Causal Nexus -

Elias spent his life following the equations in the notebook. He built the Chronos Engine, a device capable of piercing the veil of the multiverse. But as the engine roared to life, the Library began to burn. The friction of the time-fissure ignited the ancient scrolls.

Elias stood in the ruins of the Great Library, clutching a charred leather notebook. He was a "Time-Sensitive," capable of feeling the hum of a —a point where time tracks diverged and collided.

“The causal nexus divided when Nyssa changed history... causing the universe to exist in two quantum states and releasing blinovitch energy.” Tardis | Fandom Causal Nexus

"The world ends in fire," he whispered to his younger self. "Unless you build the Machine." Perspectives on Causal Nexus

He emerged decades in the past, in the same Library, before the rot had set in. There, he saw a young version of himself reading by a window. Elias looked down at his hands—they were aged, his hair now a shock of silver. He walked toward the boy, the charred notebook heavy in his hand. Elias spent his life following the equations in the notebook

He didn't have a choice. To ensure he grew up to build the machine that would bring him here, he had to give the boy the book. He had to be the spark that started the fire.

For years, Elias had been haunted by a memory: a silver-haired man giving him this very notebook when he was just a boy. "The world ends in fire," the man had whispered. "Unless you build the Machine." The friction of the time-fissure ignited the ancient scrolls

The concept is widely explored in fiction and philosophy as a way to understand our interconnected reality.