The Big Idea: Greg Egan

If you like your science fiction hard — we’re talking diamond-scratching hard, here — then you already know that Greg Egan is your man; this Hugo winner’s been spinning tales of hard SF for years that make you think and thrill at the same time. After a six-year break from novels, Egan is back with Incandescence, which features a journey to the very core of the galaxy. You know, like you do. And for those of you who are wondering just how seriously Egan takes the “science” part of the phrase “science fiction,” here’s Egan to explain the genesis of Incandescence, which involves Einstein’s greatest discovery, and how people who aren’t exactly Einsteins themselves might discover it.


Incandescence grew out of the notion that the theory of general relativity — widely regarded as one of the pinnacles of human intellectual achievement — could be discovered by a pre-industrial civilization with no steam engines, no electric lights, no radio transmitters, and absolutely no tradition of astronomy.

At first glance, this premise might strike you as a little hard to believe. We humans came to a detailed understanding of gravity after centuries of painstaking astronomical observations, most crucially of the motions of the planets across the sky. Johannes Kepler found that these observations could be explained if the planets moved around the sun along elliptical orbits, with the square of the orbital period proportional to the cube of the length of the longest axis of the ellipse. Newton showed that just such a motion would arise from a universal attraction between bodies that was inversely proportional to the square of the distance between them. That hypothesis was a close enough approximation to the truth to survive for more than three centuries.

When Newton was finally overthrown by Einstein, the birth of the new theory owed much less to the astronomical facts it could explain — such as a puzzling drift in the point where Mercury made its closest approach to the sun — than to an elegant theory of electromagnetism that had arisen more or less independently of ideas about gravity. Electrostatic and magnetic effects had been unified by James Clerk Maxwell, but Maxwell’s equations only offered one value for the speed of light, however you happened to be moving when you measured it. Making sense of this fact led Einstein first to special relativity, in which the geometry of space-time had the unvarying speed of light built into it, then general relativity, in which the curvature of the same geometry accounted for the motion of objects free-falling through space.

So for us, astronomy was crucial even to reach as far as Newton, and postulating Einstein’s theory — let alone validating it to high precision, with atomic clocks on satellites and observations of pulsar orbits — depended on a wealth of other ideas and technologies.

How, then, could my alien civilization possibly reach the same conceptual heights, when they were armed with none of these apparent prerequisites? The short answer is that they would need to be living in just the right environment: the accretion disk of a large black hole.

When SF readers think of the experience of being close to a black hole, the phenomena that most easily come to mind are those that are most exotic from our own perspective: time dilation, gravitational blue-shifts, and massive distortions of the view of the sky. But those are all a matter of making astronomical observations, or at least arranging some kind of comparison between the near-black-hole experience and the experience of other beings who have kept their distance. My aliens would probably need to be sheltering deep inside some rocky structure to protect them from the radiation of the accretion disk — and the glow of the disk itself would also render astronomy immensely difficult.

Blind to the heavens, how could they come to learn anything at all about gravity, let alone the subtleties of general relativity? After all, didn’t Einstein tell us that if we’re free-falling, weightless, in a windowless elevator, gravity itself becomes impossible to detect?

Not quite! To render its passenger completely oblivious to gravity, not only does the elevator need to be small, but the passenger’s observations need to be curtailed in time just as surely as they’re limited in space. Given time, gravity makes its mark. Forget about black holes for a moment: even inside a windowless space station orbiting the Earth, you could easily prove that you were not just drifting through interstellar space, light-years from the nearest planet. How? Put on your space suit, and pump out all the station’s air. Then fill the station with small objects — paper clips, pens, whatever — being careful to place them initially at rest with respect to the walls.

Wait, and see what happens.

Most objects will eventually hit the walls; the exact proportion will depend on the station’s spin. But however the station is or isn’t spinning, some objects will undergo a cyclic motion, moving back and forth, all with the same period.

That period is the orbital period of the space station around the Earth. The paper clips and pens that are moving back and forth inside the station are following orbits that are inclined at a very small angle to the orbit of the station’s center of mass. Twice in every orbit, the two paths cross, and the paper clip passes through the center of the space station. Then it moves away, reaches the point of greatest separation of the orbits, then turns around and comes back.

This minuscule difference in orbits is enough to reveal the fact that you’re not drifting in interstellar space. A sufficiently delicate spring balance could reveal the tiny “tidal gravitational force” that is another way of thinking about exactly the same thing, but unless the orbital period was very long, you could stick with the technology-free approach and just watch and wait.

A range of simple experiments like this — none of them much harder than those conducted by Galileo and his contemporaries — were the solution to my aliens’ need to catch up with Newton. But catching up with Einstein? Surely that was beyond hope?

I thought it might be, until I sat down and did some detailed calculations. It turned out that, close to a black hole, the differences between Newton’s and Einstein’s predictions would easily be big enough for anyone to spot without sophisticated instrumentation.

What about sophisticated mathematics? The geometry of general relativity isn’t trivial, but much of its difficulty, for us, revolves around the need to dispose of our preconceptions. By putting my aliens in a world of curved and twisted tunnels, rather than the flat, almost Euclidean landscape of a patch of planetary surface, they came better prepared for the need to cope with a space-time geometry that also twisted and curved.

