"Hi, dear E = mc 2, what are you doing? It seems that you are deeply meditating on something," a physicist saluted and chatted with the famous and great equation. "I have been pondering over the fundamental question, why does mass have energy? In fact, this thorny question has been constantly baffling me for quite a long time. Moreover, I have been asked this question many, many times over the entire last century," this great equation replied candidly...