Occam's razor, goddidit and the many-worlds theory

Occam’s razor is the problem-solving principle that when presented with competing hypothetical answers to a problem one should select the answer that makes the fewest assumptions.

Atheists have often invoked Occam’s razor to explain God away and to argue that the scientific method is a more effective means than religion to understand reality.

I myself nurture the same sentiment, which makes me feel quite uncomfortable whenever I come across with the many-worlds interpretation. In their attempt to understand the nature of reality and to put forth coherent theories that can explain how things work, physicists speculate on the existence multiple (probably infinite) simultaneous realities. I am aware that abusing Occam’s razor can lead to simplistic and inaccurate models, but at the same time I can’t escape the feeling that the many-worlds theory is a violation of this principle that parallels the goddidit attitude.

No one is really happy with any of the QM interpretations, and as a matter of practice, the “shut up and calculate” interpretation is the most popular.

Obviously, other interpretations get some intellectual traction, but only in a kind of “we know it doesn’t really matter, but it’s fun to think about” way. Many-Worlds falls into this category. The reason it’s popular is that the other interpretations seem to be even worse: Copenhagen postulates a mysterious wavefunction collapse (which really makes no sense given that observer and observed are both entangled QM systems); Bohm-De Broglie pilot-wave theory postulates a kind of unobservable non-local (infinite speed) wavefunction background. It gets worse from there, with nonsense like many-minds.

So Many-Worlds seems like a least-worst interpretation, even if it is rather extravagant. But really, shut-up-and-calculate wins for day-to-day use.

I thought the Many Worlds Interpretation was a result of applying Occam’s Razor. Which of the following is simpler:
(a) Somehow or another (God rolls a die?) a “decision” is made and the cat either lives or dies.
(b) The cat lives AND the cat dies. Get over it!

Occam’s razor can work in mysterious ways, I know. Here’s another example:

  1. The universe must have been governed by completely different physical laws initially.
  2. Goddidit.

As others have said (in their own way), the many-worlds interpretation is only a problem for Occam’s Razor if it makes more assumptions that the competing theories.

I don’t think it does. All attempts to encapsulate all aspects of the quantum world into a single coherent theory are having to shortcut and/or make leaps of faith.

To my mind, there is a perplexing question to which mankind has posed several solutions, even the best of which is pretty bad. So the application of Occam’s Razor doesn’t get us anywhere.

Well, I’d quibble with the last bit. As I understand it, the many-worlds hypothesis postulates a large, and possibly infinite, number of universes, each with its own reality, fundamental laws, etc, to explain how we observe the existence of this particular universe with the particular laws that it has. This is an alternative explanation for the existence of the observed universe to the “goddidit” explanation.

So far, so good. But this can’t tell us anything about the scientific method. The scientific method proceeds from empirical observation and since we can’t empirically observe a different universe or anything in it (if we could, how would it be a different universe?) the many worlds hypothesis is not one that either proceeds from empirical observation, or that can be falsified by empirical observation. It’s not itself any more an application of the scientific method than “goddidit” is. It’s just an alternative but equally non-scientific speculation

Does it offend Occam’s Razor? Well, goddidit involves the speculation of just the one god, whereas the multiverse hypothesis involves the speculation of a large number/an infinity of universes, so maybe that is a more extravagant speculation. On the other hand, if we set a god postulated to be all-knowing, all-powerful, etc against universes postulated to be as finite, limited and rule-bound as the one we can observe, maybe the god postulate is the more extravagant. And, either way, maybe we should bear in mind that Occam’s Razor is a useful philosophical tool, not an iron law of reality.

Be careful, my friends, in using Occam’s Razor. Many users experience shaving rash and minor cuts.

I’m an atheist and I prefer the lack of any evidence whatsoever argument. Occam’s Razor is a handy principle but I wouldn’t hang my atheist hat on it. It doesn’t prove anything and violation of it doesn’t disprove anything.

Since this thread is really about physics, though, please consider this only an aside and not a hijack.

You need to consider what you mean by SIMPLICITY.

Consider the particle horizon, or cosmological horizon. Suppose you can travel away from the earth at near c speeds, and eventually you get so far away, that you can’t make it back. Far enough away, and not even light will make it back. Space is expanding, so eventually you reach a point where no information returns, because the space expands more quickly than even the light can traverse the space. This horizon represents the edge of the observable universe.

