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Propulsion Clues from a Dark Universe

If you had a device that could manipulate the expansion of spacetime, would you have the makings of a stardrive? Miguel Alcubierre’s ‘warp drive’ concept is based on something like this. The physicist’s 1994 paper points out that the speed of light constraint applies to objects moving within spacetime, but makes no prediction about how fast spacetime itself can move. Inflation theories draw on the same idea, with the early universe suddenly expanding at rates far surpassing light speed.

So think about contracting space in front of your vehicle while creating more space behind it. Distorted spacetime carries the starship along at fantastic velocities while violating no principle dear to Einstein. The trick, of course, is energy, the necessary amount of which has been discussed in various papers. As far as I know, no one has been able to get the figure down below the total energy output of a Sun-like star, but that’s a big reduction over earlier views that it would take all the energy in the universe to make a warp drive work.

Which brings us to dark matter and dark energy, the two elephants in the room of contemporary physics. We seem to be looking at only a fraction of the universe when we gaze into the sky, with perhaps as little as four percent being made up of the things we see. Whatever dark energy does that causes the acceleration of the universe’s expansion, it’s not something that we can observe other than through its apparent effects. But you can see why in the dreams of propulsion theorists dark energy comes into play. Anything that causes the expansion of spacetime’s acceleration plays into our concepts of a genuine star drive.

Dark matter, too, is of great propulsive interest. Understanding it will give us new insights into mass, and since we are interested in accelerating objects to appreciable fractions of lightspeed, we need to know as much as possible about how mass operates (not to mention the mysteries of inertia). We can only detect dark matter through its gravitational effects, one of which is its ability to cause the bending of distant light sources, an effect familiar through our discussions of gravitational lensing.

Dark matter in Abell 520

The recent dark matter news is challenging. Scientists using data from the Chandra x-ray observatory have been studying the galactic cluster system called Abell 520, mapping the Chandra data against optical data from Earth-based telescopes. A dark matter core could be identified, but mysteriously enough, it contains hot gas but no bright galaxies. The galaxies and the densest dark matter nearby are separated, the dark matter core in one place, a group of galaxies with no dark matter in the other. “This would be the first time we’ve seen such a thing,” says Hendrik Hoekstra (University of Victoria) and could be a huge test of our knowledge of how dark matter behaves.”

Image: An artist’s illustration of the Abell 520 system shows where the bulk of the matter (blue) is found compared to the individual galaxies (yellow) and the hot gas (red) in the aftermath of a massive galaxy cluster collision. The material shown in blue is dominated by dark matter. As with the Bullet Cluster there are large separation between the regions where the galaxies are most common (peaks 2 and 4) and where most of the hot gas lies (peak 3). However, unlike the Bullet Cluster, a concentration of dark matter is found (peak 3) near the bulk of the hot gas, where very few galaxies are located. In addition, there is an area (peak 5) where there are several galaxies but very little dark matter. These observations conflict with the general understanding that dark matter and the galaxies should remain together, despite a violent collision. This raises questions about the current understanding of how dark matter behaves. Credit: CXC/M. Weiss

So just what are we dealing with here? Gravitational ‘slingshot’ effects that could separate the dark matter don’t seem powerful enough to do the job. Is there an interaction between dark matter particles of which we had no previous idea? And if so, how can we make our observations of other galaxy clusters gibe with what we’re finding in Abell 520? We’ve begun to get used to the notion that a galactic cluster should include large amounts of dark matter. Indeed, dark matter was first hypothesized to explain why individual galaxies look as they do, when visible matter isn’t sufficient to account for the gravitational effects that shape them.

No one can say whether we’re on the edge of new physics or a more conventional explanation may yet emerge. What the universe persists in reminding us, though, is that the frontiers of deep sky astronomy provide potential clues that may one day help us derive a new understanding of mass. Meanwhile, ongoing work on dark energy probes the very substance of spacetime, the manipulation of which may remain forever beyond our grasp. Or perhaps not. A universe that conceals 96 percent of what makes it work surely holds surprises galore for future engineers.

