"In the mid-1980s Philip Candelas, Gary Horowitz, Andrew Strominger, and Edward Witten... discovered that each hole—the term used in a precisely defined mathematical sense—contained within the Calabi-Yau shape gives rise to a family of lowest-energy string vibrational patterns. ...among these preferred Calabi-Yau shapes are ones that also yield just the right number of messenger particles as well as just the right electric charges and nuclear force properties to match the particles [listed in the book] ..."