But there are also 7500 known exoplanets within a few tens of thousands of light years of Earth. There are almost certainly multiples more than that we cannot see.
The "Goldilocks Zone" is also highly anthropomorphised: there are extremophiles that live in all sorts of crazy environments on Earth.
I'm coming around to the Dark Forest theory, personally, as terrifying as it is.
> I'm coming around to the Dark Forest theory, personally, as terrifying as it is.
Perhaps it's just that advanced technology is extremely rare given another comment's supposition that there could be other intelligent life, just unable to make advanced technology, or along those lines: if they have the appendages to do so, maybe their environment doesn't have the resources.
If you couple the above with the idea that FTL communication/travel is difficult or impossible, then it could take a long time for us to find evidence, and maybe by then we'll be extinct due to natural causes or devices of our own.
Or maybe there's some theistic evolution component and we are the only species in the universe with divine providence.
It seems to me that it would be impossible to prove or disprove any of those possibilities unless we actually discover extraterrestrial advanced intelligent life.
(And even then, who is to say that God didn't create Edens on other worlds? So meeting aliens still might not disprove any divinity.)
> the idea that FTL communication/travel is difficult or impossible
Not just FTL. My hypothesis is that any type of substantial interstellar travel is going to be so enormously expensive, complicated and time consuming, an advanced civilisation will only do it once in a billion years. In the form of mass exodus when there are no more habitable planets in their system or their star is going nova. As this never gives exponential growth, it is enough to resolve the Fermi paradox.
But that's simply not the case. We likely very close to the technology needed to get tiny objects to a decent fraction of lightspeed using laser arrays. Assuming genuine AGI is possible and miniaturisation continues, there's no physical reason a digital intelligence couldn't rapidly (on interstellar time scales) colonise the galaxy.
Okay, let's say I grant your two extremely optimistic assumptions. Then what? You can send a bunch of tiny sentient brains hurtling through the universe. They will have a very high chance of hitting interstellar dust and turning into a blob of plasma before they reach the target solar system. They also have no way at all to slow down once they reach the target system.
Interstellar travel requires not just being able to accelerate to incredible speeds, but also to carry enough energy and reaction mass to slow down again to (essentially) zero.
A really simple answer to the Fermi paradox is that we're the first, or in the first wave, of intelligent species, and it's just too early for the light from the others to have reached us yet. We're not just looking into the distance, we're also looking into the past. Life is less likely the farther we look.
It took a long time for the universe to create the conditions for a solar system like ours to exist in the first place, and why would have this happened so much faster elsewhere? The trend towards higher entropy/complexity is like a universal clock.
The universe might look big, but our view of it is not homogeneous. We wouldn't even see ourselves if we tried to find us, unless we were a close neighbor.
IMO the dark forest hypothesis leads to fun books but makes little sense. If a civilization is capable of the unimaginable feat of interstellar travel, surely their basic needs are well met and they aren't driven by base animal instincts anymore. They can probably engineer their own psyche. We humans will soon hit a population peak too, no exponental growth on the horizon.
Also, I don't think the timescales make sense at all. It took 200 years for industrial civilization to develop, maybe 200 more for us to travel the stars, but it takes billions of years for intelligent life to develop. I don't think there could ever be two comparable civilizations emerging at the same time, close enough to one another to compete for resources. Either the aliens found Earth millions of years ago and prevent us from ever existing, or there aren't any aliens closeby.
If you want an optimistic outlook on the far future which I think more plausible, read "Diaspora" by Greg Egan.
There's the question of motivation. It seems possible that an advanced civilization could gravitationally disrupt a small planet like mercury, turn it into solar collectors and particle accelerators and create multiple-ton quantities of antimatter and use that for interstellar travel, but they would likely choose to do something else with those resources.
People have a hard time thinking on a timescale of half a lifetime, never mind a lifetime or several lifetimes. The realistic version of the Bussard ramjet is not that you aim for c=0.1 or more, but rather with D-D fusion you can make hops of 1,000-10,000 au to Oort cloud bodies, you could possible gravitationally disrupt an object like Pluto and turn it into little ringworlds or other colonies. It might take people like that 10,000 years to make it to the next star but if they can make a comfortable lifestyle along the way why would they bother? And why would we even care enough to send them out on such a quest?
Even colonizing Mars is problematic in the sense that it's inconceivable that you could bring anything back from Mars that would give us flatlanders any economic incentive to do it. It might be a gift to a population of a billion or so people that will live there, but profitable to us? No way.
So even if you could colonize the galaxy with Von Neuman probes, it won't happen in your lifetime, your children's lifetime, etc. Our civilization might not be there to get the data from the first probes to reach other stars and the more steps removed the more the probability drops. Still there's just that tiny probability of a 'dark forest' scenario where somebody finds one of those things and decides to do something about it.
