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  #1  
Old 11-30-2011, 03:54 AM
IMfez IMfez is online now
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What is the most accurate estimate of life in the galaxy/universe?

I've read that Drake formed his famous equation to get people talking about the subject, not for actual use to make serious predictions.

Is there a more refined equation for estimating the amount of intelligent aliens in the galaxy/universe?
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  #2  
Old 11-30-2011, 05:22 AM
coremelt coremelt is offline
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AFAIK, the most accurate estimates you'll get will still vary between 1 intelligent species (eg us), and 10s of thousands across the Galaxy.

The discovery of many many exoplanets by the Kepler Space Observatory, including ones in the Goldilocks zones where liquid water would exist within 50 light years means that simple life must be very very common in the Galaxy.

But for an intelligent, technology using species, there is too many unknowns about the bottlenecks in evolution of species and civilizations to do more than take a wild ass guess at the percentage of those planets that go onto develop civilizations and the length of time that technological species last for.

Read the wikipedia article on the Fermi Paradox for some pretty depressing reasons on why we may very well be the only technology using species in the Galaxy at this moment in time.
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Old 11-30-2011, 05:26 AM
Alka Seltzer Alka Seltzer is offline
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No. The Drake equation is a good way or framing the question, but right now we have a sample size of 1 (life on Earth), and it's not possible to draw any firm conclusions from that. However, I do expect we'll make some progress on filling in it's parameters a little more within my lifetime. We are getting better at detecting exoplanets, and can expect to make some progress on the question of whether life has developed elsewhere in the solar system or not.
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Old 11-30-2011, 07:48 AM
clairobscur clairobscur is online now
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Quote:
Originally Posted by coremelt View Post
The discovery of many many exoplanets by the Kepler Space Observatory, including ones in the Goldilocks zones where liquid water would exist within 50 light years means that simple life must be very very common in the Galaxy.
.
I don't think it means that. We have no clue how likely it could be for "simple life" to appear, even granted ideal conditions (and in fact Earth might not provide "ideal" conditions, either. I think that only 20 years ago, the idea that life could thrive in the hellish conditions of the oceanic vents would have surprised many).
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Old 11-30-2011, 08:08 AM
coremelt coremelt is offline
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Originally Posted by clairobscur View Post
I don't think it means that. We have no clue how likely it could be for "simple life" to appear, even granted ideal conditions (and in fact Earth might not provide "ideal" conditions, either. I think that only 20 years ago, the idea that life could thrive in the hellish conditions of the oceanic vents would have surprised many).
The Kepler Exoplanet Survey has found two planets in the Goldilocks zone liquid water range out of 200 exoplanets found and 40 percent of stars surveyed have had exoplanets discovered. Then I'm using this:
"In 2002, Charles H. Lineweaver and Tamara M. Davis (at the University of New South Wales and the Australian Centre for Astrobiology) estimated fl as > 0.13 on planets that have existed for at least one billion years using a statistical argument based on the length of time life took to evolve on Earth.[17]*

So estimate of amount of planets with simple life in the Galaxy:

100 billion x 0.4 x 0.005 x 0.13 = 26 Million or more.

All of the above factors of the drake equation we can work out to some degree scientifically, it's the later factors of the Drake equation about evolution of simple life into intelligence that we have nothing to work with except us.

*^ Lineweaver, C. H. & Davis, T. M. (2002). "Does the rapid appearance of life on Earth suggest that life is common in the universe?". Astrobiology 2 (3): 293–304. arXiv:astro-ph/0205014. Bibcode 2002AsBio...2..293L. doi:10.1089/153110702762027871. PMID 12530239.

Last edited by coremelt; 11-30-2011 at 08:10 AM..
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  #6  
Old 12-01-2011, 07:06 PM
Trinopus Trinopus is offline
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Another thing a lot of people seem to overlook (in my experience in similar discussions) is that the Drake Equation is a tautology. It is "true" by definition, since many of the terms are variables with no fixed values.

For instance, you could about as easily say, "The number of people striking it rich gambling at Las Vegas equals the number of people who gamble at Las Vegas times the odds of a gambler striking it rich." (The joy, here, is that all three terms can be scientifically approximated.)
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Old 12-01-2011, 10:55 PM
clairobscur clairobscur is online now
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Originally Posted by coremelt View Post
Then I'm using this:
"In 2002, Charles H. Lineweaver and Tamara M. Davis (at the University of New South Wales and the Australian Centre for Astrobiology) estimated fl as > 0.13 on planets that have existed for at least one billion years using a statistical argument based on the length of time life took to evolve on Earth.[17]*

.

You can't make statistics with a sample of one. It doesn't matter how long it took for life to appear on Earth, since we don't know whether the likelihood of it appearing at all was 75% or one chance in a quintillion.
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Old 12-01-2011, 11:18 PM
coremelt coremelt is offline
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Originally Posted by clairobscur View Post
You can't make statistics with a sample of one. It doesn't matter how long it took for life to appear on Earth, since we don't know whether the likelihood of it appearing at all was 75% or one chance in a quintillion.
The full paper is here, have at it if you want:
http://www.mso.anu.edu.au/~charley/p...eaverDavis.pdf

It's estimated that abiogenesis occurred very rapidly (in geological timeframes) after the late heavy bombardment finished, possibly within 10's of millions of years.
Chemistry is the same everywhere, anywhere there is liquid water and volcanic activity you've got the building blocks for life, given time abiogenesis will happen.

The recent discoveries from Kepler seems to indicate that there is likely to be plenty of planets in the liquid water habitable zone, so to me together with the rapid timeframe for abiogenesis on earth that seems pretty convincing.
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  #9  
Old 12-02-2011, 12:30 AM
Little Nemo Little Nemo is offline
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The most accurate estimate is that we are 100% certain there is life in the universe. The accuracy of all other estimates goes down from there.
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  #10  
Old 12-02-2011, 03:43 PM
Chronos Chronos is offline
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You can in fact learn something from how quickly life formed on Earth, but in a proper Baysian analysis, you can't actually learn all that much, since it depends very much on what priors you use.
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  #11  
Old 12-02-2011, 04:01 PM
dracoi dracoi is offline
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Quote:
Originally Posted by coremelt View Post
It's estimated that abiogenesis occurred very rapidly (in geological timeframes) after the late heavy bombardment finished, possibly within 10's of millions of years.
Chemistry is the same everywhere, anywhere there is liquid water and volcanic activity you've got the building blocks for life, given time abiogenesis will happen.
But some of the people who discuss the impact theory for forming the moon also imply that this impact was a vital component for life on Earth. It blasted off a "dead" crust and put an unusually large moon in a close orbit, perfect for stirring up early oceans.

So... is it 10s of millions of years after any heavy bombardment phase or is it 10s of milliosn of years after a particular one-in-a-billion bombardment event with unique characteristics?

(or, in other terms: the fact that Joe became a millionaire just days after buying a lottery ticket tells us virtually nothing about lottery tickets in general.)
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