bubble*
Bitcoin can be a bubble. And that bubble has popped a lot of times; and will continue to pop a lot more in the future.
Bubble suggests more negatively that it was never valid to begin with which is unfair I think and especially when its been around so many years now. The price is certainly volatile and during this time, Dollar itself has varied quite alot in value.
If you want contrast pricing on Bitcoin then also look at Dollar index value. The ticker would be DXY and you should get result on google or many different finance websites.
Bitcoin is not a bubble overall but it is part of the dollar story and how dollar backs global trade while also being centred around just one countries economy which is not really a good basis for trade it seems. I do not think bitcoin takes over from Dollar but that does not make it an invalid asset, it has a utility to it which since December 2017 has improved.
This utility increase is important to set it apart from just price decline as the longest decline from 2013 onward was due to failure in a central exchange and loss of confidence from that 'deleveraging' Bitcoin had during 2013 become fractionally based thanks to Mt.Gox failed accounting and and overly centrally traded price.
Right now Bitcoin did involve itself with credit card purchases which again is a form of leveraging and leads to failure and bad pricing. This effect has lessened and I think little fraud was involved this time, I do not see the situation as serious as the mt gox failure. A fallback can be a positive and does not mean we see a lower population in Bitcoin usage, so long as development continues we have good reason for optimism.