The report that wouldn’t stay the same
In the dim mission-control room, the flight director starts an incident report. Two tiny spacecraft have just shot past each other, and four crew members radio down simple yes-or-no ticks. The report should be one neat table. Then the time stamps clash, because each ship’s clock chops the night up differently.
The flight director taps the desk. If Charlie and Daniela both wrote down what they saw, then there ought to be one plain combined record, full stop. Like a single final report that lists everyone’s answers, no matter who was moving or which clock was used.
But the flight director wants something else too. Every step, even “checking”, should be undoable in principle, like a computer log you can roll back because nothing was permanently burned in. And no ship gets to be the “real” one at rest. Takeaway: can one report stay consistent when different good clocks disagree on what counts as together?
The checks are odd on purpose. Charlie and Daniela each copy an early yes-or-no into a memory slot, but in a way that can be reversed later. After that, Alice and Bob do an audit of the whole setup, device plus memory. They can first undo the copying, then ask a different yes-or-no about the same kit.
Using one ship’s clock to decide what happened “at the same time”, the report says Charlie and Daniela can’t both have the first outcome. Using another clock, it says Alice can’t get the minus-type result if Daniela got zero. Another clock says Bob can’t get minus if Charlie got zero. One absolute table would force Alice and Bob to never both be minus.
Then the flight director lines up time a different, still-allowed way, where Alice’s and Bob’s audits count as simultaneous. Keeping the same undoable rulebook for the whole labs, the usual quantum rule says the “forbidden” pair can show up sometimes: Alice minus and Bob minus. The report can’t hold one single table that satisfies every valid time-slice.
The flight director stops writing and just listens to the quiet fans. Either “what happened” isn’t one shared list that every competent observer must agree on, or the dream of perfectly undoable checking has to fail somewhere. The sting is how quickly it breaks: a few clean impossibilities, pulled from different clocks, and the one neat report falls apart.