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Cosmic Engineering and the Movement of Stars

Avi Loeb’s new foray into the remote future had me thinking of the Soviet physicist Leonid Shkadov, whose 1987 paper “Possibility of Controlling Solar System Motion in the Galaxy” (citation below) discussed how an advanced civilization could get the Sun onto a new trajectory within the galaxy. Why would we want to do this? Shkadov could imagine reasons of planetary defense, a star being moved out of the way of a close encounter with another star, perhaps.

All of this may remind science fiction readers of Robert Metzger’s novel CUSP (Ace, 2005), which sees the Sun driven by a massive propulsive jet. A more recent referent is Gregory Benford and Larry Niven’s novels Bowl of Heaven (Tor, 2012) and ShipStar (2014), in which a star is partially enclosed by a Dyson sphere and used to explore the galaxy. In 1973, Stanley Schmidt would imagine Earth itself being moved to M31 as a way of avoiding an explosion in the core of the Milky Way that threatens all life (Sins of the Fathers, first published as a serial in Analog).

Loeb’s paper mentions technologies for moving stars because several recent proposals involve this kind of ‘cosmic engineering’ to change civilizational outcomes. The accelerated expansion of the universe will, after the universe has aged by a factor of 10, make all stars outside the Local Group of galaxies disappear as they recede. The process continues with continued acceleration. Wait long enough and we fall prey to cosmic winter, and as Loeb writes:

Following the lesson from Aesop’s fable “The Ants and the Grasshopper,” it would be prudent to collect as much fuel as possible before it is too late, for the purpose of keeping us warm in the frigid cosmic winter that awaits us. In addition, it would be beneficial for us to reside in the company of as many alien civilizations as possible with whom we could share technology, for the same reason that animals feel empowered by congregating in large herds.

There are places where we might do this, says Loeb, and I’ll talk about his ideas on them tomorrow. For today, note that in response to his previous papers on the oncoming ‘cosmic isolation,’ Freeman Dyson proposed to Loeb his own project that would move stars, bringing large-scale formations of stars down to a more manageable volume so that they will be bound by their own gravity. Closely spaced, the stellar collection avoids being dissipated in the accelerated expansion of the cosmos. And it turns out that Dan Hooper (University of Chicago) has also been pondering induced stellar motion, using the energy output of stars to cluster large numbers of them into an astronomically tight radius so that their energies can be harvested.

Image: A Shkadov thruster as conceived by the artist Steve Bowers.

Like Dyson and Loeb, Hooper has his eye on the acceleration of cosmic expansion and its consequences. So what kind of ‘stellar engines’ can we envision that could move objects as large as stars? Leonid Shkadov suggested using a star’s radiation pressure. The Shkadov thruster extracts energy from the star by using a vast mirror to take advantage of photon momentum. Let me turn back to an earlier post to reprint a diagram that Duncan Forgan uses in describing a Shkadov thruster. Forgan (University of Edinburgh) points out the difference between these thrusters and Dyson spheres, the latter being spherical and shaped so as to balance gravitational forces on the sphere by way of collecting a maximum amount of stellar energy. But here is the Shkadov thruster as diagrammed by Forgan:

Image: This is Figure 1 from Duncan Forgan’s paper “On the Possibility of Detecting Class A Stellar Engines Using Exoplanet Transit Curves.” Caption: Diagram of a Class A Stellar Engine, or Shkadov thruster. The star is viewed from the pole – the thruster is a spherical arc mirror (solid line), spanning a sector of total angular extent 2ψ. This produces an imbalance in the radiation pressure force produced by the star, resulting in a net thrust in the direction of the arrow. Credit: Duncan Forgan.

Thus the whole idea of the Shkadov thruster is not balance but imbalance. And Forgan goes on to say this about the idea:

In reality, the reflected radiation will alter the thermal equilibrium of the star, raising its temperature and producing the above dependence on semi-angle. Increasing ψ increases the thrust, as expected, with the maximum thrust being generated at ψ = π radians. However, if the thruster is part of a multi-component megastructure that includes concentric Dyson spheres forming a thermal engine, having a large ψ can result in the concentric spheres possessing poorer thermal efficiency.

Efficient or not, Shkadov thrusters interest Forgan as a possible SETI detection (Hooper also notes the possibility). Like Dyson spheres, their sheer scale and unusual features could make them visible in a lightcurve, perhaps with the aid of radial velocity follow-ups. Arguing against the idea, though, is the fact that the Shkadov thruster is probably not the technology our hypothetical future civilization would use to move its star (or stars).

I found this out when I wrote Avi Loeb in reaction to his new paper and mentioned the Shkadov idea. Loeb found Dan Hooper’s ideas (in “Life Versus Dark Energy: How An Advanced Civilization Could Resist the Accelerating Expansion of the Universe,” citation below) to be a better solution to the problem. Here is what Loeb told me in our email exchange yesterday:

The use of the momentum associated with the radiation emitted by the star for its propulsion, as envisioned in Shkadov’s thruster, is much less efficient than using the energy associated with same radiation. The radiation momentum equals its energy divided by the speed of light, c. However, the momentum gained by converting this energy to the kinetic energy of a massive object moving at a speed v is larger by a factor of 2(c/v). This is a huge factor of which Dan Hooper is taking advantage to argue that Sun-like stars can reach a percent of the speed light, 0.01c, in a billion years. If he would have used the momentum of the light emitted by the star as in Shkadov’s thruster, then the attainable speed would have been a hundred times smaller, only of order 30 km/s (similar to the speed of chemical rockets), and the journey being contemplated would have not been feasible. During the age of the Universe (10 billion years) one would only be able to traverse a million light years and not leave the Local Group of galaxies. This is not sufficient for gaining more fuel than available within the Local Group of galaxies.

