For me, the Dark Forest hypothesis is very probable. However, the whole book series assumes that interstellar travel is possible for advanced civilizations. What if no new physics is discovered, and the only way to accelerate/decelerate is to throw a mass in the opposite direction? Maybe all advanced civilizations in the Milky Way are limited to their planetary systems.
There are two ways to go to the stars: go faster or live longer (or hibernate).
If you could cryosleep, lived for millions of years, or were an AI that could just turn itself off for a while, you could go to the stars using simple chemical propulsion. No physicists’ nightmare torch rockets or warp drives required.
The crazy physics requirement is to enable interstellar flight within natural human life spans. It’s probably easier to extend that or figure out how to hibernate or become AI than it is to build an antimatter rocket or bend space time (if that is even possible).
I doubt the dark forest because Earth has been broadcasting that it’s a likely biosphere via its albedo absorption spectrum for over a billion years. If you are a hyper paranoid alien you should just blast every biosphere to kill any possible rival before it even evolves.
Side issue, but if you don't care about travel time, you also have another big problem. The frequency with which stuff happens that matters to civilizations has increased significantly over time. Meaning that the time intervals that matter have gone down a LOT as we've evolved and that seems like a natural tendency on the basis of natural selection: higher frequency strategies will tend to dominate. So then you have this massive juxtaposition between probe travel times and things civilizations care about. It's a total mismatch. By the time the probe reaches its destination and can come back, the civilization will likely have completely changed and/or forgotten about it.
This is true for us, but is also anthropocentric. We can't assume that everyone would have this problem.
Technological change is probably a sigmoid like most things. There could be people out there who have already won physics, figured out the entire unified theory of how everything works, and have developed most of the core technological stuff they ever will. At that point they might calm back down and become more stable over long periods of time. These are the kinds of civilizations that would send slow probes or one-way colony ships out and would be willing and able to wait.
It's very hard to think about potential aliens without dragging in anthropocentric or even recent-history-centric assumptions.
