WMAP 5-Year Results Released

By Sean Carroll | March 5, 2008 4:54 pm

It doesn’t seem like all that long ago that we were enthusing about the results from the first three years of data from the Wilkinson Microwave Anisotropy Probe satellite. Now the team has put out an impressive series of papers discussing the results of the first five years of data. Here is what the CMB looks like, with galaxy and foregrounds and monopole and dipole subtracted, from Ned Wright’s Cosmology Tutorial:


WMAP 5-year sky

And here is one version of the angular power spectrum, taken from the Dunkley et al. paper. I like this one because it shows the individual points that get binned to create the spectrum you usually see. (Click for larger version.)

WMAP 5-year power spectrum

The headline two years ago was “Cosmology Makes Sense.” (That was my headline, anyway — others were not quite as accurate.) This continues to be true — the biggest piece of news isn’t that the results have overturned any foundations, but that the concordance model with dark matter, dark energy, and ordinary matter continues to work. The WMAP folks have produced an elaborate cosmological parameters table that runs the numbers for different sets of assumptions (with and without spatial curvature, running spectral index, etc), and for different sets of data (not just WMAP but also supernovae, lensing, etc). Everything is basically consistent with a flat universe comprised of 72% vacuum energy, 23% dark matter, and 5% ordinary matter. The perturbations are close to scale-free, but still seem to be a little larger on long wavelengths than shorter ones (0.014 < 1-ns < 0.067 at 95% confidence). Probably the most fun result is that there is, for the first time, evidence from the CMB that neutrinos exist! Good to know.

My personal favorite was the constraint in the Komatsu et al. paper on parity-violating birefringence that would rotate CMB polarization. I was in on the ground floor where birefringence is concerned, so I’m sentimentally attached to it. But it’s also a signature of some very natural quintessence models, so this helps constrain the physics of dark energy as well.

Congratulations to the WMAP team, who have done a great job in establishing some of the pillars of contemporary cosmology — it’s historic stuff.

CATEGORIZED UNDER: Science
  • Lawrence B. Crowell

    The Komatsu et al. paper on parity-violating birefringence that would rotate CMB polarization suggests that the P-violating birefringence occurs in domains similar to magnetization domains for a temperature below the Curie point. This might mean the inflaton settles into different Mexican hat potential configurations or with different vevs.

    Lawrence B. Crowell

  • Adam

    @ Mr. Crowell:

    Have you considered that the stochastic nature of the parametrically-driven electron birefrigence would circumvent the dynamic Curie threshold and instead oscillate unstably until (pi/d^2) – 1 converges on infinity, thus causing the universe to implode?

  • onymous

    So “very natural quintessence models” isn’t a contradiction in terms?

  • http://lablemminglounge.blogspot.com/ Lab Lemming

    Can somebody please link an explanation for how the universe can be both flat and accelerating in its expansion? I don’t quite understand that.

  • http://www.davidnataf.com David Nataf

    Lab Lemming,

    You may be confusing terminology, why can’t a flat universe accelerate?
    Imagine being a 3dimensional God looking at a 2d sheet of paper universe… there’s no reason that FLAT sheet of paper can’t just expand.

    If you look at Friedmann’s equations here: http://upload.wikimedia.org/math/0/e/1/0e14ece5bb6fddb797a9d3c62fc6473d.png
    You see the second derivative of the scaling factor; for an accelerating universe that term needs to be positive. For that to happen, lambda needs to be big enough to overcome the combined negative contribution of the gravity and pressure of matter and radiation.

  • onymous

    Lab Lemming: “flat” means that spatial slices are flat, not that spacetime is flat.

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  • Lawrence B. Crowell

    A cosmology can be spatially flat, but the spacetime curved. The spacetime would be flat if the spatial surface and its evolute which foliate the spacetime are constant with no expansion. Some care must be given, for a spatial surface can be arbitrarily chosen. One can easily embed any spatial surface of choice, which is similar to a gauge condition in electromagnetism.

    One of the strange consequences of an expanding univerise is that energy is not something which can be globally defined. The energy balance of the universe is a sort of survey based on local measurements. The gravitational mass-energy density of the universe is

    $latex
    rho_t~=~rho~+~P_z~+~P_y~+~P_z~-~Lambda/(4pi G),
    $

    for [itex]rho~+~P_z~+~P_y~+~P_z[/itex] due to luminous and dark matter. The dark matter component is some 85% of this portion. The comsological constant term [itex]Lambda[/itex] is modelled as the result of quantum vacuum energy in the universe with

    $latex
    Lambda~=~(8pi G/c^2)(rho_{vac}~+~3P_{vac})
    $

    This term appears to have the condition that [itex]P_{vac}~=~-rho_{vac}[/itex] which is the source of this “negative pressure” that causes the universe to accelerate outwards. The cosmological constant defines an event horizon at [itex]r~=~sqrt{3/ Lambda}[/itex], where the finite value of the distance ~ [itex]10^{10}[/itex] ly.

