Monday, December 20, 2010

Evidence of Eternal Inflation in the CMB?

Last week, I read on the physics arXiv blog a post titled Astronomers Find First Evidence Of Other Universes, claiming that
Our cosmos was "bruised" in collisions with other universes. Now astronomers have found the first evidence of these impacts in the cosmic microwave background.

This left me deeply puzzled because I had read the paper in question:
    First Observational Tests of Eternal Inflation
    By Stephen M. Feeney, Matthew C. Johnson, Daniel J. Mortlock, Hiranya V. Peiris
    arXiv:1012.1995 (see here for an extended version)

yet seemed to have read something completely different out of it. So what's this all about?


The cosmic microwave background (CMB) we measure today is a relic from the time when the universe was only 300,000 years old and radiation decoupled from matter. Since then, photons could travel almost undisturbed. Thus the radiation, especially the fluctuations around its mean temperature, contain valuable information about the history of the universe. The CMB temperature fluctuations have been measured with great precision by the, now completed, WMAP mission and I'm sure you've all seen their skymap.

This data from the CMB temperature fluctuations, often discussed in form of its power spectrum, has allowed us to extract parameters determining the expansion of the universe and complement other data. What we know today, among other things, is that the universe is not only big, but to excellent accuracy spatially flat. That's a feature not naturally achieved with every mode of expansion. It also requires explanation why the CMB temperature is so homogeneous and isotropic, ie essentially the same everywhere with only small fluctuations around it. The currently most widely accepted model that achieves all that easily is inflation. Inflation is basically a phase of early, very rapid expansion that succeeds in solving the problems of flatness and homogeneity (and some others in addition). Inflation then has to end at some time, so matter can form and after that the expansion of the universe proceeds in a more moderate form, allowing the structures to form that surround us today (filaments, galaxies, stars).

There are several models of inflation that differ in the detailed predictions, but the rapid expansion is what they have in common. A particular variant of inflation is called "eternal inflation." As the name says, in that case inflation does not end completely but continues eternally. The way this is thought to happen is that inflation only ends locally when a metastable "false" vacuum state decays into a "true" vacuum state and subsequently continues along a local inflation scenario that ends and results in matter formation and gives rise to a patch like our own, commonly called "bubble universe." However, the areas of false vacuum never decay away completely because they expand more quickly than they can decay. As a result, new bubble universes continue to be formed out of the false vacuum eternally.

Bubble Collisions

While eternal inflation has its proponents, the most well-known probably being Alan Guth, it hasn't been particularly popular, mostly because for what observations are concerned it's a superfluous overhead to the local inflation scenario. It increased in popularity somewhat with string theorists having to face a large number of possible vacuum states, a scenario that seems to fit nicely with the continuing creation of bubble universes that together form what's become known as the "multiverse." Still there remains the question what's it matter if we can't observe it anyway.

It turns out that there are circumstances in which we could find evidence for the existence of other bubbles because initially separate bubble universes might come to overlap during their expansion in a "bubble collision." The probability of there having been a bubble collision in our past, and that bubble collision being observable yet not fatal for the evolution of life in our universe, depends on the parameters of the model.

The Paper

That finally brings us to Feeney et al's paper. Inspired by earlier work by Aguirre et al (Towards observable signatures of other bubble universes, arXiv:0704.3473) they studied the possibility that a bubble collision in our past has left an imprint in the CMB. Their paper basically presents a particular analysis scheme for the CMB temperature fluctuations. Projected on the 2-dimensional surface of last scattering, the leftover signal would have azimuthal symmetry. They assume that a bubble collision has left a mark in the CMB that consists of a slightly different temperature in such an azimuthal patch.

They use an algorithm to analyze the temperature fluctuation that works in three steps. First, search for areas with azimuthal symmetry. Second, search for edges where the temperature makes a slight step. Third, if you've found that, look for the best parameters to reproduce what you've found. They then go on to create fake CMB fluctuations with signals of bubble collisions to quantify how well their algorithm works. The picture below, taken from Feeney et al's paper, depicts the stages of this simulation. Each quarter of the skymap is supposed to show the same area, just mirrored horizontally and vertically. The upper left part shows the patch with the temperature variation from the bubble collision without fluctuations superimposed (the Mollweide projection used to plot the map distorts the shape). The upper right part adds random fluctuations. Now the task is to get the signal back. The lower left part shows the result of looking for patches of azimuthal symmetry, the lower right one the result of looking for edges with temperature steps.

After testing out their algorithm with fake data to understand what features it is able to identify with certainty, they come to the interesting part and analyze the actual CMB data. Their algorithm doesn't find edges, but identifies 4 regions of interest whose features could possibly have been caused by bubble collisions. As the authors put it, these features are "compatible" with having been caused in that way. Two of these spots of interest btw have previously been discussed, one is the well-known CMB "cold spot," the other was identified in this paper which made use of a similar analysis as Feeney et al. It is important to emphasize though that the identification of these spots was based solely on the symmetry and they were not able to find the second identifier, the edge of the spot. For this reason the authors are careful to make clear:
"Without the corroborating evidence of a circular temperature discontinuity, we cannot claim a definitive detection [...] Azimuthally symmetric temperature modulations are not unique to bubble collisions."

