why is superdeterminism not the universally accepted explanation of nonlocality?

jadrian

but isnt superdeterminism unfalsified by qm predictions?

jadrian

and kith, im sorry. i dont take pleasure in telling people the adult version of there is no santa clause, unless they ask for it.

DrChinese

I don't think this question makes sense as written. Could you rephrase?

lugita15

OK, let me give you an example of why you need special initial conditions.

In a deterministic theory, in order to predict the current behavior of any object, you need to know the initial conditions of the object, as well as the deterministic laws of the universe. In Newtonian mechanics, for example, you need to know the positions and velocities of all the particles at time t=0, and then F=ma will tell you the behavior of the particles at all later times.

Now let's consider what a local deterministic explanation of entanglement would look like. Let particles A and B be an entangled pair of photons, which are separated by a great distance and then sent through polarization detectors. We also have particles C and D: C tells the experimenter what angle he should set the polarizer that measures A, and D tells the experimenter how to set the polarizer that measures B. You can think of C and D as neurons in the brains of the experimenters if you like.

Now we find experimentally that the behavior of particle A through its measurement device is strongly correlated with the angle at which B's measurement device is set. And that angle is determined by particle D. So we have a correlation between the behavior of particles A and D.

But particles A and D are seperated by such a large distance, so they cannot communicate with each other to coordinate their behavior (unless you have a nonlocal theory like Bohmian mechanics which allow undetectable faster-than-light signalling between particles). So a local determinist has to conclude that A and D are correlated not based on a current relationship between the present states of A and D, which would be impossible, but based on a past relationship of the initial states of A and D.

This is what we mean by special initial conditions: A and D seemingly have nothing to do with each other. After all, it is A and B that were in the entangled state, and yet somehow we have to conclude that the initial conditions of A and D had to be specially set so that a correlation between A and D would be observed in the future. And instead of just D, we can have a large number of particles D1, D2, D3,... which together determine the measurement setting, so the initial state of particle A had to have been set based on the initial states of all these particles. And in the real world, almost all particles in the universe are interacting in some way with almost all other particles, so really the setting of measurement device depends on almost everything in the universe, from which we conclude that the initial conditions of the whole universe were specially set so that the right kind of correlation would be displayed billions of years later between particle A and the measuring device.

This is why superdeterminism is called "conspiratorial". That doesn't mean it's wrong, it just has some issues which make it rather difficult to construct a viable superdeterministic theory, but let me repeat that some potential first steps toward such a theory have already been taken by a few people.

DrChinese

Maybe someone is working on it, but that would pretty much be a waste of time. The entire point would be to replicate the predictions of QM.

On the other hand, the obstacles are enormous. I like your example. Once you see that your C and D could be anything (and in fact different) - radioactive decay, coin tosses, arrival time of photons from the moon, etc. - you realize the magnitude of the conspiracy.

And, like any conspiracy, it is impossible to disprove. Really, it is a ridiculous premise and I see no scientific merit in it. Although there are plenty of scientists who acknowledge it as viable conceptually, I doubt there are many who give it more than a second thought.

lugita15

No one's doing serious work on it; I was just talking about some basic proof-of-concept stuff from Gerard t'Hooft and a few others.
As I mentioned in my post, you can argue that all the particles in the universe would have to be involved in the conspiracy, because pretty much everything in the universe is interacting with everything else, be it gravitationally, electromagnetically, etc.

lugita15

The derivation of the Born rule is an important topic in the decoherence literature. Here's a typical reference:
http://arxiv.org/abs/quant-ph/0405161

IttyBittyBit

Wow, a great deal of unwarranted hostility towards jadrian in this thread, even from people like DrChinese whom I (used to) have a great deal of respect for.

It is true that superdeterminism is more of a viewpoint than a scientific theory --- but then so is the idea that all matter is made up of vibrating strings a la string theory. The latter is unfalsifiable as well (string theory can be reformulated in terms of branes to yield the exact same results) but it still serves as a useful guide for research.

Superdeterminism is a perfectly valid approach to things. Superdeterministic hidden variable theories (many of which are falsifiable) should be investigated more, I think.

Superdeterminism is only conspiratory if you don't understand it. If we were to build a set of toy Universes, some of them based on superdeterministic theories and others not, and the latter ones tended to match our Universe more closely, then it would be reasonable to conclude that the Universe is not superdeterministic and that any superdeterministic explanation would have to be conspiratory. However, such a study has never been undertaken and there is little evidence at the moment to support one position or the other.

It seems that the willingness of many people in this thread to discount superdeterminism offhand speaks more to an attempt to cling on to neo-vitalistic notions of free will than actual interest in science.

