A day or two ago I watched Primer again. I originally watched it years ago, but I decided to watch it again. I was surprised how clear the movie seemed to me now, compared to the first watching. So clear, that I decided to make a video of it!
WARNING: SPOILERS. THIS VIDEO SPOILS THE ENTIRE MOVIE "PRIMER". WATCH THE WHOLE MOVIE BEFORE WATCHING A MINUTE OF THIS VIDEO.
This video explains the events of the movie from all beginnings to all ends, in a concise and clear meta-chronological order. Excerpts from the actual movie are provided for context.
I hope this helps anyone who has problem understanding the complex plot of that movie.
-- The box transfers whatever is inside it backwards and forwards in time, between its start (point A) and its stop (point B). The objects inside can exit at any time during their ride by their own volition, but if they never make that choice, they nevertheless are automatically ejected after a random number of roundtrips averaging about 1300 rounds, and it always happens at point B. Exiting at some point in middle of A and B is extremely dangerous.
-- This means that an inanimate object inserted at point A will travel back and forth an odd number of times before exiting at point B, and an inanimate object inserted at point B will travel back and forth an EVEN number of times before exiting at point B immediately after it was inserted. Both of these examples were demonstrated to Aaron in Monday.
-- That's why they get fungus in the beginning: An object inserted today for 7 hours actually experiences about 1 year in the box, because the object can't exit earlier by its own volition.
-- This doesn't explain why they don't get fungus inside the larger boxes. It is also worth noting that fungus does not thrive in oxygen-poor argon gas.
-- It is interesting how the device they made grew from mutual discoveries, and that originally they were aiming for something completely different (antigravity). Time travel was just a side effect. In real world, many great inventions have been discovered in a similar manner. No single inventor can claim honor for the whole end product (though they often do... *pout* Edison). It is built on small independent discoveries.
-- It is also worth observing the fragile nature of the friendship between the two main guys. They keep secrets from each others. Aaron lies even to his wife about what really is making noise on his attic. And so on. And what do they use time travel for? It is a symbol of power. Men are hardwired to seek power. In terms of time travel, power is control. The farther back you can start over, the more power you have. Aaron stole Abe's position of having most power, and gave Abe an inferior one. Money is power too. The first thing they used time travel for was money. Only a passing thought was given to where the money came from.
Addendums & errata *SPOILERS*:
-- I wrote that the person who receives the phone call is the drugged time-travel-ignorant Aaron, but according to Carruth, it's actually Abe.
-- When Abe is explaining to Aaron about fungus and time travel, it is evident that Aaron has already experienced these events before. He demonstrates prescient knowledge of the upcoming "engineers when they turn 40" joke for instance. Beginning at the first park scene, any time you see Aaron, it's an Aaron that already has traveled through the Failsafe once.
-- While Aaron clearly did discover the Failsafe at Tuesday morning, it is possible he actually took the ride at some later day, not immediately. It is unexplained how he knew everything that he's telling in the phonecall. In my timeline, he doesn't know much, unless the latest Aaron tells him, but even he doesn't know yet what Abe did when he came back.
-- My explanation relies on interpreting "the boxes are recyclable" in that once you have made the trip back, you can make another trip back in the same box. The note about "modular design of boxes" was unrelated. You can reuse a box many times without folding a box inside another. This means that Aaron took back just one box, not two. When Aaron made his second trip back, he reused the same box he used the first time around. In the end, there is no "third" failsafe running somewhere still carrying Aaron to the past. And when they redid the party several times, they just used the same boxes over and over again. And, I think, they could have safely opened a box to see if Granger is inside, even though Abe did not dare at that point. Once something exits at "A end", there is nothing inside the box, for it is already a new timeline.
-- Any time they both travel, 2 new revisions are created. Any time their doubles travel, an infinite sequence of new revisions is created recursively. These are not explored.
There's more to be said, but I hit the video description length limit of 5000 characters!