In Plaga model, the trapped ion is isolated from both branches and thus orthogonality equation is not directly applicable to it.
“one does not simply measure whether a system is an eigenstate or a superposition”
We can’t do it simply, but with some efforts we can do it. We can measure was the ion in superposition or not if we repeat the experiment many times in exactly the same settings. Eigenstate will give always 1. Superposition state will give mix of 0 and 1 measurements.
The fix is needed mostly not because energy conversation, but because if we transfer any definite state, the sender destroys isolation of the ion by becoming in superposition in it (as was discussed in Quora objection to Plaga model). Here I suggest to use the mere fact of destruction of ion’s quantum state as a way to transfer information.
If the ion is isolated, that means you take a tensor product of its state with the state of the environment. If u,v are orthogonal, then a⊗u and a⊗v are still orthogonal.
Why does your “repeated measurement” method not also work to use entangled qubits to send signals faster than light? (Since measuring one qubit also collapses the state of the other.)
Or, maybe just tell me the density matrix for the ion that you expect the reciever to see if the sender sends a 0, and also the density matrix for if they send a 1?
Plaga’s article has equations and was published in a scientific journal—Foundations of Physics, 1997. The journal had small impact factor at the time and its editor was Carlo Rovelli. There is no public retraction or refutation of it, except an obscure Quora post where someone said that Plaga doesn’t endorse this anymore. Plaga had around 10 astrophysics articles in 90s.
He (or a person with the same name) works now on “LLM security in Germany”—not a really bad sign as H.Everett also turned to defense industry later.
This is extremely weak signal compared to understanding the technical argument, the literature is full of nonsense that checks all the superficial boxes. Unfortunately it’s not always feasible or worthwhile to understand the technical argument. This leaves the superficial clues, but you need to be aware how little they are worth.
Interesting coincident: Yesterday a new preprint appeared on the same topic
Quantum observers can communicate across multiverse branches Maria Violaris
It is commonly thought that observers in distinct branches of an Everettian multiverse cannot communicate without violating the linearity of quantum theory. Here we show a counterexample, demonstrating that inter-branch communication is in fact possible, entirely within standard quantum theory. We do this by considering a Wigner’s-friend scenario, where an observer (Wigner) can have quantum control over another observer (the friend). We present a thought experiment where the friend in superposition can receive a message written by a distinct copy of themselves in the multiverse, with the aid of Wigner. To maintain the unitarity of quantum theory, the observers must have no memory of the message that they sent. Our thought experiment challenges conventional wisdom regarding the ultimate limits of what is possible in an Everettian multiverse. It has a surprising potential application which involves using knowledge-creation paradoxes for testing Everettian quantum theory against single-world theories
If memory serves, the journal Foundations of Physics was long known as a place for people to publish wild fringe theories that would never get accepted by more mainstream physics journals.
I remember back in 2007, this was common knowledge, so it was big news that (widely respected physicist) Gerard ’t Hooft was due to take over as editor-in-chief, and people in the physics department were speculating about whether he would radically change the nature of the journal. I don’t know whether that happened or not. But anyway, 1997 is before that.
In Plaga model, the trapped ion is isolated from both branches and thus orthogonality equation is not directly applicable to it.
“one does not simply measure whether a system is an eigenstate or a superposition”
We can’t do it simply, but with some efforts we can do it. We can measure was the ion in superposition or not if we repeat the experiment many times in exactly the same settings. Eigenstate will give always 1. Superposition state will give mix of 0 and 1 measurements.
The fix is needed mostly not because energy conversation, but because if we transfer any definite state, the sender destroys isolation of the ion by becoming in superposition in it (as was discussed in Quora objection to Plaga model). Here I suggest to use the mere fact of destruction of ion’s quantum state as a way to transfer information.
You mean linearity equation?
If the ion is isolated, that means you take a tensor product of its state with the state of the environment. If u,v are orthogonal, then a⊗u and a⊗v are still orthogonal.
Why does your “repeated measurement” method not also work to use entangled qubits to send signals faster than light? (Since measuring one qubit also collapses the state of the other.)
Or, maybe just tell me the density matrix for the ion that you expect the reciever to see if the sender sends a 0, and also the density matrix for if they send a 1?
Plaga’s article has equations and was published in a scientific journal—Foundations of Physics, 1997. The journal had small impact factor at the time and its editor was Carlo Rovelli. There is no public retraction or refutation of it, except an obscure Quora post where someone said that Plaga doesn’t endorse this anymore. Plaga had around 10 astrophysics articles in 90s.
He (or a person with the same name) works now on “LLM security in Germany”—not a really bad sign as H.Everett also turned to defense industry later.
This is extremely weak signal compared to understanding the technical argument, the literature is full of nonsense that checks all the superficial boxes. Unfortunately it’s not always feasible or worthwhile to understand the technical argument. This leaves the superficial clues, but you need to be aware how little they are worth.
Interesting coincident: Yesterday a new preprint appeared on the same topic
Quantum observers can communicate across multiverse branches
Maria Violaris
https://arxiv.org/abs/2601.08102
Scott Aronson already wrote in FB that it is wrong.
If memory serves, the journal Foundations of Physics was long known as a place for people to publish wild fringe theories that would never get accepted by more mainstream physics journals.
I remember back in 2007, this was common knowledge, so it was big news that (widely respected physicist) Gerard ’t Hooft was due to take over as editor-in-chief, and people in the physics department were speculating about whether he would radically change the nature of the journal. I don’t know whether that happened or not. But anyway, 1997 is before that.