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Of Sails and Supernovae

When we consider pushing a sail to 20 percent of lightspeed, which is the target velocity for Breakthrough Starshot, it’s interesting to think about how laser propulsion differs from sunlight. After all, while constructing a huge laser array presents numerous challenges on Earth, we already have a star to work with, and sail technology that is beginning to be tested in space. Consider, too, that we have operational spacecraft like the Parker Solar Probe that are exploring regions close to the Sun, helping us learn more about heat shields, even as we plan missions like Solar Cruiser, whose sail would enable interesting non-Keplerian orbits near the Sun.

Wouldn’t it be easier to find ways to use our Sun’s own energies to drive our starship by getting a boost from gravitational effects? A closer look reveals the power of solar sails in nearby space (i.e., within the system), while illuminating the problems at interstellar distances.

For getting a solar sail up to the highest possible speeds, we will probably need an Oberth maneuver, which means falling deep into a gravitational well and applying propulsion at the time when velocity in that well peaks, which squeezes maximum effect out of our boost. With a sail, that would mean a so-called ‘Sundiver’ mission, bringing a furled sail shielded by an occulter (perhaps a small asteroid) breathtakingly close to the Sun and then opening the sail at perihelion for the best possible kick.

Depending on shielding and thus how close we can get to our star, we do get a substantial boost over the velocities of our two interstellar Voyagers, one of which moves at just over 17 kilometers per second. We might squeeze 100 kilometers per second out of the Sundiver maneuver, and perhaps a bit more, with future craft using sails made out of new metamaterials achieving even better. But we’re nowhere near 20 percent of the speed of light.

Solar sails certainly have broad applications as we build a Solar System infrastructure, and we can use them with Sundiver maneuvers to get into nearby interstellar space. But if we find long mission times unacceptable, we need to be thinking of alternatives when we mount a true star mission.

Other civilizations won’t necessarily have to work with the same constraints, depending on the kind of star they orbit. I’m always interested in how intelligence might exploit natural objects to achieve interstellar goals, so I took note when I saw Avi Loeb’s latest piece in Scientific American. Loeb (Harvard University), who chairs Breakthrough Starshot, is not one to avoid speculation, without a healthy dose of which we can hardly work with concepts involving SETI and highly evolved civilizations.

So let’s leave the realm of what humans can do with our small G-class star far behind as we consider what sufficiently advanced technologies might attempt. If a culture were to be a billion or more years old, how would we know where to look for it? One way into the problem is to consider the need for energy useful to Kardashev Type II and III civilizations, energy which is available in abundance around certain natural phenomena.

And given the recent attention to Betelguese and the question of when it might become a supernova, Loeb has been moved to consider the power such an event would unleash. The results make working with the flux from a G-class star seem trivial indeed. Even the best Sundiver maneuver at Sol yields velocities that would take hundreds of years to reach the nearest stars. A similar maneuver around the most luminous stars we know might reach 10 percent of lightspeed (not too shabby!). But for maximum kick, a lightsail riding the shockwave of a supernova from a star like Betelguese or Eta Carinae could be pushed to a high percentage of c.

Image: Hubble Space Telescope-Image of Supernova 1994D (SN1994D) in galaxy NGC 4526 (SN 1994D is the bright spot on the lower left). Credit: NASA/ESA.

Could a civilization time a supernova explosion accurately enough to ride the shockwave? That’s a question we can’t answer, nor can we say what kind of timeframes such a culture might operate within. Loeb imagines numerous lightsails parked around a star nearing the end of its life, perhaps placed by a civilization nearby, and perhaps left there indefinitely. If this civilization wanted to use the supernova for propulsion, it would still face numerous problems:

First, as in Starshot, the sails must be highly reflective so as not to absorb too much heat and burn up. Second,once the sails are placed in orbit around the massive star, they will be pushed away by the bright starlight or mass loss prior to the explosion. To avoid this danger, one could deploy the sails in a folded configuration and equip them with a switch that would open them up like umbrellas as soon as the explosion flash begins to rise. Third, even though the launch can start from a distance that is a hundred times larger than the size of the exploding star, care must be taken in selecting particularly empty acceleration paths – clear of any stellar debris.