Now here’s the question: is it “simpler” to assume that everything beyond the particle horizon does not exist at all? After all, this stuff is totally non-observable. We will never see or interact with it again. A particle drops of the end of the map, and it’s fuckin gone, man, out of sight forever.

So does that mean that’s it’s “simpler” to assume that everything past the horizon ceases to exist? Literally? Is that the theory you want to work with? Is that how you think the laws of physics work, that anything who travels sufficiently far from where you are currently observing no longer exists?

No. Just no.

We assume instead that physics works by simple rules, not by assuming a complicated process that POOFS things into non-existence the moment we can’t see them. Those simple rules might have “computationally intensive” implications, sure, and you can think of that computationally expensive process is somehow complex, but it’s not complex in the way that we’re talking about when we’re talking about the rules. It would be a ridiculously more complex universe if everything past the horizon from where you happen to be currently standing just vanished from existence. Why is your position special? What are the people on the edge looking at? Nothingness coming up to swallow them? …or rather, a picture very similar to what you’re looking at, where space gently recedes beyond what they can personally observe?

This is almost exactly the same idea behind the many-worlds interpretation.

It is believed that the MWI gives the absolute simplest rule for how quantum mechanics works. Is the idea “computationally expensive”? Sure. (But less so than you might think, given the weirdness of QM in general.) But the appeal of the MWI is that the rule it gives is the simplest possible rule that might possibly explain what we’re looking at when we look at quantum phenomena. It doesn’t really matter that there’s such much non-observable stuff. Physics is absolutely fine with non-observable stuff in other contexts. It’s only in this one context that people get weirded out, for some reason.

Of course, this doesn’t mean the MWI is absolutely correct. It’s “brittle” in a way other theories are not, which is to say we can easily imagine a future experimental result that would say, whoops! That sure was wrong. But if you have a certain definition of “simplicity” that accords with trimming down the rules of the game as much as possible, then the MWI sure looks like it’s the current winner right now, of the options on the table. That’s the general definition of simplicity that people who favor the MWI end up relying on, because it is – not incidentally – the same rule that says that the universe does not just pop into nothingness at the edge of observable space.

How is it “more brittle”?

What is an experiment that would rule it out?

Quantum computer scientist Scott Aaronson in this blog post cites an experiment that might do it (but probably won’t!), along with several other thoughts about what would break it. He’s also who I was thinking of when I used the word “brittle”. Good section:

All around great post. Makes the point that we might not want to put all our eggs in the MWI basket just yet.

Still, there’s an extremely strong case that the MWI should have at least an egg or two more than any other basket currently on the table. The most rigorous definitions of “simplicity” quite forcefully demand that this be so.

These days people seem to be more cautious but I have heard many times the idea that the Big Bang theory is a more elegant solution to the problem of the universe’s origin than creationism, where the goddidit attitude seems to quickly expedite clarification but then you’re left with an unexplained concept of god and more nonsense than you faced to begin with. This argument has been invoked so often that I think it is already a cliché. I for one consider it a useful principle and it seems to work out for me. I admit it is a personal predisposition, because I also tend to regard certain sophistication as some sort of ignorance in disguise.

MWI may be the simple idea scientists can think of to solve a problem but its consequences are far from simple. Is this model where there is an infinite number of universes the simplest idea science can come up with about the nature of reality? Does this infinity of phenomena fostering a ‘more’ infinite number of universes make more sense than the existence of a single universe whose profound mechanisms escape our scrutiny at the moment? Why jump to conclusions about the 5% of the analyzable content of the universe when 95% of it remains completely inscrutable?

We have clear evidence that universes can exist, as we live in one. We have no evidence at all that god(s) are even* possible, *much less what they are like.

So even before examining MWI in any detail, we see that “goddidit” comes with more assumptions, and more extreme ones. And unlike “goddidit” we already have one example of what MWI claims exists in multitudes, which again puts it well above “goddidit”.

Why not? Is there something inherent in the concept of ‘infinite’ that makes it complicated or unreasonable?

I’m not sure why you say this. It’s not actually known whether the MWI mandates an “infinite” number of universes.

From literally the first paragraph of the Wikipedia page: “In layman’s terms, the hypothesis states there is a very large—perhaps infinite[2]—number of universes, and everything that could possibly have happened in our past, but did not, has occurred in the past of some other universe or universes.” Emphasis added.

