Time Leap

Time Leap/Time Leaping refers to an action, where a user transmits their present-day memories back to their past self. Attempts to alter events in this way cause the active world line to shift to a different, preexisting world line, containing the new events.

How Does This Work?
The technology here is an evolution on the Phonewave (name subject to change). The Time Leap Machine uses a headset to read a user’s brain structure and convert that to data, which is compressed to a small size by passing it close to a black hole (somehow, physical compression and data compression are conflated). The memory data, plus a decoding program, is sent as a phone message to the past using D-mail technology. Memories are written to the recipient’s brain using electromagnetic radiation when they answer the phone message. Limitations of the Time Leap Machine include the requirement that the sender and recipient be the same person (for brain structures to be compatible) and that the maximum time that can be leaped is 48 hours (or longer after upgrades in some stories).

The effect of time leaping on the active world line is straightforward: The sender’s memory data arrives at the designated time on another world line, which then becomes active. As is the case with D-mails, the newly activated world line will be one where the immediate effects of the time leap are consistent with that world line’s predetermined events. The new world line will only differ slightly from the previous one, so the time leaper can continue to make changes to events they have foreknowledge of, causing further divergence and world line shifts. (At this point the shifts are "changes in the Present".)

Okabe: "By sending my consciousness to the past, it felt like I could make concrete changes to the past, but at the same time, the results converged."

Okabe: "There are things that can be changed, and things the world prohibits changing. An example of the former is who kills Mayuri. The latter, Mayuri dies on the night of August 13th.

Suzuha: "That’s not it. The future is determined."

Okabe: "Then why does the process change?"

Suzuha: "Because the world line changed. Okabe Rintarou, when you leap into the past and take different actions from before, Divergence should only slightly fluctuate. But that fluctuation won’t register any more than 0.000001% on the Divergence Meter. In trifling cases, it won’t even be a significant change. When you change the cause, the only result is changing to a world line that already simultaneously exists. Furthermore, those two world lines are approximately the same, so you’ll barely even feel any changes."

Okabe: "So is that why I don’t feel any response from Reading Steiner?"

''Suzuha: "It’s not that the world line before the change is annihilated. It keeps existing simultaneously as a possible world line." —'' Chapter 3, Steins;Gate

As well as explaining time leaping, the above passage nicely confirms our understanding of world lines so far: When Okabe tries to contradict the events of history, he is only activating a world line where he took those new actions all along.

Time Leaping Does Move the Position of the Present
There are various examples of new D-mails, time leaps, and present day changes being carried out in the period immediately following a time leap’s arrival, so that period of time must be active. That period of history is genuinely re-experienced, allowing people to take new actions, unlike the period of time following a D-mail’s arrival. How can it be that time leaping moves the Present, but D-mails do not? It is certainly the case that the underlying technology is the same. The difference, as highlighted in Steins;Gate, is that one allows a conscious person to travel to the past.

Okabe: "One thing’s for certain, though - My consciousness leaps to the past along with my memories."

Kurisu: "I don’t understand why that is. Okabe should be experiencing something similar to when he sends D-mails. Does consciousness exist inside memories?"

''Suzuha: "It’s bothersome since consciousness doesn’t exactly exist physically. Same with the soul. In the end, it’s about religious views. Even in 2036, the existence of the soul hasn’t been proven, and nobody’s proven the form of consciousness, either." —'' Chapter 3, Steins;Gate