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I finished the book last night. It's not a long read in terms of pages, but in the first half particularly it took me quite a few stops to ponder about what had

by cmehdy 6y ago

I finished the book last night. It's not a long read in terms of pages, but in the first half particularly it took me quite a few stops to ponder about what had been laid in few sentences. Greg Egan is awesome. (Sort-of SPOILERS underneath) I can actually grasp the Dust theory thing pretty well as I followed Durham's realizations, however I somehow can't fathom the "more practical" TVC universe stuff, and perhaps you can enlighten me: - TVC starts with borrowed compute but somehow connects to the Dust Theory, right? - The whole "TVC is software and compute-based" at first (some software is even implanted in it), but somehow becomes a self-expanding thing as the story needs it simply by being a mathematical object, am I understanding this correctly? - Why would a few minutes of compute offer Durham any more relief than a second of it, a theoretical proof of it, or a billion years of it? Since they are even in a position to kickstart something computable, it mathematically exists, therefore by the Dust theory they don't even need to start it in order for everything in the book to happen. Admittedly, that makes for a much shorter book (or a billion trillion other scenarios and then some, whatever floats one's boat) - Why would the TVC Durham enjoy the continuation while the "flesh" Durham wouldn't? I guess I'm getting personal there, but isn't part of the understanding of this wholeness of existence also the acceptance that whatever currently unsatisfactory situation is but one amongst infinity anyway, and pain is as powerful as you want an illusion to be? (in his case, alienation from society, or lack of purpose once he feels validated). This is the part where I think the book really crosses into Buddhist concepts at times. I really liked the book, and like a lot of good books it left me with more questions and wonder than I started with. For me, it does make the sound of one hand clapping. :)

lachlan-sneff 6y ago
I read Permutation City a year or two ago, so bear with me. I believe they run the computation on physical computers so that the people running in the simulation can, at any point, check if their reality is a descendant of the initial garden-of-eden configuration.
- cmehdy 6y ago
  I think I can see it: they write the software without having a clear proof (that, say, it is mathematically inconsistent and will crash). Then they execute it for long enough for its self-test phase(s) to be reasonably validated (with all the resources they can get in the "normal" world), therefore practically reassuring themselves that there's a mathematically valid outcome (in a "formal verification" sense), which ensures at least one configuration existing with their wishes (the Garden-of-Eden one). It does have the side effect of ensuring the reality that exists also has a way to know the Garden of Eden configuration (provided the people scanned are/were made aware of it prior to the scan, since it's made clear that there's no guaranteed way to know what happened to the "flesh person" after a scan when you're "reborn virtual".
ryukafalz 6y ago
It has admittedly been a long time since I've read the book, so my recollection of it may be a bit hazy, but: > Why would a few minutes of compute offer Durham any more relief than a second of it, a theoretical proof of it, or a billion years of it? Since they are even in a position to kickstart something computable, it mathematically exists, therefore by the Dust theory they don't even need to start it in order for everything in the book to happen. Admittedly, that makes for a much shorter book (or a billion trillion other scenarios and then some, whatever floats one's boat) I'd guess for "flesh" Durham's assurance that the simulation worked as well as he thought it would. It's one thing to be pretty sure it'll work in theory, but I'd imagine it'd be quite a bit more reassuring to see it in action. Of course, TVC-Durham gets to see that it works subjectively, but from outside the TVC universe the only way you can verify that it's working is to run the simulation and observe the result. I don't think they had enough compute power to run a billion years of the simulation, and a few seconds is too short to e.g. see people interacting within it.
- cmehdy 6y ago
  It makes sense, thanks. I guess I hadn't really thought about the fact that having a program written isn't having a program that is mathematically verified (as we likely all know, this is a particularly costly procedure and can hardly be done on extremely complex pieces of software - otherwise everyone would do it). So they run it long enough to "feel" like it is valid enough. And then they can't afford more. From a software engineer point of view though, it's a bit short-sighted isn't it? I can't imagine anyone writing anything beyond a calculator app (and even that..) would be certifying to you that formal verification could work on their program by simply running it for a while. Durham could have bootstrapped further cash to keep things running once in a while for show and dedicate the rest of his life to mathematically proving as many chunks as possible. But that might just be me obsessing over the concept more than Durham himself..
  - ryukafalz 6y ago
    Well, part of what Durham wanted to demonstrate to himself was that he didn't need to be running the simulation for the TVC version of him to have a subjective experience of the simulation, right? And TVC-Durham has Durham's memories as of the last brain scan, so that's also "him" in a sense. So the fact that TVC-Durham knows that the simulation isn't being run on the outside is valuable knowledge as well. It's sort of a balance between flesh-Durham having assurance that the simulation works, and TVC-Durham having assurance that his subjective experience of the TVC universe is going to continue.

