In Part I I introduced the Hard Steps model, and last time we looked at why its central pillar is dubious.

Then we asked: With no puzzle about timescales to solve, why believe in Carter’s solution to that puzzle?  The easy answer is that we do see evolutionary singularities, which suggests that the path Earth took to generating humans is very unlikely and contingent.  Even if Carter’s particular motivation for the model is wrong, surely evolutionary biology supports the existence of “hard steps” independently of that?

So next, Dan looked at the candidate hard steps.  He did a lot of work to compile various proposals for the hard steps, and found they vary a lot.  People seem to agree on abiogenesis, eukaryogenesis, and something special about humans or primates as hard steps, but other guesses are all over the map.

One error he found was people mistaking “Major Transitions in Evolution” for candidate hard steps.  This concept has a well defined meaning in biology, and eukaryogenesis is one of the major transitions, but he points out it’s a category error to conflate the two: despite the name, these major transitions don’t need to necessarily be hard or singular. This is why it’s good to collaborate with people in the fields you’re trying to publish in!

Anyway, Dan looks at what might constitute a hard step and one key is that the event be singular: unlike the evolution of the eye, which is convergent and has happened many times, a super unlikely evolutionary innovation would only be expected to happen once, perhaps because it is so complex.

But Dan points out that even though unlikely innovations will be singular, there are other explanations for singular innovations.

My favorite analogy is abiogenesis: we don’t actually know that life only started on Earth once!  Imagine that some lifeless organic matter on Earth got a fragile start on a brand new form of life going in some corner of a cave pond somewhere. What would happen? It would immediately be lunch! Life on Earth is really good at spreading everywhere and eating everything.

Life-as-we-know-it has fully occupied every available niche on Earth, so a second (or hundredth) abiogenesis has no hope of catching on and surviving.  This is sometimes called an incumbancy effect or pulling up the ladder.  In other words, just because we see only one tree of life on Earth today, all sharing a common ancestor, that does not at all mean it only evolved once.  Being singular does not necessarily imply being “hard”.

Another example of how this could happen is if a species, like cyanobacteria, so fundamentally changes the environment that it prevents an existing innovation from evolving again because the conditions that would induce it are no longer present (like oxygenating the atmosphere).

So many of the apparently singular events in the record might actually not be unique, it could just be that the first time it happened it somehow prevented it from ever happening again.

It’s also possible that many singular events are actually only apparently singular because the other instances have died out.  Dan points out an example of the evolution of plastids, organelles used in cells for photosynthesis.  This was widely regarded as a singular evolutionary event, but recently analogous and unrelated organelles called chromatophores in a particular species, which evolved only a few Myr ago.  He points out that if this rare lineage had died out, we would never know that the event wasn’t really singular and asks: how many other singularities only look that way because we haven’t found (or cannot find) any of the other lineages?

Indeed, we can’t really test the lineage of things in the fossil record: perhaps things that look like eukaryotes are actually from totally independent examples of the form that simply haven’t survived to present day!

The bottom line is that it’s not clear that there are actually any singular events in the evolutionary history of humans—which means there might not be strong evidence for “hard steps” even independent of Carter’s original argument for them.

But surely, you say, humans and our technosphere is singular?  There have never been cities and rockets on Earth before!  But Adam Frank and Gavin Schmidt are way ahead of you on that and have shown that we actually don’t have evidence that’s true!  An ancient technosphere would not be obviously technological in the geologic record.

And we’re not the only technological life on Earth! If we disappeared tomorrow, who knows what the octopi or beavers would get around to doing in a few million years…

Anyway, there’s a lot more in the paper, which I encourage you to read!  You can find it here:

http://arxiv.org/abs/2408.10293

The bottom line is that the hard steps model is dubiously justified on anthropic grounds or evolutionary grounds.  It might be right—in which case we might not expect to find other human-like species int he Galaxy—or it might not. Dan points out what work we can do to try to get to the bottom of this, but in the meantime: don’t worry about the Great Filter! There’s little to no reason to think it exists.

Enjoy!

Last time I introduced the “hard steps” model of Carter and the “Great Filter” model of Hanson.  Now on to the new stuff.

Dan Mills is an affiliate member of the PSETI Center, and a geomicrobiologist. Discussing the hard steps model with him, he became interested in diving in and seeing how it holds up to the scrutiny of someone with deep expertise in these matters, which hitherto had been the province of physicists, economists, and others without any formal biology training.

[I’ve written before about a specific affliction common but not unique to a certain kind of physicist or engineer that because what we do is hard, we can just waltz into other fields and contribute.  As xkcd put it:

And my favorite takedown of the type is from SMBC (go read it!)]

What Dan Mills found was that while there has been a lot of things right in the development of these ideas, the Hard Steps model is actually largely unjustified.  It could be right—but there’s not much reason to think so.

One big flaw in the argument is that there actually is a good reason that evolution on Earth might operate on a timescale coincident with Solar evolution.  One that had been in the literature is that the sun changes luminosity on that timescale by a bit, so that could couple the biosphere to its evolution, but the bigger one is the (somewhat recent) understanding of how tightly coupled geological processes are to the biosphere.

The biggest and most famous is probably the oxygenation of the Earth’s atmosphere.  For most of Earth’s history, the atmosphere had virtually no oxygen, but eventually oxygenic photosynthesis evolved, and began “polluting” the atmosphere with oxygen molecules.  Eventually the oxygen levels got so high that life began evolving to adapt to the new environment.  This is called the Great Oxidation Event.

And animal life on Earth requires oxygen! There’s a whole literature on this, but essentially oxygen provides a way for large animals like us to metabolize our food and get the energy we need to operate, one that’s hard to replicate any other way, biochemically speaking.

Dan charts major milestones in evolution with time against oxygen abundance on Earth here:

In this figure, the past and future of life on Earth is charted.  Oxygen makes a big jump after cyanobacteria show up, allowing eukaryotes to evolve, and then as oxygen goes up even more animals (metazoans) show up.  We are thus today in a window of habitability in which humans could have evolved.  The “death of the biosphere” in 0.5–1 Gyr is from solar evolution which will eventually boil off the oceans.

Dan’s point is that animals show up right when they’re “supposed to” (or, perhaps, “allowed to”), and humans show up shortly thereafter.  This isn’t “late” or weirdly coincidental at all!  The coincidence that Carter based the hard steps model on then isn’t between evolutionary timescales and solar nuclear timescales, but between the latter and the time it takes life to change Earth’s atmosphere, which is set by geophysical factors, which can be billions of years. That’s an interesting coincidence, but that doesn’t seem to be much importance behind it, and, more importantly, it doesn’t implicate human evolution at all!

So the fundamental underlying puzzle that the Hard Steps model was designed to answer might not exist!

With no puzzle to solve, why believe in the solution of the hard steps model?  Well, primarily because we do see evolutionary singularities, which suggest that the path Earth took to generating humans is very unlikely and contingent.  Even if Carter’s particular motivation for the model is wrong, surely evolutionary biology supports it independently of that?

Next time: challenging other aspects of the model

The “Hard Steps” model describes the emergence of “human-like intelligence” on Earth as being the product of one or more extremely unlikely events in the evolutionary history of life on Earth.  It’s famous, and gave rise to the “Great Filter” hypothesis as a solution to the Fermi Paradox—but is it right?

The model starts with Brandon Carter, a physicist who mused why it is that humans arrived right in the middle of the Sun’s main sequence lifetime.  Surely, he reasoned, if species like humans were common in the universe they’d arise quite quickly in a habitable planet’s history, not halfway through it.  What is to account for the coincidence that humans arose 4.5 billion years after the sun formed, and this halfway through its main sequence lifetime?

Brandon Carter

He considered 3 possibilities for how long it takes human-like species to evolve: they typically take a time much much less than 10 billion years (the lifetime of the Sun), or about 10 billion years, or much longer than 10 billion years.

The first option makes no sense: Earth should have had humans billions of years ago.  The second option is a bizarre coincidence: why should human evolution just happen to take around 5 billion years, and not 5 million years or 5 quadrillion years? Seems unlikely.

The third option seems wrong at first glance: if the hypothesis is that humans take trillions of years to form but we formed in only billions, surely the evidence contradicts that? But the anthropic principle explains it:  human-like intelligences will occasionally, rarely, arise exceptionally early in some very lucky systems, and those are the only places they’ll be found in a universe “only” 14 billion years old.

In other words, if it takes trillions or more years for a human-like intelligence to form on average, then in the 200 billion stars in the Galaxy, the only places we’ll find them are the amazingly lucky stars where they formed comparatively early—which is most likely about halfway through their lives.

This is a really elegant and persuasive argument!  It definitely appeals to the physicist in me, and it’s been very influential.

Since Carter’s argument we’ve come to understand that we formed rather late in the Earth’s habitable history—the sun will grow in luminosity and boil off the Earth’s oceans in “only” 1 billion years or so.  This has led to the argument that there might have been not just one but perhaps 5 or more “hard steps” that are all very unlikely, and we arrived “late” in the Earth’s habitable history because Earth is the extraordinarily rare—perhaps unique— planet that managed to accomplish all of them before becoming uninhabitable.

This model led to many authors, including physicist (and crackpot) Frank Tipler and economist Robin Hanson to embrace this framework and try to identify the “hard steps.”  Common suggestions include abiogenesis (the origin of life), photosynthesis, the evolution of eukaryotes (which a certain sort of cellular complexity), and the evolution of animals as examples of potential “hard steps”.

Each of these things is associated with an “evolutionary singularity”—something that seems to have only happened once in the history of life on Earth.  Singularities are contrasted with convergent traits like eyes—things that are so useful evolution seems to figure out a way to invent them over and over again.  By contrast, a singularity is an event that produces a trait that only evolves once—all species that have the trait inherited that trait from a single, common ancestor.  Such singularities might represent extremely unlikely evolutionary innovations that were so useful they spread widely, but so unlikely they never evolved again, despite their utility. Evolutionary singularities are great candidates for “hard steps”!

