Planck Results

The long awaited CMB results from the Planck satellite are now out, see here. A NASA press conference is about to start here.

You really should be reading about this somewhere else, from a much better informed blogger, someone expert in cosmology, which I very much am not. My non-expert impression is that, as rumored, the results are quite vanilla: 3.3 +/- .3 [Richard Easther had 3.2 +/- .2, don’t know why] light neutrinos, so no evidence for a fourth neutrino, no significant non-gaussianity. No cosmic strings, see here, which has

conclusion that there is at present no evidence for cosmic strings in the Planck nominal mission data.

In recent years multiverse mania has involved lots of claims to see evidence of other universes in earlier CMB data. Nothing about this in the Planck announcements I’ve seen, presumably they looked and didn’t find anything, or maybe thought it wasn’t even worth looking…

I’ll try and make a list of informed commentary that I find, and keep a list here. Suggestions for additions are welcome.

Richard Easther live-blogged the announcement here.
Sesh Nadathur has comments here.
Ethan Siegel has a posting with background here.
The word from Resonaances is here.

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26 Responses to Planck Results

  1. Ehud Schreiber says:

    A crucial quote from Easther’s blog: “… there is no use of polarization data — this is being worked on, but it will make a big difference when it becomes available.”

  2. Sesh says:

    Yes, there’s not much in the data for particle physicists to get excited about, though there are a few interesting little anomalies, including the fact that the best-fit Hubble parameter value is getting further away from the one that is measured by the Hubble Space Telescope team.

  3. Peter Woit says:

    Thanks Sesh,
    Added a link to your blog to suggested reading about this.

  4. Filip says:

    I follow this blog and there is a nice story about the new findings (including a nice introduction on the matter, good for non experts like me).

  5. ohwilleke says:

    The result I read in paper sixteen was Neff=3.30 +/- 0.27 v. Neff 3.046 for the three Standard Model neutrinos. So, their result is a little less than one sigma from the Standard Model value. A four neutrino model would have an Neff of a bit more than 4.05, which is about three sigma from the measured value which is roughly a 99% exclusion and is a confirmation of the Standard Model.

    Planck also combines data from multiple sources puts a cap on the sum of three neutrino masses in a three Standard Model neutrino scenario of 0.24 eV (at 95% CI) with a best fit value of 0.06 eV. The floor from non-astronomy experiments is 0.06 eV in a normal neutrino mass hierachy (based on the difference between mass one and mass two, and between mass two and mass three which are both known to about two significant digits) and 0.1 eV in an inverted neutrino mass hierachy. In a normal neutrino mass hierarchy, this puts the mass of the electron neutrino at between 0 and 0.06 eV, with the low end preferred (I personally expect that an electron neutrino is significantly less than the mass difference between the first and second neutrino type of about 0.006 eV).

    Note that a particle that is in the hundreds or thousands of eVs would not count towards Neff because it is not light enough to be relativistic at 380,000 years after the Big Bang. So, it really only rules out a light sterile neutrino, rather than a heavy one. The LSND and MiniBooNE reactor anomalies have hinted at a possible fourth generation sterile-ish neutrino of about 1.3 eV +/- about 30%, so the Planck people did a study on the sum of mass limits if there were a disfavored four and not just three relativistic species and came up with a cap on sterile neutrino mass in that scenario of about 0.5 eV +/- 0.1 eV, which is about 2.5 sigma away from the value of the LSND/MiniBooNE anomaly estimates considering the combined uncertainties.

    LEP ruled out a fourth species of fertile neutrino of under 45 GeV, and I wouldn’t be going out on a limb to say without actually doing the calculations that a fertile neutrino of 45 GeV to 63 GeV, if it existed, would have wildly thrown off all of the Higgs boson decay cross-sections observed (since a decay to a 45 GeV to 63 GeV neutrino-antineutrino pair from a 125.7 GeV Higgs boson would have been a strongly favored decay path if it existed) and is in fact therefore excluded by the lastest round of LHC data. The LEP data already excluded fertile neutrinos in the 6 GeV to 20 GeV mass range where there are contradictory direct dark matter detection experiment results at different experiments.

    But, a particle that we would normally call a sterile neutrino for other purposes in the Warm Dark Matter mass range of KeV or the Cold Dark Matter mass range of GeV to hundreds of GeV, or anything in between (including any of the possible direct dark matter detection signals or anything that would generate the Fermi line at 130 GeV), would not be a relativistic particle within the meaning of Neff which only counts particles that would move at relativistic speed given their masses at the relevant time.

