Quantum entanglement shows that reality can't be local

I want to reiterate here that MWI is a much simpler theory than Bohm's, even if the consequences of MWI might seem more complicated. At times, there have been scientists who want to apply Occam's razor to the consequences, but most scientists these days would apply Occam's razor to the theory itself.

Also, this is a marvel of a sentence: "Other than MWI and Bohm, the major interpretations (not including Copenhagen)"

"Other than Android and Windows Mobile, all major cell phone operating systems (not including iOS)"

The long and short of it is, for purely philosophical reasons you don't like the notion of the state vector collapse. You freely admit that there is no way to experimentally distinguish between your favorite interpretation and the Copenhagen interpretation. You just declare that it's not even a contender, using arguments which have nothing to do even in principle with the outcome of any experiments.

Saying that something is not precisely defined sounds to me totally like grasping at straws. Nothing's ever precisely defined in science, you could criticize any theory including Newton's mechanics by saying that it doesn't define precisely what a measurement is. Which never stopped anyone from measuring things and comparing the values they measured with what the theory predicted.

You quote someone who made an analogy with Copernicus. The Copernican theory simplified the calculations right away, whereas with Quantum Mechanics, the calculations stay exactly the same no matter what story you feel like telling yourself so that you can take the outcome of these calculations and compare them with the real world.

Let me make this clear that I'm not against MWI. I care about MWI exactly as much as about the Copenhagen interpretation (which is not very much.) I am however opposed to pretending that one of the two exactly equivalent ways of saying something is "more true" than another.

Staying within Quantum Mechanics, there are two ways of writing the equations of motion: the Heisenberg picture and the Schroedinger picture. In the former the state vector is constant but the operators are a function of time, in the latter the operators are constant and the state vector evolves with time. The two formulations are equivalent, sometimes it is convenient use one or the other for a specific calculation and often you use a mix of both (so called interaction picture.) Nobody argues that say the Heisenberg picture is "really true" as opposed to the Schroedinger picture. If someone did, that would be inane, even if they invoked Copernicus and Occam (even though the analogy with Copernicus would be maybe better, since the calculations actually are different depending which picture you choose.)

> The long and short of it is, for purely philosophical reasons you don't like the notion of the state vector collapse.

That's not the long and the short of it. I didn't say anything of the sort.

You ramble on apparently oblivious that to the fact that different interpretations of QM can and do make different predictions about what causes wave-function collapse. E.g., GRW makes different predictions from Penrose's interpretation. Why you are oblivious to this fact, I cannot fathom, as I've mentioned this fact several times now.

   http://en.wikipedia.org/wiki/Ghirardi-Rimini-Weber_theory

   http://en.wikipedia.org/wiki/Penrose_interpretation

In theory, someday we'll be able to design experiments that determine which one of these interpretations, if either, is correct.

So, as you should be able to see, this is in no way comparable to different forms for equations that make identical predictions.

As to the measurement problem

   http://en.wikipedia.org/wiki/Measurement_problem

Newtonian mechanics has no such measurement problem, so it is you who are grasping at straws. If a QM Interpretation is going to be considered a complete theory, it has to answer certain questions. For instance, if were were to train cats to operate quantum measurement devices and to perform experiments for us, and we consequently determined that measurements performed by cats did not cause wave function collapse, would that confirm or deny the Copenhagen Interpretation?

A. Neither, because the Copenhagen Interpretation doesn't define "measurement", and so we have no idea whether or not measurement by cats counts as "measurement".

You don't like cats, substitute in nanoscale molecular robots instead.

> I'm not familiar with GRW, Penrose's theory is obviously more than an interpretation

I have no desire to get into a debate on terminology. I've just been using the terminology that was taught to me in an entire semester-long class I took at MIT on QM and its various "interpretations". GRW was called an "interpretation", as was Penrose's. The term "interpretation" is also the term used on the Wikipedia page for "Penrose's Interpretation".

