- Egan, Greg.
Dichronauts.
New York: Night Shade Books, 2017.
ISBN 978-1-59780-892-7.
-
One of the more fascinating sub-genres of science fiction is
“world building”: creating the setting in which a
story takes place by imagining an environment radically
different from any in the human experience. This can
run the gamut from life in the atmosphere of a gas giant
planet (Saturn Rukh),
on the surface of a neutron star
(Dragon's Egg),
or on an enormous alien-engineered wheel surrounding a
star (Ringworld). When
done well, the environment becomes an integral part of
the tale, shaping the characters and driving the plot.
Greg Egan is one of the most accomplished of world builders.
His fiction includes numerous examples of alien environments,
with the consequences worked out and woven into the story.
The present novel may be his most ambitious yet: a world in which
the fundamental properties of spacetime are different from those
in our universe. Unfortunately, for this reader, the execution
was unequal to the ambition and the result disappointing. I'll
explain this in more detail, but let's start with the basics.
We inhabit a spacetime which is well-approximated by
Minkowski
space. (In regions where gravity is strong, spacetime
curvature must be taken into account, but this can be neglected
in most circumstances including those in this novel.)
Minkowski space is a flat four-dimensional space where each
point is identified by three space and one time coordinate.
It is thus spoken of as a 3+1 dimensional space. The space
and time dimensions are not interchangeable: when computing
the spacetime separation of two events, their distance or
spacetime
interval is given by the quantity
−t²+x²+y²+z².
Minkowski space is said to have a
metric
signature of (−,+,+,+), from the signs of the four
coordinates in the distance (metric) equation.
Why does our universe have a dimensionality of 3+1? Nobody
knows—string theorists who argue for a
landscape of universes in an infinite multiverse
speculate that the very dimensionality of a universe may be
set randomly when the baby universe is created in
its own big bang bubble. Max Tegmark
has argued that
universes with other dimensionalities would not permit the
existence of observers such as us, so we shouldn't be surprised
to find ourselves in one of the universes which is compatible
with our own existence, nor should we rule out a multitude of
other universes with different dimensionalities, all of which
may be devoid of observers.
But need they necessarily be barren? The premise of this novel
is, “not necessarily so”, and Egan has created a
universe with a metric signature of (−,−,+,+),
a 2+2 dimensional spacetime with two spacelike dimensions and two
timelike dimensions. Note that “timelike” refers
to the sign of the dimension in the distance equation, and the
presence of two timelike dimensions is not equivalent to
two time dimensions. There is still a single dimension
of time, t, in which events occur in a linear order
just as in our universe. The second timelike dimension,
which we'll call u, behaves like a spatial dimension
in that objects can move within it as they can along the
other x and y spacelike dimensions, but its
contribution in the distance equation is negative:
−t²−u²+x²+y².
This results in a seriously weird, if not bizarre world.
From this point on, just about everything I'm going to say can
be considered a spoiler if your intention is to read the book
from front to back and not consult the
extensive
background information on the
author's Web site.
Conversely, I shall give away nothing regarding the plot or
ending which is not disclosed in the background information
or the technical afterword of the novel. I do not consider
this material as spoilers; in fact, I believe that many readers
who do not first understand the universe in which the story is
set are likely to abandon the book as simply incomprehensible.
Some of the masters of world building science fiction introduce
the reader to the world as an ongoing puzzle as the story
unfolds but, for whatever reason, Egan did not choose to do
that here, or else he did so sufficiently poorly that this reader
didn't even notice the attempt. I think the publisher made a
serious mistake in not alerting the reader to the existence of
the technical afterword, the reading of which I consider a barely
sufficient prerequisite for understanding the setting in which
the novel takes place.
In the Dichronauts universe, there is a
“world” around which a smaller ”star”
orbits (or maybe the other way around; it's just a coordinate
transformation). The geometry of the spacetime dominates
everything. While in our universe we're free to move in any of
the three spatial dimensions, in this spacetime motion in the
x and y dimensions is as for us, but if
you're facing in the positive x dimension—let's
call it east—you cannot rotate outside the wedge from
northeast to southeast, and as you rotate the distance equation
causes a stretching to occur, like the distortions in
relativistic motion in special relativity. It is no more
possible to turn all the way to the northeast than it is to
attain the speed of light in our universe. If you were born
east-facing, the only way you can see to the west is to bend
over and look between your legs. The beings who inhabit this
world seem to be born randomly east- or west-facing.
Light only propagates within the cone defined by the spacelike
dimensions. Any light source has a “dark cone”
defined by a 45° angle around the timelike u
dimension. In this region, vision does not work, so beings are
blind to their sides. The creatures who inhabit the world are
symbionts of bipeds who call themselves “walkers”
and slug-like creatures, “siders”, who live inside
their skulls and receive their nutrients from the walker's
bloodstream. Siders are equipped with “pingers”,
which use echolocation like terrestrial bats to sense within the
dark cone. While light cannot propagate there, physical objects
can move in that direction, including the density waves which
carry sound. Walkers and siders are linked at the brain level
and can directly perceive each other's views of the world and
communicate without speaking aloud. Both symbiotes are
independently conscious, bonded at a young age, and can, like
married couples, have acrimonious disputes. While walkers
cannot turn outside the 90° cone, they can move in
the timelike north-south direction by “sidling”,
relying upon their siders to detect obstacles within their cone
of blindness.
Due to details of the structure of their world, the walker/sider
society, which seems to be at a pre-industrial level (perhaps
due to the fact that many machines would not work in the weird
geometry they inhabit), is forced to permanently migrate to stay
within the habitable zone between latitudes which are seared by the
rays of the star and those too cold for agriculture. For many
generations, the town of Baharabad has migrated along a river, but
now the river appears to be drying up, creating a crisis. Seth (walker)
and Theo (sider), are surveyors, charged with charting the course of
their community's migration. Now they are faced with the challenge
of finding a new river to follow, one which has not already been
claimed by another community. On an expedition to the limits of
the habitable zone, they encounter what seems to be the edge of
the world. Is it truly the edge, and if not what lies beyond? They
join a small group of explorers who probe regions of their world
never before seen, and discover clues to the origin of their species.
This didn't work for me. If you read all of the background
information first (which, if you're going to dig into this
novel, I strongly encourage you to do), you'll appreciate the
effort the author went to in order to create a mathematically
consistent universe with two timelike dimensions, and to work
out the implications of this for a world within it and the
beings who live there. But there is a tremendous amount of arm
waving behind the curtain which, if you peek, subverts the
plausibility of everything. For example, the walker/sider
creatures are described as having what seems to be a relatively
normal metabolism: they eat fruit, grow crops, breathe, eat, and
drink, urinate and defecate, and otherwise behave as biological
organisms. But biology as we know it, and all of these
biological functions, requires the complex stereochemistry of the
organic molecules upon which organisms are built. If the motion
of molecules were constrained to a cone, and their shape
stretched with rotation, the operation of enzymes and other
biochemistry wouldn't work. And yet that doesn't seem to be a
problem for these beings.
Finally, the story simply stops in the middle, with the great
adventure and resolution of the central crisis unresolved.
There will probably be a sequel. I shall not read it.
August 2017 