Superdeterminism: The path we didn’t take

They're not though. There's no generally accepted definition of what is and isn't a measuring device. And, as per the quantum eraser experiment, the exact same equipment might be considered as a measuring device or not a measuring device, depending on what happens in the future.

> So, which is the interaction that causes entanglement? I was asking for this before.

The only fully accurate answer is "look at the Schrodinger equation". But, broadly, interacting with an object in superposition in a way that depends on that superposition will cause entanglement. For example, if a particle's spin is in superposition, another particle interacting it in a spin-dependent way will cause entanglement, but interacting with it in a spin-independent way will not create an entanglement.

I appreciate that this must sound exactly as vague as the definition of a measurement. But for those familiar with QM it really isn't. If you look at textbooks, even those written from a Copenhagenist point of view, they're very clear on which physical circumstances give rise to entanglement and which don't. If you go through any undergrad-level QM textbook you'll have a clear understanding of what entanglement is and isn't.

> Well, I would expect my measurement to also have all possible outcomes given by the superposition.

Ok, but what would the subjective experience of that look like?

> Only after a one of the entangled particles is measured. Either my brain must be measured or the result must be measured. In this sense entanglement doesn’t work without an ill defined concept of measurement either.

Not true. Just by looking at the wavefunction, one can see that the wavefunction is a superposition of two distinct Everett branches that don't interact with each other - not because of some mysterious "collapse" phenomenon, but just as an emergent property of that actual wavefunction. Finding yourself in one specific branch is somewhat mysterious, but each individual branch being consistent with itself and not interacting with any other branch is absolutely normal QM.

This doesn't explain the cause of entanglement. It just explains the circumstances under which entanglement occurs.

> I appreciate that this must sound exactly as vague as the definition of a measurement

That's because it is beyond the mathematics.

> But for those familiar with QM it really isn't.

This is not true. I'm familiar with QM and it is vague to me.

>they're very clear on which physical circumstances give rise to entanglement

But, none explain the cause of entanglement. Just as none explains the cause of collapse of a wave function which is called a measurement.

> Ok, but what would the subjective experience of that look like?

I wouldn't know, because it's not what can be experienced. Some folks argue this is exactly what makes many worlds unscientific.

> Just by looking at the wavefunction,

Interesting. What kind of microscope are you using to look at wave functions? Or do you mean at the mathematical expression of the wavefunction? I'm not arguing that decorherence theories are mathematically sound and a neat theory. I'm just challenging that they offer some physical explanations beyond Copenhagen. They just take the unexplained things and replace them with other unexplained things.

> emergent property

Another empty word.

> Finding yourself in one specific branch is somewhat mysterious

Yes. And if you think about it, this is the same mystery which makes Copenhagen so unsatisfactory, just put into a different framework.

Obviously we all experience what we call consciousness, noticing ourselves noticing, and we all imagine we have free will, which really only means we don't know what we will do tomorrow.

But neither of those have anything to do with physics, except to the degree that the stuff we are made out of runs according to physics.

So, anybody supposing that either concept has anything to do with quantum physics is barking up something that is not even a tree.

What? It's like the opposite...

Currently we don't have a perfect model for quantum physics, so what do we do when we try to create a model of something where we have data for, but we don't fully understand? We use statistics and probabilities to fit/approximate the behavior behind the model. Doing this can lead to a useful but imperfect model, but that doesn't prove one way or another that the behavior of what we're trying to understand is inherently random, just that it exhibits random behavior at some level or in some way.

Now the opposite: saying things like Heisenberg's uncertainty principle is full stop proven, is itself a stop sign for thought IMO. Whereas opposing such principles, and assuming behavior isn't inherently random (i.e. the idea behind determinism), opens for testable ideas on what might actually happening behind the apparent randomness of the model. You know... one which might lead to a perfect model fully explaining the behavior (which hey isn't that the purpose of science??)

To put it backwards... the ideal in science is a model that explains how everything works, if this is ever realized it'll prove superdeterminism. To say stuff is inherently random, to me is equivalent to giving up and settling for less than the ideal...