The Density of Power
'Tis the (endless) US presidential primary season, which accounts for my not keeping up with my own blog. So let's talk politics. Not, you may be relieved to know, the Iowa caucuses, though - shameless plug time again - you can read my piece here explaining this mystery of American politics to the European Courier's readers. If you have an urgent need to know my own biases this election season, here you can read my comments at Daily Kos.
Politics is about power, and political power, like power in physics and engineering, can be characterized in part by its density - how much of it is available in a given volume of space. Consider two related terms that came into popular use roughly a century ago: gunboat diplomacy and battleship diplomacy. Both mean much the same thing: If mutual understanding through dialogue is not achieving the desired results, perhaps mutual understanding through dialogue plus a handy warship or two will produce a diplomatic breakthrough.
Gunboat diplomacy and battleship diplomacy differ only in the number and caliber of guns carried by the warship (and resulting incidentals such as size and cost). A battleship is a much greater concentration of power, but paradoxically it is the gunboat that conveys more power, because behind the gunboat, implicitly, is not one battleship but an entire fleet of them. Where Teddy Roosevelt would have had to send a battleship to encourage deference to the respect for the flag, Edwardian Britain needed only a gunboat flying the White Ensign to remind everyone exactly who ruled the waves.United Fruit Company
It was Britain's enormous maritime power density - embodied, in the early 20th century, by some 50 battleships and 120 cruisers, with scores of bases to support them - that allowed it to exercise sea power symbolically, with gunboats rather than battleships. Nearly a century later a relatively weaker Britain needed a task force to emphasize to Argentina that the Malvinas were still the Falklands after all.
At still lower power densities, even the prospect of sending a task force becomes uncertain; the only persuasive arguments are those you have at hand. Thus from the 16th through the 18th centuries European countries built Indiamen - large merchantmen, armed and equipped nearly as men-of-war - for oceanic trade: ships able to carry their own insurance, as it were. At the other extreme, the potential power density is so high that no battleships actually need to be built; nothing but gunboats (call the coast guard cutters) may be required.
It is not rocket science to see that power density would have its role in space as well. The Galactic Empire in Star Wars evidently does not have the power density it would like to have; otherwise a few star destroyers would be enough to keep those local systems in line, and the Death Stars could all stay in port. The Trek Federation, by contrast, seems in pretty good shape. In spite of great-power rivals like the Klingons, it is able to keep order using quasi-warships like the Enterprise - quite a bit more than a gunboat, but scarcely a full-fledged battleship.
The Firefly / Serenity 'Verse occupies a more ambiguous portion of the power-political spectrum. Serenity is no armed merchantman (impressive restraint for Hollywood SF), let alone an Indiaman, but there does not seem to be much law and order at her ports of call. Some armament might not be such a bad idea, if only Mal could afford it. The Alliance certainly has cruisers and presumably a battle fleet, but even after winning the War Between the Worlds, its power density out toward the rim seems fairly tenuous.
Power density thus determines the flavor of the setting. Where power density is very high, action is more or less limited to barroom brawls or stealthy capers - anything more and the place will be crawling with cops. The Patrol in Space Cadet and other Heinlein juveniles is at or near this level of power density. At a somewhat lower power density you get Honor Harrington, or any of the endless variations of space fleets. At lower power densities still you get RPG style scenarios - armed tramp freighters, space pirates, quasi-independent space stations, all jostling one another, but none able to impose its will with much consistancy.
The rocket science comes in making the physics assumptions fit the setting, and making the setting consistant with itself. If stellar empires are a travel year apart, they are probably not at each other's throats, because they are not in each other's face. Given such vast space, even formidable star empires face a low power density. A task force will take two years simply to reach enemy territory and return, not counting whatever time it spends doing whatever you sent it to do. Armed trading fleets - a return to something like Indiamen - might be plausible over such long distances. On the other hand, if rival battle fleets stand guard a couple of weeks' travel apart, the effective density of power is much higher, and armed merchant ships are far less likely. Determine the overall power density of a setting, and you will know what sorts of conflicts to expect there.