Robin Hanson is a particular advocate for this model, and proposed a “solution” to the Fermi Paradox (why no aliens are on Earth today) called the “Great Filter.”  In this model there is one “hardest step” between lifeless planets and a species that colonizes every planet in a galaxy.  It might be “behind us”—abiogenesis or one of the other “hard steps”—or it might be “in front of us”—an alien species that eradicates any species that develops spaceflight, maybe.

Both the Hard Steps model and the Great Filter model have great popular salience and widespread traction in the SETI literature, but, oddly enough, not in evolutionary biology where, one would think, it would be particularly useful if it had merit.  How odd!  Or, as Dan Mills put it in a recent paper:

Curiously, while these issues concern the evolutionary history of Earth’s biosphere, comparatively few Earth historians and evolutionary biologists have responded to Carter’s arguments in the literature, having left astrophysicists, economists, and futurists to champion the hard-steps model unchecked. Given this situation, could it be that the hard-steps model has only endured for as long as it has because the fields best suited to falsify it have been historically unengaged?

Dan is an affiliate member of the PSETI Center (and PSU alum!) and he led a paper, cheered on by Adam Frank, Jenn Macalady, and me, to examine these issues.  It’s been a lot of fun looking into this with a critical eye from someone with actual expertise in evolutionary biology.

Next time: What an actual geomicrobiologist thinks about the hard steps reasoning

Here’s a picture of my great grandparents John Henry Hattersley and Bertha Herrmann at Niagara Falls in 1910:

I’m presuming this is a real photograph and not staged with a backdrop or something, but I really don’t know. I think this was taken on Luna Island on the American Side.

I don’t know much of anything about them except that Bertha is the only non-English-origin great-grandparent of mine I’m aware of; I don’t remember my grandfather talking about them.  At one point I really got into tracking my family tree: I even discovered at one point that my lineage can be traced back to Boston Colony (via John Viall through my paternal grandmother’s father Clifford Viall Thomas). But I long ago stopped imagining that I was somehow learning about myself once I got to people beyond living memory.

It’s always bothered me when people say siblings share half of their genes. Similarly, people who can trace their decent to someone famous (Charlemagne, Jefferson) and seem to think this reflects well on their genes or something.  There are a few reasons this can’t be right, a few of which I think about in particular:

1. We share 98.8% of our DNA with chimpanzees—we must share much more than that with our siblings!  In fact it seems that the “average pairwise diversity” of randomly selected strangers is around 0.1%.
2. There is some level of discretization with DNA inheritance.  Obviously it can’t be at the base-pair or codon level, or else we wouldn’t be able to reliably inherit entire genes.  If the “chunks” we inherit from each parent are large enough, small number statistics will be push the number significantly from 50%.
3. Mutations slowly change genes down lineages
4. Combinations of genes and epigenetic factors have strong effects on traits

Point 2 is not something I really understand yet, except that talking to biologists I think the number of “chunks” that get passed down on each side is ~hundreds, but is also random making the problem quite tricky.  Still, ~hundreds means that we are probably close enough to ~50% inheritance from grandparents on each side (+/- 10% or less) that we can get a rough idea of how related we really are to people on our tree in terms of shared DNA.

So let’s take a closer good at point 1 above:

Let’s assume the amount of identical DNA we get from each ancestor is given by 2^-n where n is the number of generations back they are (grandparents: n=2, so 25% inherited DNA, ignoring discrete “chunks” and mutations). This makes sense: except for (many) details like the X/Y chromosomes, mitochondria, and probably a bunch of other things, each ancestor a given number of generations back has an equal chance of having contributed a bit of DNA to you.

Finding the amount of shared inheritance is thus a matter of going back to the first shared ancestor and counting all of the shared ancestors at that level (which will be 1 in the case of for half siblings and 2 for full siblings, except for details coming later).

So cousins share 2/4 grandparents, each of whom had a 2^-2 chance of contributing a bit of DNA, so they have 1/8 shared bits of DNA or around 12.5%.

Second cousins (the children of first cousins) share 2/8 grandparents, so the number is 6.25%. Each generation gap gives us a factor of 1/4: a factor of 2 from the extra opportunity on each line to “lose” that bit of DNA, one on each side.

Now we get into the fun of “removed cousins”, which just counts the generation gap between cousins. You don’t usually get big numbers of “removals” among living people because it requires generations to happen much faster along one line than another—big numbers like “1st cousins 10 times removed” are usually only seen when relating people to their distant ancestors.

So my kids are my first cousins’ “first cousins once removed”, and all of their kids would be “second cousins once removed”. The rule is that if you have “c cousins r removed” (so c=2 r=1 means “second cousins once removed”) then you have to go back n=c+r+1 generations from the one and n=c+1 from the other to find the common ancestors.  So removals count the number of opportunities to “lose” a bit of DNA that occur on only one side of the tree.

Putting it all together: the amount of shared DNA we share with a cousin is 2^-(2c+r+1) (siblings have c=r=0, subtract one from the exponent if the connection is via half siblings).

But there’s a limit: this only works if none of the other ancestors are related, but in the end we’re all related. If cousins have children, this increases the number of shared ancestors and raises the commonalities. And, of course, mutations work the other way, lowering the amount of identical bits.

So why is this interesting? Because the “we’re all related” thing is true at the 0.1% level in DNA, meaning that if you make c high enough, you’ll get an answer that’s below the baseline for humans. Since log₂(0.1%) = -10, we have that if 2c+r+1 >10, the DNA connection is no stronger than we’d expect for random strangers.

This means that if you meet your 4th cousins (i.e. your great-grandparents were cousins) your genealogical relationship is mostly academic and barely based on “blood”!  By 5th cousins, you’re no more related than you are to the random person on the street in terms of common DNA.

Even worse, if we have hundreds of “chunks” we randomly inherit from parents, then it’s even possible (and here I’m a bit less sure of myself) that you share no commonly inherited genetic material with someone as distantly related as a 5th cousin!

Again, this calculation makes a lot of assumptions about genes from different ancestors being uncorrelated, and in particular communities that have been rather insular for a very long time must have at least a bit more kinship with each other than they do with similar communities on different continents.  But from what I’ve gathered this effect isn’t that large: the variance in genetics within a community, even an insular one, is still usually larger than the difference across communities.  That is, the average person from one place is more similar genetically to the average from another place than they are to a random person in their own place.

And also, this doesn’t mean you can’t prove descent from someone more than 10 generations past via DNA—that might indeed be possible by looking at where common bits of DNA are in the chromosomes and similar sorts of correlations (I would guess).

Anyway, the bottom line is that it’s fun to do family trees and learn about our ancestors where we can, but we definitely shouldn’t get too hung up on the idea that we’re learning about the origins of our genes and kinship via biology—even setting aside the fact of old family trees being full of adopted and “illegitimate” children, the actual genetics dilute out so fast it hardly matters past great-grandparents.

I love the Research Notes of the AAS.  They are a place for very short, unrefereed articles through AAS Journals, edited (but not copyedited!) by Chris Lintott. They are a great place for the scraps of research—those little results you generate that don’t really fit into a big paper—to get formally published and read.

You might think that without peer review and with such a low bar for relevance, such a journal would have a very high acceptance rate, but actually I’ve read it’s the most selective of the entire AAS family of journals, including ApJL!  The things it publishes are genuinely useful, and shows that there’s a need for publishing models for good ideas that are too small to be worth the full machinery of traditional publishing.  The curation by Chris also ensures that the ideas really are interesting and worthy of publication.

A while back I wrote a Research Note on how to prove the Earth moves with just a telescope and a camera. Nothing that would leave to novel results, but it has inspired some amateurs to try it out!

For my latest note, I’ve got another trick you can do with nothing but a telescope and a camera, although in this case they’ll cost billions of dollars and do something useful and novel!

Whenever I hang out with Eric Mamajek we end up talking science and coming up with cool ideas. This often ends with one of us starting an Overleaf document for a quick paper that never ends up getting written.  But the idea we had on my last trip was good enough that I was determined to see it through!

The idea goes back to Eddington’s eclipse experiment, wherein he showed that a gravitational field deflects starlight at the level predicted by General Relativity (which is twice the level one might deduce from Newtonian gravity).

To do this, he imaged the sky during a total solar eclipse, when he could make out stars near the sun.  Comparing their positions to where they were measured during the night at other times of year, he showed they were significantly out of place, meaning the Sun had bent their rays. Specifically, he found that they were farther from the Sun by about an arcsecond (in essence, the Sun’s focusing effects allows us to see slightly behind it, and so everything around it appears slightly “pushed away” from its center.)

This led to a great set of headlines in the New York Times I like to show in class:

This is actually an example of what today we confusingly call microlensing. This actually captures a broad range of lensing effects, as Scott Gaudi explained to me here (click to read the whole thread).

the magnification pattern from individual stars. Galactic microlensing, where the images are separated by milliarcseconds, is just an abuse of the original term, and has sense come to mean cases where the images are unresolved, as @macyjhuston says.

— Scott Gaudi (@bsgaudi) September 20, 2023

Microlensing is most obvious when a source star passes almost directly behind a lens star—specifically within its Einstein radius, which is typically of order a few milliarcseconds. This level of alignment is very rare, but if you look at a dense field stars, like towards the Galactic Bulge, then there are so many potential lenses and sources that alignments happen frequently enough that you can detect them with wide-angle cameras.

In close alignments like this, the image of the background source star gets distorted, magnified, and multiply imaged, resulting in it getting greatly magnified in brightness, as shown in this classic animation by Scott.  Here, the orange circle is the background source star passing behind the foreground lens, shown by the orange asterisk. The green circle is the Einstein ring of the foreground lens.  As the background star moves within the Einstein ring, we see it as two images, shown in blue.

We typically do not resolve the detail seen in the top panel, we only see the total brightness of the system.  The brightness of just the background source is plotted in the bottom panel.