The paper is Mahdavi et al., “A Dark Core in Abell 520,” accepted for publication in the Astrophysical Journal (preprint available). And those who collect classic papers, as I do, may want the reference for Miguel Alcubierre’s “The Warp Drive: Hyper-Fast Travel Within General Relativity,” Classical and Quantum Gravity 11 (May 1994): L73–L77.

Comments on this entry are closed.

  • infosponge August 17, 2007, 15:31

    When I look at hacks like dark matter and dark energy, I can’t help but get the feeling that I’m looking at the 21st century equivalent of epicycles.

    The whole idea of dark [etc] seems pretty damn crazy.

  • andy August 17, 2007, 16:50

    Thing is, what with evidence currently pointing towards a large number of potentially habitable worlds out there, if you throw usable FTL drives into the mix, the Fermi paradox becomes a lot more paradoxical.

    I’d suggest the fact that we appear to have been left alone points towards the impossibility of practical FTL. The alternative is explaining why none of the billions of habitable worlds in the galaxy (and perhaps extending that to the nearer galaxies) have got lifeforms who beat us to FTL billions of years ago.

    I’d like to be proven wrong on this issue (I mean, if I had the chance to go visit Beta Lyrae or Mira or…) but at the moment I’m not convinced of FTL at all.

  • occam's comic August 17, 2007, 18:08

    I am with infosponge, I think that mainstream astronomy is making a fundamental mistake.

    “dark matter was first hypothesized to explain why individual galaxies look as they do, when visible matter isn’t sufficient to account for the gravitational effects that shape them.”

    The problem may be that galaxies are shaped by not just gravity. Could most of the mass of the galaxy be plasma? If so then you must include electric and magnetic forces to account for the structure that is seen. (Plasmas have moving positive and negative charges aka currents, and moving charges create magnetic fields, electrons and protons have very different masses that affect how quickly the charge is accelerated in electric or magnetic fields.)

    Didn’t I just read about how our sun’s movement through the galaxy is shaped by magnetic fields?

  • Adam August 17, 2007, 18:11

    Hi All

    Of course the Dark mass might not exist – MOND explains what’s observed quite easily. But then what does MOND imply about the Universe?

  • andy August 17, 2007, 18:53

    Purely baryonic MOND doesn’t work: you still need some component as well as dark matter to explain the results being seen. The usual candidate proposed is neutrinos.

    Then again, if dark matter particles exist, how long before particle accelerators get to the point where they can be made?

  • Kurt9 August 18, 2007, 2:19

    Most evolutionary biologists are of the opinion that the emergence of sentience and intelligence is so rare that, even if every F, G, and K star in the galaxy had an Earth-like world, we are still likely to be the only tool-using intelligence in the galaxy.

    This is the scenario that I think is most likely.

  • Quasar9 August 18, 2007, 6:38

    Hi Centauri, never say never
    but there are clear problems with travelling faster at near the speed of light or even faster than a speeding bullet, and little chance of anything with volume & mass travelling faster than the speed of light.

    Of course on earth we have information (internet) travelling almost at the speed of light, but there are clear limits to how fast a bullet train can go on or near the ground. After all it is fine watching aircraft flying overhead, but if aircraft didn’t travel at 36,000 feet they would be quite annoying to us on the ground – even if they are not going supersonic.

    The problem with faster than light on short distances – like on earth – is that something (information) would reach its destination before it was sent, but how would that information ‘know’ it was going to be sent.

    At greater distances we can have massive (and voluminous) objects travelling at almost the speed of light, but they are burning up as they streak along. So supposing you could build a spacecraft of some material that would not burn up, and you could power it, it would have to follow whatever speed limits are set up by the Space Cops (photons). Mind you speed cameras would be of little use if you are travelling faster than light.

