What are the 'three reasons' why aliens haven't visited Earth?
While many believe that extraterrestrial life exists somewhere in the vast universe, others argue that the fact that 'aliens have never appeared on Earth' is the reason why highly intelligent civilizations do not exist outside of Earth. In response to this theory, Professor Carol Oliver, who studies science communication and astrobiology at the University of New South Wales, Sydney, explains that 'even if aliens exist, there are three reasons why they haven't visited Earth.'
Aliens might exist. But there are three reasons why they're not visiting us
One reason why extraterrestrial life might not visit Earth, even if it exists, is simply that the universe is too vast. Proxima Centauri , the closest star to our sun, is approximately 40 trillion kilometers away, which is 268,000 times the distance from our sun to Earth. Astronomers have measured this to be 4.3 light-years, meaning that even at the speed of light, it would take over four years to reach it.
Even with current technology, the Parker Solar Probe, the fastest space probe capable of traveling through space, can only reach a maximum speed of 191 km per second, which is only 0.064% of the speed of light. At the Parker Solar Probe's speed, it would take approximately 6,650 years to reach Proxima Centauri. In other words, if intelligent life existed in a more distant star system and were to be developing space at the same time as Earth, it would take several thousand years for them to reach Earth.
The ' Fermi paradox ,' proposed by physicist Enrico Fermi, raises the question of why, despite the reasonable possibility of extraterrestrial civilizations existing, no traces or messages from them have been found. This can also be explained by the fact that Earth began transmitting radio waves at the speed of light into space in 1901, and these radio waves have only reached about 120 light-years away, which is only about 0.000002% of the Milky Way galaxy.
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Oliver cites the unimaginable energy demands as the second reason why aliens haven't visited Earth. As the mass of a spacecraft increases with speed, more energy is needed to accelerate it. Even if there were a civilization far more advanced than Earth's somewhere in the universe that had developed a method of travel close to the speed of light, a spacecraft moving at the speed of light would require infinite energy, making it seemingly impossible to achieve.
One might think that a civilization capable of traveling at the speed of light would also have developed unlimited energy, but if that were the case, the question arises as to why such an advanced civilization would need to use that energy and a certain amount of time to travel all the way to Earth, which is far less developed.
A third reason is the possibility that Earth is a harmful planet to aliens. Life and Earth have co-evolved over hundreds of millions of years, and oxygen, which is essential for most life on Earth, is also a highly reactive and corrosive gas.
Since 1960, researchers have developed the ability to search for extraterrestrial intelligent life by applying conventional radio astronomy. Among the largest extraterrestrial life search projects are the SETI Institute in California and the Breakthrough Listen Project based at Oxford University. However, in the 13.8 billion-year history of the universe, humanity has only been observing for about 100 years. It is safe to say that the possibility of discovering intelligent life in such a short period is extremely low. Nevertheless, Oliver quotes a 1959 paper , saying, 'It is difficult to estimate the probability of success, but if we do not look, that probability drops to zero.'
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