I’ve seen a lot of chatter on a new paper submitted to the Proceedings of the Royal Society of London by some Oxford researchers. Apparently, they’ve concluded that there is “a substantial ex ante probability of there being no other intelligent life in our observable universe.”
Here is a sample article discussing the paper:
As it says, “The authors assert that the chance humanity stands alone among intelligent civilizations in our galaxy is 53%–99.6%, and across the observable universe is 39%–85%.”
This is based upon a reassessment of the “Drake Equation,” made famous by Carl Sagan, and the probable values for each of its variables. Here is a link to that equation: https://www.seti.org/drake-equation
The problem with the Drake equation is that it has always been both too simple and too dependent upon presuppositions. As one of this paper’s researchers affirms, “the Drake equation is very sensitive to bias.” And yet, it has been leveraged, with optimistic values, to insist that we are surely not alone in the universe. Given the size of the universe, it is simply too alluring to imagine anything else. As the above article encourages us in the end, “But don’t give up entirely… It’s a big universe.”
Here are some specific issues I see in the Drake Equation that might suggest even worse odds.
R* – The rate of formation of stars suitable for the development of intelligent life.
Many characterizations of this value simply describe it as “the rate of formation of stars,” in general. Including “suitable for the development of life” is a crucial distinction, as the vast majority of stars turn out to be lethal, or at least inhospitable, to life. Further, you would need to additionally narrow the criteria if you particularly cared about hospitality to advanced life, which is actually the goal of the equation. It’s one thing to ask what environment is suitable for bacteria, which live in the most extreme places on our planet, but it’s another thing to ask what is required for long-term human flourishing. Our own Sun is often characterized as “average.” But this is only in relation to its size, not its characteristic suitability as a host star. There’s a reason why SETI has come to focus its attention on “solar analogs” in its search for extra-terrestrial life. There are relatively few such stars, and fewer still (if any known) “solar twins” that have all the features of our own, which are deemed to be fortuitous for life.
Additionally, most stars exist in regions of the galaxy that would be toxic. There are many kinds of objects in the universe that are highly energetic which you don’t want as cosmic neighbors. You not only want a hospitable environment, but you also want an environment that provides a low risk of sterilizing events occurring around you in whatever time you believe to be needed to “develop” intelligent life. For the most part, this means you want to be outside of the galactic core, galactic clusters, and spiral arms. That rules out the vast majority of the stars in our galaxy, and some types of galaxies entirely.
fp – The fraction of those stars with planetary systems.
With better and better technology, this is something we actually have hopes of quantifying. My main concern here would be that they insure that their figure represent only the planets we find around hospitable stars, and not just stars in general. There may be a difference in the number and types of planets that they find around solar analogs vs the various other types of stars.
ne – The number of planets, per solar system, with an environment suitable for life.
The planetary requirements for being “suitable for life” are always vastly over-simplified. Usually, it’s seldom more than having water and being in the habitable zone. In fact, this pessimistic Oxford paper only cares that it is a rocky planet that is in the habitable zone. There are so many more factors that are crucial, particularly if you want complex life. Things like the size of your magnetic core, the specific mix of elements in the core, the amount of tectonic activity, having a moon of a particular size, the spin axis, how elliptical the orbit is, the rotational period, the thickness of the crust, the specific mix of elements in the atmosphere, the ocean to continent ration, the diversity of minerals for soil and rock, the amount of atmospheric transparency, etc, etc. In a world where it is claimed that a bit more CO2 in the atmosphere will be a catastrophe for life, all these other factors are Armageddon by comparison.
fl – The fraction of suitable planets on which life actually appears.
This one is the most speculative of all. Given that we have no clue how life arose on Earth, and not even a proposed mechanism that could generate the information-laden molecules on which it depends, then there is no way to answer this question. In fact, it can be argued that it cannot happen by natural processes and thus this variable is zero, which ruins the whole equation. But since life is on Earth, and there is no room for miracles in “real science,” then we must press on and assign some optimistic value that is not suggestive of the statistical and logistical problems of Abiogenesis.
fi – The fraction of life bearing planets on which intelligent life emerges.
This one is not as comparatively bad as fl above, but it is also problematic. Assigning positive values here is based upon the assumption that there is indeed a natural mechanism that drives life “upward” from simple to complex, which would also apply everywhere. Evolution is an explanatory filter for some observations in the history of life on earth. Conspicuously absent from it are any known mechanistic processes that are adequate to produce the required changes. The theory is held in spite of the lack of practical and verifiable explanations, in spite of failed predictions, and in spite of counter-evidences. It is held as an incorrigible belief, and since it is “true” here it must be true out there, too. The only question left, then, is how common it is for the life that inevitably develops to become intelligent enough to communicate.