The Evergreen Tree of Probabilities ⚡ экспресс
Two common interpretations of quantum measurement—collapse (usually associated with the Copenhagen interpretation) and unitary—predict different fates for unrealized amplitudes after measurement, but until now this has not led to experimentally testable differences. In collapse, amplitudes disappear irretrievably; in the unitary picture, the apparatus registers one of the outcomes while remaining part of an entangled state that preserves all amplitudes. Using sequential single-photon measurements of a tunable quantum state, it has been shown that with three or more measurements, the theories' predictions diverge. Analysis of the joint density matrix of three measurements reveals coherence between them and confirms the unitary theory. When decoherence is explicitly introduced, the joint density matrix of the system and apparatus becomes consistent with collapse. The work clarifies the dynamics of multiple measurements and offers a new perspective on the interpretation of quantum measurement.
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”.