Brief Announcement: Sustainable Blockchains through Proof of eXercise

Cryptocurrency and blockchain technologies are recently gaining wide adoption since the introduction of Bitcoin, being distributed, authority-free, and secure. Proof of Work (PoW) is at the heart of blockchain's security, asset generation, and maintenance. Although simple and secure, a hash-based PoW like Bitcoin's puzzle is often referred to as "useless'', and the used intensive computations are considered "waste'' of energy. A myriad of Proof of "something'' alternatives have been proposed to mitigate energy consumption; however, they either introduced new security threats and limitations, or the "work'' remained far from being really "useful''. In this work, we introduce Proof of eXercise (PoX): a sustainable alternative to PoW where an eXercise is a real world matrix-based scientific computation problem. We provide a novel study of the properties of Bitcoin's PoW, the challenges of a more "rational'' solution as PoX, and we suggest a comprehensive approach for PoX.