- Is the universe anything else than a set of universes?
- Is there any hierarchically superior structure to a multiverse?
- Does the multiverse include everything there is?
- Is the multiverse static or dynamic?
- If the multiverse is a development, does it mean new universes are always created in the process?
- If new universes are created all the time, do they emerge at a random or constant rate?
- With new universes being born all the time, does the overall energy of the multiverse change (increase or decrease) in the process?
- If new universes get born all the time, does the mechanism of generating new universes itself undergo any evolution? And if so, is it a cycle or a linear process? Does it show fixed regularities or is it absolutely random?
- Is it a conceivable hypothesis that the multiverse should have a beginning? A phase where there is only one universe? Or where there is a pre-universe phase? Or anything like that?
- Is it possible that the multiverse should have an end? Where the mechanism of generating new universes collapses? Or where the entire energy thins out to such an extent that work is no longer possible throughout the entire multiverse? Or anything like that?
Answers 1-10, no one knows… only speculation.
Indeed, I should have been clearer. I will try to clarify the OP a little.
In knowledge, there is little room for absolute certainty. Some form of speculation is always included one way or another. No one knows exactly how life appeared on earth, for instance. If one asked a factual question about Big Bang before WWII, the issue could be dismissed as pure speculation.
Speculation, however, is not supposed to be random guess. An educated guess usually makes more sense than an ignorant one. The time (I guess the Enlightenment) when thinkers hoped that one day people could learn and understand everything there is to know by means of reason is long gone. When interviewed, scientists admit there are things no one will ever know and the only tool people have to ‘learn’ in certain situations is nothing but speculation.
I know the existence of the multiverse is debatable among scientists. But if the multiverse is a more elegant explanation of the existence of our universe and the phenomena in it, I wonder what rigorous thinkers have to say about basic aspects of the multiverse – this is how the list of questions in the OP has arisen.
My questions do not refer to the debate(s) regarding the existence of the multiverse or types of multiverse, but the logical implications of today’s theories. As a layman, I am curious to see how the concept of multiverse can make sense form a scientific perspective. Thank you. 
You really need to get past simple definitions.
But if you are talking about one idea of the nature of the entire gamut of existence of anything and everything, the idea of a multiverse - some set of individual universes with individual existences and possibly different fundamental mixtures of rules and laws based upon some unknown more basic set of rules. Well there are a whole lot of problems.
Many people, myself included, regard most such musing as close to useless. Sure popular physicists get lots of press and can talk breathlessly about such things on TV. But they are well and truly in the camp of “We have no idea”. There is no rigour. There is naval gazing, playing fast and loose with the word “infinity”, there is self promotion of pet physical theories (mostly string theory and supersymmetry) none of which have exactly much actual evidence in their favour (and right now, rather less than they had hoped for at this stage of actual experimental physics.)
From a rigorous point of view your 1-10 questions can be mostly summed up as “the question is ill posed” and “see above”. Really, the current state of thinking about any sort of multi/meta universe is close to pull it out of where the sun doesn’t shine and come up with fairy tales. A lot of your questions cannot even be usefully posed (rate of something requires a notion of time passing - the multi-universe guys have no notion of what time even is in their fantasies - whatever it might be it isn’t what we call time in our own universe). Structure/hierarchy implies lots of properties that are not actually considered - space, dimensions, topology of dimensions - all undefined. As to mundane things like energy, heck energy isn’t fully understood in this universe, let alone a multitude, so any idea of conservations laws is way out of understanding. You will get about as much guidance from reading H.P. Lovecraft about the real nature of reality.
Thank you for your input. The idea of the multiverse keeps popping up on TV science channels and forum boards discussions and I’m just curious about the rigorous support for it, explained in terms that a layman could understand.
I have to admit that I’m not a big fan of the idea of the multiverse either. But my attitude or anybody’s attitude shouldn’t matter. On the one hand, I don’t think people should be prevented from speculating (or making educated guesses) because many of what we regard as valid theories today used to be considered wild speculations. On the other hand, Jorge Cham and Daniel Whiteson’s “We Have No Idea” admits the testable universe is way smaller than the testable one and thus (in my opinion) thinkers can only assert something about the overall existence by speculating. The universe (as I know it and as it has been explained in the mass media I have had access to) makes relative sense. The multiverse, not as much. I think I could get a clearer picture of the multiverse if at least some of the questions above were answered. Thank you.
