SETI vs the possibility of interstellar exploration

Science News has a short article discussing a calculation someone has done showing how small the volume of space examined by SETI (Search for Extraterrestrial Intelligence) is relative the overall size of the galaxy.

With no luck so far in a six-decade search for signals from aliens, you’d be forgiven for thinking, “Where is everyone?”

A new calculation shows that if space is an ocean, we’ve barely dipped in a toe. The volume of observable space combed so far for E.T. is comparable to searching the volume of a large hot tub for evidence of fish in Earth’s oceans, astronomer Jason Wright at Penn State and colleagues say in a paper posted online September 19 at arXiv.org.

“If you looked at a random hot tub’s worth of water in the ocean, you wouldn’t always expect a fish,” Wright says.

I have no doubt that the amount of stars SETI has examined so far is a minuscule slice of the population of the Milky Way galaxy.  And if SETI’s chief assumptions are correct, it’s entirely right to say that we shouldn’t be discouraged by the lack of results so far.

But it’s worth noting what one of those chief assumptions are, that interstellar travel is impossible, or so monstrously difficult that no one bothers.  If true, then we wouldn’t expect the Earth to have ever been visited or colonized.  This fits with the utter lack of evidence for anything like that.  (And there is no evidence, despite what shows like Ancient Aliens or UFO conspiracy theorists claim.)

But to me, the conclusion that interstellar travel is impossible, even for a robotic intelligence, seems excessively pessimistic.  Ronald Bracewell pointed out decades ago that, even if it is only possible to travel at 1% of the speed of light, a fleet of self replicating robot probes (Bracewell probes) could establish a presence in every solar system in the Milky Way within about 100 million years.  That may sound like a long time, but compared to the age of the universe, it’s a fairly brief period.  Earth by itself has existed 45 times longer.

NASA image via Wikipedia

People sometimes respond that the Earth may be in some type of backwater.  The problem here is, if you know about where the Earth is in the Milky Way, in the Orion Spur off the Sagittarius Arm, about halfway between the center and rim of the galaxy, you’ll know that we’re not really in a backwater.  The backwater theory might be plausible if we were thousands of light years off the galactic plane, beyond the rim, or in a cluster far removed from the main galaxy, but we’re not.  Even then, the nature of the self replicating probe propagation is pretty relentless and would still eventually reach backwater stars.

Of course, if there is only one or a few other intelligent species in the galaxy, then it’s entirely possible that their Bracewell probe is here, just lying low, observing us, possibly waiting for us to achieve some level of development before it makes contact.  (Or maybe it has been making contact 2001: A Space Odyssey style.)

But if the number of civilization is in the thousands, as is often predicted by people speculatively playing with the numbers in the Drake equation, then we should have hundreds of those probes lying around.  Given their diverse origins, we shouldn’t expect them to behave with unanimity.  Even if one probe, or coalition of probes, bullied the others, the idea that such an arrangement would endure across billions of years seems implausible.

And the Earth has been sitting here for billions of years, with an interesting biosphere for most of that time.  The idea that none of these self replicating probes would have set up some kind of presence on the planet, a presence we should now be able to find in the geological record, again seems implausible.  Indeed, if they existed, we should expect to have at least some of them in front of us now.

Now, maybe they are in front of us, and we’re just not intelligent enough to realize what we’re seeing.  Monkeys, after all, likely have no understanding of the significance of the buildings and machinery they climb over.  It seems like something we have to keep in mind, but historically it’s never been productive to just assume we can’t understand something, and taking this principle too much to heart seems like it would make it impossible to ever dismiss any dubious notion.

So SETI largely depends on interstellar travel being infeasible.  This is actually the conclusion a lot of radio astronomers have reached.  Could they be right?  I don’t think we know enough to categorically rule out the possibility.  If they are right, then SETI will be our best chance to someday make contact with those other civilizations, even if it’s only composed of messages across centuries or millenia.

As I’ve written here before, my own conclusion is that some form of interstellar exploration is possible, and that life is probably pervasive in the universe, although most of it is microscopic.  Complex life is probably far rarer, although I wouldn’t be surprised if there aren’t thousands of biospheres, or more, in our galaxy that have it.

But intelligent life capable of symbolic thought and building a civilization?  The data seems to be telling us that this is profoundly rare, so rare that the nearest other intelligent species is probably cosmically distant.  If we’re lucky, they might be close enough that we can encounter them before the expansion of the universe separates us forever.  If we’re not lucky, we’ll never have a chance for that encounter.

