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Tegmark's level IV multiverse is the only explanation I've ever heard for why there is something rather than nothing. I intuitively lean toward it for that reason. Of course, I don't know how to put a measure on that space that explains my subjective experience, but that seems like a much smaller problem then the most fundamental problem of why anything exists in the first place.
Personally, I'd like to hear alternatives to Tegmark's theory more than I'd like to hear rebuttals.
You can tell when something has been explained because it no longer has the same air of mystery that it did at the start. The Level IV hypothesis might very well be true, but it's not an explanation.
Though beware the trap of thinking that things must have one explanation rather than, say, 562 partial explanations, 46 decent explanations, 8 good explanations and 4 truly thorough explanations, all useful and all at different levels of abstraction or organization. Seriously, humans really suck at remembering this when thinking about things removed from their day-to-day experience or where signaling games dominate, like psychology, philosophy, theology, politics, politics, politics, politics...
It's unlikely that there are no few reasons much more powerful than all the rest, that everything is aligned exactly. So if one is tempted to explain using many weak reasons, or any reasons visibly weaker than other known reasons, that would suggest that the weak reasons are fake explanations obscuring what's really going on, even if all of these reasons are true.
That's a correct, non-obvious and useful consideration generally. Though in the situation I had in mind (explaining "akrasia": the lack of a thing) there are many "explanations" that are truly useful explanations---just not uniquely powerful ones. And in (a model of) a complex system each (overlapping, continuous...) level of abstraction has its own set of ways to fail. (There's probably some kind of relevant point exemplified by our back-and-forth here.) "Irrationality", like "akrasia", is another lack-of-thing with enticing "explanations", and "rationality" is a thing.
It's funny that the ideas humans spend most of their time thinking and debating about are implicitly ideas about thinking and debating and yet they never really get around to thinking and debating explicitly about thinking and debating because the thinking and debating is actually about signaling object-level thinking and debating skills and not the less desirable meta-level ones. It wasn't really until the Greeks' development of rhetoric and logic that this trend was slightly reversed; now explicit meta-level reasoning has leaked down somewhat into modern-day implicit object-level reasoning, and explicit meta-level reasoning is a huge financial sector in the form of consultancy. But even so explicit meta-level reasoning is rarely seen in the wild.
I don't have any alternatives. But Tegmark's four levels of multiverse have clarified a suspicion I've held for a while. I think it's a mistake to lean toward this explanation.
This technique of positing multiverses to explain phenomena is just way too easy and too general of a strategy. Take any event for which we have not identified a causal regularity which produces it. Take the appearance of comets in the ancient world. The ancients interpreted these as signals from the gods. But it would be just as easy to say "Oh, there must be alternate earths with each which a different possible sky and we see this sky because we happen to be on this earth". "Perhaps there are alternate Egypts where the Nile flows over at different times of the year." Etc.
It's just too powerful of a tool. You can explain anything this way. Now Tegmark says the first level multiverse has confirming evidence, I suppose I can take his word for it (though after reading some of his stuff I'm still a little confused about how the evidence could falsify all non-multiverse theories). And certainly nothing I've said can dismiss the possibility of a multiverse at some level. But the fact that any phenomenon for which we have no other explanation can be explained by claiming that all possibilities come to be means that such explanations shouldn't be singled out from that whole set of possible explanations that haven't even been formulated. So you shouldn't lean toward it. The fact that it is the only explanation you've ever heard just means that we are astonishingly far from being able to answer the question.
And yes. I think this is a concern for QM too (that isn't an endorsement of Copenhagen, though).
Anyway, I'm pretty sure "why is there something rather than nothing" is category error/wrong question territory.
But it doesn't explain why. If all possible worlds necessarily exist, that does explain why this world exists. But why does possibility imply necessity?
The whole point of the mathematical universe hypothesis is that the above is a Wrong Question. Possibility doesn't imply necessity, possibility is necessity.
