Centauri Dreams

Not all that long ago we assumed habitable planets needed a star like our Sun to thrive, but that view has continued to evolve. M-class red dwarfs may account for as many as 80 percent of the stars in our galaxy, making habitable worlds potentially more numerous around them than anywhere. And let’s extend our notion of habitability to what Luca Fossati (The Open University, UK) and colleagues call a Continuous Habitable Zone (CHZ). Now things really get interesting, for a red dwarf evolves slowly, so planets could have a CHZ with surface water for billions of years.

But what about white dwarfs? Stellar evolution seems to rule out habitable worlds around them because we normally think of stars entering their red giant phase and destroying their inner planets enroute to becoming a white dwarf. But can a new planetary system emerge from the wreckage? We’ve already found planets orbiting close to the exposed core of a red giant (KOI 55.01 and KOI 55.02), showing that the end of main sequence evolution isn’t necessarily the end of planetary survival. We’ve also found evidence in the metallic lines in the spectra of white dwarfs for rocky bodies close to such stars, a kind of ‘pollution’ thought to be caused by the accretion of small, rocky worlds or perhaps planetesimals (see Planetary Annihilation Around White Dwarfs for more).

Image: Almost all small and medium-size stars will end up as white dwarfs, after all the hydrogen they contain is fused into helium. Near the end of its nuclear burning stage, such a star goes through a red giant phase and then expels most of its outer material (creating a planetary nebula) until only the hot (T > 100,000 K) core remains, which then settles down to become a young white dwarf which shines from residual heat. Credit: Jonathan Saurine/Science Vault.

The conditions on planets orbiting close to a cool white dwarf might be relatively benign. What Fossati and team show is that the cooling process in these stars slows down as their effective temperature approaches 6000 K, producing a habitable zone that can endure up to eight billion years. And it turns out that white dwarfs offer advantages M-dwarfs do not, providing a stable luminosity source without the flare activity we associate with younger M-class stars. As you would expect, a cool white dwarf has a habitable zone close to the star, ten times closer than for M-dwarfs. One recent study has used this to argue that a Mars-sized planet in the white dwarf CHZ would be detectable with today’s ground-based observatories even for faint stars.

But there are other options including polarized light that may be used to detect a planet with an atmosphere around a white dwarf. Normally, starlight is unpolarized, but when light reflects off a planetary atmosphere, the interactions between the light waves and the molecules in the atmosphere cause the light to become polarized. The paper notes that the polarization due to a terrestrial planet in the CHZ of a cool white dwarf would be larger than the polarization signal of a comparable planet in the habitable zone of any other type of star except brown dwarfs. Analyzing polarization is thus a viable way to detect close-in rocky planets around white dwarfs.

Would the ultraviolet radiation put out by a white dwarf disrupt the formation of DNA molecules? Fossati and company created a computer model to study the DNA dose expected for an Earth-like planet in the white dwarf habitable zone using an Earth atmosphere model. The result:

The DNA-weighted UV dose encountered at the surface of an Earth-like planet in the white dwarf CHZ becomes comparable to that of an exoplanet in the habitable zone of a main sequence star at approximately 5000 K. Interestingly, present-day solar conditions produce an average dose on Earth a factor of only 1.65 less than that for a white dwarf with solar T_eff [effective temperature]. Varying terrestrial atmospheric conditions at times produce DNA-weighted doses on Earth as high as that on a CWD planet… [T]he DNA-weighted dose for a hypothetical Earth-like planet around a CWD is remarkably benign from an astrobiological perspective, for an extremely long period of time.

So white dwarfs, the remnants of those stars not massive enough to become a neutron star, may provide us with interesting venues for life. We can even imagine a typical star going through its pre-red giant phase with a planetary system nurturing life and then, after the red giant phase is complete, beginning a post Main Sequence astrobiological phase with a planetary system in a new configuration. The notion is plausible on the strength of this paper, though the researchers point out that 10 percent of all white dwarfs host magnetic fields that could be problematic for life. This paper assumes the hosting white dwarf is a non- or only weakly magnetic star.

The paper is Fossati et al., “The habitability and detection of Earth-like planets orbiting cool white dwarfs,” accepted for publication in Astrophysical Journal Letters (abstract). Thanks to Adam Crowl for the pointer. For more on planets around red giants, see Planets Survive Red Giant Expansion.

