Can Matter be Created or Destroyed?

[Alex K]

Mass is simply the measure of how much energy of any form is contained in an object (*). Energy is conserved at short time spans, but can be converted and in particular, energy which appears as mass, can be freed from its confines and converted into other types. However, cosmic expansion removes energy from the universe via the redshift.

(*) This holds always. For example, a spring under tension has more mass than a relaxed one, precisely differing by the stored energy divided by c^2

somewhere in my reading, it was suggested that bosons (energy) are massless particles, while fermions (matter) have mass. To say that mass IS energy let's me know there's something I'm not understanding.

That statement is simply wrong. Of the four most massive elementary particles known, three are bosons - the Higgs, the Z and the W. Only the heaviest, the Top Quark, is a Fermion.

The only conceptual differences between bosons and fermions is that the latter have half integer spin and adhere to the pauli exclusion principle - that's it.