koganbot: (Default)
Five people who don't know me whom I wish I were in conversation with:

Duncan J. Watts
Sean Carroll
Nate Cohn

Er, that's only three. But I'd like this to become a meme. And if I left you out, or your gender, race, class, and musical preference, that doesn't mean I don't want to talk to you.

Funny, I barely follow Cohn (as opposed to Matt Yglesias and Josh Barro, whom I read all the time), but he once did a tweet on the "total failure of comment sections" that I want to dispute. (I only half-jokingly sometimes claim to have invented the comment thread. In any event, I think it's not only still a viable form, but one of the most essential.) Anyway, not only could my three teach me loads but there are specific thoughts of mine I want them to challenge*; also, though, I think they could use some of what my brain produces, e.g., thoughts inspired by Wittgenstein and Kuhn, things that could untangle some of their thoughts or help them express themselves to the lay people like me that they covet and court; why they shouldn't be worrying about "post-Truth" (though they should and surely do worry about American-grown fascism); what they could wonder about instead.

*I wrote about Watts here and tried to channel him here and here as to my own guesses e.g. why the Sex Pistols and Crayon Pop etc. became famous (is there a way to figure out how much was owing to luck?). I mention Carroll here, my being unable to figure out what physicists mean by "information": if information is preserved then our ability to "read" and understand it would also be preserved, right? How could the latter not be information itself? But if so, then we ourselves are preserved — hurrah! — indefinitely even into the cold dead future. Except I'm sure what I just said is wrong. I just don't know why it's wrong, and I think it would take someone real work to demonstrate that it's wrong.

(I'm assuming there's no difference in kind between "physical information" (if that's a term) and other types of information; i.e., I assume all information must in some way be "physical." Of course I don't think the word "physical" in this paragraph explains itself, and not being a physicist I don't know what I'm saying with the word much less how to explain it. (Btw, this is something I believe I can offer people: a nose for when they fall into incorrectly thinking their words are explaining themselves.))
koganbot: (Default)
Posting again on a subject I don't understand and never will: what physicists mean by "information." My brain balks at mathematical symbols, but I'm good at concepts; so my guess is that if some articulate physicist were to wander by, he or she could explain "conservation of information" in a way that doesn't totally leave me at sea. Wikipedia hasn't succeeded*, but this passage from the entry on "Black hole information paradox" is useful:

There are two main principles in play:

--Quantum determinism means that given a present wave function, its future changes are uniquely determined by the evolution operator.
--Reversibility refers to the fact that the evolution operator has an inverse, meaning that the past wave functions are similarly unique.

The combination of the two means that information must always be preserved.
What I gather from this is that: (i) any present "state" must have a unique past; you can't have two pasts leading to the same present; and (ii) the present can't lead to multiple futures. Am I interpreting this right? So a quantum waveform (?) version of a Laplace Demon** could reconstitute the past or forecast the future (or maybe, this being quanta, could reconstitute past probability wave something-or-other and forecast future probability wave something-or-other) based on what's known now. Hence information is preserved. So, however you twist it, you'll always have the same information.

Black holes seem to pose a problem for the principle )

The question I posed last time is, "When physicists say that information is preserved even after everything's been absorbed into black holes that have subsequently evaporated, do they mean that, e.g., 'The test tomorrow is at 1:00 PM' is preserved?" Certainly in my everyday use of the term "information," "the test tomorrow is at 1:00 PM" is information. So I can simplify my question down to this:

Is "The test tomorrow is at 1:00 PM" preserved (by the principle of conservation of information)? If not, what is preserved?

Changed my mind since last time )

I continue to have little idea what I'm talking about. But right now I'd reformulate the question as:

If all physical information is preserved, how can "The test tomorrow is at 1:00 PM" not be preserved?

And a corollary to that one would be:

If all physical information is preserved, and this — somehow — does not include "The test tomorrow is at 1:00 PM" being preserved, then how is it possible that "The test tomorrow is at 1:00 PM" exists even now?

