# The 4th Dimension.

1. Feb 22, 2008

### _Mayday_

Hello, I am in the process of reading Black Holes, Wormholes & Time Machines and am somewhat confused, even though it is aimed at people like myself who have very little knowledge on the subject. I am reading about the 4th dimension now but I do not understand the relevance of researching into the 4th dimension or giving it alot of thought. Jim Al-Khalilie, the author, has explained the fourth dimension as like being in a hollow sphere, and the fourth dimension would allow you to exit the sphere without getting any closer to any of the edges. What does knowing there is a fourth or second dimension universe mean? Is it just out of human curiosity or does it explain or help explain some theories. I'm really stuck here :yuck: I am very interested in this subject, so do not think that I am saying it is useless because I have no idea really :tongue:

_Mayday_

If this is in the wrong part of the site please let me know so I don't do it again...

2. Feb 24, 2008

### mhill

A great example is the film "Time Machine" .. the time traveler is trapped inside a rock so he can not move but going forward on time (moving on the fourth dimension) he moves to a place where the rock has disappeared.

Real physics in 4-D implies no motion , perhaps 4 dimension exists or is just a physical artifact to describe nature, if we could 'see' in 4 dimension i believe that the mistery of QM and Relativity could be solved.

3. Feb 24, 2008

### robphy

Note that a position-vs-time graph is a 4-dimensional "[mathematical] space".
In introductory physics, one often simplifies the discussion and considers only one-dimensional spatial motion (say, along a line)... which yields a position-vs-time graph that is 2-dimensional.

4. Feb 24, 2008

### HallsofIvy

Staff Emeritus
Are you clear on what "dimension" means? A dimension is just a number specifying a specific thing. To designate a specific point in space requires 3 numbers no matter what coordinate system you use- it is "three dimensional". Physicists study "events": things that happen at a specific place at a specific time. We require three numbers to specify the position in space and a fourth to designate the time. That is what Einstein meant when he said "Our universe is a four-dimensional space-time continuum.

It appears that the text you are referring to is talking about a possible 4th "space" dimension- that would be somewhat speculative. There are a number of theories that involve higher space dimensions but none of them have been shown to be experimentally "correct" (there isn't any question about a "second dimension"!).

The analogy with the hollow sphere is this- Suppose there existed a being that lived only in two dimesions- that could move about on a sheet of paper, that could move "up or down" or "left or right" but knew nothing about "vertical" direction. A circle containing that being would be a prison it could not get out of. But if the creature could move vertically, it would could move outside the circle. Similarly, if there were a fourth space dimension, a three dimensional person could move out of a hollow sphere.

5. Feb 24, 2008

### Fredrik

Staff Emeritus
That wouldn't actually work if the rock is just moved rather than broken up into pieces. And that movie sucked.

6. Feb 24, 2008

### _Mayday_

Thank you, that has certainly cleared things up.