Unless of course, I’m missing something?

The extraordinary low probability of intelligent life

Marc Defant gave a TEDx talk on the improbable events that had to happen in our planet’s history for us to eventually evolve, along with the implications for other intelligent life in the galaxy.

I find a lot to agree with in Defant’s remarks, although there are a couple points I’d quibble with.  The first, and I’m sure a lot of SETI (Search for Extraterrestrial Intelligence) enthusiasts will quickly point this out, is that we shouldn’t necessarily use the current lack of results from SETI as a data point.  It’s a big galaxy, and within the conceptual space where SETI could ever pay off, we shouldn’t necessarily expect it to have done so yet.

My other quibble is that Defant seems to present the formation of our solar system as a low probability event, or maybe he means a solar system with our current metallicity.  I can’t really see the case for either being unlikely.  There are hundreds of billions of stars in our galaxy, most with some sort of attending solar system.  So I’m not sure where he’s coming from on that one.

My own starting point for this isn’t SETI, but the fact that we have zero evidence for Earth having ever been colonized.  If the higher estimated numbers of civilizations in the galaxy are correct, the older ones should be billions of years older than we are.  They’ve had plenty of time to have colonized the entire galaxy many times over, even if 1% of lightspeed is the best propagation rate.

The usual response is that maybe they’re not interested in colonizing the galaxy, not even with their robotic progeny.  That might hold if there is one other civilization, but if there are thousands, hundreds, even a few dozen?  Across billions of years?  The idea that every other civilization wouldn’t be interested in sending its probes out throughout the galaxy seems remote, at least to me.

But to Defant’s broader point about the probability of intelligent life evolving, there are many events in our own evolutionary history that, if we were to rewind things, might never happen again.

Life seems to have gotten an early start on Earth.  Earth is roughly 4.54 billion years old, and the earliest fossils date to 3.7 billion years ago.  With the caveat that we’re unavoidably drawing conclusions from a sample of one planet’s history, the early start of life here seems promising for its likelihood under the right conditions.

But there are many other developments that seem far less certain.

One crucial step was the evolution of photosynthesis, at least 2.5 billion years ago.  The development of photosynthesis gave life a much more reliable energy source than what was available before, converting sunlight, water, and carbon dioxide into sugars.

And its waste product, oxygen, started the process of oxygenation, increasing the levels of oxygen in Earth’s atmosphere, which would be very important as time went on.  The early atmosphere didn’t have much oxygen.  Indeed, the rise of oxygen levels may have originally been a serious problem for the life that existed at the time.  But life adapted and eventually used oxygen as a catalyst for quicker access to free energy.

The good news with photosynthesis is that there are multiple chemical pathways for it, and it’s possible it evolved multiple times, making it an example of convergent evolution.  That means photosynthesis might be a reasonably probable development.  Still, oxygen producing photosynthesis doesn’t seem to have arisen until the Earth was more than halfway through its current history, which doesn’t make it seem very inevitable.

The rise of eukaryotes may be a more remote probability.  The earliest life were simple prokaryotes.  Eukaryotes, cells with organelles, complex specialization compartments, arose 1.6-2.1 billion years ago.  All animal and plant cells are eukaryotes, making this development a crucial building block for later complex life.

Eukaryotes are thought to have been the result of one organism attempting to consume another, but somehow instead of consuming it, the consuming organism entered into a symbiotic relationship with the consumed organism.  This low probability accident may have happened only once, although no one knows for sure.

Yet another crucial development was sexual reproduction, arising 1-1.2 billion years ago, or when Earth was 73% of its current age.  Sexual reproduction tremendously increased the amount of variation in offspring, which arguably accelerated evolution.  Who knows how long subsequent developments might have taken without it?

Oxygen had been introduced with the rise of certain types of photosynthesis, but due to geological factors, oxygen levels remained relatively low by current standards until 800 million or so years ago, when it began to rise substantially, just in time for the development of complex life.  The Cambrian explosion, the sudden appearance of a wide variety of animal life 540-500 million years ago, would not have been possible without these higher oxygen levels.

Complex life (animals and plants) arose in the last 600-700 million years, after the Earth had reached 84% of its current age.  When you consider how contingent complex life is on all the milestones above, it’s development looks far from certain.  Life may be pervasive in the universe, but complex life is probably relatively rare.

Okay, but once complex life developed, how likely is intelligent life?  There are many more low probability events even within the history of animal life.

