Are we Alone in the Universe?

Who today can answer to this question in the affirmative? A question which underlies another one: are we visited by extraterrestrial intelligences? And how could we estimate this probability?

On the occasion of the release of Nathalie Cabrol's book "Dawn of New Horizons", she is regularly asked by the media: "Reading you, we would not be alone in the universe?"

This simple question sets minds on fire: anything can be imagined!

Indeed, does it evoke the simple "extraterrestrial life", "extraterrestrial intelligences" or even "extraterrestrial intelligences that have evolved to form civilizations capable of coming to us"? Music.

In the public's ear, it goes without saying that the latter option is the preferred choice.

And when Nathalie Cabrol begins to answer in the affirmative, it creates some excitement. Fortunately, she immediately specifies the meaning and limits with all the necessary caution and rigor.

We must admit that this - after all classic - question "Are we alone in the universe?", refers to the sulfurous idea that there is a bridge between the possibility of "extraterrestrial life" and that of "extraterrestrial visits to Earth".

It creates a bridge between two shores: the first one on which a still fledgling science - that of astrobiology - is being built, and the second one on which a new science - that of the research and detection of traces of intelligent life - will soon be deployed on and around Earth!

Why and how could such a conceptual leap be justified?

To see more clearly, we can decompose this question, a bit like a game of Russian dolls:

1_LIFE From the existence of " extraterrestrial life "⇒
2_INTELLIGENCE We can assume the existence " of extraterrestrial intelligences ", and from there, ⇒
3_TRAVEL We can assume the existence " of extraterrestrial intelligences capable of coming to visit us ".

[1] makes possible [2] which makes possible [3]. Following this logic, it is possible to rephrase "the equation" of Frank Drake to calculate the number of civilizations that may be visiting us and that may be observed on Earth. What I propose in blue in the following diagram:

"The" Drake equation with its adaptation to calculate the number of extraterrestrial civilizations visiting us. Click to zoom.

This formula approaches our three steps as follows:

1_LIFE The calculation N_e of the number of planets hosting life in our galaxy. N_e is the domain of study of astrobiology:

N_e = R_* × f_p × n_e × f_e

2_INTELLIGENCE The calculation N_e × f_i of the number of planets hosting life in our galaxy that have seen the emergence of civilizations:

N_e × f_i = R_* × f_p × n_e × f_e × f_i

3_TRAVEL The calculation of the number of planets hosting life in our galaxy that have seen the emergence of civilizations capable of intergalactic travel:

N_e × f_i × f_t

The similarity with "the equation" of Drake stops at the second step [2]:

Indeed, the f_c variable proposed by Frank Drake, that is, the fraction of civilizations that emit detectable signals, could very well be close to zeroMichael Vaillant

And that would be quite wise on "their" part: recall the cautious statements of Stephen Hawkings about our own attempts at communication that he considered potentially dangerous. Thus, advanced civilizations could very well explore the galaxy and even come to visit us without us being able to detect them in any way because they would not allow it. The prudent scheme would be:

i/ Observation → ii/ Analysis and understanding → iii/ (if relevant) Communication and exchange

Without even mentioning the inevitable coordination of these civilizations among themselves that, before any potential "interference", would consist in anticipating and anticipating the nature of the exchange protocol. In short, any possible contact will not be "Star Wars"!

To be complete, we will have to adjust the values above by a parameter L', the observability window of humanity. Thus, N_v The number of extraterrestrial civilizations visiting Earth and observable through this window could finally be written as:

VISITS : N_v = N_e × f_i × f_t × L'

This formula obviously calls for research on Unidentified Aerospace Phenomena (UAP), if we make the assumption that some of these UAP are of non-Earthly origin. N_v is then resolved more directly as a fraction of the number of observed UAP. A subject that I will come back to.

And, this is one of the reasons why, inevitably, the field of research related to the study of UAP should sooner or later intersect with that of astrobiology.

Meanwhile, as this field emerges and finds its bearings, we finally realize that what is very far from us in interstellar space [1], yet inaccessible, seems mentally much more accessible than what is just around us [3]: "Out of sight, out of mind"!

As if the philosophical idea of detecting life bricks located hundreds of light-years away [1] and now structured signals through SETI [2] was abstract and distant enough not to (too much) move the scientific community and thus be made acceptable.

While the third option [3], although more disruptive, is certainly the easiest to resolve!

In fact, detecting intelligent signals hundreds of light-years away [2] is no small feat: you have to use powerful telescopes & radio telescopes, scan many wavelengths and many regions of space in the hope of finding a "structured" signal. And without certainty of getting anything if it turns out that f_c ≈ 0.

Despite this difficulty, SETI-type programs have had the merit of existing since the early 1960s.

Interestingly, setting up a research program to cover our Earth environment [3], much more accessible to observation programs, has never been done.

We will have to wait until the 2020s for such programs to be undertaken

We can imagine that this glaring absence is explained by the fact that it requires accepting that Unexplained Phenomena can cross in the terrestrial environment. And this conceptual leap that many scientists cannot yet accept: daring to address the issue of 'UFOs' or 'UFOs' can lead to ostracism and cut short any possibility of publication or professional advancement. Still for a few more years probably.

I remember, in recent times, scientists being able to produce perfectly serious papers such as that of Ian Crawford in the journal Pour la Science 275: "Where are they?", in connection with the Fermi Paradox.

Calculating that if any intelligent life had emerged in our galaxy, it would have in less than 3.75 million years colonized the entire galaxy and reached our stellar position, we would have necessarily seen them. We do not see them (#bias), so they do not exist! QED!

Or more contemporarily, Jean-Pierre Bibring who in his book "Seuls dans l'univers" defends the theory of the "rare Earth": life is an improbable accident. The default reflex is anthropocentric withdrawal, while history should carry us lessons about this. And we see how these certainties have since exploded with the growing number of exoplanet discoveries.

What has always surprised me in this type of reasoning is:

To presume that these "intelligences" would necessarily want to show themselves and/or communicate. As seen above, the relevance of the variable f_c of Drake's equation is nonetheless very debatable.
To never mention observations of unexplained aerial phenomena, as if they did not exist!

For a number of scientists the hypothesis of a possible relationship between the Fermi Paradox and UAP or UFOs is not even an optionMichael Vaillant

Fortunately, mental barriers are falling. It's time. On the one hand, thanks to scientific progress made in Astrobiology [1], on the other hand, thanks to a better taking into account of witnesses: the use of a more neutral semantics ( "UAP" replaces "UFO" progressively), to the protection of witnesses and a rise in media and political interest in these subjects.

Probably soon the subject will become 'hype' and we will see many people telling us 'They knew it well!...'