So far, humans have been exploring extraterrestrial life for decades yet have gained nothing. Currently, there is no evidence of life on any planet in the solar system, making Earth unique and lonely within the vastness of the cosmos.

Earth is the third planet from the sun, 150 million kilometres away. The closest planets, Venus and Mars, are about 55 million kilometres away, but scientists have confirmed they are devoid of life. Even Earth's moon, our only visited celestial body beyond Earth, lacks life, emphasizing the solitude of our planet.

Mercury, farther away, is also unlikely to harbour life. The gas giants Jupiter, Saturn, Uranus, Neptune, and the dwarf planet Pluto are essentially ruled out for hosting life. Therefore, Earth remains isolated and lonely in the cosmic expanse, with no companions or peers, drifting through billions of years.

This situation has made some astronomy enthusiasts despair, considering humanity may be isolated in the universe. As of now, Earth is the only known planet with life. Despite the vastness of the observable universe—approximately 93 billion light-years in diameter—the possibility of other life forms and civilizations is considered significant.

However, asserting the inevitable existence of abundant life and civilizations in the universe has also faced considerable opposition. The Fermi Paradox highlights the absence of any traces of extraterrestrial life or civilizations despite the vastness of the cosmos. In response, the Rare Earth Hypothesis has emerged.

The Mediocrity Principle, proposed by astronomers Carl Sagan and Frank Drake, posits that Earth is an exceedingly ordinary planet. According to this principle, the Milky Way is an unremarkable galaxy, our solar system is a standard one within a spiral arm, and Earth is an average rocky planet where life naturally emerged.

If Earth is indeed mundane, then within the observable universe's 93 billion light-years, there could be an astronomical number of similar rocky planets, making it plausible for numerous forms of life and civilizations to exist. Considering the timescales of the universe, civilizations that arose much earlier than Earth's 300-year-old modern science era could have reached unprecedented heights.

Despite this, the question remains: Why haven't these advanced civilizations visited Earth? Two possible explanations include the vast spatial distances in the universe, where travel between civilizations is exceedingly challenging, even at a fraction of the speed of light.

Additionally, the immense timescales make it difficult for two civilizations to exist and seek each other out simultaneously, leading to the possibility of missing each other by millions or billions of years. One culture might flourish while the other is yet to emerge, or one might decline just as the other reaches its zenith.

Despite Earth's apparent loneliness in the cosmos, scientific advancements spark contemplation about life's existence in the vast universe. Perhaps undiscovered mysteries await, and future revelations will unravel more cosmic enigmas.