Is the concept of rest mass correct?
All these years, we (me, and my classmates of Undergraduate 1st Year) have been accustomed to the concept of rest-mass, and the relativistic transformation of mass at speeds of the order of c. We had been introduced to this concept during our school-years, we were comfortable with it for quite a long period of time, until yesterday, when our teacher declared with a convincing degree of confidence, that it is not mass that changes relativistically, but rather, it is the momentum possessed by the body, that does so. Mass, as he says, is an invariant. P.S., he even declared that the conception that we had so long "cherished" in our hearts, is a wrong-one. Naturally, the whole class was wonder-struck. I am looking here for views on the subject from other, reliable sources, because I am (rather, we all are) in rather a big-dilemma whether to accept our teacher's view, or to reject it. You should know, that our undergrad. classes have started just 3 days ago, and at the very onset, we have faced a heavy-weight punch.