By Larry Klaes

One result of the biennial Astrobiology Science Conference (AbSciCon) held the last week of April in 2010 was to gather SETI specialists from around the world to look at everything from search strategies and signal processing to the best ways of creating an interstellar message. Tau Zero’s Larry Klaes has been reading the collected papers from the meeting’s SETI sessions, which have inspired him to ponder SETI’s place in the scheme of things and how our reaction to the search tells us something about who we are and who we are becoming. Readers with a long memory may recall that the first major conference on interstellar communications, held in Soviet Armenia in 1971, produced a volume of proceedings titled Communication with Extraterrestrial Intelligence, a title editor Douglas Vakoch deliberately echoes in the current work, partly as a nod to the field’s past and partly as a measure of how far it has come.

I love anthologies. There is nothing like having a collection of information or stories on a particular subject in one easy-to-find spot, particularly in book form.

Among the more prized books in my personal library are the ones which contain the presentation papers and posters of scientific gatherings about the Search for Extraterrestrial Intelligence (SETI) and astrobiology. It is always interesting to see not only how the technology designed for discovering and understanding life beyond our planet Earth has developed and changed over the years through these special publications, but also how the prevailing attitudes about alien life and how humanity should deal with it has evolved.

One of the latest such collections to follow in this tradition is titled Communication with Extraterrestrial Intelligence (SUNY Press, New York, 2011), edited by Douglas A. Vakoch, Director of Interstellar Message Composition at the SETI Institute and Associate Professor of Clinical Psychology at the California Institute of Integral Studies.

To quote from the summary on the publisher’s Web page for this book:

“In April 2010, fifty years to the month after the first experiment in the Search for Extraterrestrial Intelligence (SETI), scholars from a range of disciplines—including astronomy, mathematics, anthropology, history, and cognitive science—gathered at NASA’s biennial Astrobiology Science Conference (AbSciCon) for a series of sessions on the search for intelligent life. This book highlights the most recent developments in SETI discussed at that conference, emphasizing the ways that SETI has grown since its inception.

“The volume covers three broad themes: First, leading researchers examine the latest developments in observational SETI programs, as well as innovative proposals for new search strategies and novel approaches to signal processing. Second, both proponents and opponents of “Active SETI” debate whether humankind should be transmitting intentional signals to other possible civilizations, rather than only listening. Third, constructive proposals for interstellar messages are juxtaposed with critiques that ask whether any meaningful exchange is possible with an independently evolved civilization, given the constraints of contact at interstellar distances, where a round-trip exchange could take centuries or millennia.

“As we reflect on a half-century of SETI research, we are reminded of the expansion of search programs made possible by technological and conceptual advances. In this spirit of ongoing exploration, the contributors to this book advocate a diverse range of approaches to make SETI increasingly more powerful and effective, as we embark on the next half-century of searching for intelligence beyond Earth.”

The Dangers of Analogy

As pleased as I was to see one of these professional conference collections finally get past focusing primarily on the technical aspects of mainstream SETI and do more than just a token nod to other search concepts and the philosophical implications of contacting an alien civilization, I think there are two major points still being largely missed here. They are ones that must be addressed if humanity ever wants to actually find and talk with another set of intelligent minds.

My first issue is that we keep using the same terrestrial analogies and examples when attempting to figure out how an alien being might function and respond to the Universe and to us. Now one’s natural first reaction to this statement would be “Of *course* we use the same examples over and over! If we could ever find an actual alien life form, we would not need to keep dipping into the same wells!”

I know this appears to be a Catch-22 situation, but a large part of it stems from the fact that five decades after Frank Drake scanned two nearby star systems for a couple of months with a radio telescope, we may have increased the quantity, quality, and even the variety of methods for conducting SETI to a degree, but we have not made nearly the amount of progress in this field that we should have and could have by now.

In many respects, SETI is still stuck in the paradigm famously set in 1959, when Guiseppe Coconni and Philip Morrison wrote that landmark paper published in Nature which stated the most efficient way for a technological intelligence to communicate between the stars is by radio waves – after considering and rejecting the possibility of using gamma rays as an interstellar transmission method.

Image: Philip Morrison (1915-2005), whose paper on radio methods for SETI established early parameters for the field. Credit: MIT.

Radio telescopes were the hot, new instruments for exploring the celestial heavens in the 1950s, being perhaps one of the biggest innovations since the development of the optical telescope for astronomy four centuries earlier. Combining this field with the equally new and even daring scientific acceptance of advanced extraterrestrial intelligences as a plausible reality was nothing less than cutting edge for its day.

