The bootstrap paradox
A notebook goes round a time loop forever. Who wrote it?
Named after Robert Heinlein's 1941 story 'By His Bootstraps'
The poems nobody wrote
Sixteen-year-old Diya finds an old notebook in her bag that she has never seen before. Inside are twenty beautiful poems. A note on the front says: "Copy these out in your own handwriting. Trust me." It is signed by her.
She copies them, publishes them, and becomes famous. Forty years later, in 2066, she gets into a time machine and travels back to 2026 with the battered notebook, and slips it into her younger self's bag.
Young Diya finds it, copies the poems, publishes them… and the loop goes round again.
One day an interviewer asks her: "Where did the poems come from?" Diya opens her mouth, and realises she has no answer. She didn't write them; she copied them. Her future self didn't write them; she carried them. The poems exist, but nobody ever created them.
The puzzle
In a closed time loop, an object or an idea can exist without ever having been made.
See it for yourself
What's really going on
Unlike the grandfather paradox, nothing here contradicts itself; the loop is perfectly consistent. What is strange is that cause and effect go round in a circle, so the poems have no beginning.
Physicists who study time-travel solutions in relativity point out that the notebook itself causes another problem: every time it goes round the loop it gets older and more worn, yet it must arrive in exactly the state it left. Information, such as the words of the poems, can loop without wearing out, which is why bootstrap stories usually involve ideas, songs or inventions.
Unsolved. Whether such loops could ever happen depends on whether time travel to the past is possible, which is still unknown.
Think about it
If you could send one fact back to your younger self, what would it be, and who would have discovered it?