Wednesday, July 27, 2016

RIPE: Reconstructing Reality and Material Structure

In Plato’s allegory of the cave, he imagines chained prisoners facing a blank wall. A raging fire burns far in the background, behind their backs. The prisoners watch shadows cast by objects passing in front of the fire on the wall ahead of them. They form ideas about the true nature of the objects, from these shadows.

One can only guess the true nature of the objects from these shadows. The 2D shadows that 3D objects cast, project some information, and conceal the rest.

For example, a sphere and a cylinder can both cast a circular shadow.

Perspective is everything (google giraffe or elephant illusion if video below doesn't work).

This problem bedevils characterization of materials as well. A particular measurement or test (chromatography, rheology, thermal tests, scattering, microscopy etc.) gives us but one look at an unknown sample.

If we have a fairly good idea of what the material might be, to begin with, then perhaps this is enough.

More often than not, especially with new materials, each new test narrows the scope of the possible.

The fable of the six blind men and the elephant (which is perhaps a more pedestrian retelling of the Plato's allegory) provides a potential path out. In the story six blind men touch different parts of an elephant and form radically different notions of what an elephant is.

The only way (for the blind men) to come up with a more realistic notion of what an elephant looks like is to find ways of combining their knowledge to come up with a consensus view.

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