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[escepticos] Esterilización galáctica

Para un SAL ( Sterility Asurance Level) de 10 EXP(-6), requisito
indispensable según la UNE-CEN 556 para poner en la etiqueta de un producto
médico el término *estéril*, se requiere que el dispositivo en cuestión
reciba una dosis mínima de 25Kilorads (UNE-CEN 552); en la práctica
significa una exposición de unos 30 minutos a una fuente de unos 500.000
Curios a una distancia del orden de los metros.

A partir de aquí, papel, lápiz, imaginación y una buena dosis de capacidad
adivinatoria sobre la intensidad de los picos de radiaciones gamma para ver
si tiene sentido o no hablar de esterilizaciones a escala galáctica.

Saludos,

FerPer

At 09:27 27/01/99 +0100, you wrote:
>
>Un universo esterilizado???
>
>
>>exoScience - http://www.exosci.com/
>>
>>GAMMA RAY BURSTS MAY STERLISE THE UNIVERSE
>>  from New Scientist
>>
>>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 years. 
>>
>>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 radiation. 
>>
>>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." 
>>
>>
>>David Watanabe
>>davew en exosci.com
>>
>>____________________________________________________
>>exoScience SPACE              http://www.exosci.com/
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>>Portions Copyright (c) 1998 David Watanabe
>>
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