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6

The Nature of Information

6.1.2

Conditional and Unconditional Information

Information about real events that have happened (e.g., a volcanic eruption) or about

entities that exist (e.g., a sequence of DNA) is primarily unconditional; that is, it does

not depend on anything (as soon as information is encoded, however, it becomes

conditional on the code).

Scientific work has two stages:

1. Receiving unconditional information from nature (by making observations in the

field, doing experiments in the laboratory).

2. Generating conditional information in the form of hypotheses and theories relating

the observed facts to each other using axiom systems. The success of any theory

(which may be one of several) largely depends on general acceptance of the chosen

propositions and the mathematical apparatus used to manipulate the elements of

the theory; that is, there is a strongly social aspect involved.

Conditional information tends to be unified; for example, a group of scattered tribes,

or practitioners of initially disparate disciplines, may end up speaking a common

language (they may then comprehend the information they exchange as being uncon-

ditional and may ultimately end up believing that there cannot be other languages).

Encoded information is conditional on agreement between emitters and receivers

concerning the code.

The generation of hypotheses involves an inductive leap; they cannot be extracted

deductively from the data. How this happens appears to be beyond computation. ⁸

Typically a model will first be constructed, which will probably draw extensively on

the researcher’s prior knowledge and experience, even if only in the subconscious

realm.

6.1.3

Experiments and Observations

Consider once again the example of the measurement of the length of an object using

a ruler and the information gained thereby. The gain presupposes the existence of a

world of objects and knowledge, including the ruler itself and its calibration in appro-

priate units of measurement. The overall procedure is captured, albeit imperfectly,

in Fig. 6.1.

The essential point is that “information” has two parts: a prior part embodied

by the physical apparatus, the knowledge required to carry out the experiment or

observation, and so forth; and a posterior part equal to the loss in uncertainty about

the system due to having made the observation. The prior part can be thought of

as specifying the set of possible values from which the observed value must come.

In a physical measurement, it is related to the structure of the experiment and the

instruments it employs, and the millennia of civilization that have enabled such

8 Ramsden (2001).