Tropical Saturn.  Image credit:  Columbia University

The Odds of Intelligent Life in the Universe

Article Updated: 24 Dec , 2015

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When it comes to contemplating the state of our universe, the question likely most prevalent on people’s minds is, “Is anyone else like us out there?” The famous Drake Equation, even when worked out with fairly moderate numbers, seemingly suggests the probable amount of intelligent, communicating civilizations could be quite numerous. But a new paper published by a scientist from the University of East Anglia suggests the odds of finding new life on other Earth-like planets are low, given the time it has taken for beings such as humans to evolve combined with the remaining life span of Earth.

Professor Andrew Watson says that structurally complex and intelligent life evolved relatively late on Earth, and in looking at the probability of the difficult and critical evolutionary steps that occurred in relation to the life span of Earth, provides an improved mathematical model for the evolution of intelligent life.

According to Watson, a limit to evolution is the habitability of Earth, and any other Earth-like planets, which will end as the sun brightens. Solar models predict that the brightness of the sun is increasing, while temperature models suggest that because of this the future life span of Earth will be “only” about another billion years, a short time compared to the four billion years since life first appeared on the planet.

“The Earth’s biosphere is now in its old age and this has implications for our understanding of the likelihood of complex life and intelligence arising on any given planet,” said Watson.

Some scientists believe the extreme age of the universe and its vast number of stars suggests that if the Earth is typical, extraterrestrial life should be common. Watson, however, believes the age of the universe is working against the odds.

“At present, Earth is the only example we have of a planet with life,” he said. “If we learned the planet would be habitable for a set period and that we had evolved early in this period, then even with a sample of one, we’d suspect that evolution from simple to complex and intelligent life was quite likely to occur. By contrast, we now believe that we evolved late in the habitable period, and this suggests that our evolution is rather unlikely. In fact, the timing of events is consistent with it being very rare indeed.”

Watson, it seems, takes the Fermi Paradox to heart in his considerations. The Fermi Paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations.

Watson suggests the number of evolutionary steps needed to create intelligent life, in the case of humans, is four. These include the emergence of single-celled bacteria, complex cells, specialized cells allowing complex life forms, and intelligent life with an established language.

“Complex life is separated from the simplest life forms by several very unlikely steps and therefore will be much less common. Intelligence is one step further, so it is much less common still,” said Prof Watson.

Watson’s model suggests an upper limit for the probability of each step occurring is 10 per cent or less, so the chances of intelligent life emerging is low — less than 0.01 per cent over four billion years.

Each step is independent of the other and can only take place after the previous steps in the sequence have occurred. They tend to be evenly spaced through Earth’s history and this is consistent with some of the major transitions identified in the evolution of life on Earth.

Here is more about the Drake Equation.

Here is more information about the Fermi Paradox.

Original News Source: University of East Anglia Press Release

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Ethan Siegel
Guest
April 19, 2008 8:31 AM
One way I like to look at it is the following: It’s a question of how many steps in the creation of humanity were “difficult” to take. Maybe it’s easy to make population I stars like ours. Maybe it’s easy to make them with planets in the habitable zone. Maybe it’s easy to get water on them. But we’re the only inner planet in our solar system with a large moon. Do we need that for life? Do we need an active magnetic field in our core, and is that rare? And the biological questions are things we just don’t know — is abiogenesis common or extremely rare? Is the evolution of intelligent tool-using life like us common… Read more »
uncledan
Member
uncledan
April 19, 2008 9:41 AM

1,000,000,000,000,000,000,000,000,000,000,000,000 stars, double that in planets conservatively. Yeah, I think there’s a good chance there’s life out there. But don’t listen to me – I’m no scientist!

corey
Guest
corey
April 19, 2008 10:22 AM

I think that life is a rare thing in the universe, but rare doesnt mean impossible. I think the best evdence we have for life is all of us and if it could happen here it could happen anywere. And with the technology we have now when we search for extra solar planets in the habitable zone were seeing them as they were millions and sometimes billions of years ago so the amount of change that happens to those planets and there solar systems could be dramatic and could lead to evoluion of intelligent life.

