Back in 1961, the Nobel Prize–successful physicist Eugene Wigner outlined a thought experiment that demonstrated one of many lesser-known paradoxes of quantum mechanics. The experiment exhibits how the unusual nature of the universe permits two observers—say, Wigner and Wigner’s good friend—to expertise totally different realities.
Since then, physicists have used the “Wigner’s Friend” thought experiment to discover the character of measurement and to argue over whether or not objective information can exist. That’s necessary as a result of scientists perform experiments to ascertain objective information. But in the event that they expertise totally different realities, the argument goes, how can they agree on what these information may be?
That’s offered some entertaining fodder for after-dinner dialog, however Wigner’s thought experiment has by no means been greater than that—only a thought experiment.
Last yr, nonetheless, physicists observed that latest advances in quantum applied sciences have made it doable to breed the Wigner’s Friend check in an actual experiment. In different phrases, it should be doable to create totally different realities and examine them within the lab to discover out whether or not they are often reconciled.
Wigner’s authentic thought experiment is simple in precept. It begins with a single polarized photon that, when measured, can have both a horizontal polarization or a vertical polarization. But earlier than the measurement, in line with the legal guidelines of quantum mechanics, the photon exists in each polarization states on the identical time—a so-called superposition.
Wigner imagined a good friend in a special lab measuring the state of this photon and storing the consequence, whereas Wigner noticed from afar. Wigner has no details about his good friend’s measurement and so is compelled to imagine that the photon and the measurement of it are in a superposition of all doable outcomes of the experiment.