Answers for Authors: Where should I site a Galactic Empire? (re-published)

It's good to be Emperor...

You need an evil galactic empire, or a benevolent  planetary federation, to set your scorching page turner of space opera in. The problem is that, to help your readers suspend their disbelief, you now have to figure out a believable interstellar civilisation. And write it a plausible sounding history. With a way of being founded and of expanding that makes sense. And you can't look that stuff up with Google...

....weeeeell.... actually... 

I've spent far too much time reading papers and sitting courses on the search for extraterrestrial intelligences, so I know a surprising fact: Some very very clever brains (they include Stephen Hawking and Carl Sagan) have devoted serious man hours to what a huge galactic civilisation could be like. Not for fiction, but because they think we should be checking the sky in case there really is one somewhere.

That means there's a lot of stuff been written that can help you. Much more than a blog posts worth (I'll have to write a book... hmmm) so here I'll just try and sum up their thoughts on most important aspect, re-mixed for SciFi instead of SETI. And that big important aspect is, of course: Location, location, location.

It’s very much like looking for a house – you need to think about location, access to amenities, commuting, and what won’t break your budget. Admittedly the the plumbing is rather more complicated on an interstellar empire. And the call-out fees are a nightmare if it breaks...

"Suitable for a buyer who really likes space... ahahaha..." Never trust an estate agent nicknamed 'Slick' guys.

In much the same way that it’s only a truly exceptional house that doesn’t need the ground*, unless your empire builders can wave away fundamental laws of physics** you’ll at least need your location to fill some really basic needs:

• It will need an energy source. This probably means stars, but other energy sources – like the matter falling into a super massive black hole or the radiation beams of a pulsar, do exist. There is even a scale - the Kardashev scale - for rating any alien empires by how much power they use.
• It will need planets, or at the very least the kind of heavy elements planets are made out of  as building materials for artificial living structures like ringworlds.
• It doesn’t have to be friendly to life – your empire builders could have migrated there from a more hospitable part of the universe when they had the technology to handle the difficult conditions – but it needs to be close enough to at least one friendly environment for someone to have made the trip.

Then there are other things that it’s very useful to have, but a lack (or overabundance) of which could be overcome to a greater or lesser extent using technology or good planning:

• Commuting: You’ll probably want your empire to be small enough to get messages across in a reasonable time. Many authors do this by introducing a Faster Than Lightspeed (FTL) drive - although other methods, such as much longer than human-normal lifespans (via gene engineering or suspended animation), are also thrown about by both authors and scientists. But another way, if you’re not committed to an Earth centred civilisation, is to just set your empire in a part of the universe where the distances between stars are smaller than the five light years that the stars near Earth average (see below). If George Lucas can have a galaxy far, far away then why not you...?
• Stable environment: In the same way at you wouldn’t buy a house in the part of town where gangs occasionally leave heads in dustbins (although I once rented such a place), you wouldn’t set up a civilisation in a part of the galaxy where there are good odds that radiation from a supernova, neutron star collision, or belch from a supermassive black hole might fry it to a crisp. True, you could overcome this with technology, but let me assure you: No house alarm is truly unbeatable, and I expect that so no technological solution to stellar dangers will be either.
• Minimum age requirement: This goes hand in hand with the need for a quiet neighbourhood – young areas of the galaxy, like young clusters and star forming nebula, tend to be crowded with troublemakers like unstable blue giant stars, dense molecular clouds, and wandering black holes. Older locales tend to be much quieter, since the dangerous stars tend to have blown up or burnt out eons back. Older locales also have had more time to spawn native life forms who can rebel against (or ally with) your empire.
• Conditions suitable for life (of some kind) to arise: Not an absolute need - a sterile locale could be colonised from outside. Still, it’s simpler in terms of backstory for a thriving civilisation to grow up near to the planets that spawned them, and that means they need a few things: A stable environment, a ready supply of chemical energy, some form of chemistry complex enough to support things like DNA, and some way of mixing everything together – usually a good solvent like water – are generally regarded as the minimum. You can waive at least some of them, however, if you make your life form exotic : A.I, sentient gas clouds, energy based, or whatever your imagination can conjure.
• Life forms suitable to reach technological era: NASA and ESA are spending a lot of money looking for evidence of bacterial life on Mars, but it’s unlikely bacteria are going to build stargates or leave their home planet by anything other than accident^* . Hence you need creatures that could invent and use technology. 

Above: The stunning colours (which a human eye would never actually see) of a star forming nebula. A beautiful sight, but a very dangerous place to live.

Just based on those we can rule out some locations already: The great voids between galaxies would be impossible to build in without importing massive amounts of both matter and energy across billions of light years. Some galaxies have stars that are much further apart than normal, so trips would take longer and they would be scarce of energy and building material too. The same applies to the galactic halo, and intergalactic space. Active galaxies, where massive black holes are sucking down matter and belching back out radiation, are hard places for life to ever arise in or anywhere near. 

Above: The Andromeda galaxy - nice a roomy, lots of close packed stars, and private parking.

If you’re not employing FTL engines, or if they’re limited to some practical upper limit, you probably want some improvement on the travel times to the nearest stars to Earth -  so the Milky Way's galactic core is attractive with its close packed solar systems, but the risk of supernova, neutron star collisions, and mega flares from giant black holes make it much less attractive long-term. Something similar applies to young clusters of new formed stars, or active star forming nebula.


