A scientific explanation specifies the reason *why* some fact is the case or (or the reason why some event came about). A justification specifies someone's good reason for believing in the truth of some claim. For example, my justification for believing that the dinosaurs went extinct is that I have seen no dinosaurs around, and I have never heard any reports of living dinosaurs, but I have seen all of those fossils, and scientists whom I trust say that they have good evidence that dinosaurs once roamed the earth. But that's not the reason why the dinosaurs went extinct. The explanation (according to our best current theories) involved a large object crashing into the earth. Notice that my justification for believing that the dinosaurs went extinct does not concern my knowledge of the reason why they went extinct. Notice also that I could be justified in believing in some claim even if, as a matter of fact, the claim is false. A physician, for instance, might be justified in believing...

I, too, have heard it said that the phrase "before the Big Bang" is meaningless. One analogy I have heard drawn is between the phrase "before the Big Bang" and the phrase "more northerly than 90 degrees north latitude". Just as the latter phrase refers to no real location on Earth, so the former phrase is supposed to refer to no real location in time. According to cosmology's current picture of the Big Bang (as I understand it), the analogy is apt. (Of course, that doesn't rule out the possibility of further scientific developments resulting in corrections to the theory of the Big Bang.) It may seem unsatisfying to you that a scientific theory could just rule out as "meaningless" a notion that seems pretheoretically to be perfectly sensible. Intuitively, it seems like the question "What happened before the Big Bang?" ought to have an ordinary answer, rather than a cop-out answer like "There is no such time." However, the history of science is full of examples of questions that were once thought to...