The Time-Cone Points Both Ways

(I actually wrote this up weeks ago, but never got around to posting it. A recent discussion on jducouer's LJ reminded me of it, so I'm digging it out now.)

Many of you are familiar with the Many Worlds Hypothesis. It's the idea that, in order to explain quantum indeterminacy, you assume that every possible outcome *does* happen - in some universe or other. Looking forward in time from the present moment, reality looks like a branching tree. Or, as Borges put it, a Garden of Forking Paths.

Why has no one tried looking the other direction? Just as the present moment may *lead* to a large number of possible futures, it may also have *originated* from a large number of possible pasts. The further into the past you look, the more uncertain you become about what it actually was.

Is this meaningfully true on a macroscopic (non-quantum) scale? Idunno. But it can at least provide an interesting metaphor. The Uncertainty Principle ("You cannot measure something without affecting it") isn't really true at the human scale, but it's a useful way of talking about certain situations.

For instance, gyzki recently quoted a discussion between two Soviet 'experts' about the Cuban Missile Crisis, which had the two of them in complete disagreement about whether there had actually been warheads in Cuba. Such a discussion could have been the result of a past in which there were warheads -- or a past in which there weren't. I don't have enough information to judge. It is even possible that that information no longer exists -- that that portion of the past has become indeterminate. I think it unlikely for something that recent, but not impossible.

This idea has been floating around my head for years now. One of the frequent thought experiments is tangentially related to the Cuban Missile Crisis: the assassination of JFK. There are dozens of different theories about it. Which is true? Are any of them definitively so? It seems likely to me that such a big event, within living memory, probably does have a reasonably singular truth behind it, which should in theory be discoverable.

But what happens when you go further back? What were the real circumstances around the death of Abraham Lincoln? Or Richard the Lionheart? Or Julius Caesar? Or Alexander the Great? How far back in time must one go before the circumstances around an important event become totally fluid?

Let's try another axis of investigation. Staying within 'living memory', but altering the scale of the events under consideration. Instead of the death of world leaders, let's consider entirely trivial events. What did I have for breakfast on this date 25 years ago? I don't know. I could make some guesses based on half-remembered habits, but could not answer with any confidence. I could have come to this point in my life from a past where I had a sandwich, or a past where I heated up some leftovers, or a past where I had some Spaghetti-Os, or any number of other possibilities. That breakfast wasn't important to my life. Having not stuck in my memory, or any obvious physical record, it remains uncertain.

Things may also become uncertain due to distance in space. The entire life of a typical Chinese peasant who was born in the same year I was probably had no noticable effect on my past. He may have died young, or lived to a ripe old age, stayed poor, or become prosperous.

This is not exactly solipsism, though it might be mistaken for it. It's the idea that those parts of reality which had no lasting impact on me remain, relative to me, undecided.

The Time-Cone Points Both Ways

(I actually wrote this up weeks ago, but never got around to posting it. A recent discussion on jducouer's LJ reminded me of it, so I'm digging it out now.)

Many of you are familiar with the Many Worlds Hypothesis. It's the idea that, in order to explain quantum indeterminacy, you assume that every possible outcome *does* happen - in some universe or other. Looking forward in time from the present moment, reality looks like a branching tree. Or, as Borges put it, a Garden of Forking Paths.

Why has no one tried looking the other direction? Just as the present moment may *lead* to a large number of possible futures, it may also have *originated* from a large number of possible pasts. The further into the past you look, the more uncertain you become about what it actually was.

Is this meaningfully true on a macroscopic (non-quantum) scale? Idunno. But it can at least provide an interesting metaphor. The Uncertainty Principle ("You cannot measure something without affecting it") isn't really true at the human scale, but it's a useful way of talking about certain situations.

For instance, gyzki recently quoted a discussion between two Soviet 'experts' about the Cuban Missile Crisis, which had the two of them in complete disagreement about whether there had actually been warheads in Cuba. Such a discussion could have been the result of a past in which there were warheads -- or a past in which there weren't. I don't have enough information to judge. It is even possible that that information no longer exists -- that that portion of the past has become indeterminate. I think it unlikely for something that recent, but not impossible.

This idea has been floating around my head for years now. One of the frequent thought experiments is tangentially related to the Cuban Missile Crisis: the assassination of JFK. There are dozens of different theories about it. Which is true? Are any of them definitively so? It seems likely to me that such a big event, within living memory, probably does have a reasonably singular truth behind it, which should in theory be discoverable.

But what happens when you go further back? What were the real circumstances around the death of Abraham Lincoln? Or Richard the Lionheart? Or Julius Caesar? Or Alexander the Great? How far back in time must one go before the circumstances around an important event become totally fluid?

Let's try another axis of investigation. Staying within 'living memory', but altering the scale of the events under consideration. Instead of the death of world leaders, let's consider entirely trivial events. What did I have for breakfast on this date 25 years ago? I don't know. I could make some guesses based on half-remembered habits, but could not answer with any confidence. I could have come to this point in my life from a past where I had a sandwich, or a past where I heated up some leftovers, or a past where I had some Spaghetti-Os, or any number of other possibilities. That breakfast wasn't important to my life. Having not stuck in my memory, or any obvious physical record, it remains uncertain.

Things may also become uncertain due to distance in space. The entire life of a typical Chinese peasant who was born in the same year I was probably had no noticable effect on my past. He may have died young, or lived to a ripe old age, stayed poor, or become prosperous.

This is not exactly solipsism, though it might be mistaken for it. It's the idea that those parts of reality which had no lasting impact on me remain, relative to me, undecided.