Luncheon Encounter

I often meet Mike for lunch at Panera Bread, normally arriving before he does. I was standing in line when the man with a white mustache behind me asked how fast the line moved. I told him fairly fast as there were three cashiers. Just then three in front of us left to go elsewhere so he said it that made it move faster. Then he jokingly asked the others in front of us if they wouldn't like to go elsewhere too. (None did.) When I got my food I selected a table for four. When he got his he asked to join me. (It was rather crowded.) I agreed, of course. He was attending a conference for teachers of physics. He was a retired theoretical physicist from the University of Arizona. I had been wondering how they knew the speed of light and how they knew it was constant and took the opportunity to ask him. The speed can be measured and the original way used mirrors on mountain tops. Maxwell's equations told them it was constant. I didn't get an answer for the reason why it is the same for all observers. Mike joined us then and on hearing the man's occupation, asked me if I had asked the man my questions, which I just had. Mike introduced himself and the man said they called him J D. Mike told them about his work in statistics for the social sciences in which J D showed considerable interest.

Later I looked for him on google. After a couple of false starts I used "physics faculty" with "University of Arizona" which gave a list from which I picked out J D Garcia. From this I located several citations including two which included a picture verifying it was the correct identification.