So I have heard people sometimes say the reason for no aliens is that complex life requires so many coincidences it is just incredibly unlikely to indecently arise anywhere else in the universe. I think it is a bit arrogant to assume all life has to mimic life found here on Earth, so forgetting the goldilocks zone for a minute, you still need life to emerge from nothing over the course of billions of years. Then you need complex life to emerge from that, and eventually civilization. But you know what else you need?
Extinction.
No extinction means no fossil fuels means no industrial revolution means no spacefaring. If it wasn't for the dinosaurs, we would have nothing. Makes you wonder what we're here for.
I conclude that any advanced alien lifeform that gets to this stage will have to use a source of power not used so much on Earth. Hydro and Thermal seem unlikely, it's less portable and requires huge facilities, so it will probably have to something else. I imagine rivers of liquid gas, a space-faring civilization built upon lakes made up entirely of methane.
Edit:
It has been brought to my attention that fossil fuels are not in fact made up of ancient dead dinosaurs, and even if they were, we wouldn't need a meteor to make this happen. I just like Dinos 
The reason for the great filter is probably just radio attenuation and sci-fi megastructures can't really happen because the materials to make them aren't possible. Plus, there's another theory that people stop using big, messy radio in favor of laser and fiber pretty quickly. Like we're already going there after only a century. To actually spot someone else on radio they'd need to be using really, really, really loud and messy radio from fairly close by.
Fossil fuels are primarily from marine plankton rather than any big animals like dinosaurs. you could skip them straight to nuclear, or you could manufacture your own hydrocarbons, or a whole bunch of other things.
The most boring answer that isn't some dumb "Dark Forest" crap is just that folks are really far away, and living in space sucks and there's no real reason to actually do it, and the mega structures people think ought to be everywhere aren't actually physically possible, assuming anyone even wanted to make the silly things in the first place. Everyone assumes we're going to go up the Kardashev scale instead of just figuring out a nice population balance and retiring to a little cottage in the alps or something. Can you imagine actually building a Dyson sphere? What would you do with it? Who would vacuum the thing? How would you deliver the mail? It's silly, the dreams of children who can only think of getting bigger and bigger.
Really, really, really far away
Like really fricking far
Space, folks, it's very big
So big. Literally the biggest thing.
All the stuff that Dyson said sounds closer to me to science fiction than to anything that's actually doable. Guy was mostly just making shit up that sounds cool without worrying about whether or not it's possible, but since he's a Nobel prize laureate people took it 100% seriously.
This is true, but I think it's natural human curiosity that will drive us further and further out to space even if we have figured out how to live peacefully in our own planet without slaughtering each other. Imagining a hypothetical international people's democracy flag planted on many planets out in space is pretty cool, it would be the Star Trek timeline of events
Space travel is not guaranteed in the history of humanity. The capitalists had little interest in conquering the space. In fact, space programs would have been extensively delayed or even neglected had it not for the Russians and the Soviet space program.
Human space travel had its roots in the philosophy of Russian cosmism of the 19th century (e.g. N. Fyodorov), who believed that at the rate of technological advancements they had experienced at the turn of the century, human livelihoods would soon be improved to such an extent that Earth’s resources would be depleted and the planet itself would become over-populated.
Fyodorov’s disciple K. Tsiolkovsky envisioned that a solution to the problem would be for humanity to leave Earth and colonize the stars, and started to research the feasibility of space rockets that would allow humanity to travel through the stars.
Rather surprisingly, the roots of human space travel had little to do with colonization, imperialism or resource extraction.
An ardent supporter of the Bolshevik Revolution, Tsiolkovsky believed that the inevitability of socialism would soon make such advancements become reality, and if that were to be the case, humanity would really need to explore the outer spaces for new homes to live.
His work on rocketry would influence the pioneers of the 20th century space programs: Robert Goddard and Hermann Oberth, the American and German pioneers in rocketry, respectively, as well as an entire generation of Soviet rocket scientists (S. Korolev and V. Glushko, for example). The Soviet space program would make Tsiokovsky’s dream become a reality.
Suffice to say, if it weren’t for the Sputnik moment in 1957, NASA would likely never be formed and space rocketry gained such momentum and received such generous funding by the government. Despite the fact that they had obtained the entire German V-2 rocket team, the development of space rocketry/intercontinental ballistic missiles wasn’t that much prioritized until the Soviets raced ahead of them.
