Our universe is 13.8 billion years old. In the observable part of this universe, there are more than 2 trillion galaxies. On average, each galaxy contains 100 million stars. Most stars are orbited by planets, which in turn are orbited by moons. Beyond our solar system, we have started identifying planets in our Milky Way galaxy. Altogether, it turns out that there are hundreds of billions of potentially habitable planets in the visible part of our universe. Yet, life has been confirmed to exist on only one planet, which orbits a star called the Sun, and this star orbits a galaxy called the Milky Way. The Milky Way itself contains between 100 to 400 billion stars, at least 20 billion of which are similar to our Sun. One-fifth of these have Earth-sized planets in the habitable zone (neither too hot nor too cold for life). If even one in a thousand of these planets harbors life, then there would be a million life-bearing planets just in the Milky Way. However, no signs of life have been found anywhere in our galaxy. Are we, then, alone in the universe, or at least in our galaxy?
Answering this question isn’t easy, but efforts are being made to find answers. If Earth is the only planet in the universe to harbor life, it would mean that the chance for the emergence and evolution of life in the universe is extremely, extremely slim, and that Earth and its solar system are an extremely rare area. Otherwise, it means that life has been created and evolved in millions of places in the universe, and a significant number of those have developed civilizations. The vast potential for this and yet finding nothing has a name. It’s called the Fermi Paradox.
The Fermi Paradox
Physicist Enrico Fermi first brought this problem to our attention. He realized that our solar system is relatively young compared to other places in the universe. If civilizations in other parts of the universe had formed and mastered rocket technology, they could have spread across the entire galaxy in a relatively short time (within ten million years). Look at the evolution of civilization on Earth. Life emerged here 3.5 billion years ago, and humans appeared about 150,000 years ago. Our technological history is at most about 150 years old. In these 150 years, humans have achieved technological feats unimaginable compared to the previous 3.5 billion years. Civilizations are categorized into three types based on their technological progress: Type-1, 2, and 3. A Type-1 civilization can harness the entire energy of its planet. A Type-2 civilization can utilize the energy of its star. For example, collecting energy by surrounding the star with solar panels and transferring that energy directly to their planet (such an energy collection sphere is called a Dyson Sphere). And a Type-3 civilization can collect energy from the entire galaxy, as Fermi imagined. How could a Type-3 civilization spread throughout the galaxy? One way could be to create generational spacecraft. These spacecraft would be launched from the home planet in all directions, then they would autonomously mine resources from various star systems and replicate themselves. In a matter of thousands of years, the entire galaxy would be flooded with spacecraft.
Looking at Earth’s civilization, we have not yet been able to utilize the full energy sources of our planet, but we might be able to in the next 200-300 years. Therefore, our civilization is approximately at Type-0.73, meaning we have not yet fully achieved the definition of a civilization.
Fermi did not get far with this paradox during his lifetime. After his death, in 1975, Michael H. Hart published a research paper on this topic. He presented several arguments, such as:
- The Milky Way galaxy contains several hundred billion stars like the Sun.
- Many of these stars are likely to have Earth-like planets orbiting them. If the emergence of life is natural, many of these planets may have already developed intelligent life.
- Some of these civilizations may have developed interstellar travel technology. Earth is currently at the stage of developing this technology.
- Even at very slow speeds, interstellar travel technology should allow a civilization to colonize the entire Milky Way galaxy within a million years.
- Importantly, since a large portion of stars like the Sun are billions of years old, there has been enough time for civilizations to spread throughout the galaxy.
According to these sequential arguments, humans on Earth should have already been visited by cosmic intelligent beings. Not just theoretically, but there is also an equation for estimating the number of civilizations in the galaxy, called the Drake Equation, created by Frank Drake in 1961. The equation calculates the number of civilizations in our galaxy, but many of its parameters are difficult to accurately determine and rely on speculation. Optimistic calculations using the Drake Equation estimate the possibility of civilizations in the Milky Way to be between one thousand to ten million. If any of these civilizations emerged even just a few million years before Earth, they should have spread throughout the galaxy by now. So where are they? One answer might be ‘The Great Filter’.
