I'm not remotely a physicist, but I have a few comments, which I will do my best to confine to the limits imposed by my knowledge of my lack of knowledge.
Let us assume that you an all-powerful optimization process, and your goal is to finish an extremely long computation (say, a search for a very large Hamiltonian cycle) in the shortest possible amount of time. You have millions of galaxies to turn into computronium. What is the optimal expansion speed of your computer, considering our current understanding of particle physics, general relativity and thermodynamics?
By "optimal expansion speed", do you mean "maximum possible expansion speed given particle physics, general relativity and thermodynamics (according to our current understanding thereof)", or do you see some reason that a slower expansion would be beneficial to the ultimate goal (or is that the question)?
(Meanwhile, I'll just say that I'd first want to either prove P≠NP or find a polynomial-time algorithm for the Hamiltonian cycle problem. P=NP may be unlikely, but if I were an all-powerful optimization process, I'd probably want to get that out of the way before brute-forcing an NP-complete problem. Might save a few million galaxies that way. Then again, an all-powerful optimization process would very likely have a better idea than this puny human.)
Of all the possible Universes in Tegmark's level IV Multiverse, most don't even have a concept of Time.
I'm not sure if something without a timelike dimension would really qualify as a universe. It's really just a matter of definition, but since every mathematical structure has the same ontological status in Tegmark IV, including, say, the set {1, 2, 3}, a useful definition of "universe" will have to be more narrow than "every element of the Level IV Multiverse" and more broad than "every structure that can result from the laws of this universe".
I'm not sure if we'd be able to rigorously define what structures count as "universes" (and it's not terribly important, being that our definition of the word doesn't impinge on reality anyway), but intuitively, what properties are necessary for a structure to seem like a universe to you in the first place? I'd be pretty flexible with it, but I think I'd require it to have something timelike, some way for conditions to dynamically evolve over at least one dimension.
By "optimal expansion speed", do you mean "maximum possible expansion speed given particle physics, general relativity and thermodynamics (according to our current understanding thereof)", or do you see some reason that a slower expansion would be beneficial to the ultimate goal (or is that the question)?
Avoiding heat death may be beneficial, for example. As I wrote to Mitchell Porter, to me, the most interesting special case of the question is: if you want to build the fastestest computer in the Universe, should it expand with the s...
We have recently obtained evidence that a number of people, some with quite interesting backgrounds and areas of expertise, find LessWrong an interesting read but find limited opportunities to contribute.
This post is an invitation to engage, in relative safety but just a little beyond saying "Hi, I'm a lurker". Even that little is appreciated, to be sure, and it's OK for anyone who feels the slightest bit intimidated to remain on the sidelines. However, I'm confident that most readers will find it quite easy to answer at least the first of the following questions:
...and possibly these follow-ups:
Comments like the following, from the "Attention Lurkers" thread, suggest untapped resources:
My own area of professional expertise is computer programming - perhaps one of the common sub-populations here. I'm also a parent, and have been a beneficiary of prenatal diagnosis (toxoplasmosis: turned out not to be a big deal, but it might have been). My curiosity is often engaged by what goes on "behind the scenes" of the professions I interact with as an ordinary citizen.
Yes, I would be quite interested in striking up a conversation about applying the tools discussed here to prenatal diagnosis; or in a conversation about which conceptual tools that I don't know about yet turn out to be useful in dealing with the epistemic or ethical issues in prenatal diagnosis.
Metaphorically, the intent of this post is to provide a marketplace. We already have the "Where are we?" thread, which makes it easier for LessWrongers close to each other to meet up if they want to. ("Welcome to LessWrong" is the place to collect biographical information, but it specifically emphasizes the "rationalist" side of people, rather than their professional knowledge.)
In a similar spirit, please post a comment here offering (or requesting) domain-specific insights. My hunch is, we'll find that even those of us in professions that don't seem related to the topics covered here have more to contribute than they think; my hope is that this comment thread will be a valuable resource in the future.
A secondary intent of this post is to provide newcomers and lurkers with one more place where contributing can be expected to be safe from karma penalties - simply answer one of the questions that probably comes up most often when meeting strangers: "What do you do?". :)
(P.S. If you've read this far and are disappointed with the absence of any jokes about "yet another fundamental question", thank you for your attention, and please accept this apophasis as a consolation gift.)