Note that this blog post assumes that you have either watched the video or read the associated paper. If you haven't, what follows will probably not make a lot of sense.

The question I keep getting is some variation on the following theme: What is the relation of the QIT/zero-worlds interpretation of QM to interpretation X, where X is usually many-worlds, but is sometimes relative state. Riffing off this I'll get questions about the implications of QIT for time-travel, the relationship of QM to consciousness, and whether or not we might be able to influence the results of quantum measurements with our minds.

The short version of the answer is: QIT/zero-worlds is nothing more than a different way of looking at the math than what is usually presented in the popular press. It is a way of looking at the math that makes sense to me (and apparently, based on the feedback I get, makes sense to a lot of other people as well). But that is

*all*it is. There is no breakthrough here (except, perhaps, a pedagogical one). It turns out that all this stuff was actually known as early as the 1930s. Why Feynman was still saying that no one understood quantum mechanics in the 1960s I do not know. It is certainly not true today. But the point is that despite the somewhat sensational rhetoric ("You don't really exist; you are living in a simulation running on a quantum computer") nothing really changes as a result of QIT except your perspective. You are still every bit as real (or not) as you were before. Time travel, ESP, and telekinesis are still every bit as impossible as they were before.

The other short version of the answer is that many-worlds/relative-state/whatever are all equally valid ways of looking at QM. The only one that isn't equally valid is Copenhagen. To be sure, Copenhagen is a reasonable approximation to the truth for many practical purposes, just as Newtonian mechanics is a reasonable approximation to the truth (which is, to the best of our current knowledge, general relativity) for many practical purposes. But Copenhagen is

*conceptually*wrong, just as Newtonian mechanics is conceptually wrong. There is no "force of gravity" and the wave function never collapses. The challenge is to explain why it

*appears*to do so. That is what QIT does (IMO).

Let's take a moment to review the problem that QIT (and other interpretations of QM) purport to solve: QM is one of the two most successful scientific theories ever (the other being GR). No experiment has ever disagreed with a prediction made by QM. However, the mathematics of QM seem to be fundamentally at odds with the apparent nature of reality. The Shroedinger equation is continuous, deterministic, and time-reversible. Moreover, it describes a world where objects can exist in superpositions of states, a phenomenon which can be experimentally demonstrated through interference experiments. By way of contrast, the world appears to consist of material objects which at all times exist in some particular state and never in a superposition. Moreover, the process of making a measurement appears to be discontinuous, non-reversible, and also involves some fundamental randomness which is nowhere to be found in the Shroedinger equation. The apparent contradiction between the theory and the manifest nature of reality has historically been called the "measurement problem."

QIT solves the measurement problem by observing that you can describe measurement as a purely quantum process. When you do this, the following facts emerge (and this is what the Google tech talk and associated paper are about):

1. Measurement and entanglement are the same physical phenomenon. Measurement is nothing more than the mutual entanglement of a large collection of particles (or, to be strictly correct, of systems that manifest themselves as particles under certain circumstances).

2. Once two particles are entangled, it is not possible to "undo" that entanglement except by bringing the two particles physically together. If there were any other way to "undo" an entanglement, then it would be possible to transmit information faster than light.

3. The apparent randomness that results from a quantum measurement is just that: apparent. In actual fact, the entropy of a system that has undergone a quantum measurement does not change. The reason that there

*seems*to be randomness is that when you draw a line between the particle being measured and the measurement apparatus, you end up with positive entropy (i.e. randomness) in the measurement apparatus and corresponding

*negative*entropy in the particle being measured (which is possible because the state of the particle is a complex number).

4. The reason that two measurements made on the same physical quantity produce the same result is

*not*that the measurements are a faithful reflection of some underlying physical (or metaphysical) "element of reality" as Einstein put it. Instead, if you look at the quantum mechanical description of two separate measurements on the same system what you end up with is a mathematical description that looks exactly the same as two classical systems in classical correlation with each other, but that says

*nothing*about the actual state of the system being measured (except that it is now entangled with the measurement apparatus).

5. The apparent non-reversibility of a measurement is likewise not fundamental, but merely practical. Reversing a measurement

*is*possible in principle, but to reverse a measurement, you have to reverse

*all*of the entanglements that produced that measurement to begin with. Reversing even a single entanglement is extremely difficult. Reversing a macroscopic number of them (and you really do have to get them

*all*, every single last one), while possible in principle, is not possible in practice.

In other words, there is no measurement problem. All of the apparent contradictions between the mathematics of QM (continuous, deterministic, time-reversible) and measurement (discontinuous, random, non-reversible) can be understood purely in terms of quantum mechanics itself. Furthermore, all of this (except possibly the bit about negative entropies) was known in the 1930s. So why has QM been considered so intractably mysterious for so long? Indeed, why is QM *still* considered by many to be intractably mysterious?

I don't really know, but I suspect it's because people don't want to accept what the math is telling them. The math says, essentially, that you don't really exist (or, if you prefer, your existence is not unique -- it turns out these are two equivalent ways of saying the same somewhat ineffable thing). This is not the first time this has happened. The exact same kind of conceptual stumbling block delayed the discovery of relativity for decades. The fact that Maxwell's equations predicted the existence of electromagnetic waves moving at a fixed velocity

**c**was known in the mid-1800s. But no one took this seriously until 1905, because it was just

*obvious*that time and space are absolute and so there just

*had*to be some fixed medium through which electromagnetic waves propagated and relative to which the predicted speed

**c**was to be measured.

The similarly obvious (but nonetheless false) assumption that everyone gets hung up on today is that the universe is, in point of metaphysical fact, what it appears to be: the whole of creation, populated by material objects that exist in particular places at particular times. The answer to the puzzle: how can such a universe arise from quantum mechanics is, quite simply: it doesn't. It

*appears*to, but this is an illusion. To be sure, the illusion is quite compelling, but it is false. It is every bit as false as the illusion that space and time are two distinct things (which can also, it should be reiterated, be quite compelling).