DrChinese

I certainly hope jadrian does not feel any hostility from me, that would be the last thing I would want. He asked why superdeterminism is not universally accepted, so I thought I was answering the question. It is not taken too seriously, please don't blame me personally for that.

As I have said before many times, there are no extent superdeterministic candidate theories that I know about. Yes, I have seen a few papers from well known scientists (Gerard 't Hooft cones to mind) discussing the matter, but none of them put forth anything really specific to rebut, and none have gained much traction.

DrChinese

Yeah, that's all I had seen as well.

As you say, after a while you realize that every single particle in the universe would need to carry a local copy of all the information regarding every other particle as well. Plus a lot more information, I think, to handle the large number of possible Bell tests that could be performed.

The entire direction then takes on the attributes of an ad hoc theory, which immediately means no novel predictions will likely be forthcoming (that's what happens when you go into ad hoc mode). So I would say the outlook is bleek in terms of future prospects, and further that most scientists share this view in one way or another.

juanrga

First, since that nonlocality and entanglement are perfectly compatible with a non-deterministic viewpoint, the problem does not even exists.

Second, from a theoretical point of view determinism arises when one consider a certain kind of simple systems as the traditionally studied in physics.

Third, the assumption that universe is deterministic is outside the scope of science.

IttyBittyBit

You say that every particle must have a 'local copy' of the states of all the particles in the Universe. First of all, I don't see why this is taken to mean that superdeterminism must be wrong. Certainly, this is a much more reasonable assumption than the multiverse interpretation that every particle is associated with not one, but a huge number of different copies of the Universe (possibly several after each single measurement).

Second, if the digital physics hypothesis is true, and the entire Universe is being run on a big computer in some alien's backyard shed, this is actually exactly the kind of thing that you would expect. In a sequential computer simulation, when calculating the trajectory of any particle we have access to the states of all the other particles (i.e. a sequential digital universe must be nonlocal).

Going back to toy universes, it is actually quite impossible to create toy Universes that are not superdeterministic, unless randomness is injected from the outside. However, if the Universe itself is superdeterministic, then this is impossible as well!

A lot of the misunderstanding concerning superdeterminism stems from the fact that people do not pause to consider its full implications. If the Universe were superdeterministic, then the action of human beings would be deterministic, and of course counterfactual definiteness wouldn't be true. This is natural and what you'd expect, and if this were not the case it would be strange.

Of course, these are all philosophical arguments, and we should not spend too much time dwelling on them. This goes for arguments in support of superdeterminism as well as those against it.

What frightens me is that there is a lot of talent being steered away from hidden variable theory research, just because of these empty philosophical arguments. However, the good news is that a lot of work is being done. Take a look at: http://www.sciencedirect.com/science...7015730500147X (available on arXiv: http://arxiv.org/abs/quant-ph/0701071 - 500 references!) That's from 2005, there has been more work done since then.

lugita15

No, you can easily create a digital universe in which particles don't have access to nonlocal information.
It's true that no computer program in a deterministic universe can be non-deterministic. But not all deterministic theories have to be superdeterministic. In a superdeterministic theory, all the particles in the universe are conspiring to create the appearance of nonlocal correlations. That's not a common property of theories.
Yes, superdeterminism obviates the need for counterfactual definiteness; that is the whole reason why there is a no-conspiracy condition in Bell's theorem, and why there is a superdeterminism loophole in the first place. I don't think there is much misunderstanding about that point. But the reason that superdeterminism is not generally embraced, even among people who don't believe that humans have free will, is because it's natural to take nonlocal correlations at face value, and Occam's razor makes it hard to justify invoking a conspiratorial explanation like superdeterminism.
No, a lot of work is not being done on superdeterminism.

IttyBittyBit

He posted a question and you replied, immediately equating his (perfectly legitimate) line of thought with religious belief.

Of course, you did answer the question, and I have found your posts so far to be insightful, so I apologize if I have misunderstood.

I specifically meant toy universes that model our own Universe. Sorry if I wasn't clear about that.

Occam's razor does not apply here. It would only apply if there was a non-deterministic theory that could explain as much as a deterministic theory could and was simpler. There is no such theory as of yet; entanglement makes it difficult. All alternative resolutions to the EPR paradox make more assumptions than superdeterminism does. Why discount the one viewpoint that is intuitive and makes sense, in favor of other viewpoints that offer no increased predictive power and make more strange assumptions?

What are you trying to say?

lugita15

It's called Quantum Mechanics.

IttyBittyBit

I don't think you fully appreciate the EPR paradox.

At any rate, this discussion is becoming far too philosophical for my tastes so I see no point in continuing it.

jadrian

yeah but how can you POSSIBLY rule out that a and d did not interact in the past.