SkepticTim
Member
SkepticTim
April 19, 2008 10:33 AM
Brandon Carter published a paper “Five or six step scenario for evolution?” (arXiv:0711.1985v1 [astro-ph] 13 Nov 2007) last fall in which he evalluates “… the number of essential steps in our evolution that would have been hard in this sense, and to consider what those hard steps may have been, giving particular attention to the question of whether they could have included biogenisis itself…” In that paper he argues “…that we have already used up about five sixths of the originally available time before the aging Sun makes the Earth too hot….” After an elementary statistical analysis of “…the (very small) probability, P say, of ever completing the evolutionary chain – leading in the case of interest to… Read more »
Dave
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Dave
April 19, 2008 11:16 AM

I still like Carl Sagen’s observation he made in one of his Cosmos episodes… “we may be the only intelligent life in the universe…. after all somebody has to be first! I really don’t want to give up the thrill of looking for intelligent life, but as was once asked “If there is… where are they?”

Jorge
Guest
April 19, 2008 1:04 PM
I tend to think that all this is way too speculative to be of real value for the moment. We still have a LOT to learn before we can even begin to answer these questions about how many living worlds or intelligent worlds there are in the galaxy. We’re only now starting to answer some of the premilinary questions to that one, such as how common planetary formation really is, we haven’t gone much beyond hypothesis in other such questions, like how common the birth of life as we know it is when conditions are favorable. And we really have no way of knowing anything yet about the eventual emergence of intelligence in other worlds: there’s no statistical… Read more »
zeb
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zeb
April 19, 2008 2:22 PM

So, 0.01% chance of intelligent life occuring in 4 billion years. But there are at least 200 billion stars in our galaxy alone. If we assume only 1/1000 of those stars has a habitable planet, that would still lead to at least 20,000 intelligent civilizations in our galaxy.

Even if intelligent life is exceptionally rare, I think the raw numbers invovled almost guarantee some other civilizations exist.

Wheel of Fire
Guest
Wheel of Fire
April 19, 2008 3:45 PM

I tend to avoid violent idiots when I spot their location but they haven’t spotted me.

Assuming that beings who can create spacecraft are smarter than me, they probably mastered that same tendency long ago.

Earth is in intragalactic podunk. A blue cesspool of ignorance spinning around a loser star on the outer third spiral of a gigantic galaxy.

We offer the universe Playstation, aerosol cheese and internet pr0n. Why is anybody wondering why no civilization will contact us?

Polaris93
Member
April 19, 2008 11:16 PM
The idea that we are the *only* intelligent species Earth has ever birthed is an assumption made without either an undisputed, detailed definition of “intelligence,” or any assurance we would recognize other intelligent life-forms *on Earth* when we ran across them, let alone in the universe at large. Our species record of various forms of vicious bigotry toward others even of our own species says that we often have difficulty recognizing intelligence even when it’s literally right next door to us. How can we know whether there haven’t been other forms of Earthly life who were at least as intelligent as we are? Simple: *we can’t.” If there had been, say, an archosaurian civilization of some sort, now… Read more »
sofista
Member
April 19, 2008 5:12 PM

Cuando la gente contempla el estado de nuestro universo, la pregunta que probablemente se haga más a menudo es: “¿Hay alguien como nosotros en el universo?” La famosa ecuación de Drake, aun cuando se la interpreta con números bastante moderados, sugiere aparentemente que la cantidad probable de civilizaciones inteligentes y que se comunican podría ser muy elevada. Pero […] Fuente: Nancy Atkinson para Universe Today.