But in the rare cases where we can resolve the action, note what we can see: the background star is displaced away from the lens when it gets close, just like in Eddington’s experiment. This effect is very small, just milliarcseconds, and has only been measured a few times. This is called astrometric microlensing.

Rosie Di Sefano has a nice paper on what she dubs “mesolensing”: a case where instead of a rare occurence rate of lensing among many foreground objects, like in traditional microlensing surveys, you have a high rate of lensing for a single foreground object.  This occurs for very nearby objects moving against a background of high source density, like the Galactic Bulge.

The reason is that the Einstein ring radius of nearby objects is very large—for a nearby star it is of order 30 mas, or 0.”03.  Now, there is a very low chance of a background star happening to land so close to a foreground star, but foreground stars tend to move at several arcseconds per year across the sky, so the total solid angle (“area”) covered by the Einstein ring is actually a few tenths of a square arcsecond per year, which is starting to get interesting.

Things are even more interesting if you don’t require a “direct hit”, but consider background stars that get within just 1″ or so of the lens: even though it’s 30 Einstein radii away, the astrometric microlensing effect is still of order 1 mas, which is actually detectable!

Now, most of these background objects are very faint, so this isn’t really something you can exploit. Twice, people have used the alignment of a very faint white dwarf and some background stars to see this happen, and also once with the faint M dwarf Proxima. But most main sequence stars are so much brighter than the background stars, that their light will completely swap them.

But detecting very faint objects within a couple of arcseconds of bright stars is exactly the problem coronagraphy seeks to solve with the upcoming Habitable Worlds Observatory!  This proposed future flagship mission will block out the light of nearby stars and try to image the reflected light of Earth-like planets orbiting them.  And while it’s at it, it will see the faint stars behind the nearby one at distances of a few to dozens of Einstein radii.

So, for target stars in the direction of the Galactic Bulge, HWO will detect astrometric microlensing! And it will do this “for free”: it will be looking for the planets orbiting the star, anyway!

So, who cares? Is this just a novelty? Actually, it will be very useful: measuring the astrometric microlensing will directly yield the mass of the host star. This is great, because we have almost no way of doing this otherwise: we need to rely on models of stellar evolution, which are great but still require conversion to observables, which comes with systematic uncertainties of order a few %.  Directly measuring stellar masses will allow us to avoid those systematics, and better understand each star’s history—and that of its planetary systems.

Now, if we find planets with orbital periods of a few years or less, we can also measure the host star masses using Kepler’s Third Law, but this is an independent way to do this, and it also works on stars without planets. In principle, you could even go pointing HWO at all of the stellar mass objects towards the bulge to do this measurement, making it a pure stellar astrophysics engine (precise stellar masses don’t sell flagship missions like exoplanets do, though).

The final piece of this calculation was we needed to know what the background source density of HWO target stars were. As luck would have it, my recent advisee Dr. Macy Huston had just graduated, and the final chapter of their thesis is on a piece of Galactic stellar modeling software that does exactly this calculation for microlensing! It’s called SynthPop and you’ll hear about it soon, but in the meantime they were able to calculate how many background sources we expect from an example HWO architecture around likely HWO targets.

Macy finds that the best case of 58 Oph will likely have over 15 stars in the coronagraphic dark hole that will show astrometric microlensing, giving us a ~5% mass measurement of the star every visit. These numbers are very rough by the way—the precision could easily be better than this.

Anyway, this RNAAS was a lot of fun to write, and you can read all of the details in it here.

The bottom line is that HWO will be able to measure the masses of all sorts of stars towards the Galactic Bulge directly, with no model dependancies!

Enjoy!

Why I am Responding Here

As the head of the PSETI Center I need to address a controversy and correct some factual errors circulating about the Codes of Conduct at various PSETI-related activities, one of which led to the abstract of an early career researcher (ECR), Dr. Beatriz Villarroel, being rejected from an online conference organized by and for ECRs, the Assembly of the Order of the Octopus.  This controversy has been brewing on various blog posts and social media, and recently became the subject of a lengthy email thread on the IAA SETI community mailing list.

Sexual harassment is widespread in science and academia in general, it is completely unacceptable, and, when these kinds of issues arise, our focus and priority as a community should be to protect the vulnerable members of our community.

Much of this criticism has been directed at the PSETI Center and specifically at its ECRs and former members. This discussion has also been extremely upsetting not only for these ECRs, but for researchers across the SETI community and beyond, especially those that have been victims of sexual harassment, and to minoritized researches who need to know that the community they are in or wish to join will protect them.

For these reasons and many more, these attacks warrant a response, explanation, and defense from the PSETI Center.

Background

I don’t want to misrepresent our critics’ positions. You can read Dr. Villarroel’s version of events and their context for yourself here.

The background for this story involves Geoff Marcy, who retired from astronomy when Buzzfeed broke the story that he had violated sexual harassment policies over many years. Since then many more stories of his behavior have come to light, and the topic of whether it is appropriate to continue to work with him and include him as a co-author has come up many times. I am particularly connected with this story because Geoff was my PhD adviser and friend, and for a while I continued to have professional contact with him after the story broke. I have since ended such contact with him and apologized after discussions with my advisees and with victims of his sexual harassment gave me an understanding of why such continued association was so harmful.

This particular story begins at an online SETI conference in which Dr. Villarroel presented research she was doing in collaboration with Marcy, during which she showed his picture on a slide. This struck some attendees as gratuitous and as potentially an effort to rehabilitate Marcy’s image in the astronomical community. It also struck some as insensitive to victims of sexual harassment and assault, especially to any of Marcy’s victims that may have been in attendance.

Around this time, a group of ECRs in SETI decided to revive the old “Order of the Dolphin” from the earliest days of SETI, rechristened as the “Order of the Octopus.”  This informal group of researchers builds community in the field, and the PSETI Center is happy to have provided the it some small financial and logistical support.  The Order decided to meet online during the COVID pandemic in their first “Assembly.”  As they wrote: “In designing the program for this conference, we are also striving to incorporate principles of inclusivity and interdisciplinarity, and to instill these values into the community from the ground up.“

I was not an organizer of the Assembly, but I think it is fair to say that they wrote their code of conduct in a way that would ensure that image and presence of any well-known harasser like Marcy would not be welcome. This effectively meant that abstracts featuring Marcy as co-author would be rejected, and that participants were asked to not gratuitously bring Marcy up in their talks.

What happened: The Assembly of the Order of the Octopus and the Penn State SETI Symposia

More than one researcher that applied to attend the 2021 Assembly of the Octopus, including Dr. Villarroel, had a history of working with Marcy. To ensure there were no misunderstandings, those applicants were told in advance that they were welcome to attend the conference provided that they abided by the aspects of the code of conduct, and the language in question was highlighted.

When the organizers of the Assembly learned that Dr. Villarroel’s abstract was based on work published with Marcy as the second author, they withdrew their invitation to present that work, but made clear she was welcome to attend and even to submit an abstract for other work.

Dr. Villarroel chose not to attend the Assembly.

Similar code of conduct language appeared in two later PSETI events, the Penn State SETI Symposia in 2022 and 2023.  Dr. Villarroel did not register to attend or submit an abstract for either symposium.

What happened: The SETI.news mailing list and SETI bibliography

Another source of criticism of the PSETI Center involved me directly. At the PSETI Center we maintain three bibliographic resources for the community: a monthly mailer¹ of SETI papers (found via an ADS query we make regularly), an annual review article, and a library at ADS of all SETI papers.

Dr. Villarroel wrote a paper with Marcy as a second author which does not mention SETI directly, but obliquely via the question of whether images of Earth satellites appear in pre-Sputnik photographic plates. This paper did not appear in our monthly SETI mailer, and Dr. Villarroel contacted me directly to ask that it appear in the following month’s mailer.

I declined. As I wrote:

Hi, Beatriz.Thanks for your note.

Your paper slipped through our filter because it doesn’t mention SETI at all, or even any of the search terms we key on. Did you mean to propose an ETI explanation for those sources? At any rate, if you mean for it to be a SETI paper we can add it to the SETI bibgroup at ADS so it will show up in SETI searches there (especially if there are any followup papers regarding these sources or this method).

As for SETI.news, that is a curated resource we provide as a service to the community, and we have decided that we don’t want to use it to promote Geoff Marcy’s work. This isn’t to say that we won’t include any papers he has contributed to, but this paper has him as second author and, since I know his style well, I can tell he had a heavy hand in it.

Best,

Jason

Dr. Villarroel has taken exception to my message, saying that it implies she “wasn’t the brain behind [her] own paper.” I have also learned that Dr. Villarroel feels this implication is sexist.

My meaning here was simply that Marcy’s name on an author list wasn’t an automatic bar from us considering it—we were specifically concerned with recent work he had made substantive (and not merely nominal) contributions to. I think the first part of the offending sentence makes this clear. As someone who worked very closely with Marcy for many years (and as someone who is familiar Dr. Villarroel’s other work) I felt that I could tell that he had more than a nominal role in the work behind the paper. I felt that this and his place on the author list justified that paper’s exclusion from the mailer.

But while it was certainly not my meaning, I do acknowledge the insidious and sexist pattern of presuming that papers led by women must not be primarily their own work, and that men on the author list—especially senior men—must have had an outsized role in it. Now that Dr. Villarroel has pointed this out, I do regret my choice of words, acknowledge the harm they’ve caused, and here apologize to Dr. Villarroel for the implication. For the record: I do believe that paper was led by Dr. Villarroel and is primarily hers.

Dr. Villarroel

While I obviously disagree with some of Dr. Villarroel’s interpretations of these events, I don’t think she has publicly misrepresented them. Others have, however, perpetuated misinformation in the matter.

Specifically, I want to make clear that Dr. Villarroel was never “banned” from any PSETI-related conference, and Dr. Villarroel is not being punished for her associations with Marcy with our codes of conduct.  The prohibitions at the PSETI symposia are targeted at harassers, and include work they substantially contribute to. Dr. Villarroel is welcome to attend these conferences in any event, and to present any research that does not involve Marcy.  She and her work have not been “cancelled”, and her work with Marcy appears in the SETI bibliography we maintain.

