In quantum theory, a particle can run along two paths at once. When measured, we catch it on just one. According to Niels Bohr, all other possibilities vanish instantly — like a branch snapped off a trunk. Yet Hugh Everett insisted: the tree of reality grows all its branches at once, and we only see the one we’re on.
Researchers measured a single photon — a particle of light — three times, as if peering into the tree at three different moments. They found an elusive link between measurements — a hidden coherence. The “broken” branches hadn’t vanished; they continued to influence the visible outcome. Moreover, each measurement leaves an imprint, like a growth ring on a cross-section.
But give the tree a shake — introduce even a tiny external noise — and the delicate shoots wither, leaving only the main trunk. Then the result looks as if the branch broke off immediately. In everyday life, heat and vibrations quickly erase the traces of alternatives, making the quantum world seem unambiguous.
If branching is real, there are doubles of you who remember different experimental results — and perhaps, different life choices.
The idea of parallel worlds inspired Neal Stephenson’s novel “Anathem”.