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:
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.)
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.
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….
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
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.
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?
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.
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
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.
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
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.
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
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.
Pingback: The Lopsided Universe | Cosmic Variance
Pingback: WMAP 5-YEARS
Pingback: A Special Place in the Universe | Cosmic Variance
Pingback: Dipolo CMbr: acelerando a través del Universo | Imagen astronomía diaria - Observatorio