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Boundary Conditions for Emergent Complexity Longevity

We usually think about habitability in terms of liquid water on the surface, which is the common definition of the term ‘habitable zone.’ But even in our own system, we have great interest in places where this is not the case (e.g. Europa). In today’s essay, Nick Nielsen begins with the development of complex life in terms not just of a habitable zone, but what some scientists are calling an ‘abiogenesis zone.’ The implications trigger SETI speculation, particularly in systems whose host star is nearing the end of its life on the main sequence. Are there analogies between habitable zones and the conditions that can lead not just to life but civilization? These boundary conditions offers a new direction for SETI theorists to explore.

by J. N. Nielsen

Recently a paper of some interest was posted to arXiv, “There’s No Place Like Home (in Our Own Solar System): Searching for ET Near White Dwarfs,” by John Gertz. (Gertz has several other interesting papers on arXiv that are working looking at.) Here is the abstract of the paper in its entirety:

The preponderance of white dwarfs in the Milky Way were formed from the remnants of stars of the same or somewhat higher mass as the Sun, i.e., from G-stars. We know that life can exist around G-stars. Any technologically advanced civilization residing within the habitable zone of a G-star will face grave peril when its star transitions from the main sequence and successively enters sub-giant, red giant, planetary nebula, and white dwarf stages. In fact, if the civilization takes no action it will face certain extinction. The two alternatives to passive extinction are (a) migrate away from the parent star in order to colonize another star system, or (b) find a viable solution within one’s own solar system. It is argued in this paper that migration of an entire biological population or even a small part of a population is virtually impossible, but in any event, far more difficult than remaining in one’s home solar system where the problem of continued survival can best be solved. This leads to the conclusion that sub-giants, red giants, planetary nebula, and white dwarfs are the best possible candidate targets for SETI observations. Search strategies are suggested.

There are a number of interesting ideas in the above. The first thing that strikes me about this is that it exemplifies what I call the SETI paradigm: interstellar travel is either impossible or so difficult that SETI is the only possibility for contact with other civilizations. [1]

The SETI paradigm is worth noting in this context because Gertz is considering these matters on a multi-billion year time scale, i.e., a cosmological scale of time, and not the scale of time at which we usually measure civilization. Taking our own case of civilization as normative, if terrestrial civilization endures through the red giant and white dwarf stages of our star, that means our civilization will endure for billions of years, and in those billions of years (in the Gertz scenario) we will not develop any of the technology that would allow us to make the journey to other stars, including those other stars that will come within less than a light year of our own star with some frequency over cosmological scales of time. [2] We will, however, according to this scenario, develop technologies that would allow us to migrate to other parts of our own planetary system. I find that this contrast in technological achievement makes unrealistic demands upon credulity, but this is merely tangential to what I want to talk about in relation to this paper.

What most interests me about the scenario contemplated in this paper is its applicability to forms of emergent complexity other than human civilization. What I mean by “other forms of emergent complexity” is what I now call emergent complexity pluralism, which I present in my upcoming paper “Peer Complexity during the Stelliferous Era.” The paper isn’t out yet, but you can see a video of my presentation in Milan in July 2019: Peer Complexity during the Stelliferous Era, Life in the Universe: Big History, SETI and the Future of Humankind, IBHA & INAF-IASF MI Symposium. (Write to me if you’d like a copy of the paper.) In brief, we aren’t the only kind of complexity that may arise in the universe.

The simplest case of an alternative emergent complexity, and the case most familiar to us, is to think of Gertz’s scenario in terms of life without the further emergent complexities that have come to supervene upon human activity, chiefly civilization. In the case of a planet like Earth, possessed of a biosphere that has endured for billions of years and which has produced complex forms of life, one could expect to see exactly what Gertz attributes to technological civilizations, though biology alone could be sufficient to account for these developments. However — and this is a big however — the conditions must be “just right” for this to happen. In other words, something like the Goldilocks conditions of the “Goldilocks Zone” (the circumstellar habitable zone, or CHZ) must obtain, though in a more generalized form, so that each form of emergent complexity may have its own distinctive boundary conditions.

A further distinction should be introduced at this point. The boundary conditions of the emergence of complexity (whether of life, or civilization, or something else yet) may be distinct from the boundary conditions for the further development of complexity, and especially for developments that involve further complexity emerging from a given complexity, in the way that consciousness and intelligence emerged from life on Earth, and civilization emerged in turn from consciousness and intelligence. This distinction has been captured in origins of life research by the distinction between the habitability zone (the CHZ, in its conventional use) and the abiogenesis zone. The former is the region around a star where biology is possible, whereas the latter is the region in which biology can arise.

In a 2018 paper, The origin of RNA precursors on exoplanets, by Paul B. Rimmer, Jianfeng Xu, Samantha J. Thompson, Ed Gillen, John D. Sutherland, and Didier Queloz, this distinction between conditions for the genesis of life and conditions for the development and furtherance of life is made, and the two sets of boundary conditions are shown to overlap, but not to precisely coincide:

“The abiogenesis zone we define need not overlap the liquid water habitable zone. The liquid water habitable zone identifies those planets that are a sufficient distance from their host star for liquid water to exist stably over a large fraction of their surfaces. In the scenario we consider, the building blocks of life could have been accumulated very rapidly compared to geological time scales, in a local transient environment, for which liquid water could be present outside the liquid water habitable zone. The local and transient occurrences of these building blocks would almost certainly be undetectable. The liquid water habitable zone helpfully identifies where life could be sufficiently abundant to be detectable.” [3]

The idea implicit in defining an abiogenesis zone distinct from a habitable zone can be extrapolated to other forms of complexity: boundary conditions of emergence may be distinct from boundary conditions for development and longevity; the conditions for the emergence of civilization may be distinct from the conditions for the longevity of civilization. But let us return to the scenario of life maintaining itself within its planetary system without the assistance of intelligence or technology.

Image: This is Figure 4 from the Rimmer et al. paper. Caption: A period-effective temperature diagram of confirmed exoplanets within the liquid water habitable zone (and Earth), taken from a catalog (1, 42, 43), along with the TRAPPIST-1 planets (3) and LHS 1140b (4). The “abiogenesis zone” indicates where the stellar UV flux is large enough to result in a 50% yield of the photochemical product. The red region shows the propagated experimental error. The liquid water habitable zone [from (44, 45)] is also shown. Credit: Rimmer et al.

Whereas the CHZ is usually defined in terms of a region of space around a star clement for life as we know it, the boundary conditions for alternative emergent complexities will be optimal relative to the emergent complexity in question. That is to say, the wider we construe “habitability” (i.e., the more diverse kinds of emergent complexity that might inhabit a planet or planetary system) the more CHZs there will be, as each form of emergent complexity will have boundary conditions distinctive to itself.