Thus the problem of the Shkadov thruster: By using the momentum of stellar photons, Shkadov loses efficiency. Loeb adds: “One way to improve the efficiency of Shkadov’s thruster (by employing the energy and not the momentum of the star’s radiation) is to harvest the energy from the star through a Dyson sphere and then use it to ablate its surface on one side, generating a rocket effect.” This seems to be what Dan Hooper has in mind in his paper. The civilization in question would harvest the energy of stars through Dyson spheres that, quoting Hooper, “…use the collected energy to propel the captured stars, providing new and potentially distinctive signatures of an advanced civilization in this stage of expansion and stellar collection.”

Hooper has a SETI prospect in mind, while also thinking about collecting sources of energy, maximizing its amount in the form of starlight by a factor of several thousand. It is this prospect that interests Loeb. His paper makes the case that we already have massive reservoirs of fuel in the visible universe in the form of galactic clusters, each containing the equivalent of 1000 Milky Ways. Perhaps, then, we need no star-moving and collection project a la Hooper or Dyson, but rather need to think about reaching a galactic cluster for our fuel. Given the magnitude of that challenge, whether or not we take our home star along is inconsequential.

The speculative buzz I get from this is science fictional indeed. The nearest cluster is Virgo, whose center is some 50 million light years away, with the Coma cluster six times farther still. Thinking in terms of a civilization that could cross such gulfs takes us into Olaf Stapledon territory, a region of spacetime with which I share Loeb’s obvious fascination. I’m running out of time today, but want to look deeper into this with the help of Loeb’s paper tomorrow. I’ll also have more thoughts on ‘stellar engines’ and their origins.

Avi Loeb’s new paper is “Securing Fuel for Our Frigid Cosmic Future” (preprint). Leonid Shkadov’s paper on the Shkadov thruster is “Possibility of controlling solar system motion in the galaxy,” 38th Congress of IAF,” October 10-17, 1987, Brighton, UK, paper IAA-87-613. The Forgan paper is “On the Possibility of Detecting Class A Stellar Engines Using Exoplanet Transit Curves,” accepted at the Journal of the British Interplanetary Society (preprint). The Hooper paper is “Life Versus Dark Energy: How An Advanced Civilization Could Resist the Accelerating Expansion of the Universe” (2018). Preprint.


{ 60 comments… add one }
  • Thomas R Mazanec June 21, 2018, 13:39

    I assume the planets would follow along?

  • Mike June 21, 2018, 14:45

    Worked for the Puppeteer homeworld.

    • Thomas R Mazanec June 21, 2018, 15:41

      I would appreciate a nonfictional reference.

      • Mike June 23, 2018, 13:39

        When I learn of a nonfictional example you’ll be the first I’ll inform.

  • jonW June 21, 2018, 15:59

    One thing I don’t quite understand: since the Local Group of galaxies is already forever bound by their mutual gravitational attraction, despite the accelerating expansion of the universe, why bother rearranging the stars within a galaxy as a bulwark against expansion? Now if you could shift, say, the entire Local Group closer to the Virgo cluster so there’s be more to play with when everything else receds over the cosmic horizon, that would be something…

    This article corresponds to my understanding of our Local Group being bound: https://www.forbes.com/sites/startswithabang/2017/03/11/ask-ethan-if-the-universe-is-expanding-why-arent-we/#514cb289651f

    • Paul Gilster June 21, 2018, 17:07

      Yes, Loeb is making the same point about not needing to ‘collect’ stars — more on this tomorrow.

  • Geoffrey Hillend June 21, 2018, 16:13

    I like the idea. I think it will work. It might be easier to build a shield or many small mirrors at a grazing angle to reflect the x-rays and gamma rays in the event of a active galactic nucleus and move them in space in front of the Earth

  • Geoffrey Hillend June 21, 2018, 16:16

    Our Sun will move of the main sequence and will make the Earth inhabitable in 300 million years, so it might be premature to worry about events predicted to happen in a longer time scale like M31 colliding with our milky way galaxy in 4 billion years, etc.

    • ljk June 22, 2018, 9:15

      I will take a guess that long before 300 Million CE/AD comes along, our descendants – whether organic or artificial – will have long dispersed throughout the galaxy and beyond, so for them the approaching Andromeda galaxy (M31) may still be an issue – though perhaps a good one as they will get lots of new neighbors.

    • Antonio June 22, 2018, 9:59

      “Our Sun will move of the main sequence and will make the Earth inhabitable in 300 million years”

      Nope, it’s more like 5 billion years.

      • Fletcher Christian June 22, 2018, 15:15

        The sun will not move off the main sequence for approximately 5 billion years, true. But it will make Earth uninhabitable well before that (300 to 500 million years) because it is slowly growing in luminosity while staying on the main sequence. The Sun was about 5% less luminous in the Carboniferous Era than now.

        Unfortunately, a similar increase in luminosity would make the average temperature of Earth something like 60 centigrade – too hot for multicellular life.

