The Dark Forest

Sometimes, when Marvel, DC & co can't fill the whole horizon, there is something interesting in science fiction. In this case I am referring to Cixin Liu's books, and his Dark Forest theory, a "possible solution" to the Fermi paradox.

Fermi's paradox arises as a response to Drake's equations, which estimate a very high number of extraterrestrial civilizations in our galaxy, and in the Universe in general. The trouble with Drake's equations is that the hypotheses are quite founded on the level of what we observe, (and also the possibility of observing exoplanets has confirmed that Drake was not optimistic, but the opposite) but they do not correspond with a fact, which Fermi pointed out: if there are so many civilizations, why don't we observe them?

Many have given (or tried to give) an answer to this paradox.Some have observed that even on planet Earth many civilizations had never met, and if we assign the beginning of the history of the Mediterranean seafaring to the Phoenicians (although there are vast evidence of previous navigation) we find that it took 2700 years for the Mediterranean to meet South America, and 2900 for Australia. Not bad. There are many attempts to explain this paradox.

Cixin Liu tried to give a pretty terrifying answer, that honestly critical, because…. I had also written a book with a similar hypothesis , but to make it work I had to use a gimmick.

Cixin Liu's theory is this: alien civilizations hide because they are afraid of being attacked. Imagine the cosmos as a dark forest. You know that there are predators in the dark, and you know that some of them love to eat you (or your resources). What's the thing you gonna do? Hide yourself, says Cixin Liu. Since if you are visible you will sustain an increasing number of assaults, aimed at seizing your resources (which could also be used as livestock or as prey to be eaten, as in "Food"), Cixin Liu's theory is that all hide so as not to be found.

According to Cixin Liu, as the universe is limited in size but intelligent species multiply in number, conflict is inevitable. And since it's inevitable, everyone has taken to hiding because they don't want to be attacked all the time.

I had tried to give a similar answer in Food, and by itself it was not standing, so I had to corroborate it, with the R factor. Let me explain better.

The Fermi Paradox is a response to Drake's estimates. In Drake's estimates, the number of civilizations is high, but still very RARE compared to the number of stars and planets, ie resources. In this model, each race would have MILLIONS of stars (and related planets) available to use as a source of resources It is true that the universe is finite, but the problem is whether any race is really capable of using all these resources. . Let me give you an example: the fact that the number of women is finite does not imply a continuous duel to get them. After all, four billion women are far beyond the sexual capabilities of any human male.

Likewise, if we accept Drake's assumptions, which have turned out to be pessimistic now that we can find exoplanets, whatever resources the aliens need, there is a hell of a lot of it.

Second: if you really want to be invisible, constantly fighting will not help you. War is visible. The expansion is visible. If you need resources because you grow in number and occupy many planets, until you run out of those millions of planets at your disposal, you will hardly be able to do it in silence. You need a supply chain, which must communicate. If you choose not to communicate and transport raw materials to be invisible, you are deluding yourself that millions of tons of moving raw materials are less visible than a photon. Honestly, unlikely.

Third: if you fear war you want to know well in advance of the enemy's arrival. Even if we accept that these species camouflage themselves so as not to be seen, they will hardly accept to remain blind. A paranoid militarization may imply silence, but it will greatly amplify the tendency towards observation and exploration. Even if everyone is camouflaged, there will always be the observer who places an outpost on your house mat to watch that no armies arrive.

Then there is a problem, inherent in modern cosmology, which is rarely mentioned. That is the horizon of events. The universe expands, and its expansion accelerates. If you start traveling from the earth, at the speed of light, sooner or later you will arrive at the point where you can no longer go back, because the universe does not have the necessary time. From this "border" onwards, cause-and-effect relationships are no longer possible between you and planet earth. You are beyond the event horizon, as if you have landed in a black hole.

According to some theories, 16.7 billion years are missing from the thermal death of the universe. From the point of view of an immortal terrestrial observer, NOTHING happening "now" further away than this will ever be observed: therefore there is no possible cause-and-effect link between two points more than 16.7 billion years apart.

