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Doomsday survival odds improve ... slightly

Future of humanity Human civilisation has a slim chance of surviving long enough to colonise other planets, but the odds are much better than some earlier estimates, a new analysis shows.

The study, published on the pre-press website ArXiv.org, revisits a theoretical concept known as the 'universal doomsday argument'.

Previous analyses had suggested our likelihood of surviving existential threats such as asteroid stikes and pandemics were close to zero, says lead author physicist Austin Gerig from the University of Oxford.

But Gerig and cosmologists Ken Olum and Alexander Vilenkin suggest we could improve our chances of surviving into the deep future if we make a concerted effort to tackle the risks that threaten our existence and undertake serious space exploration.

The original doomsday argument predicts humanity's prospects of survival based on how many humans have lived so far, estimated to be around 70 billion. Given this figure, it estimates that there is a 95 per cent chance no more than 1.4 trillion humans will ever live. Factoring in the rate of population growth it estimates that we will reach this point within 10,000 years.

But the universal doomsday argument - which is a different model - assumes the universe is very large with many civilisations living in it, says Gerig.

"All of these civilisations, like ours, face early existential threats such as asteroid impacts [and] pandemics."

Civilisations that succumb to these threats are classified by the scientists as 'short-lived,' while those that survive these threats and potentially colonise their galaxy are 'long-lived'.

"We expect long-lived civilisations to be huge, easily containing a million times more people than short-lived civilisations."

That's because, in terms of probability, nearly all of the people who live in long-lived civilisations have already survived early existential threats and started colonising more than one planet in their galaxy.

"But this state of affairs is not our current circumstance," says Gerig.

"We don't know that we live in a long-lived civilisation. Therefore, long-lived civilisations are probably not common; they are probably quite rare."

"Unfortunately, this is bad news for us," he says. "If long-lived civilisations are rare, this universal doomsday reasoning suggests our own civilisation has poor prospects for long-term survival."

Weighing the odds

In their new paper, Gerig and colleagues finetune this gloomy prediction by weighing the probability of our civilisation will survive under different conditions such as nuclear wars, asteroid impacts, pandemics or climate change.

Crucially, they consider the possibility that the percentage of civilisations in the universe that survive long-term could be anything between zero and 100 per cent.

"Previously, the traditional doomsday argument suggested our chance of long-term survival was effectively zero," Gerig says.

"We have corrected the argument and performed a more thorough analysis to find that our actual chance of long-term survival is not zero, but perhaps somewhere between 1 per cent and 10 per cent."

These may not sound like good odds, but for Gerig and colleagues they are cause for optimism.

"This gives us hope," he says. "If most civilisations are complacent and do not take seriously the threats they face, then we can choose to be different."

"We can be the 1 per cent to 10 per cent of civilisations that devote considerable resources to confronting existential risks, and that seriously undertakes space exploration and colonisation so that even if these threats make one planet inhabitable, we would have other places to live."