many-worlds fail

Originally posted by KazetNagorra
Why is the ending of Men in Black silly?

I only saw the second of the two films, so I've no idea.

Originally posted by twhitehead
Because it gives a special place in physics to conciousness for no good reason. It is based on an oversized ego and confusion about what 'observer' means. There is nothing rational about it.

Von Neumann did an analysis and showed that it was not possible to tell when wave function collapse happened. Further the only thing qualitatively different to the rest of the apparatus is the observer's conscious mind. So, at that level it isn't as unreasonable as you seem to think. What is more a detector is not an observer. Assuming that there is a collapse of the wave function we cannot tell if a detector is enough to do it, maybe the detector goes into a linear superposition of states. It may be the case that it is not enough to measure the wave function and it requires a something qualitatively different to do it. I don't think the von Neumann interpretation can be lightly dismissed as you seem to think. What is more recent "delayed choice" experiments, where they entangled a pair of photons, sent one around an interferometer and did a measurement on the other tend to confirm it (as well as MWI and the normal Copenhagen interpretation) rather than rule it out - type "delayed choice quantum eraser" into Wikipedia. So, while I don't buy the notion that consciousness is what causes the collapse, I don't think it should be dismissed as a possibility either.

Originally posted by DeepThought
Von Neumann did an analysis and showed that it was not possible to tell when wave function collapse happened. Further the only thing qualitatively different to the rest of the apparatus is the observer's conscious mind.

There is nothing qualitatively different about the observers concious mind.

And are you telling me that computers cannot do science experiments? I disagree.

So, at that level it isn't as unreasonable as you seem to think.
It seems totally unreasonable to me and your explanation hasn't changed that.

What is more a detector is not an observer.
Yes, it is.

Assuming that there is a collapse of the wave function we cannot tell if a detector is enough to do it,
Yes we can.

maybe the detector goes into a linear superposition of states.
It probably does, but so does your concious mind. What else is new?

I don't think the von Neumann interpretation can be lightly dismissed as you seem to think.
Well you haven't given a satisfactory reason to think it can't.

Originally posted by twhitehead
There is nothing qualitatively different about the observers concious mind.

And are you telling me that computers cannot do science experiments? I disagree.

[b]So, at that level it isn't as unreasonable as you seem to think.
It seems totally unreasonable to me and your explanation hasn't changed that.

What is more a detector is not an obs ...[text shortened]... issed as you seem to think.
Well you haven't given a satisfactory reason to think it can't.[/b]

Your objections are entirely philosophical. Physics is an empirical science and since there is no evidence that the interpretation is wrong the possibility remains open.

A detector cannot count as an observer, if the detector is in a linear superposition of states (rather like Schrodinger's cat) then it hasn't collapsed the wavefunction. Now, if a conscious mind cannot collapse a wavefunction either then we are left with MWI as the sole candidate, if collapse happens earlier than when the results reach the experimenter's mind then the von Neumann interpretation is ruled out. However, since we have no experimental basis for making either of these claims we cannot rule out the von Neumann interpretation.

One last point, you may as well say that a tripod or a Bunsen burner can do an experiment. The computer is part of the apparatus, it is not the agent doing the experiment.

Originally posted by DeepThought
Your objections are entirely philosophical.

So is the claim. It remains silly.

Physics is an empirical science and since there is no evidence that the interpretation is wrong the possibility remains open.
It remains silly.

A detector cannot count as an observer,
Yes it can.

if the detector is in a linear superposition of states (rather like Schrodinger's cat) then it hasn't collapsed the wavefunction.
I am sure that cats count as observers too. They are concious- so that rather destroys the whole 'conciousness is special' argument doesn't it?

Now, if a conscious mind cannot collapse a wavefunction either then we are left with MWI as the sole candidate,
No, I don't think we are. What about partial collapse? After all, when you see the dead cat, you can do an autopsy and find out how it died. Clearly physics was going on prior to your discovery of its death.

if collapse happens earlier than when the results reach the experimenter's mind then the von Neumann interpretation is ruled out.
What if the collapse happens later than when the results reach the experimenters mind? If you put a scientist in a box, let him do an experiment, then only open the box a week later, when was the result of the experiment complete?

However, since we have no experimental basis for making either of these claims we cannot rule out the von Neumann interpretation.
Failing to rule something out, doesn't stop it being silly.

One last point, you may as well say that a tripod or a Bunsen burner can do an experiment. The computer is part of the apparatus, it is not the agent doing the experiment.
So what constitutes an 'agent' and why is it special? If I tell you to do the experiment, and I the agent, or are you? If you do the experiment entirely following my script just like a computer would and without your conciousness interacting directly with the results, then are you not the observer? What if the government sets up the experiment, is the government the 'agent'?
See how ridiculous the whole thing is?

Originally posted by twhitehead

Now, if a conscious mind cannot collapse a wavefunction either then we are left with MWI as the sole candidate,
No, I don't think we are. What about partial collapse? After all, when you see the dead cat, you can do an autopsy and find out how it died. Clearly physics was going on prior to your discovery of its death.
[/b]

There is no such thing as partial collapse of the wavefunction. Either the particle is in a linear superposition of states or it has a definite momentum or spin or whatever is being measured. Dissecting the dead cat won't tell you anything, the term in the wavefunction corresponding to the dead cat evolves just as the term corresponding to the live cat does - so when the box is opened the cat, if it survived, will have aged slightly and breathed in and out in the meantime, if it died it will have started the various chemical processes that occur during death.

