A New Slant on ‘The Planet of Doubt’

by Paul Gilster on October 7, 2011

Among all the planets, Uranus seems to get the least play in science fiction, though it does have one early advocate whose work I’ve always been curious about. Although he wrote under a pseudonym, the author calling himself ‘Mr. Vivenair’ published a book about a journey to Uranus back in the late 18th Century. A Journey Lately Performed Through the Air in an Aerostatic Globe, Commonly Called an Air Balloon, From This Terraquaeous Globe to the Newly Discovered Planet, Georgium Sidus (1784) seems to be reminiscent of some of Verne’s work, even if it pre-dates it, in using a then cutting-edge technology (balloons) to envision a manned trip through space.

Image: Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which it is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.

When ‘Vivenair’ wrote, Uranus had just been discovered (by William Herschel in 1781). The author used it as the occasion for political satire, and not a very good one, according to critic James T. Presley, who described it in an 1873 article in Notes & Queries as ‘a dull and stupid satire on the court and government of George III.’ Vivenair evidently put the public to sleep, for Uranus more or less fades from fictional view for the whole of the 19th Century. More recent times have done better. Tales like Geoff Landis’ wonderful “Into the Blue Abyss” (2001) bring Uranus into startling focus, and Larry Niven does outrageous things with it in A World Out of Time (1976). But although it doesn’t hold up well as fiction, Stanley G. Weinbaum’s story about Uranus may sport the most memorable title of all: “The Planet of Doubt” (1935).

What better name for this place? The seventh planet has a spin axis inclined by a whopping 98 degrees in reference to its orbital plane — compare that to the Earth’s 23 degrees, or Neptune’s 29. This is a planet that is spinning on its side. Conventional wisdom has it that a massive collision is the culprit, but the problem with that thinking is that such a ‘knockout blow’ would have left the moons of Uranus orbiting at their original angles. What we see, however, is that the Uranian moons all occupy the same 98 degree orbital tilt demonstrated by their parent.

New work unveiled at the EPSC-DPS Joint Meeting in Nantes, France is now giving us some answers to this riddle. A team led by Alessandro Morbidelli (Observatoire de la Cote d’Azur) ran a variety of impact simulations to test the various scenarios that could account for Uranus’ tilt. It turns out that a blow to Uranus experienced when it was still surrounded by a protoplanetary disk would have reformed the entire disk around the new and highly tilted equatorial plane. The result would be a planetary system with moons in more or less the position we see today, as described in this news release.

But this is intriguing: Morbidelli’s simulations also produce moons whose motion is retrograde. The only way to get around this, says the researcher, is to model the Uranian event not as a single impact but as at least two smaller collisions, which would increase the probability of leaving the moons in their observed orbits. Given all this, some of our planet formation theories may need revision. Says Morbidelli:

“The standard planet formation theory assumes that Uranus, Neptune and the cores of Jupiter and Saturn formed by accreting only small objects in the protoplanetary disk. They should have suffered no giant collisions. The fact that Uranus was hit at least twice suggests that significant impacts were typical in the formation of giant planets. So, the standard theory has to be revised.”

The questions thus raised by the ‘planet of doubt’ may prove helpful in understanding how giant planets evolve. More on this when the paper becomes available.

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Earth’s Oceans: A Cometary Source After All?

by Paul Gilster on October 6, 2011

Getting water into the inner Solar System is an interesting exercise. There has to be a mechanism for it, because the early Earth formed at temperatures that would have caused any available water to have evaporated. Scientists have long speculated that water must have been delivered either through comets or asteroids once the Earth had cooled enough to allow liquid water to exist. The former was preferred because the water content in comets is so much higher than in asteroids.

But the theory had problems, not the least of which was that comets studied in this regard showed deuterium levels twice that of Earth’s oceans. The ratio of deuterium and hydrogen, both made just after the Big Bang, can vary in water depending on its location because local conditions can affect the chemical reactions that go into making ice in space. A comparison of the deuterium to hydrogen ratio in extraterrestrial objects can be compared to water found in Earth’s oceans to identify the source of our water. Now comet Hartley 2 swings into the picture, for researchers have announced that its hydrogen/deuterium ratio is similar to Earth’s oceans.

Image: This illustration shows the orbit of comet Hartley 2 in relation to those of the five innermost planets of the Solar System. The comet made its latest close pass of Earth on 20 October last year, coming to 19.45 million km. On this occasion, Herschel observed the comet. The inset on the right side shows the image obtained with Herschel’s PACS instrument. The two lines are the water data from HIFI instrument. Credit: ESA/AOES Medialab; Herschel/HssO Consortium.

So how do you measure the hydrogen/deuterium ratio in the water of a comet? The answer is an instrument called HIFI, which operates aboard the European Space Agency’s Herschel infrared space observatory. HIFI (Heterodyne Instrument for the Far Infrared) is a high-resolution heterodyne spectrometer developed in The Netherlands that covers two bands from 480-1250 gigaHertz and 1410–1910 gigaHertz. Herschel was examining the comet’s coma, which develops as frozen materials inside vaporize when the comet moves closer to the Sun.

Remember, previous comet studies had found hydrogen/deuterium ratios different from our oceans. The difference between these comets and Hartley 2 may be that Hartley 2 was formed in the Kuiper Belt, whereas other comets studied in this regard are thought to have first formed near Jupiter and Saturn before being flung out by the gravitational effects of the gas giants, returning millions of years later for their pass around the Sun. The hydrogen/deuterium ratio we see in water ice may well have been different in the Kuiper Belt than in ice that first formed in the inner system, where conditions are much warmer. Further comets studies may confirm the idea.

Says Dariusz Lis (Caltech):

“Our results with Herschel suggest that comets could have played a major role in bringing vast amounts of water to an early Earth.This finding substantially expands the reservoir of Earth ocean-like water in the solar system to now include icy bodies originating in the Kuiper Belt.”

