Neil Agarwal

1. How does Algorand replace the proof of work in Bitcoin?

Algorand no longer needs proof of work because the next block is decided through consensus by all the users. Through BA*, users form committees and engage in agreement sessions that eventually result in deciding the next block. Moreover, Algorand avoids Sybil attacks by employing proof of stake in the block proposal step – this ensures that an adversary cannot just create several accounts to improve his or her chances of being a block proposer. 

2. Why are forks unlikely in Algorand?

Forks are unlikely because as soon as a block is declared ‘finalized,’ it can no longer be removed from the ledger. The only way forks can occur is if the block is declared tentative – this happens when there is a form of network asynchrony or more than 1/3 of the users are adversarial. Although a block can become tentative, it is rare that future blocks will also become tentative due to the probabilistic nature of the algorithm. It is of high probability that the next block after a tentative block will become finalized and therefore make the earlier tentative block finalized as well.