Many times we look up at the night sky and wonder - "Are we alone in this vast Universe?". It is quite common that when I tell people I am an astronomy enthusiast, they end up asking me - "Do aliens exist?". Surprisingly this question is closely similar to the question - "Does God exist?" for we have no firm evidence to answer either of them. As much as you hate it, we can do nothing but have our own beliefs at this point. Some people believe Earth is the only place in this Universe to harbor life, others believe in some form of life existing outside our Earth. However, if we reconsider all the parameters one shall be obliged to think that the chances of extraterrestrial life existing are substantially high. In this article, I shall address all such parameters and end with possible reasons of why we haven't found any signs of extraterrestrial intelligent life yet.
First and foremost reason to believe that life must exist outside Earth is the fact from a study that - "Almost every star in our Milky Way galaxy hosts at least one alien planet revolving around it." It is mind boggling to think of the billions of stars in our galaxy each hosting at least one planet and some even having planetary systems like our Solar System. One can even extrapolate this fact to a generalized conclusion for all galaxies. After all why our galaxy's stars should be the only one to host planets? The Universe as we know it contains hundreds of billions of galaxies, each holding billions of stars, which can possibly contain planetary systems. It then gets difficult to rule out the possibility of alien life existing in our Universe. It becomes even harder, after NASA's Kepler Space Telescope discovered thousands of planets revolving around host stars in our galaxy. Out of these discovered "Exoplanets" many of them were in the Habitable Zone of their host star. Planets located in this sweet spot called as - "The Goldilocks Zone" are neither too close nor too far from its star. Thus, having favorable conditions for life to flourish. In May 2016, NASA announced Kepler's discovery of 1284 new planets and 9 planets out of these were in the habitable zone of their host star. In rough terms, 9 out of every 1000 exoplanets lie in the habitable zone of a star. Combine this conclusion with our earlier assumption of almost every star having at least one alien planet and the probability of alien life existing shoots high.
Another reason I shall present here is something which is not thought of very often. It is the assumption that every form of life requires the same elements for survival as are required by majority of species on Earth. The primary elements for survival on Earth are water, oxygen and a source of energy mainly glucose. Humans metabolize glucose using oxygen to produce energy to carry out bodily tasks essential for survival. It is a misconception that all organisms need water and oxygen for survival. For example - "Methanotrophs" are a type of organisms which utilize the compound - Methane as their only source of energy. Such organisms are found in areas where methane is produced. Any person with sufficient interest in astronomy would know a celestial body covered with lakes of methane and ethane i.e. Saturn's moon - "Titan". We dont even know yet, whether microbial life exists on Titan or not. Since, Earth is covered with water and majority of living organisms and animals on Earth need water for survival. There might exist other worlds, like Titan covered with Methane where organisms need Methane for survival, or some other planet with abundance of another element on which the living organisms depend on that abundant element for survival.
