# MWI and Born Rule

1. Jun 23, 2010

### ThisIsMyName

I've been thinking a lot about MWI and probability lately and I can't say desicion theory is very convincing.
Obviously if MWI can't derive at the Born Rule, it is falsified.

Do you feel that MWI will ever make sense with probabilities or do you believe we can put MWI in the trashcan and start working on something else?

2. Jun 24, 2010

### Demystifier

3. Jun 24, 2010

### Demystifier

My opinion is somewhere in the middle. I think that MWI is correct, but not complete. In other words, the main ideas of MWI should not be rejected, but these ideas should be supplemented with some additional axioms/assumptions needed for the completion. A prominent example of such a completion is the Bohmian interpretation.

4. Jun 24, 2010

### ThisIsMyName

Mainly because a lot of people seemed uncertain about their views, so I figured maybe they had made their minds up now.

5. Jun 24, 2010

### Dmitry67

My opinion: Born rule is an illusion, created by our consciousness. Like 'NOW' or 'Flow of time'. There is no 'NOW' in spacetime, and time does not 'move'. It is quite obvious in SR and GR, while our common sense reasoning is crying the opposite. But who believes in our 'common sense reasoning' after so many spectacular failures?

Note: How can you derive Born rule in MWI if Born rule can't be even formulated in MWI framework? Hint: MWI does not know the word 'probability'. To start talking about Born rule one need to provide good (observed dependent? what observer? in what branch?) definition of a probability.

6. Jun 24, 2010

### cesiumfrog

Is there a simple exposition of the decision theory argument someplace?

7. Jun 24, 2010

### Demystifier

http://arxiv.org/abs/0808.2415

In particular, the author clearly emphasizes the crucial (and controversial) assumption called "Equivalence assumption".

Last edited: Jun 24, 2010
8. Jun 24, 2010

### ThisIsMyName

Dmitry67, I think everybody that has ever thought about MWI and Probability has thought of something similar.
However this doesn't let MWI off the hook, the emperical evidence still flies in the face of MWI.
Even if you say probabilities are a illusion, observation still shows Born Rule, in MWI it wouldn't.

So saying probability is a illusion or a pink elephant doesn't change anything...
MWI is still falsified until it can account for emperical evidence.

9. Jun 25, 2010

### Dmitry67

Then SR and GR are falsified too, because they use the concept of 'Block time' (eternalism) while the 'emperical evidence' tells us the opposite.

10. Jun 25, 2010

### ThisIsMyName

Dmitry67, no.
Neither is a spherical earth falsified just because our senses tells us that the earth is flat.

Let's say you set up a experiment much like the Schroedingers Cat.
Except instead of having the cat die/live lets picture 2 light bulps.
1 Red and 1 Blue.
Probability for the red one lighting up 0.001 and 0.999 for the blue one.
Carry out this experiment 1000 times in a row, and you'll have 1 occurence of red light, and 999 of blue light.

In the MWI picture, you'd expect to see 50/50 of red and blue lights since the universe branch off into 2 results everytime.
1 blue light universe and 1 red light universe.

How you can say "well in the future we might discover some theory of consciousness that shows probability is a illusion" are supposed to solve this, is really not an answer.

You could just as easily say the same for any interpretation, that a "future theory of consciousness" will explain everything and that superposition is just a illusion created by our brains and that no such thing ever existed, and therefore we can refute all interpteation of quantum mechanics...

You don't see the problem with this approach?

11. Jun 25, 2010

### K^2

The problem of Borne Rule in MWI is the same as that of classical statistical weights with "random" chance.

Say you have a bag of marbles. 1/4 of them are white, and 3/4 are black. What are the odds, at random, of pulling a white marble? 1/4. Can you prove it?

MWI results in something very similar. You end up with a superposition of world-states with observer being entangled to these. You can think of it as continuum of possible states with there being more of some states than the others. The rest is just like pulling marbles at random. Sure, you end up in all of the future states, rather than just one, but you are currently experiencing just one state, and currently, your odds of experiencing one state over another are proportional to the number of states. Just like pulling a marble, only your experience of pulling the marble is also part of the marble.

12. Jun 25, 2010

### Dmitry67

Yes, there are both branches, no matter how low is the probability of the 'rare' event.
MWI predicts that both branches exist.
It predicts, that in 'normal' branch experimenter would say - you see, Born rule works!
In weird branches it predicts that experimenter would say - WTF???
Exactly what is happening.

