Interstellar Conundrum: Is Stross Right?

by | Jun 19, 2007 | Culture and Society | 48 comments

Although people have been recommending that I read Charles Stross’ novel Accelerando for some time now, I haven’t found the time and now wish that I had. I recently read a fascinating speech that Stross gave at a Munich tech conference discussing, among many other things, how advances in computer storage will change our lives. And now his essay The High Frontier, Redux is exciting controversy, asking whether many of our ideas about spaceflight need to be reassessed in light of the enormity of the challenges we face.

Much of what Stross has to say is true, and I hope that those who haven’t read the essay will give it a look. The reason why we don’t want to minimize the magnitude of the problems we face in interstellar flight is that a clear-eyed view is needed to begin to conceive the radical technologies that may one day solve the problem. And I know too many people who learn how far away the stars really are, even the closest of them, and then throw the whole concept out as wishful thinking.

But I don’t think Stross is doing this. Have another look at the essay and you’ll note what he’s up to. He wants to “…highlight the problems I face in trying to write believable science fiction about space colonization.” Fair enough! And what exercises him as a writer is that interstellar travel requires a) outrageous amounts of energy; or b) highly efficient robot probes; or c) a magic wand. Stross doesn’t find option A easy to work with, and B isn’t as interesting for many a writer, since putting humans into interstellar space is prime science fiction material. That leaves C, and the problem there is that the day of the deus ex machina is long past. No good science fiction writer wants anything to do with springing absurd contraptions out of closets to save the day.

Now I would venture that anyone reading Centauri Dreams already has a pretty good idea of how far the stars are. Stross reduces an astronomical unit — the distance between the Earth and the Sun — to a centimeter and describes the scary result even for nearby stars. On that scale, Proxima Centauri, the nearest star, is fully 2.6 kilometers away (Stross says 2.3 — one of us has the math slightly wrong, and I wouldn’t be surprised if it were me).

But I like British astronomer William Herschel’s far more homely (and much less accurate) way of reading the distance to Centauri A and B. Herschel (1792-1871) was the first to make a serious attempt to measure this value, and he put it in terms his contemporaries could understand: “…to drop a pea at the end of every mile of a voyage on a limitless ocean to the nearest fixed star, would require a fleet of 10,000 ships of 600 tons burthen, each starting with a full cargo of peas.”

Yep, better have plenty of peas for that Centauri trip. As Stross says, the distances are mind-numbing. But I’ll differ slightly on his take on Proxima, which he describes as “…a poor choice, if we’re looking for habitable real estate. While exoplanets are apparently common as muck, terrestrial planets are harder to find.” He may well be right, but we do have planet hunter Greg Laughlin (UC Santa Cruz), who just the other day said this in his systemic blog in the context of a proposed HARPS search for Proxima planets:

“Proxima is effortlessly old, adequately quiet, and metal-rich. If our understanding of planet formation is first-order correct, it has several significant terrestrial-mass planets.”

Now let’s be careful here. Laughlin is talking about planets of terrestrial mass, rocky worlds that may or may not be in the habitable zone. The odds for any given star are that such planets are not in that zone. On the other hand, we can’t completely rule the possibility out, nor can we rule out the even more interesting scenario around the primary stars Centauri A and B, each of which may have planets within roughly 4 AU of the parent, with possibilities for the delivery of volatiles to the inner system involving Proxima itself. See this older Centauri Dreams post for more.

The energy cost is indeed staggering. But let’s assume no magic wands. When I was at Marshall Space Flight Center in Huntsville several years ago talking to NASA solar sail researchers for my book, Greg Matloff was there doing consultant duty and participated in the interviews. Matloff, the author of the highly regarded The Starflight Handbook (about which Robert Forward had the ultimate dust jacket compliment — ‘Don’t leave the Solar System without it!’), talked about solar sail missions that don’t invoke any off-the-charts wizardry.

“When you look at technology such as Tim Knowles’ stuff [a reference to ultra-lightweight carbon-carbon sail material], you realize how close we are to being able to build a generation ship. You have to start saying, with planets being discovered all over the place, if we discover an Earth-like planet around one of the three Centauri suns, and we might well find that, is there going to be a push to do that. Because we can do it. You have to look into the weird stuff, I believe, to show it doesn’t work.”

