The initial state at time T is recorded. After T+1 the delta between T and T+1 is stored. This continues for every (T+N, T+N+1) pair.

A recording of state X, is the process of saving all the information contained in X.

Calculating the delta between two state recordings is straightforward. The video game state consists of bits in RAM. RAM is manipulated after every clock cycle. The delta is simply the difference between the bits of two states.

The state is defined as all bits in RAM for a clock cycle at time T.

This is not “complete” time travel. It is not possible to travel back to any point T that came before the initial state. It is also not possible to travel to any point in the future that was not recorded before. All we can do is go back and forward in the space between T and T+N, N being the last step recorded.

I shall call this “time-local” time travel.

What is possible is the creation of different histories. For example one could travel back in time and start a new recording H1. Now it is not only possible to travel back and forward in time but also to switch from history H1 to history H0.

We define history as a “continuum” of steps from T to T+N.

This type of time travel is similar to the one shown in Rick and Morty Season 4 Episode 8 “The Vat of Acid”. In it Morty uses a “save-point-device” which makes it possible to save the current state of the universe (blue button) and then go back to it at a later point in time (red button).

save-point-device

How would an implementation as described above look like for the universe?

Recording the entire state of the universe is impossible, because there has to be some space (in the universe) where we would have to store that state. Lets call this memory-space. We can not time travel inside the memory-space, because that would lead to an infinite regression.

That would make our approach not only “time-local” but also “space-local”. “space-local” in the sense that the space where time travel works is limited and can not include the whole universe.

Lets call that “time-space-local” time travel.

Do the laws of physics allow it to record some space in the universe perfectly? With our current understanding of physics that seems highly questionable. We do not even know if the universe is discrete or continuous (Our two best current theories contradict each other. Quantum theory suggests that the universe is discrete whereas the general theory of relativity describes space and time as infinitely divisible).

Maybe saving the state of our universe is not enough but keeping track of the whole multiverse is necessary. Rendering this approach at best an interesting thought experiment.

If the universe is discrete and has an internal “clock cycle”, which moves it from one perfectly recordable state to the next, “space-time-local” time travel is possible.