Quote:
Originally Posted by Steven Lyle Jordan
The given definition of L does not say that, guys. It specifies the length of time one civilization exists, period. It's not enough to assume that two sufficiently long-lived civilizations will necessarily overlap just because they are long-lived. That overlap is another variable outside of L, and should be stated as such.
Of course, the whole equation is incredibly generalized anyway, so I suppose we could just break it all down to one variable Ue (for extremely unlikely)...
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Lets remove L from the equation for the moment. What we have now is an equation that expresses (on average) how many new civilizations develop the capability to send signals into space for any given time interval (Lets say per year). So, lets say (if we ever know the hard numbers) that running that calculation we discover that on average .01 civilizations are born every year.
Now back to L which is the average length of time such a civilization will broadcast signals into space. If L is relatively short, say 100 years, then on average, only one (100 * .01) such civilization will generally exist at one time. If L is larger, like 500, 1000, or 10,000 years, then we get 5, 10 or a 100 civilizations co-existing.
Now of course, these are only averages... really essentially probabilities. In all of these scenarios, it is possible that there will be periods with fewer than the expected number of civilizations and periods where there will be more, that being said, the equation, as is, gives you a very good idea of how likely it is that another civilization, capable of sending signals, exists.
The S variable you are proposing is what the Drake Equation was meant to calculate.
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Bill