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Black Holes, Starships and the Cosmos

by Adam Crowl

Louis Crane’s work at Kansas State University caught my eye some time back, but I was uncomfortable trying to explain it when I knew polymath Adam Crowl had so much better insight into Crane’s thinking than I did. One thing led to another, and now we can get an overview of Crane’s thoughts on black holes and starships from Adam himself. As a source of power, an artificially created black hole dwarfs alternatives, but the most intriguing possibility here is that a sufficiently advanced civilization might be able to use such a power source to propel a starship. Is forty years to Alpha Centauri a reasonable expectation with such technology? Read on.

Infinities in physics are usually a sign that something has gone wrong with theory. Towards the end of the 19th Century classical physics when applied to the heat emission from a uniformly heated cavity predicted an infinite amount of ultraviolet emissions – the so-called “ultraviolet catastrophe.” In 1900 Max Planck solved the puzzle by assuming energy was emitted in discrete amounts – quanta – and thus quantum theory was born. Similarly the gravitational collapse of stars, according to classical Newtonian gravity and 19th Century thermodynamics, should allow the release of an infinite amount of energy as the mass became infinitely small – an infinity eliminated by the theory of relativity.

Thus when infinities arise from attempts to combine quantum theory and general relativity (the modern theory of gravity) many physicists believe the theory is in error and a new quantum gravity is needed to eliminate the messy infinities. String theory is one such quantum gravity theory, but several other approaches exist. Loop-quantum gravity, for example, has been explored extensively by theorists like Lee Smolin. No clearly correct resolution to the puzzle has yet been found, but many researchers are hopeful in their quest. See this recent New Scientist story on approaches to ‘theories of everything.’

Intelligent Life and the Cosmos

One researcher in quantum gravity is professor Louis Crane, at Kansas State University, who has been working on quantum gravity theory his whole professional life. One question prompted by his investigations is of particular relevance to interstellar travel – what is the relationship between intelligent life and the Cosmos? Lee Smolin proposed a theory in which different kosmoi (the plural of ‘kosmos’) reproduce and evolve via producing slightly different daughter kosmoi – the daughter kosmoi being generated by the formation of black holes. Black holes form via stars, and stars are friendly to life, thus there is a connection, albeit accidental. Louis Crane wasn’t convinced an accidental connection was direct enough, so he wondered: Could intelligent life make black holes? And if so why?

Image: Will future civilizations be able to create black holes for use in propelling a starship? Credit: Ute Kraus.

As Einstein’s relativity has taught us, mass is equivalent to energy, immense amounts of energy. A kilogram of mass is equivalent to 90,000 trillion joules of energy. However matter, in the form of particles, is incredibly difficult to turn into energy. Several conservation laws are observed to operate in the many interactions and transmutations that particles can undergo in the high energy collisions studied in particle accelerators, and these laws prevent merely dissolving matter into energy. However in 1974 Stephen Hawking showed a link between gravity and quantum mechanics in the form of the entropy and implied temperature of the event horizons that wrap around the insides of black holes. This means that black holes radiate energy with a purely thermal output, seemingly violating the conservation laws that give particles their identities, effectively making black holes a means for converting matter into pure energy.

Harnessing a Black Hole’s Power

Thus civilizations might create artificial black holes in order to convert matter into pure energy. This process is immensely more powerful than any other known energy source in the Universe aside from the mutual annihilation of matter & antimatter. The difference is that Hawking radiation needs only regular matter to be fed into a black hole, not the inefficient creation of equal amounts of matter and antimatter from energy. To create useful amounts of energy a black hole has to be relatively small – the immense black holes created by the implosion of stars produce less than attowatts of power as the luminosity of a black hole is inversely proportional to its mass squared. To produce as much energy as a 100 watt light-bulb a black hole needs to mass 1.9 trillion tons. A million ton black hole would produce almost 360 trillion watts – in fact the energy output computation gets complicated as the black hole temperature becomes high enough to produce heavy particles via pair-production.

According to the high-energy equations used by Louis Crane the actual energy produced by a million ton black hole is 56 petawatts, the equivalent of 0.62 kilograms of mass-energy radiated away per second, meaning a lifespan of less than 17 years. To keep the black hole operating it has to be continually force-fed new mass, else it will eventually decay, exploding in an immense blast of high energy particles.

Such an immense power, 56 petawatts, is roughly 4000 times the total energy usage on planet Earth, thus black holes are over-kill as terrestrial power sources, but ideal for a different purpose – propelling starships. Very big ones. A million tons of starship surrounding a million ton black hole could use the black hole’s power as a photon drive and accelerate at about 0.01 gee. Such acceleration would allow a trip time to Alpha Centauri of about 40 years. If the starship could draw in mass from the interstellar medium its range would be effectively infinite. Such a “mass annihilation Bussard ramjet” would be the ultimate sub-light starship.

