Astronomers believe that our universe is expanding at an accelerating rate, which is curious if every particle of mass is attracted to every other. But imagine for a moment that all the matter in our ever-expanding universe is actually comprised of expanding particles, racing away from one another as they inflate through the vacuum of space. To view the crosseye stereoscopic animation below, simply cross your eyes until the left and right images converge in the center. It helps to keep your head still and level. Despite feeling a bit awkward, opthamologists actually use this method to strengthen the eyes. (It's probably worth mentioning that I am not an opthamologist... Your mileage may vary.)