A graphic shows the 'Tardis' from Doctor Who
Credit: Gregory Stewart/Unsplash

On 23 November 1963, the first episode was broadcast of a show that would become one of the longest running television series of all time. This year marks the 60th anniversary of the British classic Doctor Who, the adventures of an extraterrestrial being called the Doctor who explores the Universe in a time-travelling spaceship. It’s changed over the decades, but has stuck with a constant theme: the Doctor Who Universe is teeming with aliens. Yet the striking thing about our own Universe is that we see no sign of alien life – and not for lack of looking.

Famously, the absence of any extra-terrestrial or ET evidence was remarked on by Enrico Fermi, the Italian physicist. Fermi, who created the first nuclear reactor, was sitting with other physicists in the canteen at Los Alamos, the lab that had built the atomic bomb, when, suddenly, he put down his knife and fork, and asked: “Where is everybody?”

Immediately, everyone knew what he meant. In 1948, the mathematician John von Neumann had imagined intelligent ETs building a self-reproducing probe that flew to a nearby star and used the raw materials there to build two copies of itself. By repeating the process, such von Neumann probes could visit all the stars in our Galaxy. The Galaxy is incredibly old, so there has been plenty of time for such a civilisation to emerge. If advanced aliens exist, they should be here. The fact that they are not became known as the Fermi Paradox.

Many explanations have been proposed. Perhaps most life stalls at the single-celled stage, as ours did for three billion years. Or perhaps our Solar System has been purposefully cordoned off from alien visits to allow us to develop in peace. Maybe aliens blow themselves up or trigger an environmental catastrophe before they develop the technology needed to reach us. Perhaps they stay at home and meditate. “I’m sure the Universe is full of intelligent life,” the science fiction writer Arthur C. Clarke wryly observed. “It’s just been too intelligent to come here.”

All these solutions to the Fermi Paradox were counted by Michael Hart in 1976. According to Hart, just as most people on Earth stay at home, bar a few Christopher Columbuses, there will always be exceptions. Even if most ETs self-destruct, not all will. Even if most stay at home and contemplate their navels, not all will. Hart concluded that aliens are not here because we are alone – the first civilisation to arise in our Milky Way.

Absence of evidence, however, is not necessarily evidence of absence. In the movie 2001: A Space Odyssey, an alien artefact is found buried on the Moon. When sunlight reaches it, the astronauts hear a deafening screech in their earphones. It is an ET baby alarm, left millions of years before to notify its makers if the apes on the third planet from the Sun avoid nuclear annihilation and bridge the gulf of space between the Earth and the Moon. If such an alien artefact exists in our Solar System, we may not have found it because we have explored so little.

Another possibility is that ETs are so advanced that we would not recognise them. Does an ant know it is part of a city like London? Does a bacterium? As Clarke observed: “Any sufficiently advanced civilisation would be indistinguishable from magic.”

However, there are still high hopes of finding aliens. We have discovered more than 5,000 planets around other stars. Even the nearest star, Proxima Centauri, is orbited by at least one planet. Now, with the launch of Nasa’s James Webb Space Telescope (JWST), we can at least determine whether some of these planets possess water. Establishing this requires a planet to periodically pass in front of its star as seen from Earth. The JWST is then able to spot the characteristic dip in infrared starlight passing through the planet’s atmosphere caused by the absorption of water molecules.

Although it is a key component of life as we know it, the presence of water is insufficient to prove that a planet supports biology. However, Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics has an intriguing idea. He points out that the JWST could also detect industrial chemicals such as chlorofluorocarbons, implicated on Earth in the destruction of the ozone layer. At the moment, the telescope has better things to do – like hunting down the first stars to have formed after the Big Bang. But who knows? In coming years we might be gobsmacked to discover an industrial civilisation on a nearby extrasolar planet. It isn’t time to give up, just yet, on the idea that we might in fact live in an alien-packed Doctor Who Universe.

This article is from New Humanist's autumn 2023 issue. Subscribe now.