Possible solution to Fermi's Paradox?

Ken Kittlitz (ken@audesi.com)
Fri, 22 Jan 1999 14:47:54 -0700

Apologies if this has already been posted; we've had spotty mail service lately.

>From: Jason McVean <jasonm@merak.com>
>To: "'dicklit@lucifer.com'" <dicklit@lucifer.com>
>Subject: dicklit: galactic sterilization
>>From Andrew Yee <ayee@nova.astro.utoronto.ca>
>New Scientist
>Claire Bowles, claire.bowles@rbi.co.uk, 44-171-331-2751
>Barbara Thurlow, New Scientist Washington office
>Tel: 202-452-1178 or email newscidc@idt.net
>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
>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."
>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."

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

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