The important distinction here (and I get it, analogies are always imperfect) is that the photograph analogy has “hidden variables”. That is, each half is fixed at the moment of their separation and you just don’t know what’s in the envelopes until you open one. That’s not how entangled particles work though, and which “half” is which is not determined until the instant of measurement, at which point the state of both are known and fixed.
I’m open for counterarguments, but I always felt this was a silly way of looking at things. You cannot measure stuff at the quantum level without significantly altering what you measured. (You can never measure without altering what you measured, since we typically blast stuff with photons from a light source to be able to look at it, but for stuff that’s significantly larger than photons, the photons are rather insignificant.)
As such, you can look at measuring quanta in two ways:
Either the quantum had the state that you end up measuring all along. It is only “undetermined”, because strictly nothing can measure it before you do that first measurement.
Or you can declare it to have some magical “superposition”, from which it jumps into an actual state in the instant that you do the measurement.
Well, and isn’t quantum entanglement evidence for 1.? You entangle these quanta, then you measure one of them. At this point, you already know what the other one will give as a result for its measurement, even though you have not measured/altered it yet.
You can do the measurement quite a bit later and still get the result that you deduced from measuring the entangled quantum. (So long as nothing else altered the property you want to measure, of course…)
This is pretty conclusively addressed by the Bell Inequalities and empirically tested. It’s absolutely counter-intuitive and feels “wrong” but it is definitely how our universe operates.
https://m.youtube.com/watch?v=9OM0jSTeeBg
A relatively short but decent explainer for Bell’s Theorem and the Nobel prize winning experiment to successfully test it.
The whole idea is that the quantum particle can’t have had the state you’re measuring all along. If it did, then measuring a particular set of outcomes would be improbable. If you run an experiment millions of times, you have a choice in how you do the final measurement each time. What you find with quantum particles is that the measurements of the two different particles are more correlated than they should be able to be if they had determined an answer (state) in advance.
You can resolve this 3 ways:
1: you got extremely unlucky with your choice of measurement in each experiment lining up with the hidden/fixed state of each particle in such a way as to screw with your results. If you do the experiment millions of times, the probability of this happening randomly can be made arbitrarily small. So then, the universe must be colluding to give you a non uniform distribution of hidden states that perfectly mess with your currently chosen experiment
2: the particles transfer information to each other faster than the speed of light
3: there is no hidden state that the particle has that determines how it will be measured in any particular experiment
The important distinction here (and I get it, analogies are always imperfect) is that the photograph analogy has “hidden variables”. That is, each half is fixed at the moment of their separation and you just don’t know what’s in the envelopes until you open one. That’s not how entangled particles work though, and which “half” is which is not determined until the instant of measurement, at which point the state of both are known and fixed.
I’m open for counterarguments, but I always felt this was a silly way of looking at things. You cannot measure stuff at the quantum level without significantly altering what you measured. (You can never measure without altering what you measured, since we typically blast stuff with photons from a light source to be able to look at it, but for stuff that’s significantly larger than photons, the photons are rather insignificant.)
As such, you can look at measuring quanta in two ways:
Well, and isn’t quantum entanglement evidence for 1.? You entangle these quanta, then you measure one of them. At this point, you already know what the other one will give as a result for its measurement, even though you have not measured/altered it yet.
You can do the measurement quite a bit later and still get the result that you deduced from measuring the entangled quantum. (So long as nothing else altered the property you want to measure, of course…)
This is pretty conclusively addressed by the Bell Inequalities and empirically tested. It’s absolutely counter-intuitive and feels “wrong” but it is definitely how our universe operates.
https://m.youtube.com/watch?v=9OM0jSTeeBg A relatively short but decent explainer for Bell’s Theorem and the Nobel prize winning experiment to successfully test it.
The whole idea is that the quantum particle can’t have had the state you’re measuring all along. If it did, then measuring a particular set of outcomes would be improbable. If you run an experiment millions of times, you have a choice in how you do the final measurement each time. What you find with quantum particles is that the measurements of the two different particles are more correlated than they should be able to be if they had determined an answer (state) in advance.
You can resolve this 3 ways:
1: you got extremely unlucky with your choice of measurement in each experiment lining up with the hidden/fixed state of each particle in such a way as to screw with your results. If you do the experiment millions of times, the probability of this happening randomly can be made arbitrarily small. So then, the universe must be colluding to give you a non uniform distribution of hidden states that perfectly mess with your currently chosen experiment
2: the particles transfer information to each other faster than the speed of light
3: there is no hidden state that the particle has that determines how it will be measured in any particular experiment
See https://www.quantamagazine.org/how-bells-theorem-proved-spooky-action-at-a-distance-is-real-20210720/ for a short explanation of what ‘more correlated than expected’ means
There’s so many explanations for this (that don’t require magic) I don’t even know where to start