Earth’s environment just so happens to be mostly aquatic, providing a place for life to begin, but with enough exposed land to allow the development of land animals.  In general, land animals are more intelligent than marine ones.  (Land animals can see much further than marine ones, increasingly the adaptive benefits of being able to plan ahead.)  A 100% water planet may have limited opportunities for intelligence to develop.  For example, mastering fire requires being in the atmosphere, not underwater.

Defant mentions the asteroid that took out the dinosaurs and gave mammals a chance to expand their ecological niche.  Without an asteroid strike of just the right size, mammals might not have ascended to their current role in the biosphere.  We might still be small scurrying animals hiding from the dinosaurs if that asteroid had never struck.

Of course, there have been a number of intelligent species that have evolved, not just among mammals but also among some bird species, the surviving descendants of dinosaurs.  Does this mean that, given the rise of complex life, human level intelligence is inevitable?  Not really.  While there are many intelligent species (dolphins, whales, elephants, crows, etc), the number of intelligent species that can manipulate the environment is much smaller, pretty much limited to the primates.

(Cephalopods, including octopusses, can manipulate their environment, but their short lives and marine environment appear to be obstacles for developing a civilization.)

Had our early primate ancestors not evolved to live in trees, developing a body plan to climb and swing among branches, we wouldn’t have the dexterity that we have, nor 3D vision, or the metacognitive ability to assess our confidence in making a particular jump or other move.  And had environmental changes not driven our later great ape ancestors to live in grasslands, forcing them to walk upright, and freeing their hands to carry things or manipulate the environment, a civilization building species may never have developed.

None of this is to say that another civilization producing species can’t develop using an utterly different chain of evolutionary events.  The point is that our own chain is a series of many low probability events.  In the 4.54 billion years of Earth’s history, only one species, among the billions that evolved, ever developed the capability of symbolic thought, the ability to have language, art, mathematics, and all the other tools necessary for civilization.

Considering all of this, it seems like we can reach the following conclusions.  Microscopic single celled life is likely fairly pervasive in the universe.  A substantial subset of this life probably uses some form of photosynthesis.  But complex life is probably rare.  How rare we can’t really say with our sample of one, but much rarer than photosynthesis.

And intelligent life capable of symbolic thought, of building civilizations?  I think the data is telling us that this type of life is probably profoundly rare.  So rare that there’s likely not another example in our galaxy, possibly not even in the local group, or conceivably not even in the local Laniakea supercluster.  The nearest other civilization may be hundreds of millions of light years away.

Alternatively, it’s possible that our sample size of one is utterly misleading us and there actually are hundreds or even thousands of civilizations in the galaxy.  If so, then given the fact that they’re not here, interstellar exploration, even using robots, may be impossible, or so monstrously difficult that hardly anyone bothers.  This is actually the scenario that SETI is banking on to a large extent.  If true, our best bet is to continue searching with SETI, since electromagnetic communication may be the only method we’ll ever have to interact with them.

What do you think?  Is there another scenario I’m missing here?

Arrival, the shape of aliens, and bridging the communication barrier

arrival_movie_posterThis weekend, I watched the movie ‘Arrival‘.  It starts off with the now common scenario of several floating ships appearing in the skies around the world.  But unlike most movies in this mold, it focuses on humanity’s efforts to communicate with the aliens and understand why they’ve come.  The protagonist is an expert in linguistics.

I found this movie to be uncommonly intelligent and high quality science fiction, of a type that we rarely see in cinema.  I’ve heard it’s won and been nominated for various awards.  In my opinion, it’s well deserved.  I highly recommend it.

That said, I’m going to quibble with a couple of its aspects.  I won’t spoil anything that you wouldn’t see in the first act, but if having even bits of that spoiled bothers you, you may want to skip this post until you’ve seen it.

I’m not going to quibble with the existence of the aliens, or why they arrived when they did.  A common criticism I have of alien invasion movies is that the aliens usually choose to show up when we can resist them, rather than any of the previous 4.54 billion years when the planet was a sitting duck.  But I actually think the movie has a good answer for that, which I won’t spoil.

Okay, first quibble.  The movie goes out of its way to portray the aliens as utterly, well, alien.  On the one hand, I very much appreciate this.  Too often, media sci-fi portray aliens as humans with maybe an extra bump on their forehead or in overall humanoid form but maybe with reptilian skin or something, together with all too human emotions and attitudes.  Historically, some of this came from technological constraints on what could be shown.  But with CG technology being what it is today, this excuse, still somewhat plausible for television, doesn’t really cut it for high production movies.