    Whilst I would not presume to limit the ability to dream, for now I would settle for a nuclear submarine floated in space or a Delta Wing launched into Space. A fleet of Space Shuttles on regular trips to the Moon and Mars.

  • andy August 18, 2007, 7:19

    Kurt9: can you provide some kind of citation for that claim?

    As far as I am aware, there are quite a few tool-using species on this planet (New Caledonian Crows being a particularly interesting example), so the evolution of tool use does not appear particularly difficult.

  • Kurt9 August 18, 2007, 13:42


    Check out the following links. The first is to a paid paper but the second one is free.



    Also, there was some discussion of this in Barrow and Tipler’s “Anthropic Principle”, which was published in 1986. Even though this is dated somewhat, I think their discussion of biology is still valid.

  • andy August 18, 2007, 15:02

    Kurt9: playing devil’s advocate here, you have shown that SOME evolutionary biologists consider evolution of intelligence to be unlikely, while you have claimed earlier that MOST evolutionary biologists subscribe to this opinion.

    Then again, we have only one example of technological intelligence in the five billion year history of this planet. However, I don’t think it can be claimed that tool use, social structure, or intelligence are vanishingly rare, as we can find several examples of these in the animal kingdom (and not just in vertebrates), so the conditions that select for these traits are not excessively improbable. So getting to some kind of “pre-technologically-capable” intelligent species, like say the New Caledonian crows, may be fairly common.

    The potential chokepoints would thus appear to be multicellular life and the jump from crow/dolphin intelligence to human-level intelligence… would those transitions be vanishingly rare, as the “required several combinations of fortuitous events” people would suggest, or are there multiple ways to bridge those gaps?

  • Kurt9 August 18, 2007, 21:11

    There are multiple jump points in biology. First is the prokaryotic to Eukaryotic jump. Next is the jump to multi-cellular organisms. Then there is the increase in metabolism to allow for something like animals. Ocean to land life appears to be another jump. Internal temperature control (i.e. warm blooded animals). There are others I cannot think of right now.

    I think the gist of most evolutionary biologists (one of the papers I linked to) is that vision appears to have independently evolved no less than 40 times. Sentient, tool-using intelligence appears to have evolved only once (us).

    There are specific neurological structures (I have to look it up) that only humans have that are responsible for empathy and other emotional states. Even the primates lack these structures.

    I believe (I may be wrong here) that the cetaceons (dolphins, porposes, killer whales, etc.) have the intelligences comparable to dogs. The closest thing to humans are certain (not all) primates and crows (not the other birds).

    On the other hand, it is possible that “intelligence” may evolve in a completely different manner in other places. Perhaps a hive-like intelligence is possible (evolved from insect-like life-forms) where there are only a few or one such “individual” on the “home” world.

    More darkly, it may be that sentience is not that conducive for long-term survivability of life. Stephen Baxter addresses this possibility is several of his more recent novels as does Bruce Sterling in the short story “Swarm”. Maybe the aliens are a cross-species hive-like thing such as the Chtorrans. Or the Pattern Jugglers (continent-sized aggregates of ocean algae networks) in Alastair Reynold’s revelation space series novels. One’s mind can conjure up all kinds of neutral to unpleasent possibilities here.

    I suspect that, if alien life exists, that it will exist in some of these possible forms.

  • philw August 18, 2007, 21:31

    Kurt9 has struck a chord. Astronomers, e.g. Sagan are the ETI optimists. Those scientist who are biologists tend to be ETI pessimists for the ‘jump point’ reasons Kurt9 cited.

    I don’t think that the dark energy and dark matter phenomena are our centuries epicycles but I do think that tenure track trendy ‘String Theory’ is. Real science is falsifyable.

  • andy August 19, 2007, 7:56

    Is the prokaryotic to eukaryotic jump actually necessary to get to multicellular organisms? Just because on our planet the eukaryotes became multicellular and the prokaryotes didn’t does not mean that prokaryotic multicellular organisms cannot happen.

