"This is the only sciencefiction book I have ever
read to define the term fiber bundle."
said contributor David Moews of this book. The same for me, though I was
disappointed to see that it was only in a glossary at the end of the
book. Still, this story which focuses on the "lives" of virtual
beings in a computer contains some really nice mathematical
fiction. I especially like the section in which one virtual being
helps another (a "baby") to figure out the GaussBonnet theorem. The
question was posed in a rather sophisticated way, demonstrating real
understanding: why is it that we cannot put any curvature we want onto
a manifold? Isn't it merely a matter of the embedding (also defined
in the glossary)? Of course, the answer is "No, there are topological
restrictions", but how do you help someone to see that? Here, the teacher, Radiya, presents the pupil, Yatima, with a virtual triangulation of a sphere and asks "ver" (pronouns all start with "v" here) to try to make it flat:
(quoted from Diaspora)
Ve tried smoothing and flattening the six points. That was easy  but it made the eight triangles as bowed and nonEuclidean as they'd been on the original sphere. It seemed "obvious" that the points and the triangles could never be made flat simultaneously...but Yatima still couldn't pin down the reason why the two goals were irreconcilable. Ve measured the angles where four triangles met, around what had once been a point of the diamond: 90, 90, 90, 90. That much made perfect sense: to lie flat and meet nicely without any gaps, they had to add up to 360 degrees. Ve reverted to the unblunted diamond, and measured the same angles again: 60, 60, 60, 60. A total of 240 was too small to lie flat; anything less than a full circle forced the surface to roll up like the point of a cone... That was it! That was the heart of the contradiction! Every vertex needed angles totaling 360 degrees around it, in order to lie flat...while every flat Euclidean triangle supplied just 180 degrees. Half as much. so if there'd been exactly twice as many triangles as vertices everything would have added up perfectly  but with six vertices and only eight triangles, there wasn't enough flatness to go around.

I also really liked the description of mathematics research, called
"truth mining" in the future. Especially in this "new world" where
everyone is literally a computer, one might expect that math research
would have been completely automated to the point that it does not
involve consciousness or creativity. However, at least according to
the wise old virtual being in the book, this will never be the case.
Math research requires some intuition, and discovery requires having a
different outlook than those who came before you.
(quoted from Diaspora)
If ve ever wanted to be a
miner in vis own right  making and testing vis own conjectures at
the coal face, like Gauss and Euler, Riemann and LeviCivita, deRham
and Cartan, Radiya and Blanca  then Yatima knew there were no
shortcuts, no alternatives to exploring the Mines firsthand. Ve
couldn't hope to strike out in a fresh direction, a route no one had
ever chosen before, wihtout a new take on the old results. Only once
ve'd constructed vis own map of the Mines  idiosyncratically
crumpled and stained, adorned and annotated like no one else's 
could ve begin to guess where the next rich vein of undiscovered
truths lay buried.

There are also interesting theoretical biology and mathematical
physics aspects to the book. For instance, the virtual beings
interact with the biological descendents of humanity who have begun
deliberately altering their DNA to introduce various desired traits,
and this is discussed from both a molecular biology and sociological
standpoint. In terms of mathematical physics, the book presents the
viewpoint that quantum particles are wormholes of the spacetime
manifold. (This is where the fiber bundles come in.)
(quoted from Diaspora)
"But why a 2sphere?" Blanca duplicated the diagram, but used a circle as the standard fiber instead of a sphere. Again, no two paths through the wormhole were the same color at the crossover point; the main difference was that they took on different colors straight from the whiteness of the surrounding space, because there were no "north and south poles" now from which they could spread out. "In twodimensional space, you only need one extra dimension to avoid the singularity." "That's true," the avatar conceded. "But I used a twodimensional standard fiber because this wormhole possesses two degrees of freedom. One keeps the geodesics from colliding at the center. The other keeps the two mouths of the wormhole itself apart. If I'd used a circle as the standard fiber, then the distance between the mouths would have been fixed at precisely zero  which would have been an absurd constraint when the whole point of the model was to mimic quantum uncertainty."