    As a caveat, there is potentially a level of abuse here. Assigning the cosmological constant to a source, as I did above, for the cosmological constant is a factor of an Einstein space(time), where the Ricci curvature is proportional to the metric. This is usually thought of as a purely geometric property of the spacetime and not something due to a source of gravity.

    It is tempting to think of the universe as having a net zero mass energy. How to get [itex]E~=~0[/itex] is problematic. The metric terms in the deSitter cosmology are [itex]g_{ii}~=~exp(sqrt{Lambda/3}t)[/itex], and it is not possible to find a [itex]K_t[/itex] so that there is a stationary condition [itex]{cal L}_{K_t}g~=~0[/itex], for [itex]{cal L}_{K_t}[/itex] a Lie derivative. This Lie derivative is defined according to brackets so that

    $latex
    {cal L}_{K_t}g~=~{cal L}_{K_t}g(X,~Y)~=~g([K_t,~X], Y)~+~g(X, [K_t,~Y]),
    $

    where the brackets [itex][K_t,~X][/itex] are, for [itex]K_t~=~Apartial/partial t[/itex], not zero because the vectors X are functions of time. So there is no involutary system which defines a conservation of energy on the entire spacetime.

    Now, the cosmology will in time expand “infinitely,” and the cosmological horizon will also decay in a manner similar to the decay of black holes. Thus the horizon will receed to infinity and the evolution of the universe has as its attractor point a Minkowski spacetime that is an empty flat void with no mass-energy. So in that sense, as defined by the attractor point, the universe has zero net content, and the evolution of the universe from the vacuum, or some set of inequivalent vacua, to this final attractor point is a way that that “nothing” is reshuffled into another form of “nothing.” From a quantum gravitational perspective the Wheeler DeWitt equation [itex]HPsi([g])~=~0[/itex], means that time is not something which is also defined explicitely, but is only a bookkeeping method the analyst imposes to “organize” spatial surfaces, or the wave functional where spatial surfaces are configuration variables.

    Lawrence B. Crowell

  • CosmicVarianceFan

    Any chance someone can use an analogy to help explain or put in terms that is light on the math?

  • CosmicVarianceFan

    EDIT: (I submitted the previous comment prematurely by mistake) … Any chance someone can use an analogy to help explain or put in terms that is light on the math … with regard to the universe being flat? I try to imagine flatness in the way we see faraway galaxies appear as two-dimensional. Is that accurate?

  • Dr Dyer

    Well the comic xkcd has been on top of things for a while now. They even have a shirt(7th one down) for the predecessor to the WMAP , so maybe he will put an shirt together for the updated findings.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    CVF, general relativity says that spacetime is curved, and that curvature is what we perceive as gravity. In general the curvature of spacetime is an enormously complicated thing, as we have to keep track of (for example) how different parallel lines diverge or converge in all sorts of directions.

    But in cosmology, where we start by assuming that matter is distributed uniformly through space (but expanding with time), things simplify a great deal. The curvature of spacetime comes uniquely from two contributions: the curvature of space all by itself, and the fact that space is expanding as a function of time. A certain density of matter spread uniformly through the universe implies a certain total amount of spacetime curvature, but that can be distributed in various ways between spatial curvature and the expansion rate. So you can have a “flat universe,” which means zero spatial curvature, even though spacetime overall is curved because of the expansion.

    More at Ned Wright’s cosmology tutorial.

  • John Merryman

    If “The curvature of spacetime comes uniquely from two contributions: the curvature of space all by itself, and the fact that space is expanding as a function of time.” Than wouldn’t the speed of light have to increase proportionally, since C is the most stable measure of spacetime? Lightspeed is the ruler we use to measure these distances, so if space is expanding, wouldn’t this ruler be stretched as well? If not, than wouldn’t it be increasing distance in stable space, not the space itself expanding?

  • http://www.davidnataf.com David Nataf

    Sean,

    What do you think are the prospects for very informative, qualitatively new results to come from the Planck telescope? Will there simply be more precision of existing data, or do you think they’ll be able to elucidate previous foggy regimes of the parameter space?

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    David, I’m not an expert, but I’m optimistic that Planck will teach us exciting things. So far the CMB has helped us pin down the concordance model, but there is always the possibility that a real surprise is lurking around the corner. It will certainly constrain theories of modified gravity, for example. We’ll have to wait to see.

