Fascinating article by Paul Gilster over at Centauri Dreams: Interstellar Archaeology on the Galactic Scale. In the article, Gilster, discusses the work of Richard Carrigan of Fermilab and his recent paper, "Starry Messages: Searching for Signatures of Interstellar Archaeology."
Carrigan argues that we should broaden SETI's scope to include the archeological remnants of Kardashev III civilizations, namely those civilizations who successfully tapped into their Galaxy's entire energy output. At first blush, one would assume that a K3 galaxy would be immediately obvious, with every one if its stars enclosed in a Dysonian structure of some sort. But Carrigan makes the case that this might not be the case:
…what would happen for a civilization on its way to becoming a type III civilization, a type II.5 civilization so to say? If it was busily turning stars into Dyson spheres the civilization could create a “Fermi bubble” or void in the visible light from a patch of the galaxy with a corresponding upturn in the emission of infrared light. This bubble would grow following the lines of a suggestion attributed to Fermi… that patient space travelers moving at 1/1000 to 1/100 of the speed of light could span a galaxy in one to ten million years. Here “Fermi bubble” is used rather than “Fermi void”, in part because the latter is also a term in solid state physics and also because such a region would only be a visible light void, not a matter void.
As Gilster notes, this is long-term thinking in the richest sense; a patient, long-lived civilization could envelop a galaxy on a time-scale comparable to or shorter than the rotation period of the galaxy (considerably >~250 million years).
Civs who are busy turning stars into Dyson spheres should leave vast Fermi 'bubbles' whose infrared signature would flag their existence. But as Carrigon notes, detection might still elude us.
For example, we see M51, the Whirlpool galaxy, face-on at a distance of 30 million light years. We can say with some confidence that we see no unexplained voids larger than about five percent of M51's area, but any void features below this level would be hard to identify because of spiral galaxy structure. Elliptical galaxies might be better places to look for Fermi bubbles, because they display little structure, and potential voids should be far more pronounced.
And then there's the difficulty in separating artificial structure from natural phenomena where the tendency is to defer to the latter.
Gilster concludes:
I come back around to the premise behind interstellar archaeology, that unlike conventional SETI it does not require a civilization to have any intention of contacting us. There are numerous ways to proceed, involving the kind of Dyson sphere search Carrigan has himself conducted within our own galaxy, or looking at planetary atmospheres in hopes of finding not only biosignatures but the markers of an advanced industrial or post-industrial culture. As we continue the SETI hunt, keeping in mind how planetary change or deliberate decisions to expand into the galaxy could leave visible traces allows us to hunt for things advanced intelligence might do.
How many civilizations in our galaxy, for example, have already faced the end of their main sequence star’s lifetime? If the number is high, it may be that we can find evidence of their response in the form of planetary or stellar engineering, making stars of this description interesting targets for future searches. In any case, our model of SETI is changing as not only our technologies but our assumptions become more sophisticated, leaving us to ponder a universe in which the need for expansion or simple survival may have left its own detectable history.
More.
- Neurodiversity vs. Cognitive Liberty - November 8th, 2009 [November 8th, 2009]
- Link dump: 2009.10.13 - November 8th, 2009 [November 8th, 2009]
- Limits to the biolibertarian impulse - November 8th, 2009 [November 8th, 2009]
- Link dump: 2009.10.15 - November 8th, 2009 [November 8th, 2009]
- Neurodiversity vs. Cognitive Liberty, Round II - November 8th, 2009 [November 8th, 2009]
- Link dump: 2009.10.17 - November 8th, 2009 [November 8th, 2009]
- Cognitive liberty and right to one's mind - November 8th, 2009 [November 8th, 2009]
- TED Talks: Henry Markram builds a brain in a supercomputer - November 8th, 2009 [November 8th, 2009]
- And Now, for Something Completely Different: Doomsday! - November 8th, 2009 [November 8th, 2009]
- Link dump: 2009.10.19 - November 8th, 2009 [November 8th, 2009]
- Oklahoma and abortion - some fittingly harsh reflections - November 8th, 2009 [November 8th, 2009]
- Pigliucci on science and the scope of skeptical inquiry - November 8th, 2009 [November 8th, 2009]
- Remembering Mac Tonnies - November 8th, 2009 [November 8th, 2009]
- Link dump: 2009.10.24 - November 8th, 2009 [November 8th, 2009]
- Link dump: 2009.10.26 - November 8th, 2009 [November 8th, 2009]
- The Bright Side of Nuclear Armament - November 8th, 2009 [November 8th, 2009]
- Grieving chimps - November 8th, 2009 [November 8th, 2009]
- Elephant prosthetic - November 8th, 2009 [November 8th, 2009]
- Mass produced artificial skin to replace animal testing - November 8th, 2009 [November 8th, 2009]
- Dog gets osseointegrated prosthetic - November 8th, 2009 [November 8th, 2009]