robbinewman
Member
robbinewman
April 20, 2008 12:12 AM
Given that the entire observable universe is full of organic compounds and that the ‘spirit’ of life is ‘programmed’ to expand itself…I find it a given we are not alone. Its a bit like the early exploration of planet earth. Life and civilisations arose all over without the other ‘islands’ knowing anything about the other. It was only a matter of time until awareness merged the space between. Of course space is an even larger ocean but it also will be crossed and other consciousness discovered. As for myself…I can only book a ticket via my children. Another clever device that the spirit of life has set itself to handle the issue of time travel What happens to… Read more »
astronowanabe
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astronowanabe
April 19, 2008 6:20 PM

if tides are important for life to form that planet in the picture should have no problem.
although I would not want to be under that umbrella when the tide came in …

Astrofiend
Member
Astrofiend
April 19, 2008 7:10 PM

Wheel of Fire Says:
April 19th, 2008 at 3:45 pm

“Earth is in intragalactic podunk. A blue cesspool of ignorance spinning around a loser star on the outer third spiral of a gigantic galaxy.

We offer the universe Playstation, aerosol cheese and internet pr0n. Why is anybody wondering why no civilization will contact us?”

Oh, come on – we’re alright.

Michelle
Guest
Michelle
April 19, 2008 8:04 PM

You know, I got a question. Not about the article but about the pictures…

…With Saturn so close, how bad would the tides be anyway?

William Patrick Haines
Guest
William Patrick Haines
April 20, 2008 4:40 AM

The Galaxy is a huge place even if few prercent of stars have Earth like worlds that is still billions of worlds . Most have ages comparable to the sun .
With the huge distances involved communication is going to very dificult . So if radio is the only means to prove a civilazation than it might exist but you might never be able to locate it . Even comminication were possible and transmision had ceased could you really assume that the civilaztion had ended ?

Andrew James
Member
April 20, 2008 2:00 AM
Where’s Arthur C. Clarke when you need him? This “announcement” follows many scientists who are seeking their opportunity for fame, glory or notoriety. The application of the Fermi Paradox here is as irrelevant as Occam’s Razor / lax parsimoniae – which states that ; “All other things being equal, the simplest solution is the best.”) Sure it is indeed possible that intelligent life like us is rare or even that we are the only ones in the Universe, but where the actual proof? How do we come up with an experiment that can prove or disprove the theory without relying on methods akin to idle speculation. All this shows is that, considering the size and extent of the… Read more »
Irwin Weisberg
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Irwin Weisberg
April 19, 2008 11:57 PM

Don’t you think it would be prudent to find intelligent life on Earth before we go chasing around the galaxy for it?

TV Singh
Guest
TV Singh
April 20, 2008 12:08 AM
What amazes me most is not why humans are intelligent but why other species are not ??? After all a large number of these species have had more time than us on this planet so instead of using that probability theory of ‘no. of suns then onto no. of planets’ we should use that theory on no. of species(also in billions). All the other senses of sight, smell, hearing, touch etc. is prevalent in most species but why not ‘intelligence’. Evolution is based on the Darwinian principle of ‘Survival of the Fittest’ , have the other species not needed to evolve by this principle so why haven’t they evolved to our stage or is it that once we… Read more »
DaveM
Guest
DaveM
April 20, 2008 4:45 AM
Intelligence emerges when you have a species with a large developed brain, living on dry land and with a lifespan sufficiently long to use and develop that intellect. The difference between evolving say bigger sharper teeth in a carnivore for example, and evolving ever larger brains is that teeth get more effective as they get bigger – but they are still teeth – whereas the brain reaches a certain point in development – and becomes something different. It becomes the means to intelligence and not simply a central nervous system. The question is : why did our brains continue evolve to such a point that intelligence such as our own becomes a possibility? Why have a larger brain… Read more »
Underlings
Member
April 20, 2008 12:07 PM

If one accepts the validity of the Law of Accelerating Returns, then once technological civilization develops, the odds of reaching the ultimate heights of technological development within a very short time is highly likely.

Even if very few technological civilizations develop, they would likely exponentially expand outward from their planet of origin, and populate the galaxy in a relatively short time.

The fact that it appears not to have happened yet belies that notion…unless we happen to be the first…which seems to be rather long odds itself.

Conclusion: Who the hell knows?

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