Secret metadata from our cell phones has already begun compiling a rich 4 dimensional model of every second of every inch of our world. Gradually the existence of this immersive database will leak to the people, just gradually enough to become accepted. Common knowledge will coincide with the extinction of the obsolete concept of privacy.
Google Time Machine will be launched. Recent history will become searchable in the removed, floating, smoothly rotating fashion of Streetview.
Without warning all of Earth's history dating back to the Cretaceous will become available. The explanation will be a pseudoscience involving reflected photons rebounding from particles/planets many light years away and reconstructed into an accurate model. The public will reluctantly buy the story.
Thanks to Augmented Reality, any time period can be overlaid as a skin onto your perception. With the turn of a dial, you can witness any terrestrial event.
Tenses become confused and meaningless. Simultanaeity is redefined.
Just like Google Earth circa 2010, certain sensitive areas are altered for national security purposes. The detonations at Hiroshima and Nagasaki can be relived in every gruesome detail, but JFK's assassination will be blacked out. The bombing of Pearl Harbor is pixellated as to remove specific details. The attacks of 9/11 are tampered with in obvious ways and this is exposed in a worldwide scandal.
The extent of the tampering is called into question. A group of zealots following Philip K. Dick's Exegesis as gospel gain in popularity, denounce all of reality as the "Black Iron Prison", gather in 1980's Orange County to draw wisdom from every twitch and murmer of the amphetamine addicted sci-fi author.
Dick gives subtle clues that he is aware of the crowds surrounding him invisibly, drawing more followers, until at last, Events are altered. Perhaps hacked. Something new happens in the past. The Prophet Dick addresses his followers in a convenience store parking lot, giving a perversion of the Sermon on the Mount annointing the first row with syrupy droplets from the curved spoon-end of his slurpee straw, and announces that all of History has been a lie. Even the world we knew before GTT was an altered overlay. The progression of time is a cruel joke imposed by that program. There is no Time. The world is still. Unchanging. It is/was/has always been the Roman Empire and we the people have always been/are/always will be powerless under their rule.
The sermon happens once, is written down by thousands, but is never searchable again. It continues as a myth. A miracle. A glitch. The last reliable acount of a singly occurring event.