To Colonize the Universe

Louis Crane is sceptical of the suggested alternative space-drives – for example wormholes and warp-drives – since the negative energy needed to keep such distorted space-time stable has yet to be demonstrated in such large amounts. To colonize the Universe, Crane believes, intelligent life will need to create and control black holes, thus completing the circle which created that life in the first place. Kosmoi in which black holes can be created by intelligent activity and used to expand intelligence’s reach across that kosmos, would be favoured by the process of cosmic natural selection, since they produce more daughter kosmoi friendly to intelligent, star-faring life.

Some species of jelly-fish, the medusids, live a two-stage life-cycle – in one stage they’re immobile polyps that produce the second stage, the mobile medusa stage. One creates the other, and the other in turn recreates the first, in a never-ending cycle. Crane likens the process of cosmic creation by intelligent life, and the creation of life by those kosmoi, to the two-stage life-cycle of the medusid jelly-fish, what he calls the Meduso-Anthropic Principle.

Crane’s current research is to apply quantum gravity theory to the finer details of the process of creation and decay of low-mass black holes. The possible creation of miniature black holes by the LHC will help refine and constrain quantum gravity theory, perhaps even give us clues towards creating matter annihilating black holes. Another important area of research is the question of how to convert the intense radiation output from a black hole into a useful exhaust stream. The finer practicalities may well take centuries to achieve, but the implications go well beyond even the lifetime of our Universe, affecting the evolution of countless more daughter universes we may create in the aeons ahead.

Three Crane papers covering these ideas are “Possible Implications of the Quantum Theory of Gravity” (preprint), “Starships and Spinoza” (preprint) and “Are Black Hole Starships Possible?” (preprint).


Comments on this entry are closed.

  • Mike March 22, 2010, 11:22

    Been reading your blog for a couple months now and am really enjoying it.

    My issue with this idea and most similar power generation ideas is most everything is entropic. E=MC^2 may not be accurately seen as the energy stored in matter but instead the energy required to convert matter into energy. As a result we seem to be limited to using natural methods where producing energy is moving something to a lower energy state, is conversion of matter to energy really moving to a lower energy state?

    If we can ever find a method of producing energy that is exotropic (if such a method exists) then we can finally be in control, otherwise the only thing we will be doing is pulling from a continuously diminishing power supply (not that we’ll really care for a very long time…)

  • Darnell Clayton March 22, 2010, 13:03

    I once remember an old Star Trek story where they came across a large sphere ship that traveled through the stars thanks to black hole propulsion (the alien crew were eaten up by another alien group, but I don’t want to distract from the main point here).

    My only question is how would you be able to harness the black hole without its energy (or gravity) biting you in the rear end? (pun intended)

    And wouldn’t the radiation produced be deadly towards the crew? (and would we have to build ships made out of lead to counteract it?)

  • snactolate March 22, 2010, 13:14

    Then should we be looking at existing blackholes as possible alien artifacts?

  • Carl March 22, 2010, 15:25

    Hello, Snactolate,

    The engineered singularities described are much smaller than the observed black holes. Still, they may play a part in the First Contact. Please look up http://www.geo600.org/ which is designed to observe gravitational waves. With this technology we might find communications of extrasolar intelligences.

    Read https://centauri-dreams.org/?p=10439 for a similar article regarding black holes made for starships. The fundamental questions concerning intelligence and the universe are really part of this great interstellar venture we dream of.

  • John March 22, 2010, 15:38

    Louis Crane is of Kansas State University, not the University of Kansas.

  • Administrator March 22, 2010, 15:59

    Glad you caught that, John. I’ll make the change right away.

  • Eniac March 22, 2010, 18:16

    I wonder if Adam Crowl could be asked to comment on my (admittedly rather amateurish) idea that black holes could be handled and their radiation focused simply by the application of an external magnetic field? Is it complete nonsense?

    As I have rambled previously on several occasions (cited with slight improvements):


    Since we are talking exotic propulsion, I think that the black hole idea is pretty neat. I am not versed enough in relativistic physics to be sure, but until I hear otherwise I remain convinced that a smallish black hole can be magnetized by quite moderate external magnetic fields. The resulting magnetic fields near the event horizon should be extremely intense, perhaps strong enough to keep Hawking radiation from escaping, except as relativistic jets from the poles. This gives us a means of both grabbing the hole (by its magnetic moment) and focusing its exhaust to use for propulsion. If only we could confine the jet(s) to mostly one of the poles. Perhaps this will happen automatically with an inhomogeneous external field? Otherwise, we’d have to think of ways of stopping or diverting one of the jets, which would be messy, to say the least.