I also want to acknowledge the large power differential between me and Dr. Villarroel. I understand that I have some power to shape the field and her career, while she has almost none over my career. It is for this reason that I have avoided discussing her in public up to this point, or initiating any engagement with her at all.  If she were more senior I would certainly have defended our actions and pushed back on her characterizations of me and the PSETI Center sooner.

At any rate, I do not bear her any ill will and I absolutely do not condone any harassment of her. That said, I understand why people are upset that she would continue to work with Marcy, and they are entitled to express that displeasure, even in potentially harsh terms, especially in private or non-professional fora, as long as they are not “punching down,” doing anything to demean, intimidate, or humiliate her, or sabotaging her work.

The Order of the Octopus SOC

I also want to acknowledge the large power differential between many of the PSETI Center’s critics and the chairs and the organizing committees of our various conferences that have contributed to the Codes of Conduct, many of whom are ECRs. This is another reason that I am responding here: to give voice to those who have far less power than I that are being attacked.

Critiques of the PSETI Center’s actions here should therefore be directed at me: I am the center director and conference chair of both symposia, and I take full responsibility for our collective actions here.

What Sorts of Codes of Conduct are Acceptable

Many have argued our bar against harassers’ work is completely inappropriate, being both unfair to Marcy and even more unfair to his innocent co-authors. I disagree, and argue that it is in fact an appropriate way to protect vulnerable members of the community who are disproportionately harmed by sexual harassment and predation.

As an aside, I note that the PSETI Center is not alone in this position; it is also consistent with our professional norms. I would point to the AAS Code of Ethics which includes a ban from authorship in AAS Journals as a potential sanction for professional misconduct. Such a sanction is analogous to a ban from authorship on conference abstracts.  It is true that this ban also affects innocent co-authors, but a harasser should not be able to evade a ban by gaining co-authors. That is not guilt-by-association for the co-authors; it is a consequence of a targeted sanction. It is certainly not harassment of those co-authors.

I admit I find this whole episode to be somewhat confounding.  A small group of ECRs got together to hold a meeting and had a no-harasser rule, this was enforced, and now years later it’s the subject of a huge thread on the IAA SETI community mailing list, the subject of Lawrence Krauss blog posts, the basis of an award by the Heterodox Academy, and creating so much drama that I need to address it here.

I also find it ironic that many complaining about the Order of the Octopus being selective about who they decide to interact with at their own conference are ostensibly doing so to protect the principle of…freedom of academic association. To be clear: Dr. Villarroel is free to collaborate with Marcy or anyone else she chooses. This is a cornerstone of academic freedom. Are the members of the Order of the Octopus not equally free to dictate the terms of their own collaborations and the scope of their own meeting, and to select abstracts as they see fit? Freedom of association must include the freedom to not associate, or else it would be no freedom at all.

Now, I acknowledge that there are limits to this freedom: one should not discriminate on matters that have nothing to do with science, especially against minoritized people. But that’s not what’s going on here: Marcy’s behavior is worthy of sanction, and our sanctions are entirely focused on harassers like him and their research, and only to protect vulnerable members of the community.  As I wrote, Dr. Villaroel is not guilty by association, and is welcome at future PSETI symposia, provided she abides by the Code of Conduct.

As for what behavior is appropriate towards those, like Dr. Villarroel, who choose to work with Marcy and the like, I think this is nuanced.  Especially in large organizations, we should honor people’s freedom of association and in general this means those people should not lose roles or jobs for this choice alone. There should be no guilt by mere association, especially by past association—indeed, as a longtime collaborator of Geoff’s, including for years after his retirement and downfall, I am particularly sensitive to this point.

But the choice to work with Marcy will have inevitable consequences. If you are working with him, many people will rightly not want to do work with you that might involve them with him, and there are excellent reasons why one might avoid working with those who have an official record of sexual harassment violations. My students are wary of working with groups that involve Marcy, because this had led to students finding themselves on conference calls with Marcy, finding themselves on author lists with him, and getting emails from him as part of the collaboration.  For me to honor my students’ freedom to not associate with Marcy, I have discovered the hard way that I need to be very careful with anyone working with him, and that I must turn my own interactions with him down to zero.

Affirmative Defense of our Codes of Conduct

At any rate, we’ve done nothing wrong. We’ve decided where we at the PSETI Center will draw the line on notorious sexual harassers like Marcy and I am confident it is the right choice for us. Other meetings and organizations will deal with this in their own way that might be different from or very similar to ours, but either way I’m confident that the majority of astronomers are comfortable with the choice we’ve made.

There is a troubling lack of empathy for the victims of sexual harassment in these abstract discussions about academic freedom. When a notorious harasser’s face and name and work pops up in a talk, we need to remember their victims may be in the audience. Other victims may be in the audience. Allowing that to happen sends a message to everyone about what we, as a community, will tolerate, and whose interests we prioritize.

And the attacks on our code of conduct and the stance we have taken continue to do harm. The ECRs that helped write and enforce these codes are reminded that no matter how badly an astronomer acts, there will always be other astronomers there to apologize for them, to ask or even demand that their victims forgive them, to accept them back into the fold, to act like nothing happened, to insist that only a criminal conviction should trigger a response, to question, resist, and critique sanctions, and to attack astronomers that would insist otherwise.

If we, as a community, claim that we won’t tolerate sexual harassment, we need to show that we mean it by enforcing real sanctions that seek to keep our astronomers feeling safe. If we can’t do that for as clear and notorious a case as Geoff Marcy, then we can’t do it at all, and we will watch our field hemorrhage talent.

I am grateful to the many astronomers and others that passed along words of support to our ECRs as this criticism has rained in. I hope in the future more astronomers, especially senior ones, will speak up publicly to defend a strong line against sexual harassment in our community and show with their actions, voices, and platforms that all astronomers can be safe in our field.

¹I should have been more precise in my language. James Davenport the sole owner and operator of the seti.news website and mailer. For a while I and other PSETI Center members supplied the data that populated it (we haven’t had the bandwidth for a while now, but hope to start up again soon). This is why the issue of Dr. Villarroel’s paper went through me.  You can read Jim’s position on the topic here:

I am the sole owner and operator of https://t.co/fIfWMhWisw. I pay for the hosting out of my own pocket, and feel Marcy is not currently welcome to have his work & influence advertised by my personal labor or my "platform".

— @jradavenport.com on BSky (@jradavenport) September 30, 2023

The name of JWST, the James Webb Space Telescope is in the news again.  If you’re not familiar with the story, I recommend the Just Space Alliance video here:

which summarizes the case against keeping the name.

As I write this, I’m told the release of a NASA report on James Webb’s role in the Lavender Scare and the firing of LGBT NASA employees is about to become public. I’ve been involved in this because I sit as an ally on SGMA, the committee which advises the American Astronomical Society on LGBTQ+ issues. On this committee, I was lead on the issue of learning about what NASA was doing about this. I spoke with the Acting NASA Chief Historian, Brian Odom, about his research on this.

Below is how I see it.  If you think we should keep the name, please read the following with an open mind. Note, some of what appears below was drafted in collaboration with other SGMA members, as part of our recommendation to the AAS.

The name of the telescope really matters, and we need to get it right

The Hubble Space Telescope (HST) has shown that the name of NASA’s flagship observatories can become synonymous with astronomical discovery and gain deep resonance and symbolism among both astronomers and the public at large. Astronomers tout the discoveries of Hubble in interviews and public talks, they festoon their laptops and backpacks with Hubble mission patches and stickers, and some of the most talented young astronomers bear the title “Hubble Fellow.” For many members of the public, the Hubble Space Telescope may be the only scientific instrument or laboratory they can name.

Since JWST is in many ways a successor to HST, and is likely to occupy a similarly important role in astronomy and the public’s perception of the field, it is especially important that its name be appropriate, that it inspire, and that be something everyone who works on and with it can be proud of.

Despite this, NASA gave the telescope an uninspiring name

When the name was announced, there was a distinct sense of confusion and disappointment in the community.  “Who’s that?” was the refrain.

I and many others sort of accepted it because we didn’t really think too hard about it, but it’s a huge missed opportunity. The name doesn’t inspire. When people ask for why it’s called that, most astronomers shrug and say “he was the NASA administrator during the Apollo era” and move on to the next topic. It’s a name only a NASA administrator could love.

This isn’t to say that administrators don’t do important things that should be acknowledged! Administration is hard and good administration is so valuable it absolutely should be celebrated. And perhaps if his legacy were different astronomers would celebrate his name and be glad to see his name on this telescope.

But the name just has no resonance here.

Despite this, NASA named the telescope with no input from stakeholders

NASA’s international parters were not involved in the decision. Astronomers were not involved in the decision. The people who built it were not involved in the decision. Lawmakers and policymakers were not involved in the decision. Elected officials were not involved in the decision.

The name was poorly chosen, and does not reflect NASA’s (purported) values

The decision was made by one NASA administrator, to name the telescope after another NASA administrator, and this name has been stubbornly kept by a third NASA administrator.

This is bad precedent, and the current fallout is a great illustration of why. In James Webb’s NASA, gay employees were fired. Clifford Norton was arrested, interrogated, and fired.

This is not the organization that today’s NASA aspires to be (we hope!).

It’s not too late to change it

NASA changes the names of space telescopes and missions all the time. It‘s very common for things to have boring names on the ground (AXAF, SIRTF) and inspiring names once they’re working (Chandra, Spitzer).  We all adjust. It’s not a big deal.

At this point, NASA’s resistance has gone from stubbornness to recalcitrance. Already, NASA employees are refusing to use the name in prominent publications. The Royal Astronomical Society says it expects authors of MNRAS not to use the name.  The American Astronomical Society has twice asked the administrator to reopen the naming process (and received no response!).  This is an error that only grows as NASA refuses to fix it.