Indeed, given dust particles with a relative speed close to the speed of light, such a sail would have to be folded to reduce the area it presents in the direction of flight as soon as it reached peak velocity. An even wilder prospect: A massive enough star (Loeb mentions Eta Carinae) collapsing into a black hole could produce gamma-ray bursts (GRBs) that would drive the Lorentz factor to extreme levels. Now we’re in range of Poul Anderson’s ‘Leonora Christine,’ the runaway starship in the novel Tau Zero that crosses galaxies in far less than a human lifetime as measured by the crew, while aeons pass outside their rest frame.

We’re in Dyson sphere country here, a reference Loeb himself makes, looking into ways advanced civilizations could harvest high energy sources around them. A Dyson sphere or array, gathering the maximum amount of stellar light, might be found by its infrared signature, so Dysonian SETI, which looks for evidence of ETI in our astronomical records, has a target.

Clément Vidal has also worked this notion in his book The Beginning and the End (Springer, 2014), looking into questions like extracting energy from the accretion disk around a rotating black hole or tapping the power of X-ray binaries. We are also in Olaf Stapledon territory, asking about extraterrestrial engineering that is inconceivable to ourselves, but possibly visible as a SETI signature in the ‘watering holes’ for energy the universe makes available.

It’s hard for me to imagine a civilization with the patience to wait out a supernova explosion to drive a lightsail, but when we’re dealing with technologies that may be several billion years beyond our own, we have no business imposing our own limitations on the cosmos. Anomalies in our observations of supernova remnants would be worth investigating, although Loeb admits to the difficulty of isolating artificial components within them. Even so, dying stars conceivably have reason to be pondered by civilizations advanced enough to make use of their energy.


Comments on this entry are closed.

  • Andrew Palfreyman February 4, 2020, 15:30

    Backing off from such bewildering grandiosity, I wondered about doing StarShot purely with solar – and it will not be cheap. Here’s Tesla for example:

    The spec is (roughly) 50 GW for 2 minutes, or 1.6 GWh total.
    That’s about the projected total annual output of Tesla Megapack storage.

    Adding solar arrays into the mix (of course), by 2022 Tesla may have a projected total annual output of 1 GW.
    That would mean about 2 hours minimum to recharge that 1.6 GWh Megapack.

  • Douglas Phillips February 4, 2020, 15:50

    I have always thought that some of the difficulty we have in imagining interstellar travel (sub-light-speed, that is) is that we also cannot imagine the age of our own planet. Every time I hike the Grand Canyon and descend through hundreds of millions of years of rock strata, I try to imagine daily life on Earth continuing its ceaseless march to the future. We are such a tiny blip floating in eons of existence. Civilizations that travel among the stars may have an entirely different outlook of time.

    • H. Floyd February 4, 2020, 18:33

      Tantalizingly said! Doesn’t just go for technology. Every species has an evolutionary trajectory, too. Homo sapiens is a single frame from a very long and strange living movie.

      All the more so now. For the first time in the known history of life, evolution has a teleological trajectory: determined by the purposes we want the organism to serve.

      Our descendants a mere thousand years down the road could be capable of things beyond present imagination. Our recent history shows that just a few ounces of neural matter can go an astoundingly long way. Homo-derivatives engineered or interfaced with quantum cognition, naturally seeing paths through physical limitations that we literally cannot get our minds around. What would their material culture look like?

    • James Jason Wentworth February 13, 2020, 6:44

      If they’re immortal, or even “just” so long-lived that they might as well be, “time will be someone else’s problem” to them, of no more concern than oxygen is to us.

  • Antonio February 4, 2020, 16:54

    Talking about extreme sails… has anybody studied using magnetic sails near a pulsar?

    • James Jason Wentworth February 13, 2020, 6:47

      Ooooh–now *that* sail, and its “engine,” might together constitute a real “hot rod!”

  • Charley February 4, 2020, 18:51

    While I’m definitely not in the let’s sell the “Breakthrough Starshot” crowd, I have a political feeling that that’s what is going to be pushed no matter the particulars behind the viability or non-viability of this particular scheme. So let me (pretend) to get on board and say that I’m one of your boosters for this particular scheme.

    All that being said, I have one or two questions for the crowd as to whether or not this could be accomplished with the following type of scheme as to approachability to get the probe there in the soonest period of time applicable.