All such factors point out that life must surely exist on a place other than Earth. If it does, "Why we have not found it yet?". "Why we have not obtained even the slightest clue of alien life existing?" There can be many possible reasons, some or all of which may be responsible for our inability to find signs of alien life. One obvious answer would be that the extraterrestrial life might not be advanced enough to mark its detectable presence. Since, any life existing outside our Earth can be called as aliens. It is not necessary that all aliens should be those green headed creatures invading Earth as depicted in movies. They can even be tiny microorganisms hidden in corners of a lonely planet. We only have to look closer to be able to find them. Such microorganisms can perhaps exist in our own Solar System too. In time, these organisms can then evolve to give rise to an intelligent species able to thrive and communicate with us. This brings us to another reason that life existing outside Earth might not be advanced enough to communicate with us. To the contrary, some people believe that the aliens existing outside are advanced enough but are choosing to remain silent for some reason. They are observing us and our actions, but still choose not to communicate. However, this scenario is a little vague and best be neglected. There is another scenario, in which intelligent alien civilizations developed in one or many places in the Universe underwent an apocalypse and the entire civilization might be wiped out. This reason seems plausible. If in the future, I surely not desire so but if the Earth is struck by a giant meteorite, or comes under the impact of a Supernova, or any other natural or artificial apocalyptic disaster, then the Human race along with all its developments would be wiped out. Only thing that would reach the aliens will be our electromagnetic signals as well as light from Earth. This brings us to a final possibility - We know that light or electromagnetic radiation travels at a finite speed of 299,792 kilometers per second. Einstein's theory of relativity predicts that this speed is the ultimate Cosmic Speed Limit. Nothing can travel faster than this speed. This implies that we always see the past. What we call as present is merely an illusion! Think about it, the time taken for the light from Sun to reach Earth is approximately 8 minutes 20 seconds. Therefore, the Sun as we see it in the sky is 8 minutes old. If it were to explode at this instant, we would see it after 8 minutes. This causes a delay in the time at some event happens and the time at which light from that event reaches our eyes. At small distances this difference is negligible but at large cosmic scales light takes sometimes tens, thousands or even millions of years to reach us from a specific place. The purpose of stating all this is that, even if there exists an advanced alien civilization sending out radio signals out in the Universe about their existence, it might not have reached us yet. It is still travelling, through the cosmic void at a constant speed. Perhaps, it will get deflected from a planet, star or even get devoured by a black hole before reaching us. Some of our first transmitted signals are now expanding into space as a radio bubble with a diameter of about 200 light years. This number seems insignificant in front of the 105,700 light years of diameter of our Milky Way galaxy. This means that it would take almost 105,500 years for our radio bubble to cover the entire Milky Way. To make things harder, there exists a property of electromagnetic radiation to loose their intensity the farther they travel. Thus, it gets more difficult to detect these faint, low-intensity radio waves. This is a problem both - for us and for the alien civilization (if they exist) trying to communicate with us by sending messages.
This entire article was nothing but full of speculations and anticipations based on observations, logic and some assumptions. As I said before, there is nothing we can do but have our own beliefs until any solid evidence comes forth. However, time shall surely tell the answer to our questions. If the arguments I posed in previous paragraphs are valid, then we can rephrase our question and ask - "Are we alone, yet?"
- Thank You
First and foremost reason to believe that life must exist outside Earth is the fact from a study that - "Almost every star in our Milky Way galaxy hosts at least one alien planet revolving around it." It is mind boggling to think of the billions of stars in our galaxy each hosting at least one planet and some even having planetary systems like our Solar System. One can even extrapolate this fact to a generalized conclusion for all galaxies. After all why our galaxy's stars should be the only one to host planets? The Universe as we know it contains hundreds of billions of galaxies, each holding billions of stars, which can possibly contain planetary systems. It then gets difficult to rule out the possibility of alien life existing in our Universe. It becomes even harder, after NASA's Kepler Space Telescope discovered thousands of planets revolving around host stars in our galaxy. Out of these discovered "Exoplanets" many of them were in the Habitable Zone of their host star. Planets located in this sweet spot called as - "The Goldilocks Zone" are neither too close nor too far from its star. Thus, having favorable conditions for life to flourish. In May 2016, NASA announced Kepler's discovery of 1284 new planets and 9 planets out of these were in the habitable zone of their host star. In rough terms, 9 out of every 1000 exoplanets lie in the habitable zone of a star. Combine this conclusion with our earlier assumption of almost every star having at least one alien planet and the probability of alien life existing shoots high.
