Dear Marc,
Thank you for engaging with me even after my relatively heavy criticism.
"For you (correct me if I'm wrong), the "real world" is the observable physical universe and mathematics is a way for us humans to represent it: naturally, you find it is most important to study how mathematics does this, and hopefully improve the definition of mathematics to help it do its job better."
Yes, that is largely correct. I would only add that the effort "to improve the definition of mathematics" is for me a means to an end, which is to understand reality at the deepest level. I did not start out with the foundations of mathematics but was in some sense "forced into it" by the realization that some of the ideas I thought would explain how the universe works simply could not be expressed using the language of contemporary mathematics. As you know, this is one of the ways in which new mathematics comes about.
"For me, what is most important is to find a satisfying answer to the question "Why is there something?". It seems to me that the only answer that does not create more questions has to be something like "all abstract structures simply ARE, and one of these IS our observable universe". I believe all of mathematics (being abstract) simply IS, but it doesn't mean of course that we, human mathematicians or physicists, automatically have access to it all."
Yes, I understand this point of view because I have entertained it myself. My criticism in the last post was meant primarily to
1) compel a self-examination of what appeared to me an instance of "moving the goal post" in response to one of my challenges
2) compel an examination of what, absent further specification, appears as contradictory evidence. Note, contradictory evidence is not contradictory proof. Perhaps there is a way of overcoming the difficulty I referenced, but before we know this it has to be acknowledged as such.
Perhaps it helps if I lay out an analogous difficulty that I face in my project (i.e. I am throwing a challenge at myself in your place). As you know, ZFC is regarded currently as the foundation of mathematics because starting from it, one can define ever more complicated kinds of sets which either serve as mathematical structures e.g. groups, rings, fields etc, and as numbers. Most of these begin with the concept of an ordered pair, which is usually defined in terms of sets in a manner first given by Kuratowski. It turns out that Kuratowski's definition of an ordered pair fails for an incomplete ordered pair. It is possible to come up with a more complicated kinds of sets which satisfy the definition, but then I have to make sure that it does not unintentionally collide with other well-established set theoretic structures (or if it does, I have to make sure that this difficulty can be resolved). I have not yet solved this problem, which is to show unequivocally that there is a set which both satisfies the definition of an incomplete (and complete) ordered pair and which agrees with all the well-established structures with which the Kuratowski definition agrees, and until I solve this problem, my framework has no chance (Incidentally, the function of the Kuratwoski definition is only to make sure that ordered pairs are well-defined, beyond what I just mentioned, the definition of an ordered pair is completely arbitrary and usually forgotten about by mathematicians) .This is my version of the problem that I pointed out to you about inconsistent mathematics, in the sense that it lies at the very core of the undertaking. I acknowledge the difficulty and all the while I am working on developing the overall framework, I attempt to overcome it as well.
On the other hand, I perceived in your response to my bringing to your attention the possibility that inconsistent mathematical structures might render the maxiverse as a whole inconsistent a refusal to acknowledge that there is a problem that needs to be addressed. Since I explain the perceived refusal to myself in terms of psychology, I thought I share what I consider to be the explanation with you as well.
"You asked me to clarify my view of actuality vs potentiality, ideally with an example. I will take Tegmark's example of a dodecahedron: it is a mathematical structure, but it is not complex enough to be a physical universe --- it just exists abstractly in the space of all mathematical structures. Perhaps you would say that something that only "exists abstractly" is a "potentiality" --- fine, that is a valid way to define potentiality. "
No, I would not say that. If it has no chance of becoming an object in the real world, then, I agree, it would in some sense "exist abstractly" but it would not exist as a "potentiality". To me, the essence of the concept of potentiality is the possibility of the "coming into being" as an object in our real world.
"The way I see things, my mind also is a mathematical structure, but I know from direct experience that it does not merely have an abstract existence. It has (at least) a "mental" existence, so we could say it is an "actuality". Moreover, I perceive myself as a physical being in a physical universe: this "physical universe" is also a mathematical structure, but it is precisely because my conscious states are part of it that it makes sense to say that it exists as a physical "actuality". "
This is quite metaphysical, and I am not quite sure in what sense you are referring to your mind and your perception. There are certainly neural correlates, very small changes in the electromagnetic fields in the brain etc. that correspond to these, but I have the impression you are not talking about them. If you are talking about your mind in the sense of, say, a consciousness, or your perception in the sense of qualia, then I think it would be much more convincing to give some examples, or at least analogies, to how they can be mathematical structures instead of just positing that they are.
"As you can see, I'm looking at the philosophical roots of the concept of actuality vs potentiality, while you seem to take these concepts for granted. "
Well, based on the above discussion, I am not sure we are talking about the same thing. I have not yet tried to check it, but I suspect that even a child could tell that there is a difference between, say, the outcome of an experiment in which a fair coin which has been flipped, and the (lack of) an outcome of an experiment in which it hasn't been flipped yet. This sort of distinction, which I use, seems to me not to require deep metaphysical thoughts.
"What is potential vs what is actual is purely contextual: from the point of view of the year 2014, the year 2015 is potential, but from the point of view of the year 2016, it is actual."
Yes, that is an excellent point, and I think the reason why the operators I have defined can also be conceptualized in terms of temporal modal operators.
"Ultimately, I don't think that the distinction between actual and potential is very useful when you try to understand reality at the most fundamental level. But of course, since I believe that this most fundamental level is a spaceless and timeless abstract realm where everything simply is, that I hold such a view should not be too surprising."
Well yes, we each start out with our own intuitions, biases, and prejudices and try to work our way towards building something concrete, which in this field is still ultimately a framework that is consistent with what we already know and which makes new testable predictions. That will be the ultimate arbiter of whether our intuitions had merit or not.
I hope you found my responses useful.
Best,
Armin