I Multiverse theory -- Why don't strange things happen here sometimes?

[PeterDonis]

If you believe the Universe is quantum, you should not assume the existence of classical stuff like measurement apparati

If you believe the universe is quantum, then there is no such thing as "classical stuff"; measurement apparati are just as quantum as everything else. Which is still no argument for them not existing.

Obviously, the Universe in not just quantum

No, this is not at all obvious. What is obvious is that classical physics works, in the sense of making reasonably accurate predictions, for a wide variety of phenomena, including the behavior of things like chairs, given that such things exist (although, as already noted, classical physics cannot explain how such things exist, since it can't explain why atoms exist). But that in itself does not mean "the universe is quantum" is impossible. It means that if the universe is quantum, then classical physics must be derivable as an approximation to QM under appropriate conditions. Which is precisely what many results in QM, such as the Ehrenfest theorem, are intended to show.

if I had to pick one interpretation, it would be closer to QBism

If this is your preferred interpretation, that's fine--but then you should be using it. It doesn't appear to me that you are, since many of the things you are saying don't look anything like QBism to me, including the things I have responded to earlier in this post, and in my previous posts.

 

[PeterDonis]

My point was that the very existance of the chair is far less likely than it tunneling spontaneously through wall.

What are you basing this claim on? On its face it's obviously false, since the existence of chairs is a fact of everyday observation but nobody has ever observed a chair tunneling through a wall, so if QM's predicted probabilities were as you claim here, QM would be an egregiously wrong theory. Which it isn't.

 

[Nugatory]

When you choose one aspect to be fundamental you get MWI, Schroedingers cat, Wigner's friend, etc unobserved quantum paradoxes

Perhaps better to say that if we choose one aspect to be fundamental and then misrepresent it we will get paradoxes. The modern understanding of quantum mechanics leads to neither Wigner's Friend nor Schrodinger's Cat problems and I am totally unclear as to why you think MWI is somehow paradoxical.

 

[hutchphd]

What are you basing this claim on?

If there were no carpenters in the universe, what would be the probability of a "spontaneous" chair appearing at a place certain?
I should never try to argue philosophy. As a courtesy I will try to quantify if you really insist, but I think the outcome will not be very enlightening.

 

[PeterDonis]

If there were no carpenters in the universe, what would be the probability of a "spontaneous" chair appearing at a place certain?

Still a lot larger than the probability that such a chair would tunnel through a wall in such a universe, since to get the latter probability you have to multiply the tunneling probability we have been talking about, which is conditional on the chair being there next to the wall in the first place, by the probability that the chair will be there.

 

[Drakkith]

Obviously, the Universe in not just quantum and you assuming the reality of the measurement apparatus proves this point. It is quantum and classical. You don't even directly observe the quantum side - you infer this from experiments.

I don't buy this argument. Quantum physics tells us how things work at the very smallest scales and, conveniently, most of the complicated bits can be left out as we move to larger scales so we can do things like build buildings and cars and such with much, much easier math. When your allowed tolerances are millions of atoms across you don't care very much about the uncertainty of the position of a single electron or the like. This doesn't make the universe non-quantum, it just lets us use a simpler set of rules for many things at our scale.

 

[Drakkith]

If there were no carpenters in the universe, what would be the probability of a "spontaneous" chair appearing at a place certain?

The chair and the wall don't matter. We might as well talk about a rock tunneling through the rock next to it.

 

[GarberMoisha]

I don't buy this argument. Quantum physics tells us how things work at the very smallest scales and, conveniently, most of the complicated bits can be left out as we move to larger scales so we can do things like build buildings and cars and such with much, much easier math.

This is what I have been arguing against. Rather than assuming that quantum physics is telling you how things work at the smallest scales, you should infer that it is actually preventing you from knowing exactly how things work there. Then, once you get rid of that common misunderstanding, my argument about the nature of matter will appear more naturally.

When your allowed tolerances are millions of atoms across you don't care very much about the uncertainty of the position of a single electron or the like. This doesn't make the universe non-quantum, it just lets us use a simpler set of rules for many things at our scale.

You will always be stuck with the act of measurement. This is not just unsatisfactory but hints that the commonly held belief that matter is both Newtonian and quantum depending on how you look, is wrong. These two concept don't work together in a coherent way.

