Does life exist elsewhere in the universe?
Does life exist elsewhere in the universe?
Do aliens even exist?
Two possibilities exist: either we are alone in the universe or we are not. Both are equally terrifying. - Arthur C. Clarke
Greetings, fellow Bohron
Aliens portray our greatest fears. We fear them more than ghosts because their existence is more probable, scientifically. They are living beings like us, visitors from a place far far away in the universe. But before we can communicate with them, we will have to answer the question:
Is life outside Earth possible?
Aliens in History and Scifi
At earlier times, contemplating the existence of life outside Earth was a matter of life and death. When Italian philosopher Giordano Bruno asked a similar question, the Church held him guilty of holding views against the Catholic faith. On 17 February 1600, he was hung upside down naked before finally being burned at the stake.
1608 novel Somnium by Johannes Kepler is considered one of the earliest works of sci-fi. In the novel, Kepler envisaged a trip to the moon and a possible encounter with its inhabitants.
Countless movies featuring aliens have been directed, the most notable being A Trip to Moon, Alien franchise, E.T. the Extra-Terrestrial, Contact, War of the Worlds, Independence Day, Avatar, The Day the Earth Stood Still, Men in Black and many more.
The Scientific Search for Life
If aliens exist at all, they might look a lot different from any species found on Earth. We can’t even guarantee what factors might be responsible for the growth of life elsewhere in the universe. Nevertheless, we can still make reasonable guesses about the nature of alien life:
Liquid Water
Thanks to its ability to dissolve a wide range of solutes, water is sometimes called the "universal solvent.” Water is a simple molecule that is found outside earth as well and helps in creating a number of complex molecules. So astrobiologists think that liquid water will be a key factor in the development of life in the universe.
Hydrocarbons
All living beings on earth are made up of organic molecules, which consist of long chains of carbon atoms. The ability of carbon to bond with four more carbon atoms helps in creating complex molecules.
Self-Replication
To reproduce, living cells consist of a self-replicating molecule called DNA (Deoxyribonucleic Acid) that can form new copies and hence save the species from extinction. So alien life must also consist of some form of a self-replicating molecule.
Can life emerge from non-living matter?
In the 1950s, Stanley Miller, an American graduate of the University of Chicago, decided to test the speculation that given the right environmental conditions, life could emerge from non-living matter. Supervised by his professor Harold Urey, they set up the following apparatus:
In a nutshell, their aim was to simulate the conditions of early Earth’s atmosphere. They took water (H₂O), methane (CH₄), ammonia (NH₃), and hydrogen (H₂) and put these chemicals in an airtight glass flask.
A heater was used to produce water vapour.
Electrical sparks were fired to simulate lightning in the water vapour and gaseous mixture. The atmosphere was cooled again so that the water condensed and trickled into a U-shaped trap at the bottom of the apparatus.
After a day, Miller identified five amino acids present in the solution, which are basic building blocks of proteins, the essential components of all life forms.
The conditions applied in the experiment have been found in other parts of the solar system and amino acids have been found in a number of meteorites and cometary nuclei, hinting that life outside the Earth is a serious possibility.
Do aliens exist at all?
In 1961, Cornell University professor Frank Drake attempted to estimate the number of active and communicative intelligent extraterrestrial civilizations in the Milky Way using what is named after him, the Drake Equation.
The equation considers the following factors:
There are about 100 billion stars in the Milky Way. How many of them are stars like our sun?
What fraction of these stars have planets?
What fraction of such planets have the potential to harbour life?
What fraction of such planets actually develop life?
What fraction of these life forms are intelligent enough to communicate?
What fraction of these intelligent civilizations actually try to communicate?
The expected lifetime of a civilization.
By estimating all of these factors and multiplying them together, we realize that there could be 100 to 10,000 planets consisting of intelligent life in the Milky Way alone.
This estimate is however debatable and several criticisms of the equation have appeared over years, the most notable being the Fermi Paradox. The uncertainties associated with the existence of life-supporting parameters, the evolution of life and intelligence are large and hence the margin of error in the final estimate is huge.
The size of universe is too large to believe that there is no alien civilization. So if extraterrestrials exist, where are they and how do we communicate with them? We will find this out next time.
Sources:
Physics of the Impossible - Michio Kaku
Drake Equation - Wikipedia
Miller–Urey experiment - Wikipedia