Level 2: Intermediate
THIS the biggest question in the universe: are we alone? Philosophers have debated the question for millennia. When 16th-century Italian astronomer and Dominican friar Giordano Bruno declared that the cosmos contained “an infinity of worlds of the same kind as our own”, he was directly contravening religious dogma. He was later burned at the stake during the Inquisition, in part for daring to question Earth’s unique status.
The debate continues, in more restrained fashion, to this day. For some, the sheer size of the universe makes it unlikely that life formed only once. For others, the remarkable complexity of life on Earth is testament to its uniqueness.
Until recently, vague philosophical answers of this kind were the best science could do. The signs of life were far too ambiguous to pin down for certain, and our nearest potentially habitable worlds were too small and distant to test.
But for the first time in human history we are reaching the technological sophistication needed to provide a genuine answer. Powerful telescopes are letting us study planets in other solar systems, giving us a glimpse into their atmospheres and a flavour of what type of life might be living on their surfaces. At the same time, improved analysis of our own planet is allowing us to redefine what life might look like from afar, and is helping us to distinguish the signs of a flourishing alien civilisation from the mere geological rumblings of a lifeless world. With these tools at our disposal, answers are finally within our grasp.
To understand my optimism, it is worth revisiting the work of astronomer Frank Drake. In 1961, Drake devised a formula to estimate how many advanced civilisations were capable of signalling their presence in the Milky Way. His eponymous equation depends on breaking down that big unknowable quantity into a number of more tractable ones that can be multiplied together, such as the number of stars in the galaxy and the fraction of those likely to have planets