Though it might be that better data from the Planck satellite will allow to extract a less ambiguous signal in the coming years, this is so far clearly no evidence for a bubble collision. Feeney et al's results are just once again evidence that there's some features in the CMB.

One also has to keep in mind that their paper already starts from the assumption that the signal of a bubble collision is of such a particular sort of merely resulting in a small temperature difference. It leaves entirely open the question how likely it is that a particular model of eternal inflation would result in such a signal that is just barely observable rather than in features entirely incompatible with what we've seen so far. It is entirely unclear to me for example what would happen if the vacuum in the other bubble or possibly even its physical constants were different from ours. It seems quite unlikely that a tiny temperature modulation is all that would come out of it. I don't think anybody has at this point a comprehensive picture of what might happen in a general bubble collision. The question is then if not it is extremely improbable that our bubble was subject to a collision and that collision, rather than wiping us out, was just nice enough to reveal itself in the upcoming Planck data.

In any case, the analysis put forward in Feeney et al's paper serves to rule out some regions of the parameter space in models that produce such an imprint in the CMB. Such constraints are always good to have. It is a nice and very straight-forward paper presenting an observer's take on eternal inflation. It's a very worthwhile analysis indeed - imagine how exciting it would be to find evidence for other universes! However, so far the evidence leaves waiting.

Update: See also one of the author's guest post at Cosmic Variance Observing the Multiverse.


  1. Hi Bee,

    Something has been bothering me about Penrose's CCC that caught me thinking about inflation versus other cyclical universe scenarios.

    Whether Penrose's does not fit "other cyclical scenarios" when tied to inflation?

    Also gravitational "footprints" in WMAP as "bubbles popping."

    See: Penrose in Pittsburg


  2. Sorry for spelling of Pittsburgh

  3. You know, I've always found the false vacuum to true vacuum decay idea convoluted and tortured. I really don't even understand it. I think that the idea probably came from the need to justify the landscape idea in string theory. Often mechanisms that originate from pre-conceived ideas that have no evidence in physicality have that principle feature: tortured logic.

    I actually have been thinking about inflation quite a bit llately. I believe in it for the usual reasons. But I also think one has to take into account the scale of the universe at the time of occurrence. I think the characteristics density of the vacuum energy probably acts something like the way
    the density of gases of particles act like. There will be a very high degree of fluctuation and interaction of those gas particles (i.e. photons) in the extreme early universe. If one considers the rate of fluctuation itself as representative for the flow rate of time one has to conclude that in that early phase time progressed extraordinarily quickly in that early phase.

    So just as a tightly compressed gas will expand rapidly from a container it is released from so would the universe. But if one uses the scale of time flow just before it was released it would not be that fast at all. It's just that we are viewing that expansion from our own gravitational reference frame where time is moving much more slowly in a now low viscosity universe. Just as in relativity no velocity can be faster than light we can apply that rule here. Inflation only "appears" to have been faster that light from our different reference frame

  4. Plato, if my understanding is correct CCC depends on eternal inflation. If this is correct I think it is on thin ice. As I and many others know, including Bee and RLO (though I think they might hate being on the same team!), the universe seems to act holographically from empirical evidence.

    I agree with Bee, and have said it before myself, that asymptotic freedom is the principle that best aggregates that idea into something that mimics what we see in both the formation of nucleons and of galaxies. What asymptotic safety does is limit the amount of information per volume. In a proton it says that each quark has near infinite probability to act independently of the other two when they are infinitely close together. But when they move apart to the nominal cross section of a proton the probability of independent action of each quark with the other two is zero. The nucleon is confined and it is called strong coupling.

    There is quite a bit of evidence that this same limitation of information per volume is going on with galaxies also. That is they become confined at a particular cross section. This is really the basis for the holographic principle in the universe. If you carry this idea to it's natural progression it would mean that our universe, as a whole, would be bound together as a whole at a very late phase in it's expansion. It would quit expanding on it own and their would be complete correlation between the moments of galaxies and/or superclusters of galaxies. I think that is far more more likely than Eternal inflation.

  5. Maybe it isn't about Calabi-Yau manifolds after all. Modeling a chiral universe should not begin with mirror-symmetry postulates.

    Perturbing socks into shoes can be clever but not correct. Passable theory is not assembled absent an artificially inserted odd-parity Chern-Simons term.

    Uncle Al decries an abusive hegemony of beige, its deformed decisions, and contingent reality deficit disorder.

    Happy solstice!