    To whit: could this probe be launched toward Jupiter and then a gravity assist be applied to the probe at Jupiter, such that it performs a Sun dive close to the sun and then at closest approach to the sun, a another gravity assist is applied to the probe at which point at the most apt approach time you then turn on the laser full bore, which then adds on even more additional speed-then it would be straight using the laser straight on the probe, while it’s in Earth orbit ?
    I hopefully framed the question in a non-confusing way, but if you understand it, do you think it is a viable means to get the maximum speed out of this whole scheme?

    • Alex Tolley February 5, 2020, 0:24

      I suspect the best way to maximize velocity beyond the basic sundiver approach is to find ways to actively power towards the sun to increase the velocity at perihelion. This can be done with refractive sails, or other forms of propulsion, rather than just relying on a freefall trajectory. A similar approach might be to use a large mirror to push a sail towards the sun, similar to the way Forward’s interstellar sail allowed for deceleration at a target star.

      Once one can control huge amounts of energy, there are many ways to use it to propel a craft. Hybrid designs using different propulsion methods can then be used to provide the best performance for the given technologies.

      • Paul Gilster February 5, 2020, 7:19

        I think Charley was asking if a Jupiter assist and sundiver would help with the specific Starshot concept. The answer to that is no — IF a gigawatt laser could beam power to the Starshot sail as envisioned in the concept, the sail would be under the beam only about 2 minutes and would hit 20 percent c. Adding in the comparatively tiny effects of gravitational maneuvers would only produce a rounding error in accelerations like this. Starshot is definitely not a sundiver mission.

        • Charley February 5, 2020, 13:05

          You’re right on the money, Mr. Gilster – that’s precisely what I was saying. In my typical nerdish fashion, I got intensely curious as to whether or not your statement that a Sun dive coupled with a laser acceleration really would make a difference or not. So I spent the better part of an hour fruitlessly doing some calculations which I think I finally got correct and based upon my proximate numbers I see that if you added a Sun dive to the whole scheme you would save about two weeks (13 days) in time if you added a Sun dive to the mix. Is two weeks savings worth it ? I guess after about approximate 20 years waiting, probably not.

          • Ashley Baldwin February 6, 2020, 14:54

            In terms of “Sundiving “ I guess we are talking the Oberth effect / manoeuvre .

            As described a solar sail would be near peerless for this, given its hypothetical ultra high performance near periapsis. Hypothetical . To achieve this any sail would need to operate at or around 2-3 solar radii. So simple thermal mechanics does for this given it would need to be both massive and near impossibly thin . No known substance comes even remotely close to possessing the necessary thermal AND physical properties. Or will do for the foreseeable future.

            However, still hypothetical- but much closer to reality is “magnetoplasmahydrodynamic propulsion” . MPHD. Essentially a sophisticated form of ion propulsion but utilising hydrogen rather than Noble gases as propellant . Obtaining exhaust gas bell tire of beyond 100kms/sec ( bearing in mind remembering that Oberth essentially exploits Newton’s third law. )

            Unlike most ( and current operational ) ion thrusters, this system creates enormous thrust – close to that of the best chemical systems – but unlike them whilst maintaining a high specific impulse , ISP. On a par or better than current or upcoming ion thrusters . So high fuel efficient AND high thrust. The Oberth effect is most potent at or around periapsis – thus needing powerful thrust . A MPHD thruster requires about four mega watts of power to operate . A lot of power for sure but well within the realms of a space adept nuclear reactor . Extrapolation for sure but no more .

            Unlike a solar sail the combination of a MPHD ion thruster and nuclear power plant could be of a size that could be realistically shielded from the solar flux whilst in close proximity to the star . With a big and thick enough physical shield . In terms of the required thermal properties, The Parker Probe already possesses such shielding – that can protect it to around just eight solar radii. So again as with the nuclear reactor the technology is there and development is simply a question is scale rather than massive development .

            Unlike a solar sail the MPHD thruster/ reactor would also continue to operate well beyond the orbit of Mars. It’s principal limiting factor being only the availability of propellant . A huge burst of acceleration for starters followed by a steady increase over a very long time – possibly with a repeat Oberth thrown in at Jupiter too. That’s a lot of velocity .
            The only other limitation is that 2-3 solar radii Oberth manoeuvres produce highly parabolic pathways best suited to remote objects . Solar system or beyond . The Kuiper Belt et al (Oort Cloud, Planet 9 ?) Not reaching a big enough fraction of ‘c’ perhaps to be considered interstellar, but a big step in the right direction and more tan enough to visit cis and trans solar system space .