I'm sure we'll send some kind of vehicle to other stars eventually, but it's a super super super super super difficult engineering task to a degree I don't think a lot of people properly appreciate. Whatever your vehicle is, like if we assume realistic travel speeds, it's going to spend decades, probably centuries or even millenia, out in the deep black with no power at all, getting hit with interstellar radiation, suffering all the ill effects of long term exposure to hard vacuum. And then, when it gets close enough to another star for it's solar cells to start working again, it has to wake up and unfold and come back to life starting from near-zero temperatures, and boot up, and enough hardware and storage has to survive for it to be functional and intelligent.
The vehicle, whatever form it takes, would need to survive the most extreme environments (other than, like, every environment on earth) for a very very very long time, and still be able to wake up and perform very complex, energy intensive functions when it arrived.
I think, if we can fix some of the shit going on right now, we will probably try. I want to meet the neighbors, even if "meet" means sending letters back and forth across hundreds of light years. *
In the future their won’t be any flags.
This, plus the time it would take for signals to travel space at the speed of light, not even mentioning matter at sublight speed, makes it just implausible that we'll ever encounter another civilization (assuming there are some out there)
Plus, I remember reading that the constant expansion of the universe makes it another big factor as we are ever drifting away from most of the rest of the universe, but I'm not sure
You are correct, but the expansion of the universe is relative to intergalactic space, not interstellar. Our galaxy isn't flying apart, so it will be explorable with currently theorized faster than light speed drive systems. There's more than enough to explore in our galaxy as it is, so it will have to do when and if we ever develop an FTL drive. But traveling to another galaxy is an entirely different feet because of the expansion of the universe. You may wonder why, when it is just a distance that needs to be covered, all you should need is enough fuel and supplies... But you would also need to accelerate to many magnitudes of the speed of light in order to "catch" the galaxy you want to travel to. This is because galaxies are accelerating exponentially away from each other. An easy way to visualize it is to remember that the universe is expanding out from a central point - so take a balloon and draw two dots on it, then begin to inflate; after one breath they spread apart, after the second breath they've spread appart at a faster rate, and after the next the rate of spread continues to increase and so on. The points are spreading away from the center at the same rate, but the distance from each other is ever increasing. Therefore, their will be a day where we can no longer see any other galaxies again, because the speed of the spread will far exceed the speed of light and continue to increase for all eternity (we presume).
Except for the Andromeda galaxy, that one's headed right for us and the two are going to collide in a few billion years... Which will probably pose a major threat to all life and indeed earth itself... Maybe we should start planning to try to get to another galaxy. 🤔
I can't imagine a species skipping to nuclear. They would have spend centuries building progressively more powerful water mills or something.
Why? Wrap some copper around a magnet, bam, hydropower. What's hard about that? I don't think the math for nuclear chemistry requires burning a lot of coal, first.
idk I feel like there is a big leap between a small water mill and the Hoover dam, and can you imagine trying to mine all the raw materials using battery power?
and how are they gonna ignite the nuke
I think nuclear weapons use an array of very precisely designed high explosives to shove the elements of the core together and trigger the nuclear reaction. And yeah, fossil fuels are great as a portable high-density energy source, but there are other options; biodiesel, for instance. You're absolutely right that it would be a very, very different energy economy.
I think a lot of sci fi just assumes that all aspects of technology are going to continue improving. But a lot of them are going to run into these hard physical limits, and it's not as though the laws of physics have to bend to our meddling. A lot of sci fi trope techs may just simply not be possible to create in our universe (Cold fusion, FTL, space elevators). There's still amazing technology yet to be created, but I'm not sure that multi-planetry alien civs and megastructures are actually a thing that is really possible to exist in our universe. It seems quite possible that the universe is in fact full of intelligent life, but that everyone is mostly constrained to their own neighborhood, and not putting in the vast effort required for communicating their presence.
I think there is a convincing argument to be made that one day we will create an army of self-replicating battle bots that will be able to do just that.
We could destroy the planet with grey goo by releasing tiny little nanomachines to clean up an oil spill, and even the universe if we released drones to harvest asteroids and use the raw materials to replicate themselves. In the event it all goes OK though, they could be directed to assemble something like a Dyson Sphere, and an AI could oversee the project to maintain order as a million things would inevitably fail on such a large scale. Not sure why we would want to do it at all, but an AI-robot workforce feels a lot more realistic than organising millions of humans.
But yeah though you try to do something like this you are for sure going to bump into the laws of physics at some point.
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