  6. Exactly. And in fact we *know* that our bubble was set up in an *extremely* particular way --- you don't have to believe Sean Carroll to agree with that, you just have to believe in the second law of thermodynamics. So the overwhelming majority of bubble collisions should be catastrophic.

    Excellent post!

  7. Click here for a Chromoscope view of our galaxy and the background, which is cool because you can vary the wavelength with a slider. The CMB is best viewed in the ... guess where ... that's right, the microwave wavelength.

    That pic is the result of the one-year all-sky survey from the Planck satellite, and thus will be the 3rd generation picture of the CMB. Of course it presently has that pesky galaxy of ours in the way, and it's estimated to take 2 years for the pros to remove our Milky Way and thus reveal the CMB behind it. But we can get a clue of what it will look like in the upper-left and lower-right quadrants.

    If they then find evidence of rings then, concentric or otherwise, I'll stop being a skeptic of this and believe. But right now it looks like a stretch. It's an intriguing theory, but since we'll know more in the near future about this, I can't get too worked up about it now.

    Thanks for the explanation about Inflation, Bee. Which other cosmological models compete with it?

  8. Hi Bee,

    Thanks for this nice synopsis of Feeney’s et al recent paper and findings. I particularly enjoyed your explanation of how they are attempting to distinguish a pattern of significance from that of random distribution within the CMB data.

    This of course is not an easy task as it like picking one cloud out of the sky to say it looks like a horse or some other such object. Penrose with his CCC model also faces similar challenges and criticism, with the current debate there focused around the significance of the observations he contends being evidence, more so then the physical premise on which his theory is based.

    That is I’ve always been fascinated as to how one is able to distinguish something as random or not. Like for instance, if one is presented with some expansive yet finite subset of the decimal rendition of PI, it for the most part serves quite well as random distribution when submitted to mathematical tests, yet is clearly expressing one of the most fundamental symmetries related to physical space. Now if you take into account all the unknown mathematical constructs there are certainly out there, one gets some appreciation respective of the difficulty of the task before those like Penrose and Feeney et al.

    So from my perspective thus far, whether these patterns mark the bruises of coexisting colliding (bubble) universes or the navels of past cycles being all that remains from “aeons” of continual rebirth, I think first we have to get a much better handle on what random is, as even to ask if such a thing exists at all.

    ”From man or angel the great Architect
    Did wisely to conceal, and not divulge
    His secrets to be scanned by them who ought
    Rather admire; or if they list to try
    Conjecture, he his fabric of the heav'ns
    Hath left to their disputes, perhaps to move
    His laughter at their quaint opinions wide
    Hereafter, when they come to model heav'n
    And calculate the stars, how they will wield
    The mighty frame, how build, unbuild, contrive
    To save appearances, how gird the sphere
    With centric and eccentric scribbled o'er,
    Cycle and epicycle, orb in orb.

    -John Milton, “Paradise Lost”



  9. Hi Plato,

    This post isn't about Penrose's CCC, so let me make that brief. For all I know his idea differs from previous cyclic scenarios by the second "C," the conformal rescaling. Let me also add that this "C" doesn't make much sense to me when you look at it from the particle physics perspective. (Postulating that massive particles decay doesn't remove them because they have a non-vanishing probability to be reproduced, for example by evaporating black holes). But then I haven't studied the details of his proposal. Best,


  10. Hi Eric,

    Penrose's CCC does not rely on eternal inflation. It is "eternal" in the sense that it doesn't end, but the inflation in these cycles is not eternal - otherwise we wouldn't be here. Neither are there other bubble universes, though I suspect you could add them and create some sort of hybrid-model. Eternal inflation otoh is not cyclic, though it's self-similar. Note also that eternal inflation is thought to be eternal only into the future, not into the past, whereas a really periodic universe like Penrose's would be eternal into the past and into the future. Best,


  11. Hi Steve,

    Thanks for the link, that's a nice website indeed. Might dump that into the next "This and That."

    There aren't really good competitors for inflation, but, as always, there are some few people pursuing alternatives. What springs to my mind are varying speed of light theories (addressing the horizon problem by increasing the size of the horizon) and then there's the option of the universe being created from an earlier non-geometric phase (addressing the horizon problem by changing the notion of locality). I don't know how well these approaches score in the overall picture, not really my area. It is without doubt though that inflation of one sort or the other is the most widely accepted model. Best,


  12. Thanks for the link

    You're welcome, and it gets better ...

    Click here to see the whole sky map, of which my previous link was but a close up.

    Click here for Phil Plait's original article re same from this past July.

  13. This just in (and happy winter solstice to everyone), John Horgan at Scientific American Blogs has an excellent essay up today, Dec.21, ==> here.

    It contrasts Anthropology with Physics, and strikes me as the sort of article that would interest you, Bee.

    It's chock full of quotable quotes, and this is one of my favorites:

    The irony is that parts of physics are less empirical and more speculative than the most humanistic anthropology.

  14. Hi Steve,

    I've had a look at Horgan's article and I frankly have the opinion he doesn't know what he's talking about. He is basically claiming that everybody who thinks about physics at the Planck scale or at or even before the Big Bang wastes his (or her) time with something that is in principle unobservable. He's completely ignoring that Penrose was making a point out of a specific observable feature, the topic of this post is another such example, and since you read this blog you also know what's going on in QG pheno. This is definitely a trend that's become more pronounced within the last decade and I have the impression Horgan just missed it and is criticizing physics from the last millennium. Best,


  15. Eric, here are a few things to consider. The relevance of distinguishing inflationary model apprehension as significant in terms of classification, along side of Steinhardt and Turok, Venezianno as in the idea of "cyclical models." This was a question in mind as Bee demonstrated her post, containing an overall distinction of observation of "bubble nucleation." These dynamics are inherent geometrically as I thought of the Klein Bottled as a demonstrative example of this development.

    Penrose's "pop" was an important assumption and not a pie in the sky demonstration, as one might assume. It left an impression for me:)

    Gravitational trackers are important opinions as to being impressionable about what is demonstrative in the WMAP as evidence of things that we are only observing in correlation of, symmetry breaking dynamics as revealed in abstract notions of genus figures development at the based of those valleys?

    The idea behind the Coleman-De Luccia instanton, discovered in 1987, is that the matter in the early universe is initially in a state known as a false vacuum. A false vacuum is a classically stable excited state which is quantum mechanically unstable. In the quantum theory, matter which is in a false vacuum may `tunnel' to its true vacuum state. The quantum tunnelling of the matter in the early universe was described by Coleman and De Luccia. They showed that false vacuum decay proceeds via the nucleation of bubbles in the false vacuum. Inside each bubble the matter has tunnelled. Surprisingly, the interior of such a bubble is an infinite open universe in which inflation may occur. The cosmological instanton describing the creation of an open universe via this bubble nucleation is known as a Coleman-De Luccia instanton. Quantum Cosmology

    Take an expanding universe with its little pockets of heterogeneous quantum events. At some point one of those random events may actually "escape" from its parent universe, forming a new one, Linde said. To use the ball analogy, if it experiences small perturbations as it rolls, it might at some point roll over into the next valley, initiating a new inflationary process, he said.
    'An unexpected gift' from string theory

    I hope Bee now sees the context.

    I was inline with her thinking, from an observational point of view "as to the whole universe."


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  17. Nice to view mountains from a perspective?

    I mean of course there are POV's about such distinctions so being aware of those opposing views, we have to keep this in mind.

    Sometimes I like to call it a Mind Field Herbal Magic? I like to thnk from a "elemental perspective" about mass. While discrete in measure, it is a issue of continuity of expression that I would see this in humans as well as in nature?

    "We assume the landscape is covered by fog so we can’t see where the real peak is, we can only feel around and detect slopes and local maxima.Lee Smolin


  18. Hey bee, you wrote:

    [John Horgan] is basically claiming that everybody who thinks about physics at the Planck scale or at or even before the Big Bang wastes his (or her) time with something that is in principle unobservable.

    Really? I didn't get that impression at all, possibly because going in I know anything by Horgan will be of a pessimistic nature, and take that into account before I read a single word of his.

    I guess at greater issure is the importance of Experimental Physics vs Theoretical Physics.

    I think it's a sad and unnecessary debate. Point of fact, we need both, especially phenomenology. No WAY does all the logic of Socrates, Plato, Aristotle and their successors give us Quantum Mechanics. For that, we needed experiment. And to interpret that data, we needed theoreticians such as yourself. So we need both. It's a ying and yang thing.

    On the other hand, I HAVE noticed "a bit" (to put it mildly) of a certain stuck up "elitism" amongst Experimentalists against Theoreticians, which I find disturbing. I don't know WHY that is, perhaps because for long stretches the Swedish academy was pro-experimentalist in the awarding of NPP's?

    Case in point: the EXPERIMENT that discovered the nucleus was performed 101 years ago in Rutherford's lab, but the phenomenological THEORY that explained it was described beautifully by Rutherford 2 years later.

    So why didn't ANY BLOG celebrate the 100th anniversary of the discovery of the nucleus last year?

    Waiting for 2011, I guess. :-)

  19. happy winter solstice to everyone

    And happy summer solstice as well!

    (It was quite hot here today, some 34C or so).


  20. How did physics decide that this was in their territory and not in the realm of metaphysics? Sure, i can see how it is legitimate to investigate the physics of the Planck Scale but I think where physics is going now is ridiculous. I'm totally with Steve on that. This is physics feeding the need of wild conjectures with no physicality.

    Here is my interpretation of the 1010 AD version of this discourse.

    1st monk: But you see, there really can only be 375879 angels on the head of a pin. It has been proven beyond a shadow of a doubt by Friar David, who is the most esteemed person on these questions. Sure, there was a question about how many angels would be distributed on each pin if the number of pins was doubled, but Friar David proved beyond a shadow of a doubt that no matter how many pins there were each pin could still hold 375879 angels.

    2nd monk: Of course you are right. That is a given. But Friar John proved most convincingly that there could be at least 7984 angels that had to be accounted for in purgatory. These angels are required to lead those individuals to heaven. And we all know that Friar Ely corroborated this with irreducible logic though the divination of pig entrails. So one must add 7984 to the 375879 angels to get the total number of angels that can reside on the head of a pin.

    1st monk: Yes, your right. The pig entrails clinched it. How could I have forgotten that!

  21. I probably should explain my delayed harsh reaction. Originally I incorrectly thought that eternal inflation somehow applied to THE universe. That is, OUR universe continued to inflate.

    But after rereading Bee's article and peoples' comments to it I now understand what is going on. Instead of people using the multiverse description, which many of us think of as completely unphysical and speculative, now they are using an umbrella term, Eternal Inflation. And physicists have insidiously applied it to the multiverse idea. But now it is implicitly assumed that the multiverse is THE UNIVERSE. This is total shit and a completely intellectually dishonest attempt to bypass the fact that other universe beside our own is metaphysics and not physics.

    We all know our words can shape perception unknowingly. The whole term ETERNAL INFLATION seems to me to be a calculated way of eliminating the need to say many universes. It thus tempts people to think that there is somehow proof that there are other universes. There hasn't been any proof and there so far isn't any proof.

    So my message: ETERNAL INFLATION is an intellectually dishonest way of aggregating a very speculative idea into an umbrella term that on the surface looks non-speculative. In other words it's pure crap.

  22. I know at this point I'm probably belaboring the point but this stuff really gets to me. I'm beginning to see now how physicists going to Goldman Sachs destroyed the world. Because so many physicists depend completely on math, but without any overarching ethics, all they worry about is getting their little patch of green to make their extremely local environment look good. They want their little patch of green.

    The idea of aggregating the multiverse idea into an overarching single universe that we don't question is exactly the same idea behind bundling collaterized debt obligations into a single package that no one can reasonably value. We all know how that ended. People always want to act like they are smarter than they are. End of rant.

  23. Friar David? You mean there were Jewish monks in 1050? Cool, I didn't know that. Could that be why the Greek Orthodox split with the mainstream Catholic church around the same time? You can't prove that wasn't the reason, can you? Odd if so, as St. Paul was a Greek, AND a Jew. At least until he was blinded, right? Much to ponder. What's next, Jewish Saints?

    Seriously though, why do you let this stuff upset you? Inflation is a very new theory, only decades old, and needs more work. They're working on it. Also, if true, there will probably be more interpretations of it than there are interpretations of quantum mechanics. And so what if so? If certain aspects of it fail, don't we learn as much if not more from our failures?

    As far as the CCC goes, like I said let's hang in there for a year or 3 to see what ESA shoots back to us re the All-Sky. We'll know more then, so Penrose's thoughts, liked or not, remain in play for the time being. No worries, mate.

  24. How ever "one feels" toward "definitively" it's the end of the road for that person because they've set the course ( is the relation causal in association?) keeping it open for discussion... one still remains flexible what ever the direction the results take.

    One can change, oui! non?

    Admittedly, the experimental result is of course desired, but like the ages of our past toward enlightenment, they swing back and forth like "some pendulum" as an adjustment as a oscillatory example of the rhythm in nature of things? It will resonate for some and not for others?:)

    This thought leads through too, theoretics, then, phenomenological for a time, displaying results( years of implementation)once from a drawing board, is going back depending on those results(any results).

    According to physics Professor Andrei Linde, one of the architects of the inflationary theory, our universe—and all the matter in it—was born out of a vacuum. Cosmologist speaks of mind-bending dynamics behind the inflationary universe


    "If galaxies are the result of quantum fluctuations," said Linde with a shrug, "imagine what we are."


  25. I have to say that I have no quarrel with inflation in the first microseconds of our universe and then ended. It makes sense and it agrees with what we observe. It really is not speculative at this point.

    It is completely speculative to say that other universes emerged out of the big bang and that those other universes are still inflating. That is all it is - a fringe theory with no physical evidence to back it up. It is just a variant of the landscape in string theory. And it is required for the same reason: physicists can't understand why our universe is so remarkably suitable for life. So if anyone still thinks it's really cool that there might be other universes they should just remember that.

    And I still say it a bait and switch trick to include inflation in the name. It makes it look more legit because the concept of inflation IS pretty legit by now. The landscape and the multiverse is not legit and the string theorists who depend on the landscape, not all of them do, are just trying to trick everyone by invoking inflation in the name.