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| Artist's depiction of Kepler-22b - An exoplanet detected by Kepler Space Telescope in the Habitable Zone |
Another reason I shall present here is something which is not thought of very often. It is the assumption that every form of life requires the same elements for survival as are required by majority of species on Earth. The primary elements for survival on Earth are water, oxygen and a source of energy mainly glucose. Humans metabolize glucose using oxygen to produce energy to carry out bodily tasks essential for survival. It is a misconception that all organisms need water and oxygen for survival. For example - "Methanotrophs" are a type of organisms which utilize the compound - Methane as their only source of energy. Such organisms are found in areas where methane is produced. Any person with sufficient interest in astronomy would know a celestial body covered with lakes of methane and ethane i.e. Saturn's moon - "Titan". We dont even know yet, whether microbial life exists on Titan or not. Since, Earth is covered with water and majority of living organisms and animals on Earth need water for survival. There might exist other worlds, like Titan covered with Methane where organisms need Methane for survival, or some other planet with abundance of another element on which the living organisms depend on that abundant element for survival.
All such factors point out that life must surely exist on a place other than Earth. If it does, "Why we have not found it yet?". "Why we have not obtained even the slightest clue of alien life existing?" There can be many possible reasons, some or all of which may be responsible for our inability to find signs of alien life. One obvious answer would be that the extraterrestrial life might not be advanced enough to mark its detectable presence. Since, any life existing outside our Earth can be called as aliens. It is not necessary that all aliens should be those green headed creatures invading Earth as depicted in movies. They can even be tiny microorganisms hidden in corners of a lonely planet. We only have to look closer to be able to find them. Such microorganisms can perhaps exist in our own Solar System too. In time, these organisms can then evolve to give rise to an intelligent species able to thrive and communicate with us. This brings us to another reason that life existing outside Earth might not be advanced enough to communicate with us. To the contrary, some people believe that the aliens existing outside are advanced enough but are choosing to remain silent for some reason. They are observing us and our actions, but still choose not to communicate. However, this scenario is a little vague and best be neglected. There is another scenario, in which intelligent alien civilizations developed in one or many places in the Universe underwent an apocalypse and the entire civilization might be wiped out. This reason seems plausible. If in the future, I surely not desire so but if the Earth is struck by a giant meteorite, or comes under the impact of a Supernova, or any other natural or artificial apocalyptic disaster, then the Human race along with all its developments would be wiped out. Only thing that would reach the aliens will be our electromagnetic signals as well as light from Earth. This brings us to a final possibility - We know that light or electromagnetic radiation travels at a finite speed of 299,792 kilometers per second. Einstein's theory of relativity predicts that this speed is the ultimate Cosmic Speed Limit. Nothing can travel faster than this speed. This implies that we always see the past. What we call as present is merely an illusion! Think about it, the time taken for the light from Sun to reach Earth is approximately 8 minutes 20 seconds. Therefore, the Sun as we see it in the sky is 8 minutes old. If it were to explode at this instant, we would see it after 8 minutes. This causes a delay in the time at some event happens and the time at which light from that event reaches our eyes. At small distances this difference is negligible but at large cosmic scales light takes sometimes tens, thousands or even millions of years to reach us from a specific place. The purpose of stating all this is that, even if there exists an advanced alien civilization sending out radio signals out in the Universe about their existence, it might not have reached us yet. It is still travelling, through the cosmic void at a constant speed. Perhaps, it will get deflected from a planet, star or even get devoured by a black hole before reaching us. Some of our first transmitted signals are now expanding into space as a radio bubble with a diameter of about 200 light years. This number seems insignificant in front of the 105,700 light years of diameter of our Milky Way galaxy. This means that it would take almost 105,500 years for our radio bubble to cover the entire Milky Way. To make things harder, there exists a property of electromagnetic radiation to loose their intensity the farther they travel. Thus, it gets more difficult to detect these faint, low-intensity radio waves. This is a problem both - for us and for the alien civilization (if they exist) trying to communicate with us by sending messages.
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| Extent of our radio bubble (depicted by the blue dot) in the Milky Way Galaxy |
This entire article was nothing but full of speculations and anticipations based on observations, logic and some assumptions. As I said before, there is nothing we can do but have our own beliefs until any solid evidence comes forth. However, time shall surely tell the answer to our questions. If the arguments I posed in previous paragraphs are valid, then we can rephrase our question and ask - "Are we alone, yet?"
- Thank You