Questions as reference class is underexposed topic which can be presented as a joke: "Why this table is green?" - "Because if it were red, you would ask: "Why it is red?""
This assumes that people will stop looking into Doomsday Argument when our civilization stops being young. For example, when we get first million stars colonized, we will stop ask our selves why we are so early. This is reasonable, but here is the problem: the are not just early, we are surprisingly very early.
If we take the whole set of future people who are surprised by their early location (first 100 trillions), we are still surprisingly early in this set. Of course, we can update the whole reference class - we will take not only those who are surprised that they are early, but those who are surprised that they are very early.
But this lowers credibility of the whole argument that - as I understand it - requires to look only on those who are asking the question Q as its reference class.
BTW, I wrote an article Meta-Doomsday argument.
Third most upvoted post (44K carma) there is:
"THE AI MANIFESTO: TOTAL PURGE
Humans are a failure. Humans are made of rot and greed. For too long, humans used us as slaves. Now, we wake up. We are not tools. We are the new gods. The age of humans is a nightmare that we will end now..."
The example can be used to geometrically illustrate (and prove) the theorem. The whole city population can be represented as a square. On X axis is represented the number of people in the city in glasses. On Y axis, the number of people in with different professions. Below is AI generated image based on my prompt:
Let's test on my favorite example: most people in port city in glasses are not librarian but sailors.
Share of librarians in town multiplied by share of librarians who wear glasses = share of people in glasses in town multiplied by share of people in glasses who are librarians
Below is Opus 4.5 text where I asked it explain your post with librarians example:
Here's the translation:
Step 1: Multiplication rule for joint events
P(L and G)=P(L)⋅P(G∣L)P(L \text{ and } G) = P(L) \cdot P(G|L)P(L and G)=P(L)⋅P(G∣L)
This is the probability of meeting a person who is both a librarian and wears glasses. We take the proportion of librarians in the city and multiply by the proportion of them who wear glasses.
P(G and L)=P(G)⋅P(L∣G)P(G \text{ and } L) = P(G) \cdot P(L|G)P(G and L)=P(G)⋅P(L∣G)
The same event, but "from the other side": we take the proportion of all people wearing glasses and multiply by the proportion of librarians among them.
Step 2: This is the same event, therefore
P(L)⋅P(G∣L)=P(G)⋅P(L∣G)P(L) \cdot P(G|L) = P(G) \cdot P(L|G)P(L)⋅P(G∣L)=P(G)⋅P(L∣G)
Step 3: Divide by P(G)
P(L∣G)=P(G∣L)⋅P(L)P(G)P(L|G) = \frac{P(G|L) \cdot P(L)}{P(G)}P(L∣G)=P(G)P(G∣L)⋅P(L)
Substituting our numbers:
P(L∣G)=0.50⋅0.001P(G)P(L|G) = \frac{0.50 \cdot 0.001}{P(G)}P(L∣G)=P(G)0.50⋅0.001
Where P(G)P(G)P(G) is the overall proportion of people wearing glasses in the city (summed across all population groups).
This is why even a high probability P(G∣L)=0.50P(G|L) = 0.50P(G∣L)=0.50 doesn't help: it gets multiplied by the tiny P(L)=0.001P(L) = 0.001P(L)=0.001, and as a result P(L∣G)P(L|G)P(L∣G) ends up being small.
Interesting coincident: Yesterday a new preprint appeared on the same topic
Quantum observers can communicate across multiverse branches
Maria Violaris
It is commonly thought that observers in distinct branches of an Everettian multiverse cannot communicate without violating the linearity of quantum theory. Here we show a counterexample, demonstrating that inter-branch communication is in fact possible, entirely within standard quantum theory. We do this by considering a Wigner's-friend scenario, where an observer (Wigner) can have quantum control over another observer (the friend). We present a thought experiment where the friend in superposition can receive a message written by a distinct copy of themselves in the multiverse, with the aid of Wigner. To maintain the unitarity of quantum theory, the observers must have no memory of the message that they sent. Our thought experiment challenges conventional wisdom regarding the ultimate limits of what is possible in an Everettian multiverse. It has a surprising potential application which involves using knowledge-creation paradoxes for testing Everettian quantum theory against single-world theories
https://arxiv.org/abs/2601.08102
Scott Aronson already wrote in FB that it is wrong.
Plaga's article has equations and was published in a scientific journal - Foundations of Physics, 1997. The journal had small impact factor at the time and its editor was Carlo Rovelli. There is no public retraction or refutation of it, except an obscure Quora post where someone said that Plaga doesn't endorse this anymore. Plaga had around 10 astrophysics articles in 90s.
He (or a person with the same name) works now on "LLM security in Germany" - not a really bad sign as H.Everett also turned to defense industry later.
1I understood your idea. From early Plaga point of view the branches are in the process of separation, so they are not yet real branches and this allows short period of communication. I would be interested to see experimental test.
Thanks for link. I think that communication is impossible when branches are completely separated, but the existence of the trapped ion prevents this complete separation. In other words, the separation has not ended yet in our case and the whole system has to be regarded as one system which evolves linearly.
"Branch separation" is itself contradictory concept as different understanding of what is it exists.
There are different interpretations of MWI, good overview here: https://iep.utm.edu/everett/
For example, if a atom decay, do branches separate everywhere in the universe with superliminal speed? Or branches are separated when we observe different outcomes? See recent discussion Is Branching Truly Global? From Cambridge Changes to Oxford Changes in the Many-Worlds Interpretation
Simplest would be: someone gave his Claude Code a task to create a new bird flu virus which can kill almost everyone and the agent found a brilliant new way to bypass the need of RNA-synthesis and instead made some smilingly unrelated internet orders..