            • Charley February 7, 2020, 1:27

              Ashley Baldwin,
              I greatly appreciate what you are saying and there is a great deal of merit to your arguments. But – and it’s a very big BUT; as was clearly stated by Mr. Gilster in his reply to me, the entire purpose of this purported specific Starshot concept is to obtain a maximal velocity and a short travel time for interstellar probe, which will by its very nature be virtually massless. This masslessness (if that’s even a word) is the key to the entire success of achieving a 20 year travel time to the nearest star.

              As I clearly pointed out in the article directly above your reply, I did some simple calculations which showed that the additional velocity given by various combinations of velocity increase yields only a two week savings in travel time out of the 20 years that would be allotted to the voyage.

              Somehow, I can imagine that even using MHD or a combination ion drive to add speed can’t significantly reduce travel time without adding considerable amount of mass and complexity. That’s the thrust behind the entire Starshot concept : a virtually vanishing mass with a violent acceleration yields by laser – in theory , a system that would vastly shorten travel times that’s normally centuries under conventional techniques to a 20 year voyage.
              As for the merit of Starshot concept in and of itself, I can’t really say. Although I do not favorite it only because of the fact that they are talking about sending only a entire one gram payload – necessitating the use of lasers, which will consume the energies of the equivalent of five full-scale commercial nuclear power plants. On the surface, I suppose there’s no reason to suggest that it will not work, but is something that will work, even if technologically feasible, means that it’s a good enough reason to do that ?

              The other reason, which everybody in my opinion, seems to ignore simply because they are enamored of this proposal, is simply the fact that it will probably be almost unbelievably costly. Just recently they had the Democratic Iowa caucus, which according to news reports cost upward of almost one billion dollars to accomplish !!
              Imagine that! A billion dollars to canvas essentially one state, and that’s nothing more than voting! Having just heard that news it now puts me more in the camp that this particular interstellar scheme would probably now cost upwards, I would guess (only a guess) conservatively in the neighborhood of three trillion dollars. That’s just based upon what I have seen things escalate in an inflationary environment in this day and age. Can we afford it to send a single gram to the nearest star?

      • Jeff Wright February 8, 2020, 15:01

        This is why I hope Planet 9 might be a black hole after all.

        If you feed matter into it–you would have an x-ray jet fountain to ride, would you not?


        According to some–dropping an asteroid into the sun might give us a laser

  • Allen G Taylor February 4, 2020, 21:34

    In the third book of Dennis E. Taylor’s Bobiverse Trilogy, the good guys trigger a star to go supernova prematurely. If the fictional technique described is viable, there is no need to wait around for a natural supernova.

  • ljk February 4, 2020, 23:02

    The Parker Solar Probe has broken its own record for the fastest human-made vessel yet: 244,255 mph (393,044 km/h).


    The previous record was another solar probe, Helios A in 1976: 252,792 km/h (157,078 mph; 70,220 m/s).

  • Alex Tolley February 5, 2020, 0:12

    Billion-year-old civilizations may have the technology to use immaterial “sails” to capture the energy of supernovae. Whether that is magnetic sails (like the Plasma Magnet), or something more exotic that can reflect both radiation and matter, such sails could ride any emissions, as long as teh ships and its engines were protected.

    As for timing a supernoava, why not use technology to induce the stellar eruption? Our puny technologies have historically relied on the serendipity of natural forces to propel our engines, whether sailing ships or windmills. Even our current solar technology operates with the uncertainly of the clouds and rainfall, and wind power is relatively capricious. But suppose a civilization can control the eruptions of stars, from inducing flares, novae, and even supernovae?

    Unless we are nearing the end of possible technological development, our speculations are going to be subject to Arthur C Clarke’s 3 laws.

  • Gareth Wilson February 5, 2020, 0:18

    You probably want a Type I supernova – a white dwarf blowing apart. Type II supernovas give off 10,000 times as much energy in neutrinos as they do in light. I know you can usually ignore neutrinos, but at 100 trillion times the power of sunlight they might have dangerous effects on the ship or the passengers.

