# Is MWI really Bohmian without the non-local factor?

1. Nov 8, 2009

### Descartz2000

Is MWI really Bohmian without the non-local factor? Is this the only advantage of MWI?

2. Nov 8, 2009

3. Nov 9, 2009

### Demystifier

Re: Mwi

MWI is also nonlocal, in the sense that the wave function, being a function in a many-particle configuration space, is a nonlocal object. But one can say that Bohmian mechanics is even more nonlocal, in the sense that it contains nonlocal influences (forces) which MWI does not contain.

In my opinion, the main advantage of MWI over Bohmian mechanics is a smaller number of assumptions, while the main disadvantage of MWI over Bohmian mechanics is a difficulty to explain the Born rule. Perhaps one can explain the Born rule in MWI by adding some additional assumptions, but then the advantage of MWI over Bohmian mechanics is lost.

Last edited: Nov 9, 2009
4. Nov 9, 2009

### Demystifier

Re: Mwi

In fact, claiming that MWI has advantage of being local is rather paradoxical.
On one hand, locality is a property of the 4-dimensional spacetime.
On the other hand, MWI claims that the state in the Hilbert space is the only reality, and this state does not live in the 4-dimensional spacetime.
Thus, in a sense the property of (non)locality is not a fundamental property of MWI, so it seems that the issue of (non)locality of MWI is not an important question.

5. Nov 9, 2009

### Dmitry67

Re: Mwi

In any case, locality 'emerges' on the macroscopic level

6. Nov 9, 2009

7. Nov 9, 2009

### Demystifier

Re: Mwi

That is true, not only for MWI, but for Bohmian mechanics as well.

8. Nov 9, 2009

### Demystifier

Re: Mwi

For me, Bohmian mechanics is the simplest completion of the MWI program.
Namely, in MWI you must add some additional assumptions in order to recover the Born rule, and Bohmian mechanics provides just such assumptions in a very simple and intuitive way. I don't know a simpler way to achieve this.

9. Nov 9, 2009

### Dmitry67

Re: Mwi

Very good article, that you
What do you think about the weak probability postulate (the probability is a function of the measure of existence)?

10. Nov 9, 2009

### Demystifier

Re: Mwi

I think that such a postulate lacks an intrinsic motivation. Namely, if one did not know what one HAS to obtain (the Born rule), I don't see why one would take this postulate.

Let me use a tree analogy. Assume that the tree has two branches: one thick branch and one thin branch. The Born rule states that the probability of a branch is proportional to its thickness. However, if the tree is the only stuff that exists, then it is not clear why the Born rule is to be valid. After all, what does it mean that the thick branch has a larger probability than the thin branch?
On the other hand, if we add an ant into the story, then the origin of the Born rule becomes intuitively clear. Now the Born rule does not describe the probability of the branch itself, but the probability that the ANT will end up on a particular branch. It is intuitively clear (and can be explained quantitatively as well) that the ant has better chances to end up on a thicker branch.

11. Nov 9, 2009

### Dmitry67

Re: Mwi

It is explained:

In a deterministic theory, such as the MWI, the only possible meaning for probability is an ignorance probability, but there is no relevant information that an observer who is going to perform a quantum experiment is ignorant about

12. Nov 9, 2009

### Demystifier

Re: Mwi

I see it as an explanation why probability CANNOT be explained in MWI.