Here’s a new paper of mine, with Adrienne Erickcek and Mark Kamionkowski:
A Hemispherical Power Asymmetry from Inflation
Abstract: Measurements of temperature fluctuations by the Wilkinson Microwave Anisotropy Probe (WMAP) indicate that the fluctuation amplitude in one half of the sky differs from the amplitude in the other half. We show that such an asymmetry cannot be generated during single-field slow-roll inflation without violating constraints to the homogeneity of the Universe. In contrast, a multi-field inflationary theory, the curvaton model, can produce this power asymmetry without violating the homogeneity constraint. The mechanism requires the introduction of a large-amplitude superhorizon perturbation to the curvaton field, possibly a pre-inflationary remnant or a superhorizon curvaton-web structure. The model makes several predictions, including non-Gaussianity and modifications to the inflationary consistency relation, that will be tested with forthcoming CMB experiments.
The goal here is to try to explain a curious feature in the cosmic microwave background that has been noted by Hans Kristian Eriksen and collaborators: it’s lopsided. We all (all my friends, anyway) have seen the pretty pictures from the WMAP satellite, showing the 1-part-in-100,000 fluctuations in the temperature of the CMB from place to place in the sky. These fluctuations are understandably a focus of a great deal of contemporary cosmological research, as (1) they arise from density perturbations that grow under the influence of gravity into galaxies and large-scale structure in the universe today, and (2) they appear to be primordial, and may have arisen from a period of inflation in the very early universe. Remarkably, from just a tiny set of parameters we can explain just about everything we observe in the universe on large scales.
The lopsidedness I’m referring to is different from the so-called axis of evil. The latter (in a cosmological context) refers to an apparent alignment of the temperature fluctuations on very large scales, which purportedly pick out a preferred plane in the sky (suspiciously close to the plane of the ecliptic). The lopsidedness is a different effect, in which the overall amplitude of fluctuations is a bit different (just 10% or so) in one direction on the sky than in the other. (A “hemispherical power asymmetry,” if you like.)
What we’re talking about is illustrated in these two simulations kindly provided by Hans Kristian Eriksen.
I know, they look almost the same. But if you peer closely, you will see that the bottom one is the lopsided one — the overall contrast (representing temperature fluctuations) is a bit higher on the left than on the right, while in the untilted image at the top they are (statistically) equal. (The lower image exaggerates the claimed effect in the real universe by a factor of two, just to make it easier to see by eye.)
What could cause such a thing? Our idea was that there was a “supermode” — a fluctuation that varied uniformly across the observable universe, for example if we were sampling a tiny piece of a sinusoidal fluctuation with a wavelength many times the size of our current Hubble radius.
The blue circle is our observable universe, the green curve is the supermode, and the small red squiggles are the local fluctuations that have evolved under the influence of this mode. The point is that the universe is overall just a little bit more dense on one side than the other, so it evolves just slightly differently, and the resulting CMB looks lopsided.
Interestingly, it doesn’t quite work; at least, not in a simple model of inflation driven by a single scalar field. In that case, you can get the power asymmetry, but there is also a substantial temperature anisotropy — the universe is hotter on one side than on the other. There are a few back-and-forth steps in the reasoning that I won’t rehearse here, but at the end of the day you get too much power on very large scales. It’s no fun being a theoretical cosmologist these days, all the data keeps ruling out your good ideas.
But we didn’t give up! It turns out that you can make things work if you have two scalar fields — one that does the inflating, cleverly called the “inflaton,” and the other which is responsible for the density perturbations, which should obviously be called the “perturbon” but for historical reasons is actually called the “curvaton.” By decoupling the source of most of the density in the universe from the source of its perturbations, we have enough wiggle room to make a model that fits the data. But there’s not that much wiggle room, to be honest; we have an allowed region in parameter space that is not too big. That’s good news, as it brings the hope that we can make relatively precise predictions that could be tested by some means other than the CMB.
One interesting feature of this model is that the purported supermode must have originated before the period of inflation that gave rise to the smaller-scale perturbations that we see directly in the CMB. Either it came from earlier inflation, or something entirely pre-inflationary.
So, to make a bit of a segue here, this Wednesday I gave a plenary talk at the summer meeting of the American Astronomical Society in St. Louis. I most discussed the origin of the universe and the arrow of time — I wanted to impress upon people that the origin of the entropy gradient in our everyday environment could be traced back to the Big Bang, and that conventional ideas about inflation did not provide straightforward answers to the problem, and that the Big Bang may not have been the beginning of the universe. I was more interested in stressing that this was a problem we should all be thinking about than pushing any of my favorite answers, but I did mention my paper with Jennie Chen as an example of the kind of thing we should all be looking for.