NASA needs to think about the people using the telescope

Think for a moment about the LGBT NASA employees working on JWST today. They want to be proud of their work, proud of the telescope, proud as LGBT NASA employees.

But just to use the name of the telescope is to name a man who, undisputedly would have had them fired. This feels perverse to me.

Right now, the premier fellowship in astronomy is the Hubble Fellowship. When Hubble finally goes, will it become the Webb Fellowship? If you advise students, how would you feel recommending an LGBT student apply for that fellowship? How would you feel when they tell you they’re uncomfortable attaching the name of someone who undisputedly would have fired them to their career, to their CV, to their job title?

This, of course, isn’t just a “gay issue”. We all have LGBT colleagues, friends, and family. Beyond that, we want astronomy, space, and NASA to be inclusive and inspiring in all ways. What precedent does this whole fiasco set for that future we seek?

The telescope deserves a better name.  Astronomy deserves to have a telescope that reflects our values. America and the world deserve a telescope that inspires. Even those who are defending Webb have to concede the current name is not doing those things.

Let’s do better. Why not?

All that said, there is a lot of interest in the specific accusations of homophobia and bigotry by Webb. I’m pretty sure that will be the focus of the NASA report that’s about to come out and of most of the ensuing discussion.

I think this is a distraction. Now, the evidence seems to indicate that, at the very least, he did not see enough humanity in LGBT people needed to protect them from unjust policies. But regardless, his bigotry is not part of my argument for changing the name. (That said, if there is some sort of smoking gun document revealing his personal involvement in these firings or personal animosity towards gay people, that makes the case even stronger).

And even though they are beside my point, I find most of the defenses of Webb lacking.  Here are some common ones I see and hear:

All of the accusations against Webb (the misattributed homophobic quote, his place in the chain of command) are false.

There is a long back story to how this issue came up, of a few specific accusations that turned out to be false, and others that turned out to be very true, and so on.  You can easily find it if you Google around or search on Twitter.

The bottom line is that he had a leadership role at State during the Lavender Scare and was chief administrator at NASA when LGBT employees were fired (and worse). This is undisputed, and it is enough.

This is just a woke mob “canceling” and smearing the name of an innocent man.

This isn’t James Webb on trial. I’m not basing my argument on his being a nasty bigot, because even if he wasn’t we should still rename the telescope.

The standards for putting someone’s name on the most important scientific instrument of a generation should be very high, and there’s no shame in not having your name on it.

But what if he was, in his heart, not a bigot and actually worked behind the scenes in undocumented ways to minimize the Lavender Score? I think, given the balance of evidence, that this is unlikely, but just to entertain the logical possibility: in that case I’m sorry his legacy is caught in the middle of this and I’m sure this is infuriating for his family and people who respected him a lot, but this is much bigger than James Webb and his legacy. Again, this is not “James Webb on trial”; it’s “what should we name the telescope?”

Wasn’t Webb just a “man of his time”? Why should we judge people in the past by standards of today?

This argument all but concedes he was a bigot, which is enough to rename the telescope. But, entertaining it:

First of all, plenty of people at the time understood that sexual orientation had no bearing on one’s ability to work at NASA. Most LGBT people understood that, for starters.

Secondly, the argument that it made them susceptible to blackmail to foreign adversaries and so it was objectively reasonable to fire them is not as strong as it looks. After all, one way to fix that problem is to make it absolutely clear to employees that if they are outed, they won’t lose their livelihood.  Every fired gay employee is a gift to potential blackmailers, handing them leverage over other closeted employees on a silver platter.

But even granting he was a man of his time, this argument completely fails.

Of course we are judging the namesake of the telescope by today’s standards.  Why would we choose any other? We are here today, with the telescope of today. Its name should reflect today’s standards! Why wouldn’t it?

Don’t you worry that people of the future will “cancel” great people from our time for moral lapses by future standards?

I don’t worry about that at all. If I end up (in)famous for something and people in the year 2500 spit after saying my name because I ate meat from slaughtered livestock, which they consider an unspeakable evil—well, that makes sense right? Why would you celebrate people who lived lives antithetical to your values?

Firing LGBT people at State and NASA was the law of the land at the time.  There’s little he could have done and he wasn’t directly involved anyway.

If we concede that he was just doing his job, then we also concede away the only good argument for naming the telescope after him.  James Webb did not design or build the Saturn V rockets, he did not calculate the trajectories of the capsules, he did not walk on the Moon. He was a (by all accounts highly effective) administrator who oversaw those things.

If he gets credit for the good things that happened on his watch obviously he should get demerits for the bad.

There’s no evidence he’s a bigot. His heart wasn’t in firing LGBT people the way it was in, for instance, integrating NASA. 

There’s a double standard at play where simply listing his (very impressive!) accomplishments at NASA is sufficient for justifying the name, but when it comes to bad things happening on his watch we need some sort of smoking gun, evidence of mens rea, to understand where his heart was on the matter.

Anyone demanding evidence of his bigotry should be ready to put forward evidence of his personal virtues on other items, not just lists of things good happening on his watch.

OK: James Webb went above and beyond to integrate NASA. He gave an impassioned speech about it.

Based on what I’ve seen, we really don’t know his views on race.  We do know that Johnson charged him with using NASA as a lever to integrate the South.  We do know he was a loyal foot soldier who understood the assignment and got it done.  It’s unclear to me what extracurricular activities he was doing to promote racial equality.

But isn’t every name problematic? Everyone in the past had something that people today will object to.

First of all,  I’m sure we can find people who didn’t have a demonstrated track record of ruining innocent people’s lives like Webb’s NASA did.

Secondly, the onus of solving the problem of what the perfect name is should not be on the people pointing out the current problem! This is a great question and one that obviously needs addressing before we name a project as important as JWST. NASA should put together a process for addressing it, which means reconsidering the name of the telescope!

I used to chair the HET TAC (time allocation committee) at Penn State, and we didn’t have the bandwidth to give detailed feedback on proposals. But we did want to help out proposers, especially junior scientists, who were writing proposals that were not getting the time they requested (this is a SCHOOL after all!).

So as a compromise between that goal and the limitations of our resources, I drafted a generic “how to write a good telescope proposal” document, which I’m pretty proud of.

It’s not about how to do the technical parts, it’s about the actual “grantsmanship” involved. This can often feel like crass salesmanship, so part of my intent was to put the reader in the shoes of a TAC member who wants to give their proposal time so they can appreciate why this sort of thing is not just useful but actually an essential part of good science.

(On that note I recommend all astronomers who must compete for resources read Marc Kuchner’s Marketing for Scientists, which really helped me overcome my hangups about self-promotion, and appreciate the difference between honest (and necessary) marketing, and slimy, unethical salesmanship. In fact, one lesson I learned from that book is to write blog posts like this one!).

A lot of the advice I wrote works for any kind of proposal writing (fellowships, grants, jobs) so I’ve modified it to be generic, and pasted it below.

One piece that’s not in here is writing a proposal to meet the rubric criteria.  If you’re lucky enough to be proposing for time to NOIRLab or another body that publishes its rubric, then you can actually score your proposal against it yourself (or swap proposals with someone) to see where you can strengthen it.

OK, here it is. What have I missed?

Enjoy!

Writing a Great Telescope Proposal

Telescope time can be quite competitive, with oversubscription ratios of 2-10 or even higher. Because of this, a lot of meritorious science will not get the time requested.

This means that TAC members will select proposals not just based on their technical feasibility and scientific importance but on how well justified the science is, whether they are personally excited about the science, how well the proposal is written, and harder to define subjective criteria. Writing a winning proposal is not, then, just a matter of describing your science well, but of conveying to the committee your own sense of excitement and importance of the work. Doing this well is an art.

To illustrate this: consider two proposals, both alike in worthiness, in the fair conference room where we lay our scene of the TAC deliberations. Forced to choose between them for the last 2 nights of time, the committee cannot help but consider these factors:

1. Following the directions:
   One proposal has 12 point font throughout, 1 page of figures and references, and all the text stays in the box, just as the instructions required.
   
   The other has target tables with illegibly small entries, violates the page limits, and has text bleeding outside of the boxes. The TAC gets the sense that the proposers are trying to unfairly include more information than other proposers were allowed to include, and also that the proposers are not giving the proposal process its due attention.
2. Justifying the request for time:
   Telescope time is precious, and the TAC needs to know how much you really need to succeed.
   
   One proposal has a signal to noise calculation rooted in the underlying science. The TAC has a good sense of where the number comes from. The contingency section has a careful description of what would happen if the proposal got, say, half the time requested.
   
   The other is requesting visits to ten targets with no prioritization, with exposure times calculated for SNR of 100, with no justification for that number.
   
   One proposal notes that the time previously awarded for the project by the TAC resulted in data that has been reduced; shows a figure illustrating how the data can be translated into compelling science; and explains why additional observations are needed in order to publish. The other proposal notes that it was awarded time previously, but does not mention whether it was reduced or not, or why they need additional time.
3. Justifying the request for queue priority / temporal restrictions:
   One proposal has calculated the number of nights in the semester during which the observations could be made, justifying its cuts on airmass and moonlight contamination.
   
   The other proposal has a brief statement that they need the tight constraint because their “observations are time sensitive.”
4. Having a compelling figure:
   One proposal synthesizes what makes the science so compelling in an easy to read figure. It has large font, is not too busy, uses multiple, redundant point/line properties to clearly illustrate a third dimension, and conveys a few key ideas. From the figure the TAC quickly understands (for instance) the strength of the signal expected by the proposed observations, the new physical parameter space explored by them, or the factor by which the number of such detections will increase if the time is awarded. The caption text explains exactly what the TAC members should understand by looking at the figure, and connects it to the proposal text.
   
