Where Are All The Aliens?

Humans have always been interested in space. We gaze at the universe and wonder about our place in the stars. Alien life however is one thing that humans have always looked for. The search for extraterrestrial life has been going on for decades yet we have no conclusive evidence that aliens exist. This brings us to a paradox that is known as the Fermi paradox, named after physicist Enrico Fermi.

The Fermi Paradox

This paradox describes that apparent lack of alien life despite the high estimates supporting alien life. Consider the following points:

            – There are approximately 400 billion stars in the Milky Way galaxy with around 7×10²² stars in the observable universe.

            – A certain number of these stars would have Earth-like planets in a habitable zone.

            – As most of these stars are much older than ours and assuming that Earth is a typical planet, intelligent life may have developed there.

            – Some of these alien civilizations may be sufficiently advanced enough to allow for interstellar travel (travel between star systems)

            – Therefore, Earth should have been visited by aliens or their probes. However, no conclusive evidence of this exists.

The paradox asks, “Why is there no evidence of aliens or their artifacts on Earth, or in the Solar System?”

There is a huge number of planets in the galaxy. Even if a tiny percentage of these planets have life, then there should be life in many planets. This assumes a principle called the mediocrity principle (Earth is a typical planet).

There have been attempts to estimate the number of intelligent civilizations in the galaxy. One of the more famous estimates concerns the Drake equation.

The Drake equation was made by astronomer Frank Drake. The equation is:

N = R_*f_pn_ef₁f_if_cL

Where:

            N = number of civilizations in the galaxy with which communication may be possible

            R_* = Average rate of formation of stars in the galaxy

            f_p  = fraction of these stars that have planets

            n_e = average number of planets that can support life per star that has planets

            f₁ = fraction of n_e that actually develops life

            f_i = fraction of f₁ that develop Intelligent life

            f_c = fraction of f_i that releases signs of themselves in a detectable form

            L = length of time for which such civilizations release detectable signals to space.

The problem with the above equation is that the last four terms are completely unknown and there is no sufficiently accurate method to estimate them.Different people use different estimates for these terms but no one can accurately estimate them. Some people say that the number of such alien civilizations in the galaxy can go from 1,000 to over 100,000 while others say it would be much less.

Possible explanations to the Fermi paradox

1. Extraterrestrial life may be much rarer than thought: In most estimates the assumption that Earth is a typical planet is made. However, it is possible that this assumption is false, this is known as the Rare Earth Hypothesis, where complex life is exceptionally rare. People argue that there are a lot of conditions for life to occur, such as planet in a habitable zone, a large moon, a good atmosphere, the existence of a suitable magnetosphere, the chemistry and composition of oceans and a host of others. They say that the probability of all such conditions been met is extremely low.
2. Intelligent life may be much rarer than thought: perhaps extraterrestrial life is quite common, however they may lack the intelligence required for interstellar travel and communication. It is virtually impossible to tell whether a potentially life bearing planet has intelligent life.
3. Alien life is wiped out by extinction level events: it is possible that alien life gets wiped out by extinction level events before the lifeform is able to develop sufficiently, we all know what happened to the dinosaurs. The universe is a chaotic place and perhaps existential threats occur a lot.
4. Intelligent life has not developed enough: another possibility is that intelligent life does not have the capability to facilitate interstellar communication or perhaps they have no intention of developing such devices.
5. Intelligent lifeforms destroy themselves or others: this possibility is drawn from parts of human nature itself. History has shown that our desire to gain power has led to many destructive events. It is possible that sufficiently advanced civilizations brought about their doom through such destructive events fueled with the desire for power.
6. Aliens are too alien: current searches for aliens are based on some assumptions on the nature of these lifeforms. We assume that they communicate in human-detectable means, live in planets orbiting Sun-like stars and so forth. Perhaps alien life is very different from humans. They may communicate unconventionally using communication media we don’t even know of. Perhaps what astronomers think is background noise, it may actually be a message from alien beings.
7. We have not listened for alien signals long enough: people have being actively looking for potential alien signals for a very brief amount of time in a geological scale. Perhaps we have received signals before but we haven’t had the means to intercept them.
8. Intelligent life is too far away: consider a scenario where an intelligent civilization exists 1000 light years away. If we are to communicate with them via current technology, a signal sent from us would take 1000 years to reach them and the reply would take another 1000 years to come back. So we would have to wait 2000 years for a reply. This emphasizes the size of the universe itself. And if the distances are very long, by the time the message arrives, the alien civilization might not even exist!
9. Earth is avoided: perhaps alien civilizations are so advanced that we are treated as an experiment and the Earth, a laboratory. They may be observing us right now without us even knowing.
10. Aliens are already here: this is the one many conspiracy theorists believe. That aliens are already communicating with us but the powers that be are hiding this. The number of such theories is huge and it is clear that many people believe some of these.

The above gives an idea as to why we have not yet encountered alien life. Some say that aliens do not exist but the idea that we are the only intelligent species, living on the only inhabitable planet, in a universe so full of planets there isn’t even a number in existence to describe how many there are seems absurd.

References:

Fermi paradox – Wikipedia