But if it there were an infinite number of worlds, however defined, the case of SIMPLICITY you think you’re making still applies to regular physics processes. Does the universe extend infinitely beyond the cosmologically horizon, that is, infinitely beyond the observable universe? Is a universe of infinite space and time really the “simplest idea science can come up with about the nature of reality?” These aren’t two different questions. They are the same question. Physical space is just one kind of mathematical space in physics. The potential “space” on an MWI Universal Wavefunction is just another kind of potentially infinite mathematical space. (Everett, who came up with the original idea, did not refer to it as the MWI but as the theory of the Universal Wavefunction.)

If you’re wary of one infinity, then you should be equally wary of the other.

I’m personally uncomfortable with both: my own intuition is that physical space is unbounded yet finite, and that the MWI “worlds”, coherently defined, would end up as a finite number. Pleeeeeenty of people disagree with this, of course. My point here is not to argue “rawr, this must absolute be true!!!1!” but rather, “This is a sensible conclusion, derived directly from a mathematically rigorous definition of simplicity.”

You still haven’t come to grips with what SIMPLICITY means.

The consequences of literally every quantum interpretation are “far from simple”. The consequences of literally every advanced physics theory are “far from simple”. The three-body problem from Newtonian mechanics has consequences that are “far from simple”.

Complexity arises from simplicity.

Every sufficiently advanced collection of possible laws of physics will result in “consequences” that are as “far from simple” as it is possible to be. There is no closed-form solution to physics problems like the three-body problem. If you’re looking at a sun, a planet, and a moon, and you want to know the position of those three bodies a billion years from now, you’re going to have to deal with “consequences” that are extremely far from simple. You’re gonna have to computationally chug, chug, chug out the “consequences” of the problem, because there is no simple formula that exists that can jump you straight to the final solution. Complexity arises from simplicity. That’s not just true of QM. It’s true of practically everything that’s worth studying.

Does the MWI have “consequences” that are complex? Yes. Because every physics theory has consequences that are complex, most especially including every other possible interpretation of QM.

The MWI is simple where it counts: in the rule that describes what is posited to be actually happening. That simple rule has startlingly complex consequences, but then again, so does every other quantum rule we could possibly come up with.

Nobody is necessarily even positing an “infinite” number of universes, let alone a “more infinite” number of universes, whatever that is supposed to mean.

This is just meaningless. It has nothing to do with the MWI.

Rephrasing this question into something that could be sensibly interpreted: does positing the MWI make more sense than the existence of a “single” quantum world whose profound mechanisms escape our scrutiny at the moment?



The entire problem with positing a “single” quantum world, where our own particular world is somehow privileged in some way, is that it is a very complex idea, in exactly the same sense that it’s an extremely complex idea to assume that the universe just ceases to exist outside of our own observed universe. Why would we ever posit that the earth is the “center” of the universe in that fashion, and that any light that disappears beyond our own personal provincial particle horizon just ceases to exist? Why? What do we gain in our understanding by assuming that?

Exactly the same argument you’re making to privilege our own quantum branch could be used to privilege our own particular place within a cosmological horizon. It makes no sense in both ways.

You can see this immediately in the “pilot-wave” interpretation that was previously brought up. The “pilot-wave” interpretation does not get rid of the information of all those other many-worlds. All of those worlds are still there! What the pilot-wave interpretation says is that there is a little flag on our particular quantum branch – and no other branch! – that says “You live in really-real Reality! Congratulations! All those other branches don’t matter!”

Okay… so WHY don’t they matter? The information for them is still there in the quantum waves. Do they not matter merely because we personally like the idea that we have a special physics flag planted where we are?

Or take a clever objective collapse theory like GRW: unlike the (frankly primitive) Copenhagen interpretation, GRW says that collapse just happens “randomly”, rather than being beholden to some ridiculously undefined idea like an “observation”. It basically says that when we’re doing experiments, quantum states get entangled with such a large number of particles that at least one of them will randomly undergo collapse at the right moment, giving us the experimental results we see. Okay. But in that case, why don’t we ever see spontaneous collapse? Because the probability is low enough that it won’t happen with a single particle, but high enough that it will essentially always happen with 10^16 entangled particles. Extremely clever. I like this idea a lot. But it also gives a whiff of arbitrary probability choices. Why were those bounds on the probabilities chosen? Where did those bounds come from? Well, because those are the only bounds that work. The parameters of the theory have to be toyed with to get the result we like… and that’s also a complex idea that has to be snuck into the rules to make it all work. If only we could do 10^16 single particle experiments…

The MWI is not complex in these ways. It just says, hey, there’s a Universal Wavefunction. It evolves according to the Schroedinger equation. BOOM. We’re done. That’s the rule.