   The other proposal has a very hard to read and interpret figure filled with extraneous information, perhaps because the figure was taken from another context with little or no modification. The colorblind TAC member cannot distinguish the points and so needs it explained to them by the other members. The TAC members spend a lot of time arguing about what it is trying to convey because the caption, while technically accurate, does not interpret the figure in the context of the underlying science.
5. Showing a clear path to an important result:
   One proposal shows that these observations will triple the number of examples of a newly appreciated phenomenon. It connects this phenomenon to an important question in astrophysics, and illustrates how this is a result that the community will be excited to see, regardless of the outcome. The proposal explains the reasons this exciting science has not been done before, emphasizing the competitive advantage this telescope offers the TAC host institution in answering the question, so the TAC understands why this is an excellent use of the telescope.
   
   The other proposal is to observe a few more examples of a phenomenon that, as far as the TAC can tell, has been observed dozens of times before with other instruments. The proposal argues simply that the observations “will inform studies” of the phenomenon.
6. Arguing with strong prose:
   One proposal is easy to read, written in the active voice with tight, forthright prose that has been proofread and polished by the co-authors. The scientific justification lays out the problem being addressed clearly, emphasizing the place of these observations in the broader scientific landscape. The TAC members finish reading it quickly, with a good sense of the nature and importance of the work. A small number of key messages are in boldface or italics, so the TAC can quickly find them when deliberating.
   
   The other proposal was written in a single draft a few hours before the deadline. It is written in dense, highly technical prose in the passive voice, and filled with technical hedging, irrelevant qualifications, and unnecessary verbiage. Some references are malformed, some words are misspelled, and there are many run-on sentences. The TAC members have to reread sections of it multiple times before they can quite parse what is being conveyed. The TAC members finish reviewing the proposal with a vague sense of the importance of the science and the way the observations fit in. During deliberation, there are long pauses while TAC members hunt for a key piece of information they think they remember reading.

Clearly, the first proposal will (and should!) get the time, and the second will not. This is because even though the actual merit of the science is identical for both proposals, the first proposal makes that merit easy to see, and the second does not. So make sure you are writing the first proposal, not the second one!

In Part I I established the claim that technosignatures must be less prevalent than biosignatures, and showed that while that certainly could be true, the opposite is actually quite plausible, and by a huge factor.

In Part II we looked at the longevity term and, again, found that even though technology has been on Earth for much less time than life has, it’s still possible, and even plausible, that it typical lifetime in the Galaxy is actually much longer than that of life.

In this part, we look at two more criteria: detectability, and ambiguity.

Detectability

How detectable are technosignatures?  Except for a few things like radio and laser transmissions, it’s not actually very clear. Most technosignature strengths have not been worked out in detail!  An ongoing project led by Sofia Sheikh is to determine what Earth’s detectability is because of our technosignatures.

Héctor Soccas-Navarro proposed a nifty metric called the inchoscale that compares a technosignature strength to that produced by Earth today. So, Earth today has, by definition, i=1 for all of its technosignatures.  How does their strength compare to our biosignatures?

If you ignore one-offs like the Arecibo Message, it’s actually not clear what our “loudest” technosignature is.  To stars that see Earth transit, they could try to measure our atmospheric composition, and Jacob Haqq-Misra has worked out roughly how hard it would be to detect our CFCs, and Ravi Kopparapu has done something similar for NO_xs.  Both would be very challenging to detect…but then, so would our ozone and methane.  Which is stronger? I’m not sure.

I do know that the full SKA is supposed to be strong enough to have a shot at detecting our regular aircraft radar emissions at interstellar distances in coming decades. This means that being able to detect ichnoscale=1 technosignatures is a few decades out, and that feels similar to the time before we could detect biosignatures around an Earth analog.

The bottom line is that we don’t know whether Earth’s technosignatures are more or less detectable than its biosignatures with Earth technology from nearby stars, but it’s probably a close call, and it could easily be that technosignatures win.

Ambiguity

The ambiguity of technosignatures depends on the signature. Waste heat from Dyson Spheres any circumstellar material should generate waste heat. A narrowband radio signal, however, can only be technological (although its origin could be ambiguous).

Dynamic spectrum of the Voyager I carrier wave—a clear example of an unambiguous technosignature

So technosignatures run the gamut. Clearly, searching for an unambiguous one is better on that score, but ambiguous ones may require less contrivance—waste heat is an inevitable consequence of energy use, but there’s no reason aliens would have to use narrowband radio transmitters. Balancing this requires thinking about the axes of merit of technosignatures.

But the same is true for biosignatures! There are examples of what an unambiguous detection would look like (microbes swimming in Europa’s subsurface ocean), but there are plenty on the other end, too, especially for remote detection: detecting oxygen or methane in an alien atmosphere is a potential biosignature, but both species can also be generated abiotically.

Even iidentifying something that would serve an “agnostic” (not specific to Earth life) and unambiguous biosignature is a major challenge in astrobiology. The most probable path to success, IMO, is identifying a “constellation” of ambiguous biosignatures that together suggest strong disequilibrium chemistry maintained by metabolism (oxygen and methane together for instance).

So as far as ambiguity goes, biosignatures and technosignatures share the same problems, and neither has a clear advantage. Both have many examples of ambiguous signatures, and both can offer examples of clean detections.

Conclusions

This last point illustrates something important: biosignature searches and technosignature searches have a lot in common. Both search for the unknown, trying to balance being open-minded about what there is to find while letting what we know about Earth life to inform us. Both struggle with identifying good signatures to hunt for, how to handle ambiguity, and how to interpret null results.

But the communities don’t talk about these much between one another. Indeed, astrobiologists have called for and launched an ambitious project to nail down standards of life detection, without acknowledging or even mentioning the significant work on the topic over in SETI. Similarly, technosignature search would benefit from a this sort of rigorous exercise.

I hope our new paper will inspire better cross-pollination between the two communities, and a better balance of effort between the two methods of finding life. Since we don’t know which has a better chance of success, we should follow a mixed strategy to maximize our chances.

Our paper, written with Adam Frank, Sofia Sheikh, Manasvi Lingam, Ravi Kopparapu, and Jacob Haqq-Misra, is now published in Astrophysical Journal Letters.

In Part I, I laid out part of the argument for why SETI is not worthwhile compared to searches for biosignatures. In this part, I’ll address the next big part of the argument: longevity.

Longevity

Last time we summarized an argument for looking for biosignatures instead of technosignatures as:

Let’s take a look at that last ratio, between the time on a planet technosignatures are detectable and the time biosignatures are detectable. Need it really be small?

The zeroth-order way to think of it is in terms of the history of the Earth: biology has been here for around 4 billion years, and biosignatures detectable from space for some significant fraction of that—at least 1 billion years, say.  But our technosignatures only just recently got “loud” enough to be detectable—decades ago, say.  That’s a factor of about 10^-8!

And that’s fair, but there are a few reasons to expect in some cases it could be much larger, and even greater than 1!

Humanity may be a poor guide to longevity

Lots of people are pessimistic about our future on Earth, but we should be careful not to project our perception of human nature onto aliens. Technological alien life may be very different from ours, with a different evolutionary trajectory and relationship with its planets.

But even if we do use humanity as a guide, we should not assume we have a good sense of what our longevity is. Unless something happens that makes humans go extinct, there’s no reason to think our technosignatures will permanently disappear.  Even ecological disasters, nuclear war, or deadly pandemics, horrible as they would be, are unlikely to actually erase Homo sapiens from the planet completely.  Over geological or cosmic timescales, we might have many periods of tragedy and low population, but that only keeps the duty cycle less than 1, it does not shrink L_t by orders of magnitude.

And, of course, technology doesn’t just give us a way to end our species existence, it offers a way to save it.  We can, in principle, deflect killer asteroids, cure pandemics, and alter ourselves and our environment to survive in paces and times our biology alone would not allow.

In other words, it’s not at all clear why L_t for humans could not be orders of magnitude larger than it has been in the past.

And, even if you are pessimistic about humanity’s actual tendencies to do those things well, there’s no reason to project that pessimism onto other species.

Humans aren’t Earth’s only intelligent species

Further, even if humans do go extinct soon, that would not necessarily end Earth’s technosignatures! Most or all of the traits that make humans so good at building “big” technology with detectable technosignatures exist elsewhere in the animal kingdom. Tool use, social behavior, communication and language, problem solving, generational knowledge—all of these things can be found not just among distant relatives in Chordata but over in Mollusca, too, in the squids and octopi.

Squid communicate, hunt, and live together.

That’s important for two reasons: one is that it means that there is no reason another species could not arise that exhibits our level of technology, even in the sea.  Another is that since molluscs and mammals share no intelligent common ancestors, these traits aren’t accidents of human’s particular evolutionary pathway, but have arisen independently multiple times. This means they can arise independently again, and not just on Earth!

Also, surprisingly, we can’t even be sure something like our level of technology has not existed on Earth in the past!  Adam Frank and Gavin Schmidt have advanced the Silurian Hypothesis, that such a thing has happened—not because there is any evidence for it, but to point out the surprising fact that we have almost not evidence against it.  In fact, all evidence of Earth’s “Anthropocene” will have either disappeared or be ambiguously technological after a few million years.

In other words, we need to include other species in L_t for Earth, and we don’t really have any evidence-based reason to think that number is zero, either in Earth’s future or Earth’s past.

Technological longevity has no obvious upper limit

L_b, the lifetime of biosignatures, has a hard upper limit: the inevitable evolution of the planet’s host star which will eventually scorch the surface, and could even envelop the planet within the star.

Technology, however, has no such upper limit. In principle it could allow us to survive on a much hotter Earth, and, as we discussed in Part I, it can spread to other places where it can persist long after the biosphere that generated it.

So there is no reason that L_b must be larger than L_t, and the latter has a higher upper limit.  In other words, there could be alien species—or even future Earth species, like us—that build technology for longer than life exists on Earth.

Technology can exist without biology

Technology can outlive its creators. Obvious Earth examples include the Great Pyramids, which would serve as markers that humans where here and did amazing things for long after something happened to humans.  Our interstellar probes will last a very very long time, no matter what happens to us.  And so such technology on a grander scale from an alien species might be detectable for a very long time.