That said, in its attempt to make the aliens profoundly different, I think the movie ignores some simple realities.  Extraterrestrial life would undoubtedly be very different from Earth life, but the laws of physics put limits on just how strange it could be.

For example,we never see eyes on the aliens.  (Or at least I couldn’t ever make out any.)  Now, it’s possible that an alien that evolved in a consistently dark or opaque environment, such as an underground sea or in a thick opaque atmosphere, might never evolve vision.

But we see the aliens communicating visually, which implies some kind of ability to take in information from electromagnetic radiation (light).  And eyes weren’t a one time mutation in Earth history.  From what I’ve read, they evolved several times in independent evolutionary lines.  In other words, eyes are one of the features that evolution tends to converge on.  The aliens didn’t have to be portrayed with two stereoscopic eyes.  They could have had many, like on spiders.

The other is the overall body plan of the aliens.  They don’t come across as having much dexterity.  But as I’ve noted before, the only civilization producing species on this planet needed more than intelligence, but also the ability to physically manipulate the environment.  It’s why a primate species currently rules the planet instead of a cetacean, elephantine, corvine, or other type of intelligent species.

I’m not saying that the aliens needed to have humanoid body plans.  Ant-like bodies with prehensile limbs might have done the trick.  But the movie aliens needed to have better physical abilities than what was portrayed.  Their portrayed bodies might have been dexterous in a liquid environment, similar to cephalopods, but that didn’t appear to be the environment they were in.

My second quibble is with the effort to communicate with the aliens.  If you’ve seen the movie,  you understand this issue’s place in the plot, but the initial decision to translate written language doesn’t make that much sense.  As Seth Shostak of SETI (Search for Extraterrestrial Intelligence) has pointed out, it makes a lot more sense to attempt initial communication with pictures.

This makes sense when you consider that the earliest human writing evolved from using pictures to convey concepts.  Over time, the pictures got streamlined into symbols for each word or concept.  It was thousands of years before the idea of letters standing in for individual speech sounds developed.  Attempting to jump over all that with an utterly alien mind seems like the hard way to do it.

Of course, conveying complex information with pictures wouldn’t itself be easy.  For example, how do you get across the main question the humans had for the aliens, “Why have you come?”  But a series of pictures showing the alien ships approaching humans, followed by alternating pictures of humans dead or alive might have given the aliens a quick chance to make their intentions clearer.  And once you had a basic form of communication going, a common symbolic vocabulary could be worked out, eventually allowing more sophisticated exchanges.

A much tougher challenge might be if the aliens didn’t have visual senses.  Imagine trying to build a common vocabulary with a bat like alien that sensed the world through echolocation, or one that thought and moved on vastly different time scales, such as conscious trees.  But even then, we’d still live in the same universe, and there would have to be some common overlapping ways of perceiving the world.  It might come down to small model statues arranged in sequences to convey scenarios.

Of course, it’s always possible to engage in rationalizations to explain away these quibbles with the movie.  And as I indicated above, this is a movie that is far more intelligent than your typical sci-fi film.  Not the least because it gave me an excuse to talk about alien body plans and communication strategies 🙂

The necessity of dexterity for civilization

Today’s SMBC highlights something about humanity that is often overlooked, something that any extraterrestrial intelligence that builds a civilization would have to have.

Click through for hover-text and red button caption.
Source: Saturday Morning Breakfast Cereal – The Mammal Conspiracy

We often talk about the intelligence of dolphins, whales, cephalopods, elephants, and other species.  But something all of these species lack is an ability to alter and control their environment, at least in any detailed fashion, a capability that is at the heart of building a civilization.  When you think about the evolutionary steps that were necessary for humans to have the dexterity that we do, it starts to look like we were the benefactors of a very lucky sequence of events.

First, there needed to be a three dimensional environment like the interlocking tree branches that made the primate body plan adaptive.  Second, the primate line needed to evolve an intelligent line (the great apes).  Third, there needed to be a change in environment that led to some of those apes coming down from the trees to tall grasslands where walking upright was adaptive, freeing their hands for work other than locomotion or hanging.

Only then do we have the stage set for human intelligence to evolve.  Of course, it’s completely conceivable for alternate factors to lead to the evolution of those capabilities.  But the fact that, despite a number of relatively intelligent species in the animal kingdom, it’s only happened once on Earth should give us pause before concluding that it’s at all common for a civilization building species to evolve.

Intelligence and dexterity aren’t the only factors by the way.  Mastery of fire as a tool also seems crucial, something that seems to rule out water dwelling species like cephalopods, who if they lived longer, might have a decent chance at manipulating their environment.

