In contrast to Harvard astrophysicist Avi Loeb’s optimism that extraterrestrials are less speculative than dark matter or extra dimensions, a study posted in September of 2018 conducted by three scholars from the Future of Humanity Institute (FHI) at Oxford University, suggesting that although we exist in a universe with a potential 50 quintillion habitable planets, the expectation that life — from inorganic to bacteria to sentient beings —abiogenesis– has or will develop on other planets as it has on Earth, might be based more on optimism based on a sample of one.
Colin Blakemore, an Oxford neurobiologist not involved in the FHI study argued that a mutation in the brain of a single human being 200,000 years ago turned intellectually able primates into a super-intelligent species that would conquer the world. Homo sapiens appears to be genetic accident. Or are we?
“There is no sign that the human brain has reached its capacity to accumulate knowledge,” adds Blakemore, “which means that the wonders we have already created – from spaceships to computers – represent only the start of our achievements.”
Fossil evidence suggests that life began very early in Earth’s history and that has led people to determine that life might be quite common in the universe because it happened so quickly here, but the knowledge about life on Earth simply doesn’t reveal much about the actual probability of life on other planets. suggests the Oxford paper, “Dissolving the Fermi Paradox”.
The study was jointly-conducted by Anders Sandberg, a Research Fellow at the Future of Humanity Institute and a Martin Senior Fellow at Oxford University; Eric Drexler, the engineer who popularized the concept of nanotechnology; and Tod Ord, Australian moral philosopher at Oxford University.
The study concluded that “even using the guesstimates in the literature (we took them and randomly combined the parameter estimates) one can have a situation where the mean number of civilizations in the galaxy might be fairly high – say a hundred – and yet the probability that we are alone in the galaxy is 30%! The reason is that there is a very skewed distribution of likelihood.
“The probability of getting life and intelligence on a planet has an extreme uncertainty given what we know – we cannot rule out that it happens nearly everywhere there is the right conditions, but we cannot rule out that it is astronomically rare. This leads to an even stronger uncertainty about the number of civilizations, drawing us to conclude that there is a fairly high likelihood that we are alone. However, we also conclude that we shouldn’t be too surprised if we find intelligence!”
In an earlier study, David Spiegel of Princeton University and Edwin Turner from the University of Tokyo turned the Drake equation upside down using Bayesian reasoning to show that just because we evolved on Earth, doesn’t mean that the same occurrence would necessarily happen elsewhere; “using evidence of our own existence doesn’t show anything” they argue, “other than that we are here.”
Astrophysicist Turner and lead author Spiegel analyzed what is known about the likelihood of life on other planets in an effort to separate the facts from the mere expectation that life exists outside of Earth. The researchers used a Bayesian analysis — which weighs how much of a scientific conclusion stems from actual data and how much comes from the prior assumptions of the scientist — to determine the probability of extraterrestrial life once the influence of these presumptions is minimized.
Turner and Spiegel, who is now at the Institute for Advanced Study, argued in the Proceedings of the National Academy of Sciences that the idea that life has or could arise in an Earth-like environment has only a small amount of supporting evidence, most of it extrapolated from what is known about abiogenesis, or the emergence of life, on early Earth. Instead, their analysis showed that the expectations of life cropping up on exoplanets — those found outside Earth’s solar system — are largely based on the assumption that it would or will happen under the same conditions that allowed life to flourish on this planet.
Abiogenesis is the process by which life arises from non-living matter, such as simple organic compounds as a gradual process of increasing complexity that involved molecular self-replication, self-assembly, autocatalysis and cell membranes. Scientists study the origin of life through a combination of molecular biology, paleontology, astrobiology, oceanography, biophysics, geochemistry and biochemistry, and aim to determine how pre-life chemical reactions gave rise to life.
The Princeton researchers conclude that the current knowledge about life on other planets suggests that it’s very possible that Earth is a cosmic aberration where life took shape unusually fast. If so, then the chances of the average terrestrial planet hosting life would be low.