To an audience of astronomers, talk of baby universes tends to make people nervous, so I wanted to emphasize that (1) it was all very speculative, and (2) even though we don’t currently know how to connect ideas about the multiverse to observable phenomena, there’s no reason to think that it’s impossible in principle, and the whole enterprise really is respectable science. (If only they had all seen my bloggingheads dialogue with John Horgan, I wouldn’t have had to bother.) So I mentioned two different ideas that are currently on the market for ways in which influences of a larger multiverse might show up within our own. One is the idea of colliding bubbles, pursued by Aguirre, Johnson, and Shomer and by Chang, Kleban, and Levi. And the other, of course, was the lopsided-universe idea, since our paper had just appeared the day before. Neither of these possibilities, I was careful to say, applies directly to the arrow-of-time scenario I had just discussed; the point was just that all of these ideas are quite young and ill-formed, and we will have to do quite a bit more work before we can say for sure whether the multiverse is of any help in explaining the arrow of time, and whether we live in the kind of multiverse that might leave observable signatures in our local region. That’s research for you; we don’t know the answers ahead of time.
One of the people in the audience was Chris Lintott, who wrote up a description for the BBC. Admittedly, this is difficult stuff to get all straight the very first time, but I think his article gives the impression that there is a much more direct connection between my arrow-of-time work and our recent paper on the lopsided universe. In particular, there is no necessary connection between the existence of a supermode and the idea that our universe “bubbled off” from a pre-existing spacetime. (There might be a connection, but it is not a necessary one.) If you look through the paper, there’s nothing in there about entropy or the multiverse or any of that; we’re really motivated by trying to explain an interesting feature of the CMB data. Nevertheless, our proposed solution does hint at things that happened before the period of inflation that set up the conditions within our observable patch. These two pieces of research are not of a piece, but they both play a part in a larger story — attempting to understand the low entropy of the early universe suggests the need for something that came before, and it’s good to be reminded that we don’t yet know whether stuff that came before might have left some observable imprint on what we see around us today. Larger stories are what we’re all about.
Gary Bridgewater:
It’s probably not what you were thinking about, but COBE, WMAP’s predecessor, shows similar structures, although at lower significance because of its much lower signal-to-noise. But I don’t know about any other full-sky maps which are deep enough to be relevant to this issue, really. But of course, even limited sky data sets such as 2dF or quasar catalogs may eventually be interesting.
holo:
I’m afraid that WMAP’s polarization maps are too noisy to be useful for this, really. They barely have enough signal-to-noise to constrain a very few full-sky multipoles at the very largest scales, and not much more than that. They are useful for foreground studies, though, but for proper full-sky CMB polarization information, we’ll just have to wait for Planck..
Lawrence B. Crowell:Topology might indeed play a role here. The question is what topology, and what physics does it imply?
The “landscape “is a dirty word now? So too, is Witten ready to discard it?
I have yet to read Sean’s and their group effort work, but to go by the news reports that are selective released through his blog here.:) Oh, and the “other news source” he had identified.
So we are getting straight from the….. and as a layman how can I assess and give anything of value here, while there are better minds at work?
So let’s see.
The group is using a phenomenological approach to the theory they are expounding? So in this case, we know the hesitancy that censorship “can elevate” or “distort a view” that is vacuous in it’s explanation and reveal a distast to multiverse hypothesis and such, how so then to think that such “reverse arrow of time” can be of help to this current view? It is progressive I must admit from my perspective.
So we have a universe, a WMAP to look at, and to this extent(genus relations), how far had Mandelstam taken the mathematical of a “genus three construct?”
This then would be a layman mistake on my part if such an associative value of the universe can be made in relation to the Genus figure, yet, I would not have all my facts in place from my inexperience?
Plato, do you use a computer to help with your composition? If so I’d stop, or get an upgrade, because it makes your meaning very obscure.
Also, with bloggers here putting so much time and effort into explaining their ideas and those of fellow experts, for you to ask “As a layman how can I assess and give anything of value here, while there are better minds at work?” sounds not only rude but foolish.
How can you expect to find an infallible oracle anywhere, when everyone knows there’s no universal agreement on speculative models and how best to interpret and explain new observations?
Oh, and calling yourself “Plato” – Do us a favour!
Plato on Jun 10th, 2008 at 10:15 am WROTE:
The “landscape “is a dirty word now? So too, is Witten ready to discard it?
