Space is big. You just won’t believe how hugely, vastly, mind-bogglingly big it is.
But space is just 3 dimensions, there is also time, and there is also X. In Star Trek, apart from the usual travels in space and the occasional travels in time, we also have twice seen travels in X: a few visits to the Mirror Universe, and the Kelvinverse. These are not alternate universes, they are dimensions, because an alternate universe is a branching point, and the more time passes after the branch, the greater the deviation will be. Despite several decades after the branching point in the Kelvinverse and several centuries in the Mirror, we still see that the same people are being born, having the same meta-relationships, the same destinies. That implies that these are not separate universes but still fundamentally tied to the Prime. There is a Platonic underlying universe and these are different projections in a lower dimensional space, perhaps.
Having established that there is a dimension X, consider that it is common to H2G2. The Guide Mark II is able to directly manipulate X, even outside the X-unstable ZZ Plural-Z Alpha zones (which contains the Earth, and presumably most of the core federation, which is not coincidentally where most of the X-traveling shenanigans in Star Trek lore occur). Denizens of Plural zones are explicitly warned not to travel by hyperspace because they can be catapulted unpredictably along X, so most of the early galactic civilizations favored warp drive instead of hyperspace jumps. Much of the Second Phase of H2G2 occurs in a different X than the Primary, and we get some exposition about different-X versions of Zaphod in the Tertiary and Arthur in the Quaternary Phases, and Zaphod even managed to make a business model out of it in Hexagonal Phase.
What we know of Galactic history is that about 5 million years ago, and the “about” will become very important in just a moment, there was a Galactic Empire, where “life was wild, rich, and on the whole, tax-free. In those days, spirits were brave; the stakes were high; men were real men, women were real women, and small furry creatures from Alpha Centauri were real small furry creatures from Alpha Centauri. And all dared to brave unknown terrors to do mighty deeds to boldly split infinitives that no man had split before.” I can think of no better description of the Original Series than this. Of course, there is some distortion, as 5 million years have passed from Kirk’s “men were real men” years and the relatively depressed era of Zaphod and Ford. Magrathea allegedly got its start in this era, as a means for the fabulously ultra-wealthy to spend money on custom planets (implying at least a Kardashev Type II civilization). However, if we allow for the fact that the Golden Age of the former Galactic Empire could span a million years of its own, then Magrathea could well have existed a million years before Kirk and crew. Or much, much longer – because a Type II civilization is not a transient thing.
My theory is that the former Galactic Empire was founded about 4 million years prior to the Zaphod era, and about 3 million years prior to the Kirk era. Lets establish Kirk taking command of the Enterprise in TOS as our zero date: 0 KE (Kirk Era). Dates before this point are BK (Before Kirk). The Zaphod Era (ZE) begins approximately 1M years KE. A few important dates immediately can be established:
2M years BK: Magratheans build Mira’s Earth
2M years BK: Ford and Arthur stranded on prehistoric earth with the Golgafrinchans
1M years BK: Fall of the Galactic Empire.
300 BK: Arthur Dent rescued from the destruction of the Earth by Ford Prefect, who has accidentally traveled 5M years back in time without realizing it.
10,000 KE: the Last Temporal Cold War
1M KE: the Galactic Republic, administered by the Vogon bureacracy, at its peak. This is where most of the canonical story of H2G2 takes place.
There certainly are some problems here. But most of those can be resolved by the fact that the Galactic Republic was notoriously more irresponsible about time travel than even the Federation was during the Temporal Wars (plural). After all, the whole Cathedral of Chalesme fiasco, which led to Slartibartfast’s involvement in the Campaign for Real Time, is evidence aplenty of just how screwed up the timeline became. The vast Dark Age between the Kirk and Zaphod eras was irresistible to tinkering, profiting, and just general screwing around by the various Powers That Be.
Ultimately, a lot of the general wierdness, like Miri’s Earth, Apollo, and whatnot that happened during TOS, not to mention the strange discontinuities around the Enterprise NX-01, which could actually be another poster child for the Campaign for Real Time to protest, can be explained by understanding that Star Trek and H2G2 happened in the same Galaxy – adventures in space, time, and X. I am sure this is a field of potentially rewarding inquiry for other researchers with more procrastination time than myself to pursue.
(for the purposes of this essay, I am treating only the radio scripts of H2G2 as canon. Yes, I am a purist. The book versions, and the regrettable movies and TV shows, can be considered different-X.)