That doesn’t have to be right. There are serious problems with it that need to be taken seriously. (Look at the previously cited Scott Aaronson blog post to look at some of them.) The MWI could easily be wrong. At the same time, it pretty clearly leads the rest of the horses in the race by at least a few feet, at least according to a sensibly rigorous definition of simplicity.

The problem with your own objections are continually that you either 1) misrepresent what the MWI actually implies, or 2) offer knee-jerk objections that, if accepted, would strike down almost all of physics. Neither of these is going to work. You need to work with the MWI as it’s actually defined, without the misconceptions, and you need to offer up objections that aren’t so clumsy and blunt that accepting your objections meant we had to give up on the entire last two centuries of physics.

Occam’s Razor is a heuristic, and can’t be used to prove anything. Plus, it is often misused. Here is the definition which comes up from Googling the term

You don’t need it to disprove YEC - the evidence does that. It is useful in rejecting the hypothesis that some god created the universe and disappeared, since that explains nothing more than the secular hypothesis and involves another entity.

I wonder if any of the QM hypotheses are at the stage where they are actually competing explanations of the universe. And proponents of all of them could claim that they are simpler than competing explanations. So I’m not sure the Razor even applies here.

I thought I was clear but I wasn’t. I apologize.

The contrast I want to discuss here is not between simple and complex. I’m well aware of the fact that in many situations the simplest approach is to accept complexity and take into consideration a wide range of aspects so that your explanation can account for every little observed phenomenon.

What irks me is the sort of fraudulent sophistication that uselessly overburdens an explanation only to make a model that scientists feel comfortable with work.

Of course the use and development of mathematics has enabled physics to advance incredibly and make amazing predictions. But it is only a tool, the same as Occam’s razor, and it should not be absolutized or abused.

Right now there is an impasse in physics and important scientists favor the idea of a many-worlds reality, which seems to offer a simple and elegant solution to the problem they want to solve. For me, this approach violates Occam’s razor not because it shows so much more complexity to the accepted model of reality but because it involves such abundant assumptions that makes it preposterous, in my opinion.

It reminds me of the mythical situation when the judge was forced to find a solution to the problem of deciding what to do with an infant claimed by two different women who each stated they had given birth to it and produced equal or no evidence to support their claims. The judge’s solution was that the infant should be cut in two equal parts so that each woman should receive an equal share, which is in fact a simple and elegant mathematical solution but in practice doesn’t actually make sense.

We know the mythical judge’s solution worked eventually because he didn’t really mean it, but physicists mean it. Whenever a tv program or book popularizing current scientific ideas mentions the many-worlds theory, the notion of infinite number of universes is brought up which includes the idea that there should necessarily exist another me and you somewhere in all these universes. I’ve seen and read this ad nauseam.

I may be wrong in many respects. I’ve been wrong numerous times throughout my life and I am happy to admit it. I hope I have learned from my past mistakes and I know I will from my present ones. But the fact is our particular world is a privileged one because it is real, or what we regard as reality whose aspects and components we can quantify and measure. There are voices claiming the universe is a mere illusion. I’m sure this can be proven mathematically by brilliant minds, but before they produce evidence for it I will continue to believe my existence is a physical one. I am also convinced the many-world theory has a beautiful mathematical foundation but the lack of convincing evidence and the assumption that the infinite structure that we call universe could be multiplied infinitely give me the impression of a sci-fi fairy tale.

I see you are disturbed by my using the term ‘infinite’, which abounds in the mass media discussing the issue of many-worlds. May I know what the limited number of worlds that you are comfortable with is and how you have arrived at that number?

Comment : there are experimental findings that might let us narrow in on how this whole thing works.

  1. We might find a way to observe neighboring universes if they are adjacent in space

  2. We might recreate the big bang on a small scale and find out at certain energy densities, the laws of physics are mutable.

