If yesterday was the best day ever, wouldn't it be great to find a way to repeat it? A whimsical tale about happiness with sure appeal for science-minded kids -- and wise grandparents -- everywhere. What could beat yesterday's perfect day at the fair? Maybe nothing, one boy thinks, and he wishes he could go back and do it again. So he puts all his scientific knowledge to work, from stars to time machines to wormholes (is it possible...