Astronomy Without A Telescope – Bubblology

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One model of a hypothetical multiverse has, perhaps appropriately, some similarity to a glass of beer. Imagine an eternal false vacuum – that’s a bit like a fluid, though not all that much like a fluid – since it doesn’t have volume, in fact it doesn’t have any spatial dimensions. Then imagine that this eternal false vacuum expands.

This sounds rather contradictory since expansion implies there are spatial dimensions, but a string theorist will assure you that it all happens at the sub-Planck scale, where lots of immeasurable and unknowable things can happen – and after a few more drinks you might be willing to go along with this.

So – next, we introduce bubbles to the false vacuum. The bubbles – which are essentially independent baby universes – are true vacuums and can rationally and reasonably expand since they have four overt dimensions of space-time – albeit they may also have the other immeasurable and unknowable dimensions in common with the encompassing false vacuum.

The bubbles are the reason why it is necessary for the false vacuum to expand, indeed it must expand faster than the bubbles – otherwise an expanding bubble universe could ‘percolate’ – that is, spread throughout the all-encompassing false vacuum – so that your multiverse would just become a universe. And where’s the fun in that?

Anyhow, within such an eternal expanding fluid, bubble universes may nucleate at random points – taking us away from the coffee analogy and back to the beer. In bubblology terms, nucleation is the precursor of inflation. The sub-Planck energy of the non-dimensional false vacuum occasionally suffers a kind of hiccup – perhaps a quantum tunnelling event – making the sub-Planck virtual nothingness commence a slow roll down a potential energy hill (whatever the heck that means).

At a certain point in that slow roll, the energy level shifts from a sub-Planck potential-ness into a supra-Planck actual-ness. This shift from sub-Planck to supra-Planck is thought to be a kind of phase transition from something ephemeral to a new ground state of something lasting and substantial – and that phase transition releases heat, kind of like how the phase transition from water to ice releases latent heat.

And so you get the characteristic production of a gargantuan amount of energy out of nothing, which we denizens of our own bubble universe parochially call the Big Bang – being the energy that drove an exponential cosmic inflation of our own bubble, that exponential inflation lasting until the energy density within the bubble was cool enough to form matter – in an e=mc2 kind of way. And so another bubble of persistent somethingness formed within the eternal beer of nothingness.

The light cone of our bubble universe showing the stages of the energy release driving cosmic inflation (reheating), the surface of last scattering (recombination) and the subsequent disolution of the cosmic fog (reionisation) - cosmic microwave background photons from the surface of last scattering could show signs of a collision with an adjacent bubble universe. Credit: Kleban.

Good story, huh? But, where’s the evidence? Well, there is none, but despite the usual criticisms lobbed at string theorists this is an area where they attempt to offer testable predictions.

Within a multiverse, one or more collisions with another bubble universe are almost inevitable given the beer-mediated timeframe of eternity. Such an event may yet lie in our future, but could equally lie in our past – the fact that we are still here indicating (anthropically) that such a collision may not be fatal.

A collision with another bubble might pass unnoticed if it possessed exactly the same cosmological constant as ours and its contents were roughly equivalent. The bubble wall collision might appear as a blue-shifted circle in the sky – perhaps like the Cold Spot in the cosmic microwave background, although this is most likely the result of a density fluctuation within our own universe.

We could be in trouble if an adjacent universe’s bubble wall pushed inwards on a trajectory towards us – and if it moved at the speed of light we wouldn’t see it until it hit. Even if the wall collision was innocuous, we might be in trouble if the adjacent universe was filled with antimatter. It’s these kind of factors that determine what we might observe – and whether we might survive such an, albeit hypothetical, event.

Further reading: Kleban. Cosmic bubble collisions.

46 Replies to “Astronomy Without A Telescope – Bubblology”

  1. You’re making me thirsty. I should go look for a cold one so I can continue to explore the multiverse.

  2. Hey guys, have you heard that story how 2 multiverses collide in a steam made of chocolate?

    1. No, but I heard the one about the two bubbly universe candidates and the cosmic bar:

      – “What will you have?”, asked the bartender the first universe.

      – “I want a Cosmological Constant”, she replied.

      – “Will that be straight up, or do you hazard possible life?”, the bartender follows up.

      – “Do you think I can avoid meeting creeps in a bar?”, sighs the universe.

      1. I sort of understand some of the theory in your posts, but this joke eludes me 😉

      2. I sort of understand some of the theory in your posts, but this joke eludes me 😉

  3. Collisions before reheating and a last scattering, sounds naughty.

    At least they can leave a calling card:

    “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.”

