# Structural and Symbolic Information in the Context of the General Theory of Information
## 4 Structural Information as an Intrinsic Property  
At the same time, [PERSON] and [PERSON] suggest the vision of structural information, in which structural information may no longer be restricted to changing just \"knowledge in an intelligent system\", and may more generally be defined as the capacity of a physical system, the \"carrier of structural information\", to cause changes in a second physical system, the \"receiver of structural information\" [4; 5; 7; 8]. If in particular, the receiver is the same system as the carrier but at some later point of time, reversible microscopic dynamics described by the Liouville equation is universally understood as \"conserving [microscopic] [structural] information\" [28; 29; 30]. In contrast to this, irreversible macroscopic dynamics is commonly associated with a loss of [macroscopic] [structural] information, directly related to the growth of thermodynamic entropy (cf. [7; 8]). In the sense of [PERSON] [31], who wrote that \"a macroscopic state always comprises a large number of microscopic states that combine to an average value\", macroscopic structural information represents a portion of the microscopic structural information of a given system. This approach is consistent with the approach from Section 3. Namely, a system may have different structures, such as a microscopic structure and a macroscopic structure. In each of those structures, there exists related structural information. While the microscopic information may be conserved, the macroscopic information may decay according to the 2 nd law of thermodynamics. That is, the different structures of the same system may possess different symmetries and may follow different laws. Irreducibilities of this kind indicate _emergent_ properties or structures (see [8] and Section 5). In his famous article \"The RNA world\" about the origin of life, [PERSON] [32] wrote about \"the useful distinction between information and function,\" that \"information storage needs to be one-dimensional, for ease of copying, but molecules with enzymatic functions tend to be tight three-dimensional structures\". This quotation demonstrates that the term \"information\" is in common scientific use in situations in which \"knowledge in an intelligent system\" does not exist at all, such as before life emerged on Earth. [PERSON] refers to the structural information given by the sequence of building blocks in a chain molecule. This information is received later by the same molecule when it folds into a functioning enzyme, and by other reactants then catalyzed by it. Similarly, the information scientist [PERSON] [33] speaks about \"information\" that was generated in evolution for the first time when life began, and has allowed living structures to survive to the present day. Without retaining this structural information, living beings would be as astronomically rare among random chemical mixtures [34], as are sensible books among the random texts in [PERSON] \"Library of Babel\" [35]. Structural information available from a carrier depends on the receiver determining what portion of this information is actually received. If, for example, the receiver is a thermometer and the carrier is liquid, then all information received is the temperature of the liquid displayed by this thermometer. In essence, structural information can be extracted from a given system by \"measurement\" when, for example, a sensor is used as a receiver. Structural information also can be quantified when it is comparable to the structural information of a reference system and is reflected in a scale, such as the length scale of a mercury thermometer. A numerical value being the result of a comparison between the same kinds of structural information available from two different systems, such as by counting their parts, is a \"measurement result\". Numbers represent information in the symbolic form, or as \"symbolic information\", see Section 5.