A Further Look at Galactic Catastrophism

by Paul Gilster on September 20, 2006

Galactic catastrophism — the idea that certain kinds of cosmic events can destroy life on a periodic basis and prevent the emergence of technological civilizations — comes in a number of variants. And some catastrophe theorists believe such events don’t necessarily rule out species survival because their effects change over time. As we saw yesterday, Israeli theorist Itzhak Shechtman believes super-civilizations do arise despite the hazards of periodic extinctions, and argues that we may well find traces of their activities.

I return to Shechtman today because his paper crystallizes this interesting debate, especially when we turn to gamma-ray bursts (GRBs) as the agent of catastrophe. Shechtman examines the work of James Annis, who speculated in 1999 that although gamma-ray bursts could be deadly, their rate of occurrence declines over time. If this is the case, the universe may move into a ‘phase transition’ when the time between GRBs comes to equal the time needed for the emergence of intelligence. Suddenly the cosmos allows intelligent life the time to develop — we may ourselves live in that epoch.

But Shechtman questions Annis on numerous grounds and plugs different values into the variables he considers, with the result that he arrives at an interval between bursts that is 30 times longer than the time needed for the emergence of intelligent life. In which case, the idea of GRBs as a limiting factor loses force, and the Fermi question arises again: Where are these surviving civilizations? Another issue is that even when frequent, gamma-ray bursts need not reset the history of complex life to zero. Here’s Shechtman on this point:

Life on Earth has endured 5 major mass extinctions, 23 less devastating extinctions and many other upheavals in the last 570 million years. The most severe, the End Permian extinction, even liquidated 96% of all marine species and more than 75% of all vertebrate families, but did not succeed in eradicating life completely from this planet. Life held out tenaciously, modified, persisted and developed into its present state when it enjoys the luxury of searching for life on other planets! Thus, though the history of life on Earth is a single-case statistics, it nevertheless shows that life cannot be so easily reset to zero by ‘run-of-the-mill’ catastrophes.

What would make for a true life extinguisher? A massive star exploding into a supernova could do the trick for nearby civilizations. Shechtman uses the example of Eta Carinae, 100-150 times more massive than Sol; its explosion would probably doom life on planets within several hundred light years of the star. But such events in nearby space are presumably not common, and Eta Carinae is a solid 7500+ light years away. All this is part of the argument that life will survive and must be widespread, and that intelligent life’s engineering may be observable.

Centauri Dreams‘ take: An exploding Eta Carinae recalls a similar scenario in Richard Cowper’s wonderful Twilight of Briareus (John Day, 1974), in which a supernova plays havoc with the world’s weather. Cowper was actually the son of writer John Middleton Murry; his deft and evocative prose made stellar catastrophism a wrenchingly real concept. Whether supernovae, GRBs or any variety of more local events can reset life to zero remains a matter of conjecture, but the debate is important. Either catastrophism gives us a solution to the Fermi Paradox or, if we must discount the effect of these periodic extinctions, then the Fermi question is more pointed than ever.

The Annis paper Shechtman discusses, now available here, is “An Astrophysical Explanation for the Great Silence,” JBIS 52 (1999), pp. 19-22. An abstract of the Shechtman paper is available online.

{ 10 comments }

andy September 20, 2006 at 15:42

Maybe you don’t need huge Jerry Bruckheimer catastrophes.

Perhaps the subset of habitable worlds that can give rise to a technological, let alone a spacefaring civilisation is a very small one.

A few possibilities – chaotic axial tilt variations on planets not stabilised by large orbiting satellites, chaotic orbital eccentricity variations on planets in binary systems – these would wreak havoc with the climate, making the land surface an “extreme” environment even if the oceans are relatively stable.

There’s the issue of the superflare stars. Some seemingly sunlike stars apparently undergo huge eruptions, which could strip ozone layers, generate nitrous oxides and suchlike on planets in the habitable zone. It has been suggested this may be caused by magnetic interactions with hot Jupiters.

Habitable moons of gas giants – once the civilisation pokes its nose above the atmosphere it finds itself in the radiation belts of a gas giant. And impact velocities would be higher.

Ocean worlds – difficult to see how a civilisation on such a planet could achieve high technology. What with all the simulations of high-water-content terrestrials, perhaps Earth is an unusually warm and dry habitable planet, skirting the inner edge of the habitable zone.

Adam September 20, 2006 at 18:08

Hi Andy

All those limitations are possible, but are they sufficient to suppress ETIs sufficiently? No one knows and that’s why the search is so importent.

Adam

andy September 20, 2006 at 18:34

Definitely these are only possibilities, and we definitely don’t know enough to say what regions of the parameter space permit the emergence of spacefaring civilisations. Some of those possibilities I listed I don’t think would necessarily be fatal.

