Does it make sense for physics to predict the unphysical? I hear people say things like 


*

*"inside a black hole the laws of physics are not valid" or 

*"there can be parallel universes with different physical laws" or 

*"before the big bang there was nothing". 
Can physics really make such predictions?
Is not there a logical issue here, namely, is it possible to predict a system where all physical theories break, by using only validated/well-established/working theories of physics?
 A: Yes there is an issue, that's why people saying these things are at best borderline unscientific.
The best principle (so far) how to tell what is scientific or unscientific (we can expand it to science in general) was most probably given by Karl Popper. In short it says, that the statement (hypothesis) is scientific, if it provides any means to be potentially proven wrong.
Notice two things: first, we don't demand it to be "proven right" or anything similar, because basically you can never be 100% sure if the thing that always worked so far (like gravity, or any other milion times verified principle) doesn't suddenly stop working tommorow. So we consider all our physical understaning as a stuff that merely "worked every time we tried so far". It can be disproven once we find a case where it does not work, but it can never be proven.
Second, "means to be proven wrong" guarantees testability of the statement. In your case, if someone says that there may be parallel universes with different physics laws, he has to provide some form of prediction, that will turn out one way if he is true (that would mean non-disproving his theory, not proving), and the other if he is false (that would disprove his theory). If he doesn't provide any test, that means that measurable reality does not depend on whether he's true or not, then this statement is unscientific - unphysical. Basically, why should we care if it does not really change anything?
For the example statements listed, we would have to look at their exact wording to determine their "scientificness", because I can imagine some of them being completely ok.
