A "bubble" imo is a positive price movement when there is nothing to back it up anymore.
You can get into a cascading effect where the price is driven sky-high because people are investing in it because the prices are going sky-high turning the whole thing into a self-fulfilling prophecy.
Only when a person or a group, which have a big enough share, figure out that the price is utter bullshit and pull out (or no new investors want in) does the "bubble" "pop". Due to the fact that the price plummets and everyone already knew that the price was bullshit, will everyone start making a run for the exit driving the price into a crash.
With bitcoin it is hard to tell if we are in a "bubble". The price is based on a tekst string and has no usable value, this is equal to fiat where the paper itself has no real value. Is the euro a bubble, is the dollar a bubble? these questions are equally hard to answer. If fiat can survive bitcoin most certainly will survive since nobody controls it. Some virtual coins will therefore become strong like euro's or dollars in fiat-land and others will become virtual Zimbabwian dollars which are completely worthless.
It's all about trust and acceptance and only time will tell which will survive. As we know from historic events like VHS vs Betamax we know that it is not always the best that wins.
Are we in a bubble? Nobody knows. Does it feel like a bubble? Not to me but who am I.
You described the mechanics of a bubble very well there. In short, a bubble is when price is totally detached from real value (to the upside).
But BTCs latest movements on the upside and the downside were driven by positive/negative news, changing the game in a fundamental way. eg: China is out to a large degree = BTC is worth less now.
But there have been long threads made about that bubble discussion before. It just became totally aparent to me after that crash (I suppose we won't go much lower than the lows we have already seen, otherwise I might have to reconsider) that it hadn't been a bubble at all.
Most people on this forum (not you) think bubble means "extremely fast and high rising price", which is just stupid. Most people on here know about BTCs technical side, but seem to have absolutely no feeling for trading and economics.