  • Adam March 22, 2010, 19:36

    Hi All
    Sorry if I muddled Universities. The other day someone called my Alma Mater, the University of Queensland, “Brisbane University”, so I hope I can be forgiven a similar faux pas.
    Louis ideas deserve wider discussion and I hope I have prompted more people to look at his work afresh. As a long-time Stephen Hawking fan it’s kind of heartening that this particular idea is proving so fruitful. Confirming Hawking radiation in fluid analogues of black holes – via sonic event horizons – may well give the QGT researchers, like Louis, new insights into the space-time variety and we will see results in the next couple of years as experimentalists refine their physical models.

  • Ron S March 22, 2010, 23:26

    Eniac, I did give you a partial response to your referenced comment, which I won’t repeat here.

    As a further comment, it is important to keep separate the BH from the accretion disk. For example, a BH does *not* emit any jets; these are emitted by the accretion disk. Also, a BH has no magnetic field, but it has an electric field (though probably only a weak one when formed by stellar collapse) and angular momentum: so-called gravitomagnetism. However, the accretion disk can have some powerful magnetic affects.

    Possibly useful reference if you haven’t already seen this:

  • Adam March 22, 2010, 23:27

    Hi Eniac
    I’m no Hawking radiation expert, but AFAIK the energy locked up in a black hole’s spin (and thus magnetic field generated by its rotating charge) is radiated away before the mass-energy. That’s potentially very useful when using black holes as super-density batteries, but not as matter annihilation generators.

  • James M. Essig March 23, 2010, 1:13

    Hi Mike;

    Those are some very interesting ideas. I would love to see some technology that could convert massive particles into pure electromagnetic energy without the need for Fermi-Dirac Pair Annihilation.

    To the Tau Zero Centauri Dreams readership in general, I have the following comments regarding some particle physics news that may have longer term ramifications for the development of interstellar travel schemes.

    When considering the possible future forms of interstellar space travel, we need to consider that the book on particle physics and classical as well as quantum field theory has yet to be finished. Just as the discovery of nuclear fusion and nuclear fission has opened up the possibility of starship velocities within the 0.1 C range to 0.5 C range, and matter antimatter rockets with a fuel reaction Isp of 1 C expressed in units of C, wherein the gamma factors obtainable for the space craft are (1/2)(M0/M1), we should not discount the possibility of fundamentally new energy sources involving real mass energy particle species.

    Hints of the existence of a sterile neutrino species have surfaced once again. Such neutrinos would result in four species of neutrinos instead of the 3 Standard Model flavors and might indeed account for at least some of the Dark Matter within the universe.

    Although these sterile neutrinos would not even interact via the weak force; however, they would possess inertial mass and non-zero positive energy and so they would react to gravitational fields and could contribute to the gravitational self attraction that the real mass-energy portion of the universe feels with respect to itself.

    If the sterile neutrino exists, I am personally interested in any possibility that there might exist another lepton within the electron family, and perhaps two additional members of the quark family, along with 4 associated anti-particles for a total of 8 additional particles.

    Note that the electron neutrino is classified within a first generation of particles including the electron and the up quark and the down quark. Since these particles come in antimatter versions as well, this generation includes a total of 8 particles.

    The muon neutrino is classified within a second generation of particles including the muon and the charmed quark and the strange quark. Since these particles come in antimatter versions as well, this generation includes a total of 8 particles.

    The tau neutrino is classified within a third generation of particles including the tauon and the top quark and the bottom quark. Since these particles come in antimatter versions as well, this generation includes a total of 8 particles.

    Nature loves symmetries, and so perhaps there exist three species of sterile neutrinos, one for the electron family, one for the muon family, and one for the tauon family.

    Om the other hand, if a fourth flavor of neutrino exists such as a sterile neutrino that cannot be grouped with the three generations of known standard model fermions, then perhaps we can consider whether a 5th sterile neutrino exists, along with an additional cold heavy lepton and perhaps along with two additional quarks thus resulting in a total of 5 charged leptons and 5 charged antileptons, and 10 quarks and 10 antiquarks.

    I would throw one heck of an outdoor barbecue party if another generation or two of quarks are discovered. Mainstream QCD theorists do not expect this to happen, but as I like to say, never say never.

    Another possibility is that a sterile neutrino might indicate that a fourth cold and heavy lepton exists that might not be electrically charged. I will call this particle a psuedo-lepton because the particle might not interact with the electromagnetic, nor the weak force, as well as perhaps not interacting with the strong force.

    Such a psuedo-lepton might theoretically serve as a proxy for a yet to be discovered fifth force. If there is one psuedo-lepton, then perhaps there exist, a few or even several psuedo-lepton species along with antimatter versions.

    Alternatively, as a result of the deep symmetries that exist in nature, perhaps if there exist 3 sterile neutrinos, one for each of the three generations of known Standard Model Bosons, then perhaps there exists three species of the conjectured psuedo-leptons along with distinguisable antimatter particle versions.

    Nature seems to love to group particles in symmetrical sets and so the above speculations are intelligable to consider.