        • Antonio June 22, 2018, 16:59

          “The Sun was about 5% less luminous in the Carboniferous Era than now. Unfortunately, a similar increase in luminosity would make the average temperature of Earth something like 60 centigrade – too hot for multicellular life.”

          Your post contains its own rebuttal. Indeed, 3-4 billion years ago, in the beginning of life, solar radiation was 30% lower than it’s now! But Earth temperature has been fairly constant all this time! The biosphere has altered the climate to maintain the temperature.

          Even if it couldn’t continue doing so in 300-500 million years, for any reason, the much more capable human race could do it if needed. So I think life on Earth will be OK for another 4-5 billion years.

  • ljk June 21, 2018, 16:34

    I wonder if globular star clusters are the results of advanced ETI collecting suns? Out of 400 billion stars in the Milky Way galaxy, there are only 150 or so of them. Kind of suspicious to me.

    And of course Fritz Zwicky was ahead of the curve with his plan for moving star systems:


    Would a Nicoll-Dyson beam be powerful enough to push stars around?


  • Clément Vidal June 21, 2018, 18:31

    How do you fix the mirror in a Shkadov thruster?

    • Dmitry Novoseltsev June 21, 2018, 22:46

      It can be a dynamic structure like this: https://i4is.org/wp-content/uploads/2017/12/Principium19.pdf (pp. 33-35).

    • Dmitry Novoseltsev June 21, 2018, 22:57

      But in Forgan’s article, I was confused by the idea of detecting a reflector on transits as exoplanets. The reflector must be generally fixed relative to the course, so that the star moves in a given direction, and not turned in place. How then will the transits be observed?

  • Geoffrey Hillend June 21, 2018, 18:33

    Globular clusters have supermassive black holes in their centers which is why they are a spherical shape. Some are believed to be smaller cannibalized galaxies by our milky way galaxy. Inglis, p. 167, Astrophysics is Easy!

    • ljk June 22, 2018, 9:29

      That is how those advanced ETI hold their stellar collections together. And open stellar clusters are just collection points under construction.

  • hiro June 21, 2018, 18:42

    Why do we stop at Virgo? The Shapley supercluster is even bigger. Honestly speaking, just go straight to the densest region instead of moving at snail pace.

    • jonW June 21, 2018, 21:27

      I would love to know: how long before the expansion causes Shapley to become unreachable from the Milky Way travelling at, say, 0.1c? Imagine you set out and miscalculated, and your colony got forever stuck between clusters now uncatchably remote and receding! And what’s the slowest we could set out at right now and still reach them? At 0.01c, for example, it would take 60 billion years, which is much too late.

      • hiro June 22, 2018, 16:16

        Around 1M years from now, if we can’t travel faster than 0.1 then we deserve it; the same way if we still depend on oil, gas and coal for energy by 3000 AD, yeah we should go extinct for good no hard feeling.

        • J. Jason Wentworth June 22, 2018, 21:53

          I have always found such declarations (“If human beings can’t achieve X by Y time, they deserve to be wiped out”) simultaneously puzzling, humorous, and very sad. A lot of things that are possible aren’t done because so many attendant problems and disadvantages–which often don’t appear until (or before) the proposed project begins to move from equations and drawings to hardware–become apparent (the health obstacles of sending people to Mars are an example of this), and:

          The reasons why it is “wrong” to not travel faster than 0.1 c (or not change to different energy sources) are obscure. The first one is entirely optional (trying to avoid the heat death of the universe, which is hardly anything for us to worry about now, is ultimately futile), and the second one, while it sounds good, may turn out to be impractical, for all kinds of reasons, although fission power should be able to produce our electricity for a long time to come.

          • hiro June 23, 2018, 16:54

            Please understand that natural gas, oil and coal won’t be around by 3000 AD. A civilization that sets a goal of human landing on Mars before 25oo AD but our future cars that still need gasoline to move in 3000 AD is simply beyond pathetic.

            • ljk June 25, 2018, 10:21

              Do you have a source for this?

              • hiro June 25, 2018, 19:36

                I learnt Natural Resources 101 in a small college a long time ago and I don’t expect any change (google “world coal/oil/natural gas reserve”), that’s the first part. The second part is simple reasoning, unless we have WW III, 4, and 5, it’s hard to think this species fails to put several humans on Mars before 25oo AD. Electric cars still exists by 3k AD might be normal (it depends on whom you ask) but cars that use gasoline to power pistons should belong inside museums not on the roads.

  • Dmitry Novoseltsev June 21, 2018, 22:42

    “Freeman Dyson proposed to Loeb his own project that would move stars, bringing large-scale formations of stars down to a more manageable volume so that they will be bound by their own gravity”.

    Can we learn more about this? Where to find the source?

    • Paul Gilster June 22, 2018, 7:26

      This occurred in correspondence between Loeb and Dyson several years ago. I don’t think it has ever been published.