It is worth pointing out that the fact that the underlying truth is very different from what we naively perceive it to be is evident long before you get to quantum mechanics. You think that the chair you are sitting on is a solid object, but in fact it is mostly (>>99%) empty space. The reason is appears to be solid is that the electrons in the outer shells of the atoms that make up the chair repel the electrons in the outer shells of the atoms that make up your body (or your pants). So even in a pre-Shroedinger world, things are very different than they appear.

OK, so atoms aren't solid, but they are still (in a post-Rutherford but pre-Shroedinger world)

*classical*. They exist at definite places at definite times. It makes sense to distinguish this particular hydrogen atom that is part of a water molecule in your little finger from that hydrogen atom which is undergoing nuclear fusion in the core of the sun. It is

*obvious*that atoms are classical material objects. We can even take pictures of them and move them around nowadays. The evidence that atoms are classical is

*overwhelming*. How could it not be true?

Well, it's not true. Not only is it commonplace nowadays to take pictures of atoms and move them around, it is also commonplace to do interference experiments with them. And not just atoms, but enormous molecules have been observed to interfere. And yet, it is

*obvious*(and at this point that phrase should be ringing alarm bells in your head) that somewhere between a buckeyball and you there

*must*be a line where the world

*really does*become classical because it is

*obvious*that

*you*are classical.

Sorry to be the one to break this to you, but you're not. The evidence that you are classical is indeed overwhelming, just as the evidence that space and time are absolute is overwhelming. But in fact neither is true. The reason you can take a picture of an atom is not that the atom is really there, but because in the process of taking the picture your camera becomes entangled with the atom. Then, when you look at the picture, you become entangled with the camera. The reason you think that there's an atom there is because you are a large system of mutually entangled particles, hence quantum mechanics predicts that any particular part of you will behave as if it were a classical system in classical correlation with every other part of you. The net result is a system where every piece of it agrees that there is (or is not) an atom there. And asking your fellow humans to corroborate your intuitions doesn't help, because they too are large systems of mutually entangled particles, and as soon as they look at the same picture you have looked at, they too become entangled with it and with you and with the original atom, and so every part of

*that*system (you plus your collaborators) will agree that there was an atom there (or not).

So is the atom "really" there?

The problem with this question is that it seems like the answer should be either "yes" or "no", but this too is false. The nature of this question is more like this one:

Was Darth Vader (or, if you prefer, Anakin Skywalker) "really" Luke's father?

One the one hand, it seems that the answer should be "yes" because, in the Star Wars universe, Anakin/Vader was Luke's father. But, of course, the Star Wars universe is fictional, so what does it mean for a fictional character to "really" have any particular attribute?

The answer, IMO, is to simply observe that fictional characters like Luke Skywalker and Harry Potter are in a different "ontological category" from (classically) real things like George Lucas or J.K. Rowling. Well, the quantum wave function is also in a different ontological category than classical reality. Fiction "emerges" from (classical) reality in much the same way that classical reality "emerges" from the wave function. (The reason I hedge with "much the same way" is that there is one important difference: fiction and classical reality can both be described as classical computational processes, i.e. the math involves only real numbers, whereas the quantum wave function can only be described with complex numbers. So the process by which classical reality emerges from the wave function is mathematically different (but conceptually similar) from the process by which fiction emerges from classical reality.)

So is the atom "really" there? Well, to you it is. It is every bit as real as you yourself are, and for the exact same reason: because the atom is part of the system of mutually entangled particles of which you are a part. (This is sometimes called the "relative state" interpretation of QM.)

But let's take a different example. Instead of asking whether the atom is really "there" let us ask instead if one of its electrons is "really" spin-up or spin-down (or, equivalently, if some photon it emits is "really" polarized vertically or horizontally). You measure it, and the result is spin-up. Your friend measures the same electron and agrees, yep, it's spin-up. So you and your friend have become mutually entangled with this electron and hence are behaving just like a pair of classically correlated classical systems, just as QM predicts.

But, while QM predicts that you will be classically correlated, it does NOT (and cannot) predict what the outcome of your measurements will actually

*be*. That can only be done probabilistically, which seems at odds with QM (which is, if you will recall, purely deterministic). To understand this we have to dig a little deeper into the math. I've hinted at this before when I said that in order to extract a description of the classical world from the wave function you have to "trace over certain degrees of freedom". That is just a fancy way of saying, "discard some of the information about the system." Consider the full QM description of a particle that has been measured. Part of that description is the state of the particle, and the other part is the description of the measurement apparatus. To extract the state of the measurement apparatus you "trace over" (i.e. discard) the parts of the description that describe the state of the particle being measured. What you are left with is not one classical world, but two: one in which the measurement apparatus says spin-up, the other in which it says spin-down. But (and this is the crucial point) in

*neither*of these descriptions is the spin of the

*particle*

*actually*spin-up or spin-down. It can't be. There

*is*no description of the state of the particle being measured, because we had to throw it out in order to extract a description of (something that looks like) a classical universe, and that actually turns out to be a description of two classical universes. That is where the "multiple worlds" interpretation comes from.