    Among them the Cold Spot:

    “One of the features we identified is the famous Cold Spot, which has been claimed as evidence for a number of theories including textures, voids, primordial inhomogeneities, and various other candidates. A nice aspect of our approach is that it can be used to compare these hypotheses, without making arbitrary choices about which features in the CMB need explaining (focusing on the Cold Spot is an a posteriori choice). We haven’t done this yet, but plan to soon.”

    “The good news is that we can do much more with data from the Planck satellite, which has better resolution and lower noise than the WMAP experiment. There is also much better polarization information, which provides a complementary signal of bubble collisions (found by Czech et. al. – arXiv:1006.0832).”

  4. We all might want to ask the question, what is wrong with this? This paper

    http://arxiv.org/PS_cache/arxiv/pdf/1107/1107.2593v1.pdf

    is an overview of some standard inflationary cosmology. Equations 1 and 2 are forms which I have written on a fair number of UT blog posts. Everything seems pretty good until you get to figure 1 where the form of this inflaton field is presented. At this point either one needs to take this with a big grain of salt, or as Steve Nerlich suggests; pour your self another drink. The form of this potential is a phenomenological fit, which can’t correct in any final sense, as can’t any of the other myriad forms of the inflaton potential function I have seen. You will get rather intoxicated as you press into this.

    The Europhysics Conference on High-Energy Physics is underway right now and if you are geeky enough to follow LHC data being presented, it is energizing a lot of paper shredders and tons of phenomenology papers and theory are being shredded. The recent result on the lack of graininess of spacetime as detected by non-dispersion results from Gamma Ray Burstars demolishes lots of theory as well. Tons of this stuff is being cast off as refuse and rubbish. There are over 30,000 papers on string theory and not all of this stuff can be right. While I think there is reason to think there are “stringy” structures to the universe, most of these developments must be wrong. The recent cascade of falsification is almost alarming in a way, but frankly not that unexpected. In some ways it is refreshing and a sort of intellectual epiphany in the form of an avalanche.

    I take data far more seriously than theory, and the lack of graininess to spacetime in my mind casts some big question about eternal inflation. The old inflation model (Guth et al discussed in this paper) has some interesting merit though. So to see where things might be wrong we start with that. If you look at equations 1 and 2, these are the standard de Sitter equation 2

    (a’/a) = H, a’ = da/dt

    This is a differential equation with a trivial exponential solution a(t) = exp(Ht). The Hubble constant is equal to the square root of the cosmological constant with some other stuff. The inflaton field is a scalar field which is given by a Lagrangian density

    L = [(1/2)?_a??^a? – V(?)]/vol,

    where vol = 4?a^3/3 is a spherical volume. The ?_a??^a? = |?_i?|^2 + |?_t?|^2 which are the spatial derivatives and the time derivatives. We assume that the inflaton field is homogeneous in the space, so we set ?_i? = 0. We throw this through the Euler-Lagrange equation (look this up on wiki-p if you are not familiar with this) and you get the differential equation

    (3/4?)d/dt(?_t?/a^3) + ?_?V(?) = 0

    = (3/4?)?”/a^3 – (9/4?) ?’a’/a^3 + (3/4?)/a^3 ?_?V(?) = 0.

    The differential equation of motion when I multiply through by the volume is

    ?” – 3?’a’a + ?_?V(?) = 0. prime or ‘ = d/dt

    I leave it as an exercise for those interested to substitute the Hubble factor and play around with this, or find a solution which is not hard to do This is really a form of Newton’s second law where a force F(?) = -?_?V(?) equals an acceleration. That acceleration part has a second order part with ?”, which is a pretty standard acceleration = d^2x/dt^2 like term. There is this other term -3?’a’a which depends on ?’ that is like a velocity. When you see equations like this with velocity dependent terms you know there is something similar to a friction. The inflaton field is being diluted away and is “dying out.” So in this case there is no “eternal,” even if there are Coleman bubble nucleations which take place.

    Eternal inflation fixes this problem by posing that inflation in the false vacuum occurs on a scale smaller than L_p = sqrt{G?/c^3} ~ 1.6×10^{-33}cm. In this case the difference in scale means that the inflaton field is not subjected to the sort of expansion we observe. However, there is a problem with this lack of graininess. Further, the holographic principle indicates that physics on a scale smaller than the Planck length is dual to physics on a scale larger. We might then ponder whether the idea that eternal inflation can take place on a scale smaller than the Planck scale exists, for this requires there to be this graininess to spacetime.