Fermi’s paradox is the question which asks, if extraterrestrial civilizations are common, why weren’t we colonized long ago?  The rarity of the combination of intelligence and dexterity might give a pretty grounded answer to that question, and that’s before we even consider the likelihood of other evolutionary milestones, such as sexual reproduction or multi-cellular life.

So, when thinking about the evolution of human intelligence, be grateful for the existence of jungles and grasslands.  Without them, we might not be here, at least not with enough intelligence to discuss our evolution.

Snowden’s answer to the Fermi Paradox and its assumptions

The Fermi Paradox is the question that, if the conditions for life in the galaxy are as ubiquitous as they appear to be, so that there should be hundreds, if not thousands of alien civilizations out there, then where is everyone?  Why have we found no evidence for any for those civilizations?  And why aren’t they here?

Edward Snowden has a proposed answer:

“When you look at encrypted communications, if they are properly encrypted, there is no real way to tell that they are encrypted. You can’t distinguish a properly encrypted communication, at least in the theoretical sense, from random noise,” says Snowden. He suggests that over time all societies realize that encryption is a necessity. “So if you have an alien civilization trying to listen for other civilizations, or our civilization trying to listen for aliens, there’s only one small period in the development of their society where all of their communications will be sent via the most primitive and most unprotected means.”

This is an interesting idea, although it’s a variation of another one that’s been around for a while.  Many have speculated that a society that simply digitally encodes all of their signals might make them indistinguishable from natural noise.  Digitally encoding a signal requires protocols, which we, of course, wouldn’t be privy to.  Encryption would just make it even more unlikely that we’d detect it.

But this answer makes a large assumption, that interstellar exploration of any type is impossible, or so monstrously costly that no one ever bothers.  On the face of it, the idea of Star Trek like exploration might well be impossible.  But when you consider ideas like AI probes exploring the galaxy at 1% the speed of light, the notion of exploration being impossible starts to look overly pessimistic.  If those probes were self-replicating, they’d be able to fill the galaxy in 20-30 million years, a long time by human standards, but peanuts on geological or cosmological time scales.

Of course, another possibility is that such exploration is possible, and that the probes or similar technology are here, but keeping hidden.  We can’t eliminate this possibility, except that the idea that an alien intelligence wouldn’t be interested in researching our biosphere seems far fetched, or that if they’re doing so, that we wouldn’t find any indications of it.

Another possibility is that they are here and not being hidden at all, but that we’re simply too primitive to even distinguish them from the natural environment, similar to how a monkey probably regards a building as just another rock, or a vehicle as just another animal.  Again, it doesn’t seem like we can eliminate this possibility, but I can’t see that it’s especially productive to dwell on it.

This always brings me back to the simplest explanation, that intelligent life is profoundly rare, and that the closest civilization may be millions, or maybe even billions of light years away.

G-HAT (Glimpsing Heat from Alien Technologies)

For those interested in the post about finding advanced civilizations in other galaxies by their heat emissions, Paul Gilster at Centauri Dreams has a write up about the study, including links to additional material as well as the actual paper.

I found that this part clarified the seeming contradiction in the Science Daily article.

The currently reported work tells us that none of the galaxies resolved by WISE in this study contain Type III civilizations that are reprocessing 85 percent or more of the starlight of their galaxy into the mid-infrared. And as mentioned above, out of 100,000 galaxies, only fifty show a mid-infrared signature that could be considered consistent with reprocessing more than 50 percent of the starlight.

These fifty point to the further investigations ahead.

The overall endeavor of which the study is a part appears to be named G-HAT (Glimpsing Heat from Alien Technologies).   Gilster links to a site that looks like it has lots of additional information on it, along with some interesting articles.

Searching for advanced civilizations in other galaxies: 50 possible candidates found?

At first, this article seems like a bit of a downer:
Search for advanced civilizations beyond Earth finds nothing obvious in 100,000 galaxies — ScienceDaily.

After searching 100,000 galaxies for signs of highly advanced life, a team of scientists has found no evidence of advanced civilizations there. The idea behind the research is that, if an entire galaxy had been colonized by an advanced spacefaring civilization, the energy produced by that civilization’s technologies would be detectable in mid-infrared wavelengths.

…”Whether an advanced spacefaring civilization uses the large amounts of energy from its galaxy’s stars to power computers, space flight, communication, or something we can’t yet imagine, fundamental thermodynamics tells us that this energy must be radiated away as heat in the mid-infrared wavelengths,” Wright said. “This same basic physics causes your computer to radiate heat while it is turned on.”