That statement is just mystical dogma unless you can explain why they are the same thing. And just saying "all possible worlds exist" does not explain why they exist. Why not just some of them? Why any of them at all?
I won't say the truth of the mathematical universe hypothesis is self-evident or anything, but there's certainly nothing mystical about it. All it says is that there was never any reason in the first place to suppose there's a difference between possibility and existence. It's not like we have perfectly clear concepts of 'possibility' and 'existence' that clearly conflict with one another.
The best analogy I can think of is the statement that time is the same thing as a coherent set of universe-configurations. Why are they the same thing? Um, because that's what time is. What makes you think it's anything else? Likewise for existence: What makes you think it's anything other than possibility?
That's good to know. So the next time someone tells me that something might be a cure for cancer, I won't have to think about it or research it, because if it is possibly a cure for cancer, then it is actually a cure for cancer. And the next possible theory of 9/11 that I hear, I don't need to wonder if it's true, because, being a possibility, it's also an actuality. And I don't need to worry about what you actually mean by your writing, because whatever possible interpretation I come up with, that must be the actual intended meaning...
Wait - you're saying that's not what you meant... that all those possibilities which seem to simply not exist... you're saying that they do exist, but somewhere else, in some other world? Well, uh, that's an interesting idea... pretty radical... I don't see what evidence you could have for it... but I guess I have to admit it's possible, ha ha... But wait - isn't it also possible that these other worlds don't exist? So does that possibility - meta-possibility - "exist" somewhere too?
Now please note: I am not disputing your right to build byzantine multiverse theories and to engage in abstruse logic-chopping which will allow your new interpretation of the word "possibility" to become consistent. But it is absurd to say that "there was never any reason in the first place to suppose there's a difference between possibility and existence". You may as well say there was never any reason to suppose that the Flying Spaghetti Monster doesn't exist, or that there was never any reason to suppose that black isn't secretly white as well. There are clear differences between the everyday original meanings of possible and actual, and proposing to negate them by supposing that all possible worlds are actual is radical metaphysical innovation, and before I believe it, it is reasonable to request some evidence, or at least an argument in its favor.
This kind of thing "It is possible modal realism is false." is a nice example of a Godel-type statement that doesn't involve math.
I'm not particularly familiar with Tegmark's position (beyond looking at the website) but modal realism (which afaict is at least a pretty similar position) just declares "actual" to be a kind of indexical, like "here" or "now". Saying "we actually have a cure for cancer" is like saying "We presently have a cure for cancer." So modal realism (and I don't see why Tegmark IV couldn't do the same) doesn't negate the difference in meaning, rather it just interprets words that we're already confused about.
I'm similarly suspicious of the strategy as well (see the reply to Jordan I'm about to write). But I don't think the argument is dedicated to the negation of the difference between possible and actual.
Like what? The property of existence? How would a bit-by-bit description of an object with that property differ from a bit-by-bit description of an object without it?
By the way, here's the link to Tegmark's articles, if you haven't read them yet:
http://space.mit.edu/home/tegmark/crazy.html
It would have some extra bits saying "this object exists".
Sounds like the Ontological Argument. God exists because he's defined to have the existence bit set to 1.
Whether an object exists in some reality is a property of that reality, not of the object.
Okay, I guess it's my fault for not being precise enough. I meant a complete bit-by-bit description of an object, down to the subatomic level, or whatever level is necessary so that the description says everything that could ever be said about the object.
Such a description of, say, an apple, would differ from the description of a pear by many bits. But how would it differ from the description of a non-existent apple? You could add an 'existence' bit to the description, but it would be meaningless, because the apple already exists: A complete description of an apple is an apple. A description of a non-existent apple isn't the description of an existent apple plus or minus a few bits, it's not a description at all, it's zero bits.
