In terms of significant dates in the history of science, 8 January definitely deserves a mention. On that day in 1642, the mould-breaking astronomer and physicist Galileo Galilei died in Arcetri, near Florence in Italy. Exactly 300 years after Galileo’s death, another brilliant physicist was born in a different centre of learning – Oxford England. Stephen Hawking, as well as being a prodigious talent, has also proved himself to be no stranger to controversy.
Although separated by three centuries, these two great scientists share a common passion for seeking answers to the great questions of their day – and these are inevitably bound up with furthering our understanding of the workings of the cosmos. While Galileo was concerned with establishing the heliocentric nature of the solar system and challenging the scientific teachings of the Catholic Church, Hawking has been involved with teasing out the basic laws that govern the universe and especially with a so-called “theory of everything” that can reconcile general relativity and quantum mechanics. In Hawking’s view, the discovery of such a theory would provide us with access into “the mind of God”.
Although we now take Galileo’s discoveries for granted, in his day they were ground-breaking; for instance, the fabled experiments investigating falling objects at the University of Pisa where he produced the manuscript Du Motu (On Motion). Sometimes they were also controversial, as with his support for the Copernican theory that the earth and planets revolve around the sun. This challenged the established doctrine of the Catholic Church, which was based around Aristotelian teachings.
As an astronomer, Galileo built his own telescope. Then, in autumn 1609, he made the considered decision to turn it towards the heavens. In March 1610, he published a landmark pamphlet: The Starry Messenger unveiled his discoveries that the moon was neither flat nor smooth, but a sphere with mountains and craters. He showed that Venus has phases like the moon, proving it rotates around the sun like the Earth. He also discovered that Jupiter has revolving moons – the four “Galilean moons” of Io, Europa, Ganymede and Callisto that any of us can see through an average telescope – and which represents incontrovertible evidence of heavenly objects that don’t orbit the earth.
Although his research ranged widely, it is for astronomy that Galileo is remembered. In 1613, he published his observations of sunspots, which further refuted Aristotelian doctrine that the sun was unblemished. Although his views were considered controversial and heretical by the Catholic Church at the time, Galileo’s ideas were eventually universally accepted and, of course, underpin what we take for granted today. Perhaps just as importantly, he introduced a degree of rigour into the scientific method of the day, using mathematics to support his theories. Because of this, he played a major role in the scientific revolution and has deservedly been dubbed the “father of modern science”.
Over three centuries later, Hawking has moved our understanding of the universe several stages further and he also has not been afraid to philosophise about religion. For instance, at a 1981 Vatican conference, Hawking presented work suggesting that there might be no boundary – neither beginning nor ending – to the universe. In collaboration with Jim Hartle, he published the 1983 model, known as the Hartle-Hawking state: prior to the Planck epoch, the universe had no boundary in space-time; thus, before Big Bang, time did not exist and the concept of the beginning of the universe is meaningless.
According to this view, the initial singularity of the classical Big Bang models was replaced with a region analogous to the concept of the North Pole here on Earth. One cannot travel north of the North Pole, but there is no boundary there – it is simply the point where all north-running lines meet and end. Initially, this no-boundary proposal predicted a closed universe and so had implications about the existence of God. Hawking explained: “If the universe has no boundaries but is self-contained... then God would not have had any freedom to choose how the universe began.”
Nevertheless, Hawking did not rule out the existence of a creator, asking in his bestseller A Brief History of Time: “Is the unified theory so compelling that it brings about its own existence?” In the same book, he went on to suggest: “If we discover a complete theory, it would be the ultimate triumph of human reason – for then we should know the mind of God.” However, he suggests in the book that the existence of God is unnecessary to explain the origin of the universe, albeit that his later discussions with Neil Turok led to the realisation that it is also compatible with an open universe.
Hawking’s achievements are extensive. He is a supporter of the many-worlds interpretation of quantum mechanics. With Roger Penrose he showed that Einstein’s General Theory of Relativity implied space and time would have a beginning in the Big Bang and an end in black holes. These results indicated that it was necessary to unify general relativity with quantum theory, the other great scientific development of the first half of the 20th century. One consequence of such a unification that he discovered was that black holes actually emit radiation – so-called Hawking radiation – and they eventually evaporate and disappear. His idea that the universe has no edge or boundary in imaginary time implies that the way the universe began was completely determined by the laws of science.