TIME is fantas'tic'

Discussion of theories involving time as a dimension, time travel, relativity, branes, and so on, usually applying to the "real" universe which we live in.

TIME is fantas'tic'

Postby Flawless » Tue May 31, 2005 2:03 pm

If dimensions are like pages of notebook paper then time is the notebook.
:shock:
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Postby houserichichi » Tue May 31, 2005 2:33 pm

...and if they're not?
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Postby wendy » Wed Jun 01, 2005 1:23 am

If you draw a graph, with distance as one axis, and time as the other, you get a space-time graph of 1d space + 1d time. You can see where you are at time t to distance d.

In terms of "real time", all you see is distance. just a column.

Time is no more a succession of columns on a graph, or layers of a 2d -> 3d graph.

But to speak of "dimensions" as a page of a notebook misunderstands the metaphore. A notepad page is a metaphor for 2d, and a notebook is a metaphore for a sequence of such pages. The idea of space=time is that we can flick through the pages *as if watching a movie*.

On the other hand, the notebook could represent floor-plans of a skyscraper, and flicking through the pages represent looking at different floors of a building, or slices of a cube.

One has to keep an eye on what the pages "mean".

Space-time as a notebook is like asking someone on page 7 a question, and getting the responce from page 10. It does not happen in our time. That is, a movie exists in its entirity, and does not "unfold" as time does.

What is meant by 4d here is four euclidean dimensions, subject to a passage of time and gravity, not four dimensions including time. We're looking at four dimensions that live in the same time-thread as we do.

The metaphore of space-time as four dimensions as euclidean space leads to a severe misunderstanding of the nature of both euclidean 4-space and that of space-time, since these have -different- geometries. A tesseract in four dimensions is the same as watching slices of a cube as a movie.
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space-time

Postby Flawless » Wed Jun 01, 2005 5:49 am

I like the skyscraper metaphore... i dont know how this fits with your logic but see if we are on the same "page" tee-hee .... the skyscraper is an upside down pyramid and as the floors go up they get bigger so time appears to get slower as we asscend and the floors gets larger but in our 3d reality doesnt change at all ??

"You ask me what i am smiling at .. I ask you if you have a few million minutes to listen"
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Postby wendy » Thu Jun 02, 2005 4:57 am

If you have, for example, (x,y,z) coordinates, then they can mean anything. There is no particular demand that x or y or z is time.

If you have 2d space-time, then x,y is space, and z is time. This is the metaphor of animation-sheets stacked one on an other.

If you have 3d space, then x,y,z are all space. The metaphor of the skyscraper is this, with x,y as the floor-plan, and z as different floors.

A skyscraper is a sequence of floors: it is not a history of one of them.

In four dimensions, the extra dimension (w), is not a history of the xyz space, but rather a separate sequence of these, all existing at the same time.
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