In fact, if you don't mind waiting a bit, it can be almost trivial. All you have to do is basically get a factory to the target system; it can use local resources to build a kinetic kill projectile efficiently out of a big, local hunks of rock and local hydrogen. Launching near-light-speed projectiles from lightyears away is the emergency "oh crap! They're smart already!" option. Killing a planet that only has dinosaurs on it is dead easy for these hypothetical intelligences and there's little reason to believe they wouldn't.
So I think the dark forest hypothesis falls down on the fact that not only has Earth been broadcasting loud and clear to the stars that it has life on it ever since the Great Oxygenation Catastrophe, which was somewhere around 2 to 2.5 billion years ago, the Dark Forest theory implies that any surrounding intelligence that arose and was capable of seeing Earth on that time frame should have hit it. That has not happened. And 2.5 billion years is actually significant even on cosmological time scales.
(Also, no, the dinosaur asteroid or other events were not kill projectiles. If an alien intelligence is going to kill-projectile Earth there's no compelling reason to just sort of inconvenience life... it's going to eliminate it. Hypothesizing a race capable of launching projectiles but being too stupid to realize it wouldn't do the job is too precise a level of incompetence to believe in. As they say, there's no kill like overkill.)
Fun science fiction premise... not a solution to the Fermi paradox.
It seems safe to say that there isn't life that wants our planet.
But if nobody wants our world and they're scared of intelligent life then just send out Von Neumann probes to ensure intelligence isn't showing up elsewhere. First mover's advantage nullifies the entire dark forest.
So either they'd - already have gotten here & already have destroyed the earth when we showed intelligence OR - already have gotten here & don't care about destroying intelligence.
Or... civilizations don't experience unbounded growth over millions of years across millions of light years to begin with.
Many motives from the age of exploration could apply - imperialism, religious beliefs, religious or political differences, cultural exchange, scientific discovery, competition with others, etc. People don't always take the cheapest option; the same could be true of aliens.
We were almost wiped out after the first large impact. The impact that happened a few millennia after we killed all those awful looking smarty octopus that lived in this planet. But we could not defend against the large Comet, it come from behind the Sun and way too fast. We had minutes notice.
Some microbes survived...And here we are again typing on our keyboards. :-)
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Colonizing other planets and making them into homes for aliens long before a native civilization has a chance to arise seems more plausible than just destroying them.
(Of course, you may still have any amount of conflict with your fellow settlers, or your someone in your original species' descendants two systems over, but that's a completely different conversation.)
> There is no compelling reason to wait until a planet conclusively proves it has intelligence on it to nuke it into oblivion with a kinetic kill projectile.
Or send a technologically engineered molecule that can hijack single-cellular life to help establish your needed technology in the target solar system.
You've got two major approaches: Fling a kinetic kill projectile, or if you have the tech to get "something" into the target system at roughly orbital velocities, send some machines to do the job with local resources.
None of these things appear to have happened in Earth's past. Ironically, trying to spin yarns in which they did anyhow still end up countering the Dark Forest hypothesis, because all such attempts must either include significant probabilities of failure of the attempts or the possibility that the life out there is benevolent (to some degree, at least sufficient to avoid simply wiping us out, which on this scale is "benevolence" despite whatever else they may be doing) which itself would imply the forest isn't that dark.
If I was also murderous, I would have programmed the probes to destroy any signs of life.
So, the fact that we are still alive after broadcasting the presence of life through out atmosphere for the last couple billion years is quite reassuring.
Granted there could be some technical limitations that prevent you from observing certain systems but that pool will be much smaller than an entire galaxy of stars.
Also, don't forget that a Von Neumann probe is at a disadvantage when it arrives in a system since you want to send the minimum number of probes to each star and then have them replicate on arrival. If your probe accidentally shows up in a system that contains an advanced civilization capable of detecting and capturing it then you've given away the fact of your existence and your intent along with all the information that can be gained by studying the probe.
Also I'd expect the probes would communicate with the homeworld via relays (where they were replicated) rather than directly, so it'd take a fair amount of effort to unravel a replicator network unless you caught one of the very first probes.
And also it'd be conspicuous if there was a volume of space in your network where your probes always failed.
Signs of carbon-based life - who is to say all forms of life are carbon-based? The universe is vast, what are the odds of aliens being in our vicinity and time (light cone) stumbling upon our galaxy or star?
There's a limited number of elements, and their abundance in the universe decreases rapidly beyond the first few. Carbon is by far the most advantageous for life due to its vast ability to form complex molecules. Silicon might be a distant second. If there is other life in the universe, and if there's nothing special about us, it might not all be carbon-based, but it's extremely likely that a large amount of it will be.
Stay hidden or destroy anyone close enough to put you at risk along with themselves. This is a spoiler, but IIRC from the books the ultimate safety net was to make your solar system not only invisible... but impenetrable in either direction but essentially trapping yourself in a black hole... thus removing yourself from the equation and hopefully satiating anyone watching.
The time scales and distances involved meant that you weren't really perceived as a threat until you approached the ability to reach light speed, which made you stick out enough to be noticed in far corners of the universe. We broadcast radio, but it's not loud or far-reaching enough to be noticed by the far-out civilization destroying overlords. It was loud enough for a different nearby civilization to come destroy us in an attempt to save themselves from being destroyed along with us.
Of course, when applied in reality who the hell knows.
If such a technology is possible at all, only the very first advanced civilization had the ability to hide from all others. And only if they were able to develop it before any other civilization had been able to track them.
To some extent it might nevertheless be a reasonable strategy to keep as quiet as possible. But this strategy is less and less useful for the latecomers. If they were already tracked by a multitude of other advanced civilization they would hardly benefit from keeping quiet. Unless they (wrongly) think that they are an early advanced civilization.
However, if a couple of these civilizations start to openly seek contact to others, what can the hidden ones do? If a hidden civilization starts to fight one of these latecomers, it would need to leave its cover and make itself known to all other civilizations in its vicinity. If it follows the dark forst hypothesis, it could only do so, when it is sure that it is the only dangerous civilization in its forest.
This leaves me with the following alternatives:
- The forest is dark, because there is only one civilization out there that is very capable in hiding and has the ability to exterminate any latecomer efficiently and without traces.
- The forest appears dark, because it is thinly populated and we just have not looked enough for the others.
- We are the only ones in our cosmic vicinity.