    Given that ~85% of the real mass of the universe seems to exist in the form of Cold Dark Matter, there is a lot of room for there to plausibly exist many stable yet to be discovered massive particle species.

    As for particles that would not react with any of the known four forces, I have contemplated such off and on for about 3 decades.

    I look forward to the 7 TeV LHC collisions near the end of this month, as well as the construction of the Facility For Rare Isotope Beams, and the International Linear Collider. There is even talk of designing a Muon Accelerator. Clearly, with all of the thermodynamic degrees of freedom that this assortment of machines will provide, we can have hope for breakthroughs that can pave the way to the stars, hopefully without the unwieldly long travel times of only very mildly relativistic travel.

    See the following Physics Today for brief summary latest research involving the sterile neutrino.


  • spaceman March 23, 2010, 1:58

    The one paper refers to black hole powered starships as on the edge of possibility and that, furthermore, quantum gravity could change this picture. In other words, don’t get your hopes up about black hole powered space travel. Don’t get me wrong, I’d love to see such an approach come to fruition.

    As for whether or not black holes should be seen as alien artifacts, I would say: would an intelligent species made black hole really be distinguishable in any significant way from a naturally produced black hole?

  • Damjan Novak March 23, 2010, 7:28

    “Towards the end of the 19th Century classical physics when applied to the heat emission from a uniformly heated cavity predicted an infinite amount of ultraviolet emissions – the so-called “ultraviolet catastrophe.””

    I think the prediction was actually that of infinite amounts of power emitted at infinitesimal wavelengths, but ultraviolet was the highest part of the spectrum known at the time, hence the name. Today I guess we’d call it gamma ray catastrophe.

  • Eniac March 23, 2010, 9:20


    AFAIK the energy locked up in a black hole’s spin (and thus magnetic field generated by its rotating charge) is radiated away before the mass-energy.

    That’s what I understood, also. However, if a decaying hole demagnetizes quickly in the absence of an external field, it stands to reason that it would equally quickly magnetize in the presence of an external magnetic field. A dipole field in balance with even a weak external field should have enormous, relativistic strength very close to the event horizon, because the hole is so tiny. This “near-field” could well be strong enough to pin the charged Hawking radiation along the field lines and let it escape only at the poles, in the form of a relativistic jet. Just the kind of thing that would be useful for propulsion. The near-field may even be strong enough to break up the gamma radiation into particle-antiparticle pairs, so that all radiation becomes charged and nearly 100% of the energy goes into the jets.

    Active galactic nuclei actually do produce this kind of jet, which is a nice proof of principle, although of course somewhat unrealistic because of the difference in scale.

    There are, as I see it, two critical unknowns here, a) the time constant with which a black hole would magnetize (if at all) in reaction to an external field, and b) the field strength necessary to get the focusing effect (if any). These should be relatively easy to estimate for someone with a good grasp of black hole and plasma physics, but that is not me, unfortunately.

    To be practical, the time constant would have to be somewhere between microseconds and years, and the field strength needed would have to be no more than a few Tesla.

  • Longbeast March 23, 2010, 11:03

    Partly in response to some of the comments above…

    I have occasionally wondered whether it is possible to restrict the power output of a black hole into a pair of beams by forcing the hole to spin to such a great extent that it becomes disc-shaped. How I imagine it working in principle would be to create black hole engines in pairs, dividing angular momentum between the two as they are created, and polarising the spin of the matter used to feed them.

    They would need to be constantly fed more angular momentum to keep them in that state, but as far as I understand it, the vastly increased surface area to mass ratio should make that easier to achieve. If I have understood the mechanism of hawking radiation correctly, distributing the mass of the hole over a larger area (and volume) lowers the power output such that a much lower mass hole becomes less energetic and safer.

  • kzb March 23, 2010, 14:17

    We do not even know if black holes really exist. There is observational evidence that objects in the centres of quasars and active galaxies have strong magnetic fields and so cannot be true black holes. The “MECO” is said to fit the observations better.

    Now, an Eternally Collapsing Object, if the theory is correct (and admittedly the mainstream astrophysics community says it is NOT), will eventually turn 100% of its mass into photons.

    I do not know enough of the theory of BH’s and MECO’s, however it did strike me that, with the MECO, we do have something, at least in principle, that will convert 100% of mass into energy. What’s more, its magnetic field gives us a handle with which to hold it. James M Essig was asking about matter->energy conversion above.

  • T_U_T March 23, 2010, 16:29

    from how would such a ship be visible ? Would not mass use of such ships significantly alter the whole emission spectrum of a galaxy ? Could we tell when we look at a galaxy from distance ?

  • Athena Andreadis March 23, 2010, 16:36

    I’ve discussed this with enough physicists to know that black holes as propulsion are as likely as magic carpets. Antimatter propulsion is much likelier.

