Running Backward - Williams Jeremy

Julian Wilson, a brilliant, African-American high school senior successfully constructs the world's first time travel device a few years after his father's death in order to see him alive again, but his younger brother, Darius, a fitness meathead and self-proclaimed ladies' man, has other plans for Julian's invention after he finds out what his nerdy sibling has been up to.

At the demands of Darius, the two brothers travel farther into the past for fun and exploration, but they get more than they bargained for when they come face to face with famous black pioneers whom they've only read about in their textbooks, and after saving Rudy, a slave from the nineteenth century, by bringing him back to the present with them.

Although the brothers are cautious about not changing the past, mistakes are made, history is altered, and the present is shifted in ways that even Julian's remarkable mind can't fathom, but does Julian's invention place him in a position of cosmic duty and moral responsibility? Darius seems to think so, steering the two brothers on a journey to right many wrongs, one in particular that could forever change America as we know it...