In a planetary system with a large number of rocky worlds spaced relatively close together, these worlds could serve as “stepping stones” for enhanced lithopanspermia. [4] At each stage in the life of the parent star of such a planetary system with life, the life would be distributed among the available planets, and it would flourish into a planetary-scale biosphere on the world with the most clement conditions. When the star began to swell into a red giant, the inner planets would become inhospitable to life, but life could then migrate outward to the cooler planets. And then, when the star cooled down again, life could once again planet-hop nearer to the now-cooler star.

We do not yet know if the boundary conditions for emergent complexity longevity obtain within our own solar system. Is Mars close enough that life, going extinct on Earth, could make the transition to this cooler world, and possibly also further out to the moons of the gas giants? In The Jovian Oceans [5] I suggested that, as the sun grows into a red giant, the outer regions of the solar system will become warmer and the subsurface oceans of some of the moons of Jupiter and Saturn may thaw out and become watermoons (in contradistinction to waterworlds). These regions of our solar system may be clement to life when Earth is no longer habitable, but if life cannot make the journey to these worlds, they may as well not exist at all. We still have a billion years for sufficiently hardy microorganisms to evolve, and for collisions with large bodies to blast microorganisms off the surface of Earth and into trajectories that would eventually result in their impacting on Mars. The chances for this strike me as marginal, but over a billion years we cannot exclude marginal scenarios.

As I have noted in Life: from Sea to Land to Space, the expansion of life from Earth into space (like the expansion of life from the oceans onto land) will open up a vastly greater number of niches to life than could exist on any one planet, so that the opportunities for adaptive radiation are increased by orders of magnitude. But this expansive scenario for life in space is contingent upon the proper boundary conditions obtaining; life must expand into an optimal environment in order for it to experience optimal expansion and adaptive radiation. [6] And as the boundary conditions for the emergence of emergent complexity may be distinct from the boundary conditions for the longevity of emergent complexity, emergent complexity (like a biosphere) may flourish and die on one planet without the opportunity to exploit the potential of other niches. [7]

There are also distinctive boundary conditions for the longevity of civilization. If a civilization is to employ technological means to extend its longevity, whether through journeying to other stars, or, according to Gertz’s scenario, shifting itself within its home planetary system (“sheltering in place”), then the conditions must first be right for a life to arise, and then for civilization to supervene upon life, and finally for civilization to pass beyond its planetary origins by technological means. These boundary conditions might include, for example, an adequate supply of fossil fuels for the civilization to make its original transition to industrialization, and, later, sufficient titanium resources to build spacecraft, and sufficient fissionables to supply nuclear power or to operate nuclear rockets.

It takes a “just right” planetary system for a technological civilization to successfully make a spacefaring breakout from its homeworld — just as being a space-capable civilization is a necessary condition for spacefaring breakout, coming to an initial threshold of technological maturity in the context of favorable boundary conditions is also a necessary condition for being a spacefaring civilization. It also takes a “just right” stellar neighborhood for a spacefaring civilization to make an interstellar breakout from its home system. The boundary conditions for interstellar civilization are subject to change over cosmological scales of time, because stars change their relationships to each other within the galaxy, but there will still be regions in the galaxy with more favorable conditions and regions in the galaxy with less favorable conditions.

As I have noted in other contexts, technology is a means to an end, and usually not an end in itself, so that there is a certain fungibility in the use of technologies: if the resources are unavailable for a particular technology, they may be available for some other technology that can serve in a similar capacity. A marginal technology in favorable boundary conditions, or a superior technology in unfavorable boundary conditions, might do the trick either way. However, there are limits to technological fungibility. The boundary conditions for the longevity of technological civilizations set these limits.


[1] I have written about the SETI paradigm in my Centauri Dreams post Stagnant Supercivilizations and Interstellar Travel, inter alia.

[2] I discussed interstellar travel by waiting for other planetary systems to pass near our own in the aforementioned Stagnant Supercivilizations and Interstellar Travel.

[3] “The origin of RNA precursors on exoplanets,” by Paul B. Rimmer, Jianfeng Xu, Samantha J. Thompson, Ed Gillen, John D. Sutherland, and Didier Queloz, Science Advances, 01 Aug 2018: Vol. 4, no. 8, DOI: 10.1126/sciadv.aar3302

[4] Cf. two papers on this, “Enhanced interplanetary panspermia in the TRAPPIST-1 system” by Manasvi Lingam and Abraham Loeb, and “Fast litho-panspermia in the habitable zone of the TRAPPIST-1 system”, by Sebastiaan Krijt, Timothy J. Bowling, Richard J. Lyons, and Fred J. Ciesla, and my post Emergent Complexity in Multi-Planetary Ecosystems.

[5] This post also noted two papers, then recent, on habitability zones around post-main sequence stars, “Habitable Zones Of Post-Main Sequence Stars” by Ramses M. Ramirez, et al., and “Habitability of Super-Earth Planets around Other Suns: Models including Red Giant Branch Evolution” by W. von Bloh, M. Cuntz, K.-P. Schroeder, C. Bounama, and S. Franck, both of which are relevant to Gertz’s argument.

[6] René Heller has introduced the concept of superhabitable worlds, i.e., worlds more clement for life than Earth, thus optimal for life (cf., e.g., “Superhabitable Worlds”, by René Heller and John Armstrong), which suggests a similar implicit distinction between merely habitable planetary systems and superhabitable planetary systems, merely habitable galaxies and superhabitable galaxies, and so on.

[7] Freeman Dyson argued for the value of life that can adapt to conditions distinct from the planetary endemism that characterizes life as we know it: “…planets compare unfavourably with other places as habitats. Planets have many disadvantages. For any form of life adapted to living in an atmosphere, they are very difficult to escape from. For any form of life adapted to living in vacuum they are death-traps, like open wells full of water for a human child. And they have a more fundamental defect: their mass is almost entirely inaccessible to creatures living on their surface.” (Dyson, F. J. 2003. “Looking for life in unlikely places: reasons why planets may not be the best places to look for life.” International Journal of Astrobiology, 2(2), 103–110) Dyson’s reasons for favoring life independent of planets does not alter the fact that a lot of interesting chemistry occurs on planets that does not occur elsewhere because other environments do have not large scale geomorphological processes; however, Dyson’s observations do point to the selective value of life that can adapt to habitats without planets.


Comments on this entry are closed.

  • Thomas Goodey February 14, 2020, 16:37

    I am sorry, but I don’t believe in this emergence of complexity stuff. I think what actually happens is quite different.

    And hey, why does the writer call it “the abiogenesis zone”? Surely it should be “the biogenesis zone”?

    • Nick February 15, 2020, 18:43

      I look forward to your exposition of an alternative framework within which phenomena as diverse as cosmology and civilization can be discussed in uniform theoretical terms.