Its more that I suspect that if there is some reason for the Great Silence that involves lack of ETIs rather than simply our non-detection, it derives more from the diversity of planets and planetary systems, their configurations and their evolution, than from giant catastrophic resets. Sure, some planets will suffer gigantic catastrophic events, but I’d think that would be fairly rare.

Adam September 21, 2006 at 8:05

I think it’s misrepresenting Annis’s case to describe him as saying a GRB causes total sterilisation. Disruption of the large animals would be sufficient to impede life’s production of intelligence. If so then large scale destruction of an ozone layer would suffice to kill the land-based biosphere.

And who’s to say GRBs are the only threat? Intrusions by giant molecular clouds could wreak all sorts of havoc. The 31 Myr periodicity to extinctions might be caused by such – either directly or via dislodging comets in the Oort. The terminal Permian catastrophe is yet to be explained adequately, but deoxygenation of the atmosphere played a big role. Perhaps molecular hydrogen infall caused that?

All maybes I know, but we’re faced with several far worse prospects – we’re Alone, we’re doomed, we’re soon-to-be real estate, we’re a zoo exhibit – if we’re not close to the dawn of intelligence going off world.

Adam

ljk September 21, 2006 at 10:09

The reason for the Great Silence? I can think of one which doesn’t
invoke anything all that terribly complicated: We live in a galaxy of
400 billion stars across 100,000 light years of space. Get beyond a
few dozen parsecs and our “mighty” Sun would be a blip in anyone
else’s night sky.

Our radio and TV signals have barely created a sphere outward of
200 light years across (and most of them are faint). Our farthest
space probes have barely left ill-defined borders of our Sol system
and would need about 77,000 years just to get to the next nearest
star.

This alone makes us hardly a standout amongst the heavens.
Then throw in the less tangible factors of celestial threats, the
lifetimes of unknown alien civilizations, the possibility that any
neighbors can’t, don’t, or won’t do SETI (this applies whether
they are behind or way ahead of us technologically), and the
chance that no one is near enough for us to find, and you
wonder why ETI aren’t trying to call us every day?

At our present stage of the game, I will consider it nothing
short of pure luck if we ever detect their presence. We need
to expand our search and start actually getting out there to
other star systems to even have a chance to begin. I also
seriously wonder if we are advanced enough to understand,
deal, and communicate with technologically sophisticated
ETI. We made need to make radical changes to ourselves
and our society, or wait for our next evolutionary step to
do the job right.

Adam September 21, 2006 at 23:06

Hi Larry

Personally I think we probably have a ring in the Kuiper Belt of vNMs monitoring us – and similar young civilisations – because I suspect that oxic biospheres are incredibly rare. That’s my suspicion, that most sites for interstellar expansion will be easily terraformable planets and moons, and full-blown biospheres will be treasured for their rarity.

The galaxy is potentially a nasty place and we’re lucky to be here.

Adam

Chris Phoenix September 22, 2006 at 16:47

A few months ago, my father and I came up with a new Fermi Paradox solution that is relevent here.

It’s been speculated that the parameters of the universe are evolved/optimized for maximum diversity, or maximum black hole creation (which may benefit from intelligences running physics experiments), or some such.

Given how quickly a civilization could spread out–near light speed–using small self-propagating robot probes, the first civilization in an area might well destroy the possibility of other civilizations arising anywhere in its light cone.

A lot of civilizations is more diverse than a few large civilizations. Thus, the diversity of the universe will be maximized if civilizations arise almost simultaneously, and are protected from each other by the lightspeed barrier for the first few thousand years.

All we need to implement this suggestion is a Vingean “slow zone” that the universe can emerge from, everywhere, simultaneously, allowing intelligence to spring up where it couldn’t before…

If frequent GRB’s suppress intelligent life but do not kill off all life, and the frequency of GRB’s has decreased recently, then GRB’s could easily provide a physical basis for the “slow zone.”

Chris

David Brin September 22, 2006 at 18:45

A number of Fermi Paradox related papers, including the classic “Great Silence” article, are available at: http://www.davidbrin.com/sciencearticles.html

The range of possibilities is still truly vast. We are infants in a dangerous jungle.

With cordial regards,

David Brin
http://www.davidbrin.com

Adam September 23, 2006 at 8:32

Hi David

Could be those pesky Crystal Spheres too.

I agree with you on the dangerous jungle. What do you think the current state of play is in our Galaxy? Are we close to the first to set forth on the ocean of night?

Adam

Steve October 3, 2006 at 21:22

I’m glad that Shechtman has re-evaluated Annis’ paper – his vision of a galaxy kept primordial by GRB’s means a dearth of material for xenoarchaeologists to study.

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