The Great Filter
It’s theorized that before or after a civilization develops, it encounters a ‘filter’ that is very difficult to overcome. It could be that civilizations are inherently destined to destroy themselves upon reaching a certain level of technological capability. For example, after discovering nuclear energy, they might annihilate themselves in nuclear wars. This filter could be at two stages:
Firstly, the filter might be at the very beginning. Perhaps the initial emergence of life is incredibly difficult and exceedingly rare. The exact process of how life emerged on Earth is still not fully understood, and the natural formation of complex life might not be as simple as we think. Maybe the conditions for the emergence of life are so specific and rare that they hardly ever occur together. If that’s the case, then human civilization has already passed this filter, which no other civilization in our galaxy has. Maybe the universe was too chaotic in the past for life to emerge anywhere, and only recently have conditions become suitable for life, with Earth being one of the first planets where it happened. Time might reveal the emergence of life in different parts of the galaxy has just begun or is about to begin. In that case, the inception of civilization on Earth might be ahead, and others have not yet started but may in the near future.
Secondly, the filter might be in our future. If so, it’s a warning sign for us. It could mean that the emergence of life in the universe is very spontaneous, and life’s development and evolution are ongoing in various parts of the universe. But at a certain point, it halts. As previously mentioned, every civilization reaches a point in its technological advancement where it self-destructs. If this is our fate, then we, the inhabitants of Earth, are nearing it. We now possess technology that could potentially lead to our own destruction. Perhaps civilizations are continually being created throughout the universe and destroying themselves before they can make contact with others, making this cycle an inescapable part of civilization’s nature. Or, perhaps an ancient civilization has already reached Type-3 status and monitors the entire galaxy. Whenever they see a civilization developing to a certain point, they annihilate it instantly. Or, each civilization discovers something so specific in their scientific pursuits that would have been better left undiscovered.
The Problem of Communication?
Another highly probable scenario exists. Perhaps various civilizations are scattered throughout our galaxy, but we are simply unable to communicate with them. Our communication methods may differ from theirs. On Earth, as a species, humans cannot communicate with most other species. Humans have not managed to exchange thoughts with a sparrow. A human cannot understand what a sparrow is thinking or intending at any moment. Similarly, humans cannot impose their societal structures on a sparrow’s mind. Cosmic civilizations could be beyond our imagination. Perhaps our communication methods are too primitive and outdated, and such signals are ignored by others. In that case, we might remain alone for a long time until we learn to communicate effectively. Advanced civilizations might consider our planet too insignificant and simply overlook us. When you walk down a street and see an ant line, you likely do not attempt to communicate with them but rather ignore them. The situation could be similar. When you clear a forest for resources, you probably do not consider the loss of habitat for the various wildlife living there. It’s not that you are displacing a squirrel out of malice; you are just cutting down trees for your needs and ignoring the squirrel. A Type-3 civilization might extract resources from Earth if needed and simply ignore us. Or, they might send machines instead of visiting themselves. The machines autonomously gather resources and leave without any attempt at communication.
Regardless of which scenario is true, one fact remains: there are no signs of life beyond Earth at this moment. But would finding signs of life elsewhere be good news for us?
The Existence of Cosmic Life Could Be Bad News for Us
Space agencies have begun efforts to find signs of life in various parts of the solar system. They hope to find traces of primitive life in the soil of Mars, or in the oceans of Jupiter’s moon Europa, or Saturn’s moon Titan. However, if life is indeed found on Mars or elsewhere similar to Earth, it would be a major alarm for us. It would mean that the origin of life is indeed a spontaneous event, and life has originated on millions of planets in our galaxy. But since there are no signs of civilization anywhere, it implies that after the emergence of life, civilizations have also been destroyed before they could fully develop. In that case, a ‘filter’ is definitely waiting for us ahead.
