Weight and Quantum

• WEIGHT

Among popular listings like CoinMarketCap/CoinGecko only few projects are open blockchains, rest of 8-18k listed are privite money, free-floating or stabilized. Open blockchains are only trustless because of entrepreneurial energy bets of miners, one can grab two chains, compare chainworks, apply heuristic about mining algorithm and calculate chain weight in burned energy. Usually not important, but critical in a time of contention, forking. After absolute weight is known, it's also important how secure a chain is - how much time it would take for current global hash of this algo to rewrite it

Bitcoin is the heaviest open blockchain sitting at about 800 quadrillion Joules (assume 8 Joules/terahash average mining efficiency and grab last chainwork), the most secure with 1200 proof-of-work equivalent days of double SHA-256 (most invested and industrial algo). All other open blockchains quickly decay in Power law in weight and security from my estimates. Biggest open blockchains by market capitalization: BTC, LTC+DOGE (tied due to merge mining), XMR, BCH (ETH was one of them, no longer since September 2022), smaller ones are not very interesting for me

By weight in petajoules, very rough estimates: BTC 800, LTC 50, BCH 5, XMR 2-10. By security: SHA256b investments far outpace Scrypt and especially RandomX (Qubic was attacking XMR in the range of $mlns of attack cost or less)

So, as I see it: nothing comes close to Bitcoin, only Bitcoin Cash is moderately interesting and worth a hedge because of SHA256b tug-of-war and BCH's chain-of-signatures elegance

• QUANTUM

As I understand, biggest threat by far is Shor algo, once written as a quantum program, running at 2000+ logical qubits, once built - to coins locked in pay-to-public-key scripts, P2PK coins. Pay-to-pulic-key-hash (1x... addresses, witnessed P2WPKH - bc1...) P2PKH coins are safe from the initial vector, attacking them would require bundle of algos and will be much more expensive and probably require bigger quantum computers. It seems that a guess of 5-7 years to 2k qubits is reasonable

Best practice in Bitcoin is to have only one funding transaction per each address, otherwise it could be P2PKH with exposed public key, vulnerable on the same level

My best understanding of mitigating suggestions: BIP-360 on Bitcoin and Quantumroot on BCH that they are depend on coin holders preparing. In scenario when they don't, if a quantum attack is surprising and fast, I would expect forks of affected open blockchains - freezing consensus-vulnerable coins or letting them be revealed (effectively stolen) back into circulation

Then, I would just follow the heaviest fork between them (within Bitcoin consensus, and separately within BCH consensus), price will be the major factor of either fork staying heavy, or lightening up, and either fork retaining security or losing it