A Possible Answer to Fermi’s Paradox: Gamma-Bursts

That's the question of Fermi's Paradox, the seemingly bizarre contradiction between some estimates of a high probability of sea-faring civilizations in the galaxy, and the complete lack of any sign of them. In other words, if there should be countless worlds out there where life evolved and intelligence could develop, then why is it none of them have ever visited Earth? It seems only natural that a civilization like our own, given enough time, would travel through the cosmos, yet, there is still no confirmable sign of them. Now, a paradox is, of course, logically unresolvable unless we adjust some the facts we assume. In this case, the previously optimistic estimates could be adjusted when you include the possibility of gamma-bursts. Indeed, the frequency of these events may well answer our puzzling paradox.

Gamma-bursts are intense flashes of highly energetic gamma-rays unleashed during a supernova explosion, perhaps one of the most catastrophic phenomena in the universe. This extreme radiation has been suggested as possibly initiating the late Ordovician extinction event on Earth in the deep past, and possibly threaten Earth's future. When the beams arrive, they would affect the atmosphere on a chemical level, depleting the ozone and subsequently have lasting impacts on the food chain and biosphere. Damage to the ozone layer increases the penetration of the far more common deadly [to life] cosmic rays which emanate throughout the galaxy. The flashes themselves could damage nature's most radiation-resistant organisms, such as the bacterium Deinococcus radiodurans, a species which is able to resist 3000 times the level of radiation that a human being can endure. A gamma-ray burst would be able to tear its genome to shreds from the inside out, and from a distance (if the planet had a thin atmosphere) of up to three times the width of our galaxy.

Clearly, these events are bad news for biased biological beings such as ourselves. If they were to happen too frequently, or at the wrong time at a critical point in a planet's evolution, they could delay the arrival of intelligence, or prevent its arrival entirely. When thinking about the likelihood of other civilizations, the frequency with which these death-rays transpire needs to be considered in conjunction with a probable timeline of the evolution of intelligence. This is exactly what cosmologist James Annis has considered. He put forward an astrophysical model of a phase transition between a time when the galaxy was devoid of intelligent life, and a time when it should be full of intelligent life. According to his data, the Milky Way galaxy is currently on the cusp of this transition towards a time that life can flourish and evolve. The idea is that we're now entering a time where the frequency of gamma-ray bursts is finally low enough to allow life more freedom to evolve, as opposed to before where the frequency was higher, and a would-be intelligent species would have been prevented from rising by the radiation onslaught. Thus, the diminishing rate of the frequencies of gamma-bursts could serve as physical mechanism that allows life to prosper.

So, according to Annis, the reason for the great silence is that intelligent life has only recently (in a cosmologic scale) been given the chance to speak. Certainly, this adjusts the premises of Fermi's Paradox, which gives a much greater timescale (in the billions and billions of years) for life to spread and contact one another. The Paradox assumes other intelligent life has had plenty of time to contact us. In reality, it could be the case that they're unable to, or just starting to explore space, or as Annis postulates, the planet they're on hasn't developed intelligence just quite yet! Developments in astrophysics shedding light on humanity's aloneness in the universe? Now that's cool stuff.

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1. Melott. A. et al. Did a gamma-ray burst initiate the late Ordovician mass extinction?. International Journal of Astrobiology 3, 55-61 (2004).

2. World Science. Death from across the galaxy. (2010)

3. Annis. J. An astrophysical explanation for the "great silence". Journal of the British Interplanetary Society. 52, 19-20 (1999).

Image credit: Dana Berry (Via NASA)