  • Charley June 21, 2018, 23:09

    “New Model Predicts That We’re Probably the Only Advanced Civilization in the Observable Universe”

    The Fermi Paradox remains a stumbling block when it comes to the search for extra-terrestrial intelligence (SETI). Named in honor of the famed physicist Enrico Fermi who first proposed it, this paradox addresses the apparent disparity between the expected probability that intelligent life is plentiful in the Universe, and the apparent lack of evidence of extra-terrestrial intelligence (ETI). In the decades since Enrico Fermi first posed the question that encapsulates this paradox (“Where is everybody?”), scientists have attempted to explain this disparity one way or another. But in a new study conducted by three famed scholars from the Future of Humanity Institute (FHI) at Oxford University,…

    • ljk June 22, 2018, 9:18

      Unless they went out and directly looked for alien life, this is just another guess. But I am sure this news will be taken as gospel by those people and groups who are uncomfortable with the idea that other intelligences might be out there, especially those who are superior to humans.

      • ljk June 22, 2018, 12:24

        Here is 2013 paper co-authored by Sandberg which declares that millions of galaxies – nay, the entire Universe – could be reached and colonized by an ambitious enough ETI in due time.


        That no one has apparently colonized the Sol system or done anything similar that we can detect means that ergo there are no aliens. Hmm, where have I heard this before….

        • ljk June 25, 2018, 10:35

          In case my little comment at the end was missed, I am referring to the infamous Frank Tipler, who once advocated that since ETI had not dominated the galaxy with von Neumann machines, they therefore did not exist. There was also a Scientific American article in 2000 saying that the Milky Way could be colonized in a mere 3 million years, so again, since Earth is not being obviously overrun with aliens they must therefore not exist.

          Both arguments have serious flaws, but the authors still seem to think that just because it is theoretically plausible to colonize the entire Universe that it must happen. Antiquated thinking at best.

      • ljk June 22, 2018, 12:35

        And here is Sandberg’s co-authored 2017 paper that says ETI are sleeping in order to maximize their computation power:


        So aliens do exist, but they’re just taking a really long nap.

        But if they are awake, we better send them more “PC” messages so as not to offend across the galaxy:



      • ljk June 22, 2018, 12:51

        This is an interesting and relevant article, where I also learned that it is Toby Ord, not Tod:


        This quote from the above piece shows the kind of thinking that is going on here when it comes to certain transhumanists:

        “That’s why Bostrom hopes the Curiosity rover fails. ‘Any discovery of life that didn’t originate on Earth makes it less likely the great filter is in our past, and more likely it’s in our future,’ he told me. If life is a cosmic fluke, then we’ve already beaten the odds, and our future is undetermined — the galaxy is there for the taking. If we discover that life arises everywhere, we lose a prime suspect in our hunt for the great filter. The more advanced life we find, the worse the implications. If Curiosity spots a vertebrate fossil embedded in Martian rock, it would mean that a Cambrian explosion occurred twice in the same solar system. It would give us reason to suspect that nature is very good at knitting atoms into complex animal life, but very bad at nurturing star-hopping civilisations. It would make it less likely that humans have already slipped through the trap whose jaws keep our skies lifeless. It would be an omen.”

        • ljk June 22, 2018, 14:21

          “The galaxy is there for the taking.” Remember that.

      • J. Jason Wentworth June 22, 2018, 23:07

        Not really; as these two sentences in the article say:

        “In the end, the team’s conclusions do not mean that humanity is alone in the Universe, or that the odds of finding evidence of extra-terrestrial civilizations (both past and present) is unlikely. Instead, it simply means that we can say with greater confidence – based on what we know – that humanity is most likely the only intelligent species in the Milky Way Galaxy at present.” Also:

        I don’t know who those people who are uncomfortable with the idea of intelligent extraterrestrial beings (especially superior ones) are–even the Reverend Billy Graham, Pope Francis, and many Christian theologians (C. S. Lewis wrote extensively about it) didn’t/don’t find the idea of intelligent extraterrestrials, including older and wiser races of them, the least bit troubling or even surprising. Islam also doesn’t find it at all surprising, and neither do Buddhism or Hinduism. The only concern, which is independent of religious or philosophical position, has to do with the possibility of a malevolently or even indifferently destructive race coming to Earth (even Carl Sagan, who was very optimistic about the opportunities ETI contact would hold for humanity, said that the possibility of destructive contact, while unlikely, couldn’t be discounted and should be thought out, just in case). In addition:

        The idea of the mediocrity of our situation (which Aristarchus, Copernicus, Huygens, and others have advocated, and from which the commonality of extraterrestrial life has long been inferred) is an assumption, not a fact (rather like how Occam’s razor, a useful “rule of thumb” in choosing between alternative hypotheses, is often correct, but not always), and:

        If we could produce life “from scratch,” in the laboratory, I would be more inclined to think that the principle of mediocrity (which contends that life is common in the universe) is correct (in “Intelligent Life in the Universe,” Sagan and Shklovskii confidently predicted–in 1966–that microbes would be made artificially within a decade). Exposing mixtures of primordial chemicals to electrical discharges, ultraviolet light, or radiation produces organic molecules, but no self-replicating ones, much less single-cell microbes. As well:

        That–life getting started at all–appears to be the greatest filter, and the utter absence on Earth–save one, solitary example among millions of species–of advanced tool-using life that can create a technological civilization looks like a second, and possibly equally great, filter. I will *never* advocate that radio & optical SETI, Bracewell probe SETI (launching our own, and being attentive for signals from any alien ones), and SETA (Search for Extra-Terrestrial Artifacts [derelict probes and/or abandoned interstellar expedition debris in our Solar System]) should be abandoned (or never begun), because we don’t know “what gives” out there, but while I am ever hopeful about finding other life (or evidence of it, even in an archaeological sense), I am also ready to accept that we may be utterly alone, perhaps without even any microbial “neighbors” out there.

