Colleagues,
Rolf Landauer, a successor to Brillouin at the IBM Watson laboratory,
explained, about ten years ago, that all information is physical. I�ve
found it an extremely valuable insight. It has proved to be of primary
importance in resolving some of the daunting and seemingly paradoxical
problems that plague quantum measurement theory, as well as
misunderstandings with quantum theory in general. Landauer wrote that
�Information is not a disembodied abstract entity; it is always tied to
a physical representation. It is represented by engraving on a stone
tablet, a spin, a charge, a hole in a punched card, a mark on paper, or
some other equivalent. This ties the handling of information to all the
possibilities and restrictions of our real physical world, its laws of
physics and its storehouse of available parts.� Physics Letters A 217,
188 (1996).
Measurement, we know, is exchange of information. Since information is
physical, there must be something physical exchanged with every
measurement, just as Bohr and Heisenberg always insisted, proclaiming a
physical disturbance with every measurement. The least physical thing
that can be transferred by measurement is a single quantum of some sort,
a photon, gravitational quantum, etc. But all quanta, without exception,
possess energy, so every measurement, at every scale, must transfer at
least one energetic quantum. We have found this to be the source of the
connection between measurement (information exchange) and entropy, as
specified by the Second Law of Thermodynamics. Thus, just as we know
that the entropy of the universe can�t decrease, so the amount of
information in the universe never increases.
Cordially,
Michael Devereux
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Received on Fri Sep 2 22:53:24 2005