You are really mixed up. What you are saying is nonsense and it should be obvious that it is nonsense. Suppose I have an incomplete description of an apple; in the form of words on paper, just to be specific. I have a few thousand words describing some hypothetical apple, its color, its taste, its size, and so on. Now suppose I add however many bazillion more words I need in order to make it a complete description. What are you saying - that at some point my stack of paper turned into an apple, even though it's still a stack of paper?
The thing is, you don't need to think like this in order to have a multiverse theory. It's only this peculiar neoplatonic desire to believe that reality is mathematics (or is computation, entirely abstracted from substance) which leads to the nonsense.
IAWYC, but let me point out that you are describing your position rather than supporting it.
As a way of supporting it, imagine that there's some other universe with physics that encapsulate ours: the Dark Lords of the Matrix can cheaply run a faithful simulation of anything that happens in this universe on that universe's computers. It's clear to me that, given the setup you two are discussing, the Dark Lords would see that those extra bits aren't doing anything at all; they can be removed without altering anything that they could observe in the simulation.
Now, anything we can observe about our conscious experience is assumed to have an effect on our brains as we think of it, and thus the Dark Lords could observe it as well. (Namely, if there's a distinction between a "physically real" world and another one that's just "mathematically possible" with an identical copy of you, there's no difference from the Dark Lords' perspective between the description of your brain thinking "But I really exist!" and the description of your copy's brain thinking the same thing.) Note that this is an instance of the GAZP in action.
So by Occam's Razor, I don't think there's a justification for adding extra bits to the way the universe is described, when literally nobody within or outside the universe can be pointed to as having justification that those bits are one way or another.
Exactly. In fact, if possibility and existence are the same, the Flying Spaghetti Monster does exist.
The empirical inaccessibility of counterfactual worlds.
I'm working on a post about this. It actually turns out to be surprisingly believable.
Many scientists and rationalists won't offer a "why" alternative because we hit an information boundary at the unique cosmological singularity of the big bang. And most scientists think we should have evidence which we can use to build models that make accurate, verifiable predictions before we claim to understand the "why" of anything.
I understand that objection, but I disagree. We do have at least two pieces of relevant evidence:
The universe we find ourselves in seems to be a rather simple mathematical object. The final verdict on this, of course, is still out; but if the bottom were something extremely complicated, it would seem to be an unbelievable coincidence that the approximations we've found (QM and GR) are so tidy and so very very accurate.
We can usually think of good reasons that simpler mathematical objects wouldn't contain a great proportion of observers. The particular cosmology of our universe appears to be one of the simplest ways to make evolution of sentient life plausible— for example, QM without gravity results in a dispersive wavefunction, and remotely brain-sized interacting configurations become vanishingly unlikely.
I mean, you could build a conscious agent in Conway's Game of Life, but it seems unlikely that any not-too-complicated starting configuration would result in one (well, a chaotic one would result in very occasional Boltzmann brains, but those would be much rarer than conscious life is in our universe, more than enough of a difference to outweigh a reasonable complexity penalty on universes).
From these facts, if we expect to be "typical" elements of our reference class (i.e. conscious agents, perhaps with some additional conditions), something like the Level IV Multiverse is strongly supported, and predicts that 1 and 2 will continue to be more strongly validated. (2, in particular, is a pretty decent prediction; it says that we can't come up with a simpler cosmology-leading-to-sustained-evolution than the one we live in).
Well my comment wasn't an objection to Tegmark's mutliverse hypothesis but rather an explanation as to why its the only explanation you've ever heard.
But if may object to your objection, I disagree that QM is so very tidy. The standard model has what - 18 free parameters with values assigned as necessary to fit the experimental data? I don't know that anyone considers this tidy, or that many people think particle physics is "done". What we have for particle physics is a useful mathematical model but it isn't an elegant one.
The expectation that we should find an elegant model is not unreasonable but it is not yet accomplished.
Yes, but compare that to the number of free parameters implicit in chemistry before QM and QED came along.
Well there is a difference between saying x is more tidy than y and saying x is very very tidy.