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  28. Hi Bee,

    The transition that Penrose is referring to takes place after all the black holes have dissolved through Hawkings’ mechanism and all particles decayed leaving only photons, where space, time and yet most importantly the meaning commonly attached to entropy becomes meaningless (as it relates to information), with the frames of reference for the concept now absent with all the (subluminal) particles having been removed, to leave void containing only potential. The circles that Penrose is referring to are the gravimetric signatures of supermassive black holes that had collided long before this end state.

    In analogy I see it like the question I posed earlier, regarding how to distinguish a state of complete disorder from one of singular order, as that of a circle expressed by way of quantified information, opposed to qualitatively, to say it’s the least perimeter to contain the greatest volume. That’s to say I understand your point as to agree, there being a lot of things having yet to be resolved; such as the last word respective of particle decay and the information dilemma related to black holes, yet from a mathematical perspective I find it appealing as well as intuitive.



  29. Hi Steven,

    Well, he writes:

    "[Penrose's] proposal is literally too far out; it can never be confirmed in the way that the existence of, say, quarks has been confirmed, or the big bang itself.

    I call this highly speculative theorizing "ironic science," because it makes assertions that are more akin to literary criticism or even literature than conventional science...

    Many physicists, on the other hand, theorize about phenomena that are not only extremely remote in space and time but might not even exist. Physicists conjecture what's happening at the Planck scale, a microrealm even more distant, in a way, than the farthest reaches of the universe. They speculate about the era before the big bang, and about other universes that might be mutant versions of our own. They postulate strings, membranes, higher dimensions and other stuff whose existence, like that of God, cannot be proved or disproved."

    It is certainly true that there's very theoretical and speculative work that is difficult to imagine at present how it can ever be tested, but the whole point of Penrose's paper was to say there could be evidence for his model, like the paper I've written about in this post looks for evidence of pre-big-bang science of another sort, like the work on pheno QG I've written about many times. One can of course discuss how successful these efforts are in each case; I myself am skeptic about most of them, but there's no denying the effort is being made. Now re-read my earlier comment, makes sense now? Best,


  30. Hi Eric,

    I would agree that the term "multiverse" is somewhat nonsensical, but it's moot to argue about terminology that has spread. In the light of this very post, your complaint that the existence of other bubble universes is metaphysics is a very undifferentiated opinion, for there are cases where they do have observable consequences. The bubble collisions are one example, then there's Penrose's proposal, and Laura Mersini has another proposal. Let me be very clear on that, I'm not a friend of the multiverse and certainly not of one that's only there for philosophical reasons. I find eternal inflation has some appeal, but what I find appealing or not is quite irrelevant for science, and mostly eternal inflation seems to me to open more questions than to answer questions, so taken together I'm not too enchanted with that either. But what's it matter? These are models that somebody has proposed, and if they have observable consequences we can go look for them. That's the way science makes progress and that's what's being done here. Best,


  31. Hi Phil,

    What I was trying to say is that in a quantum universe, decay is probabilistic, the life-time of a particle is probabilistic, and the ratio of particle scattering is probabilistic, it goes both ways. A similar consideration holds for the statement that all black holes have evaporated. There's always some probability to form one again (you don't need massive particles from it, photons will do), and it will evaporate and reproduce massive particles. And of course the massive particles also continue to exist in virtual form. Basically, what I'm saying is that postulating the decay of massive particles doesn't remove them from the theory. Best,


  32. Typo, I meant: "you don't need massive particles for it, photons will do"

  33. Hi Bee,

    Yes of course and yet this all comes down to quantum theory, with respect to the treatment and conception of its fundamental principles. All I can say is there are those like Penrose which don`t completely buy into the conventional wisdom in such regard, as for instance the conception and implications of the density matrix from both the physical and underlying ontological perspective it currently taken to mandate.

    Now I’m not contending, as to have any to believe as being able to a offer solution, just to point out that while many feel such issues have been resolved or having no relevance, there are few others who are considered qualified which do. In the mean time I continue to find it interesting to watch all of this unfold and would feel very fortunate indeed that in my own life time if such things became more certain, whatever it turns out to be.

    “I feel uncomfortable about regarding such a ‘pure-state density matrix’ as the appropriate mathematical representation of a ‘physical state’. The phase factor (…) is only ‘unobservable’ if the state under consideration represents the entire object of interest. When considering some state as part of a larger system, it is important to keep track of these phases”.

    -Roger Penrose, The Road to Reality: A Complete Guide to the Laws of the Universe, page 796 (2004)



  34. Dialogue:

    -- "The Universe is all that exists by definition, therefore talking about other universes has no meaning."

    -- "But we are talking about the intriguing possibility of 'bubbles' or places with different laws unconnected to our Universe! You cannot guarantee these are not possible in principle!"

    -- "No, I can't, neither can you."

    -- "Well, there might be observational evidences."

    -- "That makes no sense. Are these technically other universes or not? Even if I momentarily accept that possibility, they are other, unconnected universes, right?"

