Attempts are also made to establish heptapod terminology in physics. Little progress is made, until a presentation of Fermat's Principle of Least Time is given. Gary explains the principle to Louise, giving the example of the refraction of light, and that light will always take the fastest possible route. Louise reasons, " ray of light has to know where it will ultimately end up before it can choose the direction to begin moving in." She knows the heptapods do not write a sentence one semagram at a time, but draw all the ideograms simultaneously, suggesting they know what the entire sentence will be beforehand. Louise realizes that instead of experiencing events sequentially (causality), heptapods experience all events at once (teleology). This is reflected in their language, and explains why Fermat's principle came naturally to them.