Hell, I don't know if it's what you call a "bubble," but I think I know why stock prices are so high. As I've said over and over, some people just have too much money, and they have to put it someplace. Bonds are paying close to zero, and thanks to a serious paucity of consumer demand, nobody is particularly interested in expanding real domestic business investment.
So, unless American companies seriously expect to sell a whole lot of crap they don't manufacture anymore to the Chinese and the Indians (unlikely), the run-up in stock prices is due more to "market forces" than anybody's intellect. Will stock prices drop again? Uh huh. Does that make it a bubble?
Maybe not. Depends on what you call a bubble. Anyway, who cares what you call it? To most of us, with just a little bit of stock market money in a TSA, who cares?