https://arstechnica.com/science/2019/03/...nd-of-can/

EXCERPT: “More than one reality exists” screams the headline. Cue sighs of tired dread from physicists everywhere as they wonder what otherwise bland result has been spun out of control. In this case, though, it turns out that the paper and the underlying theory are much more interesting than that takeaway. Essentially, modern physics tells us that two observers of the same event may never agree on the result, even if they have all possible knowledge. This is already accepted as part of special relativity, but now we have experimental proof that it applies to quantum mechanics as well.

Let’s start with the simplest possible example of how we typically resolve conflicting measurements. [...] Quantum mechanics takes this idea to a whole new level because the concept of a measurement is different. [...] Now let’s complicate things even more. [...]

This thought experiment, first outlined by Eugene Wigner, has now been realized in a real experiment. It was a bit complicated to implement. Essentially, the experiment's researchers set up an apparatus that makes measurements on polarization that, if successful, leave a record of the measurement encoded in a second photon. Thus, between the original measurement and a new one done on the second photon, we have a simple version of the Wigner experiment.

As predicted by the theory, the setup records cases where the measurement and the measurement of the measurement disagree. Indeed, the rate of agreement/disagreement is pretty much exactly as predicted by quantum mechanics. The conclusion, according to the researchers, is that there are no facts that do not depend on the observer. Or coarsely put, at the quantum level, you may have the option of choosing your own facts.

I don’t see this result as startling. We already know that there are no privileged observers in special relativity, so why should they exist in quantum mechanics? [...] It doesn’t say anything about reality, though. (MORE - details)

EXCERPT: “More than one reality exists” screams the headline. Cue sighs of tired dread from physicists everywhere as they wonder what otherwise bland result has been spun out of control. In this case, though, it turns out that the paper and the underlying theory are much more interesting than that takeaway. Essentially, modern physics tells us that two observers of the same event may never agree on the result, even if they have all possible knowledge. This is already accepted as part of special relativity, but now we have experimental proof that it applies to quantum mechanics as well.

Let’s start with the simplest possible example of how we typically resolve conflicting measurements. [...] Quantum mechanics takes this idea to a whole new level because the concept of a measurement is different. [...] Now let’s complicate things even more. [...]

This thought experiment, first outlined by Eugene Wigner, has now been realized in a real experiment. It was a bit complicated to implement. Essentially, the experiment's researchers set up an apparatus that makes measurements on polarization that, if successful, leave a record of the measurement encoded in a second photon. Thus, between the original measurement and a new one done on the second photon, we have a simple version of the Wigner experiment.

As predicted by the theory, the setup records cases where the measurement and the measurement of the measurement disagree. Indeed, the rate of agreement/disagreement is pretty much exactly as predicted by quantum mechanics. The conclusion, according to the researchers, is that there are no facts that do not depend on the observer. Or coarsely put, at the quantum level, you may have the option of choosing your own facts.

I don’t see this result as startling. We already know that there are no privileged observers in special relativity, so why should they exist in quantum mechanics? [...] It doesn’t say anything about reality, though. (MORE - details)