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Permalink Reply by Jason Dick on November 3, 2010 at 1:51pm

This picture is difficult to quantify. The problem is that there is no "super time". There is only the dimension of time that we observe (other observers see the same dimension of time, just shifted depending upon their position/motion).

But in a mathematical sense, the entirety of the universe can be described with a single 4-dimensional manifold that just exists. Different observers see different slices of this manifold at any given time, as they perceive time. But the whole thing is just there.

So a somewhat better analogy for the universe is sort of a pre-existing configuration, with our perceptions of it sort of traveling forward. I say sort of because there is actually no traveling (no super time), it's just that at any given point, due to thermodynamics, we remember the past but not the future. The future exists in the same way the past exists, but our perceptions only give us direct access to the past due to thermodynamics.

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Permalink Reply by Jason Dick on November 3, 2010 at 2:59pm

That view isn't consistent with the fact that different observers observe different "nows".

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Permalink Reply by Radu Andreiu on November 3, 2010 at 2:39pm

That's somewhat my view on it too. "Looking" from outside the space-time, everything just is and doesn't happen or unfold before your eyes. In that situation, we would see the whole dimension of time. As an analogy, if we were a point and could only move in one direction (the positive one, as it may be logical) and we could only experience the point in space where we are in a given moment, then we would experience an unfolding line before our zero-dimensional "feet". But if we were to walk outside of that line, we could easily see every point on it, including those we haven't yet stepped on. But not only the line would be one dimensional, not zero as we've experienced our world before, it could be a line that is bent in such a way that it lies in a 2D plane or even a 3D space. That's how we could have higher dimensions and not know about it. Going back to time, I think that we are only in one point of the line that represents the flow of time. Regardless of this, the line, having all the points (infinite in number, unless it's just a segment), would exist, even if we are discovering it point by point. Going all the way with this analogy, this line could be bent in such a way that it rest on an N-dimensional space, which is mathematically possible. The time line could be part of a very complex N-dimensional space in which we are only experiencing one point in a sequential order.

But, in the end, I admit it's pretty hard to think about time as a whole dimension, that exists, not unfolds. As I've heard, mathematically speaking, space and time are really similar and work basically the same. I think I've heard some high-rated physicists that they even switch places inside the event horizon of a black whole.

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Permalink Reply by David Perry on November 3, 2010 at 2:10pm

Think of it in terms of location. Say if you were in China and I was in NY. To describe each other's location we might trace an imaginary line between each other. A set of 2-dimensional co-ordinates. If as observer on the moon were to describe it without(for the sake of argument)the planet in the way as if we were in space, he would need a third dimension of spatial co-ordinates to place us in space relative to him. This is the fun part: neither of those observations take "time" into account, the fourth spatial dimension(which is the part we simply cannot perceive as a dimension, and is the part I almost give up at). At a mere quarter million miles it isn't a factor in a perceptible way, but at thousands or millions of light years, it's quite significant.
It's kind of impossible to experience time as a dimension in the same way we perceive up and down, and almost impossible to accept practically.
Now they claim there are even more dimensions. The latest I think is 11 where the math starts working better. Don't ask me, I'm just recalling what I read in one of Brian Greene's books, he's a little better at trying to explain this for non-physicists than Hawking is.
Richard Feynman said he never completely understood General Relativity. He might have just said that to make us ordinary mortals feel better. Worked for me.

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Permalink Reply by Radu Andreiu on November 3, 2010 at 2:28am

"If you can find someone that can explain it without the math, let me in on it."

Kind of hard to do that. In physics, things have long started to not make sense except in mathematical form. Maybe a kind of visual explanation might help, but it's still hard. That's because, for things to make sense for us, we need to use analogies and that's a bit difficult when we're talking about things that happen on scales beyond our imagination.

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