Subject: Re: Possible solution to Fermi's Paradox?

David Blenkinsop (
Wed, 27 Jan 1999 08:59:25 -0600

On Fri, 22 Jan 1999, Scott Badger ( wrote:
>Ken Kittlitz <> wrote:
>>>New Scientist
>>>Cataclysmic Explosions May Have Held Up Alien Visitors
>>>GAMMA-RAY bursts -- incredibly powerful explosions that may be caused
>>>by collisions between collapsed stars -- could solve one of the oldest
>>>riddles about extraterrestrial civilisations: why haven't they reached
>>>Earth already? After studying the effects of gamma-ray bursts on life,
>>>an astrophysicist has concluded that aliens may have just started to
>>>explore their galaxies.
>>>The rate of GRBs is about one burst per galaxy every few hundred
>>>million years. But Annis says theories of GRBs suggest the rate was
>>>much higher in the past, with galaxies suffering one strike every few
>>>million years -- far shorter than any plausible time scale for the
>>>emergence of intelligent life capable of space travel. That, says
>>>Annis, may be the answer to Fermi's question. "They just haven't had
>>>enough time to get here yet," he says. "The GRB model essentially
>>>resets the available time for the rise of intelligent life to zero each
>>>time a burst occurs."
>Fascinating idea, but this is where I get lost. If the clock is currently
>reset every few 100 million years, how could we still be here? Hasn't life
>been evolving here for more than a couple billion years now?

What makes this interesting is that this idea may imply that we are just extremely lucky to have gotten as far as we have, and would help to explain the seeming lack of successful galaxy colonizers coming in towards us from intergalactic distances. Notice, though, that this by itself doesn't seem so helpful for explaining why we haven't seen any ET's starting a wave of colonization from relatively nearby locations within our galaxy. Presumably, any nearby settlement-wave builders would benefit just as much from the absence of a galaxy-wide catastrophe as we apparently have.

>I would like to hear Robin Hanson's take on this new theory.

One article of Hanson's, "The Great Filter -- Are We Almost Past It", is an interesting rundown of some of the other, more local obstacles that could get in the way of evolution, and help to account for a seeming dearth of ET's. If we've just narrowly escaped being killed off by a lot of Nature's "filters", and that's the reason why no ET's, it could make a lot of sense to add this galaxy-wide GRB filter to the list of things that can go wrong. It certainly seems a discouraging theme for SETI searchers, though, unless there's some reason why planet-bound ET's would be a lot more likely to survive, to then beam their radio messages at us? Maybe large planets with dense atmospheres naturally shield their inhabitants from radiation much better, while those large-sized planetary gravity wells prevent most surviving ET's from getting into space?

Since Robin Hanson has been mentioned, maybe this would be a good time to ask a question about *another* ET article of his, "Burning the Cosmic Commons: Evolutionary Strategies for Interstellar Colonization". This article presents a novel approach to the lack of ET's by saying that they could perhaps have gone right *past* our intersteller locality, missing us, and our solar system *completely* in a hasty "rush" of an expansion wave. In this scenario the resources they need to expand rapidly have somehow been used up, so presumably star systems fairly near to us might be depleted in whatever-it-is that they need to keep their civilization going? Supposedly, they've never returned from that great expansion wave front, figuring that our locality is used up, or burnt out, so in this concept *that's* why no obvious ET settlements!

My question here, is whether this abstract "Burning the Commons" concept, or study, has any real meaning, in terms of the actual resource that would be depleted? I mean, just what could possibly be so important that it would get used up, and prevent really expansive ET's from gradually expanding into all available niches, including our solar system? For instance, one "life essential" resource that comes to my mind is *phosphorus*, but I can't imagine why phosphorus atoms would actually be destroyed by ET settlers? Actually, I suppose that's two questions: first, any reason why nearby ET's couldn't be communicative, but planet-bound, and, second, what's burned in the "Burning the Commons" scenario?

David Blenkinsop <>