Surely the early oceans were the result of both comet and asteroid impacts, but the new findings point back to comets as major players. Even so, we have plenty of work to do to understand the role of the lightest elements and their isotopes in the early Solar System. Six comets besides Hartley 2 have been examined for hydrogen/deuterium levels, all with deuterium levels approximately twice that found in Earth water. Kuiper Belt comets were once thought to have even higher deuterium levels than Oort Cloud comets, an idea the Hartley 2 results have now refuted.

The team led by Paul Hartogh (Max Planck Institute for Solar System Research) has also used the Herschel Observatory to measure the hydrogen/deuterium ratio in comet 45P/Honda-Mrkos-Pajdusakova, another Kuiper Belt comet whose data is now under analysis, so we may soon have new data to add to this story. The paper is Hartogh, “Ocean-like water in the Jupiter-family comet 103P/Hartley 2,” published online in Nature 5 October 2011 (abstract).

And there is further news out of the joint meeting in Nantes, France, of the European Planetary Science Congress and the American Astronomical Society’s Division for Planetary Sciences, where this work was announced. As noted in this article in Nature, a new study of the Sun-like star Eta Corvi, which is roughly the same age our Sun was during the Late Heavy Bombardment (when most water is thought to have been delivered to the Earth), shows that the star has an inner ring of warm dust that is rich in carbon and water. Team leader Carey Lisse (JHU/APL) thinks we’re seeing the traces of one or more Kuiper Belt-class comets being flung into the inner system, colliding with a planet there to form the ensuing ring of material.

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Resonance and Probability Around Kepler-18

by Paul Gilster on October 5, 2011

Three planets recently discovered through Kepler data provide an interesting take on how we look at smaller planets. Not that the planets around the star designated Kepler-18 are all that small — two of them are Neptune-class and one is a super-Earth. But what is becoming clear is that given the state of our current technology, we’ll have to get used to a process different from planet verification as we move to ever smaller worlds. The technique is being referred to as planet validation — it helps us determine the probability that the detected object could be something other than a planet.

Image: The orbits of the three known planets orbiting Kepler-18 as compared to Mercury’s orbit around the Sun. Credit: Tim Jones/McDonald Obs./UT-Austin.

The new system shows how this works. Kepler-18 is a star similar to ours, about 10 percent larger than the Sun and with 97 percent of the Sun’s mass. Around it we have Kepler-18 c and d, which turn up through transits. Planet c has a mass of about 17 Earths and is thought to be some 5.5 times the size of Earth. Its orbit takes it around Kepler-18 in 7.6 days. Kepler-18 d is 16 times as massive as the Earth, 7 times Earth’s size, and orbits its primary in 14.9 days. These two Neptune-class worlds are, interestingly enough, in a 2:1 resonance: Planet c orbits the star twice for every single orbit of planet d. The demonstrable resonance is ample proof that these are planets in the same system and not something else mimicking a planetary signature.

But the super-Earth, Kepler-18 b, is something else again. A team led by Bill Cochran (University of Texas at Austin) went to work with the 5-meter Hale Telescope at Palomar, aided by adaptive optics, to examine Kepler-18 to see whether the transit signal they thought to be a super-Earth was genuine. Finding no background objects that could have influenced the finding, they were able to calculate the odds that Kepler-18 b is not a planet at 700 to 1. Cochran thinks this process of planet validation is going to become much more significant as Kepler brings in new data:

“We’re trying to prepare the astronomical community and the public for the concept of validation. The goal of Kepler is to find an Earth-sized planet in the habitable zone [where life could arise], with a one-year orbit. Proving that such an object really is a planet is very difficult [with current technology]. When we find what looks to be a habitable Earth, we’ll have to use a validation process, rather than a confirmation process. We’re going to have to make statistical arguments.”

So we can with a high degree of probability rule out any of the objects — stars, background galaxies — that might in any way compromise the transit data. The planetary signature of the super-Earth seems real enough, though established in a different way than Kepler-18 c and d, whose gravitational interactions can be readily demonstrated. The planet is thought to be 6.9 times Earth mass and twice Earth’s size. All three worlds orbit much closer to their parent star than Mercury does to the Sun, the super-Earth Kepler-18 b being the closest, with a 3.5 day period.

We can also deduce an interesting possibility about Kepler-18 b, as noted in the paper:

The inner, 3.5-day period planet Kepler-18b, is a super-Earth that requires a dominant mixture of water ice and rock, and no hydrogen/helium envelope. While the latter cannot be excluded simply on the basis of the planet’s mass and radius, the evaporation timescale for a primordial H/He envelope for a hot planet such as Kepler-18b is much shorter than the old age derived for the Kepler-18 system, and such a H/He envelope should not be present. Thus, despite its lower equilibrium temperature, Kepler-18b resembles 55 Cnc e and CoRoT-7b… Kepler-18b, together with 55 Cnc e… are likely our best known cases yet of water planets with substantial steam atmospheres (given their high surface temperatures).

The discovery was announced at a joint meeting of the American Astronomical Society’s Division of Planetary Science and the European Planetary Science Conference in Nantes, France. More on the Kepler-18 results in this news release from the University of Texas at Austin. Look for these results in an upcoming issue of the Astrophysical Journal Supplement Series devoted to Kepler, which will appear in November. The paper is Cochran et al., “Kepler 18-b, c, and d: A System Of Three Planets Confirmed by Transit Timing Variations, Lightcurve Validation, Spitzer Photometry and Radial Velocity Measurements” (preprint).

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Initial Thoughts on the Starship Symposium

by Paul Gilster on October 3, 2011

I’m just back from the 100 Year Starship Symposium. The thoughts below were written yesterday evening (the 2nd), just after the event ended.