  3. We might work out that the universe is going to end in a big crunch - a repeated big bang and a slight adjustment to the laws of physics

Things like that. These theories give us an idea of it might work, but yes, they should really be thought of more as candidate unverified explanations, barely any more valid than turtles on turtles.

It’s more a thought of “well, if entropy continues how could we exist at all?”

The universe must be* eternal. Maybe when entropy is maximized the laws of physics can change.

*which is still unsatisfying unfortunately. Because how does something eternal ever come to exist.

Okay. My own apologies if I misread you.

“Abundant assumptions” sounds exactly like complexity to me.

If I, personally, were to say that an idea involves “abundant assumptions”, I would, personally, mean to say that the idea was complex, instead of simple. They are absolute synonyms to me. My own inclination to the MWI is precisely because the MWI does not have abundant assumptions. It assumes the Schroedinger equation describes reality sufficiently by itself. That’s it. That’s the core assumption, which is that it doesn’t need anything extraneous.

You seem to mean something different, though. What I have not yet seen in your post is some objective or subjective definition of what you mean by “abundant assumptions”. How do you define this?

If you have an objective definition, then if I understood it, I could use your definition to come to the same conclusion that you come to. (I am personally using an objective definition: anyone in the world who uses this definition should come to the same conclusion.) Or are you using a subjective definition? If so, you should also point that out. Since I do not share your subjective perspective, I won’t be able to implement your own subjective impression to make up my own mind about when assumptions are too abundant. But at least I’ll understand that your definition comes from internal impression, rather than an objective rule we can both share and use together.

This relates directly to my previous question:

Do you believe that the universe ceases to exist at the end of observable space?

That’s a serious yes/no question, not a joke. You should really answer it: If “yes”, then you should use your definition to explain why you think yes. (“Abundant assumptions”?) If “no”, then you should use your definition to explain why you think no.

Look at what you’re saying here: there are “aspects and components we can quantify and measure”. But we cannot quantify and measure anything beyond the particle horizon. We cannot perceive anything. Even light which is beyond that horizon will never reach us, which means it will never be quantified and measured. Does the universe keep going? Or do you assume that the universe ends at the end of observable space, that that section of reality is “less privileged” because you personally cannot quantify and measure it? What’s your answer? Much more important: WHY is that your answer? WHAT RULE do you implement to come to that answer?

The rule is a million times more important than the conclusion.

No one sensible is saying that this branch of reality is somehow not real. That is not what science says. The earth is real. What’s actually said is that the section of space that is beyond our cosmological horizon is just as real as we are, even though it cannot be measured or quantified. There is a very specific rule I am applying in order to come to this conclusion. What conclusion do you personally come to? And much more important: What rule or definition are you applying in order to reach your conclusion? An objective guideline? Or personal impression?

It is an error to stay that the MWI is necessarily infinite. I pointed out that error.

Am I “disturbed” for pointing out an error? Is it not more ideal to understand the implications an idea, before criticizing it?

A finite MWI has certain potential problems, but given that all quantum interpretations have certain problems, we are still inclined to those interpretations which might potentially have their problems solved with the fewest number of extraneous assumptions.

You tell me: how many protons exist outside of the observable universe? Is it zero?

If you can give your reasoning behind an answer to that, I should be able to give you equivalent reasoning.

You have yourself said that its important that our reality has “aspects and components we can quantify and measure”. You’re talking about math here. To measure, to quantify, is to use mathematics.

So when you use mathematics, it is to emphasize the really-realness of Reality. So your own use of math is okay. But when others use mathematics, it can be somehow “fraudulent” or “overblown” or “abused”. But where exactly is that line you’re drawing between the usefulness of math as a tool, and its fetishization?

I can tell you exactly where I personally draw that line. (But it would take a while.) What I haven’t seen from you is any of your definitions. You might have them inside your head, but I haven’t seen it on the page, and so your definitions of “abundant assumptions” and math as a “tool” compared to being “abused” seem very arbitrary. Maybe they’re not, but I can’t see right now where any of these lines are drawn.

If you’d like, I can write about where my own line is drawn first, at some length, and then you can point out where you might disagree. Maybe that would be easier.

If you can observe another universe, is it really “another” universe? Or is it just a sort of exclave?