without the work of Nicolaus Copernicus, grounded in what can now clearly be recognised as one of the earliest examples of modern science, and published over half a century before Bruno’s cinematic demise.

Nicolaus Copernicus was born in the Polish city of Torun in 1473 and benefited from a superb education after being enrolled at the University of Cracow at 18 by his influential uncle, the Bishop of Warmia. In 1496, intending to follow in the footsteps of his uncle, Copernicus moved to Bologna to study canon law, where he lodged with an astronomy professor, Domenica Maria de Novara, who had a reputation for questioning the classical works of the ancient Greeks and in particular their widely accepted cosmology.

The classical view of the universe was based on Aristotle’s not unreasonable assertion that the Earth is at the centre of all things, and that everything moves around it. This feels right because we don’t perceive ourselves to be in motion and the Sun, Moon, planets and stars appear to sweep across the sky around us. However, a little careful observation reveals that the situation is in fact more complicated than this. In particular, the planets perform little loops in the sky at certain times of year, reversing their track across the background stars before continuing along their paths through the constellations of the zodiac. This observational fact, which is known as retrograde motion, occurs because we are viewing the planets from a moving vantage point – the Earth – in orbit around the Sun.

This is by far the simplest explanation for the evidence, although it is possible to construct a system capable of predicting the position of the planets months or years ahead and maintain Earth’s unique stationary position at the centre of all things. Such an Earth-centred model was developed by Ptolemy in the second century and published in his most famous work,
Almagest
. The details are extremely complicated, and aren’t worth describing in detail here because the central idea is totally wrong and we won’t learn anything. The sheer contrived complexity of an Earth-centred description of planetary motions can be seen in Ptolemy’s Model, which shows the apparent motions of the planets against the stars as viewed from Earth. This tangled Ptolemaic system of Earth-centred circular motions, replete with the arcane terminology of epicycles, deferents and equant, was used successfully by astrologers for thousands of years to predict where the planets would be against the constellations of the zodiac – presumably allowing them to write their horoscopes and mislead the gullible citizens of the ancient world. And if all you care about are the predictions themselves, and your philosophical prejudice and common-sense feeling of stillness require the Earth to be at the centre, then everything is fine. And so it remained until Copernicus became sufficiently offended by the sheer ugliness of the Ptolemaic model to do something about it.

Copernicus’s precise objections to Ptolemy are not known, but sometime around 1510 he wrote an unpublished manuscript called the
Commentariolus
in which he expressed his dissatisfaction with the model. ‘I often considered whether there could perhaps be found a more reasonable arrangement of circles, from which every apparent irregularity would be derived while everything in itself would move uniformly, as is required by the rule of perfect motion.’

The
Commentariolus
contained a list of radical and mostly correct assertions. Copernicus wrote that the Moon revolves around the Earth, the planets rotate around the Sun, and the distance from the Earth to the Sun is an insignificant fraction of the distance to the stars. He was the first to suggest that the Earth rotates on its axis, and that this rotation is responsible for the daily motion of the Sun and stars across the sky. He also understood that the retrograde motion of the planets is due to the motion of the Earth and not the planets themselves. Copernicus always intended
Commentariolus
to be the introduction to a much larger work, and included little if any detail about how he had come upon such a radical departure from classical ideas. The full justification for and description of his new cosmology took him a further 20 years, but by 1539 he had finished most of his six-volume
De revolutionibus
, although the completed books were not published until 1543. They contained the mathematical elaborations of his heliocentric model, an analysis of the precession of the equinoxes, the orbit of the Moon, and a catalogue of the stars, and are rightly regarded as foundational works in the development of modern science. They were widely read in universities across Europe and admired for the accuracy of the astronomical predictions contained within. It is interesting to note, however, that the intellectual turmoil caused by our relegation from the centre of all things still coloured the view of many of the great scientific names of the age. Tycho Brahe, the greatest astronomical observer before the invention of the telescope, referred to Copernicus as a second Ptolemy (which was meant as a compliment), but didn’t accept the Sun-centred solar system model in its entirety, partly because he perceived it to be in contradiction with the Bible, but partly because it does seem obvious that the Earth is at rest. This is not a trivial objection to a Copernican solar system, and a truly modern understanding of precisely what ‘at rest’ and ‘moving’ mean requires Einstein’s theories of relativity – which we will get to later! Even Copernicus himself was clear that the Sun still rested at the centre of the universe. But as the seventeenth century wore on, precision observations greatly improved due to the invention of the telescope and an increasingly mature application of mathematics to describe the data, and led a host of astronomers and mathematicians – including Johannes Kepler, Galileo and ultimately Isaac Newton – towards an understanding of the workings of the solar system. This theory is good enough even today to send space probes to the outer planets with absolute precision.

At first sight it is difficult to understand why Ptolemy’s contrived mess lasted so long, but there is a modern bias to this statement that is revealing. Today, a scientifically literate person assumes that there is a real, predictable universe beyond Earth that operates according to laws of nature – the same laws that objects obey here on Earth. This idea, which is correct, only emerged fully formed with the work of Isaac Newton in the 1680s, over a century after Copernicus. Ancient astronomers were interested primarily in predictions, and although the nature of physical reality was debated, the central scientific idea of universal laws of physics had simply not been discovered. Ptolemy created a model that makes predictions that agree with observation to a reasonable level of accuracy, and that was good enough for most people. There had been notable dissenting voices, of course – the history of ideas is never linear. Epicurus, writing around 300
BCE
, proposed an eternal cosmos populated by an infinity of worlds, and around the same time Aristarchus proposed a Sun-centred universe about which the Earth and planets orbit. There was also a strong tradition of classic orthodoxy in the Islamic world in the tenth and eleventh centuries. The astronomer and mathematician Ibn al-Haytham pointed out that, whilst Ptolemy’s model had predictive power, the motions of the planets as shown in the figure
here
represent ‘an arrangement that is impossible to exist’.

The end of the revolution started by Copernicus around 1510, and the beginning of modern mathematical physics, can be dated to 5 July 1687, when Isaac Newton published the
Principia
. He demonstrated that the Earth-centred Ptolemaic jumble can be replaced by a Sun-centred solar system and a law of universal gravitation, which applies to all objects in the universe and can be expressed in a single mathematical equation: