First Observational Evidence Other Universes?

Article written: 1 Jan , 2011
Updated: 19 Jan , 2016

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

In the realm of far out ideas in science, the notion of a multiverse is one of the stranger ones. Astronomers and physicists have considered the possibility that our universe may be one of many. The implications of this are somewhat more fuzzy. Nothing in physics prevents the possibilities of outside universes, but neither has it helped to constrain them, leaving scientists free to talk of branes and bubbles. Many of these ideas have been considered untestable, but a paper uploaded to arXiv last month considers the effects of two universes colliding and searches for fingerprints of such a collision of our own universe. Surprisingly, the team reports that they may have detected not one, but four collisional imprints.

The team, led by Stephen Feeney at the University College London, considered a collision between bubble universes. They conducted a simulation based on a formulation of Einstein’s field equation, known as de Sitter space. This solution to Einstein’s equations is essentially a description of how space itself behaves. From interactions between such spaces, they determined a set of observable effects visible in the cosmic microwave background (CMB). Among them, they required that signals have azimuthal symmetry or are mirrored on both sides of the sky. Secondly, the signals should be circular in shape.

Searching the WMAP archives, the team found numerous possible signals, but eventually narrowed it town to four strong candidates.

The authors of the paper are quick to caution that these results are only consistent with the predictions of bubble universes but do not rule out other causes, or even simple blind luck from a large enough data set. To rule out other scenarios, astronomers will need to rely on instruments with higher sensitivity, such as the Planck satellite, launched in 2009, which working on completing a second scan of the entire sky with three times the sensitivity of WMAP.

If these results are confirmed, it would be support for a variation of cosmology known as “eternal inflation”. The title is somewhat misleading as the hypothesis doesn’t describe a single instance of inflation that continues eternally, but rather an eternal time period in which events of inflation, triggered by bubble collisions, can take place. Such collisions cause the rapid expansion of spaces forming universes like our own. Conversely, if a bubble is not found, “the conclusive non-detection of a bubble collision can be used to place constraints on theories giving rise to eternal inflation; however, if a bubble collision is verified by future data, then we will gain an insight not only into our own universe but a multiverse beyond.”


22 Responses

  1. iantresman says

    I found some dents in my car, clearly “fingerprints” indicating that “something” collided with my car. Something from another universe perhaps? Most of the dents are horizontally polarized, and tend to occur only on roads. All completely consistent with various multiverse theories.

  2. albone says

    I’m glad the multiverse possibility has gained some traction.
    With our universe ever expanding and headed for the possibility
    Of “The Big Rip” it’s nice to know ours Universe could be one of many.

  3. Lawrence B. Crowell says

    The main question I have with this model is the extent to which the inflation is “eternal.” The dynamics of the space manifold

    (a’/a)^2 + 8?G/\/3 – k/a^2 = 0

    is driven by the cosmological constant term /\ that has an energy density ~ 10^{110}GeV^4. For k = 0 the solution to this DE is exponential and the spacetime is de Sitter-like. The cosmological constant /\ ~ vacuum energy density, and this drops in a bubble nucleation which initiates reheating, a concept advanced by Coleman back around 1983. The vacuum energy level is determined by the scalar inflaton field, which in local regions exhibits a quadratic potential that corresponds to a bubble of nucleation.

    The vacuum energy drops enormously in a region so the vacuum is at a much lower level. So with eternal inflation these bubbles will expand at a much slower rate than the embedding spacetime which is exponentially expanding like a mad hatter.

    However, there does seem to be a bit of a problem with the eternal aspect of this. The Lagrangian for a scalar field X is L = (1/2)&^aX&_aX – V(X) (& = partial) and in QFT we work with the Lagrangian density L –> L/vol so the action is

    S = int d^3xdtL(X, &X).

    We run this into the Euler-Lagrange equation &_a(&L/&(&_aX)) – &L/&X = 0, and keep in mind vol ~ x^3. This gives a dynamical equation

    &^2X – (3/vol^{4/3})&_aX – &V(X)/&X = 0.

    If we assume the inflaton field is more or less constant on the space for a given time on the Hubble frame this DE may be simplified to

    X’’ – (3/vol^{4/3})X’ – &V(X)/&X = 0

    That middle term is interesting for it is a sort of friction. It indicates the inflaton field, the thing which drives the inflationary expansion, is running down or becoming diffused in the space. The potential function here is complicated and not entirely known, but it is approximately constant — similar to the accelerated expansion of the universe we observe. What then happens, which is not entirely understood, is that the field experiences a phase transition, the potential becomes V(X) ~ X^2 with a minimum about 110 orders of magnitude smaller than it was in the unbroken phase. The phase transition has a latent heat of fusion that is released and this is the reheating.

    The phase transition is a bubble nucleation from a high energy vacuum to a low energy one, which occurs throughout the spatial manifold of this universe. Our observable universe out to about 10^6 billion light years is one of these bubbles. The space R^3 becomes fractured into these bubble nucleation zones which exponentially expands over the long run according to the residual vacuum energy which is left. It is a sort of soap suds foam that extends throughout the space, and where each of these bubble volumes is expanding exponentially. The universe we can observe may then be about 1 part in 10^{20} of one of those “soap bubbles.”

    What is unknown is the nature of this phase transition and the sort of “Higgsing” which goes on with it. There are lots of models out there about this sort of thing. However, it seems likely the embedding spacetime will “poop out” pretty quickly, which does give an enhanced probability for interactions between these bubble nucleation zones, such as the one we observe. In fact it seems then do not even need to “bump” into each other, for they should interact by Casimir effects.

    Cheers LC

    • jcamjr says

      Unless I’m missing something obvious there would seem to be no reason to assume that after phase transition any two spacial manifolds will have the same residual vacuum energy. My question in a nutshell is … At the time of contact between nucleation zones of differing vacuum energy states should we not expect an event much like a false vacuum decay to spread through both zones and essentially act as a vacuum energy leveling mechanism ? I don’t have the math skills to express this any clearer and apologize if I’m making no sense but on the off chance that I am would appreciate your thoughts on the subject.

  4. Lawrence B. Crowell says


    Your question is relevant to this discussion.Coleman in his original paper wrote a little bit about how this could lead to the ultimate catastrophe, where the vacuum energy in one bubble transitions into that of another. However, this is not likely, for this potential function for the scalar dilaton or inflaton would be quartic and there are observable consequences for that. It appears the potential function for the post inflationary bubble is quadratic.

    A good comparison is between these bubbles and domains of magnetization in a ferromagnetic material below the Curie temperature point. Each has its own direction of magnetization and set direction. Yet they all sit within a metal and are adjacent to each other. There is no process without an external magnetic field where by magnetization domains “eat each other” and turn a metal into a large magnet or annihilate all magnetizations of domains so complete symmetry is recovered. There is a similar process here. Each of these pocket universe has its own broken symmetry phase, and the only way they can transition into each other is through superselection rules. However, the energy required for such transitions by these superselection rules is far larger than what is available.


    • jcamjr says

      Thank you, I appreciate that you took the time to answer my rather vague musings in such a clear and helpful manner.

  5. says

    I believe the cmb rings are remenants of bruises and collisions from many smaller black holes all separately preexisting together moving in a stream that pretty much impacted at the same time. the largest collision of this stream triggered what we see as the big-bang. evidence data shows the cmb is not all-sky, and vast distances well beyond our visible telescopic horizon we surely know exist galaxies that are older then the age of thr big-bang baby universe supplied by standard model lovers.

    • Hon. Salacious B. Crumb says

      Eh? This is just more gobbledegook from the master twit.
      No evidence, just wild unimaginative clap trap that means nothing.
      Just because you want the universe to be infinite to satisfy your own deranged version of plasma cosmology doesn’t make it so!
      You are a total fool, sir.

      • Harry says

        Nice choice of words there crumb. I do not understand how dark energy and dark matter can be part of so called mainstream science, and the hypothesis/theory presented in the article above can not be.

  6. neoguru says

    If we keep it up, soon science will be investigating Santa Claus, the Easter Bunny, and other stupidities. Hopefully we’ll return to the days where science actually uses EVIDENCE for their theories and not fantasy.

  7. Torbjorn Larsson OM says

    I thank Jon and Lawrence for neat summaries. Another neat summary is a guest blog from one horse’s mouth:

    While we didn’t make any clear detections of bubble collisions, we did find four features in the WMAP data that are better explained by the bubble collision hypothesis than by the standard hypothesis of fluctuations in a nearly Gaussian field. We assess which of the two models better explain the data by evaluating the Bayesian evidence for each. The evidence correctly accounts for the fact that a more complex model (the bubble collisions, in this case) will generally fit the data better simply because it has more free parameters. This is the self-consistent statistical equivalent of applying Ockham’s Razor. In addition, using information from multiple frequencies measured by the WMAP satellite and a simulation of the WMAP experiment, we didn’t find any evidence that these features can be attributed to astrophysical foregrounds or experimental systematics.

    [My bold.]

    Out go my problems with a Gurzadyan and Penrose type pattern recognition. You can find anything in a gaussian background (concentric circles, flower patterns and a resemblance of your granny’s face), the trick is to show that there is a non-gaussian deviation.

    Btw, personally I find eternal inflation bubble universes a bit harder to grasp than chaotic inflation pocket universes. Which is why I prefer to talk of the latter, while realizing that the joined parameter space for both are larger.

    For one, it is the matter of understanding the phase transition and the bubble boundaries, see Lawrence’s notes. For another, it goes back to Jon’s remark that in effect “eternal inflation” as a term describes the process and not a (our) volume of space, it seems much easier to visualize chaotic inflation as it spreads than to abstract from bubbles.

    In the realm of far out ideas in science, the notion of a multiverse is one of the stranger ones. Astronomers and physicists have considered the possibility that our universe may be one of many.

    “Strange” is a matter of taste, multiverses is the natural state of inflation writ large. I.e. if the chuck out the fully untested, non-uniform and non-copernican hypothesis that the universe emerged from a single Planck volume, what remains is that standard cosmology may observe the local end of inflation (eternal or chaotic).

    Mind, inflation needs to be more tested, but after that it is as strange to propose a single emergence as it is to propose a unique vacuum state of physics. It was a cute and, yes, “strange” idea of our forefathers, but it looks both peculiar and like a remote likelihood when looked closer at.

    Another way multiverses can’t be kept out of physics is because FRW universes seems to be zero energy. Quantum physics then gives that new universes tunnels out of existing ones. It is then fundamentally strange to propose a single universe, it would be like playing whack-a-universe to cut other universes out of physics. 😀

    The multiverse is in fact one of the oldest ideas of naturalists. I recommend following the link in the post I referenced above to the post where physicist Sean Carroll argues that the atomist philosopher Lucretius was “the first quantum cosmologist” (O.o) based on the notion of environmental selection giving rise to our universe and that there were other regions. (“Quantum”, since Epicurus previously had to invent a quantum mechanics analog “swerve” to explain matter bodies.)

    • Lawrence B. Crowell says

      There may be another level of multiverse. The flat space which our bubble is contained in is defined by strings on a D3-brane, where type IIB strings can connect up a whole foliation of these. The Dp-branes are a bit like extended quarks, and the strings gluons. So our observable universe could be just one bubble on a space which contains a vast number (about a mole) of other bubbles, and where this whole space is induced by the string modes on oneD3-brane in a huge foliated stack of such D3-branes. So there is then another level of multiverse altogether which may exist as well. These multiverses may be tied to each other through black hole singularities, and indirect evidence for their existence may also be detectable.

      There are two hypothetical levels of multiverse beyond this, leading to Tegmark’s “Platonia,” though he does not use that term, of all possible existing worlds which conform to mathematical systems. I have no idea how we will ever come to observe or measure anything about that.


  8. Torbjorn Larsson OM says

    To iantresman and neoguru I lift out the part of the guest blog intro where Carroll replies to dogmatic thinking of the religious a priori type:

    A lot of other people are aghast that this is considered science. Personally I think science talks about unobservable things all the time, and this question is going to be resolved by people doing hard work to make sense of multiverse scenarios rather than by pronouncements about what is or is not science.

    Note that what Carroll describes are unobservable things like Lucretius atoms, not their observable effects (such as our own biochemical machines). We can never observe anything directly (or in real time), but need photons to reach our eyes et cetera. To demand a fast and hard barrier between the observer and what can be observed at any one time, and the rest, is simply not possible.

    [Frankly it reminds me of creationists demanding that there are fast and hard barriers between species or “baramins” or whatever their frenzied minds think up. I’m sorry if that offends, but it is what I feel and, I think, for good reason.]

    Clearly science can help investigate hit-and-run accidents of criminology (or we wouldn’t know of that type of killers out there) and supernatural proposals of the Santa Claus type. As Hawking noted, we have known for a long time that gods aren’t a necessary (and I would say not sufficient, seeing what little gap remains) explanation of the universe and what it contains.

    Science is an open-ended process which is only framed (openly defined) by its success. Constraint theories of science has always failed in tests.

  9. Editor57 says

    It would seem this article is a little late. Response to the Penrose paper was swift and generaly negative; see this
    Finally Penrose etal respond

  10. Underlings says

    Before an idea becomes a theory, it has to be an hypothesis, right? And if we constrained hypothesizing, we’d eliminate a lot of scientific discoveries. So what’s wrong with posting multiverse hypotheses on a science news website? Especially when there’s at least some predictive evidence to support it?