      Best wishes,


  • Alex Tolley February 14, 2020, 18:38

    A distinct abiogenesis zone vs an HZ zone is an interesting idea, even if I think the example figure is incorrect.

    Stapledon’s “Last and First Men” seems to fit Gertz’s model – planetary, but not interstellar migration.

    While natural panspermia may be rare, directed panspermia is much more likely. We’ve already done some and may be inadvertently doing more. Directed panspermia to other star systems seems within our relatively near future capabilities. If we can foresee doing it, why wouldn’t other technological civilizations also do it?

    If directed panspermia is common, then abiogenesis becomes irrelevant when considering the greening of the galaxy, even the universe.

    Lastly, I do not think most “boundary conditions” are fixed. Life has a way of extending those boundaries as a feature of complexification. IOW, this is not a one-way street, but interactive/iteractive. Technology definitely provides great leaps in changing boundary conditions. Mature, advanced technology may eliminate all but a few boundaries for any extant civilization, biological or otherwise.

  • Mike Serfas February 14, 2020, 21:20

    The most persuasive paper I’ve seen on abiogenesis is Usami, 2017 ( https://www.ncbi.nlm.nih.gov/pubmed/28952648 ) which describes a one-pot ribose synthesis via the formose reaction, in which the polymerization of aqueous formaldehyde is catalyzed by hydroxyapatite. Now the spontaneous formation of a sugar from RNA should already be interesting, but think about the context: it is produced via a glyceraldehyde intermediate, on a catalytic surface studded with calcium and phosphate ions. The calcium chelates the sugars, and the phosphate has catalytic properties.

    If a glyceraldehyde from the reaction were to become bound to a phosphate somehow – perhaps if some polyphosphate were somehow present in the mineral and were to be “hydrolyzed” by the 3-hydroxy group of glyceraldehyde – then you would have G3P, the central intermediate of biochemistry. Add a formaldehyde and go a few steps further in the formose reaction and you have ribose-5-phosphate (which in modern organisms can convert back to G3P in the pentose phosphate pathway). If the anomeric carbon of the ribose forms a glycosidic linkage with some passing nitrogen compound, then it becomes a nucleotide: phosphate, ribose, and nitrogenous base all in the right positions. Such nucleotides are not just part of nucleic acids but are at the heart of basic biochemistry, NADH and FADH2. On the other hand, if the glyceraldehyde were to be reduced and somehow esterified with two fatty acids, now you have a phospholipid – not one embedded in a free-floating membrane, but one stuck to a mineral matrix with hydrophobic ends facing outward to attract passing hydrophobic compounds. Or G3P can go on into the Krebs cycle, a set of reactions in modern organisms that cycles between 2-oxobutanedioic acid and 2-oxopentanedioic acid (more commonly known as oxaloacetic acid and alpha-ketoglutarate, which tends to obscure their similarity). These dicarboxylic acids also chelate calcium ions, and they need only an ammonia to become aspartate and glutamate (another to become asparagine and glutamine).

    Thus it seems that the formose model could be a common starting point for the abiogenesis of carbohydrates, nucleic acids, lipids, and amino acids. This reaction does not require UV; and for this reason I doubt that an “abiogenesis zone” with UV radiation would be required for life to originate.

    • Nick February 15, 2020, 18:48

      Many thanks for the paper reference. I’ll look it up. You bring up an important point, and if I had thought about this longer I would have included in the above essay a discussion of the many proposed origin of life mechanisms, some of which require a UV flux above a given threshold, and some of which do not.

      The power of the distinction between genetic boundary conditions and maturity boundary conditions is that it is independent of this particular mechanism. If another origin of life mechanism—say, for example, the nuclear geyser model (https://www.sciencedirect.com/science/article/pii/S1674987116301360)—is employed, we might also observe that the boundary conditions for nuclear geysers are likely distinct from from boundary conditions for life spawned by nuclear geysers to thrive. For any given origin of life mechanism, or for any given combination of origin of life mechanisms, there may be abiogenesis boundary conditions distinct from the boundary conditions for the life thus produced to come to maturity in a planetary-scale biosphere.

      Best wishes,


      • Spaceman February 25, 2020, 20:26

        Hi Nick & Alex,

        Paul Davies is of the view that abiogenesis could be the main bottleneck on the road to intelligence. In other words, the steps leading to the first cell are exceedingly unlikely which is what Nobel laureate Jacques Monod maintained. What do you think? Do you think abiogenesis is likely a fluke event such that we may be the only example of biology in the observable universe?

        • Nick Nielsen March 4, 2020, 0:16

          The short answer is that I don’t favor a single “great filter” that entails the Great silence, so I don’t favor abiogenesis as a (or the) great filter. The long answer is rather long, and I’m still elaborating it, but it is based on what I call emergent complexity pluralism, which I briefly mentioned above in relation to my forthcoming paper, “Peer Complexity during the Stelliferous Era.” In this longer and more nuanced answer to your question, I would allow that abiogenesis of the kind of emergent complexity we find on Earth (i.e., terrestrial life, and the further complexities derivative from terrestrial life) is probably very rare, but that it occurs in a context of peer emergent complexities, which is to say, other existents no less complex than terrestrial biology, but not biology as we know it.

          Best wishes,


  • Astronist February 14, 2020, 21:52

    “this contrast in technological achievement makes unrealistic demands upon credulity” – yes, Gertz’s paper is extremely muddled and illogical.

    His arguments against interstellar travel are straw men. For example, he states: “flights at the relatively slow velocities [compared with relativistic ones] we can imagine using understood, though futuristic technologies, would take preposterously long”, “i.e. thousands or tens of thousands of years”, to reach “even the nearest stars” (p.387 in the Nov. 2019 JBIS) – even though he then goes on to mention the Daedalus study which demonstrated that nuclear fusion was sufficiently powerful for travel times of only a few centuries. And his insistence that a society capable of building starships would be incapable of solving the problems of on-board manufacturing, and that it would have to take along a whole Noah’s ark of terrestrial species accommodated in realistic simulations of terrestrial biomes – these are quite absurd. This sort of hand-waving exercise does not make an edifying read.

    His final argument is a sociological one: if I were an alien, I would not bother to embark on interstellar travel (“If there is no particularly good reason to disembark on a planet in a distal [distant?] star system, then why bother to travel there in the first place?”, p.393) – so it may safely be assumed that no alien beings would do so, either, however many alien cultures and species may exist. If memory serves, this line of argument was discredited already in Hart’s 1975 paper.


