From a Bloomberg piece (link below) :
Unlike tangible gold and silver, digital currencies haven't had hundreds of years to prove their durability.
OK, bitcoin sure looks like it's a bubble. For one thing, there's that chart:
For another, if you follow the Investopedia definition that a bubble "is created by a surge in asset prices unwarranted by the fundamentals of the asset," there's the unsettling reality that this particular asset has no fundamentals. That is, there's no stream of income or collection of assets attached to ownership of a bitcoin. Bitcoins have no intrinsic value.
https://www.bloomberg.com/view/articles/2017-12-11/what-s-the-value-of-bitcoin-who-knows