"One of your very early philosophers came to the conclusion that a fully competent mind, from a study of one fact or artifact belonging to any given universe, could construct or visualize that universe, from the instant of its creation to its ultimate end..."
"If any one of you will concentrate upon one single fact, or small object, such as a pebble or the seed of a plant or other creature, for as short a period of time as one hundred of your years, you will begin to perceive its truth."
I am reasonably sure that a single pebble, taken from a beach of our own Earth, does not specify the continents and countries, politics and people of this Earth. Other planets in space and time, other Everett branches, would generate the same pebble. On the other hand, the identity of a single pebble would seem to include our laws of physics. In that sense the entirety of our Universe—all the Everett branches—would be implied by the pebble. (If, as seems likely, there are no truly free variables.)
So a single pebble probably does not imply our whole Earth. But a single pebble implies a very great deal. From the study of that single pebble you could see the laws of physics and all they imply. Thinking about those laws of physics, you can see that planets will form, and you can guess that the pebble came from such a planet. The internal crystals and molecular formations of the pebble formed under gravity, which tells you something about the planet's mass; the mix of elements in the pebble tells you something about the planet's formation.
I am not a geologist, so I don't know to which mysteries geologists are privy. But I find it very easy to imagine showing a geologist a pebble, and saying, "This pebble came from a beach at Half Moon Bay", and the geologist immediately says, "I'm confused" or even "You liar". Maybe it's the wrong kind of rock, or the pebble isn't worn enough to be from a beach—I don't know pebbles well enough to guess the linkages and signatures by which I might be caught, which is the point.
"Only God can tell a truly plausible lie." I wonder if there was ever a religion that developed this as a proverb? I would (falsifiably) guess not: it's a rationalist sentiment, even if you cast it in theological metaphor. Saying "everything is interconnected to everything else, because God made the whole world and sustains it" may generate some nice warm n' fuzzy feelings during the sermon, but it doesn't get you very far when it comes to assigning pebbles to beaches.
A penny on Earth exerts a gravitational acceleration on the Moon of around 4.5 * 10-31 m/s2, so in one sense it's not too far wrong to say that every event is entangled with its whole past light cone. And since inferences can propagate backward and forward through causal networks, epistemic entanglements can easily cross the borders of light cones. But I wouldn't want to be the forensic astronomer who had to look at the Moon and figure out whether the penny landed heads or tails—the influence is far less than quantum uncertainty and thermal noise.
If you said "Everything is entangled with something else" or "Everything is inferentially entangled and some entanglements are much stronger than others", you might be really wise instead of just Deeply Wise.
Physically, each event is in some sense the sum of its whole past light cone, without borders or boundaries. But the list of noticeable entanglements is much shorter, and it gives you something like a network. This high-level regularity is what I refer to when I talk about the Great Web of Causality.
I use these Capitalized Letters somewhat tongue-in-cheek, perhaps; but if anything at all is worth Capitalized Letters, surely the Great Web of Causality makes the list.
"Oh what a tangled web we weave, when first we practise to deceive," said Sir Walter Scott. Not all lies spin out of control—we don't live in so righteous a universe. But it does occasionally happen, that someone lies about a fact, and then has to lie about an entangled fact, and then another fact entangled with that one:
"Where were you?"
"Oh, I was on a business trip."
"What was the business trip about?"
"I can't tell you that; it's proprietary negotiations with a major client."
"Oh—they're letting you in on those? Good news! I should call your boss to thank him for adding you."
"Sorry—he's not in the office right now..."
Human beings, who are not gods, often fail to imagine all the facts they would need to distort to tell a truly plausible lie. "God made me pregnant" sounded a tad more likely in the old days before our models of the world contained (quotations of) Y chromosomes. Many similar lies, today, may blow up when genetic testing becomes more common. Rapists have been convicted, and false accusers exposed, years later, based on evidence they didn't realize they could leave. A student of evolutionary biology can see the design signature of natural selection on every wolf that chases a rabbit; and every rabbit that runs away; and every bee that stings instead of broadcasting a polite warning—but the deceptions of creationists sound plausible to them, I'm sure.
Not all lies are uncovered, not all liars are punished; we don't live in that righteous a universe. But not all lies are as safe as their liars believe. How many sins would become known to a Bayesian superintelligence, I wonder, if it did a (non-destructive?) nanotechnological scan of the Earth? At minimum, all the lies of which any evidence still exists in any brain. Some such lies may become known sooner than that, if the neuroscientists ever succeed in building a really good lie detector via neuroimaging. Paul Ekman (a pioneer in the study of tiny facial muscle movements) could probably read off a sizeable fraction of the world's lies right now, given a chance.
Not all lies are uncovered, not all liars are punished. But the Great Web is very commonly underestimated. Just the knowledge that humans have already accumulated would take many human lifetimes to learn. Anyone who thinks that a non-God can tell a perfect lie, risk-free, is underestimating the tangledness of the Great Web.
Is honesty the best policy? I don't know if I'd go that far: Even on my ethics, it's sometimes okay to shut up. But compared to outright lies, either honesty or silence involves less exposure to recursively propagating risks you don't know you're taking.