        • ljk June 25, 2018, 10:28

          I was largely referring to those in political and military power who are far more concerned about remaining in power in their little terrestrial kingdoms over anything else, including and often especially science.

          My other group includes religious fundamentalists whom I can tell you from personal interaction do not believe in and do not want there to be any other intelligences beyond Earth — unless they reside in some supernatural realm where they can “speak” for them to the masses. An uncontrolled and uncontrollable message from the stars which they cannot filter or outright censor is quite frightening to them for similar reasons as the political and military types.

          And despite their little verbal Band-Aid at the end of their article, the authors of the above paper are still advocating for a galaxy free of non-human intelligent beings for the reasons I stated in this thread.

    • ljk June 22, 2018, 13:21
      • J. Jason Wentworth June 23, 2018, 21:19

        Science Cat (on page 4 in the Jodrell Bank Fermi ^question^ article) should be wary if Bill Nye the Science Guy ever offers him a cat treat such as “Pounce” or “Bonkers,” without having his (canine?) assistant taste-test it first—Bill may not want any competition… :-) I take issue with the characterization, on page 14, of two ideas about abiogenesis as the “Creationist idea of abiogenesis” and the “Real theory of abiogenesis (simplified).” Calling the latter one the “Real theory of abiogenesis” is an assumption, and a highly-biased one at that. If centuries or millennia of searching via SETI and starprobes (including landers) turns up not a shred of evidence of extraterrestrial life, not even microbes in highly favorable environments on/in terrestrial and Jovian exoplanets and ocean-bearing exomoons and exoasteroids/dwarf planets, the concept of creation by a creator (creatio ex nihilo) will have to be considered. (It would always be possible to argue, “We haven’t examined ^every^ planet and moon, and we may find life on the next one we visit,” but after a very large sample population ‘came up empty,’ the case for un-directed, natural abiogenesis would be very weak.) I would not be surprised if this turned out to be the case, and:

        There are variations on the creatio ex nihilo (“creation out of nothing”) concept. One (which is connected with panpsychism), which some scientists are investigating, is self-organizing creation. They have found evidence that natural systems, including biological systems, are self-organizing. The biologist Dr. Rupert Sheldrake and colleagues of his (as well as some past scientists) have noted that complex information—more than simple creatures have the capacity to store, such as the plans of termite colonies—are nonetheless accessed somehow by the creatures. (Experiments with physically-divided termite colonies showed that the two isolated populations, who were isolated from all forms of contact with each other, repaired the tunnel breaches such that they lined up perfectly on either side of the divider.) He also noted that the complex three-dimensional folding of proteins in human cells has to occur in only one way, in a precise sequence (of which there are about six billion different possible ways that it can occur), yet the protein folding virtually always—unless a foreign chemical or cosmic ray disrupts the process—occurs in the *one* correct sequence. Also:

        Sheldrake also pointed out an interesting theological concept, which medieval theologians wrote about extensively, which matches the scientific hypothesis of abiogenesis well—^mediated creation^ (from the land and sea). Genesis speaks of the Earth already existing–after being created–before life lived upon it, but being “without form, and void.” Later, God said, “Let the [Earth—the land and waters] bring forth” the various forms of life, with the more advanced ones coming later, and Man coming last. From my own personal experiments with shamanic methodology (some scientists have conducted such experiments as well [using just sonic driving], including Rupert Sheldrake and the recently-deceased anthropologist [and shaman] Dr. Michael Harner), I know that what is commonly called “reality” is just the surface of a very deep “sea.” There is other life elsewhere, and restricting the search to other planets in our galaxy (and, serendipitously at least, in other galaxies) is self-limiting.

        Other scientists have also utilized some of these techniques in more informal ways, in order to gain scientific insights. For example, the German organic chemist Friedrich August Kekulé, who discovered the ring shape of the benzene molecule, did so as the result of a dream (he had earlier discovered the structure of another molecule from another dream), as this account (see: http://web.chemdoodle.com/kekules-dream/ ) records. As well:

        If we ever do come across another civilization, and (hopefully) are able to establish two-way contact and mutual understanding with them (they could be very far away, or extinct [leaving only physical or radio–or optical–message artifacts]), an important question to ask them would be: “Has your race ever found evidence of another civilization [besides humanity], or of any life other than that on your own world?” If their answer is “No” (especially if they are a very old race with a long history of SETI and interstellar exploration), such a revelation would—and should—give us great pause. Even with the (relatively) little that we know now, it’s apparent that we could—*if* we wanted to (Orion-type world ships are within our engineering capability now—getting the money to pay for them is a different story…)—claim and colonize a lot of exoplanetary systems with no worries about being called “newcomer squatters” by any locals…

  • Harry R Ray June 22, 2018, 9:21

    Just pray that the “Dark Energy” problem we are facing is of the “manageable” variety(cosmological constant – “big lonely”)INSTEAD of the “nasty” variety(phantom energy -“big rip”).

  • Antonio June 22, 2018, 10:05

    Mmm I don’t understand why the movement in the diagram is in the F direction and not in the opposite direction. By analogy with a rocket, the exhaust is towards F, so the star would move away from F. Am I missing something?

    • Alex Tolley June 22, 2018, 11:46

      It does appear to be backward. The thrust (reaction force) direction should be towards the statite mirror. Shouldn’t the reviewers have caught this?

