According to Adric, Albert Einstein's Theory of Relativity was e=mc2, or "energy equals mass times the speed of light squared." (TV: Four to Doomsday) Amelia Rumford told the Fourth Doctor it stated that "you cannot travel in space faster than the speed of light, because the speed of light is a limiting factor. If you travelled more than a hundred and eighty thousand miles per second, you'd encounter the time distortion effect. [...] In fact, you'd arrive at your destination before you'd left your starting point."
The Doctor, in turn, called the theory "absurd", and said he'd "tr[ied] to explain the realities to poor old Albert, but he would insist that he knew best." He explained to Amelia that, aside from space warping, if one travelled in hyperspace, "another kind of space", they could theoretically avoid the time distort. (TV: The Stones of Blood)
Sarah Jane Smith told Lucy Skinner that her son Luke Smith could see the flaw in Einstein's Theory. (TV: The Last Sontaran) While the Sidhe Galastel was trying to explain his people's nomadic ways to Sam Jones, she thought he must be feeling like she would if she tried to explain the Theory of Relativity to a goldfish. (PROSE: Autumn Mist)