Will, how does the standard model turn an up quark into a down quark like when fusion turns a proton into a neutron? The explosion that was the BB, what was it composed of?
In the standard model W bosons link the up and down quarks. In fusion of an electron and proton, the electron emits a virtual W-, and becomes an electron neutrino. One of the up quarks in a proton grabs the W- and becomes a down quark.
The big bang wasn't really an explosion of anything, it was the birth of the space and time of our little pocket of the universe. Imagine the universe is the surface of a balloon. At the big bang, the balloon started inflating. That being said, we can't get all the way back the moment of the big bang- the reason is that the way we extract what should have been happening at earlier times is to take the physics we know and the universe now and run it backwards. Our knowledge of the MeV scale, though, allows us to get back to fractions of seconds after the birth of the universe (or our pocket thereof)
However, we simply don't have a lot of information on the TeV scale, but hopefully the LHC will change that eventually.