 

[Drakkith]

Rather than assuming that quantum physics is telling you how things work at the smallest scales, you should infer that it is actually preventing you from knowing exactly how things work there.

Why would I do this?

You will always be stuck with the act of measurement. This is not just unsatisfactory but hints that the commonly held belief that matter is both Newtonian and quantum depending on how you look, is wrong. These two concept don't work together in a coherent way.

No one is saying matter is Newtonian. We're saying that Newtonian physics is 'close enough' for work at our everyday scale.

 

[GarberMoisha]

Quantum mechanics in its standard form without additional assumptions does not naturally lead to infinite universes and MWI but to ignorance. This is enoded in the HUP in a very robust way and is easily visible in all iterations of the double split experiment.

 

[Drakkith]

Quantum mechanics in its standard form without additional assumptions does not naturally lead to infinite universes and MWI but to ignorance.

I assume you're referring to uncertainty when you mention 'ignorance'?

 

[GarberMoisha]

I assume you're referring to uncertainty when you mention 'ignorance'?

It is the same. Ignorance via 'uncertainty'. The fundamental term is ignorance which arises via uncertainty.

 

[Drakkith]

It is the same. Ignorance via 'uncertainty'. The fundamental term is ignorance which arises via uncertainty.

This sounds purely like a personal opinion and not something based in mainstream science. I remind you that PF rules do not allow for discussion of personal opinions in most circumstances since we aim to teach mainstream science as it is understood and practiced by the professional scientific community. You can have whatever opinion you like, but I ask that you stay within PF rules. Further posts of this nature will likely result in a thread ban or an infraction.

 

[kered rettop]

Seems an odd question. "Strange" presumably means "unlikely enough that it would cause extreme surprise if it actually did happen", and, according to both MWI and all true multiverse theories, unlikely things don't happen very often. So where's the problem? Sure, this very world you are experiencing right now will, according to MWI, have split into an incalculably vast number of worlds before you've finished reading this sentence. And a huge number of those worlds will be ones where pigs have been observed flying to a warmer clime for the winter. But the huge number is miniscule compared with the number of worlds in which this hasn't happened. So the chances of you being in a world where it has happened are vanishingly small.

 

[PeterDonis]

a huge number of those worlds will be ones where pigs have been observed flying to a warmer clime for the winter

This will only be true if there is a nonzero amplitude for the world you were in when you started reading, to transition to the world you describe by the end of your reading. Which is preposterous.

The MWI doesn't say that anything you can concoct in your imagination will happen. It only says that anything that has a nonzero amplitude in the wave function will happen.

 

[kered rettop]

This will only be true if there is a nonzero amplitude for the world you were in when you started reading, to transition to the world you describe by the end of your reading.

Correct, and I am saying that if a flying-pig world is possible in the sense of not being self-contradictory then there will be flying-pig states which are not precisely orthogonal to "our" state. Even MWI/decoherence doesn't claim that for its worlds.

Which is preposterous.

Not to put too fine a point on it, that is, at best, appealing to emotion, and at worst, begging the question.

The MWI doesn't say that anything you can concoct in your imagination will happen. It only says that anything that has a nonzero amplitude in the wave function will happen.

Which is precisely why I did no such thing. Of course if you have a proof that the amplitude is necessarily precisely zero for all values of flying pig, I would love to know about it.

 

[PeterDonis]

if a flying-pig world is possible in the sense of not being self-contradictory then there will be flying-pig states which are not precisely orthogonal to "our" state.

This is something you should be making an argument for, not just handwaving.

Of course if you have a proof that the amplitude is necessarily precisely zero for all values of flying pig, I would love to know about it.

The burden of proof is on you, not on me. Show me a wave function for our current state that has a nonzero amplitude to transition into a flying pig state.

 

[Frabjous]

Show me a wave function for our current state that has a nonzero amplitude to transition into a flying pig state.

I can almost get there. I can get to a frying pig state.

 

[kered rettop]

This is something you should be making an argument for, not just handwaving.

The burden of proof is on you, not on me. Show me a wave function for our current state that has a nonzero amplitude to transition into a flying pig state.

That's a cop-out. You're the mentor round here. You have a perfect opportunity to show me where my reasoning is wrong. Or not even wrong if it comes to that. I'd learn something and so would the OP.

 

[PeterDonis]

That's a cop-out.

