Erik's Reviews > The Arrows of Time

I time-traveled once. Literally, if not quite in the Hollywood sense of whirring machines and flashing lights. One day, while I was teaching, I traveled back in time about two hours. Smoothly, with no sensorial discontinuity (I wasn’t in the middle of talking or anything like that). The mechanical watch I had with me broke - which may lead the more skeptical to believe I merely lost track of time. Except my notebook, filled with detailed notes and time-stamped records of these past two hours, had traveled with me.

Surprised, I queried my students if the same had happened to them. It hadn’t, and they thought I was joking. It’s an irony - I won’t say strange one because it’s obvious in hindsight - that arguably the most interesting thing that will ever happen in my life also turned out to be one of the dullest. I had to repeat those same two hours (while of course only being paid for them once), which weren’t particularly exciting the first time around.

I of course tried to use my foreknowledge to improve my teaching. I already knew *exactly* where my students would stumble, the questions they would ask, the problems they would miss. But I was able to change very little. Which, if you have much experience teaching, should not be too surprising.

First of all, a veteran teacher already knows the problems and ideas that different types of minds will struggle with. Changing the probability from 90% to 100% doesn’t do much. Second, teaching is not about transmitting knowledge from teacher to student, it’s about guiding the student into their own understanding. Minds are built from the inside-out. So what if I know the questions they ask? Answering them before they ask actually hurts their learning process by short-circuiting their own involvement in the process.

But I digress. My primary point is that knowledge plays a much smaller role in both personal and civilization-level advancement than most people credit. To some, knowledge is literally the ONLY metric of advancement. But, short of a definition of knowledge so wide as to be universal, this simply isn’t the case.

Take climate change for example. We already possess the scientific and technical know-how to reduce our carbon emissions. Solar power is already more cost-efficient than any other form of large-scale power generation. Extremely good electric and hybrid cars exist. But we lack the political and economical will, discipline, and maturity to evolve our electrical habits, both personal and communal.

This third and final book in the Orthogonal trilogy is in large part about this question of knowledge’s power, especially knowledge from the future. Thanks to the special physics of the Orthogonal universe, the engineers of the Mountain develop a camera that can see light from the future. Which they shortly use to develop a messaging system able to receive messages from their future selves.

Thus is the core conflict of Arrows of Time. Half of the citizens of the mountain strongly oppose such a system, for they believe it will have detrimental effects to their psychology and sense of free will [see Ted Chiang’s short story “What’s Expected of Us” for a short but incisive take on this]. The other half believe these messages from their future could prove pivotal to the survival of their mission. After all, couldn’t they receive a warning about a near-miss from a meteor strike, thus precipitating a course change that will make that near-miss (as opposed to being struck) a reality?

As that last question presages, any time you deal with time travel and fore-knowledge, you’ll swiftly find yourself in the Swamp of Destiny (and free will and determinism and etc), and Egan does not shy away. Of course he doesn’t, he’s Greg Egan! In fact, he double-downs; another big chunk of the book involves a journey to a planet from the orthogonal cluster - that is a planet whose ‘arrow of time’ (i.e. entropy direction) is flipped from theirs. If you’ve ever seen the film Tenet, it’s basically that, with better science and consistency. If you haven’t then strange things happen like dust from the planet gets into their spaceship BEFORE it even lands on the planet (because from the “perspective” of the planet and its dust, the ship isn’t landing… but leaving).

I won’t pretend a super clear understanding of the physics explored in this book. My own personal intuition is that interaction between matter with opposing arrows of time would result in mutual annihilation, like in a matter-antimatter reaction. Indeed in some Formalisms (Feynman/Wheeler’s as opposed to the more popular Hamiltonian), anti-matter IS time-reversed matter. But in this book and in more popular physics, this symmetry is rejected. Anti-matter and time-reversed matter are different.

Overall, I found this third book the most satisfying and Egan-like. The first book suffers because large chunks of it must be spent exploring the mundane realities of the Orthogonal universe and the civilization that we’re following. Yalda - the protagonist of the first book - does science not because she has some end-goal or purpose but simply out of curiosity. This makes it inherently less dramatic and interesting than the scientific explorations of these latter two books, in which science must save their entire civilization or fix some more immediate problem (such as women dying in order to give birth).

What’s more, the science of the first book is elementary in nature - the most basic ideas of atoms/electrons (“luxagens”) and light. Different in the Orthogonal universe and thus harder to understand but still ultimately at the high-school chemistry/physics level. Whereas the science in this last book is more cutting edge, more speculative and therefore interesting, to me at least.

Even so, even though I did like this third book best, I wouldn’t change any of what I wrote in my review of the first book. The whole series is still an astounding creation, a display of genius so far beyond the achievements of most sci-fi authors as to render Egan’s books a genre of their own. But for that same reason, they’re also incredibly niche. Just look at the reviews here on GR: how many demonstrate a technical appreciation or comprehension of the Orthogonal universe?

So my conclusion is much the same. Read it, if everything I’ve written sounds like something enjoyable, but also understand that the process of reading an Egan differs greatly from the process of reading most novels. You shouldn’t expect to easily and clearly understand every sentence, diagram, and idea. But you don’t need to, either. Instead, I’ve come to consider Egan a sort of Scientific Shakespeare. Just as I can appreciate the beauty and lyricism of the Bard’s writing without perfectly understanding every single line, so too can I enjoy the beauty and lyricism of Egan’s science, even when I’ve become lost, like an Alice in Scienceland.