If one asked a typical scientist in 1959 how they envisioned the kind of alien beings they might be able to detect using radio technology, the majority of them would give the answer one would find going back to the earliest days of science fiction: As dwellers of an Earthlike planet circling a Sol-type star. The assumed beings themselves may not be exactly human-looking or behaving, but most would probably not deviate too far from the one head and four major appendages attached to a torso model. Of course there were a few notable exceptions in the fictional and factual literature of that era, but the standard ETI did not stray too far from what was found in the Sol system.

Now some other ideas for conducting SETI did arise about the same time, most notably the idea that powerful optical or infrared lasers might be used to signal with light from one world to another. While lasers did have the advantage over radio waves of being able to carry a lot of information and be much easier to detect than sifting through literally millions of radio frequencies, Radio SETI had already developed a strong following by the early 1960s and Optical SETI would not see any serious participation by observatories until the late 1990s.

Radio Silence

It has now been over fifty years since Project Ozma and there has yet to be one verified detection (meaning repeatable) of an artificial signal from an alien civilization. While I know that half a century is a proverbial drop in the bucket of cosmic time when it comes to the age of the Milky Way (ten billion years) and the whole Universe (13.7 billion years), one thing that must be recognized by now is that there is not a lot of strong or at least obvious interstellar chatter on the radio portion of the electromagnetic spectrum, at least in our part of the galaxy right now. This reduces the theory by some of the SETI pioneers that sophisticated alien societies had a vast and probably ancient interstellar communications system which we primitive humans were missing out on.

Now of course one can say that maybe there is the equivalent of the Galactic Internet and we have just not tuned into the right frequencies, or that its extraterrestrial participants purposely do not want humans and species like us among its utilizers. However, even these possibilities add up to the fact that we should be seriously conducting other types of SETI in addition to radio.

Yes, we have been doing some Optical SETI for just over a decade now and there have been a few other efforts outside the mainstream of the field, but if one looks closely at the history of SETI, they will see that the majority of projects were focused on the radio realm and until recent years were largely temporary efforts in both scope and time. There have been a few long-term SETI projects such as the one conducted at OSU from 1973 to 1998, SETI@home, and the recent Allen Telescope Array (ATA). However, these too had and have their own set of limitations; in the case of the ATA, it is under the continued threat of losing its funding. Whole realms of space and time have been neglected by our limited and limiting efforts to find other minds in the Universe due to being mired in specific paradigms as much as limits to money, resources, desire, and imagination.

Image: The radio telescope at Green Bank, WV used by Frank Drake for Project Ozma. Credit: Cosmic Search/Frank Drake.

The other hampering point for SETI is our collectively fundamental lack of appreciating the very strong possibility, even probability, that beings which evolve on other worlds – and by worlds I do not mean just Earthlike planets – are NOT going to be like humans or even other forms of terrestrial organisms.

Imagining Alien Life

Part of the blame for this is our relative lack of extensive knowledge about the cosmic realm in which we live. Take, for example, the broad layout of the known Universe: Scientists did not generally accept the fact that our Milky Way galaxy was not the only stellar island in all of reality but just one of billions until the 1920s! This was a cognitive step comparable to the realization just a few centuries earlier that Earth was but one planet circling the Sun, which in turn was just one of many billions of stars in a Universe far vaster and more complex than ever dreamed of before by the human race.

Only a matter of decades ago did we start to reveal the true natures of the worlds in our celestial backyard known as the Sol system, thanks to the development of robotic space probes capable of traveling the many millions of miles across the interplanetary void to these alien places. As often happens when one journeys to new lands, many new facts appeared and old paradigms were washed away, especially when it came to learning what worlds might make good abodes for life.

Our knowledge of worlds beyond our Sol system came even later, with astronomers proving their existence only in the last decade of the previous century. Before these discoveries, most scientists and even science fiction writers assumed that other solar systems would generally resemble our own, with small, rocky planets near their star and the giant gas worlds much farther out.

The reality of the first exoplanets found was something virtually unexpected: Massive worlds larger than Jupiter were orbiting their suns not in wide orbits taking decades to complete, but so close that these planets could circle their star in a matter of days! Granted, these early discoveries were among the easiest to detect due to the indirect methods performed to find them.