But also, technology might be able to self-perpetuate. Much has been written about the possibility of self-assembling machines and AI that would allow machines to spread and reproduce much like life. This possibility is almost certainly not limited by any fundamental engineering or physical principle, and the fact that we can even outline how it could be accomplished with something like existing technology suggests it may not be far off.  Unbound by a biosphere, why couldn’t L_t>L_b?

The bottom line on longevity

As we write in our paper:

Using Earth as a guide for our expectations for L_t /L_b is probably unreliable because we do not know L_t for Earth’s past; even if we did we should not use it to predict L_t for Earth’s future, and even if we did, we should not expect Earth to be a good guide for alien life, and even if we did, we should expect a broad distribution of longevities across alien species.

…and we should also not assume that technology must be bound to biology at all!

Next time: Ambiguity and Detectibility.

There are two major ways we can look for alien life:  look for signs of biology or look for signs of technology.

SETI includes searches for the latter—technosignatures. These might include big bright obvious information-rich beacons (in the radio or with lasers, for instance) , or they might be passive signs of technology like waste heat, pollution, or leaked radio emission from radar and communications.

I have often seen the argument that this is nice to look for but must be less likely to work than searches for biosignatures. The flaws in this argument have been pointed out and analyzed for as long as SETI has been a thing (most of them were hashed out in the ’60’s). But that discussion isn’t actually familiar to most astronomers and astrobiologists, and so working with the CATS collaboration led by Adam Frank (for Characterizing Atmospheric Techonsignatures) I’ve written a paper summarizing them.

In this series of posts I’ll break down the argument, following the argument in our new paper in Astrophysical Journal Letters.

The Role of the Drake Equation

One part of the argument goes back to the Drake Equation.

The man himself with the equation

Let’s look at why:

If we just count up the parts of the Drake Equation that lead to some kind of life to be found, we might end up with something like

where R* is the rate of star formation, multiplied by the usual fraction of stars with planets and the mean number of planets per planet-bearing star that can support life, and the fraction of those planets on which life arises.

Here, L_b is the lifetime of detectable biosignatures. N(bio) is then the number of biosignatures there are to find out there.

We can also rewrite the full Drake Equation in a similar manner for any technosignature:

Here, we’ve added f_t representing the fraction of planets where technology arises, and now L_t is the lifetime of detectable technosignatures.

Based on this reasoning, SETI looks like a terrible idea compared to searches for biosignatures! It’s a tiny, tiny subset of all possible ways to succeed, because (this reasoning goes):

Why? Because f_t <= 1 by definition, and since you need to have non-technological life before you can have technological life, L_t<L_b. This would seem to justify the huge imbalance in time and money that NASA spends on astrobiology in general compared to SETI (which has been almost zero until recently).

This is the abundance argument against technosignatures, and it is wrong, for many reasons! Let’s take a look at why.

Abundance

First of all, let’s think about the Solar System.  N(bio) is, as best as we can tell, exactly 1.  If there are other biosignatures in the solar system, we have not noticed them yet, so they must be very hard to detect.

And what is N(tech)?  Well, based purely on what we can detect with our equipment it’s at least 4!  Earth is loaded with technosignatures, but we also detect them from Mars all the time, and Venus and Jupiter also have them. We also have several active interplanetary and interstellar probes, and many many more derelict objects are out there too.

This gives us our first clue about how the reasoning above fails: if technology can spread through space, then one site of biology can give rise to many sites of technology.

And this, of course, has been appreciated by SETI practitioners for decades. It’s the basis of the Fermi Paradox, which asks why alien life hasn’t spread so thoroughly through the Galaxy that it isn’t here right now. Drake’s equation is based on the idea that it’s easier to communicate via radio waves than to travel via spacecraft, but of course one doesn’t preclude the other, and if both are happening, then N(tech) could be much larger than the equation says.

This is not really a major failing of the equation, whose original purpose was to justify SETI.  After all, if you can conclude there is something to find in the absence of spreading, that’s a sufficient condition to go looking.  The equation is often misinterpreted as foundational, like the Schrödinger Equation, as if you can calculate useful things with it.  Instead, it’s best thought of as a heuristic, a guide, and an argument.

So, how large could N(tech) be? Well, in the limit of the Fermi Paradox reasoning, it could be upwards of 100 billion, even for a single point of abiogenesis!  We’ve written about this before, for instance here.

So, the argument isn’t that this will happen, just that N(tech) has a higher ceiling than N(bio).  This long tail out to large possibilities (both in the sense that we are ignorant of the right answer, and in terms of a distribution among all of the alien species) means that it is not just possible but plausible that SETI is much more likely to succeed than other life detection strategies.

Next time: The second reasons to do SETI: technosignatures may be long-lived.

This is a guest post by Stephen Kerby, a graduate student at Penn State.

Imagine you are a galaxy-spanning species, and you need to transmit information from one star to another.  You can just point your radio dish at the other star, but space is big, and your transmission is weak by the time it reaches its destination.  What if you could use the gravitational lensing of a nearby star to focus your transmission into a tight beam while monitoring local probes? What if you could use this nice yellow star right here, the locals call it the Sun? What if the locals notice your transmitting spacecraft from their planet right next to the star?

Recently, there has been renewed interest among human scientists in using the solar gravitational lens (SGL) to focus light for telescopic observations (as in the FOCAL mission) or for interstellar communication (as described in Maccone 2011). A spacecraft positioned >500 AU from the Sun could collect focused light bent by the Sun’s gravitational field, dramatically increasing the magnification of a telescope or the gain of a transmitter for a point on the exact opposite side of the Sun (the antipode). The picture below shows how the SGL could be used for transmission of an interstellar signal, and the arrangement can be reversed to focus light onto a telescope.

In the Astro 576: “The Search for Extraterrestrial Intelligence” graduate course at the PSU Dept. of Astronomy and Astrophysics, I participated in a collaboration with over a dozen colleagues to examine a parallel question; might an extraterrestrial intelligence (ETI) be using an SGL scheme to build an interstellar transmission network? If so, we might be able to detect the transmitting spacecraft if its transmissions intersect the Earth’s orbit (as proposed by Gillon 2014). Such a spacecraft would visible opposite on the sky from its interstellar target and would be most visible if it is along the ecliptic plane (the same plane as Earth’s orbit).

While the collaboration focused on conducting a prototype search at the antipode of Alpha Centauri using Breakthrough Listen at the Green Bank Telescope (paper forthcoming!), I also conducted a side project to make predictions about what sort of engineering would go into such a transmission scheme.  A paper based on that project and co-authored by Dr. Wright was recently accepted for publication in the Astronomical Journal and is now available on the arXiv (http://arxiv.org/abs/2109.08657).

Initially, my project set out to tackle a broad question; it’s physically possible to use the SGL for an interstellar transmission, but is it productive from an engineering standpoint? After all, if an ETI needs to overcome myriad challenges to get the SGL transmission system online, it might be easier just to skip the mess and be more direct.  If we can quantify the challenges facing an SGL scheme, we might be able to predict which stars might be included in an ETI transmission network and whether our Sun is a likely host.

First, we focused on the difficulty of maintaining an alignment with the target star. Normally, when transmitting using a radio dish, you need to point the dish to within a few arcminutes of the target, depending on the gain (degree of focus) of the outgoing beam.  However, the impressive gain boost of the SGL means that the interstellar transmission could be only an arcsecond across, 60x narrower and much more intense. A spacecraft trying to aim at a target star needs to stay aligned with that much precision.

We soon found that there are numerous dynamical perturbations on the spacecraft-Sun-target alignment.  First, the Sun is pulling the spacecraft inwards; if the craft drifts closer than about 500 AU to the Sun, it can’t transmit using the SGL.  Next, the Sun is being jostled around by its orbiting planets (shown in the GIF below); the spacecraft needs to expend propellant to counter these motions, coming out to 10x greater than the inwards force. A couple of linear effects like the proper motion of the target star are small corrections as well.

This has implications for local artifact SETI searches. While the Sun has several perturbations (mostly the reflex motion from Jupiter), it is a much better host for an SGL than a star with a close binary companion or a close-in giant planet. Close binary systems like Alpha Centauri and Sirius are terrible hosts for SGL spacecraft because of the reflex motions from the other stars in the systems. If we are trying to detect an SGL interstellar transmission network, we could focus on nearby stars that are unperturbed by massive planets, like Proxima, Barnard’s Star, or Ross 154.

Next, we addressed how those challenges might be overcome.  Clearly, a spacecraft could just fire its engines and counter the perturbations to maintain the alignment with the target.  Doing a quick back-of-the-envelope calculation, we found that a modern chemical, nuclear, or electric rocket engine could maintain alignment with an interstellar target for up to a few thousand years. Table 2 from the paper shows how long different propulsion systems could resist the perturbations of the sun’s gravity (~0.5 m/s/year acceleration) or including the reflex motions imparted on the Sun by the planets (~8 m/s/year).

On a human timescale, this is a long time; Voyager 2, our longest-lived active probe, is 44 years old, and there are obviously other challenges to operating autonomously for such a long period. In artifact SETI, ten thousand years is a blink of an eye.  The universe has existed for billions of years, which means that an ETI might have activated their relay spacecraft around the Sun millions of years ago. We could only detect it actively transmitting if it has survived and maintained alignment for the whole time.

So, how could an ETI extend the longevity of their spacecraft? They could reduce the total gain of the system so that they can ignore perturbations by the planets, but that blunts the benefits of an SGL arrangement. They could use advanced rocketry like fusion engines or solar or EM sails to dramatically increase their propulsive capabilities. They could use clever navigational techniques to get efficiency in exchange for simplicity or downtime. Finally, they could just let their probes die off and fall derelict, sending along a constant stream of replacements when needed.