So do these universes "really exist"? Again, in my opinion that's like asking whether Darth Vader is "really" Luke's father. Classical universes are what you get when you take the quantum wave function and throw out parts of it. That is the mathematical fact. You can interpret this mathematical fact however you choose, with one exception: you cannot reasonably conclude that the classical universe that you live in is "all there is" because a complete description of the (classical) state of the universe is only, and can only ever be, a partial description of the underlying quantum state.

So what about all those other universes? Are they real? Well, from the perspective of the quantum wave function, yes, they are. A classical universe is just a "slice" of the wave function (i.e. the whole wave function with parts of it discarded) and the wave function doesn't care which way you slice. It's rather like if someone wrote an alternate Star Wars universe where Darth Vader was not Luke's father. The existence of such an alternate Star Wars universe would have no bearing on whether Darth Vader was Luke's father in the original Star Wars universe (the answer there would remain "yes") nor would it have any bearing on whether Darth Vader was Luke's father in the "real" universe in which both Star Wars universes were embedded (as fiction): the answer there would remain that the question is meaningless because mixing ontological categories makes no sense.

David Deutsch, for whom I have the utmost respect (I think he's actually one of the best popularizers of science ever) is a fierce proponent of the proposition that all classical universes are equally real. I respectfully disagree with him. It is true that they are all equally real from the perspective of the wave function. But I don't have the perspective of the wave function, and neither do you. You and I live in

*this*universe, and so

*to us*,

*this*universe is

*more real*than any of the other myriad universes that emerge from the wave function. There may be a transporter in the Star Trek universe, but that doesn't help Luke Skywalker escape from Emperor Palpatine because Luke can only take advantage of (and hence only cares about) what exists in

*his*universe.

What about the possibility of communicating between universes? Wouldn't that be cool? If those universes are "as real as we are", shouldn't that be possible? Well, unfortunately, no, it's not. The way in which classical universes emerge from the wave function makes communication between them impossible. You can prove this mathematically, just as you can prove that quantum entanglement can't be used to send information faster than light. This is another reason I believe that parallel universes can safely be regarded as less real than our own universe, at least by us. But reasonable people can (and do) disagree.

There's a lot more to say about this topic, but this post has already become longer than I intended it to be. I'll write more if there's interest, but I want to leave you with a parting thought (well, more of an exercise actually): remember that I said that measurements were in principle reversible. Imagine that we could actually carry out this program of undoing the myriad entanglements that constitute your making a particular observation. What would be the subjective sensation, i.e. what would it "feel like" if this were done to you?

## 36 comments:

I'm with Deutsch and the multiple-world interpretation, but most of your lengthy post doesn't actually distinguish between QIT and MWI. You spend the first section on quantum vs. classical, and then some on how Copenhagen (the most popular!) doesn't actually work.

But for people who are past all that, and just looking to choose between QIT and MWI, is it merely a matter of intuitive comfort? If I'm comfortable with MWI, would there be any additional reason for me to consider switching my conceptual framework to QIT instead?

> But for people who are past all that, and just looking to choose between QIT and MWI, is it merely a matter of intuitive comfort?

Well, it is a matter of intuitive comfort since the difference between QIT and MWI is purely rhetorical, but I'd take issue with your use of the word "merely". The question of whether or not I actually exist, or whether or not an infinite number of copies of me actually exist (whatever that could possibly mean) matters a lot to me.

To me the biggest conceptual hurdle of MWI is not the existence of parallel universes, but the fact that the supposed "shadow particles" that actually affect our universe are precisely those that propagate according to the macroscopic configuration of our universe. That rule strikes me as arbitrary and without any conceptual foundation. QIT has no such problems.

BTW, even Deutsch concedes that multiple worlds is only an approximation to the truth in his latest book:

"Universes, histories, particles and their instances are not referred to by quantum theory at all – any more than are planets, and human beings and their lives and loves. Those are all approximate, emergent phenomena in the Multiverse." [Deutsch, David (2011-03-31). The Beginning of Infinity: Explanations that Transform The World (Penguin Press Science) (p. 292). Penguin Books Ltd. Kindle Edition. p291]

Thanks for attempting to answer my question. I may not be following your words. What does "

shadow particles that actually affect our universe are precisely those that propagate according to the macroscopic configuration of our universe" refer to?I thought MWI was basically just: the wavefunction is "real", it just evolves deterministically, everything is always in superposition, "particles" are distributed throughout space, and (like you say above), the classical world illusion comes because you, the observer, get entangled by the observation. Which necessarily implies that you the observer also remain in superposition, necessarily having seen both outcomes of the experiment. Which is often informally described as "multiple worlds", but as you say from Deutsch, it's really just a single multiverse, and it's just a convenient labelling to call them "multiple worlds".

But that's what I thought MWI

was. Your quote from Deutsch doesn't seem in conflict with it, to me. It seems to describe the actual original MWI interpretation.> What does "shadow particles that actually affect our universe are precisely those that propagate according to the macroscopic configuration of our universe" refer to?

See: http://blog.rongarret.info/2009/04/on-shadow-photons-and-real-unicorns.html

(I know you read that post because you left a comment on it :-)

> that's what I thought MWI was.

This is part of the problem. Everyone agrees on the math. The trouble is translating the math into a natural-language story, so the words matter. The problem with *your* formulation of MWI is:

"Which necessarily implies that you the observer also remain in superposition"

The math clearly says this. So why don't I feel like I'm in a superposition? Why does it feel to me as if the results of quantum experiments are definite but random results?

