So with the prompting of a renewed interest I've developed in Carl Sagan, I've done a lot of thinking about my belief in alien life. What have I determined?
It is scientifically impossible for alien life to not exist.
Okay, let's step back a bit and let me preface the 'aliens' question with another one; do you believe in Evolution and Natural Selection? If you answered "no" to this question, just give up now.
Evolution is scientific fact. It doesn't mean there is no God, it doesn't mean atheists were right all along, it just means that all species on Earth slowly mutated and evolved from small microbes over millions and millions of years. You can easily adapt your spiritual beliefs to accommodate this scientific fact. Christians have done it for centuries with each new scientific revelation. The Earth is round, the Earth is millions of years old, the Earth isn't the center of the Universe, and Earth's species evolved to their current state through the process of natural selection. None of those Genesis-based debunked religious beliefs destroyed Christianity, neither will Evolution.
Okay now that we've all accepted Evolution as scientific fact (and don't we feel better?), I've also subsequently convinced you that aliens must exist. Allow me to use an unreasonably large amount of text to explain. Hopefully you don't give up on me too soon in the TL;DR filled version of the internet.
Mathematical Probability of Life on Other Planets
(skip to the bolded bits if you aren't interested in numbers)
We live in a galaxy called the Milky Way. There are anywhere from 100-400 billion stars in our galaxy. At least 100 million of those stars are exactly like our Sun. They produce the same amount of energy through fusion, emit the same light, etc. There are somewhere along the lines of 100 billion galaxies in the Universe as far as our current technology allows us to see.
So 100 billion galaxies with 100 million stars that can produce the same life-giving effects as our Sun, would equal to a rough possibility of 10,000,000,000,000,000,000 Earth-like planets, given one such planet per star.
Okay that's not likely. Additionally let's say that, like the Solar System, each star has the potential for many planets; but in order to support any kind of life it would have to be at the correct distance from its star with the same kind of orbit as Earth. Let's cut that down, let's say that only 1/9th of those planets that surround a life-giving star is at the correct distance to support life. That means that only 1,000,000,000,000,000,000 planets have the potential to support life. Whew, we really cut our potential planets down there! I was beginning to worry.
Now I'm only talking about the potential for life here. That means a planet that exists within the 'temperate' zone; just close enough to its star to draw energy and yet far enough away to not freeze or turn into a gas giant. Life also needs water, which is essentially a combination of Hydrogen and Oxygen atoms. Well Hydrogen, Helium, and Oxygen just happen to be the most abundant elements in our galaxy and probably the rest of the Universe. All it took on Earth was an unknown combination of chemical reactions to create the spark of life.
So of my estimated million trillion planets that could support life in the Universe (at least life as we know it on Earth), let's say it takes a little bit of random chance and luck to create real living organisms. The planet would have to be free of a mega catastrophe like an asteroid or comet (bigger than the one that hit our planet and killed the Dinosaurs but allowed humans to evolve). That unknown chemical reaction and whatever sparked it would have to occur, possibly a well-timed comet strike or a particularly impressive solar flare. So let's say this only happens in 1% of those planets.
That's still a thousand trillion planets that, in my imaginary calculations, would support some kind of life. But life can exist in many forms, as it has on Earth. It can also exist in many stages. It could be nothing but microbes, or maybe as advanced as a very aggressive badger. But what about intelligent life? Thinking, tool-making, speaking, constructing species that we would be able to interact with on an intellectual level? Again, let's say that in 99% of the cases of life in the Universe, life never gets much further than predator and prey of varying sizes and simple fight or flee intelligence. To hell with it, let's go a step further and say that only .1% of those planets can create intelligent life.
.1% of 1,000,000,000,000,000 is 1,000,000,000,000. That's one trillion planets, on what I think is a pretty conservative set of calculations, that would likely produce intelligent forms of life.
And you know what? That's only life that follows the same pattern as our own. For all we know life could exist on planets like Jupiter and Mercury with a completely different biology that we can only speculate at.
Do you get my meaning? The universe is so immeasurably vast, and every star and every planet must obey the same scientific laws that we do in the Solar System and on Earth, that even the tiniest chance of life evolving means that there would necessarily be thousands upon thousands of different forms of life in the known Universe.
So Where Are The Aliens?
So let's say I'm not just making up random numbers and there are 1 trillion planets that support intelligent life. Why have we never seen these other species?
The Problem of Distance
Because 1 trillion is a tiny, minuscule, and negligible number in terms of cosmology. Like I said above, there are 100-400 billion stars in our galaxy and there are probably 100 billion galaxies that exist as far as our current technology can see. Each galaxy contains somewhere between 100 million and 500 billion stars. By most estimations, that's 10 to the 22nd stars in the known Universe. 10 trillion trillion stars that we know of. That's would mean that only .00000008% of the Universe is inhabited by life. Even if there are 1 trillion advanced and intelligent alien civilizations out there, they're so sparse that we'd never come into contact with them.
I mean the observable universe is 93 billion light years across. That's a lot of space to search for intelligent life. We'd have trouble even locating any evidence of life at all, let alone meeting up and shaking hands or exchanging laser fire.
The Problem of Travel
In order for us to be able to interact with another intelligent species, one of us would have to be able to travel a great distance in some kind of space-faring vessel.
This vessel would have to be fantastic indeed. The closest star system to Earth is Proxima Centauri, at 4.37 light years away. Think about that seriously for a moment. That means if somehow it was possible to travel at the speed of light, the fastest speed we know to be possible for anything to travel, it would still take over 4 years to get from one system to another.