    LC

  5. We all might want to ask the question, what is wrong with this? This paper

    http://arxiv.org/PS_cache/arxiv/pdf/1107/1107.2593v1.pdf

    is an overview of some standard inflationary cosmology. Equations 1 and 2 are forms which I have written on a fair number of UT blog posts. Everything seems pretty good until you get to figure 1 where the form of this inflaton field is presented. At this point either one needs to take this with a big grain of salt, or as Steve Nerlich suggests; pour your self another drink. The form of this potential is a phenomenological fit, which can’t correct in any final sense, as can’t any of the other myriad forms of the inflaton potential function I have seen. You will get rather intoxicated as you press into this.

    The Europhysics Conference on High-Energy Physics is underway right now and if you are geeky enough to follow LHC data being presented, it is energizing a lot of paper shredders and tons of phenomenology papers and theory are being shredded. The recent result on the lack of graininess of spacetime as detected by non-dispersion results from Gamma Ray Burstars demolishes lots of theory as well. Tons of this stuff is being cast off as refuse and rubbish. There are over 30,000 papers on string theory and not all of this stuff can be right. While I think there is reason to think there are “stringy” structures to the universe, most of these developments must be wrong. The recent cascade of falsification is almost alarming in a way, but frankly not that unexpected. In some ways it is refreshing and a sort of intellectual epiphany in the form of an avalanche.

    I take data far more seriously than theory, and the lack of graininess to spacetime in my mind casts some big question about eternal inflation. The old inflation model (Guth et al discussed in this paper) has some interesting merit though. So to see where things might be wrong we start with that. If you look at equations 1 and 2, these are the standard de Sitter equation 2

    (a’/a) = H, a’ = da/dt

    This is a differential equation with a trivial exponential solution a(t) = exp(Ht). The Hubble constant is equal to the square root of the cosmological constant with some other stuff. The inflaton field is a scalar field which is given by a Lagrangian density

    L = [(1/2)?_a??^a? – V(?)]/vol,

    where vol = 4?a^3/3 is a spherical volume. The ?_a??^a? = |?_i?|^2 + |?_t?|^2 which are the spatial derivatives and the time derivatives. We assume that the inflaton field is homogeneous in the space, so we set ?_i? = 0. We throw this through the Euler-Lagrange equation (look this up on wiki-p if you are not familiar with this) and you get the differential equation

    (3/4?)d/dt(?_t?/a^3) + ?_?V(?) = 0

    = (3/4?)?”/a^3 – (9/4?) ?’a’/a^3 + (3/4?)/a^3 ?_?V(?) = 0.

    The differential equation of motion when I multiply through by the volume is

    ?” – 3?’a’a + ?_?V(?) = 0. prime or ‘ = d/dt

    I leave it as an exercise for those interested to substitute the Hubble factor and play around with this, or find a solution which is not hard to do This is really a form of Newton’s second law where a force F(?) = -?_?V(?) equals an acceleration. That acceleration part has a second order part with ?”, which is a pretty standard acceleration = d^2x/dt^2 like term. There is this other term -3?’a’a which depends on ?’ that is like a velocity. When you see equations like this with velocity dependent terms you know there is something similar to a friction. The inflaton field is being diluted away and is “dying out.” So in this case there is no “eternal,” even if there are Coleman bubble nucleations which take place.

    Eternal inflation fixes this problem by posing that inflation in the false vacuum occurs on a scale smaller than L_p = sqrt{G?/c^3} ~ 1.6×10^{-33}cm. In this case the difference in scale means that the inflaton field is not subjected to the sort of expansion we observe. However, there is a problem with this lack of graininess. Further, the holographic principle indicates that physics on a scale smaller than the Planck length is dual to physics on a scale larger. We might then ponder whether the idea that eternal inflation can take place on a scale smaller than the Planck scale exists, for this requires there to be this graininess to spacetime.

    LC

    1. “a lot of paper shredders and tons of phenomenology papers and theory are being shredded.”

      Is that so? I have been mistrusting of graininess since I became more versed in granular theories and their assumptions. (And with the similar problem of setting aside relativity in Bell tests.)

      But I didn’t think it would be that easy to decide to put aside the notions, nor that easy to sway the respective communities. So forgive me if I ask if this is insider information, or if I can get hold of it?

      “the lack of graininess to spacetime in my mind casts some big question about eternal inflation.”

      As the paper mentions, the false vacuum eternal inflation described here is different from the older slow roll eternal inflation that solves the reheating problem. I don’t like the former either, for similar reasons! d(>w<)b And quite frankly, they are more elaborate as slow roll is mostly just a set of potentials with a range of parameter values.

      The upshot for me in the current interest is that they are easier to test without environmental (especially anthropic) principles, and that they seem informative on the problem of statistics over infinite universes.

