Although I absolutely do not like wormholes (As a physicist, I think the physics is really bad, and I am also a black hole skeptic), the solution that Bill has landed on is the least bad version of it, and I do like the chained stargate concept and the railroad analogy. Here are a few ideas that immediately popped into mind about that:
– The stargate is analogous to a form of rail gun, which in turn justifying literally calling the travel network a railroad.
– I propose shorter jumps so that traveling on the railroad requires e.g. 50 jumps per lightyear, so that you get a hypnotic rythmic feeling to the travel, and one can then imitate the sound of an actual railroad:
https://www.youtube.com/watch?v=TA4mhuFF-Go
So traveling 7 light years requires something like small 350 jumps. It will make the travel network much closer to the railroad both in cost and feel.
However, I also think that this allows for a significant technology upgrade in a later season. The idea is as follows: on one of the alien planets, a colonist is studying alien life on the planet and finds something really really weird: transmutation and meta-materials.
There is in fact surprisingly strong evidence of transmutation in biology, even on earth. Basically, some organisms are capable of transmutating atomic elements into other elements. In effect, they are able to something akin to fusion and fission at low temperatures.
This is not merely sci-fi, but an actual phenomenon observed on earth today, and there are physicists working on explaining it and the Structured Atom Model (SAM) is one of these models to explain it.
Just being able to find transmutation is itself a really cool side plot on a planet, but there is more. One of these biological materials that they find along with the ordinary materials are so-called meta-materials. Unlike ordinary materials, these have very unusual structured properties at the atomic level that allows them to manipulate spacetime. The physical theorist Jack Sarfatti has theorized the existence of these materials and believe they can explain FTL in alien ships (if they exist).
So on this planet, FTL is not observed, but instead the biologist observes biological anti-gravity. That is, some organisms are able to hover using biologically generated meta-materials that involve the same process as transmutation.
The physics of this is absolutely fascinating and although it is currently sci-fi, it is sufficiently close to reality to warrant in a sci-fi series.
So a potential plot could be this: this xenobiologist is able to extract these metamaterials and concentrate them, for the usage of antigravity devices. This is done by creating negative spacetime curvature, and it does so at low energy levels and low temperatures.
Those, who are familier with the Alcubierre drive will immediately recognize that one of its key ingredients is negative curvature. Thus, these biological meta-materials can be used to create a low-energy Alcubierre drive!
How’s that for a plot? This in turn opens up a way of “flying” through space, instead of using the railroad. It also opens up the possibility of colonization at a far greater distance than can be reached through the railroad.
I believe that this would be a great expansion in a later season. Bill talked about a secret planet and a secret railroad to it. Well, here is a possibility of incorporating a very good reason for keeping things secret: xenobiotech.