It’s a lovely evening here in Orlando, one I’m enjoying while sitting out in front of the Hilton waiting for my taxi. I got a chuckle out of the audience at my talk at the 100 Year Starship Symposium when I mentioned something that is completely true: I’m actually a very retro kind of guy. Sure, starships are a passion, but I also restore old fountain pens, love film noir, and as I told the audience, chose an overnight sleeper train to come to Florida in rather than an aircraft.

They enjoyed the observation, probably because we’re all an odd mix of personally defined and often contradictory impulses. But as I soak up this gorgeous Florida evening, I’m feeling a profound singleness of purpose. To begin with, it’s clear to me that writing about the starship conference won’t be a matter of a single Centauri Dreams entry but rather a series of thoughts and recollections that will be scattered through any number of future articles. The experience was obviously memorable, the largest conference devoted to interstellar flight that I could have imagined, and as David Neyland, its organizer, told me, it happened because so many people came from so far in the service of a numbingly futuristic idea.

People like my friend Adam Crowl, who came all the way from Brisbane, Australia, and with whom I enjoyed good conversation throughout the event. People like Kelvin Long, the man whose inspiration put Icarus into operation, who came with fellow Icarus people like Pat Galea and Rob Swinney from the UK and Andreas Tziolas from Alaska. Marc Millis and I found an excellent Italian restaurant, and the next night I had a wonderful dinner conversation with Greg Benford over salmon and a superb Carneros Pinot Noir (thanks Al Jackson for picking up the wine tab!). I enjoyed my chats with Jim Benford as well, and it was great to see Richard Obousy, who came over from Texas. Special thanks to the many Centauri Dreams readers who introduced themselves as I walked between sessions.

If I had one criticism of what happened here, it’s that there were so many good papers to listen to, so many good people to hear, that the multi-track structure made it impossible to do everything I would have wanted to do. Michael Michaud’s paper on the long term implications of interstellar flight was a priority for me, but I had also committed to a number of readers that I would cover one of the breakthrough propulsion sessions — I was using Twitter to do a bit of live ‘micro-blogging’ — and I not only missed Michael’s talk, but found myself sitting on the floor typing, the session being completely packed as Marc Millis, Jordan Maclay, Eric Davis and Sonny White talked space drives and Alcubierre theory.

OK, you choose. Which of these would you go to and which would you regret missing:

  • “A Review of Interstellar Starship Design” – Richard Obousy (Icarus Interstellar)
  • “Light Sailing to the Stars” – Greg Matloff (New York City College of Technology)
  • “Mass Beam Propulsion: An Overview” – Gerald Nordley
  • Panel: “Structuring the 100 Year Starship” – Mae Jemison, moderator (The Jemison Group)
  • “Making Aliens” – Athena Andreadis
  • “Star Probes and ET Intelligence” – Stephen Baxter

It wasn’t easy, and it was like that all the time.

On the last day, we had a late meeting among Tau Zero and Icarus people and by the time we finished, almost everyone had left the conference facility. The venue was suddenly deserted and quiet, with that eerie sense you get when an enormous structure, seemingly at once, becomes empty. We found unused symposium programs and posters leaning up against a table. Think about this, I joked. We could collect all these and in twenty years, who knows what they would bring on eBay! We were laughing about this but I did cast a wistful glance back. Maybe we really should have picked the extras up…

Anyway, this was really a four-day conference packed into the equivalent of two days, so we were all running from paper to paper, session to session, with little time for breaks and even less time for meals until the day was over. A new meme was emerging – the ‘interstellar buzz’ – and it was palpable. I think everyone was as jazzed as I was about the fact that this meeting was even happening. How often do I get to chat with Jill Tarter in the elevator, catch up on the latest from my friend Claudio Maccone or have dinner conversation with John Cramer and Marc Millis talking about the CERN neutrino results?

Not that I was doing the talking in that conversation — I’m a writer, not a scientist, and I was in Orlando to keep learning as much as I could about a topic that’s so multi-faceted and rich that every new nugget uncovered seems to expose an even deeper vein of ore. So there was much listening to be done, banking on the willingness of scientist after scientist to share ideas and point me in the direction of further sources.

We managed plenty of Tau Zero and Icarus business as well, so in the rare free time discussions continued. The Icarus team was all over the place, and I quickly learned that if I stood even for a moment at the Tau Zero table, I would get pulled into a conversation related to one or the other (as well as my Tau Zero duties, I serve as a consultant for Icarus). My sense is that the starship conference is getting lots of pop from the media, which leads to the question of how long the interstellar buzz can be maintained. Time will tell, but my major goal long-term is to see the public getting back into the space game in terms of enthusiasm and interest, and turning Apollo-like passions toward the interstellar deep.

Can that happen? Maybe some day, and I’m not so unrealistic as to expect that a single symposium can make it happen overnight. But Dave Neyland had the right idea when he got DARPA into this game, because the DARPA imprimatur brought an intensity of focus that the community had been lacking. People who work on these topics invariably do so in their spare time. They’re separated not only by distance but the pressures of work and only occasionally see each other at conferences. An event like this can reveal how concentrated is their interest and how wide their potential audience, as long as we can build on what happened here.

I ran into a friend as I was waiting for my taxi who told me the whole thing was making him emotional, and I had something of the same reaction. What has to be said about many of the people working in this area is that they do it not only because of the utter fascination of the challenge, but because getting to the stars is a multi-generational quest for them, one they generally (though not universally) assume will not be achieved in their lifetimes, but one they believe with a passion their descendants will experience. And it is with a deep sense of commitment that they come forward to offer up their expertise for this gift to an unknowable futurity.

