Tardis Computer in Castrovalva
"HYDROGEN A gaseous universally abundant element usually assigned to the first group of the periodic system, atomically the lightest known element. Chronically very active, hydrogen is highly explosive in the presence of oxygen and consequently has a heavy responsibility for the creation of so-called life-forms (qv). Among the adherents of Scientific Mythology (qv) the basic constituent out of which the Galaxy was first formed (see EVENT ONE) and evidence offered in support of this hypothesis includes its supposed appearance in spectroscopic analysis of massive star bodies."
A fairly interesting bit of technobabble gobbledygook which wouldn’t have been legible when Castrovalva first aired. Science is presented as “mythology,” and there’s an awful lot of bet-hedging (“so-called” life-forms, the “supposed” presence of hydrogen in stars).
Note that Event One is not the Big Bang. The term is somewhat misleading.
According to the TARDIS computer, Event One is the formation of the [Milky Way] Galaxy out of an in-rush and explosion of hydrogen. Nyssa says it, too. In Castrovalva, the TARDIS is hurtling back to the creation of the galaxy, not the creation of the universe.
Scientists are still debating galaxy formation, but the theory of galaxies forming out of the collapse and contraction of clouds of hydrogen (the most abundant element) was the dominant theory in the 70s and 80s.
The other interesting thing is that TARDIS database speaks if there’s still only one pertinent galaxy, even for a time traveller. Apparently hopping the huge distances between galaxies is something even Time Lords don’t do very much (or at all). If so, might there be races as advanced as theirs in other galaxies? Do they really have the monopoly on the web of time that they think they do?
Yes, that’s a lot to extrapolate from a bit of gobbledygook that no viewer was expected to see.
ETA: One more thing. A reminder that this episode aired well before the internet came together and about a decade before the web began. “Library computers” were still part of science fiction, rather than everyday reality, except for specialized mainframes used by the military, corporations or research institutions whose databases were restricted to their own data. One couldn’t look things up on Wikipedia back then. Nor could the writers of Doctor Who!