Nevertheless, as we have come to confirm thousands of these alien places so far, the vast majority are still super Jovians that practically hug the photospheres of their parent suns, with few resembling our solar system. We have even confirmed that a number of exoworlds are residents of multiple star systems, something thought improbable not very long ago due to presumed gravitational instabilities. This should provide an intellectual caution and guide as to what we may actually find out there when it comes to alien life, as opposed to what we have been thinking for centuries concerning what lives in our galaxy and beyond.

Extraterrestrials and the Media

The other culprit in our assumptions about alien life, intelligent and otherwise, is how our entertainment and media outlets have portrayed beings from other worlds, especially since the late Nineteenth Century.

Granted, due to a severe lack of actual evidence, humans have always projected their assumptions, hopes, and fears on alien life forms going back to ancient Greece, when the concept was first seriously formulated – as opposed to making all extraterrestrial beings supernatural deities and spirits from some mystical planes of existence. However, in those days there was almost no expectation of humanity ever meeting or even conversing with their cosmic brethren, at least not until people began to seriously consider such possibilities as our science and technology advanced.

Ask a typical person, even educated professionals, what they think beings from beyond Earth might be like, and one will more often than not be given a picture that mirrors what is generally predicted in our science fiction literature and films. What one finds are beings that resemble monstrosities, either of the mindless destructive and consuming variety, or ones that desire the conquest and enslavement of humanity and every other species in the galaxy.

At the other extreme, aliens have also been envisioned as our wise and angelic saviors, saving us from our pitiful, primitive selves so that we may one day join a Federation or Galactic Brother/Sisterhood of other civilizations throughout the galaxy.

Image: From 1951’s The Day the Earth Stood Still, Michael Rennie as a humanoid alien with a message for Earthlings. Credit: Twentieth Century Fox.

All these attempts to wrestle with habitats and visualize aliens might be called part of the intellectual growing pains of a species that is literally trying to find its place and way in the vast Universe. While we have many questions left to answer, human civilization is now at a technological and knowledge stage where we can start to move beyond a number of our initial ideas and interpretations that ushered in the early days of SETI. Otherwise the field will continue to return only negative results, which may lead to conclusions that will not only derail our efforts to find ETI but even bring harm to our species and society down the road.

Searching on a Shoestring Budget

First is the need to change the fundamental elements of SETI as established over fifty years ago. While there is no logical reason to abandon the search for alien intelligences in the radio spectrum – radio still remains an easy and inexpensive way to communicate across the interstellar distances – one thing we have learned after five decades of scanning those frequencies (even longer if you include the earlier efforts to listen for any messages from Mars) is that this part of the Milky Way at the least is not currently brimming with transmissions between civilizations as the early SETI pioneers conjectured and hoped.

There is of course always the possibility that a radio transmission, either deliberate or as part of the electromagnetic leakage of a technological society, may be heading our way at any time, or perhaps already has arrived: The Wow! signal detected by the Ohio State University (OSU) SETI program in August of 1977 certainly had many of the characteristics of an artificial interstellar signal. Unfortunately, the signal was not found until hours later when a team member discovered it on a recording printout, and the signal has never repeated since, a major criterion for science.

Now there has been some expansion to the SETI paradigm in the last few decades. Most SETI programs in the United States no longer rely on government funding, which proved itself unreliable when the funding for NASA’s SETI program was abruptly cut in 1993 after one year of operation due largely to Congressional ignorance. While this has allowed a degree of freedom and latitude when it comes to expanding SETI’s parameters and techniques, these private efforts have also been subject to the whims of the economy. Ironically, the ATA depicted on the cover of Communication with Extraterrestrial Intelligence has been hit by funding problems and is so far remaining alive with public donations and the support of the United States Air Force – which is using the vast field of radio telescopes to track artificial debris in Earth orbit.

Optical SETI finally entered the mainstream in the late 1990s after decades of neglect and resistance by radio SETI advocates. It too, however, has yet to find a laser or infrared transmission from the stars.

There have been other searches for alien technologies such as the Fermi search for Dyson Shells in 2005. In reality, though, most SETI projects of all stripes have been largely sporadic, even token in the number of cases. For most of its history, SETI has been placed on the sidelines, begging and scraping for time on telescopes and suffering from misunderstandings, ridicule, and being lumped in with pseudoscience.

Image: A Deep Space Network station near Madrid. Credit: NASA.

