Temporal reversion, known in the series as "Return to the past", is one of the greatest and most useful properties of the Supercomputer. It allows the user to return back in time to a point of their choosing. Just how far back it can go is unknown, but it seems to be limited to a maximum of roughly two days. Each use of this feature doubles the processing power of the supercomputer, which in turn doubled X.A.N.A.'s potential power while it was bound to the Supercomputer in the first two seasons.
The person at the Factory Interface usually activates a temporal reversion after an attack to erase any damage caused to Earth. This resets Earth back to how it was before the attack and wipes the memories of everyone back to that point, except for people who have been scanned into the Supercomputer, who retain all their memories. Temporal reversions do not affect events or beings that are linked to Lyoko such as undoing possession or deactivating towers. Also, it cannot bring the dead back to life, as pointed out by Odd and Ulrich in Teddygozilla and False Start, respectively. Its power is based on physical alteration, manipulating every object, force, and living thing in range to a past state, and interfering with people's minds to revert their memories too, but restoring a life that has already died seems beyond its capability.
Jeremie is usually the one who activates the temporal reversion process, though all the other members of the team (except for William and Odd) are shown to be capable of activating it as well. Some of them have even attempted to use it for their own personal gain. For instance, in The Chips Are Down, Ulrich used it to win the lottery in a misguided attempt to prevent Yumi from having to move back to Japan, which got him kicked out of the group temporarily for increasing X.A.N.A.'s strength without permission. Franz Hopper, Aelita's father, used this feature 2546 times over the course of his research, becoming more and more mentally unstable with each return in time.
The return to the past program was used more sparingly after the episode A Great Day, when it was revealed that each use of the program doubles X.A.N.A.'s power. Also, since Aelita was still not fully human at that time, she was still stuck on Lyoko when a return in time was launched.
Temporal reversions can also be very dangerous; in Temptation, Jeremie used it with a headset that multiplied his intellect by 10. Every time he used it, it caused him serious brain damage. The design concept of this headset was created by Franz Hopper. Also, in the episodes The Pretender and The Secret, it is revealed that if Aelita (or anyone else on Lyoko) gets possessed by X.A.N.A. via the Scyphozoa, and a return to the past is launched without freeing the subject, it could have deadly consequences; Aelita would most likely end up under X.A.N.A.'s control for good.
Ever since X.A.N.A.'s escape from the Supercomputer in The Key, it no longer gained power when a temporal reversion was used. Because of this, Jeremie seemed more relaxed about returning to the past, even though sometimes it wasn't needed like in the first season.
In Code Lyoko Evolution, it is revealed that Laura modified the boundaries of the temporal reversion program during the episode Virus without Jeremie's knowledge to include herself to be unaffected by the memory loss effect. This seems to be the only alternative to remember events after a return to the past, which doesn't include the subject to be materialized into the Supercomputer. It was also revealed that the event can be specifically altered to erase Lyoko Warriors' memories as well by focusing it solely on the targeted warrior, if they would be too much of a risk for the group. In Mutiny, this was done by Jeremie to Laura, who lost completely every memory she had about the Lyoko Warriors and their fight against X.A.N.A. and Professor Tyron after she launched a preemptive attempt to destroy X.A.N.A. that nearly got William turned into X.A.N.A.'s slave once again.
It is unknown how and when the Lyoko Warriors first found out about this feature in the program, as it was never pointed out by Jeremie when he first discovered the temporal reversion function in X.A.N.A. Awakens.
Times When Used
- New Order
- A Great Day
- Final Mix
- The Chips Are Down
- A Bad Turn
- Attack of the Zombies
- Cold War
- Is Anybody Out There?
- Double Take
- Wreck Room
- Opening Act
- Hot Shower
- The Lake
- A Lack of Goodwill
- Guided Missile
- Canine Conundrum
- Cousins Once Removed
- Music to Soothe the Savage Beast
- Wrong Exposure
- Bad Connection
Season Five: Evolution
Some peoples' memories are immune to the return trip. This can be achieved by being run by the supercomputer, or being recognized by the supercomputer as someone to not wipe. The following individuals are immune:
|Jeremie Belpois||Gained in X.A.N.A. Awakens.|
|Odd Della Robbia||Gained in X.A.N.A. Awakens.|
|Ulrich Stern||Gained in X.A.N.A. Awakens.|
|Yumi Ishiyama||Gained in X.A.N.A. Awakens.|
|Aelita Schaeffer||Gained sometime in 1994.|
|Waldo Schaeffer||Gained, presumably, on first use.|
|X.A.N.A.||Gained, presumably, on first use.|
|William Dunbar||Gained in Final Round, though pieces of it bled through earlier.|
|William Clone||Assumed, since he was shown remembering behavior from an alternate timeline in A Lack of Goodwill.|
|Monsters||Inherent to the system|
|Laura Gauthier||Gained in Virus; lost in Mutiny.|