Photons, Bits and Entropy: From Planck to Shannon at the Roots of the Information Age

• Main Author: Mario Martinelli
• Format: Article
• Language: English
• Published: MDPI AG 2017-07-01
• Series: Entropy
• Subjects: entropy; photon; bit; second law; information theory; blackbody radiation; Planck; Shannon
• Online Access: https://www.mdpi.com/1099-4300/19/7/341

The present age, which can be called the Information Age, has a core technology constituted by bits transported by photons. Both concepts, bit and photon, originated in the past century: the concept of photon was introduced by Planck in 1900 when he advanced the solution of the blackbody spectrum, and bit is a term first used by Shannon in 1948 when he introduced the theorems that founded information theory. The connection between Planck and Shannon is not immediately apparent; nor is it obvious that they derived their basic results from the concept of entropy. Examination of other important scientists can shed light on Planck’s and Shannon’s work in these respects. Darwin and Fowler, who in 1922 published a couple of papers where they reinterpreted Planck’s results, pointed out the centrality of the partition function to statistical mechanics and thermodynamics. The same roots have been more recently reconsidered by Jaynes, who extended the considerations advanced by Darwin and Fowler to information theory. This paper investigates how the concept of entropy was propagated in the past century in order to show how a simple intuition, born in the 1824 during the first industrial revolution in the mind of the young French engineer Carnot, is literally still enlightening the fourth industrial revolution and probably will continue to do so in the coming century.