Existence of multiverses?

[astrogirl808]

Hey guys, I'm a high school astronomy student in Hawai'i and was wondering if anyone had any opinions on the existence of multiverses? If so which of the existing theories on multiverses seems the most probable based on physics/science? Any answers would help out a lot thanks so much!

[Markus Schwarz]

'Multiverses' maybe fun for science fiction, but they are not science! The main reason for that is that they are not testable (hence, they cannot be falsified): you cannot measure something which, by definition, is outside the observable universe.

[owlice]

Hey guys, I'm a high school astronomy student in Hawai'i and was wondering if anyone had any opinions on the existence of multiverses? If so which of the existing theories on multiverses seems the most probable based on physics/science? Any answers would help out a lot thanks so much!

Astrogirl, this sounds like a school assignment. Is it? If so, you should seek out some of the literature on multiverses; check out this link, for example: https://arxiv.org/search/?query=multive ... rce=header

arXiv (arxiv.org) is a pre-print server -- a place for scientists to upload their research papers before they are published -- so these papers may not have been peer-viewed (reviewed by other scientists for accuracy) yet, but it's a good place to start, and I see several papers just on the first page of that search that are relevant to your question. I would look for papers with a "Journal ref:" notation first, and for those papers without a "Journal ref:", for more than one author and authors who are affiliated with universities, space agencies (such as NASA or ESA), or observatories. You might read a couple or three to see which seem most probable to you based on the science you already know.

'Multiverses' maybe fun for science fiction, but they are not science! The main reason for that is that they are not testable (hence, they cannot be falsified): you cannot measure something which, by definition, is outside the observable universe.

Markus, you might like some of the papers at the link I supplied, too!

[neufer]

Click to play embedded YouTube video.

Click to play embedded YouTube video.

Hey guys, I'm a high school astronomy student in Hawai'i and was wondering if anyone had any opinions on the existence of multiverses? If so which of the existing theories on multiverses seems the most probable based on physics/science? Any answers would help out a lot thanks so much!

---

Multiverses may or may not be testable but agnostic/atheist scientists like myself cherish them as our own "Just So Stories" that totally exclude "divine intervention" (or Schrödinger's cat "human intervention") in explaining the world we live in.

[Chris Peterson]

'Multiverses' maybe fun for science fiction, but they are not science! The main reason for that is that they are not testable (hence, they cannot be falsified): you cannot measure something which, by definition, is outside the observable universe.

There's a lot of truth there, but I wouldn't say that these hypotheses aren't science. Some of them do offer tests (for instance, they predict certain structure in the CMB). And in general, even very speculative ideas from smart people can form the basis of science that gets developed out in the future. (String theory might be one such example.)

As theory, or even as hypothesis, most multiverse ideas remain scientifically weak, but to call them nonscientific is, perhaps, taking things a little too far.

[Markus Schwarz]

Markus, you might like some of the papers at the link I supplied, too!

I did. The first paper is about multiversions in software development, the next two are from computer science. From the context of atrogirl808's question, I assumed she is interested in the cosmological multiverse (which papers 4 and 5 write about). For more details why I consider the multiverse arising from superstring theory as pseudo-science, see this FAQ by Dr. Peter Woit, who wrote a whole book on the subject.

Some of them do offer tests (for instance, they predict certain structure in the CMB).

I think we are talking about different things. I refer to the multiverse in superstring theory and the anthropic reasoning that goes with it.

[Chris Peterson]

Some of them do offer tests (for instance, they predict certain structure in the CMB).

I think we are talking about different things. I refer to the multiverse in superstring theory and the anthropic reasoning that goes with it.

Okay. But I take the question of multiverses to extend to a variety of hypotheses which have been offered, and some definitely offer potential tests.

And, as a matter of the philosophy of science, I do not automatically require falsifiability or testability. These things are, of course, extremely important. But there are phases of scientific questioning where they may not exist. To characterize all thinking at that stage as "pseudoscience" is making a mistake, I think. Very speculative ideas can lead to future theory. I would characterize ideas about multiverses, or a lot of string theory, as currently weak science, not pseudoscience.

(I'm inclined to agree, however, that anything invoking the anthropic principle for scientific explanation might reasonably be called pseudoscience.)

[neufer]

(I'm inclined to agree, however, that anything invoking the anthropic principle for scientific explanation might reasonably be called pseudoscience.)

• A weak anthropic principle (WAP) is excellent Darwinian science, IMO.

Click to play embedded YouTube video.

<<The anthropic principle is a philosophical consideration that observations of the universe must be compatible with the conscious and sapient life that observes it, and that there is hence a survivorship bias. A weak anthropic principle (WAP) similar to the one defined by Brandon Carter, states that the universe's ostensible fine tuning is the result of selection bias (specifically survivorship bias): i.e., only in a universe capable of eventually supporting life will there be living beings capable of observing and reflecting on the matter. Most often such arguments draw upon some notion of the multiverse for there to be a statistical population of universes to select from and from which selection bias (our observance of only this universe, compatible with our life) could occur.>>

[Markus Schwarz]

(I'm inclined to agree, however, that anything invoking the anthropic principle for scientific explanation might reasonably be called pseudoscience.)