      Conversely the predictions that come out of them are not so powerful as the ones slow roll inflation makes. Nor do they seem as easy to test with Planck measurements, instead they are more suited to integrate string theory AFAIU.

      But, coming back to the blueshift catastrophe in eternal expanding universes. Slow roll inflation must have or regulate those too, eventually. In my mind the graininess results, if they hold up, would strengthen the idea of slow roll inflation as an eternal process. That is, potentially without some of the worldline involving singularities that have been a possibility before.

      1. The slow rolling potential with a pit where reheating sets in is with the older inflationary theory. There are in my opinion some problems with this as well.

        I might go into some more detail on this, but the spacetime of our universe is the boundary of an anti-de Sitter spacetime. This is really where the gravitational physics takes place. I think there is a much simpler way of approaching this, where inflation still takes place as a sort of phase transition at a quantum critical point. In doing so this might clear up a lot of this phenomenological hand waving with these inflaton potentials.

        LC

      2. Wait, so eternal inflation may be incorrect because evidence at extremely small scales points to a featureless space-time at these scales. (I assume the graininess as mentioned). Forgive me I’m a little green here.

      3. As I indicated today or above in what I wrote, this calls this sort of phenomenology into question. i would not say this means it is wrong completely. However, the lack of quantum graininess to spacetime as we measure photons from distant sources puts the ball in the court of Linde and others who promote this idea. It might still be that there is an eternal inflationary process. However, these models are layers of phenomenology which are based on various physical assumptions that have loose connections to harder or crisper physical concepts. I would prefer that our understanding of quantum cosmology be based on harder ground and more basic or “simple” physical concepts.

        LC

      4. Yes, some problems. But not the same problems, as the trick that makes false vacuum inflation possible and involves Planck scale physics is not used in slow roll.

        Slow roll is more of a semiclassical approximation if you will. Less assumptions, easier to test. (Aside from graininess, it may appear. We will see. Then again, who knew planck scale physics were so accessible!?)

        I assume you get that but I wanted to make it clearer on this thread.

        Also to clear up is if you had some more than personal judgment on this, or pointers to specific papers since it would be helpful. I have to assume not as you didn’t go into all that.

        I don’t see any deeper connection between inflation and gravity than both being part of cosmology, in fact the absence of spacetime in false vacuum/slow roll makes me think they are decoupled. At least in the sense that where inflation ends, gravity starts.

        That said, cutting Gordian knots is efficient, so I wish you a heartfelt luck with your idea!

      5. I think that the quantum aspect to spacetime is with a substratum of fields. These fermionic fields are quantized on a “deeper level,” so to speak, where spacetime is an emergent phenomenon, similar to a superconducting current. I just wrote in part on this subject above. The AdS/CFT correspondence of Maldecena means that gauge fields in our world, which is a conformally flat spacetime on the boundary of the AdS, has an equivalency to gravitons interior to the AdS spacetime.

        A gluon chain in QCD can have a correspondence with a graviton. The spacetime of our universe is a conformal flat spacetime which forms the boundary of an anti de Sitter (AdS) spacetime. The boundary of an AdS_n, n dimensions, is a conformal field CFT_{n-1}. So the boundary of the AdS_n is a conformally flat spacetime, which can be a de Sitter spacetime. The CFT_{n-1} lives on this boundary space, which has “no gravity,” or should we say the spacetime has curvature which may be conformally mapped to flatness. However, the CFT has modes which run from the UV to the IR, and at the IR this is a massive conformal theory. Mass though breaks conformal symmetry of the spacetime — one gets local curvatures, or the mass can cause the tangent plane on the AdS_n boundary to penetrate the AdS interior where the graviton exists. Yet the holographic content of this theory tells us that the UV domain is equivalent to the IR domain.

        As a result of this at energy in the renormalization group flow domain, or conformal domain, a gluon chain might then have a small quantum probability for being a black hole. If the energy could be ramped up to near the string limit (Hagedorn temperature) that amplitude for a black hole increases to near unity or one. The quantum black hole has a quantum uncertainty with respect to its event horizon. In other words the horizon mixes quantum field amplitudes of the interior and exterior, or equivalently exterior and interior states of the black hole exist in quantum superpositions. This has the effect of creating an ambiguity on the time ordering of states, or quantum bits, so information can appear outside of the black hole along a path that is not causal. This mixing of interior and exterior states on a black hole and the connection to superconductivity means this physics has analogues to Josephson junction diodes.

        There is more I could write about, such as how the de Sitter exponentially expanding spacetime of inflation and the slower accelerated universe is “conformally flat” or what the Hagedorn temperature is. But I have written quite a bit for this morning.

