There are some basic questions about the world:
1) Why does anything exist, instead of just nothing?
2) What does exist?
3) Why does that stuff exist instead of other stuff?
4) Given that stuff does exist, why is there consciousness instead of just behavior?
These questions are so basic that it would be nice to know the answers to them before worrying about specifics of our own situation.
Regarding these questions we can make highly counter-intuitive observations:
Suppose that somehow you didn't know that anything exists, and you are asked to guess: Does anything exist? My guess would certainly be "No, it would make a lot more sense if nothing exists. That is not only much simpler, it's also a lot easier to understand how it might be that nothing exists."
OK, but things do exist. So why THIS instead of THAT? We don't know. And not only that: It seems impossible to even imagine any reason why one possible thing would be selected over another. You can't say "it's because of this other thing" (whether the other thing is a law of physics, a god, or whatever) because that doesn't explain anything, it just begs the question of "So why does that other thing exist?" and we are back to the start.
There are basically two schools of thought on consciousness: 1] Dualism: Consciousness is a basic thing, which can not be due to something mathematically describable; or 2] Reductionism: Consciousness is an inevitable consequence of certain mathematically describable things. While I tend to fall into the latter camp, both ideas have counter-intuitive implications which I will not address in this post.
At least we do have ideas to debate about consciousness. Are there even any ideas about possible answers to the other questions, controversial or not?
It turns out that there is an idea which might begin to address them to some extent, called the Everything Hypothesis:
What if everything that possibly could exist does exist?
This would seemingly avoid avoid the apparent paradox of some things existing rather than other things despite there being no possible reason why that could be the case. It is also the simplest possible set of things that could have existed (other than just nothing) due to being fully symmetrical.
However, it doesn't really answer question 3). To really put question 3) to rest we would still need to know "Why does everything exist?" which would also cover question 1).
It turns out that there is an idea that could address that; this idea is sometimes called "radical Platonism" in analogy with certain ideas that Plato had, but it is really a modern idea that was perhaps, although not necessarily inspired by Plato, given a bit of philosophical confidence by his precedent.
The idea is that there is no fundamental physical reality; instead, the fundamental reality is the world of logical and mathematical possibilities (which would thus better be called actualities). Of course, it remains difficult to understand why a logically possible world would automatically be real enough to have real observers inside it; but if that is the way it is, the Everything Hypothesis would have to be true. This can be seen as a 'new version' of either Question 1 or Question 4.
While Max Tegmark is credited with the first paper on the Everything Hypothesis, various other people came up with similar ideas on their own. I was one of them.
There are variations or more limited versions of the Everything Hypothesis based on what is meant by 'Everything'. Tegmark's version of the Everything Hypothesis is explicitly mathematical: namely, that every possible mathematical structure exists. If Dualism is false, then that is equivalent to the full Everything Hypothesis. However, if Dualism is true, then consciousness and laws related to it are other things within the set of Everything.
The next question is: What does the Everything Hypothesis predict?
This can be put into familiar terms for a many-worlds model: What measure distribution on conscious observations does it predict?
At first glance, one might think that a typical observer within the Everything would see a quite random mess. If so, the Everything Hypothesis must be false, since we see reliable laws and a highly ordered universe.
However, taking a computationalist view of mind, only certain mathematical structures would support observers: those that have the equivalent of time evolution with respect to some parameter (or some suitable substitute), and have reliable laws for such dynamics. We should therefore consider the set of such dynamical structures with all possible dynamical laws. The starting state may be completely random, but the state will no longer be so random once time evolution occurs.
While we don't know how deal with the set of all possible dynamical systems, there is one subset that is much easier to handle: Turing machines, which are digital computers. A universal Turing machine can run the equivalent of any digital computer program.
So we can look at a simple universal Turing machine and consider the set of all programs for it. Such a program is just an infinitely long symbol string, which I'll call a bit string for simplicity. The machine has a 'head' that move along the string and changes bits and a few value values internal to the head.
Most programs have only a finite number of bits that actually do anything (the active region), because the head is likely to be instructed either to halt or to enter an infinite loop. The number of programs that are the same within the active region but different in the region of bits that don't do anything decreases exponentially with the number of bits in the active region, because each bit brought into the active region is a bit that can't be randomly varied in the inactive region.
Therefore, shorter and simpler programs have a higher measure (more copies) than longer programs do. The typical laws of worlds simulated by these programs are therefore likely to be as simple as possible, consistent with the requirement that observers exist within them. Perhaps, then, our own world is such a world.
That is an impressive result! It would certainly be interesting - though probably it will always be beyond our capabilities - to know exactly what would be typical for observers in the set of all Turing machine program runs to see.
However, there's a big problem here for the Everything Hypothesis: there are infinitely many possible Turing machines and digital computers in general. We can pick one, but that contradicts the fact that radical Platonism must have no arbitrary choices - no free parameters - if it is to explain why the world is the way it is. So why not just pick all of them and weight them equally? The problem there is that since there are infinitely many, the order in which we list them makes a difference to the result we get when trying to get the measure distribution. It's a very small difference for 'subjectively reasonable' choices of these parameters, but that's not the point; ANY arbitrariness completely ruins the explanatory power of radical Platonism.
Besides, what about continuous systems? Some people are content to assume that the fact that there appears to be no natural measure for them means we don't need to include them in the Everything even if we are Platonists. However, it seems to me that they are just as much legitimate candidates for existence as digital systems.
Reluctantly, I am forced to conclude that - unless there is some way of overcoming these mathematical problems that we don't know about, which seems unlikely - Platonism does not provide the explanation we were looking for. This is a paradox, because it also seems that Platonism is the only thing that even could have been a real explanation for why things are the way they are.
With the Everything Hypothesis we are still left with a 'new version' of Questions 1-2: NOT "What does exist, and why?" but "What is the measure distribution, and why?" This is a change, at least! Perhaps it is a more tractable question, but for now it is still a question which demands explanation for which we have none.
I still think that the set of all things which exist is probably very simple in some sense and that the physics we see is just a small part of it. We see the part of it that we see due to being fairly typical observers.
Perhaps the right way to derive the Born Rule of quantum mechanics would be to start with something like the set of all possible Turing machine programs and derive from it the measure distribution on conscious observations, but obviously, such a project would be all but impossible to carry out in practice. My work will focus instead on studying the consequences of the standard physics equations (which are based in large part on experimental observations). However, my criteria for implementation of a computation are general and do not depend on the assumption that the underlying system is a physical one, so in principle, they should apply even to underlying systems that are Platonic Turing machines.
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