Can I steer myself into one of the Many Worlds like this?

[StevieTNZ]

I apologise if this is an error, but I have not read the thread in detail.

Are you basically asking, can I choose the outcome of a measurement (e.g. photon polarized horizontal versus vertical, 1/2 probability for each polarization)? The standard answer is no, but there are papers and books from persons who entertain that idea.

 

[PeterDonis]

My thought experiment didn't seek to return anything to "initial condition" and neither does a quantum erasure experiment, as far as I can see.

That is exactly what "quantum erasure" does--it reverses whatever unitary interaction took place during the experiment. The term "measurement" should not be used for that interaction precisely because it is reversible. Measurements are not reversible: once a result has occurred, it has occurred and can't be undone.

I think that the erasure experiments demonstrate what I was saying above

You are wrong. They don't.

The erasure experiment, to my way of thinking, gives you the choice of letting the information leak out of the apparatus or keeping it confined therein.

Your way of thinking is wrong. That's not what a quantum erasure experiment does. Any "leakage"--interaction with the outside world--destroys the experiment; it has to be kept isolated.

In MWI terms, quantum erasure experiments never split worlds.

You really, really, really need to tell us what sources you are learning QM from. You seem to be misunderstanding things all over the place, which indicates to me that you are not using good sources. If all of your sources are Wikipedia articles or papers on advanced topics that depend on you already understanding the basics (like the Frauchiger Renner paper you linked to earlier), that's not surprising.

 

[David Byrden]

Are you basically asking, can I choose the outcome of a measurement (e.g. photon polarized horizontal versus vertical, 1/2 probability for each polarization)?

I'm entering a busy time now, so I can't get into discussions until the New Year. But, I'll summarise what I was thinking;

- An isolated system is in a superposition of two known orthogonal states.
- Both copies of it create and send photons
- The photons' timing etc. is so precisely controlled that they are not affected by the decoherence between the two copies of the system
- The photons therefore interfere, and we receive a photon whose state is a proxy for the qubit that split the isolated system in the first place
- So, if the received qubit has a polarity aH + bV, where H and V are the polarities of the photons created in the two superposed copies of the isolated system, then the entire isolated system is in a |state1> + b |state2>

- It collapses to one of our new basis vectors, with very high probability (if it collapses to the other one, the game is over and we lose)
- My assumption was that the isolated state, relative to us, now has the corresponding state. We have adjusted a and b.
- Repeat the process. The isolated state keeps sending us photons. We keep rotating the measurement basis very slightly with each measurement.
- Eventually we can adjust a and b to a desired outcome, with very high probability.

I'm interpreting QM in the "relative" way. I believe the state of the isolated system is not objective, but is relative to the information that we hold about it. And, although we have a lot of information about the contents (which we put in there), we originally have zero information about the qubit that split the contents into two states. For us, that decision literally has not happened.

Therefore, by manipulating that information, I am manipulating our knowledge of the system's state, not the system itself. I'm not trying to revive a dead cat; I believe that a live cat and a dead cat are both in there, equally real, in two distinct "worlds", and I am trying to manoevre myself around to align with one of those two "worlds".

David

 

[PeterDonis]

- An isolated system is in a superposition of two known orthogonal states.
- Both copies of it

You're not making sense. Is there one isolated system? Or are there two, prepared the same way?

- The photons' timing etc. is so precisely controlled that they are not affected by the decoherence between the two copies of the system

How can there be decoherence if the two copies are isolated? They aren't interacting if they're isolated, so there's nothing to decohere.

- The photons therefore interfere, and we receive a photon whose state is a proxy for the qubit that split the isolated system in the first place

What qubit? And what does "split the isolated system" mean? How can an isolated system "split"? It's isolated; that means it isn't interacting with anything.

I'm interpreting QM in the "relative" way.

As I've already said, I don't think your claims have anything to do with a particular interpretation of QM. You are making claims that have direct experimental consequences, which means they should be analyzable using just the basic math of QM, without any interpretation.

At this point I don't see any value in keeping this thread open, since you have repeatedly refused to say what source you are learning from QM from, you have repeatedly shown serious misunderstandings of QM and have not responded to corrections, and you are evidently trying to construct and analyze a scenario that is way too advanced for a person who by their own admission is new to QM.

Thread closed.