Deutsch's formulation is different from yours, and his formulation answers that question. His formulation doesn't refer to superposition. According to Deutsch, the multiverse *consists of* an infinite number of classical universes, of which you inhabit one, and copies of you inhabit the rest. The reason the outcomes of quantum measurements appear definite is that they *are* definite in each universe. The reason they appear random is that the outcomes are *different* in each universe, so the outcome you see depends on the universe you are in.

The problem with *that* formulation is that it has a devil of a time explaining interference. (Go pick up a copy of "The Beginning of Infinity" and read chapter 11 to see what I mean.)

BTW, "The Beginning of Infinity" is a terrific read. Highly recommended.

Very helpful, thanks. I went back and re-read that earlier post of yours. As I essentially implied with my comment on that post, I'm not sure that Deutsch's "shadow photons" are the same as Everett's Multiple Worlds. That's why it confused me when you said "

the biggest conceptual hurdle of MWI is ... shadow particles".On the other hand, I accept your followup question: if observers remain in superposition, why does the world feel classical? And why does QM appear random? I agree that those are the primary challenges for an intuitive QM interpretation.

> As I essentially implied with my comment on that post, I'm not sure that Deutsch's "shadow photons" are the same as Everett's Multiple Worlds.

Are we reading the same comment? Because I don't get that at all from what you wrote. (And why don't you think that they're the same?)

> it confused me when you said "the biggest conceptual hurdle of MWI is ... shadow particles".

Well, you edited out some pretty crucial words there :-)

Let me try to make it clearer: the biggest conceptual hurdle in the many-worlds interpretation is describing the rules under which one universe interacts with another. The reason this is challenging is that there is a tacit implication that every individual universe in the multiverse is classical, and that's wrong. Classicality is an approximation, and there's no way around that. At macroscopic scale and 300K it's a damned good approximation, but it's an approximation nonetheless. The instant you insist that particles are real, you lose. (IMO of course. Deutsch would vehemently disagree.)

I haven't (yet) read the Deutsch stuff that you're referring to, so I'm just going off your own description here. But wow, that is not how I would have described MWI to someone else. I would never mention "shadow photons", I completely agree that the classical world is only an approximation, I don't think that particles are local (I assume that's what you mean by "particles are real"). The rules by which one universe interacts with another, are nothing more (or less) than the standard QM math for superposition. Because "world" in "multiple worlds" is just an approximation, perhaps somewhat similar to the way that "species" describes useful categories of life forms (but isn't precise when you get to the edge cases).

But that doesn't sound at all like what you are describing as Deutsch's view, and/or your description of MWI. (And are those two things the same? Do you think Deutsch is describing "standard" MWI?) On the other hand, I'm not quite sure whether the framework I already understood, is the same as what you are calling QIT (given that I don't really understand the details of QIT).

I guess I need to read and study Deutsch's new book, and your QM paper, to see how it relates to what I thought I already understood (which, until now, I believed was "standard MWI").

Just a quick note of thanks, Ron, both for your YouTube video on QIT and your linked paper. I will not pretend to grasp the math at this time, no background in it. But I appreciate your efforts to clarify the issues surrounding QM's application to "reality."

Best wishes from SoCal.

Scott

My pleasure, VMC, and thanks for the kind words. Just out of curiosity, what part of the math do you not think you understand? If you know basic high school algebra and understand what a complex number is then you should be able to understand the basics of QIT.

LOL! Well, let's start with this:

(ΨU + ΨL)/√2

I read the above as "Strange Maserati Emblem" unintelligible PLUS "Repeat Strange Maserati Emblem" lost-me divided by the square root of 2.

I understand that complex numbers allow for exponential expressions to yield negative numbers and that they are useful for describing curves that go into the below-zero realm on the number line.

I do understand multi-dimensionality through working with arrays in programming, but all-in-all, I am an English major who could never have done any math at all had it not been for computers and spreadsheets. In any case, I am studying your paper and will try to get better in the math realm. My hope is to have as clear a view of the implications of QM on the "real" as you seem to have, Ron. In any case, that's about where I am at with it.

Don't let the Greek letters freak you out. The Maserati emblem is just a Greek letter called Psi, but that doesn't matter. You could just as easily call it X. What matters is:

1. It's a function (generally of space and time, but that doesn't really matter. It's a solution to the Shroedinger equation too, but that doesn't really matter either.)

2. Its value is a complex number

3. Its significance is that its value represents the amplitude of finding a particle at a particular place and time, and the amplitude is the "square root" of the probability. You square the magnitude of the amplitude to get the probability.

That's really all there is to it. The square root of 2 is there to make the total probability when you add two wave functions come out to be 1. If you were adding three wave functions there would be a square root of three there instead.

Triple Existential Crisis?

>The math says, essentially, that you don't really exist (or, if you prefer, your existence is not unique . . ..

>.. . . how can such a universe arise from quantum mechanics is, quite simply: it doesn't. It appears to, but this is an illusion. To be sure, the illusion is quite compelling, but it is false

It appears we have a triple existential crisis possibility here

1) one's life is meaningless [the original]

2) one doesn't really exist (or is not unique) [new]

3) one's life is an illusion [new]

Ron, have you suffered any day-to-day angst upon realizing the above? Often, the more knowledge, the more grief.

> In actual fact, the entropy of a system that has undergone a quantum measurement does not change.