  • Rob Flores February 14, 2020, 22:45

    If we are talking Billion Year time scales, other scenarios than
    trans-panspermia, or deliberate seeding of the outer solar system.
    It may turn out that custom biological life maybe an ideal way to create
    support systems for space-living humans or their descendants, rather
    than molecular assembly infrastructure.
    For example if future fusion generators need H2 or He isotopes, then designing entities that cycle between say Mars and Jupiter or Saturn, and are able to dive and collect and partially use materials to not only power themselves but to replicate. These would be pretty large entities(think wales x 5). That is just one designer lifeform, there
    would be many others in the mix.
    In a billion years there are likely to be many partial collapses of human civilization(if history is any guide) creatures once under human
    control would start evolving. Now this is not my idea it’s G. Benford’s
    from one of his novels. But until once realizes how much time is involved in a billion year’s passage, it doesn’t seem out of realm of possibilities. (matter of fact just like there are 7 levels of the City of Troy on Earth, there could be many Civs, whose remains are overlaid on one another.

  • George King February 15, 2020, 1:22

    I was intrigued by the discussion here and in the earlier piece linked in note 2 about waiting to star hop over to a passing star on a close approach in about a million years (assuming that we make it that long and can’t find a way around the 300,000 km/s universal speed limit in the meantime).

    The earlier article refers specifically to Gliese 710, which, per Wikipedia, is projected to pass within .221 light-years, about 14,000 AU, of Earth in about 1.281 million years.

    That potentially would put Gliese 710 within some estimates of the outer range of our Oort Cloud (and probably vice-versa), perhaps perturbing a lot of cometary bodies to head inward in both systems and possibly leading to a number of impact events in possibly both systems (if there’s anything of planetary size to hit orbiting around Gliese 710, that is).

    Anyway, Gliese 710 is a K7 Vk spectral class, 0.6 solar mass star. I understand also from Wikipedia that K-type stars have a mass ranging between 0.5 and 0.8 solar masses and – as lower-mass stars, which stay on the main sequence longer – “are stable on the main sequence for a very long time (20 to 70 billion years, compared to 10 billion for the Sun).”

    Given that Gliese 710 is toward the lower bound of the K-type mass range, I would assume then that we would be able, with such a star hop, to trade a star with around 5 billion or so years left before it goes off the main sequence (to our hazard) for one with several tens of billions of years left happily (for us) on the main sequence.

    That’s one way to extend the cosmic potential time horizon of the species substantially, without necessarily having to develop FTL travel. And that possible cascade of possibly impacting comets into a Gliese 710 system might prove to be a boon – well, prior to settlement anyway – in bringing needed materials such as water into the inner system. Again assuming that there are planets of some description orbiting Gliese 710.

    And with the substantial lead up time to the closest approach, we would be able to send any number of probes, etc. – even automated terraforming craft (assuming no indigenous life) – to scout out and possibly develop the system beforehand, as Gliese 710 inexorably worked its way toward us.

    14,000 AU still is a “fer piece,” however. Voyager 1 has traveled about 148 AU in about 42.5 years. It will take Voyager 1 about 4000 years to travel 14,000 AU at that clip. A blink of an eye, though, if you already have waited 1.281 million years for the star hop.

    That all intrigues me . . . well, as a matter of some very, very long-term planning.

    • Andrei February 16, 2020, 3:33

      I was about to reply to Astronist post above, when I did note yours.
      And indeed, if interstellar colonization projects turn out to be harder, too expensive/costly and more complicated than our more optimistic predictions for advanced societies. (Not to mention the will and political situation needed for such a project)
      Then any long lived civ will indeed have the option to ‘star hop’ when there’s an opportunity similar to that of Gliese 710, no exotic scifi technologies needed.

    • Nick February 17, 2020, 4:12

      You wrote: “…assuming that there are planets of some description orbiting Gliese 710.”

      We don’t even need to assume this much. The most obvious way to make the transfer to another planetary system passing close to our own would be to build enormous O’Neill-style habitats and power them up with nuclear generators so they no longer have to be close to the sun, then push them in the direction of the passing planetary system. The other planetary system will have energy (the star) and some form of material resources (even if not in the form of planets) so that more O’Neill-style habitats could be constructed in the new (new to us, that is) planetary system. Now there are two planetary systems moving through the Milky Way, doubling the number of opportunities to transfer to other nearby planetary systems when they pass by. Another pass by for each planetary system, and then there are four planetary systems, and so on.

      As you say, this is a matter for long term planning. Even if civilization collapses multiple times before another planetary system passes by close enough for us to make the transfer over to it, we only have to reach a rudimentary threshold of spacefaring technology in order to expand into the galaxy by this method.

      • Spaceman February 25, 2020, 23:21

        This reminds me of the cyclic apocalypse idea. I do wonder, however, if civilization could return to its previously existing level of complexity after a sufficiently catastrophic collapse.

  • Geoffrey Hillend February 15, 2020, 2:06

    After I have had a couple of UFO sightings my later in life, I began to think that maybe all civilizations get interstellar travel and leave their home planet long before their world gets too hot to live and survive. Consequently, sending radio waves to dying and dead stars I intuitively think is the last place to look for life and send radio signals and I think SETI will agree with me. I think it is better to send radio signals only after we find the best exoplanet candidate for life with all the biosignature gases, in the life belt, the right size and mass, etc. and right time, e.i., safely on the main sequence hydrogen burning.

    I predict that in the distant future, we will go to those dead stars with FTL interstellar travel and we might find the remains of some ET bases on the outer planets of systems with white dwarfs and red giants which once had Earth twins, but nobody will be there and everyone long gone to another habitable exoplanets.

    • Nick February 17, 2020, 4:19

      If we come into 1G starship technology, and are able to cruise the observable universe at speeds that allow for significant time dilation, we would be able to explore other galaxies within the time scale of only a somewhat extended human life time, but we would use up billions of years getting to other galaxies, so when we get to them it will be much later in the history of the universe. Under these circumstances, we may well find remains and ruins, and nothing but remains and ruins. The other beings exploring as we would be exploring would have left their homeworlds long before, and we would be as likely to meet as two needles meeting in a haystack.

      Also, on your point about biosignature gases, this is something I have mentioned on several occasions. As our capacity to observe other worlds over interstellar distances rapidly ramps up over the coming decades, we will get a much better sense of which stars have interesting planetary systems and we are likely to focus on these as targets for further observation, exploration, and SETI technosignature searches. Technosignature searches are essentially an extension of biosignature searches, which is a point that Jason Wright often makes.

      Best wishes,


  • Harry R Ray February 15, 2020, 10:46

    Centauri Dreams Readers: Not doing anything this holiday weekend? Yesterday, Breakthrough Initiatives released TWO PETABYTES of the most recent data from both the Parkes and Green Bank radio telescopes in the bandwidths between 1 and 12 gigahertz BEFORE any astronomers have studied ANY OF THEM in detail, and; optical spectra obtained by the Automated Planet Finder. GO FOR IT! Datamine the whole kitten kaboodle and post a comment here Tuesday if you find anything interesting! lol.

