Ethan Siegel Updates the Drake Equation

Not Even Wrong

Astrophysicist Ethan Siegel may not have been aware of the phosphorous problem when he wrote his article on fixing the Drake Equation which appeared at Forbes last week. But he certainly should have known about origin of life problem. His failure to account for the former is a reasonable mistake, but his failure to account for the latter is not.

The Drake Equation is simply the product of a set of factors, estimating the number of active, technologically-advanced, communicating civilizations in our galaxy—the Milky Way. Siegel brings the Drake Equation up to date with a few modifications.

He is careful to ensure that his final result is not too large and not too small. Too large an estimate would contradict the decades-long SETI (search for extraterrestrial intelligence) project which, err, has discovered precisely zero radio signals in the cosmos that could be interpreted as resulting from an intelligent civilization. Too small an estimate would signal an end to Siegel’s investigations of extraterrestrial intelligence.

What is needed is a Goldilocks numbers—not too large and not too small. Siegel optimistically arrives at a respectable 10,000 worlds in the Milky Way “teeming with diverse, multicellular, highly differentiated forms of life,” but given the length of time any such civilization is likely to exist, there is only a 10% chance of such a civilization existing co-temporally with us.

Ahh, just right. Small enough to avoid contradicting SETI, but large enough to be interesting.

But Siegel’s value of 25% for the third factor, the fraction of stars with the right conditions for habitability, seems much too high give new research indicating phosphorus is hard to come by in the cosmos.

The problem, it seems, is that phosphorus (the P in the ubiquitous energy-carrying ATP molecule you learned about in high school biology class) is created only in the right kind of supernovae, and there just isn’t enough to go around. As one of the researchers explained:

The route to carrying phosphorus into new-born planets looks rather precarious. We already think that only a few phosphorus-bearing minerals that came to the Earth—probably in meteorites—were reactive enough to get involved in making proto-biomolecules. If phosphorus is sourced from supernovae, and then travels across space in meteoritic rocks, I'm wondering if a young planet could find itself lacking in reactive phosphorus because of where it was born? That is, it started off near the wrong kind of supernova? In that case, life might really struggle to get started out of phosphorus-poor chemistry, on another world otherwise similar to our own.

This could be trouble for Siegel. The problem in his goal-seeked 10% result he has committed to specific values. The wiggle room is now gone, and new findings such as the phosphorus problem will only make things worse. Siegel’s 10% result could easily drop by 10 orders of magnitude or more on the phosphorus problem alone.

That would be devastating, but it would be nothing compared to a realistic accounting for the origin of life problem. That is Siegel’s fifth factor and he grants it a value of 1-in-10,000. That is, for worlds in habitable zones, there is a 1/10,000 probability of life arising from non-life, at some point in the planet’s history.

That is absurd. Siegel pleads ignorance, and claims 1-in-10,000 is “as good a guess as any,” but of course it isn’t.

We can begin by dispelling the silly proclamations riddling the literature, that the origin of life problem has been essentially solved. As the National Academy of Sciences once declared:

For those who are studying the origin of life, the question is no longer whether life could have originated by chemical processes involving nonbiological components. The question instead has become which of many pathways might have been followed to produce the first cells [1]

Fortunately the National Academy of Sciences has since recanted that non-scientific claim, and admitted there is no such solution at hand. Such scientific realism can now be found elsewhere as well.

The origin of life problem has not been solved, not even close. But that doesn’t mean we are left with no idea of how hard the problem is, and that 1-in-10,000 (i.e., 10^-4) is “as good a guess as any,” as Siegel claims. Far from it. Even the evolution of a single protein has been repeatedly shown to be far, far less likely than 10^-4.

As for something more complicated than a single protein, one study estimated the chances of a simple replicator evolving at 1 in 10^1018. It was a very simple calculation and a very rough estimate. But at least it is a start.

One could argue that the origin of life problem is more difficult than that, or less difficult than that. But Siegel provided no rational at all. He laughably set the bounds at 1-in-ten and one-in-a-million, and then with zero justification arbitrarily picked 1-in-10,000.

In other words, Siegel set the lower and upper limits at 10^-1 and 10^-6, when even a single protein has been estimated at about 10^-70, and a simple replicating system at 10^-1018.

Siegel’s estimate is not realistic. With zero justification or empirical basis, Siegel set the probability of the origin of life at a number that is more than 1,000 orders or magnitude less than what has been estimated.

Siegel’s estimate was not one thousand times too optimistic, it was one thousand orders of magnitude too optimistic. It was not too optimistic by three zeros; it was too optimistic by one thousand zeros. Siegel is not doing science. He is goal-seeking, using whatever numbers he needs to get the right answer.

Religion drives science, and it matters.