So, to convince myself that all information can be preserved while "The test tomorrow is at 1:00 PM" is not preserved, I'd have to have an explanation for why "The test tomorrow is at 1:00 PM" isn't preserved. And to do that, I'd have to have an explanation for how it can exist now without being physical information. We as physical beings sure seem to have the information that the test tomorrow is at 1:00 PM. So far I can't counter this, can't come up with an explanation of how physical beings can have nonphysical information, or what "nonphysical information" would even mean. I don't think physicists, to the extent that they've thought about it, disbelieve that "mental" and "cultural" information can be conveyed by physical information, or that the latter two sorts of information are different in kind from the former. Actually, I don't know what they think. But how would they even potentially explain the existence of "cultural information" at all if such information is not conveyable physically?

That's what I would need to explain, if I wanted to preserve the principle of "conservation of information" while denying the conservation of "The test tomorrow is at 1:00 PM." Not that I necessarily want to deny that "The test tomorrow is at 1:00 PM" can be preserved. What I'm saying is that I don't know how not to preserve it without destroying the principle of conservation of (physical) information — which for all I know is a wrong principle, but to half understand what physicists mean by it, I'm acting as if it's right. Quantum physics guys seem to believe it needs to be right. So, for the moment at least, I'm counting "The test tomorrow is at 1:00 PM" as physical information, hence preservable by "conservation of information."

So, to reiterate, I think the crucial question here, this time in bold, is: How can "The test tomorrow is at 1:00 PM" exist now without being physical information?

I'm deciding for the time being that it can't, and that therefore it is physical information.

No dif in physical status between things and conventions )

Social info has same physical status as any other info )

Footnotes )
koganbot: (Default)
What do physicists mean by information?

Every now and then I'll read a book by a scientist trying to explain a field or subfield or subproblem to laypeople like me (by Randall, Susskind, Greene, to name a few of the recent). I almost always like these books, but Sean Carroll's From Eternity To Here is the first that's really clicked for me. I wouldn't remotely claim to understand it. But I got enough while reading to follow what it was doing as it went circling and chasing a few basic questions. Fundamentally: our universe, or our part of it, seems to start with low entropy, the entropy increasing over time. (Other possibilities are explored.) Without this low-entropy start, time wouldn't have the direction it has. Why did we start with low entropy?

This actually encompasses a whole bunch of questions and contentions. I read the book several months ago, in spare time, needing all three library renewals and finishing on the last day, not thinking concentratedly enough to master one part before moving onto the next. I couldn't have mastered the parts anyway. At one point I copied down the following passage, writing underneath, "If I want to test whether I've understood the book so far, I could look at this passage and ask myself to explain it: to fill in the background, to describe how his argument got here. I don't think I can right now." I understand it even less a few months removed:

In that sense, the irreversibility that crops up when wave functions collapse appears to be directly analogous to the irreversibility of ordinary thermodynamics. The underlying laws are perfectly reversible, but in the messy real world we throw away a lot of information, and as a result we find apparently irreversible behavior on macroscopic scales. When we observe our cat's location, and our own state becomes entangled with hers, in order to reverse the process we would need to know the precise state of the outside world with which we are also entangled, but we've thrown that information away. It's exactly analogous to what happens when a spoonful of milk mixes into a cup of coffee; in principle we could reverse the process if we had kept track of the position and momentum of every single molecule in the mixture, but in practice we keep track of only the macroscopic variables, so irreversibility is lost.
--Sean Carroll, From Eternity To Here, p. 255
My question about information is this: We use the word "information" for a whole lot of fairly different stuff, but I think of it as including, e.g., "The test tomorrow is at 1:00 PM." But when a physicist like Leonard Susskind is talking about "conservation of information," I don't think he means that something like "The test tomorrow is at 1:00 PM" is preserved — e.g., would survive planets being absorbed into black holes and the black holes dissipating. But when he uses the phrase "conservation of information" he does indeed mean that all information is conserved after planets are absorbed and black holes dissipate; so I'm surmising that the sort(s) of information he's talking about differ from the type of info that would include "The test tomorrow is at 1:00 PM." But maybe the latter is included.* If so, how would that work?

*I read The Black Hole War and of course have forgotten most of what I read.

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Frank Kogan

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