  • James M. Essig March 23, 2010, 17:54

    Hi Adam;

    Here is some interesting news regarding x -ray reflecting materials based on immaculately pure artificial diamond.

    At the last link below is an excellent ABC News article about using immaculately pure artificial diamond material to reflect x-rays.

    The material will not reflect longer wave photons, however, since it can reflect x-rays, theorists believe that the materials could focus x-rays produced by x-ray generating mechanisms such as x-ray lasing apparatus etc.

    My first thought upon reading this article was that such a technology, ramped up to 10 EXP 13 Watts to 10 EXP 15 Watts for continuous wave lasers could produce very tight beams with very little divergence, which would be excellent for high gamma factor beam sails. If the beam sail would approach, say a gamma factor of 1,000, 1 keV x-ray photons would be red-shifted to a visible light frequency, yet wherein the beam might still remain tightly focused, even after traveling several light-years through space.

    The x-ray mirror might make an excellent reflector for the black hole Hawking Radiation drive space craft that you mention in this Tau Zero thread.

    If the black hole drive can be taolored to produce x-rays instead of gamma rays, immaculate diamond sails might be an excellent mechanism to power the ships.


  • David J. Williams March 23, 2010, 19:36

    I read his paper on the Meduso-Anthropic paper last year. This is a guy who isn’t afraid to think big. Great post btw.

  • Eniac March 23, 2010, 23:09

    Ron S:

    Also, a BH has no magnetic field, but it has an electric field (though probably only a weak one when formed by stellar collapse) and angular momentum: so-called gravitomagnetism.

    I seems you are right, in order to have a magnetic moment a BH has to be charged. The “no hair” theorem would seem to say so. That sure puts a serious crimp into the idea. The only way there could have a magnetic moment is if the BH spun and was charged at the same time. Both charge and angular momentum decay, apparently, so both would have to be artificially induced and maintained. Simply applying a magnetic field would not be enough, you would also have to add a charge. You could charge it electrostatically, and simultaneously apply a magnetic field, perhaps, but the resulting magnetic moment should be very weak. You do not get a very strong magnet by spinning the sphere on top of a van der Graf generator, for example, AFAIK.

    Another interesting question is whether you can feed a low mass BH. Because of the small size, they might have negligible cross section for matter, and Hawking radiation might interfere, too. Ron speaks of an accretion disk. Would there really be such a thing in a small black hole?

    Of course I agree with Ron and Athena that we will not likely have black holes to play with, I just like to think about them anyway…. plus, it is the topic of this post, after all.

  • James M. Essig March 24, 2010, 1:33

    Hi Athena;

    I too think that some form of antimatter propulsion is likely to occur before black hole based propulsion.

    One of the antimatter propulsion schemes that interests me is some form of matter-antimatter quarkonium dense fuel because of its low volume.

    Some form of exotic antimatter baryon that is not based on up and down quarks as protons and neutrons are that is stable could be a real Godsend.

    Using the relativistic rocket equation and a final payload with a rest mass of say 10 EXP 5 metric tons and an M0/M1 of perhaps 10 EXP 16, we obtain a gamma factor of (1/2)(M0/M1) = [5 x (10 EXP 15)].

    The usual caveats as to how to mitigate astrodynamic drag based breaking power, cloak the spacecraft from extremely energetic cosmic rays etc., posses some series issues, but perhaps they can be met over hundreds if not thousands + years of scientific and technological progress.

    Then there are the prospects of quarkonium pellet fuel runways, and mass driver beam supplied quarkonium fuel to the space craft.

    One can imagine the reactions of quarkonium formed from pure quarks with quarkonium formed from the antimatter versions of such quarks.

    Even if we never produce neutron dense or quarkonium dense matter antimatter fuels, the prospects for good old fashioned antimatter hydrogen ice seem highly plausible. Once again, I enjoy the pellet fuel runway and mass beam fuel supply concept with this antimatter fuel scenario.

    I do not want to say never say never with black hole based propulsion, and I can well imagine the gamma factors obtainable by the perpetually accelerating black hole ramjet may be unlimited, in fact if Adam’s concept of black hole ramjets are possible, I think they will be developed at some point. However, we know we can produce antimatter right here and now, and so perhaps designing and fielding huge solar orbiting stations to produce antimatter from converted sunlight to power particle accelerators could be of great help here.

    Note that regarding inflatable reflectors, my brother John and I jointly hold the following IP portfolio.

    *US Patent Numbers 7,612,735, 7,382,332, 6,897,832, D510,498, D508,815, D508,814, D507,925, D507,717

    *Several foreign patents issued and several pending foreign patent applications on the same general class of inventive concepts as patented within the U.S., i.e., for inventive concepts related to basic inflatable and portable renewable resource harnessing apparatus, and methods of manufacture.

