To make the question more precise, you would need to define a starting point in the past. You could set it right after the end of WW1. Or you could set it before WW1, which means that the counterfactual branches without WW2 would also include those where neither WW1 nor WW2 happened.
If you set the starting point too far, like in the age of dinosaurs, the probability of “humans did not have WW2” is almost 100%, because almost certainly humans have never evolved.
But suppose you choose the starting point to be e.g. the year 1920.
There is a tiny nitpick that technically the past is also uncertain (although much less than the future, because… something something… entropy and arrow of time), so you get a probabilistic version of 1920, but probably for all practical purposes the majority of its measure is the same as you would expect, macroscopically, and lot of noise at the microscopic level.
Anyway, let’s define “1920” as the best probabilistic distribution of 1920 we could reconstruct now.
Reconstructing the past is already technically difficult, because the particles are too many (the entire Earth? probably much more, because some observed astronomical events could have influenced something). So at this moment, this is a completely unrealistic “in principle” thought experiment.
But suppose that we have a gigantic magical machine that could dismantle the Solar system and measure each tiny particle in order to best figure out the answer to our question.
Then there is the problem of defining “WW2” in terms of positions and momentums of tiny particles. Calculating all possible combinations of particles, and evaluating whether they contribute to the “no WW2″ set, I think that would require more energy than is available in our universe.
But suppose that a magical hypercomputer from an alternative reality joins the project...
I guess, unless there are a few more technical problems that I forgot, it probably could be done.
But given the amount of magic we have assumed, it would probably be much simpler to assume that the world is a simulation, and ask the Masters of the Matrix nicely to restart the simulation 1000 times from the starting point of 1920, then return to us and show us the probability distribution.
I get that doing something like this is basically impossible using any practical technology, but I just wanted to know if there was anything about it that was impossible in principle (e.g. not even an ASI could do it).
The main problem that I wanted to ask and get clarification on is whether or not we could know the measure of existence of branches that we cannot observe. The example I like to use is that it is possible to know where an electron “is” once we measure it, and then the wave function of the electron evolves according to the Schrodinger equation. The measure of existence of a future timeline where electron is measured at a coordinate X is equal to the amplitude of the wave function at X after being evolved forward using the Schrodinger equation. But I am guessing that it is impossible to go backwards, in the sense of deducing the state of the wave function before the initial measurement is made using the measurement result (what was the amplitude of the wave function at Y before we measured the electron at Y)? Does that make sense?
To make the question more precise, you would need to define a starting point in the past. You could set it right after the end of WW1. Or you could set it before WW1, which means that the counterfactual branches without WW2 would also include those where neither WW1 nor WW2 happened.
If you set the starting point too far, like in the age of dinosaurs, the probability of “humans did not have WW2” is almost 100%, because almost certainly humans have never evolved.
But suppose you choose the starting point to be e.g. the year 1920.
There is a tiny nitpick that technically the past is also uncertain (although much less than the future, because… something something… entropy and arrow of time), so you get a probabilistic version of 1920, but probably for all practical purposes the majority of its measure is the same as you would expect, macroscopically, and lot of noise at the microscopic level.
Anyway, let’s define “1920” as the best probabilistic distribution of 1920 we could reconstruct now.
Reconstructing the past is already technically difficult, because the particles are too many (the entire Earth? probably much more, because some observed astronomical events could have influenced something). So at this moment, this is a completely unrealistic “in principle” thought experiment.
But suppose that we have a gigantic magical machine that could dismantle the Solar system and measure each tiny particle in order to best figure out the answer to our question.
Then there is the problem of defining “WW2” in terms of positions and momentums of tiny particles. Calculating all possible combinations of particles, and evaluating whether they contribute to the “no WW2″ set, I think that would require more energy than is available in our universe.
But suppose that a magical hypercomputer from an alternative reality joins the project...
I guess, unless there are a few more technical problems that I forgot, it probably could be done.
But given the amount of magic we have assumed, it would probably be much simpler to assume that the world is a simulation, and ask the Masters of the Matrix nicely to restart the simulation 1000 times from the starting point of 1920, then return to us and show us the probability distribution.
I get that doing something like this is basically impossible using any practical technology, but I just wanted to know if there was anything about it that was impossible in principle (e.g. not even an ASI could do it).
The main problem that I wanted to ask and get clarification on is whether or not we could know the measure of existence of branches that we cannot observe. The example I like to use is that it is possible to know where an electron “is” once we measure it, and then the wave function of the electron evolves according to the Schrodinger equation. The measure of existence of a future timeline where electron is measured at a coordinate X is equal to the amplitude of the wave function at X after being evolved forward using the Schrodinger equation. But I am guessing that it is impossible to go backwards, in the sense of deducing the state of the wave function before the initial measurement is made using the measurement result (what was the amplitude of the wave function at Y before we measured the electron at Y)? Does that make sense?