Since many people try to convince us that Bitcoin is a bubble and how we will lose our money eventually, I wonder if money is not a bubble actually. There exist economies in which money has a positive value in spite its market fundamental is zero. That means fiat money has zero value. Fiat money is a social contrivance. We take money from other people because we know other people will take it from us. In theory and practice the fiat money is a bubble.
If bitcoin is a bubble, then anything used as a medium of exchange is a bubble. Because they both have deflationary attributes.
The term bubble is used to quantify irregularities and anything with vanishing tendency.
The value of a currency is in it worth at usage, so if someone used 1 bitcoin to buy a pizza when the value of bitcoin doesn't equal the present value, that doesn't make the spender senseless because it matched it value at the time of usage.
Therefore, the speculative nature of currency exudes bubbles.