# Understanding fractional and higher dimensions

1. Aug 16, 2015

### PcumP_Ravenclaw

Halo,
I was reading about geometry from Tim Gowers book titled "A very brief introduction to mathematics". I came across fractional dimensions and the 4th dimension. The koch snowflake has dimension 1.2 yet he could comfortably drawn it on a 2d page (or is it complete?). Has not he just transformed the original "snowflake", scaled it, translated it, etc.. what does it have to do with dimensions? maybe, its like drawing a 3d structure on a 2d page? so this snowflake is not how it actually appears in the 1.2 dimension as drawn on 2d page? This just a extrapolation of the formulas in 1d, 2d & 3d? How do we prove such domensions exist in reality, if at all? So a 4d cube as being a cube inside a bigger cube is also for sake of visualization, like drawing a 3d cube on a 2d page?

Danke.

2. Aug 16, 2015

### Staff: Mentor

Fractional dimensions come out of the notion of measuring a coast line the length depends on how close you are.

and this on fractal dimensions:

https://en.wikipedia.org/wiki/Fractal_dimension

You could compare it to how integers were extended into rational number and then rational into real with the notion of irrational...

And so Mandelbrot extended the notion of dimension into a fractal (aka fractional) dimension.

3. Aug 17, 2015

### Staff: Mentor

A line segment has dimension one. A rectangle has dimension two, but its perimeter is one-dimensional. The Koch snowflake, in contrast, is so intricate that its perimeter is unbounded, even though it has a finite area. For that reason, it is considered to be one of several kinds of space-filling curves. Another space-filling curve is the Sierpinski triangle.

4. Aug 17, 2015

### micromass

Staff Emeritus
These are certainly not space-filling curves in the classical sense.

5. Aug 17, 2015

### Staff: Mentor

You're right - I misspoke. If they were truly space-filling, their dimension wouldn't be less than 2.

6. Aug 18, 2015

### PcumP_Ravenclaw

wha
what is a space-filling curve?

7. Aug 18, 2015

### Staff: Mentor

8. Aug 18, 2015

### micromass

Staff Emeritus
Since the curve has infinite length, I doubt that.

9. Aug 18, 2015

### micromass

Staff Emeritus
This is interesting though. Continuous functions are often introduced as "those curves that can be drawn without picking up the pencil." But I think this is not the right motivation for continuity. The curves that can be drawn without picking up the pencil are (according to me) rather the continuous functions of bounded variation. Those seem like a much better contender.

10. Aug 18, 2015

### Staff: Mentor

Micro, we have all the time in the world... :-)

11. Aug 18, 2015

### HallsofIvy

Staff Emeritus
ii
What do you mean by "reality"? This is, after all, mathematics, not physics.

Basically, yes. They are representations of a higher dimensional object in two dimensions.

Last edited by a moderator: Aug 18, 2015
12. Aug 18, 2015

### PcumP_Ravenclaw

13. Aug 18, 2015

### Staff: Mentor

No. There is no "original snowflake." There is no scaling or translation going on. Creating the Koch snowflake is an iterative process, that starts with an equilateral triangle. Let's say the triangle has sides of length 1. In the first step, each of the three sides is divided into thirds. The middle segment is deleted, and two segments whose length is equal to the deleted segment are attached to the gap formed by deleting the middle third.

Graphically, we're going from ___ to _/\_ for each side. This same process is applied to the other two sides of the original equilateral triangle. In this first step, the perimeter increased from 3 to 4. (We removed a segment of length 1/3 from each of the three sides, but added two segments of length 1/3 to each side, so each side increased from 1 to 4/3 units.) Also, in this step, the triangle went from three sides to a polygon made up of 12 segments.

In the next step, each of the 12 segments has its middle third removed, and replaced by two more segments, in the same way as described above. This is much easier to show graphically than to explain in words.

14. Aug 18, 2015