I think tech era has redefined the way people value a company? It is not based on the P/e ratio anymore, people keep buying stocks from companies that are not even making money yet. Basically most people are betting their money based on trust that these tech companies are going viral one day.
Either way, i'm not an economist so maybe that's just a high level or me being dumb
If I write you an iou for a million dollars, and you write me an iou for a million dollars, we can both be millionaires, and if everyone does that for everyone else, then we can all be millionaires, but only until too many people try to trade those IOU’s for something real at the same time.
If I then go to trade my million-dollar IOU for a house that now costs a million dollars because everybody has a million, that's a price increase. More dollars in circulation means higher prices for everything, which is inflation.
A bubble would be if I went to go buy a house and then found that your IOU was good for nothing and you didn't actually have a million dollars to give me. This was the situation in 2009 but doesn't appear to be the situation today.