    The point is that our inflatable concentrators can be manufactured out of flat pattern arrangements of a number of different types of metalized membranes and we have disclosed numerous ways in which to detune the pressurized reflectors which can be sub-ambiently pressured, super-ambiently pressured, and/or mechanically deployed.

    Our technology is very, very low in cost. In fact, we made a device out of a few dollars worth of metalized membranes and cooked the snot out of hot dogs in about 12 minutes under intermittant cloud cover.

    My bother John and I would love to find a home for our portfolio and recoup some of the cost of patent prosecution.

    I can see that grid-like electrovoltaic materials in the distant future could be used to sweep out, capture, and convert CMBR into antimatter fuel.

  • Tobias Holbrook March 24, 2010, 6:31

    “I’ve discussed this with enough physicists to know that black holes as propulsion are as likely as magic carpets. Antimatter propulsion is much likelier.”

    However… a balck hole facility can provide the massive amounts of energy required for generating antimatter. It should be possible, in theory, to get an efficiency of 100% conversion of matter to antimatter – the matter produced can be fed back in to generate more energy to produce antimatter.

    If a small black hole can be kept along with the ship, it could refuel at it’s destination. Or destroy a neighburing planet…

    As a side question; I know that the mass-energy of the ship goes up the closer to c that you go, but the same is true for the fuel. Surely that means that the total ratio of fuel-to-payload remains the same as it would be at a lower speed, so it still has the same delta-V?

  • Ron S March 24, 2010, 11:59

    Eniac: “Both charge and angular momentum decay…”

    Not really. Change the charge by dumping charged particles into the BH. The angular momentum can (in theory) be tapped to draw off energy, but it required lots of unobtanium and magical engineering.

    “Ron speaks of an accretion disk. Would there really be such a thing in a small black hole?”

    A small BH would have a small accretion disk, but yes. Send matter its way and, unless your aim is really, really good, you’ll miss the horizon and off the particle will go to infinity. If the BH is spinning, you could intersect the ergosphere and put it into a pseudo-orbit for a while. It would take a lot of particles sent in all at once in this fashion so that they interact in the near vicinity of the BH to form an accretion disk. Talk about threading a tiny, tiny needle…

    “…Hawking radiation might interfere, too.”

    Oh, yes. Since we’re talking about a micro-BH that is really hot, you would have some (!) difficulty force-feeding enough matter to overcome the outward radiation and particle pressure. This is also one of several good reasons why a BH is effectively impossible to create by, for example, attempting to focus energy and matter into a sub-Schwarzchild radius volume.

    While this sort of discussion can be entertaining and educational, I’m 100% with Athena on this: BH propulsion is an outright fantasy. Although I sure would like a magic carpet.

  • Adam March 24, 2010, 17:49

    Hi Athena & Ron S

    The behaviour of the emissions from micro-black holes gets very complicated because of their size and temperature. And that’s without factoring in quantum gravity corrections that there’s currently no accepted theory about. I wouldn’t write-off the concept just yet.

    I do agree that ‘force feeding’ will be difficult, but then nothing worth doing is ever easy.

  • Ron S March 24, 2010, 20:50

    Adam, we can’t even conceive of a theoretical path to making a micro-BH with what we do know, let alone figuring out how to feed it, and feeding it, while still out of the question, is the easier of the two problems. It’s a classic containment problem, similar to inducing fusion by laser-triggered implosions but many orders of magnitude more difficult, and almost certainly impossible. The only known effective containment mechanism to create a BH is gravitation.

    Sorry, but we’ll have to agree to disagree. I am not persuaded by an argument that says that since there is as-yet undiscovered physics in the required domain (such as QG), we can use that as a blank canvas on which to project our desires.

    The only pertinent model we have is that the universe passed through the QG domain early in its history and it resulted in a (so far) null search result for primordial black holes that could have formed at that time. I would be happy to be proven wrong, but I believe that spending time now pursuing propulsion based on a constructed micro-BH is a poor choice. Even trying to figure out how to get propulsion out of it is pointless since this strongly depends of the BH’s attributes, and these are determined by how it can be constructed, which is unknown.

  • Adam March 24, 2010, 22:57

    Hi Tobias

    In the ship & propellant’s frame of reference the rocket principle works just fine. If you measure the acceleration and integrate over time using ship-board instruments (i.e. an accelerometer & a clock), then you can accelerate to rapidities (“speeds”) higher than “lightspeed” – BUT you’ll never catch up with a light beam that is fired off from the front of your ship at the start of your acceleration. To convert from the ship & propellant’s reference frame there’s a transformation that gives your speed with respect to a ‘stationary observer’, and from that point of view you’re always going slower than light. But with sufficient propellant and acceleration you can go as fast as you like measured via the ship’s instruments. If you accelerate half-way and deccelerate back to ‘stationary’ at your destination, then light that left home as you started will have arrived just ahead of you by a time, t = 2.c/a, where ‘c’ is lightspeed and ‘a’ is the acceleration measured on-board the ship. But from ship’s clocks the trip happens exponentially quickly.

