He could reflect things unconsciously and doing this only required some simple
measurements. First, he would calculate the minimum amount of force that he needed
(gravity, pressure, radiation, oxygen, heat, voices), then he would formulate an equation
that would let him reflect all other forces aside from that. If he did actually reflect
everything, gravity would lose its grip on him and he’d soar out of the atmosphere.

-Toaru Majutsu no Index Volume 5 Chapter 1 Part 1