Emotional? Sure. Interstellar flight has long been talked about and it fills the pages of science fiction, but to see some of the best minds in a host of disciplines attacking it as a scientific problem and actually planning to create an organization that can last long enough to bring it seriously closer is a powerful experience. I’m now writing this in Orlando’s train station, having caught that taxi and resumed my work afterwards, and the sense that this was a once in a lifetime event just won’t go away. We’ll have other interstellar gatherings, but this one feels like a game-changer, one we’ll be talking about in various ways for a long time.

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100 Year Starship Meeting

by Paul Gilster on September 30, 2011

Arrived yesterday afternoon at the Orlando Hilton for the 100 Year Starship Symposium. I’ll try to get updates out on my Twitter feed @centauri_dreams when possible. The WiFi here has been mostly good but it did go down this morning for a time, so bear with me.

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Lost in Time and Lost in Space

by Paul Gilster on September 29, 2011

by Dave Moore

Dave Moore, a frequent Centauri Dreams contributor, tells me he was born and raised in New Zealand, spent time in Australia, and now makes his home in California. “As a child I was fascinated by the exploration of space and science fiction. Arthur C. Clarke, who embodied both, was one of my childhood heroes. But growing up in New Zealand in the 60s, anything to do with such things was strictly a dream. The only thing it did lead to was to getting a degree in Biology and Chemistry.” But deep space was still on Dave’s mind and continues to be, as the article below, drawing on his recent paper in the Journal of the British Interplanetary Society, attests. “While I had aspirations at one stage of being a science fiction writer,” Dave adds, “I never expected that I would emulate the other side of Arthur C. Clarke and get something published in JBIS.” But he did, and now explains the thinking behind the paper.

The words from “Science Fiction/Double Feature” in the Rocky Horror Picture Show seem particularly apt after looking into the consequences of temporal dispersion in exosolar technological civilizations.

And crawling on the planet’s face
Some insects called the human race . . .
Lost in time
And lost in space
. . . and meaning.
All meaning.

Hence the title of my paper in a recent issue of the Journal of the British Interplanetary Society (Vol. 63 No. 8 pp 294-302). The paper, “Lost in Space and Lost in Time: The Consequences of Temporal Dispersion for Exosolar Technological Civilizations,” grew out of my annual attendance at Contact in San Jose, an interdisciplinary convention of scientists, artists and science fiction writers. From the papers presented there, I got a general feeling for the state of play in the search for extraterrestrial civilizations but never felt inclined to make a contribution until it occurred to me to look at the results of Exosolar Technological Civilizations (ETCs) emerging at different times. It would be an exercise similar to many that have been done using the Drake equation only, but instead of looking at the consequences of the spatial dispersion, I’d be looking at the consequences of different temporal spreads.

My presentation of the results and my conclusions went over sufficiently well that it was suggested that I turn it into a paper, but not having any experience in publishing papers, I let the project drop until Paul got to see my musings and suggested JBIS as a suitable forum.

The Separation Between Civilizations

The core of the paper is a table showing the number of ETCs you would get and their average separations assuming they arose at various rates from a starting point four billion years ago.

I used an idealized galaxy which was a disk of uniform stellar density, that of our solar neighborhood, to keep things simple. (For the justification of why this is a reasonable assumption and to why it seems quite likely that potential life-bearing planets have been around for eight billion years, I’ll refer you to my paper.)

One of the first things I realized is that the median age of all civilizations is entirely independent of the frequency at which they occur. It’s always approximately one-third the age of the oldest civilization. If ETCs start emerging slowly and their frequency picks up (a more likely scenario), this skews the median age lower, but you are still looking at a period of about a billion years.

And the median age of all civilizations is also the median age of our nearest neighbor. There’s a fifty/fifty chance it will be either younger or older than that, but there’s a 90% chance it will at least be 10% of the median, which means that in all likelihood our nearest neighbor will be hundreds of millions of years older than us. And, if you want to find an ETC of approximately our own age, say within a thousand years of ours, you will on average have to pass by a million older to vastly older civilizations. As you can see from columns 5 and 6 in the table, if ETCs haven’t emerged with sufficient frequency to produce a million civilizations, then you won’t find one.

Once you realize that ETCs are not only scattered through vast regions of space but also scattered across a vast amount of time, then this casts a very different light on many common assumptions about the matter. Take the idea very prevalent in a lot of literature that the galaxy is full of approximately coequally-aged civilizations (emerging within a thousand years of each other), a scenario I will call the Star Trek universe. If you look at the bottom row of the table, you can see there are simply aren’t enough stars in our galaxy for this to work.

After discovering that when dealing with extraterrestrial civilizations, you are dealing with great age, I then began to look at the sort of effects great age would have on civilizations.

Age and Power

The first thing I did was to extrapolate our energy consumption, and I discovered that at a 2% compound growth rate our civilization would require the entire current energy output of the galaxy (reach a Kardashev III level) in less than 3000 years, which doesn’t look likely unless a cheap, convenient, FTL drive get discovered. What this does point out though is that in extraordinarily short times, geologically speaking, civilizations can theoretically grow to enormous power outputs.

The next thing I did was to review the literature on interstellar travel. Many of the interstellar propulsion scenarios have power requirements that cluster around the 100 Terawatt level. This is a million times that of a proposed 100 MW nuclear powered Mars vessel, which is considered to be within our current or near future range of capabilities. Assuming a society with a million times our current power consumption would find a 100 TW vessel similarly within its capabilities, then our first interstellar vessel would be 700 years into our future at a 2% growth rate.

Are these energy levels feasible? If Earth continues its current growth in energy consumption, we will overheat our planet through our waste heat alone in the next century, never mind global warming through CO2 emissions. So, it looks as if we remain confined to our planet, we will probably never have the ability to send out interstellar colony ships. There is, however, a way to have our civilization reach enormous energy levels while still within our solar system.

