Does intelligent life exist elsewhere in the universe? It's highly unlikely, say scientists
For life to evolve in the same way elsewhere in the universe, it would take longer than the projected lifespan of the Earth
Is there anyone out there? This is an age-old question that researchers have now shed new light on with a study that suggests intelligent life is “exceptionally rare” in the universe. Life on Earth has undergone a number of major “evolutionary transitions,” and some transitions seem to have occurred only once in Earth’s history, says the team from the University of Oxford. They contend that, in a universe that is over 13 billion years old, on a planet that is about 4.5 billion years old, it took all this time for multiple processes of evolution to result in life forms. Hence, the likelihood of such a favorable series of chance events happening is less probable.
The Oxford group theorizes that, for life to evolve in the same way elsewhere in the universe, it would take longer than the projected lifespan of the Earth. This ‘unlikeliness’ of different evolutionary transitions that led to intelligent life means it is likely to be slim anywhere else, the scientists reason.
“It took approximately 4.5 billion years for a series of evolutionary transitions resulting in intelligent life to unfold on Earth. In another billion years, the increasing luminosity of the Sun will make Earth uninhabitable for complex life. Intelligence, therefore, emerged late in Earth’s lifetime,” write authors in the report published in Astrobiology. They explain, “Together with the dispersed timing of key evolutionary transitions and plausible priors, one can conclude that the expected transition times likely exceed the lifetime of Earth, perhaps by many orders of magnitude. In turn, this suggests that intelligent life is likely to be exceptionally rare.”
Study author Anders Sandberg from the Future of Humanity Institute, University of Oxford, tweeted, “There is life on Earth but this is not evidence for life being common in the universe.”
There is life on Earth but this is not evidence for life being common in the universe! This is since observing life requires living *observers*. Even if life is very rare, the observers will all see they are on planets with life. Observation selection effects need to be handled!— Anders Sandberg (@anderssandberg) November 24, 2020
What are the researchers saying?
It is unknown how abundant extraterrestrial life is, or whether such life might be complex or intelligent. According to the team, there is between a 53% and 96% chance that humans are alone in the Milky Way galaxy.
The analysis explains that several transitions helped evolve life on Earth, such as abiogenesis, as well as the emergence of increasingly complex forms of life such as eukaryotic, the evolution of sexual reproduction, multicellular, and intelligent life. “These particular transitions are selected because large scientific uncertainty remains around how frequent such transitions are, and because they were prerequisites for the existence of intelligent life on Earth,” the findings state.
However, some of these transitions could have been extraordinarily improbable, even in conducive environments, say authors. They also point out that some of the steps required to achieve intelligent life appear to be far less likely than others. The team finally argues that it would be virtually impossible for that life to evolve the same way somewhere else.
“The fact that eukaryotic life took over a billion years to emerge from prokaryotic precursors suggests it is a far less probable event than the development of multicellular life, which is thought to have originated independently over 40 times,” they write. The researchers further say, “The early emergence of abiogenesis is one example that is frequently cited as evidence that simple life must be fairly common throughout the universe. By using the timing of evolutionary transitions to estimate the rates of transition (probability per unit of time), we can derive information about the likelihood of a given transition even if it occurred only once in Earth’s history.”
Arriving at the opposite conclusion that life is not rare in the universe would require evidence for much earlier transitions than the ones that occurred on Earth, or multiple instances of transitions, the investigators emphasize. They quote American evolutionary biologist Stephen Jay Gould, who said that if the ‘‘tape of life’’ were to be rerun, ‘‘the chance becomes vanishingly small that anything like human intelligence’’ would occur. “We may possibly be the only intelligent civilization within the observable universe. To conclude that intelligent life is common, an alternative model would not only need to explain why intelligence emerged on roughly the same timescale of Earth’s habitable lifetime, but also why eukaryotic life and other evolutionary transitions did so,” the investigators conclude.