Low-density physicists?

One thing that struck me when arriving at the Palais des Congrès was how sparsely populated it was by ICHEP participants. We tend to think of ICHEP as a large conference with more than 1000 participants, but in many other fields that would be a small conference; when talking on the phone to a friend who is a physician and mentioning ICHEP, she said "Well, I suppose for particle physics that's a lot of people" adding that a congress of hematologists she attended had more than 10,000 delegates. I suppose that technical or political gatherings will often be even bigger, and the Palais des Congrès is clearly laid out to handle those. ICHEP is thus a low-density conference when measured on the scale of low-energy congressology; physicists being physicists, the density becomes quite high near the coffee bar during breaks, though!