Perhaps I should try to correct this Internet list shortcoming by trying to write a first-rate list of the ten greatest moments in human history. But instead I'll try something more ambitious: I'll take a stab at making a list of the five greatest moments in the history of the universe. I will consider our entire vast universe of billions of galaxies, and ask: what five moments should be considered the greatest moments in its 13-billion-year history? For this discussion, a moment will be considered as something that occurred within a very short time span. This means items such as “the origin of consciousness” or “the origin of the first technology” or “the first development of science” will have to be excluded, as they apparently did not occur at one particular moment of time.
1. The Big Bang
The first choice on the list is an obvious one. Any list of the greatest moments in the history of the universe must include the universe's first moment, the mysterious event known as the Big Bang that occurred about 13 billion years ago. According to scientists, at the time of the Big Bang, the entire universe began to expand from an infinitely dense mathematical point known as the primordial singularity. It's hard to beat that for drama and significance, particularly since the existence of everyone depended on it going just right (scientists say that if there had been a very slightly different Big Bang, none of us would be here).
2. The First Origin of Life Anywhere in the Universe
I cannot include the origin of the first galaxy or the origin of the first planet or the first star in my list of the universe's five greatest moments, as they each occurred very gradually over a period of many years. So to find the next item on the list, I must fast-forward billions of years, to the time when microscopic life first appeared in our universe. Which planet had the honor of being the first planet on which life appeared? Almost certainly it was not our planet. Given that there are billions of galaxies, the first planet on which life appeared was almost certainly not even a planet revolving around a star in our galaxy. It was probably a planet in some other galaxy, and the first origin of life in the universe probably occurred billions of years before life originated on our planet.
Such an event of fundamental importance must have been completely unrecorded. Given the vastness of the universe, it is very, very unlikely that anyone will ever be able to figure out what was the first planet on which life originated.
3. The First Interplanetary or Interstellar Communication Between Civilizations
Another moment in the universe's history that deserves a place on my list is the first moment in the history of the universe when two civilizations existing on different planets were ever able to establish communication. Such an event may have first occurred when two civilizations existing in different solar systems were able to achieve radio communication with each other (something that is much, much easier than making contact by an interstellar voyage). Or it might have been that the first two civilizations on different planets to communicate with each other may have been planets within a single solar system.
Given the vast age of the universe, such an event very likely occurred long, long ago, probably millions or billions of years ago.
4. The First Interstellar Voyage Reaching Another Star
Another great moment in the universe's history must have been the first time that a spaceship from one solar system was ever able to reach another solar system. The distance between stars is so great that it is very difficult to estimate how often interstellar travel occurs. There could be some special physics that allows interstellar travel to occur commonly. Or perhaps there is no such physics, and interstellar travel only occurs rarely, because of the enormous costs and great lengths of time needed for the journey between stars. But very probably some civilization in the universe has launched a spacecraft that has successfully traveled from one solar system to another. The first time any such spacecraft ever reached another solar system might be considered one of the greatest moments in the history of the universe.
It might have looked like this
5. The First Interplanetary Physical Contact Between Different Intelligent Species
Another great moment in the universe's history was the first time that intelligent creatures on one planet ever made face-to-face physical contact with intelligent creatures on some other planet, creatures belonging to some entirely different species. This might have been something like a “handshake across the stars,” when an intelligent species in one solar system traveled to a planet in some other solar system, after crossing the vast interstellar void. Or, it might have been something requiring a much shorter voyage. If two planets in a solar system ever developed intelligent life at about the same time, the first interplanetary physical contact between different species might have been merely a case of astronauts from one planet traveling to another planet in the same solar system. Given the great age of the universe, it is likely that this event has already occurred, although we will never know which case of direct contact between different intelligent species was the first such event to occur in the universe's history. Such an event might have occurred after many different interstellar voyages looking to find another intelligent species.
We are used to being able to see many of the greatest moments in human history on our television screens, either by looking at photography of the event taken while it happened, or by looking at historical documentaries that describe the event very well. But the last four items on this list will forever be shrouded in mystery. Because of the incredible vastness of a universe consisting of billions of galaxies (each made up of millions or billions of stars), we will never be able to say, “This was the planet where life first evolved in the universe,” or “This was the time when two intelligent beings from different planets first stood face-to-face.” Just as our universe keeps most of its “firsts” hidden, it also keeps most of its superlatives hidden. There's no way to tell what is the biggest planet in the universe or the fastest spaceship in the universe or the biggest city in the universe or the coldest planet in the universe. Even if you restricted yourself to only trying to keep track of the superlatives or firsts of a single galaxy, the job of being a galactic Guinness would be a very, very difficult one.