Riding MUNI and staring distractedly out the window, I imagined the multiverse, that in some orthogonal world the driver had sped up and whizzed past these buildings (are they there in the other world?) a little faster, we'd hit a different sequence of lights.
... or that the buildings were slightly taller, the light hadn't distracted the driver, causing him to slow down. Or that the buildings were painted a different colour; that the cars hadn't changed lanes, forcing the trolley to slow down; that I had caught a MUNI driven by an auto-pilot; that MUNI had precedence over autos; usw.
Walking home, I found a copy of Michael Crichton's "Timeline", a novel with quantum mechanics as its trope.