How Is This Possible?

[seer]

More Than One Reality Exists (in Quantum Physics)

Researchers recently conducted experiments to answer a decades-old theoretical physics question about dueling realities. This tricky thought experiment proposed that two individuals observing the same photon could arrive at different conclusions about that photon's state — and yet both of their observations would be correct.

For the first time, scientists have replicated conditions described in the thought experiment. Their results, published Feb. 13 in the preprint journal arXiv, confirmed that even when observers described different states in the same photon, the two conflicting realities could both be true. [The Biggest Unsolved Mysteries in Physics]

"You can verify both of them," study co-author Martin Ringbauer, a postdoctoral researcher with the Department of Experimental Physics at the University of Innsbrück in Austria, told Live Science.

Wigner's friend

This perplexing idea was the brainchild of Alfred Wigner, winner of the Nobel Prize for Physics in 1963. In 1961, Wigner had introduced a thought experiment that became known as "Wigner's friend." It begins with a photon — a particle of light. When an observer in an isolated laboratory measures the photon, they find that the particle's polarization — the axis on which it spins — is either vertical or horizontal.

However, before the photon is measured, the photon displays both polarizations at once, as dictated by the laws of quantum mechanics; it exists in a "superposition" of two possible states.

Once the person in the lab measures the photon, the particle assumes a fixed polarization. But for someone outside that closed laboratory who doesn't know the result of the measurements, the unmeasured photon is still in a state of superposition.

That outsider's observation — their reality — therefore diverges from the reality of the person in the lab who measured the photon. Yet, neither of those conflicting observations is thought to be wrong, according to quantum mechanics.

https://www.livescience.com/65029-du...y-photons.html

So a fixed polarization and non-fixed polarization of the same photon happens at the same time?

[Sparko]

yeah but what if the second team actually measured the spin of the photon? Would it just end up always being the same as the first team's? Or could it end up being the opposite?

This seems like if someone has a pipe. Team one looks at the pipe and doesn't know how long it is (superposition). The first team measures the pipe and sees that it is 1 foot long (horizontal spin). The second team comes in and looks at the pipe and doesn't know how long it is (superposition).

But if the second team measures it, they would find it is one foot long too. Or could they measure it as being 2 foot long?

[Mountain Man]

Are they saying that two people observing the same particle at the same time under the same conditions will perceive contradictory things? Because it almost sounds like observations made at different times and under different conditions, in which case, making what might appear to be contradictory observations is perfectly explicable.

[shunyadragon]

These are observations from the human perspective and at present inconclusive and incomplete, but yes not in conflict with the current view of Quantum Mechanics, which is a work in progress.

[rogue06]

These are observations from the human perspective and at present inconclusive and incomplete, but yes not in conflict with the current view of Quantum Mechanics, which is a work in progress.

All science is a work in progress.

[Mountain Man]

All science is a work in progress.

What about "settled science"?

[rogue06]

What about "settled science"?

A legitimate scientist that uses that expression ought to be ashamed of themself. Now, having said that, it is true that concerning some things we have enough information that the odds that we're completely wrong about it are only a little better than discovering that the sun is actually smaller than our moon.

[Mountain Man]

As Michael Crichton famously said, "If it's science, it's not settled. If it's settled, it's not science. Period."

[TheLurch]

As Michael Crichton famously said, "If it's science, it's not settled. If it's settled, it's not science. Period."

Which is kind of a dumb statement if you don't define "settled". We know evolution takes place because we've observed it so many times. For most definitions of "settled", that would seem to qualify.

In any case, I've read a bit about what physicists are saying about the experiment and skimmed the paper. I won't have time to go into details, but the rough gist of it is:

One observer measures a quantum object, gets a result, but doesn't tell observer 2 the result.
Observer 2 later makes a measurement of that same object.

If the object isn't quantum, we'd expect them to get the same result. But the object is in this case, so observer 2 is actually measuring a different quantum system: the object + observer 1. Therefore, observer 2 could get a different result.

This was now shown to happen, with both observers being electronic devices. The original thought experiment actually involved people, which layers on a Schroedinger's-cat-like issue of whether a macroscopic object like a human observer can ever become part of a quantum system. I think the "OMG WE BROKE REALITY" response is acting like we've demonstrated that the thought experiment version is happening - which we most certainly have not.

[Sparko]

Which is kind of a dumb statement if you don't define "settled". We know evolution takes place because we've observed it so many times. For most definitions of "settled", that would seem to qualify.

In any case, I've read a bit about what physicists are saying about the experiment and skimmed the paper. I won't have time to go into details, but the rough gist of it is:

One observer measures a quantum object, gets a result, but doesn't tell observer 2 the result.
Observer 2 later makes a measurement of that same object.

If the object isn't quantum, we'd expect them to get the same result. But the object is in this case, so observer 2 is actually measuring a different quantum system: the object + observer 1. Therefore, observer 2 could get a different result.

This was now shown to happen, with both observers being electronic devices. The original thought experiment actually involved people, which layers on a Schroedinger's-cat-like issue of whether a macroscopic object like a human observer can ever become part of a quantum system. I think the "OMG WE BROKE REALITY" response is acting like we've demonstrated that the thought experiment version is happening - which we most certainly have not.

From what I read the 2nd observer didn't even make a measurement. The first observer saw the particle in superposition and made a measurement which supposedly collapses the superposition into a definite spin (this is with a quantum entangled pair) - at a second location the 2nd observer looks at the particle's twin but still sees it in superposition but doesn't measure it.

But how do you even know it is in superposition unless you interact with the particle? That's what I don't understand.

[seer]

But how do you even know it is in superposition unless you interact with the particle? That's what I don't understand.

Right...

[seer]

Which is kind of a dumb statement if you don't define "settled". We know evolution takes place because we've observed it so many times. For most definitions of "settled", that would seem to qualify.

In any case, I've read a bit about what physicists are saying about the experiment and skimmed the paper. I won't have time to go into details, but the rough gist of it is:

One observer measures a quantum object, gets a result, but doesn't tell observer 2 the result.
Observer 2 later makes a measurement of that same object.

If the object isn't quantum, we'd expect them to get the same result. But the object is in this case, so observer 2 is actually measuring a different quantum system: the object + observer 1. Therefore, observer 2 could get a different result.

This was now shown to happen, with both observers being electronic devices. The original thought experiment actually involved people, which layers on a Schroedinger's-cat-like issue of whether a macroscopic object like a human observer can ever become part of a quantum system. I think the "OMG WE BROKE REALITY" response is acting like we've demonstrated that the thought experiment version is happening - which we most certainly have not.

Let me get this right, is the same particle in two different states at the same moment?

[TheLurch]

Let me get this right, is the same particle in two different states at the same moment?

From the perspective of observer 1, who has measured it, it's in a defined states. Observer 2, who hasn't, views it as still being in a superposition of possible states.

[seer]

From the perspective of observer 1, who has measured it, it's in a defined states. Observer 2, who hasn't, views it as still being in a superposition of possible states.

So it is in two different states at the same moment?

[Sparko]

From the perspective of observer 1, who has measured it, it's in a defined states. Observer 2, who hasn't, views it as still being in a superposition of possible states.

But how would he know unless he actually interacted with it? Which would make it collapse into a fixed spin?