What would fuel such a spacecraft? How would the occupants survive? The type of ship that could accomplish interstellar travel would have to defy all the laws of physics that we know to exist. It would have to have some phenomenal source of propulsion that could get it to reach light speed. It would have to have a small or non existent source of fuel that could be contained aboard the ship. It would also have to have some way of avoiding interstellar debris while traveling. We can't even accomplish this kind of speed/fuel/maneuverability perfection in our cars, how would we do it in space?
Even a world based on Einstein's Physics would have trouble with such a thing. This is where the famous Theory of Relativity would come into play. It's a little too complicated for me to really wrap my head around, but it essentially means that if a ship travels at the speed of light time stops for those on the ship, while the rest of the world would advance in normal time. So 4 years on the spaceship traveling between planets may equal several hundreds, thousands, or millions of years for everyone else. So they may arrive at their destination to find a burnt out husk of a planet destroyed by its star, or a collapsed star.
What I'm basically saying is that such travel isn't possible in any stretch of our current scientific imagination, not even to the star system closest to us. Any interstellar travelers would have to invent an entirely new mode of travel, such as utilizing wormholes.
The Problem of Time
The Universe is estimated to be 15 billion years old. This is a number that we can't really grasp, so scientists (Carl Sagan, again) have helped us comprehend this by created a 'cosmic calendar'. It's a calendar of all time, condensed down so that the beginning of existence is 12:01 am on January 1st and the present day is 12:00 Midnight on December 31st. Here's an image showing this concept:
Intelligent life as we know it didn't exist until around 10:48 pm on December 31st, and that was the simplest communicating ancestor of man. Our ability to travel in space didn't exist until a few milliseconds ago on this scale.
In a cosmic sense of time, we are barely a blink. So it stands to reason that the same would be true for any other form of intelligent life. It would take billions and millions of years to evolve from single-celled organisms into an intelligent being no matter what planet you're on. For us to be able to interact with another intelligent species we would have to exist in the same brief blink of time. If they were any cosmologically younger than us, they wouldn't be intelligent and they'd think we were Gods or Demons and the whole trip would be wasted. So its more likely that they would be much older than us, especially if they were somehow making contact. But how much older than us can a species actually grow to be?
The Doomsday Problem
Well let's say we, or a species like us, continues to evolve and invent. We run into another time related problem. Is it possible for a species to live and evolve long enough to invent and utilize interstellar travel? Looking at our world for the past 100 years or so, how many times have we come close to a global war that would ultimately destroy civilization? Has the world become any more peaceful since the end of the Cold War? It may be a less common fear than our parent's generation, but the threat of global nuclear destruction still looms on the horizon. And think about it, even our first explorations into space were spurred by warfare. What happens in the future? If we develop a new kind of technology to travel to other star systems, do you really think that's what the governments of the world would use it for? It seems more likely, given our past history, that they would use it to create a weapon even more terrifying than a nuclear warhead. There's no reason any other species out there would fare any differently than us. With intelligence comes fear, ignorance, and suspicion. So the Doomsday question is, can a species survive long enough to create interstellar travel before they ultimately destroy themselves?
But that isn't even taking into account outside forces of planetary destruction. Such a cataclysm doesn't need to destroy all life on Earth, it just needs to hit us hard enough to stop scientific progress. The same kind of doomsday scenario can happen a dozen different ways even with a perfectly peaceful species. An asteroid or comet could hit, the magnetic poles could reverse, Global Warming could create a world-wide environmental disaster, some kind of super virus could wipe out most of the world's population, our technology could turn on us in some kind of Y2K thing, etc. The scary thing is that half of those terrifying options are part of the normal, cyclical nature of a planet's life. They WILL happen, the question is when.
Creating the technology for an interstellar spacecraft would be a massive undertaking, and doing it just for the promise and possibility of life would not work. It would likely take a collaborative effort of the entire species, at a time when most of the world's problems have been solved. We'd have to have figured out how to stop global warming, end world hunger, achieve world peace, eliminate disease and poverty, and work together to create such a thing. Do you see this happening in the near future?
Essentially acquiring the technology for interstellar travel is a race against time, we would have to travel and colonize other worlds in order to survive the inevitable destruction of this one. The same goes for any other species on any other planet in the Universe.
So to sum up in one sentence:
Alien life (even intelligent alien life) has, does, and will always exist in the Universe outside of Earth; but you and I will likely never get to see it or interact with it.
Evolution, natural science, and mathematical probability tell us that intelligent alien life exists. Unfortunately the laws of Physics, Space, and Time tell us that we'll probably never find any.
On the one hand, I'm excited by this thought. I see no reason why anyone who reports to believe in evolution and the laws of nature that govern the Universe would not believe in alien life. The only argument against the existence of extraterrestrial life is a religious one. If you believe that the creation of intelligent life was an accident, and not something that occurred due to the natural laws of nature, then you are basically saying that fate, chance, or complete randomness created life. To me, those are all just weak words for some kind of creator God. That's perfectly fine, as long as you understand that by saying that life only exists on Earth you are saying that you believe in some kind of God, some kind of force that decided that life should only exist on Earth.
Otherwise your belief in evolution and scientific truth necessarily means that you believe in the existence of life outside of human beings. And if you factor in probability you should also be able to admit that intelligent life on Earth can't possibly be a unique phenomena. In any planet where life exists the natural progression of evolution is towards an intelligent, thinking, communicating being.
But on the other hand, I'm saddened by the knowledge that although life must necessarily exist outside of Earth - it is highly doubtful that we will ever come into contact with it. I would really like to know what any such creature would look like. How would it communicate? What would its technology be like? Would it have a religious belief system? What kind of other species would have evolved alongside it?
I guess it's time to read some serious Science Fiction. If you read all this babbling, thank you. I will reward you with a great summary of my thoughts, in song and video form. Enjoy!