Observers of Quantum Events Are Also Subject to Uncertainty

It gets better. What if B is re-centered into a quantum object at the top of two positions? Then the quantum state of A is now smeared in two different ways, depending on the possibility of B’s ​​states.

In the example above, two quintessential properties of quantum systems—superposition and entanglement—turn out to be frame-dependent. “The main message is that many of the structures that we think are very important, and in some ways complete, are relative” or relative, said Anne-Catherine de la Hamette, author of the latest paper.

Even the order of events is overcome by the complexity of the quantum reference frame. For example, in another frame of reference, we may see a detector click that occurs at a certain time. But from a different frame of reference, the click may end up at a higher point of occurrence before and after another event. Whether you see clicks happening at a specific time or as the top of different orders of events depends on your choice of frame of reference.

A Stepping Stone to Gravity

Researchers hope to use these changing quantum ideas to make sense of the mysterious nature of gravity. Einstein’s general relativity, which is the classic theory of gravity, states that gravity is the warping of the fabric of space-time by mass. But how will spacetime turn if the object itself is at the height of two places? “That is very difficult to answer with quantum physics and general gravity,” says Viktoria Kabel, a researcher in Brukner’s group and author of the new paper.

Switch to a reference frame whose origin is at a higher point, however, and a large object can end up in a vertical position. It is now possible to calculate its gravitational field. “By finding the right quantum frame of reference, we can take on a problem that we cannot solve [and make it] it’s a problem that we can just use the known general physics,” said Kabel.

Such conceptual changes should be useful in the analysis of future experiments that aim to place very small crowds in high places. For example, physicists Chiara Marletto and Vlatko Vedral from the University of Oxford have proposed to place two masses in one place in one of two places and study how this affects their gravitational fields. Increasing efforts to formally define quantum reference frames can help make sense of this investigation of the interaction between gravity and quantum theory—an important stepping stone toward a quantum gravity theory.