Any commentary you can share here regarding a linkage to information entropy? Say in the context of Maxwell's Demon? [see especially reference 7 on the demon page]

Perhaps the measurement apparatus creates a bit (and positive entropy kT ln 2) and the particle creates a negative bit (and negative entropy -kT ln 2)?

P.S. pilot waves...

> Ron, have you suffered any day-to-day angst upon realizing the above?

No, absolutely not. The exact opposite, in fact. For starters, I don't believe #1, and never have. As for 2 and 3, they don't really change anything. Just because I happen to know that I'm made of bits instead of things doesn't make me any less real with respect to the things I care about. If anything, coming to understand QM has brought a rather profound (if subtle) sort of inner peace because now I feel like I know the Mind of God (speaking metaphorically of course).

> Perhaps the measurement apparatus creates a bit (and positive entropy kT ln 2) and the particle creates a negative bit (and negative entropy -kT ln 2)?

Yes, that is in fact exactly what happens. Did you not read the post? It's point #3:

"3. The apparent randomness that results from a quantum measurement is just that: apparent. In actual fact, the entropy of a system that has undergone a quantum measurement does not change. The reason that there seems to be randomness is that when you draw a line between the particle being measured and the measurement apparatus, you end up with positive entropy (i.e. randomness) in the measurement apparatus and

corresponding negative entropy in the particle being measured(which is possible because the state of the particle is a complex number)." [Emphasis added]>> 1) one's life is meaningless [the original]

> I don't believe #1, and never have.

You've been holding back on us. Forget QIT. Answer this question:

What is the Meaning of Life?> You've been holding back on us.

No, just because I believe life has meaning doesn't mean that I know what that meaning is. (Look up "non-constructive proof.") And even if I knew the meaning of life, it does not follow that I can articulate it in a way that someone else could understand. It's challenging enough explaining quantum mechanics. That's a cakewalk compared to the meaning of life.

Nonetheless, I'll take a quick whack at it here. For a much better answer read David Deutsch's book, "The Beginning of Infinity".

First, the word "meaning" has two meanings (see?) and I presume you mean meaning as in "purpose" rather than meaning as in "definition". So to avoid ambiguity, I'm going to use the word "purpose" rather than "meaning" (though it turns out that the purpose of life is found in its definition -- see below).

Second, the question itself is ambiguous. It can mean "What is the purpose of life in general?" Or it can mean, "What is the purpose of human life?" Or it can mean, "What is the purpose of *my* life (or *your* life)?" I think the last question is the one most people really care about, but that, of course, is the hardest one to answer. Personally, I believe the answer to the last question can be found in the answer to the first, and that the purpose of life is to be found in its definition: Life is (by definition) the reproduction of information, and IMO that is also its purpose. What makes this answer more profound than it appears to be at first glance is that it turns out that not all information is created equal. Some information is "better" than other information because it actually corresponds to the way the world actually works, and so it can be used to manipulate one's environment in the service of goals, and so it can be used to promote the reproduction of information, i.e. life.

A more poetic way of putting it: life is a process, and its purpose is simply to participate in it. But to fully participate in it you have to *understand* it, and that makes it profound and interesting and meaningful.

You asked.

Shadow particles: qm :: epicycles: Copernicus. By the way, I think it's time to kill the Buddha.

Life has one intrinsic meaning: love. No other thing makes life worth the time other than love. So that is the best purpose or meaning to life I can dowse out of it.

Love. Figure shit out the best you can. Have fun doing it. That's it. If you need more meaning than that, make some good shit up and build a temple in Salt Lake.

The Meaning Of Life

>A more poetic way of putting it: life is a process, and its purpose is simply to participate in it. But to fully participate in it you have to *understand* it, and that makes it profound and interesting and meaningful.

That is very rational and well-reasoned.

You put yourself in good company. It reminds me of the message of Ecclesiates, traditionally credited to Solomon (traditionally, the wisest man who ever lived). I would summarize the message of Ecclesiates as "enjoy life and obey God's commandments." Ref. Eccl 9:9-7, 12:13

Of course, the real meaning of life is~`!.&

LOST CONNECTION

> That is very rational and well-reasoned.

Why, thank you! :-)

Ron: Finally had a chance to read "Beginning of Infinity" over the holidays. Good stuff, although most of it (by now) wasn't especially new to me.

I encountered two big surprises that I didn't expect. Near the end, he's very critical of Jared Diamond's "Guns, Germs, and Steel" (and the subsequent "Collapse"), which is a book that I was very impressed by. The criticisms I had heard before were about Diamond unscientifically dismissing possible group/racial IQ differences (because the subject is painful and politically incorrect, not necessarily because it isn't a piece of the puzzle). But that's not what Deutsch complains about. I don't think Deutsch quite convinced me, but he has left me a good deal more uncertain about Diamond's thesis.

The second, was his chapter on the benefits of plurality voting ("winner take all"), over what seems intuitively to be a more "fair" proportional voting system with a parliament. And the benefits of a "two-party system", vs. again the intuitively appealing benefits of a strong multi-party culture.

I had never heard a perspective defending two-party plurality, and criticizing multi-party proportional parliaments. Very enlightening.

(Of course, the main topic of the book is science and explanations and memes, but that's old ground for us here.)

A bit of a tangent, but connected, could i ask if you guys might give us some comments on a face book conversation?

Natasha Dunlop’s idea for how the universe came into being;

Closed Door Universe Idea

Once observed the multiverse collapses and resolves to a single event pathway leading to the observation.

