Probability is a mathematical expression of the likelihood of a given scenario occurring. It is normally expressed as a number between zero and one. Zero, meaning there’s no probability of it occurring, and one, meaning it is an absolute certainty. The probability of a coin toss coming up heads, as an example, is 0.5.
So what is the probability of life existing in outer space? Well, you’re probably thinking we’re going to need something like the Drake equation and take into account the number of stars being formed within our galaxy, the fraction of those stars with planets and then the sub-category of those planets that are capable of supporting life (as we know it), etc.
But we need not go to all this effort because we already know the answer. The probability of life existing in outer space is one. It is beyond doubt. It is an absolute certainty. We know space can support life because we’re alive. We are in outer space (or, at least, our planet is).
Ok, there’s groans from the cheap seats, but this is a perfectly valid point. Without realising it, we tend to think of the Earth as the centre of the universe. We think of the Earth as being somehow special and unique, and from our perspective, it is. It’s the pride of ownership, the pride of tribalism applied to “our” planet. But Copernicus demonstrated long ago that the Earth has no special place of importance in the universe. It’s special to us, but both the Earth and the Sun are rather ordinary and average in a dull kind of way. That life exists here, in an unassuming, less-than-remarkable neighbourhood, is strong grounds for considering that it could occur elsewhere.
Ok, so what about any other life in outer space?
This is where things get particularly interesting. NASA has observed Glycolaldehyde and over 120 other simple molecules in vast gas clouds in space spanning three light years in size (which is huge. Voyager is currently on the edge of our solar system and it’s only 13 light hours away, less than one light day as compared to three light years).
Glycolaldehyde is a basic sugar that is found in both Ribose and Glucose sugars. Ribose is the building block of DNA, the basis of all life of Earth, while Glucose provides the metabolic energy for cellular life. So space is brimming with the basic building blocks for creating and sustaining life.
Another recent discovery has found 140 trillion times as much water in one small region of space than in all the oceans on Earth!
Numbers like this are meaningless until you put them in context. You probably read that last sentence in roughly a second. So if we think of seconds as a point of comparison, being the equivalent of all the water on Earth for the purpose of our analogy, then how long is a trillion seconds? Well, you’ll hit a million seconds after 11 days, but it will take you 32 years to pass a billion, while a trillion will take a whopping 32,000 years. So when we say there is an abundance of stuff out there essential for life, it’s a gross understatement. The components for life exist in such overwhelming quantities it is unfathomable.
And this brings up an interesting point. When scientists talk about the prospect of life in outer space, they talk almost exclusively in terms of probabilities. Creationists, determined to downplay any rational thinking about the universe, will often liken these probabilities to things like a 747 being randomly constructed as the result of a tornado hitting a junk yard. But this misses a crucial point, and that is the context in which things occur changes the on-going probability.
The probability of tossing five heads in a row might be slim, but after four heads, the probability of making it five in a row is actually quite good, at 0.5. In the same way, the probability of life accumulates and increases as each component required for life compounds and builds upon the previous.
150 years ago, Charles Darwin demonstrated that evolution works through Natural Selection, the gradual accumulation of inherited traits according to natural laws. Natural selection applies to living, organic creatures because of the compounding effect of numerous small changes adding up over time.
Could a similar principle apply to inorganic substances?
At first, it’s tempting to say, no. But this is not necessarily the case. Remember, the only reason Natural Selection works is because there is a mechanism in place for traits to accumulate and pile up from one generation to the next (which we call DNA). Inorganic selection is possible if there is a similar mechanism causing a compound effect.
Stay with me here.
There’s no cosmic DNA but there is the accumulation of compounds, the slow clumping of “stuff” that makes climbing mount improbable no arduous task, and that is a galaxy, accumulating into solar systems, accumulating into stars and planets. Together, they have a compounding effect, like interest in your bank.
With such an abundance of mater (metals, gases, water and pre-organic molecules like glycolaldehyde) being drawn together by gravity to form planets and moons around stars, we have, in effect, the same accumulation of the fundamental components required for life occurring all throughout the universe.
So why don’t we see ET staring back at us?
SETI are struggling with that question right now, and it seems there are a variety of possibilities. Firstly, there are a phenomenal number of stars within the Milky Way, some 200 to 400 billion of them, and it takes considerable time and effort to examine each of them. Also, we cannot see all of them. Radio astronomy can see through dust clouds, but if life existed in abundance, directly opposite us, on the other side of the galactic core at roughly the same point on a similar spiral arm, we would never be able to see it directly with a regular telescope, determine what planets there were in each system, etc. So there are limits to how well we can search.
Also, it may be that not every solar system is conducive for life. It seems our Sun is a third generation Population I heavy-element rich star. So our solar system may well be one of the early occurrences of compounding accumulation that allows life to thrive.
And the sheer distances involved mean the other several hundred billion galaxies (minimum) in our universe are just too distant for us to observe life. It would be like being stranded on a island off the coast of Africa and doubting there was any life on the distant desert shores when, in fact, the continent is teeming with the most remarkable diversity of life.
So… is there life in outer space?
At the very least there is us, but, more than likely, the universe is teeming with life because it is teeming with the building blocks for life.