There are two components to price: what the thing is worth, and what you might be willing to convince someone else to buy it from you in the future for. The latter is the speculative component. The former must be related to some intrinsic property of the thing. For example, an orange has some minimum price, because if nothing else it's composed of matter and so can weight things down. If bitcoin is useless to transact, then its intrinsic worth is zero, so its price is 100% speculative. That's not so much a bubble as just air being pressurized by no container.