Re: Possible solution to Fermi's Paradox?

Scott Badger (
Fri, 22 Jan 1999 19:38:11 -0600

Ken Kittlitz <> wrote:

&gt;>New Scientist
>>Claire Bowles,, 44-171-331-2751
>>Barbara Thurlow, New Scientist Washington office
>>Tel: 202-452-1178 or email
>>EMBARGOED FOR RELEASE: January 20, 1999, 2 p..m. EST
>>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.
>>Enthusiasts for the existence of extraterrestrials have long been
>>haunted by a simple question supposedly posed by the Nobel prizewinning
>>physicist Enrico Fermi around 1950. Fermi pointed out that the Galaxy
>>is about 100 000 light years across. So even if a spacefaring race
>>could explore the Galaxy at only a thousandth of the speed of light, it
>>would take them just 100 million years to spread across the entire
>>Galaxy. This is far less than the Galaxy's age of about 10 billion
>>So if ETs exist in the Milky Way, where are they? Maybe they don't
>>share the human urge to explore. Or perhaps there's another reason,
>>says James Annis, an astrophysicist at Fermilab near Chicago. He thinks
>>cataclysmic gamma-ray bursts often sterilise galaxies, wiping out life
>>forms before they have evolved sufficiently to leave their planet
>>(Journal of the British Interplanetary Society, vol 52, p 19). GRBs are
>>thought to be the most powerful explosions in the Universe, releasing
>>as much energy as a supernova in seconds. Many scientists think the
>>bursts occur when the remnants of dead stars such as neutron stars or
>>black holes collide.
>>Annis points out that each GRB unleashes devastating amounts of
>>radiation. "If one went off in the Galactic centre, we here two-thirds
>>of the way out on the Galactic disc would be exposed over a few seconds
>>to a wave of powerful gamma rays." He believes this would be lethal to
>>life on land.
>>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?

>>Paul Davies, a visiting physicist at Imperial College, London, says the
>>basic idea for resolving the paradox makes sense. "Any Galaxy-wide
>>sterilising event would do," he says. However, he adds that GRBs may be
>>too brief: "If the drama is all over in seconds, you only zap half a
>>planet. The planet's mass shields the shadowed side." Annis counters
>>that GRBs are likely to have many indirect effects, such as wrecking
>>ozone layers that protect planets from deadly levels of ultraviolet
>>Annis also highlights an intriguing implication of the theory: the
>>current rate of GRBs allows intelligent life to evolve for a few
>>hundred million years before being zapped, possibly giving it enough
>>time to reach the spacefaring stage. "It may be that intelligent life
>>has recently sprouted up at many places in the Galaxy and that at least
>>a few groups are busily engaged in spreading."

Huh? If all lfe is destroyed by the GRB, _and_ life starts up again on the planet, a few hundred million years isn't going to be enough time for space faring levels of intelligence to arise, is it?

Surely this fact did not escape him. So what aspect of his theory am I not getting?

Besides, Jay Gould once stated that the contingency based character of natural selection was such that if evolution were replayed millions of times,
intelligence would not appear on the planet. This was in stark contrast to my up-till-then cherished theory that attributes such as increased levels of awareness, neural comlexity, and consciousness would have good survival value. Point being, Dr. Annis seems to assume that if life appears on a planet, intelligent life is a highly probably outcome. Gould assumes the opposite.

I happen to think there's a good chance that humans are quite alone. In fact, I hope it's the case. Even if another intelligence does exist and comes across us, I seriously doubt it will be organic. And I don't want us to be found by an SI probe.

Anyone see the Babylon 5 episode where a probe appeared and gave the commander a list of 100(?) questions and if they answered all 100 correctly, it would not blow up and destroy the station because only the most intelligent
species would be allowed to live? Turns out the probe's true mission was to destroy any species that succeeded. Just another possible filter out there, I guess.

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

>>Author: Robert Matthews
>>New Scientist magazine issue 23rd Jan 99


Scott Badger