Chapter 1: What is the evidence for alien life beyond Earth?
Life As of yet, there is only one example we know of, the life we find here on Earth. There is no definitive proof of life anywhere else in the universe, but that does not mean for certain that it's not out there. If there is alien life on planets other than our own, what might they look like? What would be their biology, and what would we see of their civilization?
You might think there is no way to predict this. However, believe it or not, even though we have never seen a single alien, we can make educated guesses based in science to help us know what to expect. And it's all thanks to a simple principle. Form follows function. I'm Alex McColgan, and you're watching Astrum.
And although we cannot say with exact certainty what any aliens visiting us might appear like, or how they behave culturally and technologically, today I'm going to share with you some ideas that might mean, if they ever do land on our doorstep, you aren't completely caught off guard. But first, let's talk about why we look the way we do.
As you look down at your own body, even if you do not know what all of it does, you are an incredible example of optimization. You likely have two hands complete with fingers and opposable thumbs, ideal for grasping tools and performing fiddly, delicate operations.
You have a digestive system that is capable of taking in matter, extracting nutrients, and using them to build up or repair yourself. You have legs for locomotion, a brain for thinking, A heart that will, on average, pump 2.5 billion times across your lifetime without breaking.
All of these parts of your body perform specific functions, and have been honed over millennia to be really good at what they do, even if you don't feel it sometimes. You are an example of form following function. Thanks to natural selection and random mutation, nature is really good at figuring out what works.
When Charles Darwin was voyaging through the Galapagos Islands, he noticed that different finches had different shaped beaks.
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Chapter 2: How can we predict the appearance of alien life forms?
After observing them for a time, Darwin noticed that the finches with larger, more heavyset beaks ate different types of food than finches with smaller, daintier beaks. In fact, a large beak was ideally suited to breaking open tough seeds or nuts, while the smaller beaks were more suited to getting in nooks and crannies for grabbing insects.
This observation was the basis for his well-known theory of evolution. In this theory, thanks to genetic variation and competition, nature is constantly trying out new things to see what works. And there are certain things that give you an edge.
Thanks to all the light that was bouncing around from our sun, organisms that evolved to take advantage of this by developing sight had a bigger advantage over organisms that did not. They could find food better, or avoid predators, or generally navigate their environment. So useful is sight that nature did not just come up with it once.
We believe the eye evolved independently about 40 times over the course of life on Earth. 40 different species that previously could not see evolved eyes. This is called convergent evolution, and eyes are not the only example of it happening. Bats are not related to birds, and yet both developed wings to fly.
And speaking of bats, both bats and dolphins independently evolved echolocation to help them see in environments where light was not so plentiful. Photosynthesis has arisen dozens of times. Koalas have almost identical fingerprints to humans. This happens because there are some selective pressures that are simply universal. Everything that lives needs to gain nutrients, grow and reproduce.
And as a result, like a plant bending its roots around rocks to find softer soil, nature is good at figuring out the best way of getting what it needs. Because of the prevalence of light, eyes are just a good idea. And when something works, nature sometimes comes up with it more than once.
This means that on planets that are similar to our own, it's entirely possible that evolution would end up going a similar way. Although hypothetical aliens on other planets might not look exactly like us, they might look surprisingly similar.
I always thought that it looked silly that so many aliens in sci-fi films were humanoid, but perhaps this is more than just a way of easing pressure on the film's costume department. Convergent evolution says this might actually happen. If it worked for us, maybe it just works generally.
Any alien that made it to the stars would need to have the ability to work tools, so fingers or something similar would be a likely addition to an alien race. Large heads filled with complex brains for analysis and problem solving would also be a benefit. The human brain is the most complex of any animals on Earth, with 86 billion neurons. It's not so unreasonable that aliens would be the same.
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Chapter 3: What role does evolution play in the development of alien species?
The presence or absence of silicon or rare metals might help or hinder a computer revolution, speeding up or slowing down a civilization's progress.
Once an alien race has evolved to the point where it has become intelligent, unless it came into being through some weird mechanism we don't understand, it probably did so throughout competing its rivals and collecting resources for itself and its offspring. Civilisations made up of such creatures will most likely also have a hunger for space and resources.