- NASA Shuttle-derived Sidemount Heavy Launch Vehicle Concept - November 8th, 2009 [November 8th, 2009]
- Link dump for 2009.02.02 - November 8th, 2009 [November 8th, 2009]
- Link dump for 2009.11.04 - November 8th, 2009 [November 8th, 2009]
- Link dump for 2009.11.05 - November 8th, 2009 [November 8th, 2009]
- IEET's Biopolitics of Popular Culture Seminar - November 8th, 2009 [November 8th, 2009]
- Einstein and Millikan should have done a Kurzweil - November 8th, 2009 [November 8th, 2009]
- Affective Death Spirals - November 8th, 2009 [November 8th, 2009]
- Cure aging or give a small number of disabled people jobs as janitors? - November 8th, 2009 [November 8th, 2009]
- Would unary notation prevent scope insensitivity? - November 8th, 2009 [November 8th, 2009]
- Cure aging or give a small number of disabled people jobs as janitors - unary version. - November 8th, 2009 [November 8th, 2009]
- At SENS4, Cambridge, UK - November 8th, 2009 [November 8th, 2009]
- SENS4 overview and review - how evolution complicates SENS, and why we must try harder - November 8th, 2009 [November 8th, 2009]
- SENS4 top 10 photos - November 8th, 2009 [November 8th, 2009]
- My AI research for this year - November 8th, 2009 [November 8th, 2009]
- My AI research: Formal Logic - November 8th, 2009 [November 8th, 2009]
- My AI research: Category theory and institution theory - November 8th, 2009 [November 8th, 2009]
- My AI research: The Semantic Web - November 8th, 2009 [November 8th, 2009]
- My AI research: Features and Flaws of Logical representation - November 8th, 2009 [November 8th, 2009]
- My AI research: Graphical models and probabilistic logics - November 8th, 2009 [November 8th, 2009]
- Hughes and More engage Italian Catholicism: Image caption competition - November 8th, 2009 [November 8th, 2009]
- Surprisingly good solutions, falling in love and life in a materialistic universe - November 8th, 2009 [November 8th, 2009]
- What do you get when you cross slightly evolved, status seeking monkeys with the scientific method? - November 8th, 2009 [November 8th, 2009]
- Seeking the optimal philanthropic strategy: Global Warming or AI risk? - November 8th, 2009 [November 8th, 2009]
- Machine Learning - harbinger of the future of AI? - November 8th, 2009 [November 8th, 2009]
- At the Singularity Summit in NYC - November 8th, 2009 [November 8th, 2009]
- Katja Grace: world-dominating superintelligence is "unlikely" - November 8th, 2009 [November 8th, 2009]
- Normal Human Heroes on "Nightmare futures" - November 8th, 2009 [November 8th, 2009]
- Anissimov on Intelligence Enhancement - November 8th, 2009 [November 8th, 2009]
- Yudkowsky on "Value is fragile" - November 8th, 2009 [November 8th, 2009]
- Response to Pearce - November 8th, 2009 [November 8th, 2009]
- Creative thinking lets you believe whatever you want - December 13th, 2009 [December 13th, 2009]
- Let’s get metaphysical: How our ongoing existence could appear increasingly absurd - December 13th, 2009 [December 13th, 2009]
- Linda MacDonald Glenn guest blogging in November and December - December 13th, 2009 [December 13th, 2009]
- Link dump for 2009.11.15 - December 13th, 2009 [December 13th, 2009]
- Call 1-800-New-Organ, by 2020? - December 13th, 2009 [December 13th, 2009]
- IBM's claim to have simulated a cat's brain grossly overstated - December 13th, 2009 [December 13th, 2009]
- John Hodgman pulls off Fermi Paradox schtick - December 13th, 2009 [December 13th, 2009]
- Deus Sex Machina - December 13th, 2009 [December 13th, 2009]
- How Americans spent themselves into ruin... but saved the world - December 13th, 2009 [December 13th, 2009]
- I am my own grandpa (or grandma)? - December 13th, 2009 [December 13th, 2009]
- Link dump for 2009.11.29 - December 13th, 2009 [December 13th, 2009]
- The art of Tomas Saraceno - December 13th, 2009 [December 13th, 2009]
- Link dump: 2009.12.05 - December 13th, 2009 [December 13th, 2009]
- The Harmonic Convergence of Science, Sight, & Sound - December 13th, 2009 [December 13th, 2009]
- Working on my website - December 13th, 2009 [December 13th, 2009]
- Transhumanism, personal immortality and the prospect of technologically enabled utopia - December 13th, 2009 [December 13th, 2009]
- RokoMijic.com is up - December 13th, 2009 [December 13th, 2009]
- Why the Fuss About Intelligence? - December 13th, 2009 [December 13th, 2009]
- Initiation ceremony - December 13th, 2009 [December 13th, 2009]
- Birthing Gods - December 13th, 2009 [December 13th, 2009]
- 11 core rationalist skills - from LessWrong - December 13th, 2009 [December 13th, 2009]
- The best of the guests - December 13th, 2009 [December 13th, 2009]
- The best of Sentient Developments: 2009 - December 13th, 2009 [December 13th, 2009]
- Link dump: 2009.12.15 - December 15th, 2009 [December 15th, 2009]
- The Utopia Force - December 22nd, 2009 [December 22nd, 2009]
- Avatar: The good, the bad and ugly - December 23rd, 2009 [December 23rd, 2009]
- Singularity Institute launches "2010 Singularity Research Challenge" - December 24th, 2009 [December 24th, 2009]
- Transhumanism as a "nonissue" - December 24th, 2009 [December 24th, 2009]
- Hanson on "Meh, Transhumanism" - December 25th, 2009 [December 25th, 2009]
- Merry Newtonmas from Transhuman Goodness - December 25th, 2009 [December 25th, 2009]