Why is light travelling in "straight" line? (see restrictions) Here's a question: Why is light travelling in "straight" line? Of course there will be those of you to jump on the question and say it's not a well defined one and they'd be right. For that purpose I'll restrict the question a bit. Consider the question limited over "small" distances and far from "extreme" gravitational fields and allow for some "small" margin of error to compensate for the rest of the causes of bias. If that restriction is not quite enough, then consider the question as a fifth-grader would understand it, or picture the line drawn by a green laser in a dark room. So... is the line straight? I'd assume so. So are photons traveling in the same manner? I'd assume so... But then - there are phenomena such as interference patterns, which don't quite work if everything was plain straight, photons must be able to take multiple paths simultaneously in order to interfere with themselves. Then why doesn't that happen to the laser beam?