The Fourth Dimension - Rudy Rucker

The Fourth Dimension is an attempt to explain the concept of higher dimensions, frequently by using analogies to the 19th century novel Flatland, which was celebrating its 100th anniversary at the time this book was published.

The book starts with several chapters about what the fourth dimension would be, or how to think of it, in terms of moving fourth dimensionally. The middle section deals with space, and how the space would be represented in the dimension, how gravity and mass are expressed. Then the final third of the book looks at the notion of the fourth dimension being time specifically. Rucker emphasizes that, despite discussing spacetime, this doesn't mean that "time" is interchangeable with the fourth dimension. Time could be the 5th or 6th dimension, and there are other dimensions in between.

The book is full of diagrams, puzzles to consider, and lots of quotes from other writers about the nature of other dimensions. I found the diagrams most useful. Then I would try to answer one of the puzzles and after checking the solution in the back, feel completely lost again. The quotes mostly didn't help.

Rucker is trying to teach a little bit about the history of the notion of higher dimensions, the theories that have been advanced and discarded, and at times he goes into greater depth on that than the reader really needs. Seems to lose the point of what he's actually trying to explain in lengthy passages from a sequel to Flatland he's imagined (as opposed to actual sequels to it that have been written). That starts to feel indulgent, and not as useful to illustrate points as his more straightforward discussions.

It helps that much of this has become more common in fiction over the 30+ years since the book was published. Especially when you get into parallel universes, or things of that nature. There's a passing familiarity with some of these concepts just through repeated exposure to simplified or bastardized versions of them in pop culture.

'Of course, the whole reason for introducing the block universe was to get rid of the passage of time. But how can I say so universally experienced phenomenon is nonexistent?'