Earth, Our Environment - Class Notes
Reflections on a Grain of Salt

In "Reflections on a Grain of Salt", Carl Sagan illustrates the importance of natural laws using our ability to understand a simple crystal of salt.

The grain has about 10^16 (10,000,000,000,000,000) sodium and chlorine atoms, suppose we only want to know the positions of those atoms.

How much can we know? Our brains have about 10^11 neurons each with about 1,000 dendrites. Suppose each dendrite can store one bit of information. Then we can store about 10^14 bits of information: about 1% of what we need to know where each atom in a grain of salt is located.

But we can know the grain of salt because the locations of the atoms are not random. We have uncovered the structure of a crystal of salt and because we know the way each atom is position relative to its neighbors, we only really need to store about 10 bits of information to "know the salt grain".

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Prepared by: Charles J. Ammon
January 1997