A Ponzi scheme is a fraudulent investment operation that pays investors with their own money, or pays old investors with new investors' money, rather than with the money earned by the company itself. When not enough new investors join, the Ponzi scheme collapses and the last investors suffer losses.
Bitcoin is a free software project with no central authority, so no one can make false statements about investment returns. Just like other major currencies such as gold, US dollars, euros, yen, etc., Bitcoin has no guaranteed purchasing power and the exchange rate is free-floating. The resulting volatility makes it impossible for Bitcoin holders to predict gains or losses. The fact is that Bitcoin is being used by thousands of users and businesses due to its useful and competitive characteristics.
