Al may have retired at some time, but he never stopped doing science all the way until his 94th birthday.
Because of his background in physics, astronomy, and mathematics at CalTech, he could continue his inquiries into theory without the need for a laboratory or support. He was often a very free and original thinker who challenged the core of widely accepted, conventional theories. Some attempts are presented here.
Those of us who knew him best, though, realized that he eschewed the normal publication route in favor of private meetings with well-known scientists. We also know he was rejected by many of these workers and that this pained and humiliated him deeply.
You will have to judge for yourselves whether or not these were fresh approaches to problems ignored by other scientists that may become “cornerstones” for the future, or were blind pathways.