        LC

      6. Wow! Thank you LC for repeating all that here for me.

        Its refreshing to know we are getting that far down the road with our physics/math/science that we can explain in detail phenomenology at macro and micro levels.

        Hopefully some day soon some Smart folks such as yourself can succeed in Quantum/General Unifying Theorum (starting to resolve long-standing questions about graininess/quantum fluctuations/isometry distortion / time/space dialation, quantum gravity fields and more :o).

        My heads still reeling from the realisation that gravity behaves like a light-wave (at least in-so-far as it arrives at all points at exactly the same time at the speed of C.
        (and am excited by the recent paper suggesting polarization of gamma rays is possible – can’t wait to see what detectors are built for that one :O

        Once you start thinking about that and gravity fields and time/spacial dilation things get quirky and complex but its better to live in a multiverse anyway 😉

        Yours and Steves observations got me thinking and googling around. Thanks lads.

        Your theories are quit eloquent and I can more easily accept what is observable by our wonderful science instruments and highly qualified scientists worldwide. I know you must be qualified in your field and appreciate you taking the time to explain some pretty not so straight-forward questions I asked.

        I will bookmark and take some time to digest. I’m a little rusty on my Quantum Physics and Science lately.

        Thanks 🙂 Wezley

      7. The slow roll inflation model starts out with a vacuum energy density of <~ 10^{110}GeV^4, which is near the Hagedorn temperature for the string. This is the upper bound on energy in string theory which is about 2 orders of magnitude larger in scale (2 orders of magnitude lower in energy) than the Planck scale. This is then a quantum field which contributes to the Einstein field equation in the form,

        R_{ab} – (1/2)Rg_{ab} = (8?G/c^4).

        Here the source of the spacetime dynamics on the right hand side is the expectation of some non-gravitational source (the vacuum expectation), while the spacetime stuff on the left is classical. In a stringy approach this looks like

        R_{ab} – (1/2)Rg_{ab} + ?’R_{acbd}R^{cd} + O(?’^2R^4)

        = (8?G/c^4)

        where ?’R_{acbd}R^{cd} is a correction due to stringy physics. This is a form of Gauss-Bonnet gravity, which you can look up on wiki-p. The coupling constant ?’ is the string constant ?’ = (1/16?)L_s^2, L_s = string length or reciprocal of Hagedorn temperature. I also leave it up to the interested reader to look up things like Riemann and Ricci curvature tensors and the rest. This is a sort of semi-classical physics, but where the term is expressed as a classical-like term. If you normal order the quantum correction terms you use to compute this you can eliminate all the quantum graininess and this becomes just a classical-like correction term. As a result there is no wavelength dependency for the speed of photon propagation. In its generic setting I think this has some bearing on the structure of cosmology and this basic form of inflation is more or less correct,

        The chaotic and eternal inflationary models push the scale down to the Planck length, or equivalently up to the Planck energy. This sandwiches the left hand side of these two equations with a . This is appealing in one sense, for it put the left and right hand sides of this equation on equal terms. However, there are theoretical difficulties with making this work, and further the data suggests that none of this is physically real. What there is to quantum gravity does not manifest itself in this way.

        Maldecena demonstrated how an anti-de Sitter (AdS) spacetime in n dimensions is equivalent to a conformal field theory (CFT) in n-1 dimensions. If you put a black hole in that AdS spacetime since its Gaussian curvature is negative it repels the black hole from its boundary. It is a “box” which can hold the black hole. Near the horizon of that black hole the AdS_n decomposes into AdS_2xS^{n-2}. The AdS_2 has the isometry group for conformal quantum mechanics and it is CFT_1, the diffeomorphism group of the circle on a space S^1xZ_2, Z_2 = two points. This is two copies of the CFT and this turns out to be the Hartle-Hawking vacuum. This was worked out by Ashoke Sen last year.

        That AdS_2 in a conformal map to a disk is a Poincare disk, which is represented by Escher’s “Circle Limit” drawings. There is a form of hyperbolic dynamics, which if I introduce a type of perturbation that breaks chiral symmetry makes this dynamics equivalent to a fermion condensate state. This is the quantum critical point, and it is similar to superconductivity. So quantum gravity is really a sort of “sub-quantal” physics, where spacetime remains continuous on all scales.

        LC

      8. Wow, thanks! I appreciate the detailed run down on both slow roll/eternal inflation and your own ideas.

        You sure make it difficult to stay away from studying this more seriously. (But I love astrobiology right now! What to do, what to do…)

        I have to absorb this though.