  • Geoffrey Hillend June 22, 2018, 16:01

    The arrow is not the radiation pressure but the direction. The greek letter Psi is the symbol for the wave function and the thinner black line in the lower right quarter of the star is where the radiation pressure is which is opposite the arrow line as written in the diagram.

    • Alex Tolley June 23, 2018, 0:50

      The caption states the arrow is the “direction of thrust”, ie the direction of travel. (We certainly don’t say that the direction of thrust is the direction the gases travel from a rocket nozzle, but rather the reaction that pushes the rocket in the opposite direction.

  • Alex Tolley June 23, 2018, 19:08

    I find it a little hard to accept we will be still human enough as a species in a million years, let alone for much longer deep time. We will likely be speciating well within the next millennium with gene engineering while we establish new populations throughout our system and the nearer stars. Sentient machines will be widespread too. Cultural changes will make those populations as different from us as we are to the Bronze Age, perhaps even the Neolithic. We cannot imagine the technologies at our command in just a millennium and our current ideas will seem positively Victorian, like building tunnels under the Atlantic, brute force engineering that made no sense once aircraft were invented. So I don’t envisage ET moving stars, and as a consequence I suspect we are stabbing around in the dark for possible detection methods. We are like ants dreaming of mile-high mounds as nests, with advanced chemical communication, oblivious to human presence and electromagnetic communications.

    • Antonio June 26, 2018, 15:00

      Yeah, I totally agree. Things like water-breathing humans living in the Europan ocean or people that flap their wings on Titan’s dense atmosphere can be common in a few centuries.

      • Alex Tolley June 26, 2018, 17:42

        You are just making a reductio ad absurdum argument and a strawman at that. You have clearly watched “Titan” and suggest that I agree with the premise and science ;)

        We may adapt to some planets’ gravities, but clearly, we won’t start breathing methane in Titan or living on the Venusian surface. That doesn’t invalidate that humans will speciate if populations occupy different environmental niches and remain sufficiently separate to prevent interbreeding. It is quite possible to imagine humans living in large space colonies where populations reside in different gravity levels and remain separate, slowly evolving to their gravity level. Cultural separation of populations keeps them apart until eventually, genomic changes prevent fertile interbreeding. Gravity isn’t the only environmental variable either.

        Some engineered enhancements are possible too, for example radiation resistance, 3D spatial orientation, reduction in leg strength and size, to name just 3.

  • Geoffrey Hillend June 25, 2018, 1:03

    We will always be human. We only use a small portion of our brains. Genetic engineering is highly over rated since we can’t really do anything to the DNA nature does not already do as part of it’s potentials so that genetic inheritance is limited to the limitations of the physical environment. Playing around with the DNA gives us the illusion we can create something completely new, but the DNA is still limited to the limitations of physical reality and the environment since it is based on necessity and which is practicable for survival. Too much intellect results in a deficit of emotion and values etc. Brave New World and Eugenics are the result in the overvaluing of our so called free will which thinks it has it has absolute freedom or has to control everything including nature and the naive or youthful consciousness which thinks that removing all human limitations is a good thing. Human potentials were and are always there as potentials already in the DNA. It takes time for them to evolve and there is no short cuts with genetic engineering for genetic evolution which might not prove to be disastrous in the long term.

    Man has only been in space for a little over fifty years and I have to assume that our destiny is to travel to the stars since our technological evolution applies the space travel as well. The symbolism of the flight and reaching for the stars is freedom of thought which must go hand in hand with our genetic evolution since traveling to the stars represents an extremely advanced psychological and technological knowledge and civilization.

    • Alex Tolley June 25, 2018, 17:03

      We will always be human

      That would deny evolution. species may last 1 – 10 million years. Homo sapiens has only been around for perhaps 300,000 years, and modern humans no longer than perhaps 40,000 years. So physically there are likely to be new “human” species that are distinct from us in 1 million years. Physical evolution is faster when small populations enter new niches, as genetic drift is more evident and the environment selects for new traits. For example, lactose digestion evolved with domestic cows only since we became agrarian in Europe. This doesn’t even start to address cultural evolution and what this means in terms of effective speciation of populations.

      Genetic engineering is highly over rated since we can’t really do anything to the DNA nature does not already do as part of it’s potentials so that genetic inheritance is limited to the limitations of the physical environment

      The range of environments points to the diversity of what physical changes can occur. Just look at mammalian life forms that evolved since the KT event. Mammals have occupied almost every niche on the planet, and have both evolved to fly as well as return to the ocean.
      Genetic engineering is potentially remaking our DNA sequences by removing some codes, and we have started to create different genetic codes and even 4-base encoding. Both of those are applicable to current humans and would quickly result in speciation as populations separated under cultural influences. Some physical constraints are removed with technology, e.g. fetus brain size, as Caesarian sections remove the pelvic bottleneck on head size. Other technologies will aid humans to adapt to different environments, and some of those will be supplanted by genetic engineering, some subtle, some not so. While I don’t think we will be so grossly changed as Alice Robert’s BBC show: Can Science Make Me Perfect? in the short term, a million years of expansion into new environments plus mature gene technologies could easily make a wide range of human types. Because we can design, rather than use Darwinian trial and error, incremental, selection over large numbers of generations, speciation may be relatively quick, almost instantaneous in geological time.
      Conversely, minimizing genetic drift in a starship colony, or even a worldship, will be difficult without intervention. Moving a star with its retinue of planets, taking a billion years to reach its destination, implies that the biosphere of Earth on arrival will be unrecognizable from the one at the start. If there are even descendants of humans at the end of the journey, I would be very surprised.