For anyone who wants to read more;

see next comment

....Continued for anyone who wants to read more;

I first posted it on Online Philosophy Club in September 2013.

17 Sept 2013

This is a response to the question of how the universe emerged within the extremely narrow parameters which enable it to support life.

This stab at an answer suggests that the only outcome of a quantum multiverse can be life, and that no other outcome is possible.

We look back through time and space attempting to see the origins of our universe and ultimately our own existence. We observe a clear linear path, a single universe flowering from a surprisingly fortuitous set of universal constants, and unfolding step by step with each node and path leading onwards towards greater complexity and life.

Imagine that the clear path that we look back upon, is only one of many, of a multitude of paths covering every option conceivable, every possible fluctuation, but that now, crucially to this idea, every one of these paths has been closed and is invisible to us, except for one.

In this idea I envisage the universe developing as a quantum multiverse, in which all available possibilities are explored and taken simultaneously, and multiple universes exist alongside one another. This multiverse state exists only initially, I envisage it as being unstable. The event which causes it to crystallize, to resolve, is the act of observation / recording.

Once observed the multiverse collapses and resolves to a single event pathway leading to the observation.

To the observer no other pathway existed, and the single observable pathway appears to have been driven by chance and probability.

What this infant hypothesis does not yet attempt to state is the exact nature of the observation. Is the simple perception of an early creature's environment enough to resolve the quantum universe, or does it need to be a recording of the universal constants, in which case the development of highly intelligent life and complex culture is required?

Is the resolving event a single event resulting in a single universe, or is it resolved multiple times by different creatures / cultures / individuals?

Is it possible that further universal quantum doors close within the time frame of the life of an individual, and if so is that individual's perception and memory of their past altered in some way?

This is a very early idea, wide open with further questions. I welcome your thoughts.

The comments in the face book conversation;

.... Richard Woods commented;

That sounds like a reasonable hypothesis, there's certainly a lot of evidence that quantum effects are materialised at the macro scale. That the cosmic scale would also be subject to quantum effects seems to follow. This reminded me of a very good Google Tech Talk about quantum mechanics which starts by describing the well known double slit experiment and goes on to explaining quantum entanglement and quantum erasers. The conclusion is what your hypothesis reminded me of. https://www.youtube.com/watch?v=dEaecUuEqfc

.... I commented;

Thanks for reading and responding to my idea Rich. Great link. I see that Ron Garrett has a blog - blog.rongarret.info - and I might see if he might comment on our thoughts. Seeing link my guess is that he will disagree with the idea, seeing it based on Copenhagen in terms of the element of collapse / crystallisation. He certainly sees one classical universe as untenable doesn't he, in favour of multiple or zero, whether he would see final outcome of hypothesis as a single classical, or as a quantum? Anyway I'll try and ask.

Another quote from the link that links to idea and measurement;

Maths tell us that "Measurement is a continuum. It's not a dichotomy".

Guess this feeds into the who what can be the observer, and does it make the idea of an observation leading to crystallization of a single universe less plausible?

> could i ask if you guys might give us some comments on a face book conversation?

Not quite sure what sort of comment you're looking for here. But you might find this interesting:

http://blog.rongarret.info/2014/10/parallel-universes-and-arrow-of-time.html

@Natasha Dunlop: I suspect you guessed correctly, that your theory is built on the Copenhagen interpretation, which attempts to make consciousness and/or conscious observation "special". But that's probably the worst and least plausible of all QM interpretations. (As you yourself say: "...does not yet attempt to state ... the exact nature of the observation." That's an alarming weakness, for something that is so central to your theory.)

Nonetheless, the intuitions behind your theory remind me a lot of the Anthropic principle. You may find it interesting that it's a feasible candidate for explaining some apparently arbitrary parts of this universe ... but it doesn't require quantum mechanics at all!

Many thanks Ron and Don for your comments and for your suggested links and further reading.

I'm coming to this thread very late, via a link from a discussion on Hacker News, to post a few comments/questions on aspects of physics discussed in this article.

The only one that isn't equally valid is Copenhagen.I don't think this is correct. The Copenhagen interpretation uses the same underlying mathematical machinery and makes the same predictions for all experimental results as all of the other interpretations of QM. So it's just as valid given our current state of knowledge.

What's different about Copenhagen is that it leads to different expectations about what a future theory that has current QM as an appropriate approximation will look like: Copenhagen leads you to expect that such a theory will have an explicit collapse (i.e., non-unitary process) somewhere in it (as in, for example, the GRW stochastic collapse model), whereas interpretations like the MWI lead you to expect that no such thing will ever be part of a more complete theory. But we don't currently have any way of testing these possibilities by experiment.

To extract the state of the measurement apparatus you "trace over" (i.e. discard) the parts of the description that describe the state of the particle being measured.I don't think this is correct. You trace over degrees of freedom that are not involved in the experiment (for example, degrees of freedom describing the environment--this is done in analyses of decoherence, for example), but that's not the case for the degrees of freedom that describe the particle being measured.

If you are measuring one of a pair of entangled particles, then you would trace over the degrees of freedom that describe the

otherparticle, the one you are not measuring; but you wouldn't trace over the degrees of freedom that describe the particle youaremeasuring.That is where the "multiple worlds" interpretation comes from.The MWI does not require you to trace over the particle being measured. The two classical worlds emerge from decoherence of the two branches of the superposition after the measurement interaction entangles the particle and the measuring apparatus, and the apparatus then becomes entangled with its environment. And the reason you can "undo" measurements in quantum eraser experiments is precisely that you don't allow decoherence to occur--you have to keep the measured system and the measuring apparatus isolated from everything else.