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  • David Caughell

    CVF: Trying using a balloon. When no air is blown into the balloon, it’s flat(2-d). Yet when the first breathe is pushed into the balloon, it expands(3-d). So, using this as an illustration, now picture the universe being the balloon. There is your common english, with light of math, explaination to the expansion of the universe.

  • Brian

    Thanks for the post Sean. Is there any way that the estimate (from the WMAP website) that neutrinos constsituted 10 % of the mass and energy density at the time of recombination could lead to either an upper or a lower bound on the mass of individual neutrinos?

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    What you actually get is a limit on the sum of the neutrino masses; you can’t tell which individual ones are massive etc. From here, the limit on the sum of the masses is 1.4 eV at 95% confidence.

  • Brian T

    Could someone explain how they get the error bars on that power spectrum plot? It looks like the points are distributed much more widely than the error bars show.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Brian, it’s just the standard error of the mean:

    http://en.wikipedia.org/wiki/Standard_error_(statistics)

    The more data points you have, the broader the distribution looks to your eye, but the better-determined the mean of the distribution actually is.

  • http://deleted Secret American Planck Basher

    David (et al.) –

    I would say from conversations with many people that Planck has been so long in development that by the time it does get up and running many of its results will be anticipated by other experiments (for example, the ground based ones.) Other than primordial gravitational waves (PGWs), I don’t find much to get excited about relative to other things coming online — which will mostly be telling us about the later universe.

    I don’t find PGWs particularly exciting — they are supposedly “pinning down” a free parameter for inflation, but let’s be honest here: there are many varieties of inflation, too many, and did the WMAP result “ruling out” single-field phi^4 really change anything in the field? Not really. It was cool and fun, and worthy of celebration, but it had not enough impact on the proliferation of inflation models, and did little to provoke theorists and observers in new directions.

    Other than that, perhaps the search for non-Gaussianity will be the biggest result from Planck. But it’s hard to square with the massive amount of resources that have been expended. Could we have built a “non-Gaussian probe” better faster cheaper?

    Definitely, Planck’s results will not have the massive, stunning impact that WMAP’s no-BS settling of the concordance model (taking “concordance” here to just mean a negative pressure fluid and not a pure cosmological constant) did. (By “settle” here, I don’t mean “prove” — I mean “provide the baseline against which new models must improve upon.”)

    Anyway, as I’ve been typing this I’ve mellowed a little on Planck. Perhaps there will be something.

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  • Lawrence B. Crowell

    I guess I missed this one:

    Adam on Mar 5th, 2008 at 10:45 pm
    @ Mr. Crowell:

    Have you considered that the stochastic nature of the parametrically-driven electron birefrigence would circumvent the dynamic Curie threshold and instead oscillate unstably until (pi/d^2) – 1 converges on infinity, thus causing the universe to implode?

    ————-

    I am trying to figure out what you are meaning here. The result seems to point to some analogy with the T

  • Lawrence B. Crowell

    Retransmission, I forgot this does not like the carrot symbols
    ————-

    I am trying to figure out what you are meaning here. The result seems to point to some analogy with the T less than T_c magnetization of a metal in domains. Though some care must be given in that our observations are not across the whole of space, but are along projective rays on a past light cone. This birefringence result is an anisotropy and not an inhomogeneity result. But it does suggest that a CP violating phase in the PMNS (CKM) matrix might assume local values, which is suggestive of physics similar to more down to Earth physics of symmetry breaking and Landau-Ginsburg type of potentials. The WZW action in supersymmetry is similar to this, and this might be a manifestation or “fossil” signature of such physics in the early universe.

    Lawrence B. Crowell

  • spaceman

    Did you read about the latest measurements of spatial curvature? It is now firmly established that the radius of our Universe is greater than the size of our observable universe a fact which will make it even harder for advocates of non-trivial topology to hang out onto their “small universe” hypothesis….

  • Lawrence B. Crowell

    There are a number of reasons to suspect that the spatial manifold of the universe is simply connected. There are some energy conditions by Penrose and Hawking which point to why space, at least classically, should be simply connected. There is also the work by Gregory Perleman on the Poincare conjecture. This involves Hamilton’s Ricci flow equations, which describe how a space will evolve so it has some minimal energy configuration. Think of a balloon you have twisted up (though not tied up) and you then let it go. The balloon snaps back to its round shape. Perleman’s work with the Ricci flow equations indicate that the minimal configuration of a closed three dimensional space is a sphere. So I suspect that the universe does not have worm holes or dodecahedral portholes and the like.