Theoretical physicist Freeman Dyson proposed in the 1960s that advanced alien civilizations beyond Earth could be detected by the telltale evidence of their mid-infrared emissions. It was not until space-based telescopes like the WISE satellite that it became possible to make sensitive measurements of this radiation emitted by objects in space.

However, somewhat contradicting the title of the article and its opening passage, we have this snippet:

Wright reports, “We found about 50 galaxies that have unusually high levels of mid-infrared radiation. Our follow-up studies of those galaxies may reveal if the origin of their radiation results from natural astronomical processes, or if it could indicate the presence of a highly advanced civilization.”

I’m not entirely sure what to make of this passage given the apparent contradiction, but it sounds like we have 50 possible candidate galaxies for advanced civilizations.  (Emphasis on the word “possible” here.)

Based on the information the article provides, it seems obvious that the scientists were looking for Type III civilizations on the Kardashev scale.  A Type I civilization has harnessed all of the energy on its native planet.  (We’re not a Type I civilization yet).  A Type II civilization has harnessed all of the energy of its native star, possibly using concepts like Dyson spheres or swarms.  And a Type III civilization will  have harnessed all of the energy in its galaxy, or, at least for purposes of this study, enough to be noticeable across intergalactic distances.

Of course, we have no real idea how possible a Type III civilization actually is.  It would involve engineering on scales that currently seem hard to imagine.  But given enough time (think hundreds of millions of years), there doesn’t seem to be anything in the laws of physics that prevent it.  We also can’t be sure that some observed astronomical phenomena that we’re chalking up to nature might not turn out to be mega-structures created by extraterrestrial intelligence.

But given the age of the universe, and the fact that there’s no evidence of Earth ever having been colonized in its 4.5 billion year history, it seems likely that if there are advanced civilizations out there, they’re too far away to have reached us yet.  50 out of 100,000 galaxies sounds like about the right number.  The nearest advanced civilization may be several hundred million light years away.

Unless they find natural explanations for the high levels of mid-infrared radiation.  Then the closest advanced civilization might might be billions of light years away, or even outside our visible universe.

Three conditions are necessary for SETI to succeed

The Parkes 64 metre radio telescope at the Par...
(Photo credit: Wikipedia)

Tom Hartsfield has a post up at Real Clear Science criticizing both the Drake equation and SETI:

If you like science fiction, you’re probably familiar with the Drake equation. This famous one-line formula solves for the number of intelligent alien civilizations within our galaxy with whom we might be able to communicate. Supporters of the search for extraterrestrial life (SETI) often refer to the expression to bolster their case.

There’s just one BIG problem with the Drake equation. It’s completely useless! In fact, I believe it may actually misrepresent the search for ET and limit our ideas about it.

Hartsfield goes on the discuss the impossibility (at least currently) of knowing the values for each of the variables.  Because of this inability to test or observe the various values, he says, the formula is non-scientific.

He then takes aim at SETI (the search for extraterrestrial intelligence):

The worst thing about the Drake equation is that it gives us a false idea of grasping the problem we are trying to solve. A mathematical equation connotes some scientific study or understanding of a subject. But this is misleading: SETI is simply NOT a scientific endeavor. It’s entirely a leap of faith, albeit a leap that uses tools devised by science. It’s like searching for paranormal activity with an electronic sound recorder.

Now, I happen to think that, due to the Fermi Paradox (if there are thousands of civilizations out there, why aren’t any of them here?), the probability of large numbers of civilizations within our galaxy is pretty small.  That doesn’t mean there aren’t civilizations in other galaxies, but they may be hundreds of millions of light years away.

That being said, I think Hartsfield is being overly harsh in his assessment.  The Drake equation has never been meant to be anything other than a stimulus for discussion.  Most people who understand this subject know that it’s essentially just structuring our ignorance.  Given its original goal, and given that people still talk about it today, I think it is fairly successful.

Is it scientific?  That depends on your definition of science, but I think the variables are things humanity may be able to measure, someday.  A scientific theory doesn’t have to be testable immediately in order to be considered science; it just needs to be testable in principle.  I don’t know too many people who would actually call the Drake equation a theory, but to what extent it’s modelling the problem might eventually be testable, at some point in the future.  I think everyone acknowledges that the Drake equation is almost certainly incomplete, in that there are probably numerous factors that influence the final number that we’re simply not aware of yet, but that applies to many things in science.