    Is internal temperature control actually that unlikely? Seems to have evolved twice: in the mammals and in the dinosaurs (birds). Furthermore, is internal temperature control necessary for intelligence? Ants (for example) manage to have a social structure without it.

    Some of this appears to be covertly assuming that everything that happened in the evolution of humans is necessary for the evolution of any kind of intelligent life. I don’t suspect the evolution of advanced technological intelligence is a common occurrence, but I doubt that the route humans took is the only one.

  • philw August 19, 2007, 13:11

    What is troubling is that it took several billions years of life before the Cambrian explosion formed ‘animals’ with the various body types we know today and many other forms that went extinct simply out of bad luck. Why did it take that long? Was the Cambrian event a fortuitous anomaly? If not, what inhibited it prior? Then post Cambrian it took half a billion years to evolve (ONLY ONCE) a species that uses telescopes.

    We know of no evolutionary laws that mandate the evolution of intelligence and no social science laws that mandate emergence of technical societies. The vast majority of human societies throughout the millenia were not science & technology oriented. Had events occured differently, all humanity could still be at a ‘dark ages’ level. I for one am happy with the net.

    The belief in ETI is just that, a belief, not the certainty most often assumed by us space cadet types. No problem as long as the inevitability of ETI is not demanded to be accepted without question.

  • Kurt9 August 19, 2007, 13:22


    The likelyhood of the jumps is unknown, given that we have a current sample size of one. The fact that life was around from nearly the beginning, but that multi-celullar life came about with the Pre-cambrian explosion only 600 million years ago offers one sort of clue. Single-celled life is no doubt common but that multi-celullar life could be rarer than a “blue moon” is one possibility.

    There is also the possibility that when intelligence occurs that the intelligent beings invent bureaucracy, which then inhibits any kind of technological innovation and economic growth and, thus, expansion through out the universe. We also have a sample size of several points for this, with China being the most significant example (end of Ming dyansty).

  • david August 19, 2007, 18:25

    Evolution does not aim to create intelligence or technological species. It’s aim, in its mindless fashion, is the survival and gradual improvement of species. Evolution might actually work to limit the intelligence of a species. Why? Because more brain power equals more energy used for intelligence that might be best put to use on some physical aspect of the species such as more powerful muscles or better reflexes.

    The reason intelligence has been such a success in humans is because we got a physical structure that can make good use of it – hands. Hands which can manipulate tools with greater ease than any other species on the planet can boast. Our hands however are the product of a long line of events. Events that often required major sacrifices on our part.

    Hands came from tree climbing. For that we need trees. If the planet has no trees then some other route might be possible but we can’t be sure of it. Creatures that use speed to survive, either by out running predators or by running them down, would find hands a handicap. Hooves or paws would be better. In a fight claws are desirable, which might limit how dexterous they can be. For digging the same. In those cases evolution would work against hands.

    How often has something as dexterous and capable as human hands developed on this planet would be a relevant question to add to the thought process of how common is technological civilizations in the universe.

    How long a species lives is also another relevant question. In a human type intelligence how far could a society develop if the species only lived 10 years, 20, 30? Currently a person is usually in there 20s even before getting out of university.

    How common would trees be on a planet? Too little land and they might not evolve. Too dense an atmosphere or too high winds and they might not evolve….

    If earth like worlds are common, intelligence might also be common. But for the most part I think it would be similar to dolphins and such species. There would be no reason for their intelligence to develop aspects designed to aid them in technological innovation. Or species like crows that might now and then use a stick to some advantage. They might use tools but they would not give up advantages of their physiology to better become tool makers.

    However, several hundred billion stars is a lot of chances, so who knows what might be out there. We can guess, but until we actually look that is all it is, just guesses. We need probes to places like mars and europa to make a reasonable search for life. We need spaces observatories that can detect and study the light from earth sized planets. What worries me is that we might be alone, and that we won’t make the jump to space. A hundred billion galaxies with a hundred billion stars and a hundred trillion years to play in and life only exists for a single billion years on one measly planet. Now wouldn’t that be a shame.

