Where are they?

Ahhh Halloween.. The only day of the year when Aliens can walk among us without go undercover. Because according to many conspiracy theory there are a lot of aliens walking among us…and not only nowadays… Ancient civilizations also had good relationships with Extra Terrestrial visitors! Thanks to this testimony now we know for sure that:

– They are mostly green and they look like humans (two eyes, two legs, two arms, etc.)
– They love Mexico and U.S. (especially large US corn fields)
– They like to move heavy stone around (building pyramids, and Stonehenge like sites)
– They like to make circles in crops…

Now., to be honest I was expecting a little more from a civilization with a technology that allow them to travel hundreds of light years and withstand heavy doses of gamma radiation..  😀

OK …Enough with mambo jumbo..but the question remain.. There are aliens out there?  Let’s analyze the problem with some scientific approach… There are about 10 billion galaxies in the observable universe! The number of stars in a galaxy varies, but assuming an average of 100 billion stars per galaxy means that there are about 1,000,000,000,000,000,000,000 (that’s 1 billion trillion) stars in the observable universe! [source: University of California]. That is definitely quite a lot of stars, so there should be a shitload of alien traffic out there!.. Also, hyper-tech civilization will also requires a lot of energy and thus we should be able to see huge mega structures around.. Yet we haven’t spotted any ET yet (a part the one in the corn fields 😀 )..

So if there should be plenty of life in the universe.. where are they? this question was firstly asked by Enrico Fermi,  and became what has been known as Fermi paradox.  Basically this paradox remark the discrepancy between the high number of expected aliens with the observation of none of them… So what is happening? Well firstly we need  to estimate the number of expected alien life.. Well, the number of alien that should be able to communicate with us should depends by three main things:

– 1 .Astrophysical factors: Number of planet that have the right conditions for sustaining life
– 2 .Biological factors: How easy to develop intelligent life on those planets
– 3. Social factor: How long the average civilization will lasts and the willing to communicate.

We can estimate how probably each of these 3 points are and then try to come out with a formula.
For point 1 (Astrophysical factors) we can estimate that the number of planet (Pl) out there that has the right condition will depend from :

Pl= R * fp * ne

Where  R = the average rate of star formation in our galaxy
f
p
= the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
Pl then should be an estimate of how many planets that support life should be out there… Just notice that the fractions can range from 0 (none of them) to 1 (all of them).

For point 2 (Biological factors) where we need to estimate number of intelligent aliens (IA) able to communicate with us  on those planet it can be something like:

 IA= Pl * fl * fi

Where Pl is the planet number that we calculated before,
f
l
= 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)

Basically we take all the habitable planet and we count only the one with life able to communicate with us..

For the point 3 (Social factor) we can estimate Sc as the fraction of the intelligent civilization willing to communicate multiplied by the the average length that they will keep trying.. So:

Sc= L * fc.

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

So if we put all together the final estimation is

                                             

And that is the famous Drake equation

According with our observations, N is 0, meaning that we did not yet met any Alien. The problem with this equation is that R is incredibly high, so for having N = 0, it means that at least one of the other variable should be 0 or very very close to it… The question is.. which one?

In 1961 when this equation was written, we really had to guess all the variable there.. but today, thanks to satellites, telescopes and similar we do have a more close idea, at least for astrophysical factors of the equation . Indeed in recent years we discovered thousands planets orbiting around stars. So essentially every star has planets, so fp is close to 1.
For ne, as today, NASA has estimated around 40 billions (40.000.000.000) habitable planets (rocky, with potential liquid water etc..). And those are only in the milky way! So ne is also pretty high.

OK, so from astrophysical point of view we are sure that the universe is full of place where life could evolve.. How about biological/social?. On how many planet the life does actually evolve? That is where we still navigate in deep dark.. We have no idea on how to estimate that… however now we are sure that is one of the factors of point 2 or 3 that is close to 0. This means that life has the right condition but fails to develop.. we can investigate this further and assume one of the two things must be true:

1. Life on other planets fails to start.. Basically despite good environment conditions, life is not able to evolve and reach the same level that we have here on earth. In this case if the Biological Factor that is near 0.

2. Life on other planets starts just fine. In many planets, life with same level as earth is very common. However, something bad happen to all of them once reached a certain point. In this case is the social factor that is near 0

This two points are known as great filters. If assumption of filter 1 is true is actually good for us.. It simply means that we do are the lucky one…among all the million planets only 1 attempt succeeded and its us! Also mean that we passed the worst part and we do not have impediments in front of us. We have the potential to be the first specie to  colonize galaxies!

On the contrary if assumption 2 is true, than is really bad for us.. It means that thousands of other civilization developed to our level but then something bad happened to all of them.. so we also should be expecting something similar…

So what between filter 1 and 2 is more likely? In the past the 1st one seemed the most supported, however a set of recent papers have put assumption 2 back into the game. In particular we should consider that more a civilization improve their technology, more likely is to get wiped out, either by accident of by deliberate actions. Indeed potentially technologies able to annihilate the full civilization became more and more accessible by more people and thus there will be at least one that will push the “red button”. Even if this technologies are kept away from mostly of the people, give it enough time and there will be at least one crazy person with the right access that will blow everything up. Example of such destructive tech could be genetically modified viruses, nuclear weapons, bio stuffs, etc.

So, we do not know yet where they are, but if the filter 2 is the cause of being alone, than we should be pretty cautious about what we do..

Oh… just a small remark for the one that believe that aliens are among us. Well, I can reply with the banner of American scientist looking for aliens: “It’s Never Aliens—until It Is”… So, this simply means that if there is another (simpler) explanation than go for that…

See you in the next article…!

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