    -- "Yes, well, other universes, since they are different from ours."

    -- "But if you try to find evidences for them in our Universe, they must have to come into some physical 'contact'. There is no escape: if they are bubbles with different laws, but which somehow interact, they must be within our Universe!"

    -- "No, they are, well... elsewhere!"

    -- "This is senseless, there is nothing but one Universe! So these bubbles, if exist and leave traces inside our Universe, they must be somewhere *inside* our Universe, but outside our horizon, for instance."

    -- "Well, you may want to define things that way."

    -- "I am defining nothing, I am just stating a logical conclusion."

    -- "It's not that philosophical. Current theoretical physics points out to the fact that we may only understand our Universe by requiring other universes!"

    -- "So that is where current theoretical physics is heading?"

    -- "Well, some of it."

    -- "Excuse me, I must plant potatoes."

  35. Hi Christine,

    "Excuse me, I must plant potatoes."

    LOL, I would therefore advise you don’t look at the eyes of the potatoes too closely, as some idea relating to the spouting of many universes might be so inspired. However needless to say given the proper argument I could dig such a concept. Now what might it be called, perhaps the “Spudnik Principle: As The Eyes Have It”:-)



  36. Starting out with "an objective," a figure in can certainly say one is biased toward something depending how the writer displays the content of that dialogue.

    But of course "that Dialogue" came out of one person( Plato and Francis Bacon were not alone here)....much more creative if it can actually postulate positions and demonstrate some question as to why people do what they do and how science can come out of such dialogue.

    That's "the idea" we are looking for. Eide-looking to same.:)

    This is a writers we do not want degradation of this technique smeared with potato planting or a mash fermenting that can be quite potential in it's production.:)


  37. Of course we do not want misconceptions.

    Muons and Time Dilation?

    Microscopic black holes may be outdated now....but this does not change the collision point for examination. It presents a new area of consideration about perspective not only of what happen at the beginning of this universe, but about what can be transferred "through that time."

    One does indeed need a discerning ear as to what is being said? Noise?

    So leaving "an impression is a gain for some" while it passes by others, as it should be?

    I mean, once you go back and read, knowledge comprehension changes the outlook of what was read once before. You've changed, and you see things differently?

    How is that? Do you always see "through one position" What is that? How can you "shift" so as to see from different angles, points of view?



  38. I still think examining pig entrails is a competitive method to examining the cmb for the purpose of finding bubble universes. And it would put these would-be scientists in the proper light.

  39. Hi Eric,

    For the third and last time, WHY are you worried about speculative research at the very cutting edge of Cosmology that has zero chance of being proven for a few years? Do you have any idea how many more immediate problems there are in Physics? Click here if not. Why not tackle some of them?

    Perhaps you're immortal? Cool if so. I'm not, so I have to very careful and choosy what I wish to contemplate, sigh.

    I do like the pig entails analogy btw, but what of unicorns? :-)

    That's it for me, no more comments from me re Cosmology until Astronomy provides more data. Let the Science Journalists debate amongst themselves, I say.

  40. Steven, I think you mean well. But you haven't yet understood why this issue is so important. I'm not sure I can explain it any better than I've already done, but I will try.

    The principle is really exactly the same as what happened during the financial crisis but without the alarming results. People really are gullible, even scientists. It isn't like the ivory tower like they so often try to portray it. There's politics, self serving, and all the usual human foibles.

    These attempts to find evidence of other universes are self perpetuating. They divert energy, intellectual resources, but most of all time from the issues you described that need to be solved. Centuries from now I'm confident it will look just as ridiculous as finding the number of angels that can sit on the head of a pin. Why squander the time, as humanity did during the the dark ages? You are right. Time is extremely precious so why would I want to let others squander it. People are a lot more gullible than you think, maybe even you.

    Just because Bee says this is where physics is going now does not make it any more valuable than some of the questions people were talking about in the the middle ages. The majority can be deluded if intelligent people don't speak up.

  41. Hi Eric,

    You better watch out, you better not cry, if you meet up with Santa, you surely will die! :-)

    You wrote:
    They divert energy, intellectual resources, but most of all time from the issues you described that need to be solved.

    Agreed, except, if a PhD wishes to spend their time on this sort of thing, they have the right, regardless of what you, I, or anyone else thinks. For example, I'm 75% against SuperStrings, but I hope it's never NOT studied. Let the wookies win, so to speak. At the very least the mathematics is intriguing, whether or not it reflects reality. Speculation is what we naked primates do. It's natural. If 97% of the speculations are wrong, fine, because if so then 3% of the speculations are right! And that's how we move forward as a species. IMO, as always.

    Hi Plato,

    Thanks for that link at Cosmic Variance. I saw that, now look at the replies. George Musser, in his book on Quantum Gravity, mentions FOUR must-read websites on the subject of Quantum Gravity: BackReAction, Not Even Wrong, Cosmic Variance and The Rudeness Frame. Nice to see 3 of the four getting together in one place.