Lets look again at your experiment. You make the experiment 1000 times, and with 2 outcomes you get 2^1000 branches. To simplify, lets assume that you make it only 3 times and (as expected) always get the 'frequent' outcome: FFF. There are other branches like R(are)FF, FFR and even RRR.

So what you are doing from the god/birds view? You are doing the unfair sampling. You put your finger on the point of the Unverse wavefunction where FFF is true and ask: why Born rule is valid here?
Next question: But why our consicousness appear on the most frequent branches?[/]
Answer: It must be studied by the theory of consiousness

13. Jun 25, 2010

### ThisIsMyName

So Dmitry67, after several failed attempts by Wallace, Greaves, Deutsch and a few others, instead of thinking... gee maybe there is something wrong with this interpretation, you choose to "postpone" the problem to the future where it MAY somehow make sense in a theory of consciousness?

I am a firm believer that consciousness is nothing special, but hwat you are suggesting is very special, so this would be like a new axiom, hence the "elegance" of MWI is out the window.
Atleast until you have this theory of consciousness, and you have once again managed to put consciousness in the middle of the measurement problem.
Exactly what MWI tries to avoid.

14. Jun 25, 2010

### Fredrik

Staff Emeritus
People have tried to do such things, but failed miserably. Kent's article "Against many-worlds" has comments about some of them.

This is incorrect. No MWI that I've heard of predicts violations of the Born rule.

I don't think consciousness is anything more than physical interactions in a system that's also interacting with its environment, but I still think consciousness has a role to play in a more straightforward MWI (...one that doesn't throw away the Born rule). Something like...when a subsystem of the universe (e.g. an atom) interacts with its environment (which includes a measuring device and a physicist), there are many ways to decompose the universe into "worlds", but there's only one decomposition that produces worlds where the subsystem's environment can contain stable records (e.g. memories in a human brain) of the result of its interaction with the subsystem. So "consciousness" isn't actively changing anything, but the "branches" would be defined by the only decomposition into "worlds" that describes worlds were information can be stored...and those are the only ones that can contain conscious observers.

15. Jun 25, 2010

### GeorgCantor

Alternatively, one could give up dreaming of a theory of everything.

16. Jun 25, 2010

### Dmitry67

No, I dont suggest to give up or postpone, I am just thinking that the question is much deeper than one expects. Trying to 'explain' Born rule in its current form is nothing more like a desperate "brute force attack" (it terms of computer science). Born rule must be reformulated before we can try to 'explain' it.

And yes, consciousness (closely related to AP) is special. For example, we are now 13.7Gy away from Big Bang. But no observers can observe anything before say 10^6 years. Do you agree? This is another example of unfair sampling.

17. Jun 25, 2010

### ThisIsMyName

18. Jun 25, 2010

### Demystifier

Then you have not heard enough.
See e.g. the contribution of Graham in the book
B.S. DeWitt and N. Graham (eds.), The Many-Worlds Interpretation of Quantum Mechanics

19. Jun 25, 2010

### ThisIsMyName

Any of the proponents actually read the papers or seen/heard the talks by people like David Albert, Adrian Kent, Huw Price, Tim Maudlin, Roderich Tumulka etc.?
These present pretty clearly the problems of MWI.
Even proponents of MWI have accepted that MWI is hanging by a very thin thread, check out Jacques Mallah www.onqm.blogspot.com
He goes through each argument and debunks it and present a last resort, which too have major problems.

20. Jun 26, 2010

### Fredrik

Staff Emeritus
I think we briefly talked about that article before. I haven't really tried to understand it. It didn't look good to me, and it gets thoroughly trashed in Kent's article. (That whole book looks pretty bad).

I think they're good arguments against Everett's MWI, which isn't so much of an interpretation of QM as a redefinition of QM. But I would also say that if you just postulate that QM (as defined by the standard axioms) actually describes a physical system, you have actually defined a MWI that can't be debunked.

Max Tegmark mentioned Kent's "Against many-worlds interpretations" in his "Many worlds or many words". He dismissed it in a way that I find rather interesting. He just said that "...most of its claims were subsequently shown to result from misconceptions[31]". That reference [31] looks pretty bad to me, and as far as I can tell, it hasn't been published anywhere. It's interesting that a peer-reviewed article can dismiss another peer-reviewed article as useless nonsense simply by referencing something unpublished that probably is useless. Makes me wonder how much peer review really means.

Last edited: Jun 26, 2010