The Origins of the Highest Energy Particles in Nature: where we are and where we go next

TL;DR

This paper reviews the development of multi-messenger astronomy and upcoming instruments aimed at uncovering the origins of the universe's highest energy particles, highlighting past progress and future prospects.

Contribution

It provides an overview of key advancements in multi-messenger astronomy and discusses future projects to solve the mystery of cosmic ray origins.

Findings

Integration of multi-messenger data has advanced understanding of cosmic rays.

Upcoming instruments will significantly improve detection capabilities.

Long development times impact the deployment of new observational tools.

Abstract

In his Nobel Prize lecture Victor Hess urged that different instruments, working together, should be used to solve the problem of the origin of cosmic rays. I review some of the key developments that have opened up the new fields of direct and indirect multi-messenger astronomy and that are guiding us to the solution of this riddle. I then discuss, very briefly, some of the new instruments that are shortly to come on line and give examples to show the long lead-times from conception to implementation that occur in this field. I conclude with some remarks about very ambitious future projects. The paper is not intended as a review: rather it is an attempt to set down issues discussed in the Hess Memorial Public Lecture given at the 2019 ICRC in Madison, Wisconsin and accessible at www.icrc2019.org.