  • Alex Tolley February 5, 2020, 0:36

    One point I would make is: ‘why would a civilization want to project matter across the stars at all?”.

    We seem trapped in the idea that biologically based entities will want to travel between the stars. It is teh basis for “romance” novels of travels. But apart from the need to transport a replicator, there is no need for argosies of ships. Everything, including biological entities, will be manufactured or born in the target star system, where the matter already exists. On a galactic scale and timeframe, the replicators can be sent at relatively slow velocities and allowed to spend a long time building the infrastructure and cultivating the biospheres before populating it. The patterns of intelligence could be transmitted to the star and embodied locally, avoiding the need to transport matter, and having the important information travel at light speed.

    The bottom line is that the civilization will only rarely need to send a ship, and these most likely would spread from star to star in the pattern of Von Neumann replicators, only in this case, to transport the universal replicator like a very sophisticated 3D printer.

  • Zanstel February 5, 2020, 4:17

    I doubt that this kind of idea could work. When the energy is not the constraint, the maximum acceleration is, when the system of acceleration is throught some kind of “pushing” (direct momentum transfer to the back of the ship)
    The ideas of use gravity waves or specially frame distorsions around black holes or neutron stars (halo drivers) are different, because the ship could be “moved” as a whole, instead of being pushed on the back, so inside the ship don’t need to feel the acceleration (more like being crushed).

    • Michael Fidler February 5, 2020, 17:10

      Interesting comment and gravity waves could be generated on a much larger scale at the super black hole in the core of our galaxy. If we want to find what to alien civilizations is like gold to us the best place is where gold is produced in huge quanities, at the core of our galaxy. The other side of the story is that these mergers could spark the vacuum or creates huge areas of quantum entanglement. Our understanding is still very limited but the core of the galaxy is the place to look for the gods!

  • andy February 5, 2020, 5:02

    One of the Stephen Baxter novels (Manifold: Space I think) featured a civilisation that went around the Galaxy artificially inducing supernovae to use them as propulsion for their solar sails. Of course, they didn’t check whether the locals were ok with this behaviour…

  • Phil Tynan February 5, 2020, 6:41

    No-one can say Avi Loeb lacks for imagination. But even a Kardashev II Civilization might find waiting thousands of millenia a little daunting – not to mention be leery of the sheer destructive effects of a nearby supernova.

    Why not detonate novae instead? Sagan and Shklovskii wrote of detonating artificial novae and supernovae using gamma ray lasers in their seminal “Intelligent Life in the Universe”, and the theme has certainly been picked up in fiction. Larry Niven’s ‘Monks’ would trigger nova-like reactions in main sequence stars to propel their light-sail craft if a customer threatened to strand a Monk ship in-system by refusing or being unable to build them a launching laser complex. In Manifold:Space, Stephen Baxter had species of ‘Crackers’ trigger novae in nearby stars to propel their huge interstellar sail-craft. He even has a species aiming to exploit the jet of future gamma ray burster to ensure its own intergalactic propagation. Arthur C. Clarke incorporated the idea of artificially-induced novae in his classic short-story Crusade where he referenced the rash of novae in Aquila in the first quarter of the last century. So the idea of ‘artificial novae’ certainly has an established pedigree.

    The idea of artificially inducing nova-like reactions has also been studied a little more seriously (for those values of ‘studied’ which include wild ideas like this). Proposals range from high frequency lasers (x- or preferrably gamma), to manipulating electroweak unification scale energies to produce beams of massless non-Abelian magnetic monopoles (which presumably would catalyse higher rates of fusion in some critical region) to Alexander Bolonkin’s chromospheric penetrator warhead which would detonate within the solar mantle triggering a massive short-lived (explosive) rise in solar luminosity (albeit he was only considering it as a doomsday weapon).

    Although some white dwarf systems might have colonizable asteroid belts or even terraformable planets (maybe even life-bearing worlds, although I still can’t see how such a world, spiralling in to the claustrophobic habitable zone of a star that had left its red-giant and later planetary nebula phase, would have sufficient volatiles to maintain a long-term biosphere), I could imagine fleets settling such systems temporarily (i.e., for a few millenia) building up their numbers and resources before arranging their dispersal to many other more distant and inviting systems, riding the light from a nova they had kindled.