  • Harold Shaw February 15, 2020, 16:59

    I think Gertz’s main argument makes complete sense. The quorum sensing, gestalty mess of people and institutions called civilization will pursue methods of survival that maximize the return on investment for people and institutions preserved. This assumes that civilization is rational. In the context of a civilization’s host star transitioning through RG to WD, regardless of how viable the method for transporting people and institutions across light years, there will almost certainly be ways to employ those methods in situ with a much higher return on investment. For the cost of sending one world ship light years away you could build many world ships and keep them close. This math would be broadly applicable to digitized people and institutions as well.

    I disagree that we can assume civilizations that weathered their star’s transition would be likely to signal their existence. I think civilization’s with extremely old and immovable assets would be the least likely to reveal the location of those assets. They wouldn’t necessarily hide but instead employ a “since you can already see us” METI strategy that functioned within their natural visibility profile. This approach to METI would be available to any civilization and would arguably decrease the risk posed by having an unavoidable visibility profile. The method is analogous to the way many lifeforms use bright colors to signal potential predators that they are aware they can be seen.

  • Harold Shaw February 15, 2020, 19:28

    I understand boundary conditions as emergent systems. The environment imposes a topography of conditions (an emergent complexity where bounds are unnecessary or thoroughly relative) and a life form (a necessarily bound emergent complexity) can employ abilities that allow it to maintain shape within that topography. The ultimate boundary conditions for an organism would be equivalent to that organisms range within the topography. A technological people can enlarge its territory (analogous to decreasing the number of possible boundary conditions) by employing technology while non-technological organisms would need to adapt and evolve. Life an people being persist by managing plasticity of form and functionality.

    In deep time, people being and technology may be fitter than life without technology or people being. Civilization may provide more stable elasticity and more information content. Civilization would discover the furthest limits of the boundless environment and plastic and inviolate form. The superior scale and extent shape of nature will bind the conditions of maximized plasticity and security of specific form. The limits imposed by nature could be extremely limiting and deep time may only offer a few viable habitats. Deep time will select for civilizations existing within those habitats.

    The combobalation of civilization could deliver a people living within massive habitats for billions of years. Human civilization could persist for a billion years or more with homo sapiens only minimally changing. Civilization could deliver a people that in turn delivers the smartest possible, toughest possible, and someone’s prettiest person. We would mistake them the proposed probe design for Breakthrough Starshot.

  • Robin Datta February 16, 2020, 3:13

    Thank you JNN for this insightful piece (and as always, PG for hosting!).

    The vastness of the subject is such that any attempt to summarize the whole of it is akin to biting off more than one can chew.

    And as has been said:
    J. B. S. Haldane, in Possible Worlds and Other Papers (1927), p. 286: “The Universe is not only queerer than we suppose, but queerer than we can suppose”.

    Nevertheless, a few thoughts…

    Complex body forms do not necessarily lead to intelligence. A whole slew of impelling circumstances brought us to where we are.

    Ingestion of an aerobe and its mitochondrion by an archeon resulting in a eukaryote. Hemoglobin to ferry oxygen to remote parts. Erythrocytes to keep viscosity down. Endoskeletons allowing freer body movement with larger body size. A circulatory system to move stuff around. Lungs for a better gas exchange than with gills. Continuous forest canopy to promote brachiation with 3-axis shoulder movement which later facilitated wielding of weapons and tools. Overlap of visual fields with binocular vision needed for depth perception during brachiation, later assisted in the wielding of weapons and tools, and stereoscopic vision for fashioning them. Adequate thumb length and opposability for a strong pinch to permit such fashioning. Control of fire shrinking teeth, and upright stance freeing the upper extremities from locomotion and modifying the upper airway, which together with the shrinking teeth allowed for modulation of sound into speech.

    If one of these items were missing, this blog wouldn’t be around, unless some other path to intelligence were followed. Complex life in itself does not assure the emergence of intelligence, no matter how long it hangs around.

    Liquids with a free surface need an adequate gas (atmospheric) pressure on them to keep them from boiling away. Water moons will need an adequate atmosphere.

    Technology is the control and directing of energy flows. These flows may be used to fashion matter into useful objects, destroy objects, or to move matter around. Advanced technologies are more sophisticated ways of controlling energy flows.

    • Mike Serfas February 16, 2020, 10:13

      Minor point: it may not have been “ingestion” per se: see https://www.nature.com/articles/s41586-019-1916-6 which just came out a month ago. Perhaps the cytoplasm of a cell is (conceptually) a mass of now-fused cellular projections, in which the mitochondria are entangled?

    • Harold Shaw February 16, 2020, 15:21

      Having only one data point for intelligent life creates a conundrum where we don’t know how thoroughly our path describes all possible paths to civilization. If we use too many events from our past we’re calculating the odds that an exact copy of Earth can exist. The rare Earth hypothesis is unavoidably polluted with noise. It is also easy to describe an event from our past in a way that exaggerates the odds it could repeated.

      Imo, endosymbiosis is frequently mischaracterized to exaggerate the improbability of mitochondria. There are several eukaryotic organelles/structures that are believed to have formed through endosymbiosis. Two of those structures, chloroplasts and mitochondria are power houses cellular metabolism and both led to explosions in the complexity of life. Endosymbiosis looks like a boundary condition that emergent complexity can repeatedly overcome. The universe may never deliver an exact copy of a chloroplast or mitochondria, but I don’t see why it couldn’t deliver versions even better suited for complex life.

    • Nick February 17, 2020, 4:27

      Robin, you’re welcome.

      The points you make here are exactly why I have started to emphasize emergent complexity pluralism rather than SETI or METI or similar derivatives that assume very similar pathways for emergent complexity in our universe. I expect there to be a lot of emergent complexity in the universe, but only a vanishingly small proportion of it will be “like” us, even when being “like” us still embraces being radically different. That is why I have introduced the concept of emergent complexity peers, which are other forms of emergent complexity that resemble human activity at the very low resolution levels of observation over interstellar distances.

      We’ve become familiar with trying to think through scenarios of similar but different civilizations (i.e., peer civilizations), but we need to go further back down the chain of emergent complexities that led to us, where each major threshold of emergence not only represents something new in the universe, but also represents a threshold at which other forms of emergent complexity can branch off to their separate destinies in the universe.

      Best wishes,


  • Michael Fidler February 16, 2020, 10:15

    The boundary conditions are actually the opposite from what this paper calls the abiogenesis zone. The error and our bias via our own nature is where the largest real estate and time that these conditions (UV/water) exist. The Hertzsprung – Russell Diagram is great but does not show the true lay of the land, the few stars that explode and form black holes, pulsars and large white dwarfs are like the movies, super stars and guest stars. They are bright, beautiful and romantic, but are short lived, where all the real long lived stars of hard working life, that make up the multitudes are the most numerous. M dwarfs make up 80% of the star population in our galaxy and 98.5% of the all stars in the huge old giant elliptical galaxies at the core of the galaxy clusters. They are old and may exist at 1,000 to one for G type stars. That little arrow with flares pointing down at the M dwarfs now takes on a much larger area of real estate over a much longer time period. Do you see the bias yet?
    Now the dwarf aliens look at us with our puny eyes and wonder how we can see anything! Their huge infrared eyes see a universe filled with beautiful red dwarfs that we cannot even see!!!

