Let’s start by considering our hypothetical quantum system that can, when observed, come up either heads or tails. Gaining a sense of what exactly Ormrod, Venkatesh and Barrett have achieved requires a crash course in the basic arcana of quantum foundations. Holding on to absoluteness of observed events, it turns out, could mean that the quantum world is even weirder than we know it to be. (Cavalcanti, along with physicist Howard Wiseman and their colleagues, defined the term “absoluteness of observed events” in prior work that laid some of the foundations for Ormrod, Venkatesh and Barrett’s study.) Ormrod, Venkatesh and Barrett’s paper “addresses the question of which classes of theories are incompatible with absoluteness of observed events-and whether absoluteness can be maintained in some theories, together with other desirable properties,” says Eric Cavalcanti of Griffith University in Australia. “If we ever can recover absoluteness, then we’re going to have to give up on some physical principle that we really care about.” “It’s a demonstration that there is no pain-free solution to this problem,” Ormrod says. Such theories would, for instance, banish the possibility of a coin toss coming up heads to one observer and tails to another.īut their work also shows that preserving such absoluteness comes at a cost many physicists would deem prohibitive. In a recent preprint, the trio proved a theorem that shows why certain theories-such as quantum mechanics-have a measurement problem in the first place and how one might develop alternative theories to sidestep it, thus preserving the “absoluteness” of any observed event. This, in short, is why our imagined quantum coin toss could conceivably be heads from one perspective and tails from another.īut is such an apparently problematic scenario physically plausible or merely an artifact of our incomplete understanding of the quantum world? Grappling with such questions requires a better understanding of theories in which the measurement problem can arise-which is exactly what Ormrod, along with Vilasini Venkatesh of the Swiss Federal Institute of Technology in Zurich and Jonathan Barrett of Oxford, have now achieved. that observed events are not absolute,” says Nicholas Ormrod of the University of Oxford. “One major aspect of the measurement problem is this idea. But this accounting doesn’t define what constitutes a measurement-hence, the measurement problem.Īttempts to avoid the measurement problem-for example, by envisaging a reality in which quantum states don’t collapse at all-have led physicists into strange terrain where measurement outcomes can be subjective. Standard quantum mechanics accounts for what happens when you measure a quantum system: essentially, the measurement causes the system’s multiple possible states to randomly “collapse” into one definite state. Could they be certain that their result was an objective, absolute and indisputable fact about the world? If the coin was simply the kind we see in our everyday experience, then the outcome of the toss would be the same for everyone: heads all around! But as with most things in quantum physics, the result of a quantum coin toss would be a much more complicated “It depends.” There are theoretically plausible scenarios in which another observer might find that the result of our physicist’s coin toss was tails.Īt the heart of this bizarreness is what’s called the measurement problem. They perform the quantum coin toss and see heads. Imagine a physicist observing a quantum system whose behavior is akin to a coin toss: it could come up heads or tails.
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