  • philw August 19, 2007, 22:12

    “How often has something as dexterous and capable as human hands developed on this planet would be a relevant question to add to the thought process of how common is technological civilizations in the universe.”

    -phil: At least 3 times,Apes/humans, Elephant trunks and squid/octopus. Ocean life probably can’t invent telescopes.

    How long a species lives is also another relevant question. In a human type intelligence how far could a society develop if the species only lived 10 years, 20, 30? Currently a person is usually in there 20s even before getting out of university.

    -phil: excellent point

    How common would trees be on a planet? Too little land and they might not evolve. Too dense an atmosphere or too high winds and they might not evolve….

    -phil: there’s thought that most ‘Earths’ might be close to 100% ocean. Bad news for discovery of fire and technology.

    I think the odds favor us as the only telescope building society in the Local Group and likely beyond. Sad news.

  • johnF August 20, 2007, 7:13

    Dark matter, dark energy and mond, are attempts to explain puzzling observations, not proven facts, so I’m often worried by how much stock some sections of the scientifc community put in them. That said I agree with philw that they have the edge over string theory of being testable. Faster than light travel may well be to our current propulsion technologies what a jet engine is to sail driven ships; something we only learn to do after we’ve gone most places the slow and difficult way.
    Sadly (although I dearly hope to be proven wrong) I think dreams of contacting ETI will have to be put away for a long long time, as a lot of the arguments against it being common above hold water, particularly when the silence surrounding us is considered. The search for extraterrestrial life has more hope (IMO): we have evidence that life arose fairly quickly on earth once the conditions were right, we have found life on earth almost everywhere there is liquid water and an energy source, and we also have several worlds our space probes can reach that have signs of liquid water and available energy sources. One humble little methanogen hanging on in a film of water between two ice crystals in the martian soil would be a huge boost to hopes of finding ETI, because then we would know for sure that life is not confined to one tiny world (even if it were transplanted via a meteroite from earth it would be proff positive that life can spread from planet to planet where it does arise). My hope is that I live long enough to see a discovery that small and that profound, although if the battlestar galactica drops into orbit around earth tomorrow I won’t be complaining!

  • andy August 20, 2007, 12:14

    Regarding the “you need trees to have hands” thing: I wonder about creatures which move food around: for example to move it into stores (e.g. squirrels and other rodents). A somewhat plausible scenario that might be an alternative to swinging around in the trees: perhaps coevolution with plant-equivalents (“fruits” evolve to become trickier to get into so that only one type of animal can get at it, which is an evolutionary “arms race” that has several terrestrial examples) could drive the development of complex manipulators.

    Plus to think about: does an individual organism have to have complex manipulators to develop technology anyway? Lots of organisms with simple manipulators might be able to do the trick – maybe if the intelligence is something like the social insects.

    As for the technological capabilities of oceanic life, who knows? Is fire an absolute necessity, or would other heat sources (e.g. black smokers, submarine eruptions) do? Or what about if they build rafts of some kind?

    Again, the objections seem more that it is incredibly unlikely that humans evolved, rather than intelligent life in general.

  • david August 22, 2007, 1:08

    Again, the objections seem more that it is incredibly unlikely that humans evolved, rather than intelligent life in general.

    Human DNA contains about 3 billion base pairs. So a random mutation of human DNA has about 3 billion possible outcomes. Do a hundred million mutations and the set of possible outcomes would be immense. Even if we were to separate humanity into two groups with no interaction between the two they would differentiate. If this would happen from two human groups starting from the same place then imagine how different life that had a totally difference start.

    Life on planet X around star Y might not even develop bones. Rather they might use harden skin to simulate bones. Or they might grow small tree like structures within themselves that would perform the same function. Or they might even just have tubes that they fill with air. Imagine a creature that can change its shape, within reason, at will. Need to reach something high up then just fill a tube in the neck. Need to run, grow long legs in a few seconds. There’s a flood, just inflate some tubes and float until it goes down.

