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Announcements & News => Astronomy & Science => Topic started by: Ivan on August 05, 2015, 10:50:24 PM

Title: Just for fun - Drake equation
Post by: Ivan on August 05, 2015, 10:50:24 PM
Leading on from something Desp mentioned, I thought I'd post it here, as it's actually a very interesting hypothetical equation (copied across from wiki):

N = R*  fp  ne fl fi fc  L

N = the number of civilizations in our galaxy with which radio-communication might be possible (i.e. which are on our current past light cone);

R* = the average rate of star formation in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fl = the fraction of planets that could support life that actually develop life at some point
fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space[8][9]

Title: Re: Just for fun - Drake equation
Post by: Ivan on August 05, 2015, 11:04:47 PM
Recently revised in the light of modern approach towards discovering life elsewhere:

And from a purely statistical point of view, on the basis of this equation with best guesstimates, you might expect to find thousands of intelligent civilisations within our own galaxy!

However highly unlikely that life might spontaneously create itself, if it can do so, then life should be abundant in the Universe, through sheer force of numbers. However, life may be so special it has only ever been created once, here. The only hope we ever have of answering this fundamental question, is to discover unrelated life elsewhere in the universe - which is something we may never do.

Title: Re: Just for fun - Drake equation
Post by: desperate on August 06, 2015, 08:48:26 PM
I think It's a huge task searching for ET life, not only do we have few clues as to what wavelength of signals to search for nor the direction to look, but the distances make finding a signal very improbable even if there were thousands of intelligent species transmitting a signal. If the Galaxy is about 150,000 LY diameter there could easily be several thousand LY between each civilisation which means that a signal would be several thousand years old by the time we recieved it. If we were not sure it was real to confirm it would take twice that long again to send an enquiry and then recieve an answer.

The best hope is to broadcast some kind of mathmatical number such as PI and hope that someone else would pick it up and correctly interpret it, whether it comes from a long dead civilisation or not though would probably never be known. I believe we are doing just that but at the moment the signal would only have reachd 40LY distance which I guess is very unlikely to find our neighbours.


Title: Re: Just for fun - Drake equation
Post by: mespilus on August 06, 2015, 09:30:44 PM
I seem to remember a James Burke show about the Drake Theorem back in the '70's.

Aren't we in a less crowded bit of the galaxy,
so in a 'where are 'people/lifeforms' likely to be' question, we're not in the area statistics would suggest 'they' look?

Still we have been sending radiowave pollution for what, 90 odd years now,
so the time pips are getting closer to something.

Title: Re: Just for fun - Drake equation
Post by: Ivan on August 06, 2015, 11:58:23 PM
This statement is taken from the second link in my last post:

according to SDE, the average distance we should expect to find any alien intelligent life form may be 2,670 light-years from Earth. There is a 75% chance we could find ET between 1,361 and 3,979 light-years away. - See more at:

Statistics is a wonderful thing, and allows us to predict quite accurately how random stuff behaves. So according to this, we are likely to be around 2500light years from the nearest civilisation capable of broadcasting, but our best equipment will only detect signals from 500 light years or closer - so we need to be 5 times better before we are statistically likely to find anything at all.

There are scientists (eg Stephen Hawking) who suggest that we should definitely not transmit 'hello, we are here' signals - because when you bear in mind that we have only had the capability to do so for 50years or so - a mere blink of an eye in cosmological terms - any civilisation receiving the signal is statistically likely to be much older than ours - in which case if they are unfriendly, we're in trouble (and if humankind is anything to go by......). Luckily our radio light cone, being mostly omnidirectional, fades to background noise at a light year or so.