———————
String theory might be said to be too unconstrained. LQG is too constrained. 🙂 To me these things are really math-methods more than being theories in a proper sense. They both have interesting things to say, but it is best not be believe either — belief is for religion and politics.
you wrote:
how far had Mandelstam taken the mathematical of a “genus three construct?”
—————————-
I could fill this with a lengthy essay, but I will keep this short. I think the issue is with the moduli of gravity or quantum gravity/cosmology. In particular how does one get a matching conditions on the moduli space for the instanton state “pre-tunneling state” and the tunneling state. Mandelbrot geometry in spacetime has some interesting issues with the separability of moduli. My suggestion of the Poincare homology sphere is in part meant to address this issue.
Beyond mathematics there are also physical issues, which are really more important. In particular we need to discard what might be called excess baggage. Physically this amounts in part to a generalization of the equivalence principle where non-inertial and inertial frames are treated on the same basis.
These is a possible related issuewith Shean’s paper. This data might be related to gravitons stretched out an imprinted on the post inflationary universe. In the paper:
http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.0665v2.pdf
there appears noise in the LIGO detectors which ound like the gravitational analogue of the CMB. Maybe we are getting signals from the decoupling of gravity & gauge fields analogous to the deionization phase of the universe about 380,000 years after the big bang. This might be data from the universe from within some 10^10 Planck times into the “shebang.” Maybe in time we will get data on the full spectrum, but all so the anistoropic distribution. That will tell us something about the scaling of the universe at large. This gravity wave noise might then be from the universe at a distance so that z ~= lambda/lambda_0 ~= 10^{40}! That is rather impressive given that the most distant galaxies have z ~ 7 and the CMB is z ~ 1000.
So are we getting some data which is related to an anisotropy of gravitons? We don’t know, but we can be certain that the future holds many surprises.
Lawrence B. Crowell
Lawrence B. CrowellMy suggestion of the Poincare homology sphere is in part meant to address this issue.
I am currently trying to learn to understand the Poincare Conjecture and the lessons in this are amazing to me. Going to a universe in a three manifold description I made the link when it referred “the set in which every point that belongs to a region could be mapped to every point in the box or clear Aquarium.”
That such a logic leading from Euclid’s element could have ever gotten to something so abstract as seeing “routes in space” as I have detailed them in “satellite travel above” and in terms of Lagrangian points Is an amazing thing for me to grasp, as much, “the departure from the fifth postulate, to non-euclidean geometries. For a layman like me, this is exciting way to think.
A bulk perspective now instead of “an anisotropy of gravitons?” Well my views are suppose to be telling when I write the way I do and I am glad some people do get them, or bother to ask.
Thank you Lawrence for the courtesy and helpful information.
John Ramsden,
I meant it John, when I said there are better minds then mine here because I am truly at a disadvantage and it is to mean nothing more then, “I have a lot of work to do to catch up sometimes.” Some will be able to read more into what I am saying then others.
It’s true, I am enamoured with Plato and everything about him.:) But yes, I know he’s dead physically, but not in, what remains of him. Those who write about him. Those who speak of the Solids.
Even people like Coexeter who represent a new stage in my view of taking geometries to amazing new spaces or Banchoff. Garret Lisi model and E8 complexity are attempts, are they not of modelling of our universe? Or maybe even Tegmarks fascination?
Anyway, back to the post of Sean’s here.
The idea to me of” time reversals” had to have some inclination to include Gr at the inception of a new universe, or, of connecting the “beginning and end” in the very nature of this universe now.
Where is Zero point entropy? Does it exist in any positions in our universe that would be considered the place where such beginning and ends make then self known?
What would be the physics of this place?
I am thinking in my layman mind that it is contained in the “moment of the collision process” where we are experimentally moving to words a “supersymmetrical view.” Navier Stokes equations are then considered and the viscosity then provides for this opening to “time reversal and such?”
Of course I am all over the map:) But to me such a concentration of of gravity in my views of the universe belong to the idea that a gravity perspective is now contained in the “bulk view.”
Plato wrote:
>
> I said there are better minds then mine here
Ah. Sorry, I misinterpreted your question to mean are there better minds (on other blogs or forums for example) than the blog authors here!
I must say it did seem a somewhat implausible thing to ask, and perhaps I should have read between the lines; but it just shows how easily a “discursive” writing style (using as nice a word as possible) can be misunderstood 😉
Pingback: Populär Astronomi - » Universum är skev. Men Max Tegmark sommarpratar
Re: #8 ” that this ‘lop-sidedness’ cannot be explained by Gaussian statistics?”
