Science fiction works are commonly classified on a spectrum ranging from “soft” to “hard”. The distinction lies in the fiction’s attitude toward the physics (or other science) involved in the story. In soft sci-fi, the physics is ad-hoc, created as needed to serve the story, with no consistent theory behind it; only its outlines are apparent, with the details glossed-over. Most television sci-fi, such as Star Trek, falls into this category; so do many venerable sci-fi novels, such as Dune, Ender’s Game, and Foundation.

Conversely, hard sci-fi pursues a more committed relationship with the laws of physics. While the author may still add new physics for story purposes—cheap faster-than-light travel being a popular choice—it is constructed in a way that makes it fit in with real-world physics; it is plausible that there could be a deeper theory behind it. The details have been well-thought-out and may be discussed at length; likewise, the technologies encountered in the story have been conceived with real-world engineering principles in mind. Works that lean toward the “hard” end of the spectrum include most anything by Arthur C. Clarke, Robert A. Heinlein or Larry Niven; Peter F. Hamilton’s Night’s Dawn trilogy; Neal Stephenson’s Anathem.

As hard sci-fi goes, Greg Egan’s is harder than most. Usually, if an author wants an interstellar civilization, he or she must introduce wormholes, hyperspace, warp drive, or some other method of getting characters from one place to another without them dying of old age. Not Greg Egan. In his books set in the Amalgam, a galaxy-spanning civilization millions of years in the future, people travel at the speed of light—by having their minds digitized, broadcast across space in a laser pulse, and loaded at the destination into an artificial body built to their specifications. A round trip to another star may take hundreds or thousands of years, but their friends and family at home will still be there—aging and (unintentional) death having long since been abolished. Egan’s stories have plenty of hyper-advanced, “magical” technology, but it’s all plausible extrapolation from known laws of physics. The real world doesn’t appear to permit faster-than-light travel, and neither does Egan permit it in his fiction.

However, Egan’s latest series, Orthogonal, takes the concept of hard sci-fi far beyond anything I’ve read before, from Egan or any other author. The series consists so far of the two novels The Clockwork Rocket and The Eternal Flame, with the third and final volume, The Arrows of Time, to come out this fall.

What makes this series so special is that Egan has not simply created fictional characters, planets and technologies; in these books he brings to life an entire alternate physics—and not just a set of ad-hoc phenomena created to enable a story, but a physics with a depth, consistency, and unity comparable to the real thing. He is able to do this because his physics closely parallels ours. Egan makes one decisive change: flipping a sign from negative to positive in the metric of spacetime, so that in his universe, spacetime is locally Euclidean instead of locally Minkowski. He then rebuilds the central theories of modern physics, including relativity, thermodynamics, electromagnetism and quantum mechanics, on this modified foundation—and finds many fascinating and surprising consequences. He works out the properties of a world that obeys this alternate physics, then sets a story in that world.

It’s a marvelous achievement, and one that could only have been done by an author with a deep understanding of real-world physics. The concept is breathtakingly elegant: a simple change to one critical equation is the seed from which grows a rich fictional cosmos, replete with strange and beautiful phenomena that are quite logically and mathematically sound, yet unknown to us.

Egan rightfully wants to show off the physics he’s developed; consequently, many of the characters of the Orthogonal series are scientists who seek and gradually find the laws that govern their universe. The novels contain no equations, but you will frequently see graphs and diagrams illustrating the theories and experiments the characters pursue. These scientists aren’t human, of course—but while their bodies are alien, their thoughts, emotions, frustrations and dreams are quite human. And they practice science the same way we do. This is another reason these books are valuable: they depict the day-to-day activities of scientists doing science, with a taste of the confusion, argument, squabbling over resources, and political maneuvering that make real-world science so maddening—and the occasional moments of clarity and triumph that make it worthwhile.

They don’t stop with physics, though; Egan’s characters go on to investigate chemistry and biology. These aren’t worked out to the same degree of detail as the physics, naturally, but they’re quite interesting nonetheless. In particular, the creatures of Orthogonal’s world have a very different method of reproduction than what we’re familiar with. They have male and female sexes like we do, but with a frankly horrifying twist—you’ll have to read the books to find out more.

Finally, in addition to everything else, the Orthogonal novels are feminist novels. In their world, just as in ours, traditional attitudes hold women to be subordinate to men, and institutionalized sexism is the norm. A common thread recurring throughout Orthogonal is that of women challenging and overcoming the resistance of male authorities, colleagues, friends and family to secure professional advancement, personal liberty, or even just physical safety from those men who would do violence to them. Egan aims for a realistic depiction of science, and he does not shy away from the sexism that sadly remains a very real and tangible aspect of science—and of our society in general. In these books, though, the facts of the aliens’ biology make their sexual politics even more explosive and dire than ours.

If you’re a fan of hard sci-fi, especially if you have some physics background or don’t mind putting in some effort to grasp a tricky concept now and then, Orthogonal is well worth your time. But these are far from being textbooks in a veneer of plot—they tell a powerful story with inspiring characters whose struggles and choices are as remarkable as the strange laws of their world.