  6. fuzzy says:

    Oh gosh, there is no evidence for sterile neutrinos! But … so many theorists have speculated on this possibility in the recent years, that at this point it is really necessary to ask oneself: What should we think of them?

    Do you think that their job is anyway justified, like that of a lousy actor? They have been unlucky, as a poker gambler could be? Or, they tried to do something legitimate, as a lawyer who tries an ambiguous cause? Or, rather, we should say that they haven’t been able to understand the nature, they failed their goal of scientists, and misled other colleagues?

    What I think is evident, but I do not believe that their failure will leave any track in their record. Rather, their useless work will have served to increment the list of people who cited them: thus, in good company, they will be ready to do a new mistake. That’s how the circus works!

  7. Peter Woit says:


    You’re rather harsh…. I rather think that one should feel the pain of those engaged in trying to find a viable theory that goes beyond the SM, since that has so far been impossible. It may be that the neutrino sector is our only hope left to see non-SM physics (i.e non SM with neutrino masses).

  8. useless says:

    Why is their work useless? It is easy to forget now that, back in the 1920s, to explain the continuous energy spectrum of beta decay electrons, Bohr, Kramers and Slater were willing to say energy is not conserved in individual decays, only statistically overall. Bohr was willing to consider that the electrostatic potential was not 1/r but 1/r^{some other power}. As for nuclei such as alpha particles, to explain the charge/mass ratio, Rutherford and many others believed in nuclear electrons.

  9. fuzzy says:

    Dear Pete, searching for theories is an important activity, sure, but one thing is to do this by sticking to good principles, one thing is to follow fashions. I know there are serious scientists who are trying their best, but also too many people working as such, that rather of being engaged in searching for a theory, are busy in searching an opportunity of publishing, citations, prestige and such. I also feel that neutrino physics is a promising avenue, first of all because there are useful measurements, but this does not mean that anything connected to neutrinos is a valid starting point. A good theorist (working in neutrino physics or elsewhere) should be able to know the difference between what is valid and what is of little value somewhat in advance, I feel.

    Dear “useless” (dear colleague 🙂 thanks for the relevant feedback. In my view, one thing is to speak of solid experimental fact, another thing is to exaggerate the relevance of facts not fully assessed and partially contradictory among them. We knew that this type of sterile neutrinos that are being discussed were a muddy hypothesis, even without the Planck satellite (though it was possible to select the facts that one wanted to consider). Moreover, I remember that “not even wrong” is a sentence of a guy who was very prudent in publishing his ideas, including those on continuous beta spectrum, that have superseded the wrong hypotheses of Bohr. I think we should rather strive toward Pauli, Schrodinger, Feynman rather than exercising our unchained imagination or to show our talent in producing sexy names or forcing experimentalists to do some more measurement.

  10. Sesh says:

    I think the reason Richard Easther quoted Neff as 3.2 +/- 0.2 was because that was what Efstathiou said in the first media briefing. I don’t know why that was – either both Easther and I misheard, or maybe Efstathiou just misremembered the numbers.

    Incidentally, if combined with recent measurements of the deuterium fraction by Pettini and Cooke, the Planck constraint on Neff is even tighter: 3.02 +/- 0.27. I’m not sure how much these deuterium measurements are trusted though.

  11. physics_dude says:

    I’m a little confused, Peter. I’ve read about two anomalies that cannot be explained by the standard cosmological theory — anomalies that were first detected by WMAP, and have been detected again by PLANCK. Yet, both you and Jester dismiss it. How come?

  12. Peter Woit says:


    I’m no expert, so relying on others. Jester and most of the other experts I’ve read about this don’t seem to find these anomalies to be of great significance, and their arguments for why seem to me compelling. But, for more details, you need to ask them.

  13. Low Math, Meekly Interacting says:

    Perhaps I’m wrong, but my understanding now is that even if one could come up with a reasonably compelling explanation for the anomalies, their nature makes it impossible to rule out their being a statistical fluke…unless we can start observing other “universes”.

    I’m a bit chagrinned to learn that the Planck data are quite literally as good as it will likely get when it comes to observations of the CMB. That would seem to bode rather poorly for the prospect of getting greater cosmological insights to BSM physics any time soon.

  14. ohwilleke says:

    “I’m a bit chagrinned to learn that the Planck data are quite literally as good as it will likely get when it comes to observations of the CMB. That would seem to bode rather poorly for the prospect of getting greater cosmological insights to BSM physics any time soon.”