I'll leave further comments in your follow-up article as well.

> The Copenhagen interpretation uses the same underlying mathematical machinery

No, it doesn't. Copenhagen holds that wavefunction collapse is an actual physical process, which is non-unitary, and hence takes the Born rule as an *axiom*.

> and makes the same predictions for all experimental results

That's not quite true. It's is true that Copenhagen makes the same predictions for all systems where the end result is a measurement on a single particle. But it fails for measurements on entangled particles, not mathematically, but *rhetorically*. Copenhagen barely even acknowledges the *existence* of entangled particles, treating them as an intellectual curiosity rather than as the central physical phenomenon that they actually are. If you don't believe me, look at the third volume of the Feynman lectures. He doesn't mention entanglement *at all*. (This is ironic considering that Feynman went on to invent quantum computing, though that happened 20 years later.)

> > To extract the state of the measurement apparatus you "trace over" (i.e. discard) the parts of the description that describe the state of the particle being measured.

> I don't think this is correct.

Of course it is correct. If you have a description D of a system S that consists of two parts, P and A, and you want to know what is the state of A then you have to discard the part of D that describes P, which leaves you with the description of A. How could it possibly be otherwise?

> The MWI does not require you to trace over the particle being measured. The two classical worlds emerge from decoherence

Semantics. Tracing is a mathematical operation, decoherence is a physical one. "Decoherence" is just the name given to the process of creating a large network of mutual entanglements. Tracing is the math you do in order to describe the state of a part of such a system.

Copenhagen holds that wavefunction collapse is an actual physical process, which is non-unitary, and hence takes the Born rule as an *axiom*.So do all of the other interpretations. I know there have been attempts to derive the Born rule in the context of, for example, the MWI, but I'm not aware of any that have been successful.

it fails for measurements on entangled particles, not mathematically, but *rhetorically*.There is no such thing as a "rhetorical" prediction. The mathematical prediction is the prediction. The "rhetorical" part is just a story in ordinary language that some people choose to tell about what's going on. It's not part of the theory and it's not part of the prediction.

If you have a description D of a system S that consists of two parts, P and A, and you want to know what is the state of AThis is not what's going on in a measurement. You want a description of both P and A, because that's how you know that the measuring device correctly reflects the state of the measured system.

If, as I said, you are measuring one particle of an entangled pair, then you have a description of a system S that consists of

threeparts, P1, P2, and A. You trace over P2 (the particle not being measured) in order to make predictions about the outcome state of the subsystem P1 x A.Peter: "

The mathematical prediction is the prediction. The "rhetorical" part is just a story in ordinary language that some people choose to tell about what's going on. It's not part of the theory"I'm not sure that I understand what you're trying to say here. Don't

allthe competing "interpretations" of quantum mechanics, share the same underlying mathematics? They all agree on the QM equations, they all agree on the "mathematical predictions". That isn't what this discussion is about.The

onlything they disagree about, is the "rhetorical ... story in ordinary language". Isn't that what we're discussing here? How to intuitively think about the mathematics?If you want to reduce the discussion to mere mathematics, then why are you even talking about "Copenhagen"? Copenhagen adds no new mathematics to QM theory, so if you only want to discuss mathematics, you can't even have a conversation about Copenhagen.

Also, Peter: "

Copenhagen [is] just as valid given our current state of knowledge."I don't think that's true either. You seem to be relying on the theory being "consistent" with currently known evidence. The requirement of consistency is certainly necessary for a plausible theory ... but it's hardly sufficient. (There are obviously an infinite number of theories consistent with any possible data set, but they aren't all equally plausible.)

If all you require is the lack of falsification, then you're vulnerable to claims like Russell's teapot.

Or, to give a closer analogy, consider the theory that all photons emitted by our sun, in a direction opposite to the earth, simply vanish from the universe and violate conservation of energy. We have no way of observing any of these photons, so we can't get any concrete evidence to distinguish this silly theory from our current theories of physics. And one can imagine some future luck, perhaps, where maybe there is a mirror that happens to be placed 1000 light years away, which might reflect some of those photons back to earth. So you might posit that someday, in the future, we actually will observe evidence about whether those sun-emitted photons away from the earth just vanish from the universe, or else act like every other photon we've observed.

But it is

notthe case that, until we observe such a luckily-placed mirror, we must necessarily conclude that the "photons vanish" theory of physics is just as plausible as the standard one, merely because of consistency with current evidence. That is far too weak a standard.The Copenhagen interpretation is in a similar situation. Yes, it matches the QM equations for those situations we can currently test. And then it also posits a ridiculously complex and implausible mysterious new physics that is untestable, on the basis of exactly zero evidence.

There are many, many reasons to reject Copenhagen ... and being "consistent" is hardly a strong enough endorsement to overcome the drawbacks.

@Peter:

> This is not what's going on in a measurement. You want a description of both P and A, because that's how you know that the measuring device correctly reflects the state of the measured system.

Ah. There's yer problem right there. :-)

You say you want a description of both P and A. And you can have that, but it will be a quantum description, i.e. it will be Schroedinger's cat.

