It’s a question that has been pondered many, many times before: If other planets are so plentiful, then why have we never seen any other life in the universe? Known as the Fermi Paradox, this question continues to confound scientists – but one team think they have an answer.
A study led by astronomers from Harvard University and the University of Oxford (to be published in the Journal of Cosmology and Astroparticle Physics, pre-print on arXiv) speculates that life on Earth might have formed relatively early in the universe. This, they say, could explain why we seem to be alone at the moment.
“If we are very early, if we are premature in cosmic time, that explains why we haven’t yet seen any other civilizations around,” Rafael Batista, a study co-author from the University of Oxford, told IFLScience. “We might be the first ones, or one of the first ones.”
They note how life in the universe could not have begun until 10 million years after the Big Bang, when stars gave rise to the elements necessary for life such as carbon and oxygen. But there are a host of important factors in determining whether life can exist. One of these is the mass of a star, which dictates how long it can stick around for – the higher its mass, the shorter its lifespan.
Stars that are three times more massive than our Sun will likely face their demise before life has a chance to evolve. But stars less than 10 percent of our Sun’s mass, red dwarfs, can survive for 10 trillion years, giving plenty of time for life to take hold. This means that the further into the future you go, the more likely it is for life to exist.
Batista added that while it is likely simple life exists elsewhere, it can take a long time for complex life like us to evolve – and it requires a very stable environment. Consider that on Earth, which is 4.5 billion years old, the first complex life didn’t arise until at least 3 billion years ago, and the first modern humans not until 200,000 years ago.
If life can exist around low mass stars, then that places us in the first 0.14 percent of the habitable period of the universe. While there may be other habitable planets out there, maybe we are one of the stable few that has seen complex, sentient life take shape so far.
All hope is not lost, though. In our galaxy alone, there are billions of planets, many of which may be habitable. One would hope, then, that there should be others that have life like us even today.
"It's not all doom and gloom," said Batista.