I think calling SETI unscientific is simply engaging in polemics.  SETI is definitely a long shot.  But the search is being conducted carefully and empirically.  Saying that the people who are going about it aren’t being scientific, comparing them to paranormal investigators and the like, is just making a value judgment about their enterprise while pretending to be objective.

Now, as I said, I do think SETI is a long shot.  There are certain things that have to be true for it to work.

  1. There needs to be a large number of civilizations out there.  Enough that a number of them are close enough for us to detect them.
  2. Pervasive interstellar travel needs to be impossible, or so monstrously difficult that hardly anyone bothers.  Otherwise they would have been here long ago.  Even if only 1% of light speed is achievable, that’s still fast enough for a fleet of self replicating probes to colonize the galaxy in 100 million years.   (No, there’s no evidence that they’ve been here, despite what the Ancient Aliens people say.)
  3. They need to communicate in a manner that is detectable with our current technology.  If there are civilizations out there, they may be advanced in ways we can’t fathom, and us attempting to listen in on them may be far more fruitless than a primitive hunter-gatherer tribe attempting to listen in on global communications, by watching for smoke signals.

It seems to me that these three constraints make success for SETI unlikely, but not impossible.  And nothing about how unlikely it is to be successful necessarily makes it unscientific.

Personally, given 2 above, one strategy to find extraterrestrial intelligence may be to search for probes in the solar system.  It may be that there are several already here, laying low.  Of course, if they are here and dormant, you have to wonder what they’re waiting for, how far advanced the civilization on the third planet is going to have to be before they initiate contact.  And given the vastness of the solar system, if they don’t want to be detected, the chance of us being able to do so seems remote.

Complex life in the universe may be much rarer than previously thought

At least, according to a couple of astrophysicists: Complex life may be possible in only 10% of all galaxies | Science/AAAS | News.

The universe may be a lonelier place than previously thought. Of the estimated 100 billion galaxies in the observable universe, only one in 10 can support complex life like that on Earth, a pair of astrophysicists argues. Everywhere else, stellar explosions known as gamma ray bursts would regularly wipe out any life forms more elaborate than microbes. The detonations also kept the universe lifeless for billions of years after the big bang, the researchers say.

…The sheer density of stars in the middle of the galaxy ensures that planets within about 6500 light-years of the galactic center have a greater than 95% chance of having suffered a lethal gamma ray blast in the last billion years, they find. Generally, they conclude, life is possible only in the outer regions of large galaxies. (Our own solar system is about 27,000 light-years from the center.)

Things are even bleaker in other galaxies, the researchers report. Compared with the Milky Way, most galaxies are small and low in metallicity. As a result, 90% of them should have too many long gamma ray bursts to sustain life, they argue. What’s more, for about 5 billion years after the big bang, all galaxies were like that, so long gamma ray bursts would have made life impossible anywhere.

This is sobering when considering how much life might be in the visible universe.  It doesn’t really change the possibility of life on the exoplanets in our neighborhood of the galaxy.  I still tend to think we’ll find evidence of life in the light spectrum reflected off one of those exoplanets within a few decades.  And there’s this caveat in the article:

But are 90% of the galaxies barren? That may be going too far, Thomas says. The radiation exposures Piran and Jimenez talk about would do great damage, but they likely wouldn’t snuff out every microbe, he contends. “Completely wiping out life?” he says. “Maybe not.”  But Piran says the real issue is the existence of life with the potential for intelligence. “It’s almost certain that bacteria and lower forms of life could survive such an event,” he acknowledges. “But [for more complex life] it would be like hitting a reset button. You’d have to start over from scratch.

Most of my regular readers will know that I already tend to think that microbial life is the most prevalent in the universe, that complex life is rare, and that, due to the Fermi Paradox, intelligent life is profoundly rare.  Having biospheres periodically purged every few hundred million years throughout most of the universe probably just makes complex and intelligent life orders of magnitude rarer yet.

I usually say that our closest neighboring civilization may be in another galaxy.  If these findings stand, it might be more likely that they’re hundreds of millions, if not billions, of light years away.  Of course, it’s also possible that civilizations arise more often than I’m thinking, but that virtually all of them get wiped out from a gamma ray burst before they get a chance to spread.

Either way, the chances of us ever meeting any of them appear to be increasingly unlikely.

The article finishes with some possible advice for SETI:

The analysis could have practical implications for the search for life on other planets, Piran says. For decades, scientists with the SETI Institute in Mountain View, California, have used radio telescopes to search for signals from intelligent life on planets around distant stars. But SETI researchers are looking mostly toward the center of the Milky Way, where the stars are more abundant, Piran says. That’s precisely where gamma ray bursts may make intelligent life impossible, he says: “We are saying maybe you should look in the exact opposite direction.”

