On Mon, 25 Apr 2011 16:11:51 -0400, Yousuf Khan
wrote:

Well, actually, the density wave theory wasn't conclusively proved yet
to call it debunkable, true. But somehow the density wave theory had
become the favoured theory.

No theory is ever proven, conclusively or otherwise. The density wave
theory is favored because it has both theoretical and observational
support. This new theory forms a theoretical basis, but is thus far
missing any observational support. And of course, as I noted, both
theories can be correct- they are not necessarily mutually exclusive.