It claimed to be secure and wasn't. The seed that claimed 128 bits of entropy in some cases only held 72, or 40, and the wallets were emptied not by breaking the math, but by searching the small space the seed actually occupied. Security here was a lie. Improbability was asserted, never generated. The block cannot be counterfeited; its improbability is witnessed by its own cost. The block burns where everyone can see it.
The security is not a property, it is a purchase. Exergy is the portion of energy that can still do work; the rest is entropy's cut. A block is ~79 bits of overcome improbability — 5.4×10²³ expected hashes, exact from the header's nBits, no assumptions. The Landauer floor — the least the universe could charge, granting one ideal bit per hash — is ~1,500 joules, the energy in a drop of gasoline. At that cost every coordinate would be easily forgeable. Instead, the spend is ~10¹³ joules, ~3 gigawatt-hours. The block costs seven billion times what physics demands and the overpayment is the arrow: what makes the coordinate un-redoable is precisely the exergy destroyed above the minimum. The ledger strengthens as it ages.
This exergy also anchors the blocks in time — a temporal coordinate. The stars on the other hand are a clock that you can read ahead. With mechanical equations you can compute where Mars will be next Tuesday, or where it was on any night centuries ago. Biff with an almanac, not an anchor for time.
The next block hash exists in no almanac; nothing computes it ahead. The only way to learn tomorrow's hash is to let the network burn its way there — every hash actually run, in order, paid for in joules that are irreversibly spent. You cannot spend tomorrow's joules today. Quoting a block proves you came after it: there was no almanac to cheat from, no way at any price to have known it sooner. The star clock is free and tells everyone the same time. The block clock, the timechain, has to be paid for — and the payment is the proof. Forging a coordinate isn't just redoing one block, it's redoing every block piled on top of it since. The past gets more expensive every ten minutes.
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