    We at least have weeks or months to absorb this round before the polarization data becomes available. This data, among other things places meaningful bounds on quantum gravity theories.

    Also, while our observations of the CMB won’t necessarily get all that much better, data from other sources should make it possible in combination with Planck data to leverage more out of it. For example, if we can determine the neutrino masses and hierarchy independently of Planck, this allows us to very finely constrain the properties of anything other than the three known active neutrinos that shows up in Neff.

    Similarly, if we used extra solar system deep space probes to make paralax distance measurements of unparalleled accuracy, we could discern if any part of the estimate of the cosmological constant and Hubble parameters corrected for by Planck and attributed to factors like uncertainties in red shift measurements for Standard candle Ia’s in fact has any possible other source.

  15. Alessandro Melchiorri says:

    A sterile neutrino is perfectly consistent with the Planck data.
    If you actually look at the real numbers here:
    you see that Planck alone gives Neff=4.5\pm1.4 at 95% c.l., while Planck+HST
    3.7\pm0.5 at 95% c.l..
    In few words is just when you combine with ACT data (the highL dataset) that you get a lower number.
    The Planck collaboration preferred to be conservative and has put 3.3\pm 0.3 at 68% c.l. in the abstract, but there is plenty of space for a fourth sterile neutrino (that does not necessary gives you 4.05 ! it depends on how and when it decouples from the primordial plasma !) and it is actually suggested if you combine with HST. The value of the Hubble constant from CMB is indeed model independent and if leave the neutrino number as free you get a very good agreement with HST.

  16. Alessandro Melchiorri says:

    sorry I meant model dependent ! 🙂

  17. Richard says:

    while our observations of the CMB won’t necessarily get all that much better

    I’ve read that a couple places, but I’m unclear on its meaning.

    Is is that angular resolution and spectral resolution are at physical limits? If so, are these limits those of any detectors or are we talking cosmological fuzzing so detector physical limits are irrelevant? Are Earth orbit and launch-feasible detector size any constraint?

    (I know the argument that accelerated expansion will leave our galaxy alone in a black universe, but in the meantime?)

    Pointers appreciated. It’s something of a novelty to be in possession of the best possible data.

  18. Sesh says:


    For the temperature anisotropies, the limiting factor is cosmological. The process of recombination, which is what makes the universe transparent to photons, is not instantaneous. As a result, photon diffusion washes out anisotropies on small scales, which is what causes the exponential damping of the higher peaks in the power spectrum (this is called Silk damping or diffusion damping).

    So getting better angular resolution doesn’t help – at even smaller scales there essentially aren’t any anisotropies there to measure. (Of course, this is a relative statement: if you could build a reference blackbody with an order of magnitude better temperature stability and put it into orbit, you could measure smaller temperature differences.)

    In terms of polarisation measurements though, Planck isn’t quite at the achievable limit. Here there are other experiments planned. And one could also measure distortions of the blackbody spectrum of the CMB, which provide a different probe of inflation, and for which the best experimental constraints available still come from COBE/FIRAS.

  19. Shantanu says:

    Peter one thing to note, although I maybe wrong on the finer details,
    limit on energy scale of inflation is around the GUT value, so another
    blow to GUT.

  20. David Nataf says:

    Observations of the CMB could very much improve with future experiments by better removal of background.

    We are in the Galaxy, and as such an important souce of microwaves are …. the Galaxy… as well as background Galaxies giving sources everywhere.

    Planck has to remove all of this:

    Before they can give a CMB map, which is extremely hard, and is not done perfectly at this point. They also need to account for the fact that foreground galaxy clusters lead to lensing of the CMB photons, as well as the Sunyaev Zeldovich effect, for which you will find separate papers already out, and countless more in the future.

    There is a lot more work to do in CMB science.

  21. Low Math, Meekly Interacting says:

    Thanks for clarifying perspectives, David & Sesh!

  22. paddy says:

    Thanks to Peter, Sesh, David, and all the knowledgeable commentators’ for their blather and links to even more blather. And note…blather is NOT meant as a derogatory term.

  23. Pingback: Planck results on the CMB, and latest on the Higgs | Mostly physics

  24. Gian-Luca says:


    do the new results from the Planck satellite shed any light on whether the cosmological constant decreases with time? You discussed this topic in some of your previous blog posts. The issue would be of interest to many!


  25. Peter Woit says:


    Not sure what you’re referring to, I’m not very well-informed about whether there’s evidence for a time-varying CC. I don’t see any reason Planck would have results about this, and haven’t heard anything about it. If they did have such results, I assume they would be well-publicized.

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