Since according to the latest estimates the universe is 46 billion light years large, each point is immersed in a kind of "bubble", a bubble that will NEVER receive any "current" signal from what is beyond that limit. . If you travel at the speed of light you are immortal, since time tends to zero: you can, in theory, travel 16.7 billion light-years, and you will arrive "in the day". The trouble is that for the rest of the universe ("at rest") your journey lasted 16.7 billion years, with the small problem that as the universe expands, now you are (actually) already 28 billion light years away. And you can no longer go back, let alone communicate with the base: no cause-effect relationship is now possible. So MUCH BEFORE 16.7 billion years, you would step out of the earth's event horizon, aided by the expansion of the universe.

This greatly reduces the problem: we do receive the light of the past, because in the past the universe was smaller (the age is 13 billion years, but the size is 46 billion years light, so it has already expanded quite a bit), but if we imagine what happens "NOW" at more than 6-7 billion light years, we will NEVER know. The light that starts from there "now" will NEVER reach us: "while" it travels the universe will expand again, and "during" the journey the 6-7 billion light years will become more than 16.7, and therefore there will not be enough time to receive the signal. There is no possible cause and effect relationship between us and something more than 6-7 billion light years away.

The relationship was possible in the past because the universe was smaller and expanding more slowly, but now the limit is 6-7 billion light years (depending on the Hubble constant, which looks very ballerina).

What does this mean? It means that to "see us" (which requires a cause-and-effect relationship between us and them) a species "outside" the bubble would literally have had to predict, if not hypothesize, our existence 6/7 billion years ago. If it does "today", we don't have to worry about it, since the universe doesn't have enough time for them to come here anyway. (assuming we last until the end, of course). In practice, to make war on us they would have to say something like: "Do you see that empty space? Well, in a moment that we will never see there will be a civilization that builds Hamburger, to which we will wage war for any reason, sending an army that does not he will never come back and never give news of him again. "

In my opinion, getting funding for such a military project is difficult.

And we are optimistic, because we are using a physical limit, which is the death of the entire universe. But now there is a problem. When will the human species end? Let's make an optimistic estimate, and let's still give ourselves 100,000 years. One thing follows: that the event horizon of the human species is only 100,000 light years. Whoever leaves "now" from a more distant point will NEVER arrive in time to interact with us.

So if we lower the limit to 100,000 years, over 100,000 light years away it is no longer possible to interact with us. No cause-effect link is possible, starting from "NOW", for more distant objects. ( This way of seeing things requires a comparable universal date, that is a "NOW", which the theory of relativity excludes: but the concept remains. In the 4-dimensional pseudometric of relativity, there is a bubble of 100,000 years beyond the which there are no cause-and-effect links with our species, if we wish 100,000 years of life ).

Understand that if we begin to restrict the universe into bubbles that NEVER communicate, and we restrict a possible "empire" of Homo Sapiens to 100,000 light years, all this need for war is not there, for the simple reason that it does not there is a real POSSIBILITY of war.

Then you will say: hey, but you wrote FOOD.

True. To write "Food" and make it stand up I had to use several assumptions:

1. that there is a type of flight, called "hyperspace" capable of avoiding the relativistic effects of the relativistic movement, at the cost of losing contact with reality during the flight.
2. that there is a SECOND type of flight, called "subspace", capable of avoiding the geometric effects of spatial dimensions, leaving time intact. (basically collapsing ordinary spatial dimensions as in m-brane theory, but staying in contact with them)

but at this point the amount of resources available to each species was so enormous that I could find no reason to wage war. Why would the reptilians and the Diaspora have to fight when they could extract any raw material from anywhere, in arbitrarily large quantities? It would have been irrational. And in fact, I put the R factor into it: wars are waged for RELIGIOUS reasons.

That is, NOT rational wars, where eating the opponent is a religious ritual. (for the rest, then, read Food).

And here I come to the conclusion: Liu's hypothesis is not rational, in the sense that the (known) physics of things excludes a universe at war, or a universe-ecosystem with a food chain. The only way we could have a universe "at war" would be wars totally unrelated to physical reality, or wars of religion.

So no, the Dark Forest theory is interesting, logical, but incompatible with physics as we know it.

In favor of Cixin Liu it must be said that in his book, terrestrial physics is the result of a disinformation campaign of the incoming enemy, a campaign conducted with the express purpose of making it difficult for us to build effective defense weapons.

The rest is spoilers.