A weak anthropic principle (WAP) is excellent Darwinian science, IMO.

But that is exactly my point: the multiverse of string theory heavily relies on the anthropic principle. The short version is: Superstring theory only works in 10 dimensions. But we only observe 4 (three spatial and one temporal), so the other 6 need to be somehow 'compactified', i.e. made so small that we do not observe them. It turns out that there are roughly 10^500 ways to 'roll up' the 6 dimensions, and each of these leads to different values for the physical constants (speed of light, rest mass of the electron, etc.). As far as we know, there is no reason why one compactification is preferred to any of the others. This is where the anthropic principle comes into play: we just happen to be in the part of the multiverse with 'our' natural constants, because if we were in any of the others, we wouldn't be here to ask. End of story!

One of the problems I have with this, is that it stops all kind of scientific endeavor. According to the above paradigm, asking fundamental questions like why the universe has the properties it has is pointless, because the answer is that the multiverse 'did it'. Furthermore, we cannot test superstring theory, so we cannot find out if it is the correct theory in the first place. [This is also the mistake Dawkins makes, when he argues with the untestable string theory and anthropic reasoning (I haven't watched the video, but have read 'The God Delusion')]

[BDanielMayfield]

Consider the origin of the Multiverse hypothesis. It is an idea without fundamental factual support that was put forward as an answer to the Fine Tuning "Problem". But if the one and only universe that we know to actually be in fact real was in fact "tuned" as it were, then the need for such an idea evaporates.

Bruce

[Chris Peterson]

Consider the origin of the Multiverse hypothesis. It is an idea without fundamental factual support that was put forward as an answer to the Fine Tuning "Problem". But if the one and only universe that we know to actually be in fact real was in fact "tuned" as it were, then the need for such an idea evaporates.

There is no one multiverse hypothesis. There are several, with fundamental differences. And, of course, there's really no "fine tuning" problem. It's not even an issue.

[owlice]

Markus, you might like some of the papers at the link I supplied, too!

I did. The first paper is about multiversions in software development, the next two are from computer science.

Yes, I know. I didn't say ALL of the papers... I said "some of the papers at the link I supplied."

From the context of atrogirl808's question, I assumed she is interested in the cosmological multiverse (which papers 4 and 5 write about).

Yes, I made the same assumption. I also assume a high school student is capable of looking at that list and picking out some of the relevant papers. It's nice that you have demonstrated that you are capable of doing so! I wasn't expecting that from you!!

For more details why I consider the multiverse arising from superstring theory as pseudo-science, see this FAQ by Dr. Peter Woit, who wrote a whole book on the subject.

I don't need more details and in fact, find your comments not very helpful in this context, though admit you did answer the first part of the student's query as to whether anyone here had opinions about multiverses! Perhaps the student and her teacher will be interested in your take on the matter. Since I suspect the second part of her query is the more important part, I tried to steer her to resources she can use for that.

[neufer]

One of the problems I have with this, is that it stops all kind of scientific endeavor. According to the above paradigm, asking fundamental questions like why the universe has the properties it has is pointless, because the answer is that the multiverse 'did it'. Furthermore, we cannot test superstring theory, so we cannot find out if it is the correct theory in the first place.

Click to play embedded YouTube video.

There will always be folks trying to figure out what the fine structure constant is exactly using math & physics.

However, there is no point for everyone to play around with what is probably a futile effort(; and one that probably promotes:

SAP over WAP).

There are plenty of things to test and more data coming in than we know what to do with.

[neufer]

'Multiverses' maybe fun for science fiction, but they are not science! The main reason for that is that they are not testable (hence, they cannot be falsified): you cannot measure something which, by definition, is outside the observable universe.

There's a lot of truth there, but I wouldn't say that these hypotheses aren't science. Some of them do offer tests (for instance, they predict certain structure in the CMB). And in general, even very speculative ideas from smart people can form the basis of science that gets developed out in the future. (String theory might be one such example.)

As theory, or even as hypothesis, most multiverse ideas remain scientifically weak, but to call them nonscientific is, perhaps, taking things a little too far.

Just as Gödel's incompleteness theorems tell us that:
there are mathematical truths that can't be proved,
there are going to be scientific truths that can't be tested.

'Multiverses' allow us for the first time to generate self consistent creation hypotheses
based upon 21st century science and the law of large numbers.

The only other self consistent creation hypotheses are all based upon bronze age science & pseudoscience.

You take your pick (...or remain agnostic).

[astrogirl808]

Thank you everyone for responding! This was a school project and your answers helped out a lot.

[fizzixprof]

Astrogirl, this sounds like a school assignment. Is it? If so, you should seek out some of the literature on multiverses; check out this link, for example: https://arxiv.org/search/?query=multive ... rce=header

Good eye, this is an assignment for my astronomy class where Astrogirl was given the direction to ask experts a question where either she could not find the answer to via Google or the answers were too complex or contradictory. She also asked a local astronomer and included his response in her final work as well as snippets from this conversation. Thanks to everyone who participated!