This attitude can be blamed primarily on the following:

• A sincere yet misguided old school view that solar systems are rare (and thus life) due to the pre-nebular hypothesis of how planetary systems form, which involves one star passing by another and pulling material from its photosphere into nearby space to form a debris ring around that sun, which eventually becomes the various worlds of a solar system.
• Antiquated views going back to Aristotle and Plato and reinforced by various religious, political, and psychological factors in later centuries that hold we and Earth are the spiritual and literal focus of existence and as a result no other beings exist in the Universe, which until the most recent era was considered to be relatively small compared to what we know now.
• The popular (read general public) take on aliens, which between their portrayal in most science fiction has created a virtual belief system in beings who can be either our destroyers or saviors. Aliens in our culture are also often used as substitutes for various human groups in science fiction and as comic relief. Seldom do these images add much to the scientific database of ideas on how and what our cosmic neighbors may truly be – though they do have something to say about human attitudes and thoughts on this subject. The results are a misinformed public and politic and a scientific community that is more embarrassed and dismissive than encouraged to pursue the search for any real ETI.

This comes to the second point: Making the human race truly aware and appreciative of our place in the real Universe, beyond the confines of our pale blue dot, as Carl Sagan so famously referred to the planet Earth.

Public Perception of the Cosmos

I know that on an intellectual level we have come a long way from the time of Nicholas Copernicus when he cautiously introduced in 1543 the idea that Earth circled the Sun and not everything orbiting our planet or otherwise focused upon it and us. Nevertheless, there are plenty of people living now who, despite access to vast amounts of information as never before, either do not know/appreciate that we live on a rotating planet orbiting a star or just do not care due to their education level, the quality or lack thereof of their everyday lives, and the fact that the vast majority of us have never been into space and in many cases cannot even see the stars and most other celestial bodies from the surface of Earth due to light pollution.

Which leads to my third and key point: Are we as a species and a society truly capable of finding, understanding, interacting, and dealing with an intelligence which evolved on an alien world? Or is this the ultimate reason as to why our current SETI efforts have so far found no definite signs of anyone else in the Universe? If the answers to these questions show that we are still too immature for such an endeavor, should we just give up and hope that some day natural evolution will make us a bit more cosmically oriented? Or should we strive to build something that will complete our goals for SETI, METI, and CETI?

As pointed out previously, our combination of cultural ignorance, apathy, paranoia, and misdirection due to the depictions of aliens in most science fiction has left us in numerous fundamental ways little advanced from the perceptions and theories about ETI going back centuries.

For a prominent example of what I am referring to, read up on the history of the astronomical study of Mars in the late Nineteenth through the early Twentieth Century, from the time when Italian astronomer Giovanni Schiaparelli first noted the (in)famous canals crisscrossing the face of the Red Planet in 1877 to the era when the first robotic space probes finally began to reveal the true nature of Mars in the first decades of the Space Age.

Even though the stories refer to a world we now know is not inhabited by an intelligent alien race, advanced, dying, or otherwise, if one removed the location of the planet in question from the literature of the day on the subject – especially those works by Percival Lowell – the topics of conversation would be remarkably similar to the ideas and debates going on to this day regarding ETI, even with over a century of hindsight in our favor.

Accepting the idea that our seeming lack of success with SETI and METI is due to limitations with our experience and technology with these fields, could it be that we are ultimately just not capable of dealing with a species not from this planet due to the state of our biological evolution? Humanity certainly has enough issues and misunderstandings with members of its own species, to say nothing of other high minds on Earth such as the cetaceans. So how can we expect to grasp the truly alien?

Moving Past Biological Evolution

Will the beings that eventually come form this planet which can find, understand, and interact with ETI not be humanity but minds that we created? Hugo de Garis calls them Artilects, which is short for Artificial Intellect. We have the potential to build beings which would have intellectual capacities that dwarf ours with ease, ones that could easily handle intelligences from other worlds. It has been speculated that if there are other advanced minds out there, they will be the alien versions of Artilects, the natural and ultimate step in the process of biological evolution across the Universe. Of course this could all be short-sighted too, but it does offer one explanation as to the seeming silence out there: Current humanity just is not on the same playing field when it comes to cosmic correspondence compared to a mind unfettered by relatively slow biological evolution.

So what do we do? Do we just become overwhelmed by the Cosmos and give up trying to understand and explore it? Besides the fact that such an action will not happen at least collectively so long as we are alive and have a civilization (even during the European Dark Ages there were still groups of people who strove to record and comprehend the world around them, limited as their capabilities were), the short answer is no – though a few caveats, improved resources, and better attempts to appreciate the Universe as it really is and not as we wish it to be are in order.