To it it's a cop-out to reverse the burden of proof when you are challenged to support a positive claim.

You're the mentor round here.

That doesn't mean I'm obligated to give you a response just because you think you're entitled to it.

You have a perfect opportunity to show me where my reasoning is wrong.

I've already told you: I don't think the wave function has a nonzero amplitude for what you're claiming. It's up to you to show that it does, since you are the one that made the claim about flying pigs. You have already agreed with me that a nonzero amplitude in the wave function for such a transition is necessary to support your claim. So it's up to you to show that in fact such a nonzero amplitude exists. You can't just assume that there is a nonzero amplitude for anything you like.

 

[kered rettop]

To it it's a cop-out to reverse the burden of proof when you are challenged to support a positive claim.That doesn't mean I'm obligated to give you a response just because you think you're entitled to it.I've already told you: I don't think the wave function has a nonzero amplitude for what you're claiming. It's up to you to show that it does, since you are the one that made the claim about flying pigs. You have already agreed with me that a nonzero amplitude in the wave function for such a transition is necessary to support your claim. So it's up to you to show that in fact such a nonzero amplitude exists. You can't just assume that there is a nonzero amplitude for anything you like.

Well, that's exactly what I do assume - on the basis that people who appear to know what they're talking about make it. This whole thread is predicated on a) such worlds being physically possible and b) that transitioning is possible.
For instance, the third paragraph of Sascha Vongher's article
https://www.science20.com/alpha_meme/are_terrible_quantum_states_phenomenal-87197
simply asserts both. (If you are squeamish, I recommend you do not proceed any further in the article. Vongher clearly intends to shock.)

To it it's a cop-out to reverse the burden of proof when you are challenged to support a positive claim.
That doesn't mean I'm obligated to give you a response just because you think you're entitled to it.

I don't recollect saying that I was entitled to anything. But assuming the goal of our discussion is to reach an agreement, either party could move it on if they address what the other says. And I think you are capable.
I'm not - not in the terms you want. So the discussion will remain stalled unless you choose to enlighten me.

I've already told you: I don't think the wave function has a nonzero amplitude for what you're claiming. It's up to you to show that it does, since you are the one that made the claim about flying pigs. You have already agreed with me that a nonzero amplitude in the wave function for such a transition is necessary to support your claim. So it's up to you to show that in fact such a nonzero amplitude exists. You can't just assume that there is a nonzero amplitude for anything you like.

And you can't just assume that there is a zero amplitude for anything you don't like.

 

[PeterDonis]

that's exactly what I do assume - on the basis that people who appear to know what they're talking about make it

I've seen it asserted without argument in articles, yes. I've never seen it actually argued for. So I remain skeptical. But I don't think we're going to resolve that here.

assuming the goal of our discussion is to reach an agreement

In cases like this, there is no generally accepted mainstream answer, so we should not necessarily expect to reach agreement.

you can't just assume that there is a zero amplitude for anything you don't like.

It's not a matter of me not liking the flying pigs. It's a matter of Occam's Razor. In the absence of some kind of evidence or argument that a transition from our current world to a world of flying pigs is possible, it seems to me that the more parsimonious assumption is that it's not. Either that or we should just refuse to take a position at all until somebody comes up with some kind of actual argument.

 

[PeterDonis]

This whole thread is predicated on a) such worlds being physically possible and b) that transitioning is possible.

The thread is about whether such things are possible. It is not about just assuming it.

 

[kered rettop]

I've seen it asserted without argument in articles, yes. I've never seen it actually argued for. So I remain skeptical. But I don't think we're going to resolve that here.

In cases like this, there is no generally accepted mainstream answer, so we should not necessarily expect to reach agreement.

It's not a matter of me not liking the flying pigs. It's a matter of Occam's Razor. In the absence of some kind of evidence or argument that a transition from our current world to a world of flying pigs is possible, it seems to me that the more parsimonious assumption is that it's not. Either that or we should just refuse to take a position at all until somebody comes up with some kind of actual argument.

Well I'm willing to bet that the assertions are grounded in a decent argument but as you don't know of one and neither do I, we appear to have reached an impasse.

 

[PeterDonis]

I'm willing to bet that the assertions are grounded in a decent argument

If there is one, it should appear somewhere in one of the articles on the subject, or, better still, in a peer-reviewed paper.