  11. William928 says

    As a layman, I contend that any subject that fosters inquiry can only be positive. Perhaps discussing the unknown or unexplored idea or theory will lead to further groundbreaking discoveries. Isn’t that one of the principle functions of Science?

    • Member
      Jon Voisey says

      Fostering honest and intelligent inquiry is a wonderful thing. However, not every notion performs this. For example, Intelligent Design Creationism doesn’t lead to honest or intelligent inquiry because it’s grounded in misinformation, and intended to lead people away from a conclusion by presenting half truths, outright lies, logical fallacies and and perversion of scientific processes. It contributes nothing. The same is true with the “plasma cosmology” model. It misleads people with pseudoscientific gibberish, misinformation on evidence, and doesn’t follow any true scientific process. That’s neither honest nor intelligent.

  12. astrohrishi says


    Why is bubble universe a possible option while Penrose’s cyclic universe theory sounds more appealing…


  13. kurzastar says

    Strange to read this article today. I’ve been thinking many hours today about how I’d get a thought I have had into a short story for a creative writing website. The gist of it is that, even after a flat earth in the center of the universe around which all things revolved, we humans are still so impressed with our ability to think that we create hypotheses to explain things which may just be unexplainable or at very least completely outside of our ability to understand them.
    My current favorite is a yet undetected energy which is accelerating the expansion of the universe. An energy that is cold and doesn´t produce anything visible on the electromagnetic spectrum. So I postulated a “Bubble Universe” in a “Soda Extraverse”.
    Imagine opening a bottle of soda. Bubbles appear, seemingly out of nothing. It is however a reaction of the contents of the “Soda Extraverse” which have experienced a sudden change in pressure. This initial “Big Fizz” takes place in the first fractions of a second of the existence of the “Bubble Universe”.
    The Universe then continues to expand at a more subdued rate as the contents of the “Soda Extraverse” react under a more stable local pressure. When the “Bubble Universe” reaches a critical size it can no longer remain its position in the “Soda Extraverse” and starts to “Float to the top” where it encounters a continually reducing external pressure and as such the expansion of the “Bubble Universe” accelerates.
    Further still, at a point in its existence the “Bubble Universe” reaches the extreme limit of the “Soda Extraverse” it experiences “The Big Pop” and seemingly disappears. In fact it has just released its own contents into “The Night Club Extremaverse”
    It may seem like a silly story and I will admit it has no basis in science but I firmly believe that the likelihood that this universe is effected by the physics of what is outside of it, a physics which is completely beyond our grasp, is higher than the likelihood of this universe being totally isolated from external influences.

  14. Lawrence B. Crowell says

    The soda idea is not completely half baked. Pouring the soda water into a glass is analogous to the generation or quantum tunneling of the space out of the vacuum or from an instanton associated with a black hole in some other space (universe). The process generates lots of fizz, and the bubble are generated by the myriads, and our observable universe is one of these bubbles. Of course unlike the drink the bubbles persist as the “drink” medium is “infinite.” Yet as I indicate above there is a “friction” associated with the inflaton scalar field and the “soda” will go “flat.” The huge inflation process will then wind down. Of course the bubbles do remain and are inflating at a much more modest rate than the initial inflation of the space.

    I should have thought of this on New Year’s eve and proposed a toast of Champaign.

    As for the “Crumb” comments, while they may be a bit barbed, they do express an irritation I feal. It seems that after the Apollo 11 landing Americans turned their back on so much of real science, or turned to bizarre alternate ideas, religions, crack-pottery, and fell into some disillusionment after the Nixon resignation. We still have not shaken that off. I have spent all but my childhood in this age of social confusion. DAMNED!


    • Member
      Aqua says

      “…this age of social confusion.”

      Be Thee Reborn,
      with the Renewal of Thy Mind.

      Buck up MATE! A prediction…. our science will soon create an energy replacement for fossil fuels. Expect incredible resistance to this from the ‘status quo’ factions…. but economic turnover will become inevitable and the accompanying opportunity for social evolution most welcome!

      • Lawrence B. Crowell says

        The issue is not about some future energy source, or techno-magic. It is that the American people have magnificently transformed themselves into a population of idiots.

        The rest of the world’s political powers are looking upon this situation eagerly, for they may … .

        It sucks being in a declining civilization.


Comments are closed.