There was panic about doomsday but as I and other programmers stretched the year field from two to four characters, apart from scattered hiccups the lights stayed on. Everything about Y2K was known — the problem, the solution, and the deadline.

Q-Day is something else entirely.

Q-Day is shorthand for the moment when quantum computing crosses a line we assumed would hold—when the mathematics that secures modern life can be broken, and broken quickly.  On Q-Day the locks will be quietly and rapidly picked. And the unsettling part is that the thief may already have your safe, waiting for the day the combination becomes trivial to compute.

Today's encryption is a lock that would take an ordinary zeros-and-ones computer longer than the age of the universe — 26.7 billion years — to pick. The most widely used system—RSA with a 2,048-bit key—relies on the virtual impossibility of factoring "the product of two very large prime numbers."

A sufficiently advanced quantum computer, however, would not try every possible combination. It would use a fundamentally different method—one discovered by MIT mathematician Peter Shor—to solve the problem efficiently. What today is impossible would become routine. The world's assumption of security would no longer hold.

Data stolen today—bank records, corporate secrets, medical files, state communications—can be stored until the day it becomes readable, what analysts call "harvest now, decrypt later." It gives today's thieves a speculative claim on tomorrow's knowledge. But like all speculative claims, its value depends on time, uncertainty, and the actions of others. The longer the delay, the more likely the data is obsolete, replaced, or secured in a different manner or place.

There is no agreement about when Q-Day will likely arrive.  "Google thinks it could happen by 2029, while Adi Shamir—one of the cryptography experts behind the development of RSA encryption—believes it's at least 30 years away."

Meanwhile, something else is headed our way:

The technological singularity, the point where artificial intelligence surpasses human intelligence and begins improving itself in an unstoppable loop, is most commonly predicted to arrive between 2035 and 2045. That window has been shrinking. A few years ago, most experts placed it decades away. Now, some of the most prominent voices in AI believe the precursor step, artificial general intelligence (AGI), could arrive before 2030.