    Lawrence B. Crowell

  • Jason Dick

    Secret American Planck Basher,

    Well, the free parameter in question is a pretty important one, in my view: the energy scale of inflation. Pinning down the energy scale of inflation is a pretty big step in making any significant statements about what inflation actually is. There are also measurements of the CMB out to smaller scales, which will provide further, much more significant constraints on various other inflationary parameters. It’s also a big help to make use of the same instrument for both the large angular scales and the small angular scales, as there are always uncertainties that crop up when combining different experiments. Then there’s the fact that additional sky coverage improves measurements at all angular scales, and so Planck will be able to do better out to somewhere around 10-20 arcminutes or so than any ground-based instrument can possibly do.

  • Daniel de França MTd2

    I’ve been trying to access this site for a few days. It seems to work for everybody in other countries, except for me, no matter what ISP I used. Now, I used a foreign proxy, and finally accessed it. Could it be that NASA is blocked Brazil to access this site?

  • http://deleted Secret American Planck Basher

    Energy scale of inflation. Is it really “important”? Yes, in the context of inflation models, but I don’t see it as having much of an impact beyond the “conclusions” section of Yet Another Inflation Paper. It will kill 60% (? — high side) of models on a good day, but it won’t open up vistas. Once upon a time there was the consistency relation, a lot harder to check, but today even that’s old hat.

    Measurements to smaller scales. Once past 10 arcminutes or so, you’re in the damping tail and will learn nothing more of the early universe. Getting l of 700 won’t really help much with l of 3000 except you might know the input cosmological parameters a bit better.

    As for the other benefits you mention. Yes, of course there will be a lot of data. I just don’t see it as really changing things, pushing the field, in new directions. And I say that as a guy with Kolb and Tuner on his desk and a couple of early universe ideas out in the literature and in my head. I wish there was a measurement from Planck that I’d be truly excited about, but right now it’s a grab bag of things that other places will cover as well.

  • Lawrence B. Crowell

    Jason Dick on Mar 10th, 2008 at 1:19 pm
    Secret American Planck Basher,

    Well, the free parameter in question is a pretty important one, in my view: the energy scale of inflation. Pinning down the energy scale of inflation is a pretty big step in making any significant statements about what inflation actually is.

    —————–

    In cosmology the time dependency of the metric coefficients means there is no Killing vector which as an isometry defines an energy conservation. As strange as it might sound, conservation of energy in cosmology is not definable. The only conservation law we really have is the continuity equation

    $latex
    nabla_aT^{ab}~=~0
    $

    plus conservation based what ever spatial killing vectors might exist.

    Lawrence B. Crowell

  • John Merryman

    Spaceman,

    According to Inflation theory, it is many, many times the size of the visible universe. To the point that, from our perspective, it is just about spatially infinite. Curvature seems mostly a function of the time dimension, in that the analysis of redshift and CMBR says it is only13.73 billion years old.

    http://en.wikipedia.org/wiki/Cosmic_inflation

    “Cosmic inflation has the important effect of smoothing out inhomogeneities, anisotropies and the curvature of space.”

    Basically it explains how the factors which suggest an infinite universe can exist in a finite model.

  • Lawrence B. Crowell

    If inflation expanded a small spherical cosmology into a flat spacetime, this spacetime may well be of infinite extent. A finite cosmology, or a three dimensional ball with a two dimensional boundary, requires that boundary conditions exist there. This is somewhat problematic. However, even for an infinite dimensional R^3 space the topology change likely means that some topological information is either lost (destroyed) or is transformed into some other form. What that is is difficult to say, maybe a ‘t Hooft-Polyakov monopole.

    Lawrence B. Crowell

  • John Merryman

    Lawrence,

    Doesn’t the Uncertainty Principle essentially show that some information is destroyed in the very process of measuring other information?

    Since I view time as a consequence of motion, rather than the dimensional basis for it, I think monumental amounts of information are destroyed and replaced every moment. I would posit the current credit meltdown, as well as the rest of history, as proof.

  • Lawrence B. Crowell

    Quantum mechanics is the unitary evolution of a wave function, which completely preserves quantum information (Q-bits). Quantum fluctuations are really a manifestation of measurement, or some decherent process, when a quantum system couples to some unspecified set of states. These states can be in a measurement apparatus. Yet pure quantum mechanics is perfectly time reversal invariant and preserves all the information in the initial conditions of a quantum system.

    Lawrence B. Crowell

  • John Merryman

    Lawrence,

    If time is a measurement, than what physically exists is perfectly conserved, as it passes from one macro-state to the next. It is only these macro states that are created and consumed.

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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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