Limited as our SETI and METI efforts may be, they have been of benefit to our species. Look at the number of sections in the CETI book devoted to our attempts at communicating and understanding an alien mind. Such exercises not only help us for the day when we do detect an ETI at least at some levels, but they are very good at helping us deal with each other.

Take note of the Pioneer Plaques and Voyager Interstellar Records now wending their ways into the wider Milky Way galaxy. Even if an interstellar species finds them one day in the far future, even if the ETI cannot understand what is on these golden objects or miss their purpose and presence entirely, the plaques and records have done much to make us see ourselves as members of one species on a planet in space. I have read that the music on the Voyager Interstellar Records was one of the first collections of world music ever put together.

Perhaps most importantly, these pioneering attempts at METI justify their existence by the very fact that a collection of humans had the desire and ability to be aware to the possibility of other beings in the Universe and make an effort based on the higher scientific and technological ideas and tools of the day to reach out to them in a way designed to benefit both parties.

So let us keep the radio on and tuning through the static for whoever may be out there. The beauty of radio is that you can work on other things while listening to it.

Michael Chorost is a science writer whose research interests grow directly out of his personal experience. You may have already read about his struggle with hearing loss — a problem he has dealt with since childhood — in his book Rebuilt: How Becoming Part Computer Made Me More Human (Houghton Mifflin, 2005). It’s natural to find Chorost writing often on things like cochlear implants and neurotechnology, but intriguing to find that he is also a SETI advocate, and one who believes his hearing issues have a bearing on a field he has studied passionately all his life. In fact, the book he plans next, which follows on 2011’s World Wide Mind (Free Press) will be a SETI title.

So what’s the connection between deafness and hunting for signs of an extraterrestrial civilization? Chorost sees it as a matter of isolation and communication, as he notes in a recent entry on the Psychology Today site. Is the entire human race subject to deafness? It is in the sense that we have no idea whether or not we live in isolation or in a galaxy populated with other intelligences. Our ignorance of our place in the universe becomes its own kind of perception problem, a deafness SETI has been trying in vain to remedy for the last fifty years.

Image: Dish antenna of the 43-metre (140-feet) radio telescope at the Green Bank observatory in West Virginia. Credit: Seth Shostak/Science Photo Library.

It’s an interesting idea, and one the author develops by looking at a recent article by Atul Gawande in The New Yorker. Gawande focused on the effects of solitary confinement on people, relating the story of one prisoner held in such conditions in a maximum security prison who began to lose his mind. The argument is that without encounters with other people, we find our psychic integrity threatened. In the case under study, prolonged isolation led to compulsive behavior, panic attacks, hallucinations and increasing paranoia. Looking at how people relate to those around them, Chorost wonders about a planet-wide pattern of isolation:

I think the analogy is pregnant and poignant, but unproven. Still and all: crazy prisoners, crazy planets. Contact and communication with other planets might have a calming effect on a civilization, giving it perspective and self-knowledge. After all, it’s mainly through interaction with other people that we get feedback on our behavior. We know ourselves by how people reflect us back to ourselves. The Other is a kind of mirror. Right now, humanity has no way to see itself in perspective. We just don’t know what’s abberational in intelligent species, and what’s normal.

So we could be looking at one more possibility for explaining the Fermi paradox. Extraterrestrials are not here because they think we’re lunatics. It’s not a likely scenario, and Chorost doubts it applies, but there is something to be said for the idea of planets facing existential loneliness:

I think that deafness and planetary isolation have something in common. A deaf person knows how easy it is to become profoundly cut off. (If civilization collapsed and the electricity went out for good, my rechargeable cochlear implant batteries would last me about a week.) I think of our planet swimming in the starry blackness, studded with radio telescopes peering anxiously into the void—and hearing nothing. To me, that feels a lot like being deaf.

When I was growing up, my uncle from Florida used to drive up once a year for an extended visit. He was already going deaf at the time and thought it was from the effect of aircraft engines (he had serviced radio equipment for Eastern Airlines his entire career). In any case, over the years his deafness became profound. Like Chorost, he was also fascinated with SETI and the idea of finding other intelligences. He had huge problems communicating with people in conversation, but he built a world out of books and kept a massive library. I often wondered, when deafness closed off his interests in music and shortwave radio, whether he felt the same sense of bafflement I feel when walking on a starry night, wondering whether there is anyone out there sharing this universe, pointing instruments into the sky and asking why no one speaks?