Nikki Weststeijn

Information is a concept that has become a point of focus in many disciplines other than information theory, but it is often unclear precisely which concept we are referring to. There are namely two main types of information. On the one hand, there is Shannon information, which is the most standard concept of information in information theory and which quantitatively measures the information contained in an information source. On the other hand, there is semantic information, which is more in line with the everyday understanding of the term “information” and which concerns information that is always about something. Whereas Shannon information is characterized as being quantitative, objective, physical and mind-independent, semantic information is characterized as being qualitative, subjective, mind-dependent and evidently semantic. It thus seems that there is a dichotomy between these two concepts of information. The main question of this thesis is to find out whether Shannon information is really that different from semantic information, i.e. to characterize the relation between Shannon information and semantic information. We will look at the concept of Shannon information in information theory and physics and clarify the relation between information and entropy. We will also look at quantitative accounts of semantic information by Dretske, Bar-Hillel and Carnap, and Floridi and at how we can use Situation Theory, Dynamic Epistemic Logic and Logic of Functional Dependence to model the flow of information.

Relational Quantum Mechanics is an interpretation of quantum mechanics proposed by Carlo Rovelli. Rovelli argues that, in the same spirit as Einstein’s theory of relativity, physical quantities can only have definite values relative to an observer. Relational Quantum Mechanics is hereby able to offer a principled explanation of the problem of nested measurement, also known as Wigner’s friend. Since quantum states are taken to be relative states that depend on both the system and the observer, there is no inconsistency in the descriptions of the observers. Federico Laudisa has recently argued, however, that Rovelli’s description of Wigner’s friend is ambiguous, because it does not take into account the correlation between the observer and the quantum system. He argues that if this correlation is taken into account, the problem with Wigner’s friend disappears and, therefore, a relativization of quantum states is not necessary. I will show that Laudisa’s criticism is not justified. To the extent that the correlation can be accurately reflected, the problem of Wigner’s friend remains. An interpretation of quantum mechanics that provides a solution to it, like Relational Quantum Mechanics, is therefore a welcome one.