Part 3/9:
A pivotal point Andreas makes is the vital role of proof-of-work in ensuring the immutability of Bitcoin’s ledger. Many associate blockchain technology with unchangeable records, but he clarifies that it is specifically Bitcoin’s proof-of-work mechanism that guarantees this feature.
Rewriting history on Bitcoin would require an immense computational effort—re-calculating the proof-of-work for all subsequent blocks—which is practically impossible at scale. Even colluding miners with 99% of hashing power could only manipulate recent blocks (roughly the last few dozen) before being detected. Beyond that, changes become computationally infeasible, making Bitcoin's ledger effectively immutable over the long term.