When I was doing my continuing education course in astronomy from the University of Oxford late this year (2019), we have to have to participitate in countless academic and forum discussions almost everyday before we could complete the course
In one Unit of the couse was one on Astrobiology where under this sub-unit was one on Frank Drake equation. I shall reproduce below this sub-unit:
8.6 The Drake equation
"One of the early advocates of SETI, Frank Drake, created an equation which helps you estimate the number of communicating civilizations in the galaxy. To make an estimate you need to know a large number of unknown values – so essentially the equation is structured guesswork. As we learn more about exoplanets and about life, we are able to narrow down some of the numbers, and the equation gives you a feel for how likely you are to ever communicate with aliens.
The equation gives you N, the number of communicating civilisations in the galaxy:
N = R * fp * ne * fl * fi *fc * L,
where R is the average rate of star formation in our galaxy; fp is the fraction of stars with planets; ne is the number of Earth-like planets per Solar System; fl is the fraction of those which evolve life; fi is the fraction of those that evolve intelligent life; fc is the fraction of intelligent lifeforms that develop technology for communicating with aliens; L is the lifetime of a communicating civilisation, in years.
We currently believe that R is approximately 7 stars per year. We are getting more and more data on fp and ne all the time. Whilst fl may be a small fraction, fi and fc may not be, if we think intelligence and communication are consequences of evolution. L is very hard to guess, since we are the best and only example of a communicating civilisation, and we’ve been communicating for less than 100 years!
In 1961, Drake and his colleagues came up with the following estimates for the numbers:
N = 1 * 0.25 to 0.5 * 1 to 5 * 1 * 1 * 0.1 to 0.2 * 1000 to 100,000,000 This gave Drake a value of N in the range 1000 to 100,000,000 communicating civilisations in the Milky Way."
(Source: University of Oxford)
Below was what I replied for the forum discussion
I am amazed how did Frank Drake come up with his equation when there is no data to work on to substitute into his equation.
The only world so far we know that has life on it is on this planet Earth of ours. None of the planets, dwarf planets or any other body in our own Solar System has any. So are the many and increasing numbers of exo-planets in other stellar systems being discovered has any.
In the absence on the data of life existence, how is it possible for anyone put some theoretical numbers on his equation to predict the numbers of life as we know it, let alone civilization, or even intelligent civilizations in existence in our Milky Way Galaxy?
At the moment we just have one point (Earth) to work on. We can’t do very much with just one point or a single data. We don’t even have another number to join two points together to extrapolate anything further.
Whatever cooked-up data we like to substitute into Frank Drake equation, it would just be guesswork and theoretical. This is just not scientifically real
We can of course put any numbers we like. That’s not a problem, but are they real numbers? Is that statistically correct? In statistics if we want to draw a scientific conclusion we must have as large a population as possible, the larger the numbers, the better to represent a true population.
Maybe we have some idea on R which is the average rate of star formation in our galaxy as discussed in Unit 5, and fp as the fraction of stars with planets (based on the numbers of extra solar planets we have discovered so far as argued in Unit 6).
Maybe we can even extend the equation to “ne” as is the number of Earth-like planets per Solar System based on habitable planet as discussed in 6.8 on The Goldilocks Zone.
But to go further than that, further away into the equation is a bit difficult. Even if we imagine the closest possibility we can use to substitute into the initial part of the equation, it would just be intelligent guesswork, let alone put in some theoretical or imaginary data into the full equation
We may come out with a result which may be far out from statistical reality on facts and figures
I cannot imagine how Drake and his colleagues in 1961 came up with the following estimates for the numbers as:
N = 1 * 0.25 to 0.5 * 1 to 5 * 1 * 1 * 0.1 to 0.2 * 1000 to 100,000,000 communicating civilisations in the Milky Way?
Even SETI programme with all their arrays of radio telescopes and world-wide citizen search has not shown up any intelligent life this far.
However, this does not mean there is no other life in this horrendously immense Milky Way Galaxy of ours, let alone in the entire Observable Universe.
Stand Alone World:
For us to believe we are the only world that harbours life on it, is like us standing on a vast, vast seashore of sand, and saying beneath our feet there is only one, and only grain of sand, on which surface teems tiny microbes, while all the other grains of sands as far as our eyes can see over and across the horizon are all sterile
Is that what we believe? Is that a statistically probability? We will be extremely arrogant and haughty to believe this.
What I express here in this forum is just my personal view.
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