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Intelligent life is an extremely unlikely certainty. It is unlikely, because the number of
things that have to go right before it can occur is truly mind-boggling. And yet it is a certainty,
because it did occur, right here on Earth, with you and me. And once an event has occurred,
the odds of that occurrence become 100%, no matter how unlikely it seemed to begin with.
As near as we can tell, this was quite unusual. As we look out across the universe,
we think we see desolate, lifeless planet after desolate, lifeless planet. Still,
given the sheer number of planets that exist, how likely is it that intelligent life sprang up,
not once, but twice? Or even more times? Are we alone in the universe? What are the probabilities?
I’m Alex McColgan, and you’re watching Astrum. Today, we shall have a stab in the dark at
solving these mysteries and see what we hit. To begin with, though, let’s start with a caveat.
If we’re going to try to figure out what the odds are of intelligent life existing in the universe,
we should ask ourselves the question; what do we mean by life? Life on planet Earth comes in many
shapes and sizes. From the tallest trees to the smallest microbes, from spindly insects to birds
or fish or humans, our planet is teeming with life. We generally understand what we mean when
we say “a living thing”. We might define it by it moving around, or by it growing.
Generally speaking, scientists define life as any system that is capable of eating, metabolising,
excreting, breathing, moving, growing, reproducing and responding to external stimuli.
Essentially, they are aware of their surroundings in some way, they seek resources,
they take those resources into themselves, and use them to grow or create more of themselves.
And then they get rid of any waste that’s left over. Ew. Some forms of life are much more active
than others, but even things like plants can move to face the Sun, open their buds, or spread out
their roots over time. So, we look at these things and consider them living. Even on Earth, though,
there are some systems like viruses that push the boundary of what it means to be a living thing.
Viruses are so simple, that they lack the ability to reproduce by themselves, or to metabolise.
Instead, they get cells they infect to do that work for them. Are viruses alive? They certainly
have proved devastating to other populations of living things, and we can definitely think
of them that way. But it’s a debate that still rages on in the scientific community.
So, although there are certain qualities that are fairly universal for living things here on earth,
we must be careful about how we go about defining life.
For instance, most living things on Earth make use of water to function.
It carries important nutrients around our bodies, and is so vital for all life on Earth that we
consider the absence of water to be a serious red flag if another planet doesn’t have it.
But if an alien was somehow able to exist by pumping liquid methane through its body instead
of water, would that stop it from being a living thing? Probably not. So, let’s keep an open mind,
but roughly let’s define life as those things that seek out resources, grow and reproduce.
Whether those creatures are predominantly water, like us, or whether they are made from some other
elements, or even pure energy, it doesn’t really matter. All we care about is the likelihood of
them reaching a level of intelligence where they might be able to talk to us.
To get to that level, there are still a number of things that need to go right. To begin with, they
would most likely need a star to orbit. As near as we can tell, life cannot exist without energy.
They would need a planet that suited them. They would need to compete with other organisms for
limited resources, thus encouraging them to adapt and progress. In time, they would need to develop
problem-solving skills and intelligence as a way of gaining those resources and out-competing their
rivals. Their civilisation would then have to survive without accidentally becoming extinct
due to a freak meteor strike or earthquake or global freezing. They would also have to not
destroy themselves. They would have to invest in technology, and would have to develop a level of
technology that allowed them to reach out across the universe. They’d also have to have a desire
to talk to any potential neighbours as opposed to being intensely isolationist, and finally
would have to broadcast a signal out to us for long enough that we would be able to spot them.
All of this is by no means certain. However, as was pointed out by astronomer and astrophysicist
Frank Drake in the first SETI meetings in 1961, all of this could be used to calculate
the probability of us finding alien life. He laid all this out in his famous Drake Equation:
This may look a little complicated, but its based on a very clever and logical idea.
Using the same logic that says you can figure out how many students are in a school by calculating
how many students were inducted into the school at the start of each year, and then multiplying that
by the number of years students studied for, Drake reasoned that the way of calculating the number of
civilisations in our galaxy whose electromagnetic emissions are detectable could be calculated,
provided you knew the rates at which all those other steps happened. Let’s break it down.
N is the number we’re looking for – how many alien races are out there for us to see or hear.
This will give us an idea of the odds of finding them. R* is the rate of formation of
stars suitable for the development of intelligent life, in number per year. Not all stars are very
suitable for life to develop, as some are too cold, or too hot, or generally too unstable.
We need to know how many are being born that could support life. fp is the fraction of those stars
with planets. ne is the number of those planets, per solar system, with atmospheres and material
compositions suitable for life. If they’re covered with lava, or are completely devoid of atmosphere
or water, it’s unlikely that life could form there, based on our own planet’s example.
fl is the fraction of how many of those planets that could support life actually do support life.
fi is the fraction of planets for which that life becomes intelligent.
fc is the fraction of times that life advances enough technologically to start sending out
signals of their existence. And finally, L is the length of time a civilisation exists, on average.
If you combine all of these elements, you could accurately predict how many
alien civilisations we would be able to see up in the night sky, right now.
Of course, you might have noticed a drawback with this equation. Some of these numbers are
simply not known by us. But, where’s the fun in not giving it a go anyway?
By inputting the numbers that scientists currently believe to be most likely, and by making a few
assumptions of my own along the way, we will attempt to solve the drake equation. If you think
that any of my numbers seem unreasonable, let me know in the comments down below! So, with that,
let’s see how many alien civilisations we might reasonably expect to see out in the night sky.