The result was an alternative, low-tech path into some of the most beautiful truths we’ve yet discovered about the universe. To add to the drama, though, there needed to be a sense of urgency; the intellectual progress of the aliens had to be a matter of life and death. But having already put them beside a black hole, danger was never going to be far behind.

Incandescence: Amazon | Barnes & Noble | Powell’s

Visit Greg Egan’s Incandescence page, which features quite a lot of supplementary material. Also visit his listing of his works available online.

15 Comments on “The Big Idea: Greg Egan”

  1. Excellent, thank you for posting this. Diaspora is on my list of favorite SF books of the past few decades and Incandescence is already in my “to read” pile.

    I did have a couple of questions if Mr. Egan is following this thread: is “Glory” set in the same universe since it also seems to be about the Amalgam? Are there other stories that should be seen as being in this same setting aside from “Riding the Crocodile?”

  2. One of the reasons that I take a historical and storytelling approach to teaching Physics is that the development of science follows a chain of events — change the chain and though the science doesn’t technically change, the words we use, the examples we cite and the worldview we use do.

    The development of Quantum Mechanics is based on the development of the electronic structure of the atom, with the big breakthrough coming from the Schroedinger Wave Equation. However, some fifty years earlier, we had all the experimental evidence to produce QM from the discontinuity in the heat capacity. I’ve been working for many years on some aliens who took the Thermodynamics path to Modern Physics, and how it changes their worldview, let alone mucks up the communications when they meet the humans.

    Huh. If I ever write a comedic first contact story, maybe I should call it “Meet the Humans.” (grin)

    Dr. Phil

  3. Mensley: Yes, “Glory” is set in the Amalgam universe, though there’s no link at all to the events in the novel. Another story of which the same is true, “Hot Rock”, will be published in Jonathan Strahan’s anthology Godlike Machines later this year.

    Ari B: Yes there’s a chance, but it’s not certain yet and it certainly won’t be soon. Your best bet in the immediate future would be Amazon UK or second-hand.

    Dr. Phil: Alien QM sounds fun. Humans already have plenty of trouble agreeing on the language and meaning of that.

  4. Well, this is timely. I was planning on heading out to my favourite bookshop today, now I have one more book to add to my list. I LOVE me some headache inducing hard sci-fi :)

  5. I love physics, so these sound great. (Plus, his name is easy to remember, as I live in Eagan, MN!)

  6. I’m really glad I saw this, I had forgotten Incandescence was coming out.
    i loves me some greg egan.

  7. A six year hiatus from novels? I knew it had been a while but… If Incandescence is half as good as “The Big Idea” implies it will be worth the wait. Welcome back Greg. Now if we could convince Terry Dowling and Sean McMullen to be more prolific too…

  8. Being a UK-er, I have had the great pleasure of reading Incandescence already, and I just wanted to point out that this Big Idea piece doesn’t even tell the half of it. The “alien renaissance where they work out GR” story (which does a wonderful job of both celebrating and subverting the “loner who has worked out the truth” cliche) is amazing, but we get another perspective on the civilisation involved from the Amalgam protagonists in another plot strand that’s full of its own brilliant ideas, and the two are very cleverly woven together in a way that wonderfully undercuts another huge SFnal cliche (I shall avoid detail because it might be considered spoilery).

    If hard SF is even slightly the sort of thing you like, you will love Incandescence. Buy it now.

  9. I noticed that the Egan backlist is out in print again in the UK…but not the US. Boo, hiss, US publishers! We want our diamond-hard SF!

  10. I had almost given up on waiting for a new book from Egan, and then randomly I found the Youtube “trailers” for Incandescence. This story sounds just as compelling as any other he’s written, and I can’t describe how excited I am to get a chance to read it. I wonder if I’ll be able to find it here in Canada?

    PS. I love the description “Diamond-Hard Sci-Fi”. But are diamonds really hard enough? Surely we can do better.


  11. I got this book as a Christmas present, and though I don’t read much these days, I read it in a couple of days, chuckling to myself as I understood at least part of what was going on (I don’t know enough relativity theory to understand the details, but I did catch the “we’re not really agreeing with Newton’s physics” part).

    Now, don’t get me wrong: Egan’s work is highly enjoyable, and I absolutely recommend it to anyone who’s interested in “Hard SF”, but, as happened with some of his previous books, the end left me a bit frustrated. He’s absolutely great at imagining weird situations and making them understandable (at least to someone with moderate-to-high scientific background), but not so good at finishing books, I’d say.

  12. @Philippe D: Well, I have to disagree there. In my opinion Diaspora´s end is one of the most mind-boggling endings I have ever read.

    ** Spoiler **

    Speaking of which, if Mr. Egan is still reading these comments, I’ve always wondered this: are the Transmuters, in their ‘one fixed state per universe’ state, still supposed to be computed and thus still conscious? Perhaps in a similar way than the protagonists of Permutation City were alive and well, their data scattered in time and space but that making no difference to them. I ask this because my initial reaction was that we were supposed to assume that they were somehow ‘dead’, but on further reflection I don’t think that’s consistent with a strict interpretation of your other ideas about the nature of consciousness.

  13. Fantastic read, but even I (who has studied some of the science at university level) found the story a bit hard going at times… or should I say ‘the science’. Having said this, the whole premise is exciting, and I loved reading it and look forwards to a new Egan book. I found myself making comparisons to earlier Vernor Vinge at times, and that is a good thing!