Dark Age of Technology
"In ancient times, men built wonders, laid claim to the stars and sought to better themselves for the good of all. But we are much wiser now."
- Archmagos Ultima Cryol - "Speculations On Pre-Imperial History"
"The Day Science begin to study non-physical phenomena, It will make more progress in one decade than in all previous centuries of it's existence"
- Nikola Tesla
The Dark Age of Technology (or just the Age of Technology) was a period of history before the Imperium of Man, where human civilization flourished and spread throughout the stars. It takes place shortly after the discovery of the Warp-drive and the Navigator gene.
Thanks to Warp travel and the Standard Template Constructs, humanity is able to spread far and wide, settling millions of planets and driving out the xenos-civilizations before them. The result is something of a golden age for humanity, with technological wonders (beyond even the Adeptus Mechanicus's ability to
recreate comprehend) being constructed and laws of physics being re-written.
The Age of Technology ended because humanity became too dependent on technology and on Warp travel. They lost the former with the rebellion of the Men of Iron, and they lost the latter as the increasing incidence of psyker rampage (by not being able to control their powers) and Eldar partying too hard caused Warp storms, Enslaver plagues, and close encounters of the daemonic kind on settlements and spacecraft (think "Event Horizon"). With humanity disrupted by these losses, the aliens that were thought to have been driven off, came back for that sweet sweet vengeance, and so humanity fell into a period that would later be known as the Age of Strife.
The "Dark" in "Dark Age of Technology" comes because, after the Age of Strife, the wars of the Great Crusade and Horus Heresy, and then the long millennia of the Age of the Imperium, almost no records remain of this age. It is "dark" because it is almost entirely unknown, and the closest thing we can know about how Humanity lived during this Age was the Interex, that were more advanced than the Imperials, but were unfortunately wiped out by the Luna Wolves, manipulated by Erebus. It is also called a "Dark Age" because it was a spiritual dark age compared to the "glorious modern age", because humanity used to worship science (which may or may not have caused the birth of the Omnissiah), rather than the God-Emperor of Mankind. The irony of this is lost on every human in the setting. The only remnants of the technological wonders of that age (called "archeotechnology" or "archeotech," which the Adeptus Mechanicus furiously seeks), are the STC, that could be the Imperium's salvation. Others, like the Men of Iron, are best left alone (or better yet, destroyed). Pff... good luck getting a tech-priest to not poke around the possibly-dangerous ancient technology, though.
Although sources differ and generally conflict, most point to human technology in this time gradually approaching but nowhere near surpassing that of the pre-Slaanesh Eldar. Highlights of the technology that has been hinted canonically, include still-pristine warships with bridges made of solid light, something equivalent to time-weapons, and a cloud of sentient nano-machines that can kill you by making your blood explode. Dark Age humanity wasn't nothin' to fuck with.
TL;DR: It's basically Star Trek meets Atlantis.
List of reasons why the Dark Age was kickass
A.k.a. why the Emperor is kind of a failure.
- Widespread immunity to all diseases and poisons (The Panacea).
- Far more widespread use of anti-gravity.
- Guns that can travel their ammo back in time so they can hit their target with 105% accuracy and shoot blackholes.
- Robots with the strength of Space Marines that numbered in levels close to the Imperial Guard.
- On a similar note, Sentient AI's. Or close enough too it to be highly capable but not close enough to be people.
- Imperator Titans were practically universal in most planet's PDF.
- Average humans performing really hazardous duty like deep space mining or maintenance of a voidship's plasma coils had access to Terminator armour. Well, not exactly Terminator armour as the Space Marines use; but those incredibly durable exoskeletons-cum-spacesuit that were used by civilians while performing their day job back then served as the template from which Terminator armour was developed by the AdMech. After they recovered a bunch of them during the Great Crusade, they only had to add auto-senses, black carapace interfaces and whatchamallicks to allow a Space Marine to use the suit like a regular set of Power Armour.
- Weapons that could shoot enemy ships in the middle of a warp jump.
A basic Fanon timeline of the Dark Age of Technology http://www.heresy-online.net/forums/155-homebrew-40k-fluff/211473-fanon-history-dark-age-technology.html#post2375305