Our solar system may have as many as a trillion comets and KBOs orbiting it, ten times the mass of the Earth, all nicely broken up. (There may be more comets in our solar system than there are stars in our galaxy.) And as this is the bulk of the easily accessible material, it would be logical to assume that eventually this is where the bulk of our civilization will finish up.

A hydrogen-fusion powered civilization could spread throughout our cometary belt, and with no grand engineering schemes such as the construction of a Dyson sphere, it could, through the cumulative growth of small, individual colonies, eventually build up a civilization of immense power and size. For example, if each of a 100 billion comets were colonized with a colony that used 1000 MW of power (a small city’s worth) then the total civilizational power consumption would be in the order of 1020 Watt. Pushing it a bit, if there was a 20,000 MW colony on each of the 5 trillion comets in the Oort cloud and the postulated Hills cloud, then the total civilizational power consumption would be 1023 Watt, that of a red dwarf star.

For this society, interstellar colonization would be but another step.

The End of a Civilization

Ian Crawford has done some analysis of galactic colonization using a scenario in which a tenth-lightspeed colony ship plants a colony on a nearby star system. The colony then grows until it is capable of launching its own ship, and so on. This produces a 1000-2000 year cycle, with the assumptions I’ve been using, but even if you work this scenario conservatively, the galaxy is colonized in 20 million years, which is an order of magnitude less that the expected age of our nearest neighbor.

Of course, all the previous points may be moot if a civilization’s lifetime is short, so I then looked into the reasoning advanced for civilizational termination.

Various external causes have been postulated to truncate the life span of a technological civilization–Gamma Ray Bursters are a favorite. When you look at them though, you realize that anything powerful enough to completely wipe out an advanced technological civilization would also wipe out or severely impact complex life; there’s at most a 10,000 year window of vulnerability before a growing civilization spreading throughout the galaxy becomes completely immune to all these events. This is one fifty-thousandth of the 500 million years it took complex life to produce sentience. So any natural disasters frequent enough to destroy a large portion of extraterrestrial civilizations would also render them terminally rare to begin with. If extraterrestrial civilizations do come to an end, it must be by their own doing.

There’ve been numerous suggestions as to why this may happen, but these arguments are usually anthropocentric and parochial and not universal. If they don’t apply to just one civilization, that civilization can go on to colonize the galaxy. So, at most, self-extinction would represent but another fractional culling akin to the other terms in the Drake equation. There’ve also been many explanations for the lack of evidence of extraterrestrial civilizations: extraterrestrials are hiding their existence from us for some reason, they never leave their home world, our particular solar system is special in some way, etc., but these are also parochial arguments; the same reasoning applies. They also fail the test of Occam’s razor. The simplest explanation supported by the evidence is that our civilization is the only one extant in our galaxy.

Into the Fermi Question

The only evidence we have about the frequency and distribution of ETCs is that we can find no signs of them so far. This has been called the Fermi paradox, but I don’t regard this current null result as a paradox. Rather I regard it as a bounding measurement. Since the formation of the Drake equation, two major variables have governed our search for ETCs: their frequency and longevity. This leads to four possibilities for the occurrence of Exosolar civilizations.

  • i) High frequency and longevity
  • ii) High frequency and short life spans
  • iii) Low frequency and longevity
  • iv) Low frequency and short life spans

These four categories are arbitrary, in effect being hacked out of a continuum. The Fermi paradox eliminates the first one.

We can get a good idea of the limits for the second by looking at an article that Robert Zubrin did for the April 2002 issue of Analog. In it, he postulated a colonization scenario similar to Ian Crawford’s but cut the expanding civilizations off at arbitrary time limits. He then found the likelihood for Earth having drifted through the ETCs’ expanding sphere of influence in the course of our galactic orbit. The results indicated that unless all civilizations have lifetimes of under 20,000 years, we are very likely to have been visited or colonized frequently in the past. But to have every civilization last less than a specified time requires some sort of universalist explanation, which is hard to justify given the naturally expected variation in ETCs’ motivation.

Nothing that we had seen so far eliminates the third possibility however.

Implications for SETI Strategy

Finally, in the paper, I turned to reviewing our search strategies for ETCs in light of what has been learned.

Given that ETCs will most probably be very distant and have a high power throughput, then looking for the infrared excess of their waste heat looks like a good bet. Low frequency but high power also implies searching extra galactically. Take the Oort cloud civilization I postulated earlier and assume it colonizes every tenth star in a galaxy like ours. Its total power consumption would be in the order of 1030 Watt. This would show up as an infrared excess of one part in 107 to 108 of a galaxies’ output.

I found other ideas like searching for ancient artifacts and using gravitational lensing for a direct visual search seem to have some potential, but when I looked at radio searches, this turned out to be one of the least likely ways to find a civilization. The problem quickly becomes apparent after looking at Table I. Any ETCs close enough to us to make communication worthwhile will most likely be in the order of 108 to 109 years old, which gives them plenty of time to become very powerful, and therefore highly visible, and to have visited us. If civilizations occur infrequently, as in the top row of Table I, then the distances are such that the communication times are in the order of 10,000 years. If civilizational lifetimes are short but the frequency is high, then you still have enormous distances. (You can use Table I to get some idea of the figures involved. The last two columns show the distances at various frequencies for civilizations within 1000 years of our age. For ten thousand years move those figures up one row, for 100,000 years two rows, etc.) Under most cases, the signal reply time to the nearest civilization will exceed the civilizations’ lifetime–or our patience. Looking for stray radio signals under the distant but short-lived scenario does not look very hopeful either. To send a signal tens of thousands of light years, an effective isotropic radiated power of 1017 – 1020 Watts is required, and while this is within sight of our current technology, the infrastructure and power levels are far in excess of anything required for casual communication even to nearby stars.

The results of all my thinking are not so much answers but, hopefully, a framing for asking the right questions.