> the fact stands that there is no experimental way, even in principle, to distinguish between MWI and Copenhagen.

That is not a fact; your assertion is false:

     http://en.wikipedia.org/wiki/Many-worlds_interpretation#Comparative_properties_and_possible_experimental_tests

See the text starting at "However, in 1985 David Deutsch published three related thought experiments which could test the theory vs the Copenhagen interpretation."

He has a book. I haven't read it, but I'm sure he must discuss this issue in it.

In any case, I'm sure you can come up with a definition of "measurement" that might make the Copenhagen Interpretation experimentally indistinguishable from MWI, but why? MWI is and always will be a simpler theory, and thus preferred by Occam's razor.

The problem with the Copenhagen Interpretation is that it is NOT a scientific theory. It is not a scientific theory because it is not falsifiable. It also builds non-fundamental things like "measurement" right into the fundamental laws of physics, which is absurd. Copenhagen is not falsifiable, because if I were to attempt to falsify it by demonstrating that a "measurement" did not cause the wave function to collapse, you could always assert that I had used the wrong definition of "measurement".

GRW, on the other hand, can be seen as a sub-interpretation of the Copenhagen Interpretation because it rigorously defines the term "measurement". I.e., entanglement of the particles in question with a "large enough" collection of additional particles. "Large enough" here needs some experimental tuning, but some day we may be able to perform these experiments and attempt to falsify GRW. Because we can falsify GRW, it IS a scientific theory.

Most other collapse interpretations that I have heard of can likewise be seen as sub-interpretations of Copenhagen, in that they define "measurement".

One of those sub-interpretations is the Wigner Interpretation, or the "consciousness causes collapse" interpretation. Counter to your previous assertion, we could in theory experimentally determine whether this is true via trained rats: (1) Train a rat to perform measurements, (2) kill the rat before it has a chance to tell you the results, (3) check to see whether wave function has collapsed. We can do this because there are experiments that will tell you if two particles are entangled or not.

Animal consciousness not good enough for "measurement"; it needs to be human? Okay, Nazis could in theory perform this experiment, as could future evil alien overlords.

Now let's go back to MWI: I think that many people have a misconception about MWI, and perhaps this is due to its name. (If we had stuck to the name "Everett Interpretation" perhaps that would have been better.) MWI doesn't really imply multiple worlds. It implies one very complicated superimposed world. It is also the simplest theory, as it does not add the complication of wave function collapse. Furthermore, it is completely consistent with every bit of data that has ever been collected.

Another misconception is that MWI asserts that the "other worlds" that fall out of it are "real". This is not the case. MWI is agnostic on this issue. For instance, Stephen Hawking is in favor of MWI, but he doesn't like the name, because he thinks that asserting that the "other worlds" are "real", rather than just mathematical artifacts of the theory, is not something that we can scientifically know.

Executive summary: MWI is the simplest theory, and is consistent with all data. By Occam's razor, we are required to give this theory preference until we have evidence that contradicts it.

The counter argument to the above is that the ontological cost of all these many worlds (or maybe even the complicated superpositions of state) is too great, and that this somehow violates Occam's razor.

Well, first of all it doesn't, since Occam's razor these days is almost always taken to prefer the SIMPLEST THEORY, regardless of additional philosophical worries like, "It's just creepy to think that there might be so many other worlds."

Furthermore, this objection is based on a misinterpretation of MWI. MWI is completely agnostic about the ontological status of these "other worlds". It's just a mathematical formulation for making scientific predictions. There are many cases in the history of science where "creepy" things fall out of the math, if we were to grant them the status of being ontologically "real", and yet we don't reject the theories because of this. E.g., virtual particles and advanced waves. Sometimes scientists at some point decide that mathematical artifacts of theories are "real". E.g., virtual particles. And at other times, they remain just mathematical artifacts. E.g. (maybe), advanced waves.

Are the other worlds in MWI "real"? You tell me! Science cannot answer that question. This does not imply that MWI isn't the best theory.