So, we’ve used the dynamical features of the Sun and solar system to predict a few engineering challenges that must be overcome to use the SGL for transmission or science.  Then, we used those challenges to predict what to look for during an artifact/radio SETI search at the antipode of a nearby star.  As mentioned earlier, a collaboration is analyzing observations at one such antipode.  With a few proposals flying around, it looks like it will soon be an exciting time to be a gravitational lens!

If I were an eccentric trillionaire and wanted to help detect signals from an ETI, I would fund the construction of the All-Sky-All-Time-All-Wavelengths array.  Placing millions of telescopes of all kinds around the globe and across the solar system, I could survey every single spot in the sky at all wavelengths, nonstop. Certainly, if an ETI is sending signals then we should be able to detect them with a system like that. Sadly, no amount of money in the world can make this dream a reality, so we need to narrow down our SETI investigations. We can’t look for signals all the time or at all wavelengths or at every position.

A valuable avenue of SETI research is making predictions to guide observations to those with a reasonable chance of providing valuable scientific results.  In the past, notable predictions of this type include the hypothesis of “watering hole” frequencies and focused searches on stars that can observe Earth as a transiting exoplanet. Artifact SETI, the search for signs of physical ETI technology near our own solar system, starts with educated guesses about what that technology looks like.

Of course, it’s impossible to say now whether there actually is an ETI-placed spacecraft using the SGL to transmit until we’ve surveyed more antipodes. Still, our research into the challenges of operating an SGL relay is informative both for our SETI searches, and for aspirational proposals to use the SGL for our own science.

In this series on the content of my recent paper on the arXiv (and accepted to Acta Astronautica) I’ve mostly just described ways to do SETI.  I conclude with some highly subjective advice on SETI for those jumping into the field.

1. Read the literature

There are a lot of SETI papers, and very few of them have ever been cited. Going through it as we have for the SETI bibliography, it’s striking how many times the same ideas get discussed and debated without referencing or building on prior work on the topic.

This is partly because the field is scattered across journals and disciplines, and because there’s no curriculum (yet!). The result is a lot of wasted effort.

Fortunately, you can now keep up with the field at seti.news and search the literature at ADS using the bibgroup:SETI search term.

2. Choose theory projects carefully

I was taught by my adviser (who got it from his adviser, George Herbig) to “stay close to the data”. I took this to mean both to always make sure I understood the data and didn’t go chasing data reduction artifacts (I like to try to see strong signals myself, by eye, in the raw data when I can to confirm it’s real), but also to in theory projects really think hard about what the data say, and how it might mislead.

The most useful theory projects are the ones that help searches. A paper that calculates the observability of a particular technosignature using parameters that let observers translate their upper limits into constraints on technologies is staying close to the data.  One speculating on the far future fate of aliens at the edge of the universe—well, it may be very interesting, but it’s not close to the data.

Two topics that I think are probably overrepresented in the literature are the Fermi Paradox and the Drake Equation. Now, I’m very proud of the papers I’m on about the Fermi Paradox, so I won’t say to avoid the topic, but ultimately the Fermi Paradox is not actually a problem that I think demands a solution. Such work also works best when it leads to observational predictions, and so informs searches and the interpretation of data.

But continuing to argue about it after so much ink has been spilled about it, and in a situation where we have so little data to go on, creates diminishing returns. Kathryn Denning describes the “now-elaborate and extensive discourse concerning the Fermi Paradox” as being “quite literally, a substantial body of analysis about nothing, which is now evolving into metaanalysis of nothing.” continuing, “I would not suggest that these intellectual projects are without value, but one can legitimately ask what exactly that value is, and what the discussion is now really about. And, refering to early work on the problem:

Thinking about that future [of contact with ETI] was itself an act of hope. Perhaps it still is. But I want to suggest something else here: that the best way to take that legacy forward is not to keep asking the same questions and elaborating on answers, the contours of which have long been established, and the details of which cannot be filled in until and unless a detection is confirmed. Perhaps this work is nearly done.

I think she’s right, and this goes for work on the “Great Filter” and “Hard Steps” models in SETI, too.

The Drake Equation, similarly, occupies a big chunk of the theory literature. The equation is very useful and in a way sort of defines the field of SETI, but ultimately it’s a heuristic and its purpose is to help us think about our odds of success. But even Frank will tell you that while it’s useful to plug in numbers to get a sense of whether SETI is worthwhile (it is!), it’s not meant to be solved or made exact. It’s not a foundational equation like the Schrodinger equation from which one derives results, it’s more like a schematic map of the landscape to help orient yourself.

So while there’s no problem with using the Drake Equation to illustrate a point or frame a discussion, I think working to refine and make it better is to misunderstand its role in the field.

3. Think about the nine axes of merit

Sofia Sheikh has a very nice paper describing how to qualitatively describe the merit behind a particular technosignature.  When proposing a new technosignature, I recommend thinking about them all, but a one in particular: “ancillary benefits,”. This gets to Dyson’s First Law of SETI Investigations: “Every search for alien civilizations should be planned to give interesting results even when no aliens are discovered.”

There are three reasons for this. The first is the funding paradox that null detections must be used to justify yet more effort. If there are ancillary benefits, then this is easier. The second is that doing other work with the data or instruments you use means you stay connected to the rest of astronomy (this also helps junior researchers get jobs and stay employed). The third is that it’s easy to get discouraged after years of null results. Having something to work on in the meantime helps keep one going.

This point should not be taken too strongly however. Radio data of nearby stars might really have no practical application beyond a null detection, and that’s OK. Those null detections are still good science! Also, the skills one uses to do that search, and the equipment built to do it, are all transferable to interesting astronomy problems.

4. 4. Engage experts

Lots of SETI papers written by physicists (and others) go way outside the authors’ training. There’s a particular tendency among physicists (and others) to feel like since we’re good at physics and physics is hard and everything is fundamentally physics, that we can just jump into a field we know little about and contribute.

Engaging experts in those fields will both help us not make mistakes and broaden the field by bringing them into it so they can see how they can contribute. It’s win win! And we should do it more.

5. Plan for success when designing a search

One should think hard about upper limits and what result one will have when one is done searching before one starts the search. This is easier said than done, but really helps sharpen one’s work, and ensures that a useful result will come out at the end.

It also helps draw in experts! A SETI skeptic might not want to help you, say, look for structures on Mars lest they be drawn into another Face on Mars fiasco, but if they see that they’re contributing to an upper limit (that confirms their priors!) on such faces, they will be more likely to really help.

6. Stay broad minded

We all come to the problem of SETI with very different priors for how SETI can succeed, and so will invariably encounter practitioners pursing what we feel are very unlikely or misguided paths to success. It helps to remember that the feeling may be mutual

In particular, we can acknowledge the value in the exercise of, say, considering ‘Oumuamua as an alien spacecraft without falling into the “aliens of the gaps” trap. That is we should distinguish between claims that

1. Our prior on a particular technosignature is too small, using a particular case study as an example, and
2. A particular case study is likely to be a technosignature

The first is entirely appropriate. Before ‘Oumuamua, I did not think much about the possibility of alien spacecraft in the solar system. Now, I think I have a much better informed prior on the likelihood and form of such a thing.

The second requires extraordinary evidence because our prior on such a thing is (presumably) quite small.

7. Stay skeptical, but not cynical

I’ll close by just quoting the end of my paper:

Not all SETI researchers believe they will have a good chance of success in their lifetimes, but such a belief surely animates much of the field. It can therefore be challenging to maintain a scientist’s proper, healthy skepticism about one’s own work, especially when coming across a particularly intriguing signal.

I suspect everyone who engages in the practice long enough will come across what looks to be a Wow! Signal and, at least briefly, dream of the success that will follow. The proper response to such a discovery is a stance of extreme skepticism: if one is not one’s own harshest critic, one may end up embarrassing oneself, and losing credibility for the field. It is at these moments that Sagan’s maxim should have its strongest force.But one should also not let the product of such false alarms be a cynicism that leads one to focus entirely on upper limits and dismiss all candidate signals before they are thoroughly examined as just so much noise. There is a wonder that brought many of us into the field that must be nurtured and protected against the discouragement of years or decades of null results that Drake warned about. One should cherish each false alarm and “Huh? signal” as an opportunity for hope and curiosity to flourish, “till human voices wake us, and we drown.”

You can find the paper here.

Last time I discussed the “kinds of SETI” I laid out in my new paper on the arXiv. This time, I’ll discuss a nifty plot I made about upper limits.

At a workshop at the Keck Institute for Space Science a couple of years ago, I put together a graphic describing how I think we should think about placing upper limits in SETI:

The idea is that if you do a search and find nothing, you need to let people know what it is that you did not find so that we can chart progress, draw conclusions, and set markers down for what the next experiment should look like. My analogy is the dark matter particle detection community, which (similarly to SETI) must solve the funding paradox of using a lack of results to justify continued funding.

The idea is that you have some parameter that marks the strength of a purported (ambiguous) technosignature (like waste heat for Dyson Spheres).  If you perform, say, a search of all-sky data along that axis, then you will end up with many potential detections. Virtually all of these are (presumably) natural sources, so what can you do?

Well, the easiest first step is that one of the sources is the strongest, meaning that you instantly have an upper limit: no technosignatures exist above that threshold. If you’re the first to interpret the data that way, then you’ve made progress!  We now know something we didn’t before.

Then the sleuthing kicks in.  What are those top, say, 10 sources?  Are they all well-known giant stars with dusty atmospheres and certainly not Dyson Spheres?  If so, then you’ve just lowered the upper limit.

As you work your way down, your upper limit keeps improving, and you keep learning about what’s not out there. You also learn what you need to do to weed out all of the false positives to get to more meaningful and stringent upper limits.

This works for almost any technosignature with many confounders: structures on the moon, transiting megastructures, “salted” stars.

This formalism even works for machine learning-based anomaly detection, although in that case it might be hard to translate your upper limit into something physically meaningful, because the mapping between an anomaly score and the characteristic of the technology that would give that score might be obscure.

Next up: advice!