  • Geoffrey Hillend June 25, 2018, 1:36

    We will certainly benefit from a complete knowledge of the human genome and genetic engineering in the future. My point is that a balanced view does not over value it.

  • Geoffrey Hillend June 26, 2018, 18:35

    I disagree that we will be a new type of human a million years from now. Our brains might be a little more intellectually developed when considering the entire population of the world or the level of the collective consciousness as a whole. The genetic changes that represent this would not be that much. People of the future might need more mental stimulation. We will become more knowledgeable about psychology and the human mind or how people think and view the world and have superior technology. Also the primitive of today is different than the primitive of the past due to language yet the potential for language was always there. Using my scientific intuition I can see that we are pretty much complete physically as the human species. In other words, we have to change within mentally and not physically since a lack of knowledge and unconsciousness defines the limits of inner our outer perception and apperception. The human race of the future will have a huge knowledge in science, psychology and physics which has been built up over hundred and thousands of years. In other words they will know more than us and know how to deal with the problems we have to as a human race and physics since they will be solved in the future by us

    • alex Tolley June 27, 2018, 1:34

      You are saying that in 1 million years, humans of that era will be more physically similar to us than we are to Neanderthals, Denisovans and even H. erectus? I’m not buying that. Added to the evolution of the hominid line in the past, humans will be adapting to new environments, some natural, some artificial, coupled with the potential to modify ourselves directly. We can already envisage some of those directed changes today. In just a millennium, at least a sub-population of humans will be different from us. Those differences may be less gross physically, but they will be there. Make enough changes, including changing chromosome number and they will be a new species. Technology will be both an enhancer and a driver of evolution. Just as some people are unable to speak correctly due to variants in the FOXP2 gene and cultural technology has largely eliminated them, technology will drive evolution so that humans will adapt and that will be seen in the genomes of those populations best adapted to that world. If 4 color cones in eyes to enhance color vision became advantageous, those rare cases would increase in te population. We know how to splice in those extra genes, so populations could benefit more quickly. Add those genes to the germ line and you have directed evolution that will potentially separate those populations. Enough changes and speciation occurs.

      It seems almost inconceivable that some humans will not want to modify themselves and their progeny, as well as others who will refuse to change. If the modifications are beneficial, those populations will eventually dominate.

      I don’t think we are even talking about 1 million years, but possibly 1 millennium.

  • Geoffrey Hillend June 27, 2018, 16:18

    Quote by Alex Toley: “You are saying that in 1 million years, humans of that era will be more physically similar to us than we are to Neanderthals, Denisovans and even H. erectus?” Absolutely. If we go far back in time enough to the hominini the brain size changes. Homo sapiens hhttps://en.wikipedia.org/wiki/Human Homo sapiens haven’t changed much in 300,000 years. I don’t think we can extrapolate from those previous changes to conclude that there must be more of the same in the future.
    Also we can’t change the chromosome number without causing harm to the human body: “A change in the number of chromosomes can cause problems with growth, development, and function of the body’s systems. These changes can occur during the formation of reproductive cells (eggs and sperm), in early fetal development, or in any cell after birth. A gain or loss of chromosomes from the normal 46 is called aneuploidy.” From the article: “Can changes in the number of chromosomes affect change and development.” https://ghr.nlm.nih.gov/primer/mutationsanddisorders/chromosomalconditions

    • alex Tolley June 27, 2018, 18:32

      AFAIK, we could not interbreed with H. erectus so that means in 1 million years we have evolved sufficiently from our common ancestor to be a new species, i.e. H. sapiens. While we are classed as a different species from Neanderthals, we know that there must have been some interbreeding from our genome makeup. That alone should be sufficient evidence that 1 million years will see a new human species separate from us.

      However, we are making rapid strides in understanding how our genome works so that we can engineer both small and large changes. Today we just are trialing treating genetic diseases with gene replacement, but inevitably we will start adding new traits, and later grosser changes. We can see how to do that with embryo studies of other animals and so there will be no inherent technical issue with doing the same for humans, once our ethics change. George Church has shown how we can technically become disease free by replacing some codons, and I see no inherent reason why a host of function changes cannot be made. I don’t expect humans to replace limbs with flippers, but there will be physical changes that can be made to pre-adapt us to new environments.

      Out ape cousins have 24 chromosomes so I doubt that careful addition of new chromosomes is de facto bad. We already know that those with XYY and XXY sex chromosomes are fine. As animals and plants have different chromosome numbers, there is nothing inherently problematic about this, other than the need for selection. We can design and engineer the result that took millions of years of evolution. It looks difficult today, but in the 22nd century, it may be at school science project level.

      So we have natural Darwinian evolution that tends to result in slow speciation, but certainly in 1 million years, and technology that will drive “natural” evolution as a new niche, and technology that is used to directly change genomes, which will be very fast.

      We will have to disagree on what “not changing much” means in practice. But bear iun mind we will not be competing just with ourselves, but with our technological artifacts and the consequences of our technology choices. I find that a thrilling prospect.

