Where are the Aliens?
👽 Where are the Aliens:
The drake equation expects the total number of civilizations in the milky way alone to be around 10,000, even with conservative guesses for its parameters. This follows from the Miller-Urey experiment that wherever the elements important for life exist, life should naturally and quickly follow. The elements that make terrestrial life are some of the most common elements in the universe. It would make sense if life started popping everywhere in the universe.
So, where are all the aliens?
The problem is that we have never detected any sign of intelligent civilization. Even if there were 10,000 planets teeming with life, the distance between us and our nearest neighbors on average would be thousands of light years away, which makes it hard to test this hypothesis. We can speculate all we want, but we are still in the dark. This is a testament to how incomprehensibly huge our universe is.
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👾 Fermi’s Paradox:
Italian physicist, Enrico Fermi, came up with an explanation of why we have not encountered an alien species (Arny and Schneider). Fermi paradox states that if there were intelligent life forms able to travel among the stars, we should have seen them already. A species armed with interstellar travel should take about a million years to colonize the whole milky way, which is an insignificant amount of time when compared with the life of our galaxy.
This leaves us with two possible solutions: 1) The Great Filter, and 2) We are the first ones to the party.
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🚀 The Great Filter:
The Great Filter explains the Fermi Paradox. Why don’t we see aliens? The Great Filter acts as an obstacle that is so hard to overcome that no species has done it so far. Interstellar travel may turn out to be so bizarrely difficult that no alien species have overcome it. This would mean that all intelligent civilizations (if they exist) are restricted to their home star system, isolated from the rest of the galaxy. Galactic communication over radio would be extremely slow due to large distances, which explains why we have not heard from anyone yet.
Due to the vastness of the cosmos, it seems extremely hard to communicate with alien civilizations using radio searches, but there is another way to identify planets teeming with life.
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🌍 The Gaia Hypothesis:
In 1974, chemist James Lovelock and microbiologist Lynn Margulis came up with a unique way to indicate if a planet has life (Palen and Blumenthal). It was suggested that living organisms change the atmosphere of the planet they live on to make it more habitable to them. This happened on our planet for billions of years. Cyanobacteria (precursors to plants) used carbon dioxide and released oxygen.
In the early days of Earth, the oxygen levels were extremely low, but over billions of years oxygen levels rose and now it’s the second most abundant gas in the atmosphere at 21%. The abundance of oxygen level could be one of the triggers of the Cambrian explosion, which saw all sorts of complex life appear on our planet.
This is called the Gaia Hypothesis, the idea that living organisms change the chemical makeup of their home planet. It’s named after the Greek personification of Earth as a Goddess (Palen and Blumenthal).
Another example of the Gaia hypothesis is how plants react to the weather. When it’s too cold, plant metabolism is slowed down. Less carbon dioxide is converted to oxygen. More carbon dioxide in the atmosphere results in the greenhouse effect and the temperature of the planet goes up, exactly what the plant life needed. On the other hand, when the atmosphere is too hot, the plant metabolism speeds up, which results in less carbon dioxide in the atmosphere (the reverse greenhouse effect). The temperature cools down.
Therefore, we can look for alien life, by looking for water and gases like those required for terrestrial life on extraterrestrial planets.
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[1] Arny and Schneider, *Explorations: An Introduction to Astronomy.*
[2] Palen and Blumenthal, “21st Century Astronomy.”
[3] Palen and Blumenthal, “21st Century Astronomy.”