But there are good locations to be found - here are a few suggestions: 

• A multiple star system. The Universe abounds with stars and solar systems that are bound in small clusters by gravity, orbiting about each other. The individual stars are usually much less than a light year apart, often only light months or weeks, but there’s usually enough room between them for each star to have a habitable zone and fully developed system of planets. You could invent your own such star system - which is what the writers of the Battlestar Galactica remake did - for example: Four red dwarf stars with seven planets orbiting each star, might plausibly give you twelve habitable worlds (three in the habitable zone of each star) all packed into a light month of space^.  There would also be another sixteen uninhabitable but potentially mineable worlds. True, this is the entry level galactic empire - but it’s limited extent is compensated for with other advantages. In particular, if you want a real locale that is also close to Earth, then the nearest star system to Earth (the three star cluster of Proxima, Alpha, and Beta Centauri) actually fits the bill^^: Small by galactic standards, but still an empire greater than every civilisation of Earth combined.
• Globular clusters:  These collections of hundreds of thousands of stars have a lot to recommend them – they’re old, so there are few or no dangerous, radiation spitting, potentially explode-ey young stars around. Instead most of the stellar population are red dwarfs, with their tight wound systems of planets, or red giants destined to die relatively quiet deaths. Average distance between stars is down to less than three light months – so even a sub-light speed starship could cross between several star systems over the course of a year. On the downside: Planets orbiting any Sun-like stars would be pulled out of orbit by neighbouring stars, and Globular clusters are generally quite poor in heavy, planet building elements, so only fairly small planets (like Earth) would form around their stars. But these aren't showstoppers: Planets orbiting red dwarf stars would be much more likely to stay with their suns, as these hug their planets much closer, and some of these clusters do have enough planet forming elements. On top of that the age of these stars - 5 billion years at least -  makes it more likely for a technological civilisation to have had time to arise^°. Globular clusters are not without hazards to navigation However: The long dead blue super stars, the absence of which makes the cluster fairly quite, will have left behind things like black holes and pulsars, which will be concentrated in the core. 
• Open clusters: Open clusters, on the whole, are not great spots for civilisation building - most open clusters are both too young for any worlds to have given rise to complex life, and are filled with big, radiation spitting, supernova prone, blue stars. Older ones, where things have settled down, are rare – the members of open clusters are usually born with enough speed to escape the cluster, so they drift apart in a few tens of millions of years. But some of the biggest have got enough gravity to have stayed together for hundreds of millions, or even billions, of years. Examples are places like the Beehive cluster, which is coming up on 3/4 of a billion years old, and is composed mainly of red dwarfs and sunlike stars. Near the clusters core these are packed within maybe as little as 1/2 a light ear of each other, and while these clusters may not be old enough time for technological life to arise (that took over 4 billion years on Earth), they have had time for a stable ecosystem to form that would support colonists. 
• Ultra compact dwarf galaxies. These are quite a new discovery, and something of a mystery – tiny galaxies less than 200 light years across, that are as jam packed as the cores of globular clusters. Like globular clusters they’re mainly made of older, redder, stars and many of the same things apply to them, but they have higher levels of planet building heavy elements. 
• Giant elliptical galaxies: For the big dawgs only – old and stable but up to 6,000,000 light years across, one of these could be home to a titanic empire of trillions of star systems – and is more likely to be so than the Milky Way ever will: The majority of stars in these galaxies are old, stable, and long lived - and there are trillions, so they have a good chance of having spawned a civilisation. But these are vast, vast places that could swallow our galaxy without noticing, so your empire builders better have mastered a powerful means of FTL travel, immortality, or both. 

These are just suggestions, but there are locations out there to fit most plot needs. The question is, simply, what kind of empire does your Imperial Majesty want? 

Above: The Voyager 2 probe encounters the planets of a red dwarf star.

*  Space stations, maybe, would count.

** You could write an empire like that: A civilisation so advanced it can more or less conjure matter and energy out of nothing, lurking in the utter darkness between the galaxies. Sounds like it might have some potential in a very Lovecraftian way, no? But a civilisation that advanced would be capable of almost anything, and so would suffer from the superman effect – it’s almost impossible to write a story for them because it’s impossible to think up a problem or obstacle they couldn’t solve almost instantly. If you don’t believe me I cite every superman film since superman 2 as evidence. 

^* There really are plausible ways bacteria might naturally leave their home planet and colonise another by accident, such as riding the debris from a giant asteroid strike, but you’d need to be writing a very esoteric story for that to count as an empire. Some kind of communal bacterial intelligence might work, but you’d have to have your heroes charge into battle against the evil empire by scrubbing every kitchen work surface on the planet with Dettol. 

^For hard SF writers: That means the furthest worlds could be travelled between in five months with a starship that could hit 20% of lightspeed – a speed many researchers believe we could reach with engine designs we could build in the next century. A radio message could make the same journey in one month, giving a slightly better messaging time than existed between the furthest corners of the Roman empire.

^^Two sun like stars (alpha and beta centauri)about the same distance apart as the Sun and Saturn, with a red dwarf star (proxima centauri) orbiting the larger two at a distance of ¼ of a light year. There’s a confirmed planet in the habitable zone of the red dwarf, and a possible detection of one in a very tight orbit around one fo the Sun like stars. Small, undetected planets in the habitable zones of the sun like stars are possible. It’s very plausible to put a human colony around each of the stars, with the occupants able to visit each star system in less than a year with sub light speed engines. A small empire of three solar systems - but still bigger than every empire on Earth combined.

°^A civilisation taking in a whole such cluster would control hundreds of thousands of systems, but its inhabitents would need to be longer lived than modern humans, or have FTL – these clusters are often over a hundred light years in dimeter despite being so close packed.