Whether they gain these things through clever diplomacy or aggression, it is most likely that they will want them. Form follows function. This quest for expansion and seeking more and more energy and resources led Soviet astrophysicist Nikolai Kardashev in 1964 to propose the Kardashev scale for classifying the different kinds of alien civilizations that might exist out there.
He grouped civilizations into three kinds. Type I civilisations can completely utilise the energy available on their planet. We have not quite reached this point as a species, so we are roughly a 0.7 on Kardashev's scale.
Type II completely utilise the energy available from their star, possibly by building a giant megastructure such as a Dyson Sphere to capture and utilise all of its energy output. Type III civilisations would be able to utilise the entire energy output of its galaxy.
We have seen no evidence of an alien civilisation such as this one, which is for the best as they would likely see us in the same way we see bacteria. Mildly interesting, but otherwise completely beneath their notice.
Other scientists since Kardashev have proposed further additions to this scale, Type IVs that use all the energy in the universe, Type Vs that use all the energy in multiple universes, or even the enigmatic Type Omega, capable of utilising energy sources beyond even that, perhaps existing outside of time entirely. Such a civilisation would essentially be gods.
We would have no way of detecting them, because nothing in the universe would exist except in the way they wanted it to, and we would have nothing to compare their existence against.
While this may seem like a bleak outlook for humanity, if we ever came across another alien race under this theory, we would almost certainly end up competing for resources in one way or another, or just getting steamrolled by a vastly higher power. But there are actually other possibilities for alien development too. After all, not all humans are interested in expanding ever outwards.
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Chapter 4: How do environmental factors influence alien biology?
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 civilization 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 it's based on a very clever and logical idea.
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Chapter 5: How do we search for habitable exoplanets?
Perhaps they believe that we will either figure out how to get along, or else we'll wipe ourselves out. Either way, in the meantime, it is better they stay hands-off. As any parent will tell you, sometimes telling a child something is not enough for a lesson to sink in. Sometimes experience is the only effective teacher. There might be a galactic community out there just waiting to welcome us.
violence, indifference, benevolence. In theory, any of these or all of these in some combination might be the reasons we don't hear from alien life. Ultimately, we would be wise to tread carefully. Meeting alien civilizations might sound exciting, but it would inevitably come with terrible risks. And possibly fantastic rewards. Is it worth the gamble?
Looking up to the stars on a bitingly clear night, a horizon away from the nearest town, you'll feel alone. But as your eyes adjust, you are embraced by the light of an entire universe. Surrounded by such scale and wonder, It's hard in that moment to imagine that we are it, isn't it? That we are the only life the universe will ever know, confined as we are on this pale blue dot.
Perhaps we are alone. Or maybe, just maybe, given enough time, nature's laws conspire to make life not just probable, but inevitable. I'm Alex McColgan, and you're watching Astrum. Join me today as we explore the chaotic transition from chemistry to biology on our planet, seeking answers to some of the most debated and fervent questions in science. What is life?
How could life have emerged on Earth in an environment that would kill us as we are today? And can it begin all over again elsewhere in the universe, or even on our own planet? To begin to answer those questions, let's imagine that while walking across a barren desert, your foot kicks a stone.
It wouldn't occur to you that someone put it there or crafted it, since the stone is too simple an object. Now, imagine instead that you stumble across a glistening, precision-made, embossed gold pocket watch. William Haley argued that because, unlike a stone, a watch obviously requires a designer, you'd have to assume that someone had made the watch and placed it there.
And because, when you truly think about it, life is far more intricate than a watch. life too must require a designer. It's a compelling argument, isn't it? Even the simplest forms of life are far, far more intricate than a watch, and if a watch requires a designer, surely so must life. Unfortunately, the argument doesn't quite work. But why?
What really is the difference between a man-made machine and mankind? Charles Darwin's work on evolution and the origin of species crystallized the idea that life evolves and that all life began from one common ancestor.
Therefore, I should infer from analogy that probably all the organic beings which ever have lived on this earth have descended from some one primordial form into which life was first breathed. And there it is, emergence, life from chemistry, something different than the sum of its parts. Darwin understood that life needs no designer.
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Chapter 6: What are the chances of finding intelligent life in the universe?
Despite creating extremely localized order, life degrades free energy to heat, increasing entropy in the universe overall. Unsurprisingly, given that you're watching this video, it's clear that entropy allows for, or even encourages, the development of life. So how did the building blocks of life seemingly defy entropy in constructing order from chaos?