    O be a fine girl kiss me!

    Me is the most important and Kiss is to keep it simple stupid!

    • Mike Serfas February 16, 2020, 19:35

      Don’t forget the subdwarfs! Kapteyn b is just 12 light years away from us (was 7 light years at the end of the ice age, but we missed the bus). Hotter temperatures from a lower mass star might somewhat counter the tidal locking problem – Kapteyn b is 5 times the mass of Earth at 0.168 AU in the cold but (with greenhouse gas) habitable zone. Oh, and 11.5 billion years old, survivor of a galactic collision. See https://www.space.com/26115-oldest-habitable-alien-planet-kapteyn-b.html .

      • Michael Fidler February 18, 2020, 19:40

        Thanks Mike, but there’s a problem with this planet as Andrew LePage of Drew Ex Machina has explained:
        Kapteyn b: Has Another Habitable Planet “Disappeared”?
        Kapteyn c is still listed in NASA’s exoplanet catalog. Planetary systems orbiting low-mass M-dwarf stars seem to be the rule. This seems surprising that more RV results have not been forthcoming with a positive or negative result for Kapteyn b. These nearby planetary systems should high on the list of targets for the new radial velocity measurements. The new instruments should be able discern the rotation period of the star from the radial velocity signature of the planets. Kapteyn is a bright 8th magnitude M1 red dwarf at 12 light years distance with a low amount of stellar activity. The age of 11.5 billion years would make it a interesting target for SETI and may have tecno signatures that can be observed from earth. It seems unusual that there have been no updates on this system since 2015!

  • Alex Tolley February 16, 2020, 18:14

    I agree with you on this. While we might be seeing this as Douglas Adams metaphor for a puddle that thinks that the shape of the mud depression is just perfect to accommodate the puddle, I do think we are a very fortuitous result of contingent evolution.

    Many people still seem stuck in the idea that evolution has “worked up to” the ascent of man a the peak. It is even reinforced when we write objective functions for genetic algorithms that drive the populations to evolve to some desired performance outcome. But this is not the case at all. Contemporary humans are the first to become highly technological after 4 billion years of life emerging, 2 billion years for eukaryotes to evolve, less than a billion years for multicellularity, hundreds of millions for the only phylum with a baackbone, less than 100 million years for the primate line to evolve, less than a million for modern humans, and even 40-80,000 years for the “cultural explosion” that led to agriculture and cities just 10,000 years ago. We have been in a Malthusian state for all but the last few centuries. In all that time, no other species is as remotely capable as we are. As tool users and builders, birds are trapped by their wings and clawed feet. Whales are trapped by having flippers even were they to remerge onto land. Just look at how important our hands are just to grasp and manipulate objects. Watch a cat try to pick up a pen by hooking it with its claws and perhaps holding it in its mouth. But even if cats were to evolve human hands and levels of intelligence, they are not socially hierarchical, a feature that lends humans to organize relatively easily.

    I don’t doubt there may be other species that can build civilizations like ours, but I suspect they will not be analogs of squid, alligators, crows, or cats. Functionally, they will have features that serve as analogs of what allows we humans to develop civilization.

    James Lovelock (of Gaia fame) recently stated that there may be no technological civilizations anywhere else in the universe, let alone just our galaxy. That may be very pessimistic, but it shows just how improbable he views our evolution and our particular aggregation of characteristics that allowed our current civilization to emerge.

    All we can do is search for signs of other technological species with the tools at our disposal as our technological capabilities increase.

    • Nick February 17, 2020, 4:35

      I hadn’t run across this remark from Lovelock, but I am pretty much in agreement with it. However (and this is a big however), other sequences of other contingencies may have led to other forms of complexity in the universe that are not our peers, but which are nevertheless no less complex than we are. It wouldn’t be terribly difficult to quantify some complexity index and start putting some numbers to the complexity in our biosphere, and thus start building a scale that we could use as a comparative measure for complexities elsewhere.

      Simon Conway Morris is known for his arguments that any other intelligent being would have to be much like us (thus excluding analogs of squid, alligators, crows, or cats, etc.), and, in a very narrow sense, I don’t think he’s wrong, but I think the parameters of his thought are much too narrow. In a comprehensive conception of the place of humanity in the universe, I’m more interested in a scale of complexity as suggested above, than in other beings like us producing civilizations like us.

      Best wishes,


    • Ron S. February 17, 2020, 16:01

      “…it shows just how improbable he views our evolution and our particular aggregation of characteristics that allowed our current civilization to emerge.”

      This reminds me of the story of following the track of a drunkard through the snow to find him slumped at the base of a light pole. The investigator concludes that the only way to reach the light pole is to follow the exact same track. And if you try it you will indeed reach the light pole!

      The reverse can also be true. Imagine the first to do a rain dance. Everyone declares success because the next day it rains. When future repetitions by others fail the blame is put on the dancer not doing it properly rather than the dance itself.

      Extrapolation from a paucity of data and limited understanding of the universe can be terribly unreliable.

      • Alex Tolley February 18, 2020, 16:49

        To comment on your drunkard’s walk analogy. Evolution is much more like a trek across the USA during the era of western expansion. There were many methods that were tried, few worked, as there were so many obstacles to be tackled en route. Most trails led to different destinations, not the same one.

        Superficially, there appears to be convergent evolution of form – ichthyosaurs, sharks, and dolphins. While their shapes are similar, shaped by hydrodynamics, their brains are very different – only dolphins from the mammalian line have decent intelligence. Most motile phyla have brains, but they have evolved very differently. Could scaled up insect brains be as capable as human brains? Bear in mind, no other species has even remotely reached our level of intelligence, even before we developed tools to enhance our cognition, despite the far longer time frame to develop such intelligence.

        This isn’t to say that ETI doesn’t exist. AI pioneer John McCarthy thougtht ETI intelligence would be evolutionary convergent with our human intelligence. At this point, there is no way to test that hypothesis, although SETI is trying. Were the fictional heptapods’ intelligence in “Arrival” convergent on human intelligence? That Louise Banks learns to translate the heptapods messages suggests that it is. In real life, we have yet to translate any other species “language”, although we have some simple sound/action : meaning dictionaries. Mathematician Keith Devlin has suggested that even that bedrock of SETI communication – mathematics – may not be universal despite our assumptions. Lastly, what can seem like intelligence, e.g. social insects building complex structures, is the result of swarms of individuals doing very simple things. Arguably that is conceptually little different than our neurons processing signals, yet emergent thinking appears.

