MDMD(1): Forbidden Symmetries

[jporter]

>>While fivefold symmetry is naturally "forbidden" in crystal formation, as
>>Penrose points out, certain quasicrystalline structures, have been
>>discovered  which are based on fivefold symmetry. Penrose states: "...a
>>remarkable feature of the quasicyrstalline tiling patterns...is that their
>>assembly is necessarily *non-local*" Meaning that there has to be some way
>>in which the evolving pattern (which is aperiodic!) is "known" many atoms
>>ahead of where the structure has already formed.
>
>Actually, Penrose is flat out wrong, although a way of doing so was not
>known at the time.
>--
>-Matthew P Wiener (weemba at sagi.wistar.upenn.edu)


Yes, he may have been wrong about the non-local process, etc., but he
admitted at the time that he was speculating, and not at all sure, so I
don't think your characterization of him being "flat out wrong" is
appropriate.

More importantly to my post, however, he was (and is) flat out right
concerning the forbidden nature of five-fold symmetry regarding
crystallization.

jody