Is there life elsewhere in the Milky Way?
Dmitri Pittas
The question of life elsewhere in the universe is cause for speculation and controversy as we have not yet observed the green-skinned, one-eyed aliens of Sci-fi films. As we cannot observe every solar system in our galaxy, we cannot completely rule out the possibility of extra-terrestrial life, however as time goes on with no evidence of this other life, we become increasingly doubtful. Nonetheless, we can attempt to solve this problem via a probabilistic argument, through mathematics, physics, an analysis of Earth’s history and how life was able to begin. It is important to understand that the feedback mechanisms I shall discuss later take place over hundreds of millions of years, geological timescales which are unfathomable to the human mind, which has an average lifetime of a mere 80 years. Earth itself was formed 4.56 billion years ago, and the Universe some 13.7 billion years ago. 1 I shall refer to life frequently, and when I do, I refer to life as we know it, with a carbon backbone, which passes all the constraints for something to be categorized as alive on Earth, including movement, sensitivity and reproduction. This is important to our calculations, as it could be possible for life to be formed in another way in which humans cannot comprehend.
Firstly, I shall outline the Drake equation, used for calculating the possibility of intelligent extra- terrestrial life: 2
N= R ∗ * f p * n e * f l * f i * f c * L
• N is the number of civilizations in our galaxy with which communication might be possible • R ∗ is the rate of star formation in our galaxy • f p is the fraction of stars which have planets • n e is the number of planets that could potentially support life per star • f l is the fraction of those planets that go on to develop life • f i is the fraction of those planets that proceed to develop intelligent life or civilizations • f c is the fraction of civilizations that develops a technology to release a detectable signal of their existence into space • L is the length of time for which such a civilization releases detectable signals into space
There are certain values for these that we know already from NASA and the European Space Agency’s research, including R ∗ which is, on average, 2 new stars formed per year and f p which is 1, so, each star in our galaxy, on average, has at least one planet. 3
Next we must calculate n e , by establishing Earth’s characteristics throughout its history which made it favourable to life, and the frequency of themall occurring elsewhere in our galaxy. In order to establish
1 Cox 2014. 2 Howell 2018a. 3 Graham87 (n.d.)
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