        It seems to me that we are in agreement that when you push the phenomenological potential of inflation up you will run into blueshift catastrophe/planck scales. Before that there is no inherent problem, as in other similar cases (black body radiation, EM theory, what have you). What’s sauce for the goose is sauce for the gander.

        I didn’t know, but suspected, that at least some types of inflation could have their singularities regulated (in relativistic non-granular fashion) by string theory regulation.

        Pushing into the planck scale, which experiments now may do, shouldn’t be a problem as such. Either string theory regulation is up to the task (I have to study those difficulties, sounds from your comment that normal ordering gets problems), or something else can solve this.

        I have to assume the data that suggests problem is what we are debating.

      9. The Planck scale is a bitch to probe. It is 16 orders of magnitude smaller than the scale we can probe with particle experiments, such as the LHC. These tests with dispersion from gamma ray burstars are rather interesting, for this is an indirect way to probe the Planck scale. These results do change some things, and sometimes wonder if this is not the modern equivalent of the Michelson-Morely experiment.

        LC

      10. Yes. Until supersymmetry is tested, there is a loophole I think (whether to use the 5 or 6 dim model).

        I rethought that point: supersymmetry is reasonable even though it may not solve SM problems. LHC latest push direct supersymmetry testing way up the energy scale (1 TeV I think), but it could happen at Planck scales or it could predict some Higgs.

        [In fact, the concurrent statistical twitch at ~ 120 GeV Higgs in several experiments on several accelerators could be the NUHM1 minimal supersymmetric model as I understand it. Another kind of “bubble”, or air castle.]

        In any case they *are* interesting, since the reinforce earlier experiments whether they surpass them or not!

        I like your analogy, it rings so very true on many levels.

    2. “a lot of paper shredders and tons of phenomenology papers and theory are being shredded.”

      Is that so? I have been mistrusting of graininess since I became more versed in granular theories and their assumptions. (And with the similar problem of setting aside relativity in Bell tests.)

      But I didn’t think it would be that easy to decide to put aside the notions, nor that easy to sway the respective communities. So forgive me if I ask if this is insider information, or if I can get hold of it?

      “the lack of graininess to spacetime in my mind casts some big question about eternal inflation.”

      As the paper mentions, the false vacuum eternal inflation described here is different from the older slow roll eternal inflation that solves the reheating problem. I don’t like the former either, for similar reasons! d(>w<)b And quite frankly, they are more elaborate as slow roll is mostly just a set of potentials with a range of parameter values.

      The upshot for me in the current interest is that they are easier to test without environmental (especially anthropic) principles, and that they seem informative on the problem of statistics over infinite universes.

      Conversely the predictions that come out of them are not so powerful as the ones slow roll inflation makes. Nor do they seem as easy to test with Planck measurements, instead they are more suited to integrate string theory AFAIU.

      But, coming back to the blueshift catastrophe in eternal expanding universes. Slow roll inflation must have or regulate those too, eventually. In my mind the graininess results, if they hold up, would strengthen the idea of slow roll inflation as an eternal process. That is, potentially without some of the worldline involving singularities that have been a possibility before.

    3. …In some ways it is refreshing and a sort of intellectual epiphany in the form of an avalanche.

      Lawrence,
      Clearly you are as accomplished with metaphors and imagery as you are with calculus and quantum cosmology. Thanks for all of your posts.

  6. “We could be in trouble if an adjacent universe’s bubble wall pushed inwards on a trajectory towards us…”

    This doesn’t seem very likely. Such a massive matter-antimatter exchange would be violent and thus highly visible across the radiation spectrum. It’s also imaginable that such a intersection would be a very unique phenomenon and distinguishable from other high energy collisions such as merging black holes, Quasars, and supernova.

    Of course, it could be a momentary intersection with our universe and on a scale too small to be detectable from Earth? Perhaps there is some physics involved that would close such a bridge quickly such as a radiation feedback loop. Perhaps someone with more knowledge can comment on this.

    Regarding the CMB:

    If I recall variations in the CMB were not major, or otherwise largely explainable as variations in density. Is there any evidence from the CMB that could have a divergent origin?

    The only cosmic phenomenon that comes to mind is the Dark Flow. I remember LC had a hypothesis that this may be the result of a dipole effect caused by another universe intersecting our own somewhere beyond the the visible cosmological horizon.

    Hopefully there is someway to investigate the multiverse theory further.

    1. The first question should be one for those in the know.

      Meanwhile, as I remember it, those bubble domain walls moves with the speed of light. If our universe encroach on another, it is too far away to be seen; it should have happened in the observable universe to be such. If another universe encroach on ours, we will never see it before it is too late and our local universe changed (destroyed).

      The one on CMB and potential observation I answered below, with an example.

