2.2 World Period, Technology, Media, and Available Objects Lock
Day Zero takes place in a world roughly equivalent to 2003.
This is a global world lock, not only a detail of Part 4. It affects, from Part 1 onward, what characters know, how they communicate, what can be found in stores, vehicles, homes, warehouses, and convoys, and how culture returns later.
The world is a world of DVDs, video stores, CDs, burned CDs, Discman players, early MP3 players, a rare and expensive iPod, radio, television, home computers, simple digital cameras, flip phones or old phones, home internet, and news websites that can gradually collapse under load and failing infrastructure.
There is no modern smartphone culture in the saga, no iPhone, no TikTok, no Twitter, no Instagram as a central space, no consumer AI, and no world where every character carries a supercomputer in her pocket.
Every future object found in the field must fit this period: DVDs, tapes, CDs, burned CDs, CD players, early MP3 players, a rare iPod, radio, car tape decks, simple projectors, small generators, old digital cameras, batteries, cables, old chargers, desktop computers or old laptops.
Any object that did not exist or was not plausible in a 2003 world does not enter the story.
Immediate implication for Part 1: Family Video / the video store in Chapter 2 is not only a plot location, but a period anchor. It locks DVDs, movie shelves, rental culture, movie arguments among Steve, Robin, Mike, Dustin, Will, and Lucas, and the pre-collapse world as physical material that can later be found, carried, lost, and returned to the camp.
Implication for the music line: Finchel, especially Rachel and Finn, do not bring music back through streaming or a modern digital world. They bring it back through body, voice, lyric notebooks, CDs, burned CDs, Discman, early MP3 players, a rare iPod if found, old speakers, batteries, a generator, and live instruments. This prepares culture and music returning in Parts 4 to 7.