Recent observations and analysis by Benjamin Wandelt indicate (just below the level where they announce “detection” in the forthcoming Phys Rev Letters but instead say “evidence for”) “non-gaussianity” in the CMB.
This earlier paper by Yadav and Wandelt claims ‘detection’:
* Amit P. S. Yadav and Benjamin D. Wandelt, Detection of primordial non-Gaussianity (fNL) in the WMAP 3-year data at above 99.5% confidence.
Their abstract finishes with: “We conclude that the WMAP 3-year data disfavors canonical single field slow-roll inflation.”
This may be the start of the collapse of Alan Guth’s “inflation” – the unifying principle of Cosmology since Big Bang.
What, Dr. Sean Carroll, should we focus on in relating your theories and this data interpretation?
Plato on Jun 11th, 2008 at 12:51 am
I am currently trying to learn to understand the Poincare Conjecture and the lessons in this are amazing to me.
————
… as I have detailed them in “satellite travel above” and in terms of Lagrangian points
———————-
The Poincare homology sphere is related to his conjecture. Yet the homology sphere is a sphere with the rotational group SO(3) “modulo” a discrete set of rotations which describe a polytope or polyhedra. The homology sphere is a boundary of a region of four dimensions with a quaterionic structure. If the four manifold is a 4-sphere then the 3-homology sphere bounds both of then and there is then a quaternionic structure in the whole 4-space. At the time Poincare worked on these matter, in the late 19th century, quaterions were a “hot item.” Indeed Maxwell originally formulated his EM equations according to quaterions.
Lagrange points are regions where the Newtonian gravitational forces from two main bodies and centripetal force on a third “test mass” cancel out. For the Earth and sun alone these are fixed points. The L_1, L_2 and L_3 points have potential functions (in the accelerated frame) which are saddle point configurations, and are thus not stable, but quasistable. Another problem is that there is a perturbation due to the moon, so the Lagrange points are not fixed points, but wobble around in Lissajous orbit.
So to get there is tricky. The craft is placed in a highly elliptical orbit that approaches the Lagrange point. The RTG on the craft then after 3 passes nudges the craft into the Lagrange points. Also, since the Lagrange point is a saddle potential one needs to perform station keeping to maintain a “trim” on the orbit. This requires occassional rocket burns. This will continue until Sept 2009, after which WMAP will go silent and become “lost in space” as space junk. The Planck spacecraft will be launched later this year and will provide better data, including measurements of B-mode polarizations.
Astro-navigation is a bit like golf, you have a certain par for a mission and the objective is to get the ball in the hole, craft to its orbit, libration point, planet etc.
Lawrence B. Crowell
Lawrence,
Thanks again.
Moving to polytopes or allotrope seem to have values in science? Buckminister Fuller and Richard Smalley in terms of allotrope.
I was looking at Sylvestor surfaces and the Clebsch diagram. Cayley too. These configurations to me were about “surfaces,” and if we were to allot a progression to the “projective geometries” here in relation to higher dimensional thinking, “as the polytope[E8]”(where Coxeter[I meant to apologize for misspelling earlier] drew us to abstraction to the see “higher dimensional relations” toward Plato’s light.)
As the furthest extent of the Conjecture , how shall we place the dynamics of Sylvestor surfaces and B Fields in relation to the timeline of these geometries? Historically this would seem in order, but under the advancement of thinking in theoretics does it serve a purpose? Going beyond “planck length” what is a person to do?
Thanks for the clarifications on Lagrange points. This is how I see the WMAP.
Such concentration in the view of Sean’s group of the total WMAP while finding such a concentration would be revealing would it not of this geometrical instance in relation to gravitational gathering or views of the bulk tendency? Another example to show this fascinating elevation to non-euclidean, gravitational lensing, could be seen in this same light.
Such mapping would be important to the context of “seeing in the whole universe.”
Pingback: A New CMB Anomaly? | Cosmic Variance
Pingback: Superhorizon Perturbations and the Cosmic Microwave Background | Cosmic Variance
Fool!
The earth is flat and is 6000 years old.
The sun, which is 1/2 the size of the earth orbits in a perfect circle around the earth.
The moon which is 1/2 the size of the sun orbits the sun and the earth.
Oh, yeah and in the end of days a giant seven headed snake will come out of noware and brand 666 on everyones head! 🙂
Watch out for Poes Law!
Pingback: Occam’s Machete » Blog Archive » Did the Big Bang Start From a Single Point?