This, in his view, opens up quite a can of interstellar worms. Will they accord us whatever rights, if any, they grant their little green or silver or blue brethren? Still, Fermi reckoned that Earth was a fairly typical planet revolving around a fairly typical star.
There ought, he reasoned, to be civilizations out there far older and more advanced than our own, some of which should have already mastered interstellar travel. Yet, strangely enough, no one had shown up. In the nineteen-sixties, an astronomer named Frank Drake came up with the eponymous Drake equation, which offers a way to estimate—or, if you prefer, guesstimate—how many alien cultures exist with which we might hope to communicate.
Key terms in the equation include: how many potentially habitable planets are out there, what fraction of life-hosting planets will develop sophisticated technology, and how long technologically sophisticated civilizations endure.
Loeb proposes that Fermi may be the answer to his own paradox. Humanity has been capable of communicating with other planets, via radio wave, for only the past hundred years or so. Thus, not long after humanity became capable of signalling to other planets, it also became capable of wiping itself out. A message an earthling might take from this admittedly highly speculative train of thought is: be wary of new technologies. Loeb, for his part, draws the opposite conclusion. The initiative has funding from Yuri Milner, a Russian-Israeli billionaire, and counts among its board members Mark Zuckerberg.
We could also run a great evolutionary experiment, one that might lead to outcomes far more wondrous than seen so far. Traces of their visits were recorded in legends and also in artifacts like the Nazca Lines, in southern Peru.
Why had people created these oversized images if not to signal to beings in the air? Now eighty-five, he lives near Interlaken, not far from a theme park he designed, which was originally called Mystery Park and then later, after a series of financial mishaps, rebranded as Jungfrau Park.
The park boasts seven pavilions, one shaped like a pyramid, another like an Aztec temple. He tended to side with Loeb, who, he thought, was very brave. In publishing his theory, Loeb has certainly risked and suffered ridicule. The Navajo Nation, which sprawls across close to eighteen million acres, has been hit hard by the pandemic.
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How worried should we be about covid spreading among wild animals? For example, last month Tom Westby and Christopher Conselice, both at the University of Nottingham in England, made headlines when they calculated that there should be at least 36 intelligent civilizations in our galaxy capable of communicating with us. The estimate was based on an assumption that intelligent life emerges on other habitable Earth-like planets about 4. Answering questions about the likelihood of abiogenesis and the emergence of intelligence is difficult because scientists just have a single piece of information: life on Earth.
Even that is subject to uncertainty. Yet another problem with making assumptions based on what we locally observe is so-called selection bias. Imagine buying lottery tickets and hitting the jackpot on your th attempt.
Reasonably, you might then assign a 1 percent probability to winning the lottery. This incorrect conclusion is, of course, a selection bias that arises if you poll only the winners and none of the failures that is, the tens of millions of people who purchased tickets but never won the lottery.
Enter Bayesian analysis. To calculate the odds of some event, such as abiogenesis, occurring, astronomers first come up with a likely probability distribution of it—a best guess, if you will.
Such assumptions are called Bayesian priors, and they are made explicit. Then the statisticians collect data or evidence. Finally, they combine the prior and the evidence to calculate what is called a posterior probability. In the case of abiogenesis, that probability would be the odds of the emergence of life on an Earth-like planet, given our prior assumptions and evidence. The posterior is not a single number but rather a probability distribution that quantifies any uncertainty.
It may show, for instance, that abiogenesis becomes more or less likely with time rather than having a uniform probability distribution suggested by the prior.
If life does not arise before some maximum time, t max , then, as its star ages and eventually dies , conditions on the planet become too hostile for abiogenesis to ever occur. The researchers worked with a few different prior distributions for this probability. They also assumed that intelligence took some fixed amount of time to appear after abiogenesis. Although the evidence that life appeared early on Earth may indeed suggest abiogenesis is fairly easy, the posteriors did not place any lower bound on the probability.
For instance, Kipping questions the assumption that intelligence emerged at some fixed time after abiogenesis. This prior, he says, could be another instance of selection bias—a notion influenced by the evolutionary pathway by which our own intelligence emerged.
That suggestion is exactly what Kipping attempted, estimating both the probability of abiogenesis and the emergence of intelligence.
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