 

[PeroK]

That's a cop-out. You're the mentor round here. You have a perfect opportunity to show me where my reasoning is wrong. Or not even wrong if it comes to that. I'd learn something and so would the OP.

Let's start with a model of the solar system where the Sun and planets are assumed to be perfect spheres. This model works for solar system dynamics but can't be taken literally. If all we knew about the planets was their orbits, then there would be no reason to assume anything else. It would, however, be scientifically invalid to postulate the planets are perfect spheres. This is perhaps a subtle point, but it's worth thinking about. Until you have examined a planet, it's invalid to publish a theory of planetary geology based on this assumption. Even though the "perfect sphere" model is the best you have available.

Next, let's consider the model of an infinite, globally flat universe. This model is supported by the cosmological data and is the best available. Again, however, it's invalid to assume this model is literally true and make assertions like there being an infinite number of duplicate planets Earth out there. Until you have evidence for these duplicates, it's an invalid application of the infinite universe model.

Finally, if we have a mutliverse theory or MWI of QM, then the same scientific rigour applies. Just because that model is the best fit for a certain set of observations does not allow us to take model literally, and extrapolate it without limit. These alternative worlds with habitually flying pigs cannot be assumed to exist until the model has been tested in this respect.

One problem with stating the existence of such worlds is that the theory only needs to be tweaked - in a way that does not significantly alter the model's predictions in its current domain of applicability - in order for all the unobserved but extrapolated phenomena to vanish.

In the above cases, the Earth's active surface does not affect its orbital dynamics. In the second case, the universe could turn out to be large but finite. In the third case, a tweak to QM could rule out the existence of habitually bizarre worlds.

In my opinion, it's pointless to discuss such extrapolations as though they must or may be valid.

 

[PeroK]

Well I'm willing to bet that the assertions are grounded in a decent argument but as you don't know of one and neither do I, we appear to have reached an impasse.

One thing you have to be aware of is that even the greatest physicists may have debatable ideas when they step beyond theoretical physics. Personally, I don't feel obliged to believe what may be wild speculation, no matter who is doing the speculating.

 

[gentzen]

And you can't just assume that there is a zero amplitude for anything you don't like.

If an amplitude of $10^{-1000}$ leads to totally different conclusions than an amplitude which is exactly zero, then the corresponding interpretation has robustness issues. In fact, the consistent histories approach runs into this kind of trouble. One way how Griffiths tried to overcome this was by hoping that some input data could be slightly perturbed, and that thereby all those annoying nearly-zeros could be turned into exact zeros. PeroK above has basically suggested the same thing.

However, one of the strength of MWI compared to consistent histories is that it is perfectly fine with such approximate zeros. At least for the popular "self-locating uncertainty" approach to probability in MWI, this follows from the observation that from a decision theoretic perspective the probabilities from MWI should (or even "must") be treated like normal probabilities. And this implies that a possible outcome with a probability amplitude of $10^{-1000}$ should have a negligible impact on your decisions.

(If somebody objects that this amplitude of $10^{-1000}$ still implies the existence of some outcome, one could counter this by analyzing the role played by that existence in some popular MWI approaches, and how MWI actually makes things better instead of worse by not insisting on the impossibility of those outcomes.)

 

[Morbert]

If an amplitude of $10^{-1000}$ leads to totally different conclusions than an amplitude which is exactly zero, then the corresponding interpretation has robustness issues. In fact, the consistent histories approach runs into this kind of trouble. One way how Griffiths tried to overcome this was by hoping that some input data could be slightly perturbed, and that thereby all those annoying nearly-zeros could be turned into exact zeros.

Do you have a reference for this discussion?

 

[gentzen]

(If somebody objects that this amplitude of $10^{-1000}$ still implies the existence of some outcome, one could counter this by analyzing the role played by that existence in some popular MWI approaches, and how MWI actually makes things better instead of worse by not insisting on the impossibility of those outcomes.)

For example, if the measure of existence concept is used, then there is no significant difference between a nearly vanishing measure of existence and a completely vanishing one. An analogy which came to my mind triggered by the word "measure" is that mathematics avoids problems by accepting the existence of sets of measure zero. It even accepts the existence of non-measurable sets... And in general, this strategy tends to reduce the number of problems, except when people start taking "mathematical existence" literally as for example in the Banach-Tarski paradox.