    Here's hoping we have a fifth. Check out the brand spanking new:

    Toy Universes

  42. Hi Plato,

    I’ve looked to your clarification and although coming from the horse’s mouth find Bee’s synopsis clearer as it gives a much better overview regarding the method of analysis and the mapping as displayed. It also lends one a better sense of where such ideas sprang leaving a better grasp respective of their theoretical context and soundness.

    The thing I find interesting is such investigations are taking physicists into logic and mathematical waters which present the same as what puzzles many mathematicians today, as it relates to set theory, its cardinality and the meaning of randomness. I would also suspect this in part is what has those like Eric so frustrated respective of the time and effort given to such pursuits.

    However for me it’s interesting to consider how closely physical reality is represented and dictated by mathematical reality. That’s to say within mathematics not only do they consider how many angels can reside on the head of a pin, yet there are situations where it depends on what pinhead one is referring as even to find pin heads reside within other pinheads. The bottom line being today it is mathematics and not physics where the battles rages in an attempt to determine what can or what cannot be known, while physics determining what aspects of that knowledge play a role in the substance and actions of what we call physical reality.

    Physicist Lee Smolin writes in Three Roads to Quantum Gravity that topos theory is "the right form of logic for cosmology" (page 30) and "In its first forms it was called ”intuitionist logic'" (page 31). "In this kind of logic, the statements an observer can make about the universe are divided into at least three groups: those that we can judge to be true, those that we can judge to be false and those whose truth we cannot decide upon at the present time" (page 28).

    -Wikipedia, Constructivism



  43. Hi Phil,

    Why did Bee fight the mathematical ideas of Tegmark so much?

    The contention about mathematical perspective is one that has been going on for a while.

    Some do not realize what they are fighting in "dismay over" by what science is supposed to establish so they call it not substantial qualification for truth seeking. Irresponsible science at it's worst?

    The math has to be inclusive of all that precedes it, so the pursuance is fundamentally a stepping off point from where science currently lives. Seeing, on two levels. You see.

    You have changed.

    My contention is that the mathematical realm sits very close to the birthing of souls ideas about the course mapped out on creation.

    Sending minds to journey to such times is not without regard for the understanding of what that creation means in the values put forth from perspective of science and the mathematical basis.

    Dirac said it best in terms of the algebraic notion and visualizations of dynamics are two parts of the same human being, that some can work one side of the venture better then the other.

    The clarifications answered the issues of inflation and eternal inflation along with the categorization of cyclical universes.

    Secondly the string landscape.

    Thirdly bubble interaction as rings. A visualization that has been "haunting me" has been of a sphere rising and passing a two dimensional surface. As the sphere gets larger and passes through, "the ring" gets bigger.


  44. Phil,

    I struggle with such abstractions myself to ask for "conceptions to become manifest as visualizations" that help me to understand better.

    What you need to know about Lee at that point was, his continuing efforts took him to a place of disembarking from the ideas around this in realizing his extent of Genus development, had come to some stalemate in his mind according to the knowledge he had at the time he wrote his new book.

    If there was an addendum to that book Lee would have to acknowledge this by recognition of his talks with Jacques Distler. These ideas at the time speak very clearly to what was manifesting from the string landscape in terms of valleys and mountaintops.

    He also had a aversion to symmetry in terms of what Plato represented from "that point of view?":)

    So you see even authors have to change with the times even though they may be speaking from a synopsis of where they have been and what they have concluded.

    That's just the way of it, and the way we change.


  45. In regards to statements about Lee Smolin. This in no way has lessen my respect for Lee and leaders in science and theoretic. They do need each other.

    See:Finiteness of String Theory and Mandelstam


  46. Plato wrote (second reply to this post):

    Sorry for spelling of Pittsburgh

    Oh, that's fine. Most "burgs" end with a "g", not a "gh". Perfectly understandable.

    And ... you're in good company! Peter Woit doesn't know how to spell "Lazaridis", and Lisa Randall can't spell Supersymmetry, if you care to recall our conversation from last Jan. 27th which I linked to.

    So it's not just you. :-)

    However, if you want a REAL challenge, tell us how to spell the last name of Big Ben, the Pittsburgh Steelers quarterback. The Onion covers that ground: here. :-)

  47. Hi Steven,

    At dial up speeds it takes a very long time to see some links(You tube) so I save myself the time until I do have access to such speeds for name pronunciations(site taking to long to load).

    A year's already past..amazing isn't it.

    Max Tegmark:From people who believe that the physical world is in some deep sense not mathematical, I'd love to hear more specific ideas about what they are proposing instead.The Mathematical Universe

    I would like to say that a core group here has become quite proficient in the understanding of information linking that supports context of their points of view as if "an index to the right or left" can become quite extraordinary, as if one brain is connecting neurons from all parts of the brain too, other people.:)



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