Living in the Multiverse–Is it Science?

by Max Andrews

Is the multiverse hypothesis a legitimate scientific theory?  That is, are there regularities that illuminate and reflect underlying laws of nature by testing these laws and making predictions that can be either verified or refuted by experimentation and observation?  Generally, these are the guidelines for something to be scientific, can it be verified and falsified?  Before I continue, we need to make a distinction in two fundamental philosophies of science: instrumentalism and realism.

Instrumentalism:  Scientific theories are not intended to be literally true and accepting a theory requires us to believe only that its observational consequences are true.  Observation statements are literally true and science is only about these statements and the observations that verify them.  A few strengths of this philosophy is that it doesn’t conflict with common sense realism; we can believe in straightforward observations.  Plus, it’s more modest and non-commital than scientific realism.  A few weaknesses are that scientists seem to assume the realist view of the world in their “un-thinking” moments.  The instrumentalist should be able to draw a clear cut distinction between what is and what is not observable, which creates limitations on what really is observable (i.e. naked eye, magnifying glass, microscope, electron microscope, cloud chamber, etc.). This also raises the question, at what point is the objecting being observed really being observed, and so real, but then one bit smaller is not observable and thus not really existent?

Scientific Realism:  Scientific theories are intended to be literally true, and accepting a theory involves believing that it gives a true description of reality, “as it really is.”  A few strengths of this is that it makes the aspect of explanatory power superior to instrumentalism because explanation requires real things that cause the chain of causality.  Explanation by means of fictitious entity is not explanation at all.  Instrumentalism cannot explain the actual success of science, especially science’s making predictions, which are empirically adequate (i.e. Boyles-Charles Law, pv=k).

I’m going to argue that we should adopt the realist position partly because it is common sense and because it means and ends in explanation provide a robust sense of explanatory power that lacks instrumentalism and the metaphysical baggage it may carry is less deleterious than instrumentalism.

Before proceeding any further I need to define what I mean by multiverse.  Multiverse isn’t monolithic.  For simplicity’s sake, let’s go with Max Tegmark’s versions of the multiverse (Brian Greene makes a distinction of five levels but aren’t too different from Tegmark’s).  A level one multiverse is, for the most part, more space beyond the observable universe.  So, if we were to go to the “edge” of this universe, there would be more space.  This isn’t controversial and is pretty much a settled issue (same landscape).  A level two multiverse comes out of inflationary cosmology, which is typically associated with other bubble universe spawning from a cosmic landscape and slow-roll inflation.  A level three multiverse is where it gets pretty weird.  This is usually associated with the Many Worlds Interpretation of quantum mechanics and a rule of thumb, what can happen does happen.  Consider a film of every state of affairs.  A man asks a woman for a drink. In one scenario she says yes and in another she says no.  Both happen.  A level four multiverse is the cherry, it equates physical existence with mathematical existence–it’s the ultimate ensemble.

Let’s consider the issue of accessibility.  Can we access another universe?  For the level two multiverse there is room for interaction.  There is more space between two Hubble volumes (the observable space in a closed system/bubble universe).  If the rate at which the bubbles expand exceeds the rate at which the swelling of space that propels them to separate (keep in my inflationary cosmology), the bubbles will collide.  If they’re really close then there will be so little intervening space that their rate of separation will be slower than their rate of expansion.  Calculations show that if we had such a collision with another bubble universe then the impact would send shock waves rippling through space, generating modifications to the pattern of hot and cold regions in the microwave background radiation (see Brian Greene’s The Hidden Reality, 166-167).  Consider the image below.  This image is of the CMB and the key for bubble collision detection was using a specified algorithm for detecting temperature modulations that would occur in such events (See this paper for calculations).

The signatures of a bubble collision at various stages in the analysis pipeline. A collision (top left) induces a temperature modulation in the CMB temperature map (top right). The "blob" associated with the collision is identified by a large needlet response (bottom left), and the presence of an edge is determined by a large response form the edge detection algorithm (bottom right).

This can also be tested at CERN.  The Brane multiverse and level three mutliverse are striking similar.  Brian Greene discusses how we can test the validity of Branes:

If we are living on one of these giant membranes, then the following can happen: When you slam particles together — which is what happens at the LHC — some debris from those collisions can be ejected off of our membrane and be ejected into the greater cosmos in which our membrane floats,” he says. “If that happens, that debris will take away some energy. So if we measure the amount of energy just before the protons collide and compare it with the amount of energy just after they collide, if there’s a little less after — and it’s less in just the right way — it would indicate that some had flown off, indicating that this membrane picture is correct.

Is this too far fetched? Is this special pleading?  Well, consider the advances in science within the last century.  We build incredibly sophisticated equipment and measure the undetectable on many levels, the question is at which point to we consider something undetectable or inaccessible?  Space, time, and spacetime are the scaffolding for general and special relativity, yet you’ve probably never grasped spacetime in the same way you grasp a book.  There are several historical instances of a theory’s success being used as an after-the-fact justification for its basic architecture even though that architecture remains beyond our ability to access it directly. Consider so many examples in quantum mechanics such as the cloud chamber.  For a non quantum example, consider the problem of the cosmic horizon (the horizon problem).  At the beginning of our universe everything existed in a tiny dense point.  Inflation occurred and it propelled space faster than light. It slowed down and is now speeding back up.  Objects, or for the sake of illustration, observers beyond the cosmic horizon can never interact with us and we can never interact with them.  Should we then believe that the space beyond that point of horizon doesn’t exist because it is inaccessible to us?  My point is that science is no stranger to theories that include elements from basic ingredients to derived consequences that are inaccessible.

