But what a tangled history this paper presents. First of all, how does a 1962 paper get onto arXiv? A quick check reveals the uploader as David Derbes, a name that should resonate with Dyson purists. Derbes (University of Chicago Laboratory Schools, now retired) is the power behind getting Dyson’s lectures on quantum electrodynamics, first given at Cornell in 1951, into print in the volume Advanced Quantum Mechanics (World Scientific Publishing, 2007). He’s also an editor on Sidney Coleman’s Lectures on Relativity (Cambridge University Press, 2022) and has written a number of physics papers.
“Gravitational Machines” has been hard to find. Dyson wrote it, according to my polymath friend Adam Crowl, for the Gravitational Research Foundation in 1962; Centauri Dreams regular Al Jackson corroborates this in an email exchange, noting that the GRF was created by one Roger Babson, who offered a prize for such papers. Astrophysicist Alastair G. W. Cameron added it to his early SETI tome Interstellar Communications: A Collection of Reprints and Original Contributions (W. A. Benjamin, 1963). The paper, a tight six pages, does not appear in the 1996 volume Selected Papers of Freeman Dyson with Commentary (American Mathematical Society, 1996).
So we can be thankful that David Derbes saw fit to post it on arXiv. Al Jackson noted in his email that Greg Benford and Larry Niven have used Dyson’s gravitational concepts in their work, so I suspect “Gravitational Machines” was a paper known to them at this early stage of their career. A recent phone call with Jim Benford also reminded me of the Dyson paper’s re-emergence. Listen to Dyson’s familiar voice in 1962:
The difficulty in building machines to harness the energy of the gravitational field is entirely one of scale. Gravitational forces between objects of a size that we can manipulate are so absurdly weak that they can scarcely be measured, let alone exploited. To yield a useful output of energy, any gravitational machine must be built on a scale that is literally astronomical. It is nevertheless worthwhile to think about gravitational machines, for two reasons. First, if our species continues to expand its population and its technology at an exponential rate, there may come a time in the remote future when engineering on an astronomical scale will be both feasible and necessary. Second, if we are searching for signs of technologically advanced life already existing elsewhere in the universe, it is useful to consider what kinds of observable phenomena a really advanced technology might be capable of producing.
There’s the Dysonian reach into the far future, sensing where exponential technology growth might lead a civilization, and speculating at the most massive scale on the manipulation of matter as a form of engineering. But here too is the Dyson of ‘Dyson Sphere’ fame, tackling the question of whether or not such a project would be observable if undertaken elsewhere in the cosmos, just as he would go on to bring numerous other ideas on ‘technosignatures’ to our consciousness. Hence the term ‘Dysonian SETI,’ which I’ve often used here on Centauri Dreams.
Dyson goes on to speculate on the nature of eclipsing white dwarf binaries and their output of gravitational radiation, working the math to demonstrate the strength of such systems in terms of gravitational wave output, and finding that the output might be detectable. However, what catches his eye next is the idea of neutron star binaries, although he notes that at the time of writing, these objects were entirely hypothetical. But if they did exist (they do), their gravitational output should be “interesting indeed.”
…the loss of energy by gravitational radiation will bring the two stars closer with ever-increasing speed, until in the last second of their lives they plunge together and release a gravitational flash at a frequency of about 200 cycles and of unimaginable intensity.
It’s interesting that at the time Dyson wrote, Joseph Weber was mounting what must be the first attempt to detect gravitational waves, although he seems to have found nothing but instrumental noise. The LIGO (Laser Interferometer Gravitational-Wave Observatory) team would go on to cite Weber’s work following their successful detection of GW170817 in 2017, produced just as Dyson predicted by a neutron star binary. Calling such waves “a neglected field of study,” the 1962 paper adds this:
…the immense loss of energy by gravitational radiation is an obstacle to the efficient use of neutron stars as gravitational machines. It may be that this sets a natural limit of about 108 cm/sec to the velocities that can be handled conveniently in a gravitational technology. However, it would be surprising if a technologically advanced species could not find a way to design a nonradiating gravitational machine, and so to exploit the much higher velocities which neutron stars in principle make possible.
At the end of the paper posted on arXiv, David Derbes adds a useful note, pointing out Dyson’s prescience in this field, and adding that he had secured Dyson’s permission to publish the article before the latter’s death. But as typical of Dyson, he also stressed that he wanted Weber’s contribution to be noted, which Derbes delivered on by inserting a footnote to that effect in the text. We can all thank David Derbes for bringing this neglected work of a masterful scientist back into wider view.
In the next post, I want to talk about how these gravitational wave energies might be exploited by the ‘machines’ Dyson refers to in the title of the paper. The paper is Dyson, “Gravitational Machines,” now available on arXiv.
