"Deep down things": in what ways is information physical, and why does it matter for information science?

Introduction: Rolf Landauer declared in 1991 that ‘information is physical’. Since then, information has come to be seen by many physicists as a fundamental component of the physical world; indeed by some as the physical component. This idea is now gaining currency in popular science communication. However, it is often far from clear what exactly this statement means; exactly how is information physical? And why this should matter for information science? The purpose of this paper is to clarify just what is meant by the physical nature of information, and the significance of these considerations for our discipline. Methods: A selective literature review and conceptual analysis, based on literature from both physical science and information science. Results: The prospect of attempting to make links between objective and subjective conceptions of information has been strongly advocated by some authors and doubted by others. The physical nature of information can be understood from three main perspectives: the relation between information and physical entropy; the strongly informational nature of the quantum view of nature; and the possibility of recasting physical laws in informational terms. Conclusions: Based on this analysis, we muse on the relevance of such issues to information science, with particular reference to emergent properties of information. Apart from the added public awareness of the i-word in a very different context from the norm, it may that that there are general laws and principles, or at least useful metaphors and analogies, linking the concept of information in the physical, biological and social domains.