      Ironically, in general there are no CMB anomalies according to a thorough analysis of the WMAP team.

      Of course it is not complete because people insists on looking for all sorts of anomalies (as they should, only not the same anomalies over and over). But “Dark Flow” is one of those anomalies that were tied to CMB and IIRC rejected by that paper; but please check me on that.

  7. Another nice article – Thanks Steve!! The beer analogies really got my brain juices flowing 😉

    Some of the posts here were very quality as usual 🙂 However, maybe not the jokes 😉

  8. Another nice article – Thanks Steve!! The beer analogies really got my brain juices flowing 😉

    Some of the posts here were very quality as usual 🙂 However, maybe not the jokes 😉

  9. Yo Steve, I’m a bit late at this beer-drinking party, but…

    At the last paragraph, in the beginning of the last sentence, it should be It’s (It is), not “Its”.

  10. OK. Just got back from the applied physics experiment [staring at the beer glass observing bubble nucleation].

    Just a few thoughts Steve, LC, Torbjörn –

    If you don’t have a problem with a bubble-like spacetime consisting of mostly nothing (within a non-zero-point vacuum) appearing out of a void of mostly nothing (a larger non-zero point vacuum), then cheers!!

    I would like to ask a few innocent questions… Are we sure observing the perimeter of our space-time based-off – data from WMAP and Plank data reduction/interpretation that the isometry is roughly spheroidal (I guess an analogy is we are inside the baloon trying to observe its outer wall from the inside seeing its inside wall at microwave CMB wavelengths?)

    Am I correct to assume it is possible and also likely there is a flatness about our space-time, ie the isometry is more analagous to a paraboloid / hyperboloid shape? Certainly observing almost all galaxies and macro-structures in our cosmos there is this repeating theme of mostly flat structures which bulge in the middle…

    If this were so then it would auger more towards a multi-verse connected by black & white holes in more of a total nothingness. Yes bummer earch space-time universe would experience a big-rip and be torn apart by the vacuum but there’s always “the arrow of time”…

    I remember reading about 8 months back on some astronomy sites that there were some (MIT/cambridge?) scientists proposing a model where our universe appeared at the big bang as a white hole emerging out the funnel of a black hole. It was dissected and some scientists don’t accept this model or point to deficiencies with observed data but I like it – It all fits nicely and is Occum’s razor-like – we observe SMBH’s and possibly white holes in early AGN’s… Also it would seem our first stars started forming within <1 Billion Years as a sort of plasma condensate when cooled (to 1-2000K?)…

    Please don't shoot the messenger. I am quoting some stuff from memory and hope Steve you might know the paper I refer to?

    Cheers – Wezley

    1. That is too much to reply to in one comment for me. :-/ I take the first and start of the last one for now.

      – No I don’t think a process is a problem, physics is based on them. If we can wrap our heads around an expanding universe where spacetime beget expanded spacetime, we can analogue our merry way.

      – White holes in general, but perhaps especially tied to black holes, seems to have problems. Que LC, I hope; when physicists says “there is nothing here” I generally feel that I don’t have to understand that particular problem.* I don’t think many physicists believe those constructions will ever work.

      We have certainly never observed anything like them, despite your handwaving at that point, so they are unlikely a priori as well.

      ————-
      * You can easily come up with many exceptions to that. Say, Newton’s “action-at-a-distance”. Why something fails can be informative!

      1. Thanks Torbjorn – You know the old saying “A little knowledge can be dangerous” – Well I am probably quite dangerous with my wild assumptions here but honestly I am just prodding you and LC because I am trying to get my head around some of the ideas cosmologists (and this article) talk about – in particular trying to understand how our space-time isometry / 4d shape is deduced/derrived from the WMAP/Plank data by current cosmologists [cue LC]. I appreciate your comments – Maybe I’ll be a little less dangerous in my next discussion 😉 LC/Steve ?? 🙂

      2. Hi Wez,

        The observable universe appears to be flat, not spheroidal – this does not favour the bubble hypothesis, unless it’s a really big bubble. It is clearly expanding, so it must have been smaller in the past and its past streches back at least 13.7 billion years. We know that much with reasonable confidence.

        I’m not sure we have more options than to consider that the universe either appeared out of nothing – or it is eternal. I don’t think a multiverse is more than a theoretical possibility – but it’s good when theoreticians offer testable predictions. If we ever do find an inexplicable circle in the sky, then maybe it’s all true.

        I think more than one author has run with the big bang / white hole idea. I wrote one up here: http://www.universetoday.com/85682/astronomy-without-a-telescope-small-bangs/ Maybe they referenced the paper you are thinking of?