by cmehdy 6y ago

lachlan-sneff 6y ago

I read Permutation City a year or two ago, so bear with me. I believe they run the computation on physical computers so that the people running in the simulation can, at any point, check if their reality is a descendant of the initial garden-of-eden configuration.

cmehdy 6y ago
I think I can see it: they write the software without having a clear proof (that, say, it is mathematically inconsistent and will crash). Then they execute it for long enough for its self-test phase(s) to be reasonably validated (with all the resources they can get in the "normal" world), therefore practically reassuring themselves that there's a mathematically valid outcome (in a "formal verification" sense), which ensures at least one configuration existing with their wishes (the Garden-of-Eden one). It does have the side effect of ensuring the reality that exists also has a way to know the Garden of Eden configuration (provided the people scanned are/were made aware of it prior to the scan, since it's made clear that there's no guaranteed way to know what happened to the "flesh person" after a scan when you're "reborn virtual".

ryukafalz 6y ago

It has admittedly been a long time since I've read the book, so my recollection of it may be a bit hazy, but: > Why would a few minutes of compute offer Durham any more relief than a second of it, a theoretical proof of it, or a billion years of it? Since they are even in a position to kickstart something computable, it mathematically exists, therefore by the Dust theory they don't even need to start it in order for everything in the book to happen. Admittedly, that makes for a much shorter book (or a billion trillion other scenarios and then some, whatever floats one's boat) I'd guess for "flesh" Durham's assurance that the simulation worked as well as he thought it would. It's one thing to be pretty sure it'll work in theory, but I'd imagine it'd be quite a bit more reassuring to see it in action. Of course, TVC-Durham gets to see that it works subjectively, but from outside the TVC universe the only way you can verify that it's working is to run the simulation and observe the result. I don't think they had enough compute power to run a billion years of the simulation, and a few seconds is too short to e.g. see people interacting within it.

cmehdy 6y ago
It makes sense, thanks. I guess I hadn't really thought about the fact that having a program written isn't having a program that is mathematically verified (as we likely all know, this is a particularly costly procedure and can hardly be done on extremely complex pieces of software - otherwise everyone would do it). So they run it long enough to "feel" like it is valid enough. And then they can't afford more. From a software engineer point of view though, it's a bit short-sighted isn't it? I can't imagine anyone writing anything beyond a calculator app (and even that..) would be certifying to you that formal verification could work on their program by simply running it for a while. Durham could have bootstrapped further cash to keep things running once in a while for show and dedicate the rest of his life to mathematically proving as many chunks as possible. But that might just be me obsessing over the concept more than Durham himself..
- ryukafalz 6y ago
  Well, part of what Durham wanted to demonstrate to himself was that he didn't need to be running the simulation for the TVC version of him to have a subjective experience of the simulation, right? And TVC-Durham has Durham's memories as of the last brain scan, so that's also "him" in a sense. So the fact that TVC-Durham knows that the simulation isn't being run on the outside is valuable knowledge as well. It's sort of a balance between flesh-Durham having assurance that the simulation works, and TVC-Durham having assurance that his subjective experience of the TVC universe is going to continue.