This material
is based on Egan's reading of the books Gauge
Fields, Knots and Gravity (Series on Knots and Everything, Vol 4)
by John Baez, Javier P. Muniain and Knots and Physics (Series on Knots and Everything, Vol.1)
by Louis H. Kauffman.
Contributed by
Arturo Magidin
Incorporated into this novel is the short story "Wang's
Carpets", which also appeared separately in some SF collections. This
story is "a First Contact story about a
form of life made out of (Hao) Wang tiles."

(quoted from Diaspora)
It was astonishing. Paolo hoped Elena was tapping the library, wherever she
was. A colony of algae would have been more "advanced" — but this incredible
primordial creature revealed infinitely more about the possibilities for
the genesis of life. Carbohydrate, here, played every biochemical role:
information carrier, enzyme, energy source, structural material. Nothing
like it could have survived on Earth, once there were organisms capable of
feeding on it?and if there were ever intelligent Orpheans, they'd be
unlikely to find any trace of this bizarre ancestor.
Karpal wore a secretive smile.
Paolo said, "What?"
"Wang tiles. The carpets are made out of Wang tiles."
Hermann beat him to the library, again.
"Wang as in twentiethcentury flesh mathematician, Hao Wang. Tiles as in
any set of shapes which can cover the plane. Wang tiles are squares with
various shaped edges, which have to fit complementary shapes on adjacent
squares. You can cover the plane with a set of Wang tiles, as long as you
choose the right one every step of the way. Or in the case of the carpets,
grow the right one."
Karpal said, "We should call them Wang's Carpets, in honor of Hao Wang.
After twentythree hundred years, his mathematics has come to life."
Paolo liked the idea, but he was doubtful. "We may have trouble getting a
twothirds majority on that. It's a bit obscure ..."
Hermann laughed. "Who needs a twothirds majority? If we want to call them
Wang's Carpets, we can call them Wang's Carpets. There are ninetyseven
languages in current use in CZ?, half of them invented since the polis was
founded. I don't think we'll be exiled for coining one private name."
Paolo concurred, slightly embarrassed. The truth was, he'd completely
forgotten that Hermann and Karpal weren't actually speaking Modern Roman.
The three of them instructed their exoselves to consider the name adopted:
henceforth, they'd hear "carpet" as "Wang's Carpet"? but if they used the
term with anyone else, the reverse translation would apply.

Contributed by
Doug Nadworny
This is how all Science Fiction should be, totally engaging, with well developed worlds. I consider this to be one of the best Sci Fi novels I've ever read. On every level it excels. I've read some of Egan's works previously and can't understand how I missed this one, or why no one ever recommended it.

Contributed by
Naren H
Interesting ideas in the book, but they are not enough. And like most hard scifi, it becomes quickly dated. As a work of literature, it is one of the worst books I have ever read. Character motivation and development is laughable (when it isn't annoying) and clumsy. Dramatic tension is almost nonexistent. I don't know why I finished this book. I almost abandoned it several times as I was reading. I wish I had  life is too short to waste on works like this one.

Contributed by
Anonymous
SEMINAL WORK. brilliant and inspiring.

Contributed by
John C. Konrath
I have highly ambiguous feelings about this novel. On the one hand it is clearly an intellectual work with numerous scientific and mathematical concepts and I believe that there are not nearly enough works of this type, but I'm concerned that anyone who hasn't majored in mathematics or modern physics would find it unintelligible. Furthermore, most popular scientific books are written with the intention of simplifying advanced scientific concepts for laypeople, but Mr. Egan seems to unnecessarily obfuscate the concepts embedded in this novel by needlessly resorting to scientific jargon.
This having been said, "Diaspora" posses many philosophical question that are worthy of consideration, not the least of which is the "meaning" of existence. Moreover, this work induces one to to consider the limits of scientific advancement and it's moral implications.

Contributed by
R. D. Ogden
a good story that provokes serious thinking about truth in math, and what are the invariants of consciousness that make unique sentient individuals.

Contributed by
Catherine Asaro
I enjoyed your section on Wang/s Carpets/Dispora by Greg Egan. He does a brilliant job. I wrote a 6000 word essay on Wang's Carpets years ago and felt like I barely scratched the surface. His ideas are brilliant. The essay is called "Strange Loops of Wonder." It first appeared in Tangent magazine and was later reprinted in Projections: Science Fiction in Literature & Film edited by Lou Anders.

