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How far away from earth is it still possible to detect oxygen and/or methane levels in the atmosphere?

Light years with the right telescope. It’s just spectroscopy.

Yes but only a tiny fraction of our sun's light would pass through earth's atmosphere on its way out of the solar system, I didn't think spectroscopy would be possible very far away.

If I was a technologically advanced civilization, I would send robotic Von Neumann probes around the galaxy to keep tabs on things at close proximity.

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.

Wouldn't that be the most difficult and expensive way to simply monitor for life or technosignatures? Compare that to simply (relatively speaking) building massive space based optical and radio observatories that can observe every visible star. The light reaching you has already made the trip, you just have to collect it. If you were murderous, you could launch an attack from your home system rather than waiting for the probes to spread from system to system.

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.

I wonder if everyone is therefore incentivized to not send out such probes, then. Since no one can guarantee they are advanced enough that their probe won’t get captured by someone more advanced who just sends back a scarier probe as a thank you gift.

So have your replicators approach a system from an unexpected vector; one course correction in interstellar space should be enough.

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.

You just need enough light to do spectroscopy. I’m not really aware of a limit other than being in our light cone.

You don’t destroy the system because you want to inhabit it yourself. This assumes that life is looking for similar habitats and that it’s not simpler to create an artificial planet anyway.

If there is oxygen breathing carbon based intelligent life that wants our planet they could've easily spotted and taken it anytime within the past 2 billion years.

It seems safe to say that there isn't life that wants our planet.

Or maybe that carbon based intelligent life that wanted our planet it's us.

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. :-)

Why would anyone come from light years away to inhabit a planet. It would be cheaper to just build habitats or colonize a planet in their solar system. There is almost nothing we can provide to a civilization capable of traversing between start systems.

All resources are scarce.

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.

relatively scarce, sure. There are millions of times more of all the resources Earth has between us and any civilization coming from light years away. By the time they needed Earths resources they’d have to have gobbled up large chunks of, if not the whole, Galaxy.

Right but the whole premise of the Fermi Paradox is that it doesn't take long (on a galactic scale) to gobble up the entire galaxy using STL transit if you're dealing with a constantly growing civilization.

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.

Well okay but I believe that premise is flawed. It still takes millions of years for one (which is a long time on human timescales) and it’s more likely civilizations Balkanize and begin fighting each other if they even were to be so resource driven they wished to colonize the galaxy that quick which I don’t think we have any reason to believe is true.

>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.

> Why would anyone come from light years away to inhabit a planet.

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.

This seems to be projecting a human trait that is itself obsolete to us unto civilizations that share no common culture or genetics and are leagues ahead of us technologically speaking. Not to mention the age of exploration was driven by economics. Seems foolish to me.

Or they did want it and used it for seeding more complex life so they could eventually create homo sapiens. Like the start of the film Prometheus.

Which would mean that the dark forest is still false right?

The aliens in Scott Westerfeld's Fine Prey invade Earth for a novel reason. It's ROT-13 (https://rot13.com/) encoded to avoid any spoilers.

Gur nyvraf ner ynathntr areqf. Gurl bpphcvrq Rnegu fb gung uhznaf jbhyq perngr n arj qvnyrpg bs gurve ynathntr.

If I use humanity as a model, then we don't see other great apes as dangerous competitors. Rather we see them as interesting curiosities. We want them to stay alive. But it's hard to resist the desire to turn their habitats into something economically productive.

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.

For the purposes of this conversation, colonizing other planets effectively is destroying them. After that, no natural intelligent competitor will arise and surprise you, because you're right there to keep an eye on everything.

(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.)

"Too precise a level of incompetence to believe in." That's the most beautiful wording I have read in some time...

Hat tip: https://www.shamusyoung.com/twentysidedtale/?p=615 "That is a very specific level of tired."

(Major spoilers for The Expanse below.)

> 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.

That's a variant of what I discuss in another reply, but well underscores my point of just how easy this is if you happen to get there anywhere in the 2.0-2.4 billion window Earth has had prior to intelligence. If you colonize the system in any manner, be it biological, technological, whatever, for Dark Forest purposes that's equivalent to destruction; there is no longer a threat of natural competing life.

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.

It’s funny that that wouldn’t have been a spoiler if you hadn’t mentioned the name of the work.

Why get a factory to the target system when you can launch kill projectiles to all the systems in the galaxy from home?