Life similar to that on Earth requires carbon, oxygen, nitrogen, phosphorus and sulphur. If any of these were not present, life, as we know wouldn’t have originated and evolved. Apart from this, the planet should be at a particular distance from its star such that conditions (like temperature) are conducive to sustain life, it should have sufficient amounts of oxygen, water etc…. These are the main conditions for life to flourish in a planet. Since the universe is extremely big, it is entirely possible that an infinite number of planets satisfy all these requirements, giving rise to infinite number of civilizations.
Another possibility is that, life on other planets might be entirely different from ours, that we are not able to recognize. For example, silicon might be a substitute for carbon, giving the lifeforms a crystalline morphology and enabling them to exist even at high temperatures or there could be lifeforms that can breathe in Nitrogen and use ammonia as a substitute for water. We never know…
So, we accept that there is a very high possibility that life exists elsewhere. Now, the next question arises. Why haven’t we found one or why haven’t they made contact? Like I said, we probably aren’t intelligent enough to detect an entirely different lifeform. Moreover, how have we tried to make contact? The SETI uses radio frequency signals. Any of these cases is possible:
· Probably, they detected these signals, but are too primitive to know how to respond.
· Probably, their means of communication is entirely different from ours and hence, they did not think these radio signals were sent to make contact.
· In a more likely case - they responded, but we are not intelligent enough to detect or comprehend these signals.
· Probably they are much more intelligent than us that they just don’t care to respond to primitive, unintelligent civilizations.
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