Quantum Timelock

Spiritron record anchoring band.
A Quantum Timelock is a metaphysical event, it calculates the average “value” of each parallel world’s events, then locks past events down. A phenomenon that separates what was, and is, from what might be.
Our universe allows for countless possibilities and creates many parallels worlds and histories with different developments.
The universe has a finite amount of energy to spend maintaining each parallel world. Because the universe itself would expire if these realities were to expand without limit, it conserves energy by, excising worlds, at specific intervals, that have veered too far from the strongest, most stable timelines.
The Moon Cell has concluded that the universe we perceive of, which should be unstable, is being stabilized across the present, past, and future by this culling process and by quantum time locks.
The easiest way to visualize the process is to envision time as a giant tree, one that would grow indefinitely if left alone. The excision process is comparable to trimming the unneeded branches and leaving only the trunk of that tree.
History that becomes a part of the “time lock”1 will not change, even if it is affected by the past and future. The incidents that occur during a time lock will, in fact, never change, no matter what happens.
Even if one were to go back in time before the time lock to try and change history, once one reached the time lock, history would be forcefully restored to what was already registered there.
In a universe with quantum time locks, the outcome that is registered in an quantum time lock will not change. A time traveler can only alter the “process” by which it happens, but never the “result.”

For example, imagine that there was a war in Britain, and that the “result” that was locked in afterwards was that Britain was destroyed.
Even if you could manage to travel back in time and affect history so that Britain flourished, the war ended peacefully, and everyone had a happy ending… the moment that history reached the time lock, it would cause whatever “corrections” were necessary to ensure that, despite your efforts, Britain was still destroyed.
You might be able to change the lives of one, two, or perhaps even a handful of people, but you could not change the course of the vast river of human history.
That is the “Quantum Time Lock,” also known as the “Foundation of Human Order” in the world of magecraft.

On the other hand, it could be possible to deny human history from its foundations by destroying a quantum time lock through some great feat. But even with that method the most that could be done is deny human history beyond the destroyed quantum time lock.

The ones who can determine the next coming quantum time lock are those living in the era. Past and future intervention cannot affect the quantum time lock.
Archimedes’ goal in this game is to completely destroy the Moon Cell before the next quantum time lock, leading to a base world that would start from that precondition.
While it is normally not something that could happen, to do that Archimedes continued to shift across worlds.
If Archimedes were to completely shut down the Moon Cell before the setting of the next quantum time lock from his subjective perspective, he would achieve victory.
Although Archimedes emerges victorious on several occasions, he is not able to destroy the Moon Cell in any timeline.
While Archimedes was endeavoring to bring his plans to fruition, the Main Character was able to prove proved the route of a world that was average yet with the most potential to grow, and the quantum time lock was decided.
And just like that, Archimedes’ plans went up in smoke.
By the way, the timeline where the Main Character entered the titan’s cavern with Archimedes and was split into several pieces (right after the start of the main story of EXTELLA) is listed as “Quantum Time Lock A,” while the True Nero route ending is “Quantum Time Lock B.”
No matter what Archimedes does within this timeframe, the final “result” has already been determined.

Translator's Notes
  1. ^ Literally “anchoring band” or “lock.”
Fate/EXTELLA material: Encyclopedia of Fate EXTELLA