    Of course travelling beyond a few thousand light years means you run into a very hard radiation storm that we’ve discussed here before. That’s the downside of extreme relativistic travel even via the ‘infinite range black-hole ramjet’ that I described above.

  • Adam March 25, 2010, 19:27

    Hi Ron S

    Your concerns are reasonable and I’m not arguing we should pursue such as a focussed program of research. Nor is Louis so arguing. Instead quantum gravity will sharpen our view of the probabilities or not and is worth researching for its own sake even without workable black-holes at the end-point.

    Solar-sails, laser-beams and fusion rockets are sufficient for current interstellar studies. I think antimatter fusion-triggering may be worthwhile, but antimatter in bulk is far from practical – arguably as far off as black-hole rockets IMO.

  • Adam March 25, 2010, 19:37

    Hi again
    We can look at force-feeding a micro-hole as a problem akin to nuclear fusion reactions. Classically there should be no proton-proton fusion below about ~10 billion K, but it happens down to 3-5 million K at levels sufficient to power low-mass stars, like our Sun. Quantum tunnelling means there’s a non-zero probability of it occuring, sufficient to provide enough deuterium to power the Sun – most of the energy of the Sun is actually from deuterium fusion, but it has to be made via proton-proton fusion.

    Similarly the Hawking radiation field of a mini-hole forms a ‘potential barrier’ that it’s hoped can be tunnelled through via accreting particles, with quantum corrections to the horizon providing a bigger target for a more rapid accretion rate at the size in question. Or so I’m hoping. But that’s knowledge that can only be won the hard-way.

  • Eniac March 25, 2010, 22:38

    Caution, more wild speculation below!

    Not that I consider it likely, but just because we have not found primordial holes does not mean they do not exist. They may over time all have been captured by planets or asteroids and sit in their centers, quietly lurking until dug out. The problem with this idea seems to be that small holes will decay in violent explosions, and large holes should be detectable by their mass, probably with no room in between…

    It is also conceivable that large black holes can produce small black holes from as yet unsuspected violent QG processes at their surface. There might be a steady stream of them coming from the galactic center, producing gamma ray bursts when they decay. Perhaps future space cowboys will ride out into space to lasso and harness suitable black holes like wild horses….

  • Eniac March 25, 2010, 22:53

    Ron, I am confused. Please pardon my ignorance. I think earlier some time you said decaying BH’s lose their angular momentum faster than their rest mass. Yet you replied “not really” when I stated so in this thread. Do small black holes radiate off their charge and/or angular momentum or not? If they do, do we know the rates of decay?

  • Ron S March 26, 2010, 10:45


    One of the ways they have searched for primordial black holes is by predicting and then searching for GRBs with the predicted signature. This of course assumes that theory of BH evaporation is correct and that there is a sufficiency of the critters for the statistical distribution and expected rate of demise as a detectable GRB. There are of course lots of questions since this necessarily straddles the line on what is known and not-quite-known physics. Regardless, the search has returned a negative result. Interpret that as you will.

    I don’t think I said that about BH loss of angular momentum (didn’t Adam say something like that?). But, no, they don’t radiate off their charge. Hawking radiation should be net neutral in electrical charge, and you can’t siphon it off with a bunch of coils and such. All you can do is drop in charged particles to change it.

    If you do set up that network of coils around the BH to generate an electrical current from a spinning BH (that is, one with angular momentum), you end up taking away from the angular momentum, not the electrical charge. This (according to Kip Thorne, if I understand him correctly) requires threading a magnetic field through the ergosphere with those coils, though the coils themselves stay outside.

    As Adam mentioned, there are inevitable uncertainties in this picture, especially as the BH gets close to the critical point of total evaporation. So, again, interpret this all as you will. Also, keep in mind that I am not a physicist, just someone with some science training who has (stupidly!) delved into the theory and mathematics of GR.

  • Eniac March 26, 2010, 23:35

    So, does anyone have a good feeling for whether a reasonably charged, rotating micro black hole could have a sufficiently strong magnetic field near its horizon to trap Hawking radiation and channel it to the poles?

  • Adam March 28, 2010, 15:57

    Hi Eniac
    Much Hawking radiation is totally uncharged so magnetic channelling is unlikely to make a difference. I know the usual pedogogic picture is of particle/antiparticle pairs, but that doesn’t real adequately describe what comes out.

  • Eniac March 30, 2010, 12:58

    Thanks, Adam, that makes sense.

    I recall reading about higher order, non-linear QED effects that allow photon-photon interaction and in particular the interaction of photons with electromagnetic fields. Such that, in a sufficiently strong magnetic field, photons would generate particle/antiparticle pairs, which would then be channeled. The field would have to be extremely strong, but then a dipole field goes with 1/r^2, and a micro BH is awfully small. I wonder if that could make a difference here.

