From Wikipedia's article on Ponzi Scheme:
A Ponzi scheme is a fraudulent investment operation that pays returns to separate investors, not from any actual profit earned by the organization, but from their own money or money paid by subsequent investors . . . The system is destined to collapse because the earnings, if any, are less than the payments to investors.
Bitcoin does not, never has, and never will pay returns, therefore it cannot be a Ponzi scheme. It
may be a
bubble, but that is completely different.
From the same article:
A bubble is similar to a Ponzi scheme in that one participant gets paid by contributions from a subsequent participant (until inevitable collapse), but it is not the same as a Ponzi scheme. A bubble involves ever-rising prices in an open market (for example stock, housing, or tulip bulbs) where prices rise because buyers bid more because prices are rising. Bubbles are often said to be based on the "greater fool" theory. As with the Ponzi scheme, the price exceeds the intrinsic value of the item, but unlike the Ponzi scheme, there is no person misrepresenting the intrinsic value. With the greater fool theory in mind, some may invest even though they believe the securities are overpriced due to a bubble.