To begin with, we can input our values with reasonable certainty. Scientists looking at the
Milky Way galaxy can accurately predict how many stars form every year, as we have many examples
to draw from. Depending on who you ask, the number ranges from between 3 and 7. Let’s say 5,
at a conservative estimate. Fp is easy to solve too. Through recent astronomical observations by
the Kepler space telescope, it’s become apparent that planets are very common in the solar system,
with each star on average having one. So, let’s set this number high as well – let’s say 90%.
However, the number that we currently predict is at a suitable distance from their stars,
as well as having the ideal mix of elements that would produce life similar to ours is much lower.
Of the 100 billion planets in the solar system, perhaps as few as 300 million fit into this
category. Obviously, this does not account for alien life that’s significantly different from us,
but let’s discount them for the moment as then this would be even harder to predict.
This gives us a percentage chance of 0.3% - quite a small chance that one of the planets in a solar
system is suitable for life. So, 0.003 for ne. So far, so substantiated by evidence. Here is
where things get a little tricky. For the number of times that life has arisen, we have only one
example to draw on – life on Earth. To date, we have not proved that life arose on Mars or
Ganymede, for all the conjecture on that front. So, we can take this estimate one of two ways.
As near as we can tell from the fossil record, as soon as the planet cooled down enough, life came
into being, which might indicate a high value for fl. Perhaps as high as a certainty [1]. But on the
other hand, from what we know, all life originated from a common ancestor. Which is to say, life
formed on this planet from non-biological matter exactly once, and has never risen up again since.
Scientists have looked for evidence of bacteria that might have independently come into being,
but so far haven’t found any. This may be a coincidence. Perhaps life did arise multiple
times, but the life that arose first was more advanced and so out-competed the newly formed
simple bacteria into extinction. Still, it means that life is either incredibly certain, or a
million to one. Let’s go with the more pessimistic number, and see where that takes us. fl = 0.0001%
We encounter the same problem for the arising of intelligence. There are numerous examples of
animals displaying forms of intelligence. Octopi can open jars and solve puzzles,
and some birds and apes can use tools or even use sign language.
Perhaps this proves that given enough time, life always evolves into becoming more intelligent.
However, if we want to be strict about it, we could also accurately say that of all
the millions of species that have existed on the Earth, only 1 actually was intelligent
enough for our purposes. Us. Which makes the odds seem very low for it happening.
Let’s once again input our one million to one value for fi, again to just be pessimistic.
In terms of how many become technologically advanced enough to start communicating, I think
that this number is likely much higher. Although we only have one species to compare to again,
it’s worth noting that humans are unintentionally chatty with the universe, quite by accident.
Thanks to industry and transport, we are altering the chemical composition of our atmosphere, which
is something an alien race could detect, certain molecules in our atmosphere are only there because
they are man-made. We also send signals out into space thanks to our radio signals and satellites.
Sometimes we even send signals out into the stars deliberately,
such as the Arecibo message which was broadcast from Earth in 1974, and contained information
about human civilisation and history, expressly so any aliens that heard it could learn about us.
Although these signals would not travel far on the grand cosmological scale of things before becoming
dispersed and indistinguishable from background radiation, we WOULD count as a communicating race.
So, I’m going to predict this number as high. Let’s say 70% of intelligent races
reach this level. Finally, how long do civilisations survive? For this number,
we sadly do not even have a single example. We will not know how long our race will survive
until we all die out, by which point there will be no-one left to write down the final figure.
However, although there are numerous dangers that could end us as a species,
ranging from meteor-strikes, nuclear war, or even solar flares, the longer we are able to survive,
the more likely it is that we will go on surviving. This is because once humanity
spreads out, we become more and more resilient to a species-threatening catastrophe. If we are
on multiple planets, a comet hitting Earth would no longer threaten the survival of our species.
If we are in multiple solar systems, a solar flare would no longer be able to get all of us.
Species could in theory reach a sort of immortality level in this way,
lasting for potentially billions of years as long as they could get out of the danger range.
Let’s be optimistic and use this figure. What does that give us for the Drake Equation?
Based on these assumptions, our answer is… 0 in our galaxy. If civilisations lived for a trillion
years (which is longer than the universe has existed for), we’d still be at 0 for these values.
Given these odds, our chances of ever hearing from another civilisation is next to non-existent.
But that’s just the thing with this kind of estimate. If we instead assumed that life arising
was certain, and that intelligence arising was certain too, our final answer for even a
1000 year civilisation would no longer be 0. Instead, that comes to an answer of 9 in our
galaxy. Nine intelligent races, who might be up in the stars right now trying to communicate with us.
And if races routinely do make it to functional immortality to the point where their civilisations
last for a billion years, then we would see as many as 9,450,000 in our galaxy. Or more! I know
these are hypotheticals, but I find this very interesting. Putting the numbers through the
equation make it a bit more tangible, a bit more magical and exciting even. According to
the Drake equation, the sky could be completely silent, or absolutely teeming with alien life.
If it is the former, then we should probably prepare ourselves for a long,
lonely existence. We should learn to get along with each other, because we are all
the life we are ever going to see. There will be no aliens stopping by to say hello.
But if it’s the latter, it leads to a very important question… Where are they all?
But that is a question we will have to look at in the next video of this series. For now,
my own biggest takeaway from this is the need to try to refine some of these numbers. Through the
efforts of rovers like Perseverance on Mars, we are already taking steps towards attempting to
find alien life within our own solar system. The more we are able to narrow these numbers down,
the more certain we will be as to our odds of finding alien civilisations. Until we find one,
it’s all a question of odds. And whether the chances are high or low, well, that’s
very much up to you, so write in the comments? What do you think? Or what would you rather?
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