Time Reversal and Conversations

29 03 2007

My boyfriend was just telling me about a recent cover story in New Scientist magazine, which had a provocative title about remembering the future, but apparently just said something about how the brain processes information about the future and about the past in similar ways. At any rate, it stimulated a conversation about what it would be like if there were beings that “remembered” the future the way that we remember the past. After trying to figure out whether this would necessarily involve them experiencing things in reverse order, I at least came up with an argument that we wouldn’t really be able to effectively communicate with these beings (at least given some aspects of certain theories of conversation). This is true even bracketing any concerns about strange thermodynamic properties of these systems, or concerns about being able to produce sensible utterances that individually have meaning to both these speakers and us.

On some standard models of conversation (with Stalnaker’s, I believe, as a paradigm of some sort), the state of a conversation can be represented by some set of information that is in the common ground, together with the separate information states of the two speakers. (Let’s assume there’s only two speakers for convenience.) Whenever someone utters something, this updates the common ground, and presumably also updates the other speaker’s beliefs.

However, if one conversational participant remembers only the past utterances in the conversation, while the other “remembers” only the future utterances, then you get a bit of a problem. It no longer makes sense to model the common ground as including all earlier utterances (and their logical consequences), for just the same reason that we don’t model it as containing all later utterances. So in some sense, the common ground shouldn’t contain any utterances at all from this conversation – it can only include the background presuppositions. So the conversational context never changes. But this seems to make individual utterances pointless then, if their point is to change the conversational context.

Of course, we might be able to get information from one another, but it seems like it wouldn’t work like any sort of conversation, or probably even through intentionally saying things to one another. It would have to just be through observation.

Another interesting side note we realized in discussing this is that there’s a sense in which intention is the natural future-directed counterpart of memory, rather than prediction. After all, intentions are the mental states that have direct causal connections to future events, while predictions generally involve some sort of indirect connection involving previous past events. (Let’s leave aside self-fulfilling prophecies, like the things the Oracle telling all those people in Greek myths.) Of course, a far higher proportion of intentions end up not connected to the appropriate action than is the case for memories and the appropriate experience. That is, it’s much easier to have an intention that you don’t carry out than it is to have a false memory (though both are certainly possible).




9 responses

29 03 2007
Time Reversal and Conversations « Antimeta < Lingüística desde Castilla-La Mancha

[…] esta entrada, Time Reversal and Conversations « Antimeta, se discute esta afirmación. Informar acerca del futuro no es predecir, sino desear que el futuro […]

29 03 2007
Lukas Biewald

I think your argument depends on what you think it means to remember the future. If you use the Bill and Ted’s Excellent Adventure model of the future, I think you could have a completely normal conversation with someone that only remembered the future. First they say something and then you would write down what you wanted to say to them in the future. Now they will suddenly remember you saying it. After the conversation you can read your list of things you were gonna say.

The real question is if two of the future remembering beings can have a conversation with each other.

Ok, back to work…

29 03 2007

Terry Pratchett has an interesting take on this in his Discworld books. One of the characters in Ankh-Morpok, Mrs Cake, “has a tendency to answer questions people haven’t asked yet, but gets a migraine if they don’t ask the question she’s already answered”

From: http://en.wikipedia.org/wiki/List_of_Discworld_characters#Other_inhabitants_of_Ankh-Morpork

30 03 2007
Jed Harris

The title story in Ted Chiang’s Stories of Your Life is a meditation on what it would be like to “remember ahead” — and how it would affect one’s feelings about one’s experiences. Chiang’s imaginary situation is more like a “block universe” in which future and past are equally determined, and remembering ahead is more like a perception of the whole pattern of events. It’s a very interesting attempt to imagine how this would seem / feel.

31 03 2007

Lukas: Of course two of the future-rememberers can have a conversation with each other; the situation is exactly symmetric to two past-rememberers conversing. The only thing that would prevent the FRs from being able to converse would be if we assumed some sort of constraint on sequences of actions which is not symmetric under time-reversal; e.g., some sort of causality constraint that privileges the forward direction of time in some way. But by postulating future-rememberers, it seems to me we’ve implicitly chosen to not assume any such constraint.

Kenny: I don’t know if it’s fair to say that none of the various methods we have for exchanging information with future-rememberers involve intentionally saying things to them, but rather all have to be through (chance) observation alone. After all, building off of Lukas and his invocation of Bill and Ted’s Excellent Non-Standard Model of Causation, suppose the following sequence of actions went down:

1. Polly the Past-Rememberer: I’ve suddenly forgotten the capital of Alabama. This is going to bother me all day. Oh, here comes Fred the Future-Rememberer; maybe he knows. I’ll wait for him to give me his reply, and then I’ll ask him the question (the latter being necessary in order to ensure the former).
2. Fred: I think it’s Montgomery.
(Polly happily realizes this is indeed the capital, and dutifully completes the conversational protocol.)
3. Polly: Hey, Fred, do you know what the capital of Alabama is?
4. Polly walks off into the sunset, her mind suddenly at ease…

If the order of these events was 1, 3, 2, 4, they would be an entirely unremarkable everyday conversation, of the sort that involves intentionally saying things to one another to effect an information transfer. As it happens, that is not the chronological order in this story, but is still basically the order of the chain of causality of the events. Event 3 remains the direct cause of event 2, and if Polly hadn’t intentionally asked the question, it’s quite unlikely she would have received her answer (when I forget state capitals, at any rate, chance observation of unsolicited remarks rarely helps me to recall them). So it seems to me like this sort of thing should be called a genuine conversation between past- and future-rememberers, and that various other useful conversational protocols of this sort exist which would transfer information in a manner dependent upon intentionally saying things to each other.

It’s even possible to imagine the common ground evolving over the course of the dialogue, though this is more contrived:
1. Polly only knows the capital of California. Fred knows the capitals of California and Delaware. The common ground is knowledge of Sacramento.
2. Polly says: I know the capital of California is Sacramento.
3. Fred says: I know the capital of Delaware is Dover.
4. Polly knows the capitals of California and Delaware. Fred only knows the capital of California. The common ground is knowledge of Dover.

In this case, the common ground manages to change. However, the fact that the common ground changed wasn’t really useful for the participants, it seems, though both participants did get some use out of the exchange anyway.

31 03 2007

Er, at the end of that, in step 4, I meant of course to say that Fred only knows the capital of Delaware. His bizarre, typo-induced belief at that point in Dover as the simultaneous capital of California could hardly be called _knowledge_…

31 03 2007

Wow, that’s interesting. Really strange things can happen with these people!

2 04 2007
Mike T.

there’s also a character on Lost who “remembers” the future. the details are a bit vague, but as best i can tell he remembers the future because he already lived it (in the standard, past-to-future direction) and then got snapped backwards somehow. but he only remembers it in snippets and flashes, and of course can remember the past in the standard way in addition. so he can have normal conversations. it sounds to me, though, like you’re thinking more about a character who lives backwards through time, in the way that Merlin was sometimes said to.

10 04 2007

I think this marks the very knowledge as what should make computers understand language to understand the users utterance in whatever content as to solve the problem of linguistic between formats of knowledge and their domain. Because its indeed a conversation whichs act on past comments to aply to future one’s or vice-versa whe certainly meet in mistake of our language picture to solve our knowledge about something that whas said before. As treu to remember knowledge about what should fit in our present your NOW to fill in linguistic data to questions or knowlegde at hand. I think there is a point in what meaning truly is for conversations in any sence.

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