# What do you mean by 'multi-dimensional'?

1. Jan 17, 2010

### upkiran

What do you mean by 'multi-dimensional'?

2. Jan 17, 2010

### tiny-tim

Welcome to PF!

Hi upkiran ! Welcome to PF!

"multi-dimensional" simply means that a space has more than one dimension.

What is the context? Does this come from a particular book?

3. Jan 17, 2010

### upkiran

Re: Multi-dimensional

Hi..

I want to know how do you realise multi dimensions. For example when you say that a tesseract is a 4-D object how do you expain its dimensions. what is the base to constructing a tesseract???

4. Jan 17, 2010

### tiny-tim

hmm … what's a tesseract?

ah … one of those … http://en.wikipedia.org/wiki/Tesseract" [Broken].

ok … you can "draw" a 3D version of a tesseract (eg the http://en.wikipedia.org/wiki/File:Schlegel_wireframe_8-cell.png" [Broken])

but like a 2D copy of a cube, you lose some information.

In a 2D copy of a cube, some of the lines intersect (in 3D they don't), and the angles between the faces aren't 90º.

Similarly, in a 3D version of a tesseract, some of the faces intersect (in 4D they don't), and some of the angles aren't 90º.

Four dimensions are the minimum necessary to have all the angles 90º, and to have none of the faces or "hyperfaces" intersecting where they shouldn't.

Last edited by a moderator: May 4, 2017
5. Jan 17, 2010

### Chronos

Re: Multi-dimensional

In spacetime you need 4 dimensions to define a position - 3 spatial and one of time. Extra dimensions, mainly spacial, are posited by string theory. The need for these extra dimensions is controversial and no observational evidence for their existence has yet emerged.

6. Jan 18, 2010

### upkiran

Re: Multi-dimensional

Hi...

Ok now lets go a step further... Consider an object said to have more than 4 dimensions... If space and time constitute four of these dimensions how would you describe the remaining dimensions???

7. Jan 18, 2010

### tiny-tim

You just call them "extra dimensions".

(you can give them names if you like … but "what's in a name?" )

8. Jan 18, 2010

### upkiran

Re: Multi-dimensional

The name is not important...

I was talking about its existance or characteristics... i mean any dimension other than "THE FOUR" are said to be of the order of planck length, right.. If so cant those dimensions be explained using only the x,y,z and t coordinates???

9. Jan 18, 2010

### tiny-tim

No, they have nothing to do with the x,y,z and t dimensions.

(just like t has nothing to do with the x,y and z dimensions )