  • Al Jackson February 5, 2020, 10:19

    Surfing a supernova… there is a story for that.
    Howard Waldrop and I wrote a story about a Bussard Ramjet escaping a supernova by ‘surfing’ on the shock wave. Published in 1976 in the anthology Faster Than Light ed. Jack Dann, George Zebrowski.


    • Paul Gilster February 5, 2020, 10:42

      And it is one hell of a good story!

    • ljk February 5, 2020, 21:59

      Is that the story about the robotic star probe with AI monitoring a star that will go supernova that thinks it cannot escape the explosion and an even smarter AI tells it to turn part of itself into a “surfboard” to ride the shockwave to survive the event? I love that story and clearly I remember it all those years later! Is it online?

      • Robin Datta February 7, 2020, 0:11

        Search online Sun up pdf Jackson Waldrop.

  • Coacervate February 5, 2020, 21:20

    OK, first I am a chemist and I’m speculating over whisky/sodas with a pal on a warm NZ summers PM. What little I know about rockets I know only from what I read on CD. But reading this made me wonder… lets say Betelgeuse once had a life-sustaining planet some millions of years ago. Further suppose some of that life was clever enough to anticipate their star’s end and looked out across their neighborhood for a decent-looking rocky planet to which they might relocate. Here we are a mere 700 ly (?) away with all this oxygen and water. Should we be on the look out for … well you get the idea… and I’m sure others have thought it through more thoroughly. Still, wouldn’t that just be the coolest, black swan, terrifying thing ever. Like District 9, Only we would probably be the restricts

    • Alex Tolley February 6, 2020, 15:31

      It would be a remarkable coincidence if ET started arriving just in the narrow time frame where we have the wherewithal to do much “watching the skies”. Far more likely they would have arrived in deep time, perhaps tens of millions to billions of years ago.

      James Lovelock (of Gaia Hypothesis fame) doesn’t believe there is intelligent life (of human-level) anywhere else in the universe. His argument is that we come from a unique set of contingent circumstances that makes the probability of another highly intelligent species vanishingly small, despite the large numbers of possible living worlds.

      I always liked Olaf Stapledon’s “Last and First Men”, where the 18th men lived on Neptune, now warmed by our sun that had become a red giant. Migrating within a star system makes a lot more sense to me than trying to move planetary populations to another star, Maybe seeding an exoplanet, but not a migration. Depending on our respective biologies, ET may have a hard time surviving on Earth without isolation or very advanced technology. Migrating to a sterile, or near sterile world may be the better bet.

    • Antonio February 6, 2020, 18:15


      – For the most part of the history of life on Earth, oxygen was not used by living beings. Indeed, it was toxic to them. So that “with all this oxygen and water” is quite antropocentric.

      – On average, every star in the galaxy has at least 2 or 3 planets. So no need to travel 700 light-years in search of a planet.

  • Michael T February 6, 2020, 2:30

    Having sail ships at the ready for a supernova would make a nice lifeboat system if you had enough warning. Exactly what you put on those lifeboats depends on mass capabilities – maybe crew, maybe just data storage for playing back or reproducing yourselves elsewhere.

  • Mike Serfas February 6, 2020, 8:06

    It would be nice if it didn’t take quite _that_ long to figure out how to generate and store antimatter in bulk quantities and react it safely for a space mission. I admit NASA doesn’t have a precise timetable ( https://www.nasa.gov/exploration/home/antimatter_spaceship.html ).

  • Gary Wilson February 7, 2020, 14:37

    I usually love reading Lovelock’s ideas but I can’t agree that we will be found to be uniquely intelligent in the universe! That is ridiculous and we will never know the answer with respect to the universe or possibly even our galaxy. Time and space are too vast for us to ever know whether we are uniquely intelligent. Surely it is a question of probability given the vast amounts of time available when considering life occurring and evolutionary time scales. I think there will be at the very least dozens if not hundreds of intelligent species in our galaxy at any one time using the Drake equation and very conservative numbers for the various factors in the equation. If intelligent life has arisen here it will arise elsewhere. That surely is a certainty. Arguing otherwise seems specious to me. How many planets have we checked for the presence of life of any kind again in any way that guarantees the answer? So far we have 1 out of 1 habitable planets to infer answers from. And yet Lovelock says no matter how many planets we survey the numerator will remain 1???