      • Paul Gilster June 27, 2018, 19:41

        “AFAIK, we could not interbreed with H. erectus”

        Evidently we could, as judging from work discussed in Yuval Harari’s ‘Sapiens: A Brief History of Humankind’ (Harper, 2015), though I admit I’m only about a third of the way through it.

  • Geoffrey Hillend June 28, 2018, 18:13

    It’s interesting to know that we could breed with H. erectus, but of course that will never happen unless we get the viable DNA of 100, 000 year old frozen, primitive baby and put it into a human egg to give birth to a primitive man. The odds are against that. The results would be a dangerous reversal of evolution if we breed a primitive man with today’s man. I am very impressed what we can do now with gene therapy today and also the cutting edge changing of our immune T cells and programing them to fight cancer without any harmful side effects to the other cells in our body. I don’t think we need to change our chromosomes, but I am not against experimentation which is how we learn things. Consequently, our DNA today with already 3.1 billion base pairs and 46 chromosomes has all it needs to adapt naturally to reach any level of evolutionary advancement or the highest level of consciousness in time. Also we cannot skip any steps in evolution and go straight to the top which since we are not psychologically and mentally equipped to get the best out of a DNA which represented the man of the future. If we could get a baby from the future which was from a time which was one million years in the future, it would be under stimulated in a civilization and society which was so far behind it. It’s the collective DNA which we share in common and collective knowledge that go hand in hand like nature and nurture. As a result, I predict that we will always have 46 chromosomes. In our entire human evolution, we never needed any more chromosomes and I don’t think we will ever need any more in the future.

    The DNA is always changing from mutation, but what about the DNA that doesn’t change through mutation which is inherited? Surely, we can’t have the same DNA that was passed on from the Bronze age, the middles ages and 19th century, but we do. My point is that the DNA of this future man won’t look different than today’s human DNA. It will still have 4 base pairs and 46 chromosomes and 3.1 billion base pairs. We don’t have to change the system of human genetics itself to make it better since it has the ability to improve and adapt through heredity and mutation already built into it do to it’s complexity which can adapt all environments on Earth, etc. These potentials given by nature were there from the beginning of life or are locked into the DNA’s complexity which is based on necessity, survival and the limitations of our physical environment. As far as evolution and heredity is concerned, we have not yet done anything that nature is not already doing with the DNA today or in the entire past of evolution. This is called natural selection and if man interferes with the DNA, he still is making the same choices as nature since she built this system on necessity to adapt to our physical environment which has physical limitations that are predictable, but not all possibilities which represents the imagination and the danger of the overzealous attitude to overvaluing our free will and genetic engineering.

  • ljk July 6, 2018, 12:12


    Sunscreen: Photometric Signatures of Galaxies Partially Cloaked in Dyson Spheres

    Brian C. Lacki

    (Submitted on 29 Jun 2018)

    SETI searches have so far come up negative for Kardashev Type III societies that capture all starlight from a galaxy. One possible reason is that shrouding a star in a megastructure is prohibitively expensive. Most of a galaxy’s starlight comes from bright stars, which would require structures even larger than the classical Dyson sphere to enclose.

    Using a custom spectral synthesis code, I calculate what happens to the spectrum and colors of a galaxy when only stars below a luminosity L_min are cloaked. I find the photometric signatures of galaxies with L_min ~ 30 L_sun) result in galaxies with unnatural colors and luminosities. Late-type galaxies in NIR and early-type galaxies at UV-NIR wavelengths become redder than uncloaked galaxies as L_min increases. Late-type galaxies get bluer in UV and blue light when they are cloaked, with colors similar to quasars but very low luminosities.

    By selecting on color, we may find Type III societies in large photometric surveys. I discuss how different metallicities, ages, and initial mass functions affect the results.

    Comments: 22 pages, 15 figures, submitted

    Subjects: Astrophysics of Galaxies (astro-ph.GA)

    Cite as: arXiv:1807.00077 [astro-ph.GA]
    (or arXiv:1807.00077v1 [astro-ph.GA] for this version)


    • ljk July 6, 2018, 12:19

      This has been brought up before this in blog, but a refresher never hurts: Galaxy NGC 5907 has been considered as a possible haven for Kardashev Type 2 and/or 3 level civilizations, as it apparently has far more many red dwarf suns than a spiral galaxy of its type and age should. What astronomers are calling red dwarf stars may actually be suns enshrouded in Dyson Shells or something similar.


      Worth a look, don’t you think? In fact, does anyone know if those recent examinations of galaxies for technological civilizations include NGC 5907? While I think those studies leave a number of things to be desired when it comes to finding advanced ETI, I am still curious if they included the aforementioned stellar island in their check list?

  • ljk September 10, 2018, 10:43

    Dyson Spheres (Shells really) in Newsweek – progress:


    To quote:

    Intriguingly, their analysis identified one star in particular—known as TYC 6111-1162-1—for which the data revealed discrepancies which closely matched those that are predicted for Dyson spheres.

    Currently, there is no strong evidence to suggest that this star is, in fact, enshrouded by a vast alien megastructure; if there was you would have heard about it, clearly. The distance discrepancy could potentially arise because the star is part of a binary system, for example, or it could be explained by other unknown factors. But the results of the study do indicate that TYC 6111-1162-1 is the best Dyson sphere candidate discovered to date, making it a promising target for future research.

    Link to the paper:


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