Matloff has studied sail mission concepts using so-called Sun-diver trajectories that deploy a sail at perihelion. In a subsequent telephone interview, he added: “We’ve learned that it is quite possible to take both large ships and small probes to the nearest star within a thousand years or so. Using the sail alone. But it is very difficult to get the trip time down below 800 or 900 years.” Alan Bond and Anthony Martin would use a key Matloff paper on this subject for their own classic paper (see below for citations) discussing worldships and the two technologies they thought could power them — nuclear-pulse engines and hyper-thin solar sails.

None of which is to deny the enormous challenges that Stross talks about. But again, I catch his reference to his dilemma as a craftsman of words when he says, “…the conclusion I draw as a science fiction writer is that if interstellar colonization ever happens, it will not follow the pattern of historical colonization drives that are followed by mass emigration and trade between the colonies and the old home soil.”

Now colonization is quite another matter from robotic probes, and I can certainly believe that historical colonization drives, trading routes and the rest are not a likely analog for future star missions. Stross could be right that humans — as opposed to intelligent machinery — may not get to the stars, but even on that score I’m reminded again of Robert Forward. His vast lens in outer Solar System orbit focusing laser light from a power-rich installation near the orbit of Mercury could theoretically launch a crewed Epsilon Eridani mission with return capability, with travel time within a single human lifetime.

An engineering nightmare? To be sure, the magnitude of building installations that require lenses hundreds of kilometers across to focus a laser pushing a vast sail are almost beyond comprehension. But even today, we see the nano-technology revolution proceeding apace, and have to speculate about what effects it may have on the building of large structures in space. Give up on the notion of thousands of human workers in spacesuits welding joints into place and you’re left with the possibility of ‘growing’ a Fresnel lens inside the orbit of Uranus that could serve the purpose.

Far-fetched? You bet. But I think the future usually is far-fetched. If I were a practicing science fiction writer like Stross, I too would see how difficult it must be to craft a believable future within technology that is explicable to a broad readership. The man has a good point! But I believe that if we can come up with even faintly plausible scenarios that don’t drift far from understood physics today, then we can certainly assume better scenarios as some of today’s computing and nano-tech trends continue to develop.

We can also assume that the innate human impulse to do seemingly impossible things will keep theorists focused on this quest. Leave magic wands out of the equation and ask yourself whether, if we could build the infrastructure to launch a Forward-style lightsail with human crew, we would have volunteers to fly the mission. Ponder as well the energy resources that will have to be realized for this kind of journey and ask whether we really are gradually evolving into a Kardashev Type 1 civilization. Because if we are, and if we keep imagining and planning and doing, we may yet make this wildest of improbable dreams happen.

And if it takes a thousand years to build the tools needed to launch such a mission? Ten thousand? Then some of our descendants may just see the Centauri stars up close. What matters is not when but whether we go. I wouldn’t advise betting against a long-term optimism that may, by its own drive and pluck, find a way to push to Centauri and beyond. As for Charles Stross, I still plan to read Accelerando. This guy knows his stuff, and articles like his help to frame and focus the terms of the debate.

A final thought: Stross has one comment that has me baffled. As one who thinks we need to build a space-based infrastructure to help protect our planet from space debris, I found myself surprised to read this:

‘We can’t afford to keep all our eggs in one basket’ isn’t so much a justification as an appeal to sentimentality, for in the hypothetical case of a planet-trashing catastrophe, we (who currently inhabit the surface of the Earth) are dead anyway. The future extinction of the human species cannot affect you if you are already dead: strictly speaking, it should be of no personal concern.

Stross calls such arguments about future catastrophe ‘quasi-religious,’ for reasons that escape me. If we can identify an incoming danger and mount a mission to avert possible species extinction, shouldn’t we be working on the technology needed to do the job? And if the beneficiaries are our great-grandchildren instead of ourselves, what of that? Isn’t that the sort of commitment we should be making to our descendants?

Addendum: See the comments below for Stross’ response to these questions. We’re a lot closer on this than I had realized.

And now, the promised citations: Matloff’s paper with Eugene Mallove is “Solar Sail Starships: Clipper Ships of the Galaxy,” Journal of the British Interplanetary Society 34 (1981), pp. 371-380, and the related “The Interstellar Solar Sail: Optimization and Further Analysis” is in JBIS 36 (1983), pp. 201-209. The worldship article is Bond and Martin, “World Ships: Concept, Cause, Cost, Construction and Colonization,” JBIS 37 (1984), pp. 243-53. Also see their “Worldships: Assessment of Engineering Feasibility,”‘ JBIS 37, pp. 254-256 (1984).