      3. I had one of those strange waking epiphanies one morning thinking it could be quite possible our space-time described could be described as two inversley symmetric parabolic cuves

        [f ~ g means lim_{ntoinfty} frac{f(n)}{g(n)} = 1](
        [(f)c(1/z)dz =2pi(i) P = f(x) = ax2 + bx + c ])

        a logical consequence and predictor of our space-time quanta / vacuum emerging from a white hole into (an almost 0 point vacuum – it sounds fast and dangerous but it’s almost as though white holes and black holes in theory can do this kind of magic at a distance wall-street creation dance where one borrows energy to appear and is pulled by a strong negative repulsion (by almost 0 point vacuum / inflation) of the matter through white holes and pays it back though black holes (either way through either tunnel if you accept some of the more unconventional wormhole theory but i digress… .

        I personally feel there is more than anecdotal evidence that the bright source emissions in early highly-red-shifted AGN’s may contain White holes, and if so observing these should be able to assist in constraining models and theories further.. In particular how strongly polarized GRBs can be and at what rates will I believe elucidate us all greatly in the near future, thanks to humanity’s best scientists and engineers.

        Thanks for your time – I really have enjoyed reading and sharing info in the posts..

        Best,

        Wezley

      4. There are some LaTex stuff there, There is something that looks like a Cauchy integral. However, I am not sure what the mathematical objects are supposed to represent.

        LC

      5. Hello LC,

        Forgive me my math really isn’t good – the latex character wouldn’t play nice with my cut and past. My attempt at mathematics is intended to show how two inversely symmetrical parabolic curves could be joined using the Brouwer fied point theorem – http://en.wikipedia.org/wiki/Brouwer_fixed_point_theorem

        f(x) = x = 1 as a function integrating two perfect parabolas (using a quadratic function) to join the two parabolas – f(x)=ax2+bx+c. I haven’t specified the amount of stretching on the parabolas (dependent on the functions of time and the inflation).

        It is just a quick patchwork of a generalised shape which I believe the cosmos may be emulating as its 3d construct.

        Interested in your thoughts. Am i way off? by order of magnitude, by 1 ?? 😉

    2. The CMB does not represent a boundary to spacetime. The universe at a time in the past was radiation dominiated. As it expanded and temperatures dropped matter dominated and the plasma phase ended. The CMB is where in looking outwards and equivalently back in time the event of this decoupling.

      LC

  11. The crazy thing is that I believe we are already seeing the interactions taking place. A prime example of this is the fact that all of the galaxies in the Universe are not only moving outward, but they are also moving towards the relatively same direction (Dark Flow), which brings up the chance of this being the gravitational pull of another Universe next to ours. #mindblown

    1. This is not correct. All galaxies in the universe are not moving in the same direction. Only a small (but still spatially massive) portion of the galaxies in a sky show signs of this effect.

      1. There is no effect at all. most physicists conclude. It is what was discussed the other day in the comments below.

        The WMAP analysis exclude these anomalies in general as they build on flawed CMB statistics; Wright and Keisler have pinpointed these flaws in the Dark Flow hypothesis.

        Whatever it is, it isn’t a “prime” example. More like the rank scrap of meat in the waste bin behind the ‘hood McDonald.

        An example of statistical analysis that isn’t pattern driven is the one I mentioned that happened to include the Cold Spot but also other CMB features. The jury is still out on that one, or such in general; the fact that you can make bad statistics doesn’t exclude that you can make good statistic. (O.o)

      2. There is no effect at all. most physicists conclude. It is what was discussed the other day in the comments below.

        The WMAP analysis exclude these anomalies in general as they build on flawed CMB statistics; Wright and Keisler have pinpointed these flaws in the Dark Flow hypothesis.

        Whatever it is, it isn’t a “prime” example. More like the rank scrap of meat in the waste bin behind the ‘hood McDonald.

        An example of statistical analysis that isn’t pattern driven is the one I mentioned that happened to include the Cold Spot but also other CMB features. The jury is still out on that one, or such in general; the fact that you can make bad statistics doesn’t exclude that you can make good statistic. (O.o)

  12. I suspect that the above explanation of this theory does it about as much justice as explaining how …oh let’s say the LHC works to a duck in Spanish by someone who only speaks Japanese!

    1. Well, it is a brief summary, as intended. But a fair one what I can see, for example the reason to omit slow roll inflation could be that false vacuum is now popular et cetera.

      So it comes down to usefulness. I think it works as a starter or update. Could you do it better?

  13. It seems as though Michael Moorcock’s idea of the Multiverse was correct all along. How long before the eternal Champion hoves into view.

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