[davidgerard]

> I'm quite sure I've read somewhere that information cannot be lost in the absolute sense, lost to us: yes, lost irrevocably and irrefutably: no.

This is probably not quite at the requested standard of backing up a claim, and sounds very like "but you can't prove it isn't true!" But I'm not the one making a claim.

In any case, please back up your claim. What is "the absolute sense"? How does it differ from "in a practical sense", with examples?

> In short: if you're smart(fast, precise, determined) enough to look at the individual molecules of a puddle of brain-goo. And if you can infer the way it has collapsed by ray tracing those molecules back through how they collided with each other/the walls of your mold then it should be possible to reconstruct the spatial form of the brains at least. That's a pretty big IF obviously, but equally obviously not impossible. If only you can look deep/far/fast enough.

Noise floor. In this case, thermal noise.

Also, you literally can't know that much about all the molecules in your puddle of goo. (Heisenberg.) We do not live in a Newtonian universe.

[SCHiM]

http://en.wikipedia.org/wiki/Entropy_in_thermodynamics_and_i...

http://phys.org/news/2014-09-entropy-black-holes.html

http://phys.org/news/2014-09-black-hole-thermodynamics.html

Ben Crowell, phd in physics:

http://physics.stackexchange.com/questions/83731/entropy-inc...

The reason I didn't/don't back up those claims is because I'm really not knowledgeable about those subjects. I'm not sure what good sources are/how legitimate they are, but I have read it one day. Even if I cannot interpret the technical jargon behind it and/or give more nuance to my claim due to a low understanding of the subject.

Given a bit of googeling to "can information be lost", "conservation of information" one finds the articles I linked to above.

But you have dodged my refutal of your initial claim, the one I was really responding to, that: 'sufficiently advanced AI' is not just a stop-gap-word for magic. Because in this case it doesn't stand for "I don't know how or why but this and this", but instead it stands for "I don't know why(in the motivational sense), but given a bigger brain one can use and interpret finer instruments, which in turn enables us to extrapolate further back in time".

[davidgerard]

None of your links support your claim that winding the clock back is even theoretically possible, and the stackexchange link seems to say it isn't: "The resolution is that entropy isn't a measure of the total information content of a system, it's a measure of the amount of hidden information, i.e., information that is inaccessible to macroscopic measurements." Even if you're assuming a physical God, that physical God can't get good enough measurements.

[SCHiM]

I think that perhaps our views of the world are slight off-kilter/incompatible.

I agree with you that even godlike-AI must have an upper bound on what they can extract from a 'puddle of atoms'. It's obvious that given a handful of atoms it's not possible to predict what happened to a completely different bunch of atoms 5 billion years ago at the other side of the (observable) universe. That's also not what I'm claiming.

What I do claim is that, given enough smarts, it's possible to do this to a bunch of molecules present in the brain-goo.

I'm assuming here that whatever it is that makes the brain 'tick' is located on the molecular level, and not a lower level.

As to your claim of being able to 'turn back time', don't we do this all the time?

If we look at the link we've both referenced, say we had two pictures of the last milliseconds of the book falling, and we knew the exact time between when these pictures were taken then we can turn back the time right? We know exactly how/when/where the book was if we can interpret those pictures.

In a similar way, the information about the locations of the molecules in the 'brain goo' is available to a 'sufficiently advanced AI'. Thus what I'm arguing is that this is not information that is 'lost' in the way that we've been discussing so far.

Therefore it's also not 'magic' when people refer to such AI, because when they do they have this in mind. Not some law-bending/breaking super godlike-ai, but rather a system with the resources needed to stitch together the complete video from the last two images.

[davidgerard]

> I think that perhaps our views of the world are slight off-kilter/incompatible.

Yeah, possibly. I blame LessWrong fatigue. It's an entire site made of handwavy claims that, no matter how far you trace back through the links, never quite actually get backed up. So I tend to be harsh on similar claims, particularly when they appear to be from that sphere (judging by the buzzword "sufficiently advanced AI", which is in practice used to put forward outlandish claims and then try to reverse the burden of proof).

I actually started reading the site because of a friend who was getting into cryonics. I'd hitherto been neutral-to-positive on the idea, but the more I investigated it the more I went "what the hell is this rubbish." (Writeup is at http://rationalwiki.org/wiki/Cryonics which is a very middling article, and is still about the best critical article available on the subject ...) The handwavy claims are endemic, quite a few rely on effective magic (actual answers from cryonicist: "But, nanobots!" or "sufficiently advanced AI") and it really is largely just ill-supported guff, even if I'm being super-charitable to the arguments. Extracting a disprovable claim is nearly bloody impossible itself.

> As to your claim of being able to 'turn back time', don't we do this all the time? >If we look at the link we've both referenced, say we had two pictures of the last milliseconds of the book falling, and we knew the exact time between when these pictures were taken then we can turn back the time right? We know exactly how/when/where the book was if we can interpret those pictures.

But we couldn't do that if the data had been destroyed. That's the claim way up there: the information is recoverable from the mashed-up goo. The two pictures have been destroyed, we have the book sitting on the floor, there's nothing to reconstruct the fall in sufficient detail.

I say this because whenever I've seen an actual neuroscientist who's been asked this sort of question (can we recover the information with a magic AI or whatever), they answer "wtf, no, it's been utterly trashed. No, not even in theory. You can't even measure it. It's been trashed utterly." The questioner usually comes back with "but if we use a SUFFICIENTLY ADVANCED AI ..." i.e., if we let them assert their conclusion. And first they'd have to show you could measure stuff on the nanometre scale without messing it up. Let alone, e.g., reconstructing the precise locations of proteins in a cell after they've been denatured by cryoprotectant. Remember that it's a claim about physical reality that's being made here.

(A couple of examples, from scientists who would LOVE to be able to preserve and get back this information: http://lesswrong.com/r/discussion/lw/8f4/neil_degrasse_tyson... http://freethoughtblogs.com/pharyngula/2012/07/14/and-everyo... )

>In a similar way, the information about the locations of the molecules in the 'brain goo' is available to a 'sufficiently advanced AI'.

Remember that there is no way to distinguish two molecules of the same substance. You're requiring more information than can actually be measured (Heisenberg).