This book series is for anybody who is curious about motion in nature. How do things, people, animals, images and empty space move? The answer leads to many adventures. This volume presents the best ones about extremely fast, powerful and distant motion. In the exploration of motion – physics – special and general relativity make up two important stages.

Special relativity is the exploration of nature’s speed limit, c.  General relativity is the exploration of the force limit c4/4G. The text shows that in both domains, all results follow from these two limit values. In particular, cosmology is the exploration of motion near nature’s distance limit 1/√Λ . This simple, intuitive and unusual way of learning relativity should reward the curiosity of every reader – whether student or professional.

The present volume is the second of a six-volume overview of physics that arose from a threefold aim that I have pursued since 1990: to present motion in a way that is simple, up to date and captivating.

In order to be simple, the text focuses on concepts, while keeping mathematics to the necessary minimum. Understanding the concepts of physics is given precedence over using formulae in calculations. The whole text is within the reach of an undergraduate.

In order to be up to date, the text is enriched by the many gems – both theoretical and empirical – that are scattered throughout the scientific literature.

In order to be captivating, the text tries to startle the reader as much as possible. Read- ing a book on general physics should be like going to a magic show. We watch, we are astonished, we do not believe our eyes, we think, and finally we understand the trick. When we look at nature, we often have the same experience. Indeed, every page presents at least one surprise or provocation for the reader to think about.

The motto of the text, die Menschen stärken, die Sachen klären, a famous statement on pedagogy, translates as: ‘To fortify people, to clarify things.’ Clarifying things – and adhering only to the truth – requires courage, as changing the habits of thought produces fear, often hidden by anger. But by overcoming our fears we grow in strength. And we experience intense and beautiful emotions. All great adventures in life allow this, and exploring motion is one of them. Enjoy it.