Very Special Relativity
Time travel is simple to understand when you make up a bunch of stuff.
The Theory of Very Special Relativity holds that the dimension of time is fungible with space and energy, such that an individual can travel to the years 1885, 1955, 1985, 2015 as a function of the Flux Capacitor constant (1.21 gigawatts).
The reason that the universe ordered itself in these discrete units of 30-year increments puzzled scientists for decades, until "Plotnum Mechanics" was proposed, which suggested that these years served to make interesting time-travel adventure stories. Individuals travel in "packets" of 30-year intervals because that's easy to understand.
However, neither the theories of Very Special Relativity nor Plotnum Mechanics address the human issue of how gross it feels to be hit on by your high-school aged mother. Those questions are better left to the philosophers.