Hi Paul
Another Dyson idea that’s been obscured by time is his Plasma Brake concept. Akin to a Mag-Sail or even the E-Sail, it was derived from the observation of the orbital decay of the ECHO satellites.
Though maybe CD has covered it before and I’ve just forgotten – thus even more reason to revive discussion of it.
Yes, I would like to get back into that one. Will plan to do just that == I have an email in your direction on that topic.
Now I want to use Saturns gravity to lift matter off Titan.
Lots of hydrocarbon fuel.
A was thinking a tether type arrangement whereby plastic tethers with tanks every so often would be fed out towards Saturn…and Saturn’s gravity just keeps pulling.
The tanks detach from the tether such that they go into their own orbits.
A lot of propellant could be removed from Titan if things are spaced out just so.
Like Dyson take the orbital distance the ‘sling’ system to be circular with a semi major axis of 1000 km.
Consider a ship approaching with a velocity V. The velocity gain is approximately 2V. Velocity gains then are of the order of .002 to .006 c. Not bad for free energy, except one has to live in the vicinity of or travel to such objects.
There is bad news.
Lifetimes of these binaries against gravitational wave energy loss and hence orbit decay to collapse which is a function, for circular orbits, of distance and masses of the binary.
If both binaries have the same mass there results :
White Dwarfs ~ 30 years
Neutron Stars ~ 18 years
Black Holes ~ .1 year
Larger orbital distances have larger lifetimes but smaller velocity gains. Achieving high fractions of the speed of light does not look promising for Dyson gravitational machines.
Opps! V above is the circular speed of the white dwarf, neutron star or black hole pair.
Two obreth burns timed well would probably deliver much more delta v than the gravity wave gain.
Weber is a controversial figure but a brilliant one. With regard to his detector experiments, due to its modest sensitivity the frequency of cataclysmic astronomical events would have to be far higher than it is to hope that one is close enough to have a chance of being detected. Happily for us, they are not so frequent and therefore are on average very distant.
About the new comment box: please make it larger. It’s difficult to compose a comment longer than a couple of sentences without having to scroll back and forth. The new one is prettier but that’s about it.
Working on the comments issue over the weekend. I hope to have this resolved some time next week.
The Dyson paper is short so I spent a few minutes reading it. The scheme has flaws. The biggest one that occurred to me is due to the large difference between the small velocity of the spacecraft compared to large orbital radius for the two massive compact objects. This is not comparable to a conventional planetary slingshot maneuver as depicted in figure 1.
The craft must navigate many interactions with the two massive objects during its approach to the system. Each gravitational interaction will accelerate the craft and alter the trajectory toward the center of the system. Since the craft has little maneuverability the insertion trajectory must be precisely set. Worse, depending on the relative velocities and orbital period there may be no accessible solutions.
I would be surprised if this hasn’t been noticed and commented on over the past 60 years.
I don’t know what Ron S. means by
“the large difference between the small velocity of the spacecraft compared to large orbital radius for the two massive compact objects.”
What has the small velocity difference compared to large orbital radius mean?
For this ‘maneuver’ it’s the transfer of momentum from the binary system to the small ‘scattering’ object that counts.
The tiny mass space ship robs some energy and momentum from the binary system, but just like the bounce maneuver in the solar system the amount is infinitesimal.
The real problem is two things, the small boost one gets when the compact binary is widely separated, secondly to get a large boost the binary has to be a tight one, but then gravitational radiation limits it life time, that is especially true of neutron stars and black holes.
Yeah the guidance , navigation and control for this is difficult. But!, we a talking about an advanced civilization with advanced technology. This whole maneuver would be a piece of cake for them!
This brings up the problem. How many of these white dwarf, neutron star, black hole binaries are there? What is their space distribution? My guess is , per galaxy, not that many. As I pointed out in my comment , from Dyson’s, configuration, they don’t live that long against gravitational radiation induced collapse. Longer lived ones , with bigger orbital distance, don’t give you much velocity to rob.
After all if an advanced civilization has interstellar flight and can reach one of these binary systems it has already mastered the high speed! Why go grab a fraction of that when you can already do it?
(By the by didn’t Greg Benford (or was it Niven) use one of these system in a science fiction story?)
Paul, I have also looked around in the literature and the only ‘Binary-bounce-maneuver’ I find is Dyson’s.
However there are studies of single star scattering from binaries in the astrophysical literature. But that is a three body thing not an infinitesimal body from a binary. Tho I have not canvased the extensive literature there is.
I don’t know if Dyson did a back of the envelope calculation of this process and did not document it in the little paper. This exercise is just undergraduate mechanics. I have seen Dyson do this before. He originally didn’t detail Dyson Sphere calculations , even his expansion in his collected papers is a bit terse. But for a physicist who could reconcile Feynman and Schwinger details like these are left up to mere mortals! (as an exercise!)
