The Big Bang in Stephen Hawking's Office

The mottled blue-green pattern on the ball was Hawking’s all-time favourite scientific image of what he called ‘the fingerprints of creation’. It shows variations in the oldest visible light in the universe, taken by the Wilkinson Microwave Anisotropy Probe (WMAP), a space telescope that released its results between 2003 and 2010.  

The light is in the form of microwaves, shorter wavelength radio signals, and the ball shows the temperature variations across the sky in this light: red for hotter, blue for cooler, when the universe - now 13.7 billion years old - was just 378,000 years old. 

At the time the microwave background was discovered by chance, there were two competing theories for the origin of the universe: the Big Bang theory and the older “Steady State theory”, which stated that the universe has existed forever. 

In 1964, Arno Penzias and Robert Wilson, working for the Bell communications company, picked up noise on a microwave communications antenna repurposed as a radio telescope and could not initially figure out where it was coming from.  

Pigeons (the ‘horn antenna’ was full of droppings) and other disturbances were ruled out until theoreticians who had been working on the origins of the universe nearby at Princeton University recognized what the antenna was detecting:  their models predicted that the Big Bang would leave a faint signal, the cosmic microwave background, CMB. 

At that time, Stephen Hawking was finishing his PhD, repurposing theories developed for black holes to describe the origins of the universe, and his work was published still unaware of the CMB discovery. But from that point onwards, Hawking recognized that astronomical confirmation could be found quickly, even for the most complex theoretical work. Much of Hawking’s subsequent research focused on theories that could be confirmed while he was still around, and the moments when relevant data were released constituted major milestones in his career. 

In the years after the discovery of the cosmic microwave background, scientists could exceed the precision of ground-based instruments by taking measurements from balloons and rockets that briefly left and peeked beyond the atmosphere before returning to Earth with exciting new data. They compared the wavelength and strength of the signal with detailed theoretical predictions of what should be left over from the primordial explosion. Thanks to these measurements the scientific community became convinced by the late 1970s that there had been a Big Bang. Around that time, having been busy with theoretical work on black holes, Stephen Hawking began to focus again on his earlier interests in cosmic creation.  

By the late 1970s, a new generation of scientists was formulating the theory of ‘cosmic inflation’, an extraordinary growth spurt that they calculated was necessary to explain why the universe looks the way it does today.

Cosmic inflation proposed that in the briefest instant after the big bang (an undecillionth to an octillionth of a second), the universe expanded at an immensely accelerated rate.  This idea was not intuitive and had its critics. However, this debate could be settled by obtaining high resolution maps of the microwave background, detecting tiny fluctuations in the faint glow of the Big Bang where,  for example, one part of the sky has a temperature of 2.7251 Kelvin (degrees above absolute zero), while another was a fraction cooler, at 2.7249 Kelvin.  

Scientists were looking for ‘anisotropies’ or patchiness in the signal. If inflation was right, the resulting map of the largest structures that humans are able to discern could be thought of as vastly magnified versions of quantum fluctuations that started out close to the Big Bang smaller than a subatomic particle: these were frozen into the fabric of space-time and stretched as inflation expanded the universe. 

The Soviets, who contributed significantly to inflation theory, also launched the first space telescope to measure the microwave background in 1983. But convincing measurements of this mottled pattern would have to wait for the launch of NASA’s COBE (Cosmic Background Explorer) probe in 1989.  

The first Nobel Prizes for science produced during a space telescope mission were awarded for these results in 2006. When the research was first published in 1992, Stephen Hawking said “It is the discovery of the century, if not of all time”.  

Hawking was inspired by how cosmic inflation turned quantum fluctuations in the early universe into complex features around us, from stars and galaxies to ultimately ourselves. Already an influential scientist in the late 1970s, he helped set the research agenda for inflation and its observation by COBE and probes that could follow. This included fostering scientific exchanges with the Soviet Union, and culminated in a key scientific workshop in Cambridge in 1982.   

Another came two decades later, by the time of Hawking’s relocation to his office at the new Centre for Mathematical Sciences, when WMAP was about to start taking the most precise measurements of the microwave background. His 60th birthday celebration in 2002 saw a workshop celebrating progress since 1982 and set the agenda for what would be possible with WMAP and beyond. The microwave background signal could also be used to investigate other mysteries, from dark matter and dark energy, to the final fate of the universe. 

WMAP took measurements at a thousand times higher resolution than COBE and, in 2007, NASA's education team produced an inflatable ball showing the results, which were a dramatic vindication of inflation. Some of these balls eventually found their way to Hawking, into his office, and would even be bounced around family parties by his grandchildren.