        Whether there are contemporaneous ETIs out there, or non-contemporaneous ETIs that have left artifacts and messages, or we are alone, the future offers many interesting possibilities if we can survive and prosper long enough.

  • Adam Crowl February 17, 2020, 8:05

    Hi Nick,
    Thought-provoking discussion, but maybe a bit too parochial in a temporal sense. The Stelliferous Era is followed by a trillion times longer Degenerate Era, which might be the true home of intelligent life. If Robin Spivey is right about neutrino-heating of iron-cored planets, as well as the formation of (ultimately) millions more planets than stars, then all this gungho stellar-powered Life is the precursor ecosystem to the mature Biosphere that will last until the last Super-Galaxies fall apart in 10 trillion trillion years.
    Maybe this is still the time of Galactic Infancy and we’re just not thinking far enough ahead…

    • Nick February 17, 2020, 14:45


      I’ve been focusing on the Stelliferous Era, but the principles are applicable beyond the Stelliferous. If some novel form of emergent complexity emerges during the Degenerate Era, we may be able to distinguish between the boundary conditions for its emergence and the boundary conditions of its maturity. Projected at an even larger scale, the Stelliferous Era could define the boundary conditions for the emergence of intelligence and the Degenerate Era could define the boundary conditions for intelligence to come to maturity, if, as you say, the Degenerate Era is the true home of intelligent life. This latter scenario is not too different from the Aestivation Hypothesis, which responds to the Fermi paradox by arguing intelligent life goes into hibernation, waiting for a cooler era in the later history of the universe.

      Best wishes,


  • Geoffrey Hillend February 17, 2020, 17:38

    Nick, the idea that we can travel into the future with a relativistic time machine is only science fiction and a myth. The twin paradox is only a myth because it is invalidated by specially relativity. It is still generally accepted by the layman who has not taken the time to do the necessary thought experiment to invalidate it with the rules of special relativity. For example, in the LCH, protons are accelerated to 99.9999 percent the velocity of light, so they have seven thousand times their rest mast, but there are not any ships, technology or people that can stand 7000 G’s so there is no way for any spacecraft to get anywhere near ninety nine percent of light velocity. Another example is the surface of a neutrons star where time slows down thirty percent of normal, which is not enough to save that much time, but nothing can survive on the surface of a neutrons star without being crushed.

    Do to specially relativity and inertial forces being equivalent to gravity, the G forces at one third the speed of light are a whopping 25 G’s or twenty five times the force of gravity on the spacecraft, and the space travelers inside the ship. I have to conclude that the idea that astronauts could travel to the Andromeda galaxy at ninety nine percent of the speed of light in one human lifetime is impossible, a myth. The twin paradox is a myth and we can’t make a time machine to travel into the future with a relativistic rocket, another myth.

    • Robin Datta February 18, 2020, 1:13

      While any significant fraction of lightspeed is probably unattainable by foreseeable technology, G forces are felt in gravitational fields and with changes in momentum. Outside of gravitational fields, and absent changes in momentum, G forces will not be felt.

    • Mike Serfas February 18, 2020, 11:27

      Look up “Space travel using constant acceleration” on Wikipedia. At one earth gravity it takes about a year to get near the speed of light. With a propellantless 1g drive you could travel the galaxy in 12 years – your time. Also look up “rapidity” – essentially, from your point of view you simply keep speeding up in a Newtonian way, relative to landmarks in the foreshortened galaxy you move through. There is never a point where crushing acceleration makes you give up or treacly space holds your ship back – the galaxy simply makes weird responses (foreshortening and fast forwarding to the far future) as you move through it.

  • Geoffrey Hillend February 17, 2020, 17:41

    Consequently, if anyone wants to go to another galaxy, they have to develop FTL technology.

  • Michael Fidler February 17, 2020, 17:58

    Huge bacteria-eating viruses close gap between life and non-life.
    Large bacteriophages carry bacterial genes, including CRISPR and ribosomal proteins
    February 12, 2020
    University of California – Berkeley
    Bacterial viruses, called bacteriophages, are simple genetic machines, relying on their bacterial hosts to replicate and spread. But scientists have found hundreds of huge phages that carry a slew of bacterial proteins that the phages evidently use to more efficiently manipulate their microbial hosts. These proteins include those involved with ribosomal production of proteins and the CRISPR bacterial immune system, as if the phages are a hybrid between living microbes and viral machines.

    “Scientists theorize that space aliens may already be here, but we don’t recognize them.”
    SAN FRANCISCO CHRONICLE, February 16, 2020.

    “The intriguing possibility is they are, in fact, here, but we just don’t know it,” said Andrew Fraknoi, the emeritus chairman of the astronomy department at Foothill College who recently taught a course on aliens at the University of San Francisco’s Fromm Institute and believes space aliens could very well be microscopic or unrecognizable as a life-form.

    Fraknoi is on the board of the Search for Extraterrestrial Intelligence, known as the SETI Institute, based in Mountain View, where questions about alien civilizations are often discussed. He has long speculated that members of a civilization billions of years old might by now have evolved into a mechanical-biological mix, like a robot with a brain, capable of living for thousands of years as they travel through space.

    But it is also possible, he said, that advanced civilizations would have sent into space thousands of tiny canisters holding the germs of life programmed to incubate and grow when they encounter suitable conditions around a star.”

    Another Reason Why We Might Have Never Seen Alien Probes: They’re Tiny Micro-Machines.
    What if alien spacecraft are already in our midst – and we don’t know about them because they’re tiny nano-structures? That’s the new idea put forward by one scientist seeking to explain the Fermi paradox.

    On the interstellar Von Neumann micro self-reproducing probes.
    In this paper we consider efficiency of self-reproducing extraterrestrial Von-Neumann micro scale robots and analyse the observational characteristics. By examining the natural scenario of moving in the HII clouds, it has been found that the timescale of replication might be several years and even less – making the process of observation quite promising. We have shown that by encountering the interstellar protons the probes might be visible at least in the infrared energy band and the corresponding luminosities might reach enormous values.

    Interesting, hiding in plain site…

  • Gary Wilson February 18, 2020, 14:35

    A very interesting article Nick. The basic ideas seem foundational to me. To establish any sort of set of comprehensive boundary conditions for emergence of life (abiogenesis) or various forms of sentience will require hundreds if not thousands of years of investigation, but you have created the beginnings of a framework to study and categorize such conditions. As humans we tend to think small and parochial. The universe will continue to surprise and in fact shock us with diverse ways to arrive at intelligence I believe. And once intelligence arises it will work very hard indeed to sustain itself in increasingly difficult conditions. I don’t believe interstellar travel is impossible for biological lifeforms, let alone artificially intelligent beings created by biological lifeforms. Give us a few thousand years (if we survive that long) and we will surely find ways to explore and possibly inhabit nearby star systems as well as expanding our foothold here in the solar system, and I believe other intelligent beings will do the same. Thank you again for this intriguing set of ideas.

