Knives determine ages of humans Free

I would like to correct one small but common error in the article by Graham Fleming and Mark Ratner (Physics Today, July 2008, page 28). The terms “Stone Age,” “Bronze Age,” and “Iron Age” do not “refer to humans’ increasing mastery over those materials.” They have a specific meaning: the material most commonly used for making knives during the period in question. Today we are still firmly in the Stainless Steel Age, but there is evidence that we may be moving toward the Plastic Age—especially in airports.