Chapter 12, Problem 1RQ

What is the purpose of the Drake equation? Define each of its terms, and describe the current state of understanding regarding the possible values of each term.

To determine

The purpose of Drake equation and current understanding of each term.

Answer to Problem 1RQ

The purpose of Drake equation is to find the number of civilizations existing in the galaxy from which signal can be expected.

Explanation of Solution

Drake equation was proposed by astronomer Frank Drake in the first conference of search for extraterrestrial intelligence held in West Virginia. Drake proposed an equation which will help in determining the number of civilization in the galaxy from which signal can be expected. The term civilization stands for only those civilizations that can have radio or other technology.

Write the expression for Drake equation.

    $\text{Number}\text{of}\text{civilisation}=N_{\text{HP}}\cdot f_{\text{life}}\cdot f_{\text{civ}}\cdot f_{\text{now}}$

Here, $N_{\text{HP}}$ is the number of habitable planets, $f_{\text{life}}$ is the number of planets that might have life, $f_{\text{civ}}$ is the fraction of those planets that have civilization capable of interstellar communication technology at some time and $f_{\text{now}}$ is the fraction of planets having civilization at present.

$N_{\text{HP}}$ is the number of planets that are habitable. There are billions of planets in this universe but out of them all only few have the possibility where life can evolve.

$f_{\text{life}}$ helps in determining the number of habitable planets that actually have life.

$f_{\text{civ}}$ is the fraction of planets that have civilization capable of having life that, might have radio or any interstellar technology at some time. These fraction thus only have chance to communicate to outer world.

$f_{\text{now}}$ are the fraction of planets that currently have civilization in them and can communicate.

Currently there is only one habitable planet out of five star systems. So the $N_{\text{HP}}$ value can be determined but the value of $f_{\text{life}}$ is difficult to determine. Currently only planet is supposed to have life i.e. earth.  Planets like mars may have life but it is still not proven. So, only earth has life in the whole galaxy. The $f_{\text{civ}}$ value is based on the number of civilization that is formed in our universe.

There are many solar system formed even beyond formation of sun hence there might be number of civilization being formed in those time. Hence from this fact there might be a chance to evaluate $f_{\text{civ}}$. The $f_{\text{now}}$ value depends on the survival of life on a planet.

The galaxy formed 13 billion years ago had intelligence only after almost 10 billion years ago. This makes the ration of life on planet and the evolution of life on planet to be small which leads to the fact that there might have been multiple civilizations formed which are now undetectable today.

Conclusion:

Thus, the purpose of Drake equation is to find the number of civilizations existing in the galaxyfrom which signal can be expected.