The next question is obvious.  Let’s backtrack to our philosophy of science, are all of our measurements merely depictions of a fundamental fiction or do they equate to reality?  I would argue for reasons I’ve already suggested, and for theological reasons, that this is real.  Theologically, philosophical realism is our best access to natural inquiry, from which we base a natural theology and revelation on.  The concept of an exponentially large landscape of reality is rich with beauty and elegance.  How does this not reflect the creativity and aesthetic beauty of a Creator?


12 Responses to “Living in the Multiverse–Is it Science?”

  1. Max,

    First off, excellent post here. I really enjoy thinking about cosmology and astronomy. Admittedly, I’m a total nerd. I’ll be linking your post in my next “really recommended posts” (probably the 13th).

    Anyway, I definitely don’t think there is a multiverse. The reasons being numerous, but my main problem is it seems to lack real evidence. Granted the points you make above, it still seems to me there is an observational, ontological gap between ourselves and actual other universes.

    It seems to me there is a redefinition going on here; rather than referring to other dimensions, the term now used is ‘universe.’ But is not our own “universe” in a sense all there is?

    Again, I’m totally a layman when it comes to this.

    But then I also wonder why you are so much for the multiverse. Theologically, what value does it have? (This is not an objection, but a genuine question–I saw your tweets about it and I wonder what makes you like the multiverse so much.)

    Anyway, great post, got me thinking.

    • What evidence would you need for you to believe that there is a multiverse? You say you need observational evidence, what is it about the WMAP data doesn’t meet the criterion you need for observational data? Also, if you have questions as to the ontology of a multiverse what prevents you from questioning the ontology of this universe? It’s the same spacetime continuum so at what point do you draw the line from real and not real? This begs the question, are you an intrumentalist or realist? I assume you’re a realist since you doubt the ontic status of other universes.

      I guess you could say that universe is being demoted. Universe could mean, universal all physical matter but that’s not what I mean. When I say universe I mean this closed system or our Hubble volume. Take for instance the historical demotion of universe Kant used. Centuries back the Andromeda galaxy was viewed as a floating universe. Then there were more galaxies that were discovered and they were called floating unvierses as well. So this demotion of the term has it’s precedent. By multiverse I mean all physical matter and the aggregate of all systems. I’ll be doing a blog post soon on my theological attraction to it :-)

      • Max,

        Again, I am 100% a layman and the only things I’ve read on the multiverse are philosophical as opposed to scientific. Could you recommend some resources?

        I can see where the “demotion” of the term universe would work, but it seems to me that that could then cause confusion over what “multiverse” means. In my experience of running into the term in philosophy (and presumably your own in some cases), it often means the existence of all universes which are possible. It seems like that’s what you’re referring to regarding a level 4 multiverse.

        But that is where I fail to see evidence. How could we know that there are nearly (or literally) infinite universes parallel to our own, shifting only choice by choice from our own (in some, for example, I ate breakfast this morning and therefore I’m not so hungry)? What evidence do we have for that?

        You wrote about “WMAP data” for the multiverse, but (again, as a layman) I looked up some links on that and it seems to only show data about our universe–the density, age, etc. It doesn’t seem to confirm parallel universes.

        That’s what I’m having difficulty understanding. Why think there is a multiverse in the sense of “all possible worlds exist”?

        I’m going to have to do more research on this topic :).

      • Oh, and for clarification, I believe that the level two multiverse exists. I’m open to level 3 and 4 but I’m not there yet, primarily because they are dependent on quantum interpretations, such as the many worlds interpretation, which run into a few ontic problems I have with the nature of reality that I haven’t come to research enough to solve.

      • A few of your questions I actually answer in his blog post. Be careful of equivocating versions of the multiverse with the evidence for a particular model. I use the WMAP data for the level two whereas your objection is based on the parallel multiverse which is level three. You’ll find physical evidence for the level three at CERN if we find that after a particle collision we have less information than what we started with (the Brian Greene quote). So, just be careful on what evidence you require for each level of the multiverse because what you’re looking for you won’t find. The paper I cite on the WMAP data is modest, we’ll know more in five or six years when we apply the same algorithm to the new and better Planck data. With regards to the definition of multiverse, you recognize that my clarification of the term universe works but then it confuses multiverse, how does that work? After my clarification, what ambiguity do I need to clarify still, sorry, I don’t understand. As for more information on the mutliverse, types, and number of universes see the papers I list at the end of this blog post:

  2. Also, Max, if you could recommend any books on the multiverse from a theistic perspective I would really appreciate it.

  3. I don’t think level one and two multiverses would be a problem at all to Christianity. But levels three and four are the giants.

    I wonder what happens to our whole notion of personhood and free will if even a level three multiverse were to exist. That in another universe I would be a murderer, rapist and so forth. According to Wikipedia though, there’s an “unreal” interpretation of the MWI which states that the other worlds aren’t as “real” as ours?

    • I agree. The fist two have no problems. I do see the conflict in the latter two. I’m actually currently working on a paper for EPS on the compatibility of all four levels. I think it works, I don’t see any logical restriction, but it’s a hard pill that I haven’t swallowed yet either lol. I developed this model of Thomistic modal realism that I’m working on for EPS. I’ll be coauthoring it with David Beck.


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