New Estimate on likely no. of alien civilisations in our galaxy

Elckerlyc

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To quote from this article: “They would be quite far away … 17,000 light years is our calculation for the closest one,”

Contactable? How are we going to contact these civilizations? Any Q&A will take 34000 years. Our civilization will be gone before the answer arrives. And all this doesn't answer the question were all the life-signs from older civilizations are.
This number is so theoretical, it's basically meaningless. IMHO.

I'm disappointed it's not 42...
Likewise! It must be an error...
 

Justin Swanton

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The real problem is the impossibility of communicating with any hypothetical alien civilisations should they arise. The laws of physics apply everywhere in the universe: there is a draconian limit to how far communication signals can be transmitted and still be discernible against background radiation. Military radars - each costing hundreds of millions of dollars - are by far the most powerful signal transmitters ever constructed, nonetheless their maximum range is about 200 light years. And we're talking about hypothetical civilisations living thousands of light years away. So in all probability, even if they are talking to us we will never hear them.

Sure, we could beggar the world economy by building a far more massive transmitter, but why would we do that? It would take centuries or millennia to get a reply and by then the civilisation that constructed the transmitter will be long gone. Technological advances aren't going to change things - a powerful signal needs a powerful energy source, no matter how sophisticated the tech. You could try the Moties' lasers, but they need to be aimed at a single planetary system that also isn't too far away. Which one if you don't already know where life is?

Sorry about the cold water. :(
 
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Astro Pen

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Despite the fact that it negates half my literary output I suspect that their figure is out by 35.
You need a lot more than mere habitable zones and active biology.
Opposable thumbs, farming, a sweet spot oxygen level that supports fire but doesn't torch everything and a Francis Bacon, to name a handful from thousands.
Of course it is possible that herds of wildebeest will eventually produce aluminium alloys, calculus and semiconductors but I'm not banking on it :)
 

Ori Vandewalle

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I don't think we know the full breadth of possible conditions that could support intelligent life. We know present Earth is in the space of possible conditions, but N=1 statistics are notoriously poor.
 

Ori Vandewalle

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Reading through the paper, most of the work is in calculating the current number of high metallicity stars more than 5 billion years old and the number of Earth-like planets in the habitable zone of said stars. The former they estimate by looking at the star formation history of other galaxies (mirroring our own galaxy at younger ages). The latter comes from Kepler data.

The "Astrobiological Copernican Principle" isn't the main thing; it basically amounts to setting the "fraction of habitable planets that give rise to aliens with radios" terms from the Drake equation to 1. They're pretty upfront about the limits of the whole approach, though. From the paper: "The traditional approach toward examining whether CETI have formed in the Galaxy has been proposed through the use of the Drake equation (Drake 1965). This has remained the primary method for inferring the likely number of CETI in our Galaxy, yet it is fundamentally an unsolvable equation (prior to any extraterrestrial life being found)."
 

Biskit

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Our civilization will be gone before the answer arrives.
I'm sorry, that's just the reality of any customer help-line.

"Welcome to the Zargian Empire. Your call is important to us and you are 16,000 lightyears into the queue. If your enquiry is not urgent, press one now and a warship will get back to you as soon as it is available..."
 
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