I read somewhere there are at least 6 possibilities:
- Dark forest theory - read at least book 1 and 2 of three body problem series or google for spoilers
- A filter exists, or more plainly something that always causes a civilization to eventually fail.
- Similar to Star Trek, other civilizations are waiting for us to pass a threshold before contact is made.
- Carl Sagan: the universe is so large and intelligent life is so sparse, we just haven’t come across them yet.
- Life on our planet is unique to the entire universe
- Could also be a mixture of some of these.
Whatever it is, it’s a fascinating problem and I like Carl Sagan’s approach.
An addendum to 4:
We could be one of the first, so life is unusually sparse during this period of time.The universe is old, but it takes a lot to build up the components needed for life as we know it. The first two generations of stars wouldn’t have created the exotic materials in quantitie we needed to seed a world with the requirements for life.
And life couldn’t have realistically happened much faster in a 3rd generation system than it did in our system.
There are some very old 3rd Gen stars, but it’s less common and iirc they’re not close to us.Tldr
This is early phases, life is going to get more common over the next few billion years.
Earth is so big that I’ll never explore every spots on earth. But I think there are still living things in places that I’ll never go to.
不要回答，不要回答，不要回答。
The assumption that other life has both the capacity and desire to explore the universe is flawed. Think of all the variety of life that has ever existed on Earth. How many of those species have ever attempted to travel to space?
Next imagine a species that does want to explore the universe to find other life. Would it make more sense for them to focus their efforts looking to the outer rim of the galaxy with the lowest number of celestrial bodies, where we are, or more towards the center where there is a statistically higher chance of finding life?
If there is an alien species with the capability and desire to explore the universe, and they search the less dense outer rim of the galaxy, and they happen to stumble upon our tiny spec of dust in the sandstorm, what if they don’t communicate in a way perceivable by us (and vice versa)? They may have flown right without realizing we were here and we could have looked right past them at the same time.
It’s also possible that ancient alien theorists are right. We have been visited. They kicked it with ancient humans for a while before heading back home to tell their friends about us and arrange future visits. The round trip could easily take 10s of thousands or even millions of years.
Going off the ancient alien theory, if real, my belief is that we haven’t been visited again because they haven’t made it home yet to tell anyone about us 😂
Our universe is not only vast it is expanding in all directions. The universe almost certainly has intelligent life at various time and places. That any develop sufficiently to communicate by radio broadcasts of sufficient power within the relatively tiny area of our ~100 years or so of our being able to listen considering the time it takes for signals to reach us mean that our sampling window is just too small.
Imagine a sphere centered around earth spreading out in all directions. The outer edge represents the space where their radio could have reached us by now since we became capable of listening and even bothered carefully listening. Meaningful systematic SETI is like 1970’s and forward. So ~50 light years or so. Anything further hasn’t reached us yet. Anything closer may have already passed us. Maybe they stopped. Maybe they moved onto something past radio, or maybe they are dead.
For example, humanity has had aproximately 125 years or so of radio where someone could detect us. Not a long time. We are already breeching 7 of 9 planetary boundaries, environmental limits that once breeched work like a timebomb that risk our civilization’s collapse and possible extinction. We could nuke ourselves out of existence at any minute for the last 75 years. How long will we be broadcasting for? That expanding sphere of space where our radio has reached will hollow out if/when we stop broadcasting. So alien civilizations that want to listen to us can only be in that very thin slice of space between when we started and when we stop broadcasting. Compared to the universe, it’s nothing. Our galaxy, the milky way is 84000ly in diameter to give you some perspective.
For us to find alien life, our two civilizations both have to fall within our imagenary expanding hollow sphere of radio listening and their hollow expanding sphere of broadcasting. We’ve barely scraped the smallest corners of our own section of the unfashionable part of the spur on a minor spiral arm of our galaxy. 50ly/84000ly= 0.059% of our galaxy for anyone currently broadcasting. Our listening sphere goes back in time and out in distance a lot further, but has similar limitations. If anyone in our nearest neighbouring galaxy, Andromeda, was broadcasting, they would have had to do it ~2.5 million years ago for us to hear it now. If they did it ~2.500050 million years ago, we missed it because we weren’t listening.
Here is a map of stars withing 50ly of us.
Edited for clarity and something aproximating correctness. It still sucks, but I’m too hungover.
If it turns out to be the former, I don’t blame them.
The universe is vast. The assumption that any species could travel to another is a flawed one.
“Space,” it says, “is big. Really big. You just won’t believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to space. Listen…” and so on.
The Hitchhiker’s Guide to the Galaxy
And even if they could, it’s hard to imagine a reason to travel to another star system.
The expansion of a species beyond a single star system for any reason is dubious, there’s really just no reason to do it, and the cost is extremely high (given known physics).
I say there’s no reason to leave the solar system, but I think that probably needs some explanation, because the obvious reason that may come to mind is probably overpopulation on earth and looking for other habitable planets. The thing is, in order to travel to another star system you need to really master surviving in space; if you can build a colony ship, you can build space habitats. But if you can build space habitats, then you have enough material and energy right here in the Sol system to support quadrillions of humans living in space habitats. In other words, there’s no reason to leave for tens of thousands of years.
All that is to say, if you aren’t traveling to other star systems for your own species, you probably aren’t doing it for others.
If we built a self replicating probe and sent it to the nearest system, and from there it sent off 2 more probes and so on, in 2 million years they’d have reached every system. The only cost would be the initial probe. and any species that has mastered it’s own star system could do that. They could send out their own genetic material and spread their form of live.
They don’t have to go themselves out into space, they can send automated machines. We’ve already started doing just that with very basic machines for scientific curiosity. I see no reason why we wouldn’t send out replicating probes when we have the technology to do it.
However we do come back to Fermi’s Paradox: the universe is 13800million years old. So far we have no evidence a probe has reached our star system. Where are they? Maybe we just haven’t stumbled across one yet. Or maybe life really is very rare?
However we do come back to Fermi’s Paradox: the universe is 13800million years old. So far we have no evidence a probe has reached our star system. Where are they? Maybe we just haven’t stumbled across one yet. Or maybe life really is very rare?
Well there are actually some pretty convincing explanations for for the Fermi Paradox. The one I like most is that despite the 13800 million years, we’re pretty early for complex life, and we may just be the first technological civilization in the Milky Way.
The theory goes that while there are a lot of older stars out there, there aren’t a lot of 3rd generation stars. When some stars get to the end of their life, they collapse and then go supernova, leaving behind a dust cloud in which other stars can then form. Here’s the thing, many heavy elements are only produced through nuclear fusion during a supernova. (Basically everything heavier than iron, about 3/4 of the periodic table). So that second generation of stars contain more heavy elements within the star. When the second generation goes supernova, more heavy elements are created.
Life exists on earth thanks to all of the complex chemical reactions that can take place on earth. But all that may only be possible because we’re a 3rd generation solar system with all our fancy heavy elements, and 3rd Gen star systems are relatively new, we’re quite early on the scene.
So because of that, we’re certainly an early civilization, and we might be… the first.