Considerations in SETI searches have tended to focus on the nearby and a close time period and were set when our knowledge in this field was in its infancy. There’ve been some refinements to our approach since them, but generally our thinking has been built on this base. It’s time to carefully go over all our assumptions and reexamine them in the light of our current knowledge. The Fermi paradox needs to be explained — not explained away.

The paper is Moore, “Lost in Time and Lost in Space: The Consequences of Temporal Dispersion for Exosolar Technological Civilisations,” JBIS Vol. 63, No. 8 (August 2010), pp. 294-301.

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A New Confirmation of General Relativity

by Paul Gilster on September 28, 2011

Einstein’s Special Theory of Relativity remains much in the news after a weekend of speculation about the curious neutrino results at CERN. Exactly what is going on with the CERN measurements remains to be seen, but the buzz in the press has been intense as the specifics of the experiment are dissected. It will be a while before we have follow-up experiments that could conceivably replicate these results, but it’s interesting to see that another aspect of Einstein’s work, the General Theory of Relativity, has received a new kind of confirmation, this time on a cosmological scale.

Here we’re talking not about the speed of light but the way light is affected by gravitational fields. The work is out of the Niels Bohr Institute at the University of Copenhagen, where researchers say they have tested the General Theory at a scale 1022 times larger than any laboratory experiment. Radek Wojtak, an astrophysicist at the Institute, has worked with a team of colleagues to analyze measurements of light from galaxies in approximately 8,000 galaxy clusters. Each cluster is a collage of thousands of individual galaxies, all held together by gravity.

Image: Researchers have analysed measurements of the light from galaxies in approximately 8,000 galaxy clusters. Galaxy clusters are accumulations of thousands of galaxies (each light in the image is a galaxy), which are held together by their own gravity. This gravity affects the light that is sent out into space from the galaxies. Credit: Niels Bohr Institute/ Radek Wojtak.

The Copenhagen team was looking specifically at redshift, where the wavelength of distant galaxies shifts toward the red with increasing distance. Redshift has been used to tell us much about how the universe has expanded since the light being studied left its original source. Normally we think of the redshift being the result of the changing distance between the distant light source and ourselves as we both move through space. This is the familiar Doppler shift, and it could be either a redshift or, if the objects are approaching each other, a blueshift.

But another kind of redshift can come into play when space itself is expanding. Here the distance between the distant light source and ourselves is also increasing, but because of its nature, we call this a cosmological redshift rather than a Doppler shift. Gravity can also cause a redshift, as light emitted by a massive object is affected by the gravity of the object. The loss of energy from emitted photons shows up as a redshift commonly called a gravitational redshift.

The General Theory of Relativity can be used to predict how light – and thus redshift – is affected by large masses like galaxy clusters. In the new work, we’re focusing on both cosmological and gravitational redshift, effects apparent when the light from galaxies in the middle of the galactic clusters is compared to those on the outer edges of the cluster. Wojtak puts it this way:

“We could measure small differences in the redshift of the galaxies and see that the light from galaxies in the middle of a cluster had to ‘crawl’ out through the gravitational field, while it was easier for the light from the outlying galaxies to emerge.”

Going on to measure the total mass of each galaxy cluster, the team could then use the General Theory of Relativity to calculate the gravitational redshift for the differently placed individual galaxies. What emerged from the work was that the theoretical calculations of the gravitational redshift based on the General Theory of Relativity were in agreement with the astronomical observations. Says Wotjak:

“Our analysis of observations of galaxy clusters show[s] that the redshift of the light is proportionally offset in relation to the gravitational influence from the galaxy cluster’s gravity. In that way our observations confirm the theory of relativity.”

Does the testing of the General Theory on a cosmological scale tell us anything about dark matter and its even more mysterious counterpart, dark energy? On that score, this Niels Bohr Institute news release implies more than it delivers. The new work confirms current modeling that incorporates both dark matter and dark energy into our model of the universe, but beyond that it can provide no new insights into what dark matter actually is or how dark energy, thought to comprise 72 percent of the structure of the universe, actually works. We can make inferences from our understanding of the behavior of the light, but we have a long way to go in piecing together just what these dark components are.

The paper is Wojtak et al., “Gravitational redshift of galaxies in clusters as predicted by general relativity,” Nature 477 (29 September 2011), pp. 567–569 (abstract).

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A Machine-Driven Way to the Stars

by Paul Gilster on September 27, 2011

Are humans ever likely to go to the stars? The answer may well be yes, but probably not if we’re referring to flesh-and-blood humans aboard a starship. That’s the intriguing conclusion of Keith Wiley (University of Washington), who brings his background in very large computing clusters and massively parallel image data processing to bear on the fundamental question of how technologies evolve. Wiley thinks artificial intelligence (he calls it ‘artificial general intelligence,’ or AGI) and mind-uploading (MU) will emerge before other interstellar technologies, thus disrupting the entire notion of sending humans and leading us to send machine surrogates instead.

It’s a notion we’ve kicked around in these pages before, but Wiley’s take on it in Implications of Computerized Intelligence on Interstellar Travel is fascinating because of the way he looks at the historical development of various technologies. To do this, he has to assume there is a correct ‘order of arrival’ for technologies, and goes to work investigating how that order develops. Some inventions are surely prerequisites for others (the wheel precedes the wagon), while others require an organized and complex society to conceive and build the needed tools.

Some technologies, moreover, are simply more complicated, and we would expect them to emerge only later in a given society’s development. Among the technologies needed to get us to the stars, Wiley flags propulsion and navigation as the most intractable. We might, for example, develop means of suspended animation, and conquer the challenges of producing materials that can withstand the rigors and timeframes of interstellar flight. But none of these are useful for an interstellar mission until we have the means of accelerating our payload to the needed speeds. AGI and MU, in his view, have a decided edge in development over these technologies.