What you really want (or at least what most people really want) is a *classical* description of both P and A, i.e. a description that simultaneously says "A in in the indicating-spin-up state" and "P is in the spin-up state". But you can't have that. The only way you can get a classical description out of a quantum one is to ignore (i.e. trace over) part of the system. If your system is fully decomposable into A and P and you want a classical description of the state of A, then you have no choice but to ignore the state of P because that's all there is.

> There is no such thing as a "rhetorical" prediction.

Of course there is. Here is an example, quoting from Feynman:

"If an experiment is performed which is capable of determining whether one or another alternative is actually taken, the probability of the event is the sum of the probabilities for each alternative."

This is a rhetorical prediction because it does not define what is meant by "an experiment is performed." It is precisely this vaguery that leads to all the hand-wringing over Schroedinger's cat, Wigner's friend, delayed-choice experiments, and quantum erasers. At the extreme, if you take a common but informal definition of "performing an experiment" then you end up with the EPRG paradox.

Feynman's quote is one of the most prominent manifestations of the Copnehagen interpretation, and it is wrong. It is a reasonable approximation to the truth in a narrow set of circumstances (single unentagled particles and an overly restrictive notion of what an "experiment" is), but conceptually it is 100% wrong.

Don't all the competing "interpretations" of quantum mechanics, share the same underlying mathematics? They all agree on the QM equations, they all agree on the "mathematical predictions".Yes, that's my point.

That isn't what this discussion is about.I think it is. The title of this post was "Are parallel universes real?" You can't say something is real unless the mathematical predictions (provided they agree with experiments) are only compatible with it being real. But if there are multiple interpretations of QM that all agree on the mathematical predictions, and some say parallel universes are real while others don't, then you can't say they're real. You can only say your preferred interpretation says they are.

If you want to reduce the discussion to mere mathematics, then why are you even talking about "Copenhagen"?Because Ron did in the article; he said it wasn't a valid interpretation. I'm saying it is. Ron thinks it isn't because it "fails rhetorically"; but my point is that there is no such thing as "fails rhetorically". Copenhagen, as you agree, uses the same math and makes the same predictions as all other interpretations. That means it's as valid as any other interpretation. If you don't happen to like the "rhetoric" that Copenhagen uses, that's a matter of personal preference, not physics.

Yes, it matches the QM equations for those situations we can currently test. And then it also posits a ridiculously complex and implausible mysterious new physics that is untestable, on the basis of exactly zero evidence.No, it doesn't. The Copenhagen interpretation is just an interpretation of QM. It doesn't make any predictions that QM doesn't make.

If there are people who are using something they call "Copenhagen", but claiming it predicts new physics beyond what the QM math predicts, then their "Copenhagen" is not an interpretation of QM; it's a different theory (because it makes different predictions). In principle we could distinguish the two theories (standard QM and whatever "Copenhagen" such people are using) by doing an experiment for which the two make different predictions. But if such a "Copenhagen" exists, it's not the one we're talking about in this discussion, since we have all agreed (I think) that the "Copenhagen" we are talking about is an interpretation of QM and makes the same predictions that QM makes (and no others).

You say you want a description of both P and A. And you can have that, but it will be a quantum description, i.e. it will be Schroedinger's cat.Until it's measured, yes. After measurement, no. After measurement, I can make predictions about all future measurements that I can possibly make by using the state of the system P x A that describes the result I observed. That's what the math of QM says to do.

What you really want (or at least what most people really want) is a *classical* description of both P and A, i.e. a description that simultaneously says "A in in the indicating-spin-up state" and "P is in the spin-up state". But you can't have that.Sure, I can. I just described how.

What you would like to say here is that the state of the "full system" has multiple terms, each of which describes a P eigenstate and the corresponding "indicator" state of A; and that the state I described above is not the "right" state to use, because it only includes one term of that "full state". However, you have no experimental evidence for this; you only say it must be that way because you believe that unitary evolution is never violated. But our actual evidence doesn't say unitary evolution is never violated; it only says unitary evolution isn't violated in reversible processes. We do not have any evidence that irreversible measurements are also unitary.

This is a rhetorical prediction because it does not define what is meant by "an experiment is performed."Not in the quote you gave; but the standard definition in QM is that an "experiment is performed" when an irreversible interaction takes place.

I realize that many people working in quantum information theory don't talk this way, but the key processes studied by quantum information theory that give rise to all the talk about things like "parallel universes" are reversible; that's the whole point. If you can "quantum erase" an interaction, then the interaction is reversible. But such an interaction, from the standpoint of "collapse" interpretations like Copenhagen, doesn't even count as a "measurement" (or as an "experiment being performed", in Feynman's language). Yes, that means that "measurement" and "experiment" are very bad terms to use in this connection, since the reversible interactions that happen inside quantum information labs certainly meet the ordinary person's definition of "measurements" or "experiments". But that's an issue of language and terminology, not physics.

You might also be tempted to say that, from the standpoint of an interpretation like the MWI, all interactions are in principle reversible. I agree that, from the standpoint of the MWI, that's true; but we certainly do not have experimental evidence that all interactions are reversible. We only have experimental evidence that particular tightly controlled interactions in systems that are carefully isolated from their environments are reversible.

If all you require is the lack of falsification, then you're vulnerable to claims like Russell's teapot.Rather than try to respond to this here, I'll just point at an article I wrote on Physics Forums:

https://www.physicsforums.com/insights/fundamental-difference-interpretations-quantum-mechanics/

In short: the reason people differ so strongly about QM interpretations is that there is

nointepretation of QM that doesn't require you to give up some strongly held intuition. Different people choose different ones to give up.Post a Comment