Not only are there scientific questions here that we might not be able to answer, there are philosophical questions, as well. If we’re going to talk about “everything that exists”, then just what do we mean by “exist”? If something cannot possibly have any influence on us or anything that we know, does it still exist?
Although the answer to the question may be the same in each case — “We don’t know” — OP might clarify which unanswerable question he is asking. “Multiverse” is ambiguous.
The term may refer to the alternate worlds in a “Everett Many Worlds” interpretation. This interpretation helps explain why each of us thinks he is still alive, despite close calls with death.
The term is also applied, I think, to the notion that our Big Bang produced universes not part of our “observable universe” and where physical laws might be different.
In Tegmark’s CUH, all possible computable (mathematical) universes exist.
Among other hypotheses about multiple universes is Penrose’s Cycles of Time. According to this, the state of the universe shortly after the Big Bang and the universe a googol years from now are very similar: with only massless particles, no clock exists, notion of scale is lost, so the Cold Death when blackholes have all evaporated and protons have decayed can be the (“post-inflation”) Big Bang of a new universe! (As I understand Penrose’s hypothesis, the Second Law isn’t violated: the high-entropy Cold Death becomes the low entropy Big Bang due to a rescaling ?!??!?)
The problem with Penrose’s idea is that, even if the massive particles number zero, they still exist. Take a universe containing protons and electrons, and decay all of the protons and annihilate the resulting positrons with all of the electrons. Your universe will now contain nor protons nor electrons… but if, in this new universe, you produce a strong enough electric field, the vacuum will polarize into new electron-positron pairs, which have exactly the same properties as the electrons and positrons we have now. Electrons, in other words, still exist.
Since there are very few answers to the OP that can be said to be 100% factual, let’s go over to IMHO.
samclem, moderator
I would submit that time is a dimension (or dimensions) of (the/a) universe, so the answers to questions 4~10 are not meaningful: a multiverse would exist outside of the bounds of time.
If there are no electrons or positrons (and no other massive particles) so there are no charged particles in existence, is it even possible to create an electric field?
I can’t say I’m not disappointed.
This shouldn’t be about me, but it’s annoying when I am asked to show a type of rigor that specialists do not seem to care about. Here’s an example I found only several days ago: physicist speculating about the time before time.
As a layman I like to be informed and consider all these ideas in good faith, but I can’t refrain from understanding the kind of frustration a religious person may have when he is asked to show maximum of reason and logic while presenting his view on Creation on the one hand, but on the other hand he should accept a physicist’s leap of faith with no scorn or criticism, because if he doesn’t, he will be accused of being narrow-minded and ignorant.
There are books and articles dedicated to the existence of more than just one universe. The ideas, arguments and demonstrations come from physicists, like Stephan Hawking himself. But if these concepts are virtually useless because they can’t be used to build descriptive proposition about what is out there, don’t they make some sort of esoteric scientific mythology?
And what’s the purpose of its dissemination to the public anyway?
A little, yes. A lot of popularized science is based on things that might be true, as opposed to things that are known. The entire field of String Theory is like that: no one has ever observed a “string” and it might never be possible at all. ST is still elegant and lovely, and worth playing with, solely as a “what if.”
Same for multiverse models. They are (at this point) only “mythology,” but very pretty, and suggestive. They offer abstract explanations for observed facts.
There has been a very long and deep tradition in the sciences of making theories accessible to “the common man.” It keeps the field from falling into the “arcana” of, say, alchemy, where discoveries were kept jealously secret. The whole idea, in science today, is to publish your findings, so everyone can know.
An educated and informed populace is wiser than the opposite. Knowing how to reason clearly regarding astronomy is going to be strongly correlated with reasoning clearly on economics, law, medicine, and civics. Ignorant people are more easily tricked and duped than knowledgeable people.
I hope to visit as many of these universes as I can and see for myself what they’re like. I’ll send dispatches back.
I humbly doubt that.