Stross: The Interstellar Improbability

by | Jun 18, 2007 | Culture and Society | 19 comments

Science fiction writer Charles Stross, always an insightful voice when it comes to the future of technology, offers up an incisive look at the problems of interstellar flight in his The High Frontier, Redux. The article is in the queue for discussion here, but since I can’t get to it until tomorrow afternoon — and since comments are already flying about what Stross has to say — I’ll set up this topic as a gathering point for those comments until the larger post goes online. Read Stross when you can, as anyone seriously interested in interstellar possibilities needs to understand the magnitude of the challenge. We’ll run through some of the issues tomorrow, and look at one Stross comment I find completely puzzling.

Geological Activity on Tethys and Dione?

by | Jun 18, 2007 | Outer Solar System | 1 comment

Centauri Dreams doubts that most space scientists expected to find as much activity around Saturn as the Cassini probe has revealed. Enceladus was spectacular enough, with its geysers spewing material hundreds of kilometers above the surface. And now we find indications that two other moons — Tethys and Dione — are active worlds as well. More Cassini close passes will be needed to firm this up. For that matter, data already collected from previous flybys may contain still more clues, which is how things work in planetary science these days — we collect information at a rate far surpassing our ability to keep up with the inflow.

In any event, Cassini’s arrival in Saturn space in 2004 made it clear that centrifugal forces caused by the planet’s fast rotation (10 hours and 46 minutes) compressed plasma into a disc from which cold, dense plasma from the planet’s inner magnetosphere was being flung into space. Hotter plasma from the outer magnetosphere quickly moves in to fill up the gap. The plasma, made up of negatively charged electrons and positively charged ions, is readily manipulated by the giant planet’s magnetic field.

This European Space Agency news release explains how Jim Burch (Southwest Research Institute) and colleagues have used Cassini’s Plasma Spectrometer to pinpoint the source of at least some of the ejected electrons near the orbits of Tethys and Dione. “This new result, says Andrew Coates (University College, London), “seems to be a strong indication that there is activity on Tethys and Dione as well.” Thus the possibility that both these moons are undergoing interesting geological processes that we’ll soon be studying via future flybys.

Tethys and Dione

Image: Image: This is a compound image made from separate images of Saturn’s two moons, Tethys (to the left) and Dione (to the right), taken by Cassini. The two moons are flinging great streams of particles into space, according to data from the NASA/ESA/ASI Cassini mission to Saturn. The discovery suggests the possibility of some sort of geological activity, perhaps even volcanic, on these icy worlds. Credit: NASA/ JPL.

The paper on this work is Burch et al., “Tethys and Dione as sources of outward-flowing plasma in Saturn’s magnetosphere,” Nature 447, pp. 833-835 (14 June, 2007), with abstract here. With the telltale electrons now detected, Burch’s team now looks toward tracking ion activity as the study of plasma around these small moons intensifies.

A Possible Planet around Fomalhaut

by | Jun 16, 2007 | Exoplanetary Science | 20 comments

Watching the motion of the stars they orbit has been how most of the planets beyond our Sun have thus far been discovered. Such radial-velocity methods are getting more precise all the time, but a likely planet around the nearby star Fomalhaut comes out of an entirely different line of research. Alice Quillen (University of Rochester) is an expert on stellar disks and the planets that help to shape them. And she has learned to predict a planet’s size and position from her studies.

In the case of Fomalhaut, Quillen worked with Hubble Space Telescope imagery showing the star’s surroundings in greater detail than ever before. The Hubble images took advantage of a coronagraph to mask the light of the star to bring out detail in the dimmer ring, confirming what astronomers had previously noted — Fomalhaut is off-center within its ring.

Fomalhaut and Its Dust Ring

Image: Hubble’s view of Fomalhaut’s dust ring. Credit: University of Rochester/STScI.

