Dear Laurence,
Without any exaggeration, you gave us one of the most profound responses we ever had for this text. Thank you so much for your deep attention, and, of course, for your high rating of the essay. Below I am giving our response to your points.
1. "What about another alternative, namely, that the logical structure and indeed the existence of our universe cannot be explained at all?"
We fully agree that this option must be properly considered. I think though that in fact we reflected this way of reasoning just after the citation of Wittgenstein:
"Here Wittgenstein criticizes a silent acceptance of a composite and special mathematical structure as the ultimate explanation of the world. Such explanation barred from further questioning and not subject to reasonable ground of its own existence is an affirmation of unreasonableness of this ground. In other words, it is an acceptance of absurdity as the ultimate foundation of existence. Such superstition destroys the meaning of fundamental science by undermining the importance of reason, subjected by this superstition to the absurd."
Your comment shows us that this option has to be outlined one more time on p.7.
2. "the ground and guarantee of mathematical consistency has to be something outside the network of mathematical structures. Considerable additional argument is required to show that the external something is a mind or at least mind-like."
I like that you are stressing this point, Laurence, and we would be happy to see any additional argument in this direction. However, I think our argument, why this "something" can be only mind, is solid (same p.3):
"This unity must not only somehow bind every one of them [i.e. the mathematical forms] together but it has to guarantee their self-consistency. The forms though are mental entities. They are not thinkable without a mind which contains them as truly self-consistent [and so guarantees their self-consistency]. Thus, we have to conclude that this unity, the terminus of Tegmark's being, is an absolute mind, even if it is not mentioned at all. "
3. "Third, in this same place on page 3 you assert that Tegmark's mathematical absolute has "total indifference to the forms it contains." This contrasts with your position that Ultimate Mind (or Absolute Mind) grants to each of its constituents "its own special significance", as you say in a comment above."
It is the implicit transcendental mind of Tegmark's multiverse, which is indifferent, Laurence. As we wrote:
"the terminus of Tegmark's being is an absolute mind, even if it is not mentioned at all. What makes this mind special and distinctive from its various platonic versions is its total indifference to the forms it contains. That is what Tegmark calls "the mathematical democracy". "
The absolute mind of Tegmark cares about one and only one thing: mathematical consistency. After that, all forms are "democratically equal" for that mind. We are showing that this hypothesis is inconsistent with physics. To be consistent with that, we have to conclude that the absolute mind is not that indifferent; at least it cares about mathematical elegance as well.
Finally you say, "In any event, you have brought forward an issue that has been too much neglected. Perhaps in the future you will say more about it."
I fully agree. We think that this essay, among a few other works, sheds light onto that new field of philosophy where physics meets none other than theology in a very rigorous way. The people who are capable of such a level of discussion are rare, which makes your current and, hopefully, future thoughts on this subject most desirable.
Cheers,
Alexey Burov.