    My thoughts on this change so rapidly. With just one world to look at our assumptions are probably very biased. We think in terms of squirrels and apes and humans. What else can we do other than create fantasy worlds that we have no idea if they are realistic or not. However if you take any large number to the power of a large number, no matter how large they are the result is still going to be even or odd. The same is the result with life on other worlds – it is either intelligent or not. Maybe. Or maybe with a whole different start those worlds will be so different that deciding if something is intelligent or not won’t even be relevant – it will be just too alien with not only a totally different physical structure but with a whole different way of processing and organizing information. Even within humanity two groups can have such different ways of thinking and ways of viewing the world that conflict results.

    Hurry up with the starships, I want to know.

  • Stuart August 23, 2007, 20:10

    occam’s comic, astrophysicists do already measure and take into account magnetic fields within galaxies.

  • Peter Fred August 31, 2007, 1:21

    The Tully Fisher law could mean what it says it means.

    The spreading infrared luminosity from the central cloud of hot gas in between the two clusters of Abell 520 could actually be causing the gravitational light bending.

    In the 1919 solar eclipse study, it could have been the hot spreading luminosity from the sun that was causing the light bending and not the yet-to-be-specified
    property of the mass of the sun that was producing the warping of the nearby space.

    I have been trying for years to get someone to replicate my experiments so that somebody besides myself would begin to believe that spreading infrared radiation is gravitationally attractive.

    And now Mahdavi et al have found fairly clear-cut evidence that supports this far-reaching but easy to demonstrate notion.

    Maybe its not the dark matter that is difficult to see, it’s the light.

    Peter Fred

  • Dr. Edward Henry Dowdye, Jr. December 16, 2007, 2:11

    This is a response to
    “Propulsion Clues from a Dark Universe” and “occam’s comic” who said: “I am with infosponge, I think that mainstream astronomy is making a fundamental mistake.” I agree with this statement.

    For decades now some very important fundament principles of mathematical Physics have been incorrectly applied to the theory of gravitational lensing or just simply ignored. This has lead to an erroneous understanding the effects the gravitation of point-like masses should have on rays of light as suggested by the light bending rule of General Relativity. At least two very important fundamental principles of mathematical Physics were hardly applied or not mentioned at all by the researchers of gravitational lensing, namely the principle of Gauss’ law and the principle of optical reciprocity. The principle of Gauss’ law here is the analog of the principle of Gauss’ law of Electromagnetism, where a gaussian surface encloses an electric charge as opposed to a gravitating mass. The Gauss’ law simply states that the flux of the gravitational field through the different surfaces enclosing the same mass is constant. That means that the enclosed point masses are the only sources of the field lines of gravitation. This together with the principle of reciprocity is direct proof that the observer does not have to be co-linearly aligned with the lens and the source in order to be able to observe an event of gravitational lensing as predicted by the light bending rule of General Relativity.

    Historically, the only observable light bending effects on rays of light have been virtually those effects that are due to an indirect, not a direct interaction between the light rays and the gravitation. The thin plasma atmosphere of the sun represents such an indirect interaction between the gravitational field of the sun and the rays of light from the stars. There is convincing observational evidence from Astrophysics that a direct interaction between light and gravitation is yet to be observed. All indications show that the microlensing concept is merely a failed attempt to explain the lack of observation of macrolensing.

    Details: http://www.extinctionshift.com/SignificantFindings.htm

    A paper on this subject has been published in the renown refereed journal Astronomische Nachrichten, “Time resolved images from the center of the Galaxy appear to counter General Relativity”, Dowdye, Jr., E.H., Astronomische Nachrichten, 328, Issue 2, 2007,pp 186 -191

    Dr. Edward Henry Dowdye, Jr.

    Take a look at: http://www.extinctionshift.com/SignificantFindings.htm