distant planets

[Iron Greasel]

I still don't understand how matter bends space. I would make sense if all the matter in what we call the universe was just parts of four-dimensional matter like in the classic rubber sheet example. But most people I've seen appear to think that they are three-dimensional. Also, if matter also bends time it would have to be at least 5-dimensional. electomagnetic waves could be n-dimensional particles that only have a small part of them lodged in our set of dimensions.

Time being a fourth dimension makes sense, in a way. Only thing I don't understand is why and how are we moving in it? I would more eagerly believe that the time is not a dimension, and things just change without moving anywhere.

[shamrock_uk]

Don't think of them as being separate things and its less of a headache.

According to the theory of relativity, space and time are not separate things but instead different parts of a four-dimensional continuum. The space-time continuum is the theory that space and time are interconnected. Space is three-dimensional, and time is one-dimensional, so together they make up the four-dimensional space-time. Space-time is a continuum because, as far as we know, there are no missing points in space or moments in time. It's hard to picture a four-dimensional continuum since our universe is three dimensional, but you can still know how it works. Think of it as a three-dimensional coordinate system (x,y,z), with one more coordinate for time.

and

The space-time continuum is the theory that space and time are interconnected. Space is three-dimensional, and time is one-dimensional, so together they make up the four-dimensional space-time. Space-time is a continuum because, as far as we know, t here are no missing points in space or moments in time. Explaining how spacetime works is extremely long and complicated. An excellent book to read, full of examples and illustrations, is Lewis Carroll Epstein's Relativity Visualized.

both from here.

And just to confuse you even more, these guys also want a 5d version of things.

I think your way of thinking about being sat still and things changing it also fine - that's probably how I look at it. Maybe light cones aren't a bad way to illustrate it?

[Vaskez]

Originally posted by Iron Greasel: Time being a fourth dimension makes sense, in a way. Only thing I don't understand is why and how are we moving in it? I would more eagerly believe that the time is not a dimension, and things just change without moving anywhere.

I also said "moving in it" as an analogy. Whether you like it or not you are changing with time. Think of it as moving along a time-line as time goes on - that's how you're moving in the time dimension. Like I said, I like to think of a dimension as just an axis along with which entities change. Just like you are different at different points on the x,y and z axis, you are different at different points in the time axis. Not the most accurate description but I think it's a useful analogy.

[Thoran]

IMO time is definitely a dimension... it's just one with unique properties. Humans even use it as a proxy for a physical dimension on a regular basis.

Take a cat scan of a human brain for instance. It's a 3 dimensional object projected onto a 2 dimensional medium (your pc screen). Since the screen is 2d there is NO way it can fully represent a 3d object UNLESS you use time as a proxy for the third physical dimension. You use your mouse wheel to scroll backward and forward through slices of the cat scan and your brain internally reproduces a 3d representation from the 2d + time image.

As far as n-dimensional space/parallel universe and all that stuff... we've got a LOT to learn, and that's moving into the wildly theoretical realm. It may have value and it may be bunk, but I have no doubt there are stranger things waiting to be discovered than we can imagine.

[Iron Greasel]

Time is not necessarily a dimension. If it is, then all moments, past and future, can be found from it if we look at it from a fifth dimension. If it isn't, there is no past and future. Only present.

Imagine and elevator with windows moving down. If you look out throuh the windows you see the walls of the shaft moving up. But you can't possibly know whether you are moving down through the elevator shaft or there is no shaft and the walls moving upward are just an illusion created with a few pulleys and a photo of the wall on a bedsheet.

Does that make any sense at all?

[shamrock_uk]

Originally posted by Iron Greasel: If it is, then all moments, past and future, can be found from it if we look at it from a fifth dimension.

I think Hawking said exactly this actually in one of his books.

[Vaskez]

Busted!

[shamrock_uk]

Hey, he could be wrong [img]smile.gif[/img] He was wrong about black holes, why not this?

[Vaskez]

Why, what did he say about black holes that was wrong?

[Hivetyrant]

Originally posted by Vaskez: Why, what did he say about black holes that was wrong?

I agree, what did he say that was wrong?