“After all if an advanced civilization has interstellar flight and can reach one of these binary systems it has already mastered the high speed! Why go grab a fraction of that when you can already do it?”
I strongly agree. Nevertheless it’s an interesting thought experiment.
“What has the small velocity difference compared to large orbital radius mean?”
A clumsy description on my part. Let’s try this again.
C is put on an orbit that basically has it diving into the A-B system from afar. While it remain far away it will accelerate inward, approaching but never reaching the systems escape velocity. For WD in a tight orbit this might be no more than 100 km/s, and higher for NS in a tighter orbit. That’s the easy bit.
As C approaches the system it “feels” an additional tug as A and B, in rapid succession, sweep past it. The trajectory of C turns more directly into the A-B system and accelerates. This continues for many orbits, with the effect growing with every encounter. Recall that we’re talking about a slow initial velocity (v) for C and an A-B orbit period of 10’s to 100’s of seconds. That is, v<<V.
The final encounter, if insertion is mathematically and practically possible on a precise trajectory after those many encounters, is really the only one we want: to slingshot from a deep dive close to the surface of A or B. Get it wrong and C is destroyed or swings past and hope for an encounter with either A or B on the far side of the system. But there is little ability to maneuver because C, by definition, can't substantially accelerate on its own.
It's an ugly problem to solve and perhaps it can be by minds better than mine. I'm sure an existing software modeling system can deal with this 3 body problem.
"I don’t know if Dyson did a back of the envelope calculation of this process and did not document it in the little paper."
It would be interesting to know.
Developments in the UFO/UAP Phenomenon with Avi Loeb
Much spculation including mention of gravity, quanum gravity and the creation of new universes: John Michael Godier’s Event Horizon podcast.
There is a sort of gravity and light machine we could build but I don’t know how useful it would be. We could use mass in a geometric configuration as a gravity lens. For instance if we say look at the earths gravity focal line of several thousand AU’s distant it could be reduced greatly if the earth’s was spaghettified. In effect some of the gravity waves and light would be allowed to get a lot closer to the earth’s mass or any mass for that matter, millions of times closer, and be bent towards it to a focal point.
I emailed Professor Dyson once and received a reply almost as soon as our 12 hour time difference would permit – astounding.
Beginning in 1976, Professor David Blair at the University of Western Australia once had a significant percentage of the world’s niobium locked up in the form of a bar, with four others around the world, configured to ‘ring’ were they to detect gravitational waves, which of course they did not to measurable sensitivity. They were capable of detecting these if the source was close. David went on to work with the LIGO consortium.
Words escape me to describe the loss that Professor Dyson’s passing is to our community. His legacy lives on though.
Dyson really was quick to reply. I had a similar rapid exchange with him twice, in both cases involving something fairly minor, and I really appreciated that he took the time to answer so swiftly. Words escape me as well about the magnitude of our loss.
The ‘sticky beads on a rigid rod’argument is meant to demonstrate the energy carried by gravitational waves as frictional heat (as the beads slide back and forth along the rod).
At first this seemed confusing to me, as an expansion or contraction of spacetime will expand or contract everthing in that space. However in this context it appears that ‘rigid’ realy means a rod where the internal molecular bonds subject to the tidal forces are able to continually re-establish the length of the rod (in the new metric) as spacetime expands and contracts. The sticky beads would only be partiall bound (sticky, not rigidly) and therefore oscillate along the rod.
This suggests another way to build a gravitational energy harvester.
However there is also an argument that the tidal forces due to gravitational waves with a sufficient high frequency would jerk or strain too quickly for the intermolecular forces to adjust. That doesn’t look pretty.
Ever since a young age, I was fascinated by the concept of controlling gravity. Once I learned some physics, I realized that the issue with controlling gravity is that it is so weak compared to electromagnetism… but then I realized gravity control isn’t fictional at all. We’ve already done it.
When Henry Cavendish set up his torsion balance apparatus to empirically measure the gravitational constant, he was manipulating gravity by arranging lead spheres.
More recently, John Walker (founder of Autodesk Inc.) demonstrated that you can
bend spacetime in the garage with a home-made version of Cavendish’s setup. Obviously, there are a lot of x-factors to control (vibration and air currents be the most prominent), but the fact that we can even detect the gravitational pull of 2kg paving stones in a home setup proves that gravity control is technically accessible to the hobbyist.
I assumed that the fields we could manipulate using current engineering would be too feeble to achieve anything practical. Then I read about the proposal to use a “gravity tractor” to nudge threatening asteroids onto safer orbits. Utilizing a carefully selected trajectory, a spacecraft could transfer impulse to the asteroid using only its gravitational field.
Granted, this is a fairly limited use of “gravity control”, but it is something we could achieve with 21st century engineering. Sometimes, I find that the technology described in science fiction is already here. It just didn’t take the form (or flash) promised in the old serials.