Researchers report regularly on steady advancements in robotics and AI and many are even comfortable speculating on AGI and MU. It is true that there is wide disagreement on such matters, but the presence of ongoing research and regular discussion of such technologies demonstrates that their schedules are well under way. On the other hand, no expert in any field is offering the slightest prediction that construction of the first interstellar spaceships will commence in a comparable time frame. DARPA’s own call to action is a 100-year window, and rightfully so.

Wiley is assuming no disruptive breakthroughs in propulsion, of course, and relies on many of the methods we have long discussed on Centauri Dreams, such as solar sails, fusion, and antimatter. All of these are exciting ideas that are challenged by the current level of our engineering. In fact, Wiley believes that the development of artificial general intelligence, mind uploading and suspended animation will occur decades to over a century before the propulsion conundrum is resolved.

Consequently, even if suspended animation arrives before AGI and MU — admittedly, the most likely order of events — it is still mostly irrelevant to the discussion of interstellar travel since by the time we do finally mount the first interstellar mission we will already have AGI and MU, and their benefits will outweigh not just a waking trip, but probably also a suspended animation trip, thus undermining any potential advantage that suspended animation might otherwise offer. For example, the material needs of a computerized crew grow as a slower function of crew size than those of a human crew. Consider that we need not necessarily send a robotic body for every mind on the mission, thus vastly reducing the average mass per individual. The obvious intention would be to manufacture a host of robotic bodies at the destination solar system from raw materials. As wildly speculative as this idea is, it illustrates the considerable theoretical advantages of a computerized over a biological crew, whether suspended or not. The material needs of computerized missions are governed by a radically different set of formulas specifically because they permit us to separate the needs of the mind from the needs of the body.

We could argue about the development times of various technologies, but Wiley is actually talking relatively short-term, saying that none of the concepts currently being investigated for interstellar propulsion will be ready any earlier than the second half of this century, if then, and these would only be the options offering the longest travel times compared to their more futuristic counterparts. AGI and MU, he believes, will arrive much earlier, before we have in hand not only the propulsion and navigation techniques we need but also the resolution of issues like life-support and the sociological capability to govern a multi-generational starship.

The scenario assumes not that starflight is impossible, nor that generation ships cannot be built. It simply assumes that when we are ready to mount a genuine mission to a star, it will be obvious that artificial intelligence is the way to go, and while Wiley doesn’t develop the case for mind-uploading in any detail because of the limitations of space, he does argue that if it becomes possible, sending a machine with a mind upload on the mission is the same as sending ourselves. But put that aside: Even without MU, artificial intelligence would surmount so many problems that we are likely to deploy it long before we are ready to send biological beings to the stars.

Whether mediated by human or machine, Wiley thinks moving beyond the Solar System is crucial:

The importance of adopting a realistic perspective on this issue is self-evident: if we aim our sights where the target is expected to reside, we stand the greatest chance of success, and the eventual expansion of humanity beyond our own solar system is arguably the single most important long-term goal of our species in that the outcome of such efforts will ultimately determine our survival. We either spread and thrive or we go extinct.

If we want to reach the stars, then, Wiley’s take is that our focus should be on the thorny issues of propulsion and navigation rather than life support, psychological challenges or generation ships. These will be the toughest nuts to crack, allowing us ample time for the development of computerized intelligence capable of flying the mission. As for the rest of us, we’ll be vicarious spectators, which the great majority of the species would be anyway, whether the mission is manned by hyper-intelligent machines or actual people. Will artificial intelligence, and especially mind uploading, meet Wiley’s timetable? Or will they prove as intractable as propulsion?

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The SN 1987A Experiment

by Paul Gilster on September 24, 2011

If neutrinos really do travel at a velocity slightly higher than the speed of light, we have a measurement that challenges Einstein, a fact that explains the intense interest in explaining the results at CERN that we discussed on Friday. I think CERN is taking exactly the right approach in dealing with the matter with caution, as in this statement from a Saturday news release:

…many searches have been made for deviations from Einstein’s theory of relativity, so far not finding any such evidence. The strong constraints arising from these observations make an interpretation of the OPERA measurement in terms of modification of Einstein’s theory unlikely, and give further strong reason to seek new independent measurements.

And this is followed up by a statement from CERN research director Sergio Bertolucci:

“When an experiment finds an apparently unbelievable result and can find no artifact of the measurement to account for it, it’s normal procedure to invite broader scrutiny, and this is exactly what the OPERA collaboration is doing, it’s good scientific practice. If this measurement is confirmed, it might change our view of physics, but we need to be sure that there are no other, more mundane, explanations. That will require independent measurements.”

All this is part of the scientific process, as data are sifted, results are published, and subsequent experiments either confirm or question the original results. I’m glad to see that the supernova SN 1987A has turned up here in comments to the original post. The supernova, which exploded in February of 1987 in the Large Magellanic Cloud, was detected by the “Kamiokande II” neutrino detector in the Kamioka mine in Japan. It was also noted by the IMB detector located in the Morton-Thiokol salt mine near Fairport, Ohio and the ‘Baksan’ telescope in the North Caucasus Mountains of Russia.

Neutrinos scarcely interact with matter, which means they escape an exploding star more quickly than photons, something the SN 1987A measurements confirmed. But SN 1987A is 170,000 light years away. If neutrinos moved slightly faster than the speed of light, they would have arrived at the Earth years — not hours — before the detected photons from the supernova. The 25 detected neutrinos were a tiny fraction of the total produced by the explosion, but their timing matched what physicists believed about their speed. The OPERA result, in other words, is contradicted by an experiment in the sky, and we have a puzzle on our hands, one made still more intriguing by Friday’s seminar at CERN, where scientists like Nobel laureate Samuel Ting (MIT) congratulated the team on what he called an ‘extremely beautiful experiment,’ one in which systematic error had been carefully checked.

