The Fermi Paradox

The Fermi Paradox

Caio Henrique Rodrigues

University of Colorado at Boulder

Abstract

        This paper briefly discusses the Fermi Paradox, possible solutions and reasonable objections against these solutions. The main focus of this paper is give the reader a good notion about this paradox. The Drake Equation is introduced on section 2  basically to demonstrate a simple example of how scientists try to evaluate the probabilities for radio-contact with ETI and the following sections explain the contradiction between these estimatives and the lack of evidences of ETI.

1. Introduction

        The humanity reflects about extraterrestrial life since the Greek antiquity. One of the strongest arguments for the existence of inteligent life forms beyond Earth has been created by Metrodorus, disciple of Epicurus: "To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field sown with millet only one grain will grow.". The argument of infinite space is not used anymore, but the astronomers nowadays consider our galaxy large enough to make Metrodoru's argument valid

        In the second half of the 20th century the debate on extraterrestrial life was largely shaped by the Fermi Paradox and the Drake equation . The Fermi Paradox is the contradiction between the absence of evidence for extraterrestrial intelligence in our galaxy (or in our local neighborhood) and the calculations that suggest that the galaxy should be full of ETI (extraterrestrial intelligence). It seems that every civilization would inevitably end up seeking to spread itself beyond its own planet. The three reasons why it seems to be natural is: exploration, colonization and survival.

        When a certain technological level is reached by an arbitrary civilization it would start to explore the nearby stars to begin its own process of exploration; this process could start just by curiosity.

        Colonization is something hard to think about since we assume that the civilizations that are able to explore other stellar systems are probably more reasonable than us.

        Survival is probably the most important reason why civilization would seek to spread itself in the galaxy. Every star has a limited lifespan, our sun, for example, will last for more 5 billion years, therefore space flights and interstellars flights will be crucial.

        The origin of the Fermi Paradox was first documented by the astronomer Eric Jones in 1985. It seems that Fermi formulated his question "Where is everybody?" during a lunch time conversation at Los Alamos with his friends in 1950.

2. The Drake Equation

        This equation was proposed in 1961 by an American astronomer called Frank Drake, since then this equation became one of the most important quantitative tools to evaluate the probabilities for radio-contact with ETI.

        Its original formulation is:

[pic 1]

where,

•  is the rate of star formation;[pic 2]
•  is the fraction of stars with planetary systems;[pic 3]
•  is the average number of planets around stas;[pic 4]
•  is the fraction of planets where life have developed;[pic 5]
•  is the fraction of planets where intelligent life developed;[pic 6]
•  is the fraction of planets with technologial civilization;[pic 7]
•  is the average duration of the radio-communication phase of such civilizations;[pic 8]
•  is the number of radio-communicating civilizations.[pic 9]

        What we can notice in this equation is the fact that some of the terms which should be a function of time are not. The term , for example, should be a function of time since we know that the rate of star formation 4 billion years ago is not the same as of today. Hence N should also be a function of time. However this is not very problematic since the astronomers say that in the particular case of the Milky Way, which is a Spiral Galaxy, it is reasonable to assume that the rate of star formation is constant.[pic 10]

        Since the formulation of Drake equation a lot of scientists tried to come up with reasonable numbers to find a good value for N and what they concluded is that any number between 1 and  is considered to be reasonable.[pic 11]

3. "Where is everybody?"

        The simplest solutions to the Fermi Paradox that we can think of is saying that we have not observed enough or we are probably the first civilization in our galaxy to reach a technological level to start looking for ETI. Some people even say that the appearance of intelligent life is so weak that the planet Earth is probably the only one in the galaxy where it ocurred. These arguments does not seem to be valid because they give a special role to Earth and the history of astronomy basically told us that we are not special in the universe at all.

        Another very interessant solution consists of simulations of the civilization's expansion in the galaxy. Even if the space flight were really fast, the process of expansion would be very slow though. The amount of time required to colonize the entire galaxy would be something close to the age of the galaxy and that is the reason why the solar system was not yet reached.

        We also have to consider the difficult to perform space flights, this type of task can be way more difficult than what we have predicted so far. The radiation in space, the spatial dust, the limited amount of supplies and all of the obstacles that we can think of could make this task unrealizable. Therefore the answer for the paradox formulated by Enrico Fermi is not as simple as the paradox itself.

4. How to detect other civilizations?

        The astronomers desmonstrated that the presence of planets around stars is something very common and we also know that when a planet have all the necessary conditions to generate life, the life present on this planet tends to evolve in the direction of an increasing complexity. Thus we can imagine that there are a lot of other intelligent civilizations around several stars. But the main question is "How can we detect other civilizations?", we could think of sending a lot of spaceships to explore different exoplanets but it would cost a huge amount of time and energy. The closest star from us is 4,3 light-years away and it would take several thousands years for us to arrive there, even using the current technology to produce a really good spaceship. Therefore this method to detect other civilizations is not very useful.