We have been talking about whether economics is a real science. Physicists are mostly pretty suspicious of economics, because it isn't enough like physics. The problem with that defining principle, I think, is that it depends far too much on the state of the science at a given point. Physics, today, is a very mature science - possibly even an arthritic science. The same might be said of chemistry and geology, and biology isn't far behind. If you want to compare economics, you might need to compare it with pre-Galilean physics, or chemistry before Lavosier, or geology before continental drift.