By examining our universe, we humans have learned some pretty interesting things. For example, we know that the universe we live in is about 13.8 billion (that’s 13,800,000,000) years old from measuring microwave background radiation in space. To put into perspective this amount of time, we can only trace modern human history back around 12,000 years ago, to a stone structure called Gobleki Tepe in what is current day Turkey.
Even taking things farther back, say, to the earliest points we’ve discovered anthropologically into human history, our species still only reaches back about 2 million years. Still barely scratching the surface of times long journey. Yet in just a short period, we’ve done amazing things. We’ve launched ourselves into space, escaping our natal world; a feat, to our knowledge, perhaps never before replicated by any organism in the universe!
However, space is very big. Bigger than our words have power to explain in human contexts. I can tell you that the observable universe is roughly 47.5 billion light years across. To try and put that in perspective, our solar system is only 0.5 lightyears. But this still is unfathomable in some regards, because even half a light year is still almost 10 trillion kilometers (6 trillion miles). One trillion is a thousand billion.
Saying that space is very big is perhaps the greatest understatement in human history. Some would say it is hubris to consider ourselves alone in so much space. Perhaps it is. Yet even with the incredible time and distance that exists in our observable universe, there are a number of factors to consider in where our blip on the structure of it fits.
Given the enormity of space and the almost eternity-like time which has elapsed so far, if even only 1 percent of all the planets in our galaxy also held life, around 40 billion worlds would be life sustaining, with most of those having existed for billions of years longer than our own earth. However, when we look into the night sky with all our incredible telescopes and technology we cannot see evidence of any neighbors. So where are they? This concept is called the Fermi Paradox, and it is one that has baffled scientific minds for many years. Even in conservatives estimates, it would be radically unlikely for us to be alone in our galaxy, let alone the universe. Or would it?
Many models used to calculate how many advanced species there could be in our galaxy only account for possible planets in the Goldilocks zone of their star (the region distant enough to allow for liquid water). But there are likely many other factors to be considered. Our sample size for life at this time is, sadly, only one: Earth. So in this thought experiment, let us use Earth as our comparison. Earth is in the Goldilocks zone of our sun, Sol. It also has a moon, and four gas giants orbiting the same star. Those gas giants, especially the largest, Jupiter, have acted as gravitational bouncers, pulling life destroying asteroids, meteors, and comets into themselves over the millennia. These are all crucial elements. But there is one more: Iron. Without the element iron, no life could exist on Earth.
The element iron can only be formed in the heart of a dying star. As they run low on hydrogen to burn, they must fuse new elements from their available material, until heavier elements are formed, like iron, oxygen, and carbon. All essential to life. This means that only after the first stars began to explode would the elements necessary to create life be proliferated into the cosmos. The length of time needed for a star to reach the end of its lifespan varies depending on size, and likely many of the first stars were so large that they died gloriously within 10 million years of their formation. However, given the requirements for these particular materials that facilitate life, it is not strange to consider their rarity across the universe.
Our galaxy is 13.6 billion years old. Many of the stars in our galaxy which are similar to our own, with planets in the Goldilocks zone, are around 10 billion years old. Our star is about 4.6 billion years old. Life on earth, according to paleontological research, is likely to have occurred 3.7 billion years ago. There are about 100 billion stars in our galaxy. Of those stars, about 17 percent have planets. We have only mapped one percent of the stars in our galaxy, and around two percent of those have stars in their Goldilocks zones. With these numbers considered, the number of stars in our neighborhood that could support life is still 3,400,000. Yet in the grand scheme of our cosmos, it is a pitifully small number.
All that time, all those elements, countless dying stars across the cosmos, to lead to this moment, right now, where we are able to read and explore these wonders for ourselves. For everything we know, there are billions of things we do not. Yet, our curiosity can allow us to continue our journey through time and space, wondering what is our there, waiting for us to discover it.