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"'There is no difference between Time and any of the three dimensions of Space except that our consciousness moves along it,' says the Traveller. That turned ou

"'There is no difference between Time and any of the three dimensions of Space except that our consciousness moves along it,' says the Traveller. That turned out, amazingly and counterintuitively, to be true. 'In surprisingly short order this notion would become part of the orthodoxy of theoretical physics,' says Gleick." What? Spacetime does contain four dimensions, but the whole reason that time travel is fiction, rather than fact, is because the time dimension is different from the space dimensions.

Razengan 10y ago
I wonder. If the universe is deterministic, and nothing is random, then Time could be thought of as a vector whose values encompass all the properties of everything in existence and the direction of changes in each of them. If we knew all the "rules" that govern those changes and could make a simulation that captured the current state of everything, we could traverse back and forth along that vector (but probably not beyond the instant when that simulation was turned on, because then it would have to simulate itself...)
- scardine 10y ago
  We can calculate things like if the moon is ever going to leave Earth's orbit and we can tell it was much closer to Earth in prehistoric times. We can predict the future and recall the past, just not in a scale that is practical for our mundane lives. Personally, I think this is a humility lesson: in the grand scheme of things, the entire span of a human life is less than a tiny drop in the ocean of time.
- baytrailcat 10y ago
  This was a prevalent idea in physics till quantum mechanics burst into the scene. I don't remember where I saw it, this the most convincing argument I heard regarding simulating future: Our universe is actually the most efficient computer that can simulate the future with our physical laws. Meaning, at any given time, it is not actually executing a pre-determined program, it is busy computing the future.
  - codethief 10y ago
    You don't really need quantum mechanics for this argument, though. Even in a non-quantum world, non-linear and, in particular, chaotic systems effectively prevent you from predicting the future. While you could do it in theory, in practice you would need do know every single variable very precisely because the outcome of chaotic systems can change drastically due to a small change in initial conditions (which is colloquially known as the butterfly effect). Quantum mechanics just makes this even harder or downright impossible (think of determining the exact values of the wave function or predicting the outcome of measurements). But even if we did know all the variables, we'd then still need to simulate every single atom to predict the future, so we'd basically be building another universe. So, you're right, in that sense the universe is the most efficient computer simulating our physical reality.
jacobolus 10y ago
You’re right that “There is no difference between Time and any of the three dimensions of Space [...]” is kind of misleading, but it’s only half wrong. The special relativity story is more nuanced. There’s no single “time direction”. Which direction in spacetime looks like “time” vs. a mix of “space” and “time” movements vs. “space” depends on your reference frame. Every “faster-than-light velocity vector” can be considered the direction of “time” for some observer, just as every “slower-than-light velocity vector” can be considered a direction in “space” for some observer. A vector like “the vector difference between the position of the earth now and the moon half a second in the future” (by our measurement) is, for some other reference frame, a pure movement in time. In just the same way, “the vector difference between the position of the earth now and the moon two seconds in the future” is a pure distance in space indicating simultaneous-in-time events, for some other reference frame. Or perhaps we should even say that the “reference frames” and a split between space and time dimensions are an abstract concept that we impose on top of the 4-dimensional spacetime. We can work out all of our physics in a 4-dimensional context without explicitly splitting “space” from “time”. https://en.wikipedia.org/wiki/Spacetime_algebra#Spacetime_split https://en.wikipedia.org/wiki/Spacetime_algebra#Spacetime_sp... In just the same way, if you have a two-dimensional Euclidean plane with no externally imposed markers on it, there’s no inherent notion of “up” or “left” – those depend entirely on what kind of reference you pick. Imposing some specific coordinates is sometimes useful for understanding the geometry and solving particular problems, but itÍ’s in some ways arbitrary.
- charlieflowers 10y ago
  Reminds me of the final book in the Hitchhiker's Guide "trilogy". The advanced version of the Guide is calibrating itself so it can perform "reverse temporal engineering" on behalf of Ford. It asks a series of questions, one of which makes no sense, and then says something like, "Oh, time travels in that direction for you."

Razengan 10y ago

I wonder. If the universe is deterministic, and nothing is random, then Time could be thought of as a vector whose values encompass all the properties of everything in existence and the direction of changes in each of them. If we knew all the "rules" that govern those changes and could make a simulation that captured the current state of everything, we could traverse back and forth along that vector (but probably not beyond the instant when that simulation was turned on, because then it would have to simulate itself...)

scardine 10y ago
We can calculate things like if the moon is ever going to leave Earth's orbit and we can tell it was much closer to Earth in prehistoric times. We can predict the future and recall the past, just not in a scale that is practical for our mundane lives. Personally, I think this is a humility lesson: in the grand scheme of things, the entire span of a human life is less than a tiny drop in the ocean of time.
baytrailcat 10y ago
This was a prevalent idea in physics till quantum mechanics burst into the scene. I don't remember where I saw it, this the most convincing argument I heard regarding simulating future: Our universe is actually the most efficient computer that can simulate the future with our physical laws. Meaning, at any given time, it is not actually executing a pre-determined program, it is busy computing the future.
- codethief 10y ago
  You don't really need quantum mechanics for this argument, though. Even in a non-quantum world, non-linear and, in particular, chaotic systems effectively prevent you from predicting the future. While you could do it in theory, in practice you would need do know every single variable very precisely because the outcome of chaotic systems can change drastically due to a small change in initial conditions (which is colloquially known as the butterfly effect). Quantum mechanics just makes this even harder or downright impossible (think of determining the exact values of the wave function or predicting the outcome of measurements). But even if we did know all the variables, we'd then still need to simulate every single atom to predict the future, so we'd basically be building another universe. So, you're right, in that sense the universe is the most efficient computer simulating our physical reality.

jacobolus 10y ago

You’re right that “There is no difference between Time and any of the three dimensions of Space [...]” is kind of misleading, but it’s only half wrong. The special relativity story is more nuanced. There’s no single “time direction”. Which direction in spacetime looks like “time” vs. a mix of “space” and “time” movements vs. “space” depends on your reference frame. Every “faster-than-light velocity vector” can be considered the direction of “time” for some observer, just as every “slower-than-light velocity vector” can be considered a direction in “space” for some observer. A vector like “the vector difference between the position of the earth now and the moon half a second in the future” (by our measurement) is, for some other reference frame, a pure movement in time. In just the same way, “the vector difference between the position of the earth now and the moon two seconds in the future” is a pure distance in space indicating simultaneous-in-time events, for some other reference frame. Or perhaps we should even say that the “reference frames” and a split between space and time dimensions are an abstract concept that we impose on top of the 4-dimensional spacetime. We can work out all of our physics in a 4-dimensional context without explicitly splitting “space” from “time”. https://en.wikipedia.org/wiki/Spacetime_algebra#Spacetime_split https://en.wikipedia.org/wiki/Spacetime_algebra#Spacetime_sp... In just the same way, if you have a two-dimensional Euclidean plane with no externally imposed markers on it, there’s no inherent notion of “up” or “left” – those depend entirely on what kind of reference you pick. Imposing some specific coordinates is sometimes useful for understanding the geometry and solving particular problems, but itÍ’s in some ways arbitrary.

charlieflowers 10y ago
Reminds me of the final book in the Hitchhiker's Guide "trilogy". The advanced version of the Guide is calibrating itself so it can perform "reverse temporal engineering" on behalf of Ford. It asks a series of questions, one of which makes no sense, and then says something like, "Oh, time travels in that direction for you."