Quillen’s models examine ring/planet interactions for young stars, around which the dust is fine enough to act much like a fluid, and older stars where larger bodies have begun to form. The Fomalhaut offset, more than 15 times the distance between Earth and the Sun, suggests a hidden planet in a highly eccentric orbit. Quillen has this to say:

“Something had to skew that planet, and that’s what we’re working on now. There may have been fantastic planetary collisions early on that changed their orbits. We’re working on figuring out how many more planets of what size you’d need to account for that elliptical orbit, and to account for why there is no other dust inside that ring.”

We won’t know for sure whether Quillen and team are right until we’ve got the tools to make an actual detection. At 25 light years from Earth, Fomalhaut is likely to receive detailed study by coronagraph or starshade technologies on future planet-hunter missions. But don’t be surprised if a Neptune-class world fitting Quillen’s increasingly fine-tuned model turns up in the system there. Up tight against the inner side of the ring, its presence would explain nicely how ring dust is being so clearly displaced.

The paper is Hosseinbor, Quillen et al., “The formation of an eccentric gap in a gas disc by a planet in an eccentric orbit,” Monthly Notices of the Royal Astronomical Society (OnlineEarly Articles), with abstract available.

Cramer’s Time Experiment Funded

by | Jun 15, 2007 | Exotic Physics | 23 comments

When you’ve read Analog as long as I have — and I date back to the days when it was named Astounding — you develop a real fondness for some of the primary players. That’s one reason I’m glad to hear the good news about John Cramer’s time travel experiment, which has received enough private donations to be pursued. Cramer’s ‘Alternate View’ columns have been running in the magazine since 1984, covering everything from cosmology to space drives and quantum mechanics. I’ve always admired his clear, straightforward style.

A physicist at the University of Washington, Cramer caught the attention of the press in recent months by discussing his hopes of testing the idea of quantum retrocausality. Here we’re in the domain of what Cramer calls the Transactional Interpretation, in which the processes of quantum mechanics involve waves traveling both forward and backward in time. His experiment, which may begin as early as next month, will test whether photons can communicate in reverse time.

The notion, absurdly reduced, is this: Entangled photons seem to be able to affect each other no matter how widely separated in time or space, the so-called Einstein-Podolsky-Rosen paradox that illuminates the bizarre nature of quantum mechanics. Do a measurement on one and it has an immediate effect on the other. Cramer is testing whether this ‘spooky action at a distance’ is the result of communications that move backwards and forwards in time.

I won’t run through the experimental apparatus again since we’ve covered it before, both in Of Time Travel and Funding and in an article called Backwards in Time? Each contains links to further background for those interested. But what pleases me is that this is the kind of experiment — relatively inexpensive, highly controversial and fraught with implications — that seems ideal for philanthropic rather than government funding. It’s a pleasure to see such money flowing, even though a broad consensus in the scientific community seems to hold that Cramer is wasting his time and other people’s money.

The Seattle Post-Intelligencer wrote up the funding story on the 12th and provided this quote, noting the consequences of failure:

Cramer said it’s possible that the primary goal of his experiment could fail and yet still produce something of value. Some new subtlety about the nature of entanglement could be revealed, he said, even if the photons don’t engage in measurable non-local communication. The “disentanglement” itself, he said, could be quite revealing.

“It wouldn’t be as nice as a positive result, but it would certainly be interesting and publishable,” Cramer said. If there is an interesting negative result or a half-positive result, he said he will buy more precise equipment to see if he can tease out what’s happening. Cramer has all the money he needs for this phase, but he hopes to see a second phase.

Cramer, whose credentials include work at the Brookhaven National Laboratory’s Relativistic Heavy Ion Collider and Europe’s CERN particle physics installation as well as his time at the University of Washington, has received more than $35,000 from people who read about his ideas on the Internet. The cash has flowed in from artists, scientists, business people, and space enthusiasts like Walter Kistler, founder of Kistler Aerospace. More traditional sources like NASA’s Institute for Advanced Concepts and the Defense Advanced Research Projects Agency had already turned down Cramer’s proposal.

What next? We’ll see whether the Transactional Interpretation receives any support in the experiments soon to be launched. Meanwhile, have a look at one of Cramer’s ‘Alternate View’ columns called A Farewell to Copenhagen?, in which he discusses a quantum test called the Afshar Experiment, and provides background on the competing Copenhagen and Many Worlds Interpretations. No one knows what will come next out of his laboratory, but anything connected with time travel seems to have caught the eye of Net watchers, so we’re sure to hear about it quickly.