- Myths are not essential in building and refining one’s ability to reason. One’s capacity to think logically and grasp highly abstract concepts can be developed by means of studying Latin or mathematics, for example. I believe myths should be used to exercise one’s faculty to reason only in a fun and supererogatory manner with no consequences on one’s beliefs and behavior.
- Cultivating myths can result in a community that includes both wise and ill-advised members. People indoctrinated with theories supported by little or no evidence are not less ignorant than people indoctrinated with opposing theories supported by little or no evidence. The inculcation of sets of theories that require a relatively equal amount of faith will lead to equally ignorant groups of people.
- Knowledgeable people can be better manipulated than ignorant ones. Paradoxically, people who show an interest in a field of knowledge and have acquired some information of it are more likely to retain or hold false ‘facts’ related to it. In addition, if people become knowledgeable by being inculcated with myths, they will wind up holding mainly societal truths, a set of things that they as a group all believe in and revere as right, correct and good for them as a group.
The Straight Dope prides itself on fighting ignorance. Users of its message boards nurture the feeling that they are informed and rational. This is the reason why I myself feel comfortable to (sporadically) converse with people here.
The multiverse as presented by certain scientific theories is a Western concept. I would expect at least part of the SDMB users to be familiar with its theory and, in the case of those who tend to believe in the concept, to be able to speculate on it.
But the questions in the OP remain largely unanswered and I get reproached for inquiring about speculations, addressing philosophical questions, and failing to understand the concept of time. In my defense, I would say that (a) it is scientists (and not me) who speculate and propose the multiverse as the ultimate structure of reality; (b) at its highest level, every field of knowledge tends to address philosophical questions as well (which is partly why the highest academic degree is named PhD); and (c) speculatively or as a mind experiment, time can be considered as a dimension pertaining to other universes as well or even to the entire multiverse.
In my opinion, “an educated and informed populace” should produce some explanations in relation to the questions in the OP. On the other hand, I may have overrated the explanatory power of the concept of multiverse. I have no problem with regarding this theory as pure myth and giving it a rest.
I regard the Multiverse Concept as nothing more than a possible scenario to explain our anthropic reality: how did our universe lead to Humans? In the MV concept, we are the equivalent of the one version of Hamlet typed out in a room with 10,000 monkeys in it. It offers a possible way to Humans that depends on random chance and massively huge volumes of variations. Woo hoo!
Since it can’t be experimented on, for now, it is nothing more than speculation. But it’s not a myth - it’s just a theory that can’t be proven but still a real attempt to noodle an answer. I don’t buy it personally, and agree that it should be treated as nothing more than a gossamer-thin idea at this point, but the concept is worthy of speculation.
That’s going a bit too far.
If you absolutely insist, you can call it “nonsense” in the technical sense: an idea that cannot (at this point in time) be tested. (But very far from “nonsense” in the common usage of the word.)
It’s in the same category as “Is there intelligent life outside our Solar System?” There may be, and the notion is far more serious than “pure myth.”
Myths make declarations: Zeus begat Castor and Polydeuces. Scientific speculations are more in the nature of questions: What if there were other universes.
Also, myths are known to be untrue. Scientific speculations are not.
I do not understand this post. Scientific hypotheses are very different from myths; that’s true even for hypotheses which are not falsifiable.
Darwin advanced a theory of evolution though he knew nothing about genetic mechanisms: does that make his theory a “myth”? Alfred Wegener developed a theory of continental drift though he didn’t understand the details: was his theory just a myth?
And I think you must focus on a particular “multiverse” theory before you can ask specific questions. In #8 I listed four different multiverse theories all completely unrelated to each other. The Wikipedia article shows nine different models of multiverse due to Brian Greene alone. You focus on questions involving time (“created … rate … beginning … end”). Any answers may be unsatisfactory anyway, but I think you should first focus on a specific multiverse model to make discussion more tractable.
I was reminded of this thread while watching a YouTube titled “The No Boundary Proposal.” A claim is made that this formulation will allow researchers to make falsifiable predictions about a certain type of multiverse. Perhaps the Board’s physicists can shed light.
The program is Episode 5 in a series titled Before the Big Bang. (If the episodes are ordered by increasing difficulty I definitely need to backtrack to Episode 1.)