    • Alex Tolley February 7, 2020, 18:30

      Simply changing the probabilities if life and the emergence of technological civilization in the Drake equation gives a range of ET from 1 (us) to a large number. If the probabilities are small enough, even the universe contains just us as the sole intelligent species. We simply don’t know what the probabilistic are. Falling back to the Copernican idea that we are average lends bias to the idea there must be many other civilizations out there. Unfortunately, if the Great Filter is ahead of us, then we don’t know if the either probability is low, or just that filter is perhaps the reason we don’t see evidence of ET.

      That is why the discovery of biosignatures is important. It tells us if life is (very) rare or common. If common, then it is worth continuing SETI. If extremely rare, then maybe there is little point in expending resources for SETI ( unless ET is not biological and has expanded beyond its home system).

      I prefer to be optimistic about life, but await confirmation rather than be dogmatic in my beliefs. As for ETI, if it doesn’t exist, then so be it. We, or our descendants, can freely occupy the universe. We needn’t be fearful of going to the stars and making new homes there.

      As for being lonely if ETI is not there, I suspect we will evolve both new species of intelligent life, both biological and artificial, that we will create the friends to talk with eventually.

      It might well be fun for our civilization to play God.

      • Mike Serfas February 9, 2020, 19:47

        It can’t be ruled out that they try to avoid playing God, or at least do it in a more godlike manner. If advanced civilizations exist, they can probably spy out what is going on in your house better than the terahertz antenna array on a Huawei cell phone; they might do better than fMRI scanners. Perhaps a silent prayer is more than sufficient to speak to them – the question then is on them whether they wish to speak back or otherwise violate the purported Prime Directive. One option might be to leave the historical simulation (reality?) intact, but remedy the issue in some other forum using a duplicate, modified or replacement copy of the person seeking contact. It is very hard to rule out what could happen with technology (or social philosophy) more than a few hundred years advanced over our own… it is becoming hard to rule out what is possible with what exists now.

  • Gary Wilson February 8, 2020, 16:07

    Again, with respect, this is an unanswerable question as far as the entire universe goes, so we will never know the complete answer. Yes, we could be the only intelligent species in the universe. However depending on how you define intelligence there are theoretically several intelligent species here on Earth alone. If you define it as the ability to become space faring, then yes there is only one so far. But as far as probability goes, I would say among those that predict (and we can only predict at this point) these things the likelihood that we stand alone, even in this galaxy is surely very, very low. Now that we know at least something about the prevalence of planets and the prevalence of habitable planets, anyone saying we are unique must make the argument that all other habitable planets only contain non-sentient species. Life is the great defier of entropy, and time is the great ally of life. Evolution will do its thing wherever it gets the opportunity and there will be enormous amounts of opportunity out there. Evolution allows for the transition from simple to complex organisms over time. This will occur elsewhere and eventually will lead to sentience. We know this based on what has happened here. People who think there are other sentient beings in our galaxy are more likely to be correct than people who think we are unique. We might, over time prove this or we may never know the answer, sad to say.

  • Gary Wilson February 8, 2020, 16:16

    One final thought. I think everyone on here tends to speculate, since there is so much we don’t know. Speculation is different than dogmatism. I have no axe to grind one way or the other. Sadly those alive today (even young people) will probably never know the answer to this question. Based on the tiny amount of data we have (nearby space is not full of any type of communication from aliens that we are aware of) I would say that intelligent life of the space faring or EM communicating variety must be rare enough that we haven’t definitely seen it. But that might only mean that the nearest sentient life is earlier in technological development than we are and are only 50 light years away for example. There are at least 200 billion stars in our galaxy, and almost certainly trillions of planets. I’ll put my bet on other intelligent life being out there but will never collect on it.

    • Antonio February 9, 2020, 15:21

      Yeah, I agree that this community, and the interestellar/astrobiological community at large, is too much speculative. And worse, speculations tend to be highly anthropocentric, more so in recent decades. I would like to see more practical initiatives, to actually search what is out there, instead of simply doing calculations. That means focusing a lot more on METI, not only SETI, and the development of actual interstellar travel (Starshot is a good project, but we need also to seriously develop fusion rockets and antimatter storage systems, and not only theoretical studies like Icarus).