  • Geoffrey Hillend February 18, 2020, 17:55

    Quote by Robin Data: ” Outside of gravitational fields, and absent changes in momentum, G forces will not be felt.” This is correct for Newtonian physics or universal gravitation, but not correct for special and general relativity. According to special relativity anything with mass can’t reach the speed of light because it would take an infinite amount of energy or become infinitely massive. With special relativity, objects experience length contraction as they approach the speed of light which is what happens with the relativistic protons in the LHC. Relativistic particles in the LHC have more than 7,000 times the rest mass and the extra mass is expressed by many virtual quarks and gluons and the extra mass is from the work we do to speed it up so that the kinetic energy is equivalent to mass. The extra mass is used to make new particles through particle collisions, e.g,, the Higgs boson. E equals mc squared. The more we speed up a particle or any material object, the more kinetic energy, the more the inertial mass and gravitational attraction it has. Matter and energy warp space time and that warping of space time is gravity. Inertial force is equal to gravitational force. Consequently, relativistic mass has “mass, inertia, and gravitational attraction.”

    • Robin Datta February 19, 2020, 10:03

      “mass, inertia, and gravitational attraction.” Indeed.

    • Ron S. February 19, 2020, 13:57

      It’s momentum, not mass. Please don’t recycle that hoary misconception.

      • Robin Datta February 20, 2020, 2:49

        As I noted, ” G forces are felt in gravitational fields and with changes in momentum”. No change in momentum and no gravitational field: No G-force. Regardless of velocity.

    • Ron S. February 20, 2020, 10:33

      “…7,000 times the rest mass and the extra mass…”

      Your original commentary and your reply (which you wrote out of place further below) is wrong. Let me try again with a fuller explanation.

      In both Newtonian and relativistic dynamics mass is invariant. What does change is momentum and, yes, kinetic energy. As (relative) velocity increases the calculated momentum and kinetic energy in the two theories increasingly differ.

      Physicists have avoided the “increasing mass” terminology for well over half a century because it is wrong and has led to misconceptions, as you seem to be demonstrating.

      “…is expressed by many virtual quarks and gluons…”

      Instead of you directing me to Google I will direct you to any university level physics textbook. Some are available free online.

      • Mike Serfas February 20, 2020, 16:00

        That seems like a semantic issue. Even if relativistic mass has been out of fashion for half a century, it was routinely used in successful tests of the theory for half a century before that.

        If relativistic mass is never to be invoked as a concept … what is the rest mass of a proton? Do you exclude the relativistic mass of moving quarks, and energetic but massless gluons? (I would ask about the Higgs interaction while I’m at it but I’m afraid I might not understand the answer!)

        • Ron S. February 21, 2020, 10:56

          The issue is more than semantic. For example, there is the misconception that if you travel fast enough you can create a black hole. You cannot since the mass is invariant.

          An accelerated proton has tremendous kinetic energy, and it is that which is so useful for particle physics collisions. In essence providing the energy that in a violent interaction that will convert mass and energy back and forth.

          Regarding early work, when the interrelated nature of mass and energy was understood the individual conservation laws became one: conservation of mass-energy. But treating them as equivalent can lead the unwary astray quite easily.

          Kinematics does not cause conversion between mass and energy. It isn’t even self-consistent since different observers would disagree on the measured mass and energy.

          Traditional nomenclature does have its own momentum ;-)

  • Dr. Zimmerman February 19, 2020, 13:11

    The rapid development of Musk’s starships appears to weaken the idea that science and technology will stay dormant for years. In short order, we will have the technology to colonize Mars and then suitable moons. Assuming that intelligent life won’t be able to go interstellar is an odd duck idea. We are still in the horse and buggy era and things are changing rapidly.

    • Nick Nielsen March 4, 2020, 0:08

      Science and technology have been dormant in some fields of research for decades. While I hope that the private enterprise push at present may bear fruit in the long term, we have no assurance on this point. Musk may come and go, and the world returns to its routine after a few years of excitement. I wrote about possibilities like this at some length in my previous Centauri Dreams post, Bound in Shallows: Space Exploration and Institutional Drift. Human history shows me that long periods of stagnancy are not only possible, but they are the rule rather than the exception.

      Best wishes,


  • Geoffrey Hillend February 19, 2020, 14:46

    Anyone who has read an introductory book on quantum mechanics knows momentum is mass times velocity which has kinetic energy. One can look that up in google.

  • Mike Serfas February 22, 2020, 18:23

    Alright folks, for boundary conditions you can’t get any more “far out” than this:



    Reportedly (4.1 sigma) the alpha constant is DIFFERENT when you look far away in opposite directions in space. To summarize their model (with considerable risk of error) the alpha constant is smaller by 1.1E-15 per year in the direction of Beta Camelopardis, and larger by the same degree toward a spot just north of the Southern Triangle. The constant doesn’t seem to vary by enough to make life impossible within the observable universe … still, it is, nominally, a constraint. :) Also a clarion call for interesting new physics… if it can be confirmed.

    • Michael Fidler February 23, 2020, 7:05

      The number 137 is one of the greatest mysteries in physics.

      The Fine Structure Constant or a.
      “When I die, the first thing I shall consider asking the devil is – what is the meaning of the Fine Structure Constant?” Wolfgang Pauli

      Herbert G. Dorsey III tells us that “the fine structure constant is the ratio between an electron’s spin momentum and its orbital momentum and is equal to approximately 1/137.”

      Now we are getting somewhere!

  • Harry R Ray February 24, 2020, 11:06

    “Stabilization of dayside surface water via tropopause cold trapping on arid slowly rotating tidally locked worlds”. by Feng Ding, Robin D Wordsworth. Sorry. this does NOT apply to Proxima B or ANY of the TRAPPIST-1 habitable zone planets, because even though they rotate slowly with respect to Earth’s rotation, they do not rotate SLOW ENOUGH! Possible candidates: LHS 1140 b, K2- 72 e, Kepler 442 b, GJ 667 C c, Kepler 1229 b, GJ 667 C e, Kepler 62 f, Kepler 186 f., TOI 700 d. BIG DOWNSIDE: JWST, E-ELT, LUVOIR, or ANY new telescope planned to come online within the NEXT GENERATION(with the possible exception of HabEx, though even here, the prospects are remote AT BEST)will ONLY be able to detect CO2 on these planets, because the percentage of water vapor in their atmospheres will be SO LOW that it will remain well below the the threshold for these telescopes to detect, and only relatively nearby ones like LHS 1140 b will have any chance of having atmospheric CO2 detected.