How does a living cell build up that can power itself, encode itself with DNA, construct itself too, and have the ability to evolve? And how can it do it all piece by piece while being functional at every step, even though each part is essential? How on Earth could life emerge?
Well, there is little consensus on the precise way that life actually emerged on Earth, but let's explore the molecules that, without exception, build every single life form on Earth. Perhaps life offers clues to its own origin.
The key basic building blocks life uses today in no particular order are fatty acids, amino acids, and nucleotides, and all three are believed to have been present on the early Earth, and have even been found on asteroids in our solar system. The first are fatty acids, and despite having little chemical functionality, they create structure and have an extraordinary function built in.
These long chain molecules make up cell walls of all life on Earth and are believed to have made the first membranes of protocells. Membranes are barriers and fundamental to create an individual unit. After all, you can't have a house without walls or a country without borders. That's not a political statement. Remarkably, cell-like structures made from fatty acids form spontaneously in water.
As anyone who's failed to make simple mayonnaise will know all too well, oil and water don't like to mix. These fatty acids, with a water-loving head and a water-hating tail, will spontaneously arrange to minimize water's contact with the tail and maximize it with the head. These simple pressures can create a bilayer membrane with a cavity for an early cell to call home.
This is called a liposome. Unbelievably, these liposomes can also spontaneously divide and speed up chemical reactions by encapsulating and concentrating the molecules in a smaller space. This is a perfect example of how unexpected life-like behaviours can emerge out of the laws of quantum mechanics.
But won't these crude divisions just go wrong and kill the cell more often than not in hot, salty water? Well, yes, there's a good chance. However, the environment isn't a simple system. It's impure. There are other molecules floating around that can stabilise the cell walls further, like amino acids.
A diverse range of these building blocks were present on early Earth and are even present in our solar system. Today, life uses 20 different amino acids to make all the cellular machinery within us like enzymes and ion channels, as well as larger structures like muscle and hair. There is a miraculous relationship between amino acids that make up proteins and our next building blocks, nucleotides.
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Chapter 7: What is the Kardashev scale and how does it classify civilizations?
So, have any exoplanets like these been found? Well, out of the thousands of exoplanets that have been discovered, 16 of them are thought to be rocky planets and sit in the Goldilocks zone, or the habitable zone of their respective stars. Let's just remind ourselves of the ingredients needed for life as we know it. We believe that liquid water needs to be present.
Liquid water is essential because biochemical reactions can take place in water. Water is also an excellent solvent that easily dissolves and carries nutrients and other compounds in and out of cells. Life forms on Earth are made primarily of water. In fact, our human bodies are more than 60% water.
Life also needs sufficient protection from cosmic and solar radiation, which can break down and damage cells. On Earth, this protection comes from our magnetic field. there also needs to be essential chemicals found in the ground on Earth, and an energy source, which for us is the sun.
So the Goldilocks zone is where, assuming other conditions are right, liquid water could theoretically pool on the surface. This zone is always different depending on the parent star, and how big and hot it is. Looking at our own solar system, Venus might just be in the Goldilocks zone, as well as Earth and Mars.
We already know that only 1 in 3 planets in our own solar system's Goldilocks zone can have liquid water, so just being in the right place is not always enough. The type of star is also important. Our star, although seemingly active on the surface, is actually quite stable compared to a lot of other types of stars. The sun will likely be 10 billion years old before it burns out.
On the other hand, the hottest types of stars will only last for millions of years in comparison. It is thought that this is not enough time for life to form around it, certainly not animal life that can communicate as we understand it. So we have a lot of filters we can now use to narrow down our search for habitable worlds.
Out of the original 3,797 confirmed planets, 16 are terrestrial planets that orbit within the Goldilocks zone of their stars. However, the habitable zone of some stars means the planets are close enough to be tidally locked, meaning only one face of the planet sees its star.
This proximity to the star also means the planet is exposed to a lot of solar radiation, sometimes thousands of times more than we are exposed to on Earth.
In other words, out of those 16, only 4 are likely candidates to be Earth-like, although it is worth mentioning that exoplanets in systems like the TRAPPIST-1 system could still be habitable or have life even if all the planets are tidally locked. but the TRAPPIST system is worthy of its own video, so I won't expand on it here.
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