  • ljk April 11, 2011, 10:18

    Planets Could Orbit Singularities Inside Black Holes

    The discovery of stable orbits inside certain kinds of black hole implies that planets and perhaps even life could survive inside these weird objects, says one cosmologist

    kfc 04/11/2011

    It’s easy to imagine that black holes gobble up everything they encounter, consigning this stuff to eternal oblivion. Right?

    Well, not quite. Today, Vyacheslav Dokuchaev at the Institute for Nuclear Research of the Russian Academy of Sciences in Moscow points out that certain black holes can have a complex internal structure. And that this structure ought to allow photons, particles and perhaps even planets to orbit the central singularity without ever getting sucked all the way in.

    A black hole is a region of space where gravity is so strong that nothing can escape, not even light. However, cosmologists have known for some time that there are regions inside charged, rotating black holes where objects such as photons can survive in stable periodic orbits.

    Dokuchaev’s contribution is to study these orbits in detail and to explore their dynamics. One of the problems that would at first seem to scupper any chance of planetary orbits inside a black hole is the way that the dimensions of space and time behave.

    It’s well known that a traveller passing through a black hole’s event horizon arrives in a region in which the radial dimension becomes time-like, rather than space-like. Conventional orbits are clearly impossible here.

    But travel further in and there is another horizon where the dimensions switch back again (at least, inside charged and rotating black holes). This is the inner Cauchy horizon and it’s beyond here that Dokuchaev says the interesting orbits for massive planets exist.

    He calculates that the stable orbits are nonequatorial and have a rich structure (see picture above). They would also be brightly illuminated by the central singularity and by photons trapped in the same orbit.

    That raises an interesting question: whether a planet in such an orbit could support a complex chemistry that is rich enough to allow life to evolve.

    Dokuchaev clearly thinks so. “Advanced civilizations may live safely inside the supermassive BHs in the galactic nuclei without being visible from the outside,” he says, somewhat speculatively.

    Of course, such a civilisation would have to cope with extraordinary conditions such as huge tidal forces and the huge energy density that builds up in these stable orbits as photons become trapped. There’s also the small problem of causality violations, which some cosmologists predict would plague this kind of tortured space-time.

    Dokuchaev has taken an interesting idea and pushed it as far as he can. It’s one I suspect readers can have a lot of fun with too.

    Ref: http://arxiv.org/abs/1103.6140: Is There Life Inside Black Holes

  • ljk April 30, 2011, 0:06

    Black Holes: Attractors for Intelligence?

    Authors: Clement Vidal

    (Submitted on 21 Apr 2011)

    Abstract: The Search for Extra-Terrestrial Intelligence (SETI) has so far been unsuccessful and needs additional methods. We introduce a two-dimensional metric for civilization development, using the Kardashev scale of energy increase and the Barrow scale of inward manipulation.

    To support Barrow’s scale limit, we contend with energetic, societal, scientific, computational, and philosophical arguments that black holes are attractors for intelligence. An application of the two-dimensional metric leads to a simple, consistent and observable hypothesis to test the existence of very advanced civilizations.

    We suggest that some already observed X-Ray binaries may be unnoticed advanced civilizations, of type KII-Bomega. The appendix provides an argumentative map of the paper’s main thesis.

    KEYWORDS: SETI, black holes, Kardashev scale, Barrow scale, star lifting, XRB

    Comments: Presented at the Kavli Royal Society International Centre, “Towards a scientific and societal agenda on extra-terrestrial life”, 4-5 Oct 2010. 16 pages, 1 figure and 2 argumentative maps

    Subjects: General Physics (physics.gen-ph)

    Cite as: arXiv:1104.4362v1 [physics.gen-ph]

    Submission history

    From: Clément Vidal [view email]

    [v1] Thu, 21 Apr 2011 22:29:17 GMT (579kb)


  • Adel Mansour June 22, 2012, 13:52

    I apologize in advance for my sheer ignorance in physics, but I would like to ask: Don’t black holes propell high energy gamma rays in two opposite directions perpendicular to their two poles and the accompanying accreation disk ? In that case how would you make up for the opposing force create by the forward thrusting gamma jet ? Deflecting it backwards, in my view, will not solve the issue because you still have its thrusting force negating the force created by the the rear thrusting gamma jet.
    I don’t know, so that’s why I am asking. Any answer ?
    Thanks in advance.

  • Adam June 22, 2012, 18:23

    Hi Adel
    It’s all about reflecting the forward facing gamma-emissions backwards. To do that will require a very efficient gamma-ray mirror. Alternatively if the black hole is physically attached (via magnetic fields etc) to the ship, then absorbing or diffracting the forward facing emission produces a net difference between the directions and thus a net thrust.