Is Mass Conserved?

My question isn't directly concerned with states of matter, but it is that I recall Sheldon Glashow (spelling) who i believe is a theoretical physicist (?) said that when matter is converted into other matter that 'the law of conservation of mass' doesn't hold true entirely, and that some of the mass is actually, not there. The numbers 'displaced' were very small and unnoticeable. is this true? and if it is, what happens to the displaced mass?
- Christian (age 15)
Rapid City, South Dakota

I'm not sure what Glashow was talking about at the time but it is true, mass (as in sum of the rest masses of particles) is not necessarily conserved. Total energy, on the other hand, is conserved.   In an atomic bomb, isotopes of Uranium split into several pieces.  The total mass of the pieces is less than the mass of the Uranium.  The lost mass in converted into energy.  E =  mc² -->  Kablooie, as Calvin would say to Hobbes

LeeH

(published on 04/07/2010)