In the event that the von Neumann interpretation is correct then a cat is probably a viable observer. You can replace the cat with some non living macroscopic thing that is altered by the decay. Schrodinger had a habit of trying to get his cat referred to in scientific journals, it was credited as a co-author in at least one of his papers. So don't start obsessing about the cat being a viable observer, its significance is that it's a

If a consciousness is insufficient to collapse a wavefunction then the detector isn't going to do it either and there is no wavefunction collapse. That leaves us with MWI as the only game in town.

Originally posted by DeepThought
There is no such thing as partial collapse of the wavefunction.

Wrong terminology maybe.

Either the particle is in a linear superposition of states or it has a definite momentum or spin or whatever is being measured.
Are you sure its an 'either or'?

Dissecting the dead cat won't tell you anything,
It will tell you that complex physics was going on inside the cat prior to you opening the box. Complex physics that simply doesn't work without collapse of the wave function. I think you are forced to choose between:
1. A many-worlds scenario going on inside the box,
2. or wave function collapse propagating backwards through time
3. wave function collapse prior to the box being opened.

I believe that 3 is the correct answer with macro objects basically being immune from wave function modelling.

In the event that the von Neumann interpretation is correct then a cat is probably a viable observer.
What about a worm?

So don't start obsessing about the cat being a viable observer,
The reason why it is popular is irrelevant to whether or not it is a viable observer and any points I may have made in that regard.

If a consciousness is insufficient to collapse a wavefunction then the detector isn't going to do it either and there is no wavefunction collapse.
What if a detector is sufficient?

That leaves us with MWI as the only game in town.
I disagree.

Originally posted by twhitehead
Wrong terminology maybe.

[b]Either the particle is in a linear superposition of states or it has a definite momentum or spin or whatever is being measured.
Are you sure its an 'either or'?

Dissecting the dead cat won't tell you anything,
It will tell you that complex physics was going on inside the cat prior to you opening the box. Com ...[text shortened]... detector is sufficient?

That leaves us with MWI as the only game in town.
I disagree.[/b]

Of course it's an either - or. There aren't any other alternatives, either a particle is in a definite state or it is in a linear superposition of states.

How do you know that complex physics won't work without wavefunction collapse?

Wavefunction collapse prior to the box being opened is ruled out. See the Wikipedia page on "delayed choice experiments".

If a detector is sufficient to collapse a wavefunction then a conscious observer will too. If a conscious observer cannot collapse a wavefunction then a detector can't either. In that case there is no wavefunction collapse and the only two interpretations of quantum physics that have no wavefunction collapse are MWI and Bohmian mechanics. There are experimental grounds for thinking that Bohmian mechanics is ruled out (Aspect et al.) and so MWI is all that is left.

Originally posted by DeepThought
I only saw the second of the two films, so I've no idea.

The ending of Men in Black is as silly as the von Neumann interpretation of quantum mechanics.

Originally posted by DeepThought
How do you know that complex physics won't work without wavefunction collapse?

Its kind of obvious.

Wavefunction collapse prior to the box being opened is ruled out.
I disagree.

See the Wikipedia page on "delayed choice experiments".
Will do. But I bet there are no cats involved.


Imagine this scenario. You have three Schroedinger boxes. In the first you put a computer, in the second you put a cat and in the third you put a lab assistant.
The boxes are set up to do an experiment and then destroy the computer and kill the cat and lab assistant but not before they record the results of the experiment.
Now you are saying that when the three boxes are opened, the results will be different depending on whether the computer or the lab assistant did the recording. You are not so sure about the cat.
Silly.

Now lets have a larger box with two compartments. The experiment takes place in compartment one and the results are recorded by computer. The other compartment contains the lab assistant who never sees the results of the experiment.
When the box is opened will the lab assistants presence in the box have affected the results?

Originally posted by DeepThought
See the Wikipedia page on "delayed choice experiments".

https://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser
or
https://en.wikipedia.org/wiki/Wheeler%27s_delayed_choice_experiment
?

Originally posted by twhitehead
https://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser
or
https://en.wikipedia.org/wiki/Wheeler%27s_delayed_choice_experiment
?

Either really, the Wheeler page is theoretical, in the sense that they are talking about a series of thought experiments. The quantum eraser page is about an actual practical experiment.

Originally posted by finnegan
So MWI looks messy to you. Our ability to understand this is not, to my mind, a critical test of the model. In any case, learning how to visualise models of the universe is quite an art form in itself. My favourite is the discovery that knitting is the best way to produce descriptions of some mathematical models. Why does the collapse of a wave form ha ...[text shortened]... only one of many models to accommodate. You will really have to think more flexibly to keep up.

Since nobody knows the truth, all of this is speculation till some evidence turns up. One such evidence is the large circular pattern of coolness in the CMB.

Originally posted by twhitehead
So why are we in this one and not the other?
Because it is impossible to be 'in the other'. We are in this one because we labelled it 'this one' because we are in it.

Back in universe Z, when we measured the position of that electron. You seem to be saying that it was impossible for us to discover that the electron was in position B.

OF COURSE when we are here, we are not there. That doesn't address my question.

Originally posted by twhitehead
Looks like a probabilistic outcome to me.
Well it isn't. It is related to the anthropic principle only much simpler. In both universes there is someone asking the rather stupid question 'why am I in this one and not the other one?' Its all a matter of perspective. You are seeing yourself as an entity distinct from the universe that has been thrust i ...[text shortened]... the universe and as such it is nonsensical to ask why you are there and not in some other universe.

MWI claims our universe splits in two (in the scenario we're laboring under). You have agreed we do not find ourselves in universe B. I merely ask why did we take one path and not the other. It's not my fault you have no solution.