Navigating Known Space
The Milky Way is a bustling city of four
hundred billion stars a hundred thousand lightyears across
. The exciting part is downtown, the galactic core where the
stars jostle close, packed dense around a black hole the mass
of two and a half million suns. The core is a violent place.
In the Known Space universe it's is actually exploding, though
humanity won't find out about it for twenty thousand years.
In the real universe the core is full of dense gas clouds,
intense radiation and frequent supernovae. There's no reason
that a world in the core couldn't develop life, but it isn't
likely to last long before some galactic catastrophe wipes
it out again. By contrast, Known Space is an insignificant
backwater a few dozen lightyears in diameter. It's located
on the unfashionable side of the Orion arm, out in the quiet
suburbs of the galaxy. Nothing exciting ever happens out here,
which is a good thing from the perspective of complex life.
The stories that encompass involve a few
dozen worlds in our stellar neighbourhood. Humanity has colonized
a handful, the Kzinti have a substantially larger number.
We know of a few other species but have only a vague idea
of the number of worlds they might occupy. Known Space is
one of the larger and better developed science fiction universes,
but the stories have really only scratched the surface of
what's out there. Known Space is tiny compared to the galaxy,
it's immense on human terms. As part of the background research
for Destiny's Forge I downloaded the Gliese Near Star catalog
and used an excellent piece of freeware called 3D Starmap
to map out just what's out there in our immediate neighbourhood.
I discovered there are well over twenty five hundred stars
within fifty lightyears of Earth. It now seems that most if
not all stars have planets, so, if our system is typical,
with ten planets, three of them being at least theoretically
capable of supporting life at some point in their history,
that puts about eight thousand worlds within our grasp. That's
a lot of real estate. Not all of those worlds will be even
marginally habitable. However we now enough about life to
expect to find it anywhere the minimum requirements are present,
liquid water and a source of energy. Even the water may be
optional. Life may require only a solvent of some kind, with
water being just a common and therefore easy choice. With
baseline conditions that easy to meet its clear are hundreds
of useful planets and billions of species yet to be discovered
out there. Intelligent life will be much rarer, how much so
is very difficult to guess. Still, there's a lot out there..
There are places worth getting to in Known Space.
In Niven's universe starships get to those
places using the quantum hyperdrive. Hyperdrive is a technology
gifted by the Outsiders, deepspace dwelling aliens whose biological
working solvent is liquid helium. It works only where space
is relatively uncurved, which is to say far, far away from
a star's gravity well. It is a natural technology for a deepspace
species to develop, and a very difficult one for any civilization
that likes to live on planets. The outsiders sold the technology
to humans from WeMadeIt in return for the use of icy outer
planet moons for their own purposes - a very good deal indeed.
We don't know how the technology works, the Outsiders won't
sell that information, at least not for a price we can afford.
However we do have a few basic facts. We know that it takes
you from star to star at a constant rate of three light years
a day. We know that entering a gravity well will make the
engine vanish - or perhaps more accurately will return the
ship to normal space and leave the engine behind in hyperspace.
We know that ships travel through hyperspace, whatever that
is, exactly. We know that if you look through a window into
hyperspace it does funny things to your visual perception,
and we know that hyperspace navigation is done with a mass
reader, a device that requires a living mind to watch it.
This isn't much to go on, but we can still
learn a lot about hyperdrive from it, in outline if not in
detail. Einstein's speed-of-light speed limit is absolute
for material objects moving through normal space, but the
laws of physics as-we-know-them don't automatically rule out
wormholes and other exotic solutions to the problem of faster
than light travel. Hyperdrive can be taken to exploit this
kind of structure in some systematic way. The three-light-year
per day absolute rate of travel can then be taken to represent
some fundamental characteristic of the structure of hyperspace.
On possibility is that there are two opposing forces acting
on a ship in hyperspace transit, one which is rate-independent,
like gravity and one which is rate-dependent, like air resistance.
Force A continually accellerates the ship, and Force B continually
decellerates it. As the ship goes faster and faster under
the influence of Force A, Force B builds up until it exactly
balances Force A, and the ship's speed becomes constant. This
is exactly akin to a freefalling parachutist reaching terminal
velocity. Exactly what Forces A and B are is another question.
The universe as-we-know-it contains only four forces, so we
have some serious looking to do. Even without knowing what
they might be, we can know about how they will act. Their
most important characteristic is that, like gravity, they
act on the ship's mass. This ensures that the three-light-year
per day limit will be completely independent of anything but
the characterstics of the forces themselves. No streamlining
or power increase will serve to speed up the ship, which corresponds
to what we know. We'll deal with the question of the much
faster Quantum II hyperdrive described in Crashlander in a
This reasoning implies that a ship's hyperspace
engines have nothing to do with actually moving it through
hyperspace, that's taken care of by Force A and Force B. The
inevitable conclusion is that their only job can be moving
the ship in to hyperspace. It's possible that once in hyperspace
a ship will stay there until the drive is used to move it
back out again, which makes the intervening journey free and
makes all trips take the same amount of power. However we
also know that running a hyperdrive ship into a gravity well
makes the ship vanish, unless the gravity gradient is very
steep, in which case only the engine will vanish. We also
know that there must be some constant power requirement to
driving a ship through hyperspace, or there would be no reason
not to build tremendously huge ships. The Quantum in the name
gives us a hint here. Quantum systems are always arranged
in discrete energy levels, and some levels are more stable
than others. Lasers work by pumping electrons from their rest
level to a high, unstable level from whence they immediately
fall to an intermediate semi-stable (technically metastable)
level, where they sit until a photon of the right frequency
comes along to trigger them into the ground state, emitting
another, coherent photon in the process.
... Page 2