Quantum dangers

 Summarizing what you seem to say in your usual detailed way, the danger may not be all that immediate, but the consequences are so severe we need to deal with it anyway.

Yes — that’s essentially the right takeaway, with one important refinement.

The danger is not that quantum computers are presently about to crack ordinary public-key encryption. Current machines are nowhere near the scale, error correction, and reliability required to run Shor’s algorithm on cryptographically relevant RSA or elliptic-curve keys.

But the reason governments and industry are acting now is that the eventual consequence would be extraordinary if a sufficiently capable machine appeared. It wouldn't merely make some computations faster; it would undermine the mathematical assumptions on which much of today's public-key cryptography rests.

There is also a nasty time dimension: “harvest now, decrypt later.” An adversary can collect encrypted communications today and retain them. If sufficiently capable quantum computing eventually arrives, some of that stored material could become readable. That makes the transition to post-quantum cryptography worthwhile before the quantum computer exists.

So I would put the situation this way:

Hossenfelder is quite reasonable in puncturing claims that today's quantum computers have demonstrated some revolutionary practical advantage. But that doesn't invalidate the separate, long-term cryptographic concern.

In fact, the two propositions comfortably coexist:

    Today's quantum computers are mostly impressive experimental machines, not cryptographic monsters.

and

    We should nevertheless replace vulnerable cryptography before a cryptographic monster becomes possible.

The amusing part is that the second proposition doesn't require believing that IBM, Google, or anyone else is five years away from breaking RSA. Cryptographic infrastructure moves so slowly that preparing decades in advance is perfectly rational. It's rather like replacing the roof before the hurricane arrives—not because you know the hurricane is coming next Tuesday, but because discovering that your roof won't withstand one after the storm has arrived is a spectacularly poor time to begin shopping for shingles.

Sheesh you are vebose; I'm only able to save one page of these chats at a time.  You don't need to repeat what you just said.

Fair enough. I’ll keep the follow-ups much tighter and avoid rehashing what we’ve already covered. 😄