There are probably 10,000 stars for every grain of sand on Earth, in the observable universe. We know that there might be trillions of planets. So where are all the aliens?
Some key facts
The entire observable universe is about 90 billion light-years in diameter. There are at least 100 billion galaxies each with 100 to 1000 billion stars. Recently we’ve learned that planets are very common – and there are probably trillions and trillions of habitable planets in the universe, which means there should be lots of opportunity for life to develop and exist.
Right but where is it? Shouldn’t the universe be full of spaceships like on StarTrek? Let’s take a step back…
The universe is too big and ever-expanding
Like I’ve explained in a previous blog (read “All you need to know about the Universe and space travel“), if there are alien civilizations in other galaxies there’s no way we’ll ever know about them because basically everything outside of our direct galactic neighborhood [the so called local group] is pretty much out of our reach forever because of the expansion of the universe.
Even if we had really fast spaceships it would literally take billions of years to reach these places traveling through the emptiest areas in the universe. So let’s focus on the Milky Way.
The Milky Way is our home galaxy it consists of up to 400 billion stars that’s a lot of stars roughly 10,000 for every grain of sand on earth there are about 20 billion sun-like stars in the Milky Way – estimates suggest that 1/5 of them have an earth-sized planet in its habitable zone (the Goldilock zone: the area with conditions that
enable life to exist). If only 0.1% of those planets host life there would be 1 million planets with life in the Milky Way!
But wait there’s more: the Milky Way is about 13 billion years old in the beginning it would not have been a good place for life because things exploded a lot but after one to two billion years the first habitable planets were born. Earth for instance is only 4 billion years old so there have probably been trillions of chances for life to develop on other planets in the past.
If only a single one of them had developed into a space traveling super civilization we would have noticed by now. What would such a civilization look like? There are three categories
A type one civilization would be able to access the whole energy available on its planet. In case you’re wondering we’re currently around 0.73 on the scale and we should reach type one sometime in the next couple of hundred years
Type two would be a civilization capable of harnessing all of the energy of its home star. This would require some serious science fiction but it is doable in principle. Concepts like the Dyson Sphere a giant complex surrounding the Sun would be conceivable.
Type three is a civilization that basically controls its whole galaxy and its energy.
An alien race that’s this advanced would probably be God-like to us, but why should we be able to see such an alien civilization in the first place? If we were to build generation spaceships that could sustain a population for around 1,000 years we could colonize the whole galaxy in 2 million years. Sounds like a long time but remember the Milky Way is huge so if it takes a couple of million years to colonize the entire galaxy and there are possibly millions if not billions of planets that sustain life in the Milky Way and these other life-forms have had considerably more time than we’ve had then: Where are all the aliens?
The Fermi Paradox
Today, there are numerous potential ‘solutions’ to the Fermi paradox, including explanations like:
- We’re overestimating the prevalence of intelligent life in the Universe. We might be the only ones
- We’re overestimating the desire of any single life form to willingly transmit information
- The information is there, we’re just not seeing it or understanding it
- The information was there, and might be there again, but humans haven’t been listening long enough to detect it. We might be living in the wrong moment to detect such signlas
- Humans are the first to arrive at the interstellar stage and we’re too early to detect other civilizations. Maybe, like Elon Musk suggests, we just have to venture to the Stars and become the first type three civilization to keep the delicate flame of life existing and spread it until the universe breathes its final breath – vanishes into oblivion.
Here we look at possible solutions to the Fermi Paradox.
So will we be destroyed or does a glorious future await us? Space travel is hard. Although possible, it’s an enormous challenge to travel to other stars. Massive amounts of materials have to be put into orbit and assembled.
A journey of maybe thousands of years needs to be survived by a population big enough to start from scratch. And the planet might be not as hospitable as it seems from afar. It was already extremely hard to set up a spaceship that could survive the trip.
An interstellar invasion might be impossible to pull off. Also, consider time: the Universe is very old. On Earth there’s been life for at least 3.6 billion years. Intelligent human life for about 250,000 years. But only for about a century have we had the technology to communicate over great distances.
There might have been grand alien empires that stretched across thousands of systems and existed for millions of years and we might just have missed them. There might be grandiose ruins rotting away on distant worlds. 99% of all species on Earth have died out.
It’s easy to argue that this will be our fate sooner or later. Intelligent life may develop, spread over a few systems and die off, over and over again.
But galactic civilizations might never meet. So maybe it’s a unifying experience for life in the Universe to look at the stars and wonder “Where is everyone?” But there is no reason to assume aliens are like us, or that our logic applies to them. It might just be that our means of communication are extremely primitive and outdated.
Imagine sitting in a house with a Morse code transmitter: you’d keep sending messages but nobody would answer, and you would feel pretty lonely. Maybe we’re still undetectable for intelligent species and we’ll remain so until we learn to communicate properly.
And even if we met aliens we might be too different to be able to communicate with them in a meaningful way.
Imagine the smartest squirrel you can, no matter how hard you try, you won’t be able to explain our society to it.
After all, from the squirrel’s perspective, a tree is all that a sophisticated intelligence like itself needs to survive. So humans cutting down whole forests is madness; but we don’t destroy forests because we hate squirrels. We just want the resources. The squirrel’s wishes and the squirrel’s survival are of no concern to us.
A Type three civilization in need of resources may treat us in a similar way.
They might just evaporate our oceans to make collecting whatever they need easier. One of the aliens might think for a second “Oh, tiny little apes! They built really cute concrete structures, oh well now they’re dead.” before activating warp speed. But if there is a civilization out there that wants to eliminate other species, it’s far more likely that it will be motivated by culture rather than by economics. And anyway it will be more effective to automate the process by constructing the perfect weapon, a self replicating space probe made from nano-machines.
They operate on a molecular level: incredibly fast and deadly,
with the power to attack and dismantle anything in an instant. You only need to give them four instructions:
One, find a planet with life.
Two, disassemble everything on this planet into its component parts.
Three, use the resources to build new space probes.
Four, repeat. A doomsday machine like this could render a galaxy sterile in a few million years.
But why would you fly light years to gather resources or commit genocide?
The speed of light is actually… not very fast. If someone could travel at the speed of light, it will still take 100,000 years to cross the milky way once, and you’ll probably travel way slower. There might be way more enjoyable things than destroying civilizations and building empires.
An interesting concept is the Matrioshka Brain. A mega-structure surrounding a star, a computer of such computing power that an entire species could upload their consciousness and exist in a simulated universe. Potentially, one could experience an eternity of pure ecstasies without ever being bored or sad, a perfect life. If built around a red dwarf, this computer could be powered for up to ten trillion years.
Who would want to conquer the galaxy or make contact with other life forms, if this were an option?
All these solutions to the Fermi Paradox have one problem. We don’t know where the borders of technology are. We could be close to the limit or nowhere near it. And super technology awaits us, granting us immortality, transporting us to other galaxies, elevating us to the level of gods. One thing we do have to acknowledge is that we really don’t know anything. Humans have spent more than 90% of their existence as hunter-gatherers. 500 years ago we thought we were the center of the universe. 200 years ago we stopped using human labors as the main source of the energy. 30 years ago we had apocalyptic weapons pointed at each other because of political disagreements.
In the galactic time scale we are embryos. We’ve come far, but still have a long way to go. The mindset that we really are the center of the universe is still strong in humans, so it’s easy to make arrogant assumptions about life in the universe.