In the Quantum World, Even Points of View Are Uncertain | Quanta Magazine

To see how, consider two frames of reference; we will label them A and B. Suppose the origin of A is attached to a quantum object that has the probabilities of being found in different places. From B’s point of view, A’s location is contaminated elsewhere. But from A’s point of view, the distance to B is removed. It seems that B is the superior.

It gets better. What if B is also attached to a quantum object in a higher two-dimensional space? A’s quantum state is then split in two different ways, depending on the potential states of B. Because choosing B’s quantum state determines A’s state, A and B are now entangled.

In the example above, two quintessential properties of quantum systems – superposition and entanglement – depend on the reference structure. “The main message is that most of the goods that we think are very important, and in an absolute sense, belong to a relationship” or a relative, said Anne-Catherine de la Hamette, co-author of the paper. recently.

Even chronology succumbs to the power of quantum reference frames. For example, from another frame of reference, we can see the click of the detector occurring at a certain time. But from a different frame of reference, clicks can end up being more likely to happen before and after another event. Whether you see clicks happening at a particular time or at a higher order of events depends on the choice of frame of reference.

A stepping stone to Gravity

Researchers hope to use this flexible quantum theory to understand the mysterious nature of gravity. Einstein’s general definition, the classic theory of gravity, states that gravity is the distortion of space-time by a massive object. But how will spacetime be distorted if the object itself is at the height of two places? “It’s very difficult to answer with conventional quantum physics and gravity,” said Viktoria Kabel, a researcher in Brukner’s group and co-author of the new paper.

Switch to a reference frame whose origin is at a higher level, however, and a large object can end up in a clear position. Now it is possible to calculate its gravity. “By finding a simple quantum reference frame, we can take on an intractable problem [and make it] a problem for which we can only use ordinary physics,” said Kabel.

Such visual changes should be useful for evaluating future experiments that aim to place large numbers of people in superpositions. For example, physicists Chiara Marletto and Vlatko Vedral from the University of Oxford proposed to place two masses at each point of two spheres and study how this affects their magnetic fields. The increasing effort to formally define quantum reference frames can help to understand this investigation of the interaction between gravity and quantum theory – an important step in the study of quantum gravity.

Renner thinks that quantum reference frames can also be a tool for elucidating the foundations of quantum physics. A few years ago, he and his colleague Daniela Frauchiger devised a quantum theory experiment that creates a logical contradiction. The resulting confusion seems to suggest that physicists must give up at least one of the many well-accepted theories about our world — say, that quantum theory is universal and applies to humans. together with atoms.

Renner, however, now suspects that the confusion arises simply because physicists did not take reference frames seriously. No one has yet found a way to write this or other thought experiments using quantum reference frames, but doing so “could lead us to a resolution of the differences,” he said.

It won’t be easy, because quantum reference frames come with many unsolved problems. For example, with old reference frames, if you change your view from one frame to another, this change can be reversed: you can return to your original point of view. It is not clear that this is now universally possible with quantum reference frames.

Also, at this point, there is no standard way to define and translate between quantum reference frames. Different groups of physicists have different approaches. They all seem reasonable [at] at first glance, but they’re not enough,” Renner said.

Ultimately, however, quantum reference frames may be essential to understanding the quantum world.