> If a civilization is capable of the unimaginable feat of interstellar travel, surely their basic needs are well met and they aren't driven by base animal instincts anymore.
That is a bit like saying a human isn't driven by base instincts because we are so large and advanced compared to amoeba. We have concerns and options that are so far beyond the amoeba's comprehension that it makes no sense to even talk about an amoeba comprehending. And yet we are still driven by the same basic resource-acquisition logic as any microbe. Being more advanced again is unlikely to change that.
Although I do agree that the Dark Forest hypothesis seems unlikely. It seems more reasonable to suggest that gravity wells and interstellar distances are a barrier that cannot be economically overcome, so intelligent life is bound to its own rock and eventually dies there. Then the odds just favour us not detecting life out there in whatever time period we've been looking.
That is if you assume the aliens will board a ship with conventional forces and enact a human style invasion.
Now what if the alien was not even sentient. A giant configuration of some structure of chemistry just floating through interstellar space, catalyzing reactions when inputs are met, lying in wait otherwise. It might not “die” in the sense that any other mass of atoms doesn’t “die.” When faced with some input it might swell up in size, divide and diffuse elsewhere. Akin more to a random chemical interaction among a few molecules in pure solvent than life as we know it.
Chemical structures like this could potentially be the wildfire patrolling the universe for fuel vs some spacefaring roman empire.
One might argue encountering something like this would be more akin to a natural catastrophe (like a killer meteor) rather than an alien invasion.
Stephen Baxter wrote a novel in which galaxies would be regularly wiped out by a natural phenomena, and that explains why there are no aliens in his universe. It's "Manifold: Space" if you're interested.
Life as we know it is just chemical reactions occuring within some membrane or walled environment. I don’t see why that definition couldn’t be extended to self sustaining chemical reactions that aren’t bound by a membrane or wall structure. The purpose of that membrane or wall is to just establish favorable conditions for the chemistry within the cell. If conditions could be established without such a membrane there wouldn’t be a reason for it. If reactions were energetically favorable across a wide spectrum of conditions there wouldn’t be a need for it either.
There are some that consider fire to be a form of life. I don’t think that is such a wrong idea if we are to consider how wide the scope of possibilities are in the universe.
Extremophiles don't tend towards complexity, though.
And if each common variable has, say, a 10% range in which complex life can occur, you don't need that many to start reducing probability a lot.
- Orbital stability?
- Tidal and seasonal ranges?
- Magnetic fields?
- And the big one - properties of our Sun & solar system that make it different to others of a similar age? For example, are there galactic-scale properties that affect the surface environment of planets on a long enough time-scale, so that, just as Earth exists in the habitable zone of our Solar System, there is a relatively narrow galactic habitable zone?
All the more reason though to get some telescopes built that can glean more detailed information on exoplanets. We might be in for another shock like the Mariner probes, or it might be 180 degrees the opposite.
> I'm coming around to the Dark Forest theory, personally, as terrifying as it is.
If you're silent with the intent of remaining hidden, then that behavior must have been learned. Either you evolved from a prey type of species, or a non-apex predator.
It would be strange of humanity is the only apex-ish predator intelligent-ish life form in the universe that blasts signals into space without consideration of who might hear them.
We don't have telescopes capable of receiving accidental emissions from Earth (say television) at interstellar distances. It seems reasonable that you could use the gravitational lens of a star to do so if you could launch a probe to 800 au for each and every star system you want to monitor.
As we transition to digital technology, our transmissions look more like broadband noise as opposed to having a strong carrier wave, cellular communications in 2025 are far less visible than, say, television broadcasts of 1975.
Deliberate attempts to communicate with other intelligent life are quite forlorn. This message was sent to a globular cluster 25,000 light years away
There a few 100,000 stars there, somebody there would have to be looking at our sun in particular at the right time, then it would take at least 25,000 years to get a message back to us, in which case it is likely that we'll be extinct, collapsed back to hunter-gatherers, or maybe advanced but forgotten that we sent the message or don't care anymore.
> If you're silent with the intent of remaining hidden, then that behavior must have been learned. Either you evolved from a prey type of species, or a non-apex predator.
Or you learned it in a non-evolutionary way, through logical reasoning.
No it is not necesarily learned. Even among species on earth a lot of behaviors are not learned but inherent. In other words, selection acts on a spectrum of behaviors and those with some fitness advantage you are likely to see more frequently in the next generation of offspring, extending until lineages of that offspring with that behavior are potentially all there is.
A dark forest planet need not learn to be a dark forest planet in the same way an earth colored beetle need not learn to perfectly mask itself against the dirt from a bird; the fitter mutation given the context of the environment won out.
The "Goldilocks Zone" is also highly anthropomorphised: there are extremophiles that live in all sorts of crazy environments on Earth.
I'm coming around to the Dark Forest theory, personally, as terrifying as it is.