Image: In February 1987, light from the brightest stellar explosion seen in modern times reached Earth — supernova SN1987A. This Hubble Space Telescope image from the sharp Advanced Camera for Surveys taken in November 2003 shows the explosion site over 16 years later. Supernova SN1987A lies in the Large Magellanic Cloud, a neighboring galaxy some 170,000 light-years away. That means that the explosive event – the core collapse and detonation of a star about 20 times as massive as the Sun – actually occurred 170,000 years before February 1987. Credit: P. Challis, R. Kirshner (CfA), and B. Sugerman (STScI), NASA.

It’s true that OPERA was working with a large sample — some 16000 neutrino interaction events — but skepticism remains the order of the day, because as this New Scientist story points out, there is potential uncertainty in the neutrinos’ departure time, there being no neutrino detector at the CERN end. As for the GPS measurements, New Scientist labels them so accurate that they could detect the drift of the Earth’s tectonic plates. Can we still tease out a systematic error from the highly detailed presentation and paper produced by the CERN researchers? They themselves are cautious, as the paper makes clear:

Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results.

A prudent policy. Let’s see what subsequent experiments can tell us about neutrinos and their speed. The paper is The OPERA Collaboration, “Measurement of the neutrino velocity with the OPERA detector in the CNGS beam,” available as a preprint.

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On Neutrinos and the Speed of Light

by Paul Gilster on September 23, 2011

If you’re tracking the interesting news from CERN on neutrinos moving slightly faster than the speed of light, be advised that there is an upcoming CERN webcast on the matter at 1400 UTC later today (the 23rd). Meanwhile, evidence that the story is making waves is not hard to find. I woke up to find that my local newspaper had a headline — “Scientists Find Signs of Particles Faster than Light” — on the front page. This was Dennis Overbye’s story, which originally ran in the New York Times, but everyone from the BBC to Science Now is hot on the trail of this one.

The basics are these: A team of European physicists has measured neutrinos moving between the particle accelerator at CERN to the facility beneath the Gran Sasso in Italy — about 725 kilometers — at a speed about 60 nanoseconds faster that it would have taken light to make the journey. The measurement is about 0.0025 percent (2.5 parts in a hundred thousand) greater than the speed of light, a tiny deviation, but one of obvious significance if confirmed. The results are being reported by OPERA (Oscillation Project with Emulsion-Tracking Apparatus), a group led by physicist Antonio Ereditato (University of Bern).

Neutrinos are nearly massless subatomic particles that definitely should not, according to Einstein’s theory of special relativity, be able to travel faster than light, which accounts for the explosion of interest. According to this account in Science Now, the OPERA team measured roughly 16,000 neutrinos that made the trip from CERN to the detector, and Ereditato is quoted as saying that the measurement itself is straightforward: “We measure the distance and we measure the time, and we take the ratio to get the velocity, just as you learned to do in high school.” The measurement has an uncertainty of 10 nanoseconds.

It’s hard to do any better than Ereditato himself when bringing caution to these findings. Let me quote the Science Now story again:

…even Ereditato says it’s way too early to declare relativity wrong. “I would never say that,” he says. Rather, OPERA researchers are simply presenting a curious result that they cannot explain and asking the community to scrutinize it. “We are forced to say something,” he says. “We could not sweep it under the carpet because that would be dishonest.”

And the BBC quotes Ereditato to this effect: “My dream would be that another, independent experiment finds the same thing. Then I would be relieved.” One reason for the relief would be that other attempts to measure neutrino speeds have come up with results consistent with the speed of light. Is it possible there was a systematic error in the OPERA analysis that gives the appearance of neutrinos moving faster than light? The timing is obviously exquisitely precise and critical for these results, and a host of possibilities will now be investigated.

This paragraph from a NatureNews story is to the point:

At least one other experiment has seen a similar effect before, albeit with a much lower confidence level. In 2007, the Main Injector Neutrino Oscillation Search (MINOS) experiment in Minnesota saw neutrinos from the particle-physics facility Fermilab in Illinois arriving slightly ahead of schedule. At the time, the MINOS team downplayed the result, in part because there was too much uncertainty in the detector’s exact position to be sure of its significance, says Jenny Thomas, a spokeswoman for the experiment. Thomas says that MINOS was already planning more accurate follow-up experiments before the latest OPERA result. “I’m hoping that we could get that going and make a measurement in a year or two,” she says.

Unusual results are wonderful things, particularly when handled responsibly. The OPERA team is making no extravagant claims. It is simply putting before the scientific community a finding that even Ereditato calls a ‘crazy result,’ the idea being that the community can bring further resources to bear to figure out whether this result can be confirmed. Both the currently inactive T2K experiment in Japan, which directs neutrinos from its facility to a detector 295 kilometers away, and a neutrino experiment at Fermilab may be able to run tests to confirm or reject OPERA’s result. A confirmation would be, as CERN physicist Alvaro de Rujula says, ‘flabbergasting,’ but one way or another, going to work on these findings is going to take time, and patience.

The paper “Measurement of the neutrino velocity with the OPERA detector in the CNGS beam” is now up on the arXiv server (preprint).

Addendum: For an excellent backgrounder on neutrino detection and the latest measurements, replete with useful visuals, see Starts With a Bang. Thanks to @caleb_scharf for the tip.

And this comment from a new Athena Andreadis post is quite interesting:

If it proves true, it won’t give us hyperdrives nor invalidate relativity. What it will do is place relativity in an even larger frame, as Eisteinian theory did to its Newtonian counterpart. It may also (finally!) give us a way to experimentally test string theory… and, just maybe, open the path to creating a fast information transmitter like the Hainish ansible, proving that “soft” SF writers like Le Guin may be better predictors of the future than the sciency practitioners of “hard” SF.

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