CS 39R:  Symmetry & Topology
Lecture #13 -- Mon. 11/27, 2017.


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Warm-up:

Compare your own findings with this solution sheet:
wallpaper
      symmetries

Wallpaper Symmetries

How to find the elements of Wallpaper Symmetries ?  -- any questions?

4 Project Presentations:


 https://www.youtube.com/watch?v=lT2oeNkTOAk
 https://docs.google.com/presentation/d/1m9US2ACq44z2gkkQ2dgJvEAWhwy8Gsai0yctVCXqfj0

I have placed your Presentation Slides into the directory "ProjectPresentations"
If you would like to share yours, please send them to me.

Final Assignments:
-- For next class, prepare an "Elevator Speech" (60-90 seconds).

-- By December 11, write a Project Report (2-4 pages; use some figures from your slides).

Your Questions about the 4th Dimension:

Is there a practical application for the regular 4D polytopes?
I have not been able to think of one ...
Check the web for possible responses, e.g.,:  Applications of Higher Dimension Formulas
The regular 4D polytopes are a piece of pure mathematics.
Often it takes several decades before a new insight in mathematics is used in some other discipline.

Another example of questionable usefulness:

Earlier in 2017 there was news of  “The largest known prime number:  2^74,207,281 - 1“

This number is  22,338,610 digits long.

It is estimated that there are about 10^17,425,163  prime numbers less then the next smaller known prime.

That means we know only a fraction of about 10^-14 of all the prime numbers in this neighborhood.


Is this knowledge useful?   Is mathematics useful? 

But mathematics can be beautiful!

By strict logical reasoning one can derive new mathematical insights
that are irrefutable and not subject to later change.

By analogy from 1-, 2-, and 3-dimensional spaces, we can derive 4- and higher-dimensional spaces.
And then we can show unambiguously that in 4D-space there are exactly six totally regular polytopes.

No science or religion has this kind of internal consistency and permanence.

 

All fields have some

Threshold Concepts

These are concepts that integrate prior understanding and transform it to a higher perspective. 
They produce irreversible “AHA!” effects.  Examples from mathematics:
-    Notion of a function, say, z = func(x, y)
-    Limits:  Sum of 1 + ½ +1/4 + 1/8 + …
-    Euclid’s parallel lines  (no such things exist!  Even a light beam bends in the presence of gravity).
-    Concept of infinity
(Nothing we know is truly infinite).   
-    The infinite plane.
-    The projective plane  and understanding what happens when one goes through infinity.
-    Euclidean spaces of  higher dimensions.
-    An unambiguous way of identifying and classifying symmetries.

Hopefully, by exposing you to some such threshold concepts,
this will broaden your thinking and expand the style in which you may think.



Going beyond the 4th dDimension !!

Regular Polytopes in Four and Higher Dimensions  (remainder)

If you are brave enough, look at: "A 10-Dimensional JewelPPT


Homework Assignments:  Due: Dec. 4, 2017.

Prepare Your  "90-seconds Elevator Speech".

Please take the Course Evaluation survey.
Work on your final Project Reports:  Due Dec. 11, 2017.



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