Absolutely nothing about Bitcoin is a secret. It is one of the most open technologies in the world. Its open source, anyone can review the code, anyone can contribute to the code, anyone can run the software voluntarily and participate in the network, and anyone can use the network without permission. The entire history of all Bitcoin transactions is visible to anyone in the world too.
A Ponzi scheme is a fraudulent investing scam promising high rates of return with little risk to investors. The Ponzi scheme generates returns for older investors by acquiring new investors. This is similar to a pyramid scheme in that both are based on using new investors funds to pay the earlier backers. For both Ponzi schemes and pyramid schemes, eventually there isnt enough money to go around, and the schemes unravel
When you understand the technology behind Bitcoin and the reason it was invented, you will see that it is actually the total opposite of a Ponzi scheme.