“Fossil evidence suggests that life began very early in Earth’s history and that has led people to determine that life might be quite common in the universe because it happened so quickly here, but the knowledge about life on Earth simply doesn’t reveal much about the actual probability of life on other planets,” Turner said. “Information about that probability comes largely from the assumptions scientists have going in, and some of the most optimistic conclusions have been based almost entirely on those assumptions.”
Joshua Winn, also at Princeton, said that Turner and Spiegel cast convincing doubt on a prominent basis for expecting extraterrestrial life. Winn, who focuses his research on the properties of exoplanets, is familiar with the research but had no role in it.
“There is a commonly heard argument that life must be common or else it would not have arisen so quickly after the surface of the Earth cooled,” Winn said. “This argument seems persuasive on its face, but Spiegel and Turner have shown it doesn’t stand up to a rigorous statistical examination — with a sample of only one life-bearing planet, one cannot even get a ballpark estimate of the abundance of life in the universe.
“I also have thought that the relatively early emergence of life on Earth gave reasons to be optimistic about the search for life elsewhere,” Winn said. “Now I’m not so sure, though I think scientists should still search for life on other planets to the extent we can.
While discoveries by NASA’s Kepler Space Telescope of potentially habitable exoplanets tend to stoke the expectation of finding Earth-like life, they do not actually provide evidence that it does or does not exist, Spiegel explained. Instead, these planets have our knowledge of life on Earth projected onto them.
Yet, when what is known about life on Earth is taken away, there is no accurate sense of how probable abiogenesis is on any given planet, Spiegel said. It was this “prior ignorance,” or lack of expectations, that he and Turner wanted to account for in their analysis, he said. “When we use a mathematical prior that truly represents prior ignorance, the data of early life on Earth becomes ambiguous.”
“Our analysis suggests that abiogenesis could be a rather rapid and probable process for other worlds, but it also cannot rule out at high confidence that abiogenesis is a rare, improbable event,” Spiegel said. “We really have no idea, even to within orders of magnitude, how probable abiogenesis is, and we show that no evidence exists to substantially change that.”
Spiegel and Turner also propose that once this planet’s history is considered, the emergence of life on Earth might be so distinct that it is a poor barometer of how it occurred elsewhere, regardless of the likelihood that such life exists.
In a philosophical turn, they suggest that because humans are the ones wondering about the emergence of life, it is possible that we must be on a planet where life began early in order to reach a point so soon after the planet’s formation 4.5 billion years ago where we could wonder about it.
Thus, Spiegel and Turner explored how the probability of exoplanetary abiogenesis would change if it turns out that evolution requires, as it did on Earth, roughly 3.5 billion years for life to develop from its most basic form to complex organisms capable of pondering existence. If that were the case, then the 4.5 billion-year-old Earth clearly had a head start. A planet of similar age where life did not begin until several billion years after the planet formed would have only basic life forms at this point.
“Dinosaurs and horseshoe crabs, which were around 200 million years ago, presumably did not consider the probability of abiogenesis. So, we would have to find ourselves on a planet with early abiogenesis to reach this point, irrespective of how probable this process actually is,” Spiegel said. “This evolutionary timescale limits our ability to make strong inferences about how probable abiogenesis is.”
“It could easily be that life came about on Earth one way,” said Turner, “but came about on other planets in other ways, if it came about at all. The best way to find out, of course, is to look. But I don’t think we’ll know by debating the process of how life came about on Earth.”
Again, said Winn of MIT, Spiegel and Turner offer a unique consideration for scientists exploring the possibility of life outside of Earth.
“I had never thought about the subtlety that we as a species could never have ‘found’ ourselves on a planet with a late emergence of life if evolution takes a long time to produce sentience, as it probably does,” Winn said.
“With that in mind,” he said, “it seems reasonable to say that scientists cannot draw any strong conclusion about life on other planets based on the early emergence of life on Earth.”
However, as Arthur C. Clarke, physicist and author of 2001: A Space Odyssey wrote, “The idea that we are the only intelligent creatures in a cosmos of a hundred billion galaxies is so preposterous that there are very few astronomers today who would take it seriously. It is safest to assume therefore, that they are out there and to consider the manner in which this may impinge upon human society.”