Eavesdropping on E.T. and the possibility of interstellar travel

Gabriel Popkin as an article at Inside Science about a study that looks at the possibility of intercepting communications between other alien civilizations.  The idea is that communicating across interstellar distances is best done with lasers.

So far, the optical search for extraterrestrial intelligence has focused mainly on the hope of receiving—and recognizing—an intentional, laser-encoded message. Researchers use dedicated telescopes or mine astronomical data collected for other purposes, like the Sloan Digital Sky Survey, to search for light pulses that could not be produced by any known object like a star. So far, no one has reported a light pattern that suggests an extraterrestrial intelligence.

But rather than look for light beamed directly at us, astronomers could also try to intercept signals sent between two distant civilizations. If advanced beings have existed for millions of years, they may well have found each other and started talking. Eventually many light beams would penetrate the intergalactic darkness, creating a criss-crossing network of communication beacons. As our solar system revolves around the galactic center, could we meander into the path of one of these beams?

While an interesting idea, the study largely concluded that this is unlikely to happen.

Unsurprisingly, he found that the chance of intercepting another civilization’s messages increased as more civilizations joined the communications network. He also found that the interception probability increased dramatically as the angle through which the beams spread out increased.

But the probability of accidentally wandering through a beam remained small as long as the beams were narrow, or collimated, like a typical laser. The beams would have to spread out about 1,000 times more widely than a standard laser pointer—in other words, more like a flashlight beam—before we have a decent chance of intercepting them, Forgan says. Sending out such a wide beam would require far more energy than emitting a tightly collimated one.

This isn’t too surprising.  Interstellar space is vast, and solar systems are (relatively) tiny.  As the article discusses, the aliens would have to go expensively out of their way to increase the odds of being detected by a third party.

One thing I find interesting about these studies, is that they have an implicit assumption: that interstellar travel or exploration is impossible, even robotically.  Because if it is possible and there are indeed hundreds of civilizations in the galaxy, then there would likely already be a communication relay in every solar system, and a vast interstellar communication web network.  If so, then our system would almost certainly have multiple beams interacting with other nearby stars.

If the aliens don’t want to be detected, it is possible that they could keep their relay stations in the Oort cloud, the region of comets and other icy bodies extending for a couple of light years out from the sun.  Of course, avoiding detection would have to be a major priority for them to keep their facilities so far away from the free solar energy of the sun.  But they could have decided to do so as soon as they noticed a tool using species developing on the third planet.  And if staying  hidden is a priority, we’re unlikely to find them for a while.

But, is the assumption that interstellar travel is impossible a valid one?  Or are SETI and other astronomers being overly pessimistic?  Most people are aware of the speed of light limitation, that nothing can travel faster than light.  But lamenting that issue is actually a bit of sour grapes, since we don’t even have the foreseeable technology to get to a significant percentage of the speed of light.  Just getting to 10% of c (the speed of light) will require astounding amounts of energy.

But it’s hard to imagine that in the centuries and millennia ahead, that we won’t be able to cobble together some method of getting to at least 1% of c.  There have been designs around for decades, such as the Orion Project, which would use nuclear explosions to propel a craft up to a high speed.  And there are many more speculative designs out there that could conceivably improve on that.

The problem is that Orion would still take centuries to reach the nearest star.  It’s easy enough for science fiction writers to wave their hands and imagine robotic probe machinery working that long, but engineering it is a different matter.  Still, Voyager 1 is four decades out and is expected to work at least another decade, albeit in a very low power mode.  Building a probe that could work for centuries would be difficult, but it remains an engineering challenge, not a fundamental limitation of physics.

And I think that’s why I remain optimistic that interstellar exploration will ultimately be possible, at least with robots.  Because the issues to be overcome are engineering ones, not fundamental scientific ones.  It’s hard to say whether those engineering challenges will be overcome in a century, a millennia, or farther out, but insisting that they never will seems unnecessarily pessimistic.

But as soon as we reach that conclusion, we’re back to wondering where everyone is (the Fermi Paradox).  Either they (or more likely their robotic representatives) are already here in the solar system, and hiding, as described above or in some other way, or they’re simply not there.  Or perhaps more accurately, the nearest neighboring civilization is millions of light years away in another galaxy, far enough away that they haven’t had time to reach us yet, if they ever will.