Anders Sandberg, Eric Drexler and Toby Ord have looked at the wide range of possible probabilities for each part of the Drake Equation estimate of technological civilizations in the universe. They analyzed the wide ranges of answers for each parameter.
They incorporate models of chemical and genetic transitions on paths to the origin of life, and show that extant scientific knowledge corresponds to uncertainties that span multiple orders of magnitude.
When the model is recast to represent realistic distributions of uncertainty, they find a substantial probability of there being no other intelligent life in our observable universe.
This is why we must preserve the light of consciousness by becoming a spacefaring civilization & extending life to other planets https://t.co/UDDP8I1zsS
— Elon Musk (@elonmusk) June 25, 2018
They came to following conclusions
1. it is not at all unlikely ex ante for us to be alone in the Milky Way, or in the observable universe.
2. taking account of observational bounds on the prevalence of other civilizations, then updated probabilities suggest that there is a substantial probability that we are alone.
3. pessimism for the survival of humanity based on the Fermi paradox is unfounded.
The point estimate for each of 9 parameters is 0.1, so the product of point estimates is a probability of 1 in a billion. Given a galaxy of 100 billion stars, the expected number of life-bearing stars would be 100, and the probability of all 100 billion events failing to produce intelligent civilizations can be shown to be vanishingly small: 3.7 × 10−44.
If it were uniformly drawn from the interval [0, 0.2]. Monte Carlo simulation shows that this actually produces an empty galaxy 21.45 % of the time: a result that is easily reconcilable with our observations and thus generating no paradox for us to explain. That is to say, given our uncertainty about the values of the parameters, we should not actually be all that surprised to see an empty galaxy. The probability is much higher than under the point estimate approach because it is not that unlikely to get a low product of these factors (such as 1 in 200 billion) after which a galaxy without ETI becomes quite likely.
In this toy case, the point estimate approach was getting the answer wrong by more than 42 orders of magnitude and was responsible for the appearance of a paradox.
When they take account of realistic uncertainty, replacing point estimates by probability distributions that reflect current scientific understanding, they find no reason to be highly confident that the galaxy (or observable universe) contains other civilizations, and thus no longer find our observations in conflict with our prior probabilities.
They found qualitatively similar results through two different methods:
using the authors’ assessments of current scientific knowledge bearing on key parameters, and using the divergent estimates of these parameters in the astrobiology literature as a proxy for current scientific uncertainty.
When they update this prior in light of the Fermi observation, they find a substantial probability that we are alone in our galaxy, and perhaps even in our observable universe (53%–99.6% and 39%–85% respectively). ’Where are they?’ — probably extremely far away, and quite possibly beyond the cosmological horizon and forever unreachable.
Another Recent observation suggests that it may be tougher for life to arise because of lack of Phosphorus
Cardiff University researchers have found very little evidence of phosphorus – which is essential to life on Earth – around the Crab Nebula, a supernova remnant around 6500 light years away in the direction of the constellation of Taurus.
Phosphorus is one of six elements on which Earth’s organisms depend, the findings cast doubt on whether life similar to our own would be able to exist on other planets.
Phosphorus is crucial to the compound adenosine triphosphate (ATP), which cells use to store and transfer energy. Astronomers have just started to pay attention to the cosmic origins of phosphorus and found quite a few surprises. In particular, it is created in supernovae – the explosions of massive stars – but the amounts seen so far don’t match our computer models.