Goddamn Particle

Hey, did you hear that Planck released its results today? The universe remains preposterous, if still pretty awesome. And it might be lopsided, which is intriguing.

Planck says that dark matter makes up 26% of the universe, while the best-fit WMAP number from a few years ago was 23%. This led me to joke on Twitter that we needed a model in which the dark matter density was rapidly increasing. Just a joke, people!

I hope to say something more substantive soon, but in the meantime there’s plenty of good stuff around the web; at the risk of leaving many people out, see Ethan Siegel, or Jester, or simply refuse to see the universe through anyone’s filter but your own and read the original papers. (An even thirty of them, helpfully indexed by the ultramodern system of Roman numerals.)

Meanwhile, our old friend the Higgs boson has not gone away. Here’s the second of the videos I did for Sixty Symbols while visiting the UK (after the first one I did on quantum mechanics).

The comments on the YouTube page are nicer than average. Maybe it’s the British temperament.

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31 Responses to Goddamn Particle

  1. I thought the two videos for Sixty Symbols were superb. You’re really good at this ‘explaining’ lark. Also, I’ve to come to think of Brady Heron as a remarkably able interviewer. More video/Tv appearances, please, Sean. You really help with the learningz.

  2. Vince Mounts says:

    I think you mean “Sixty Symbols” not “Sixty Seconds.”

  3. Bill Brett says:

    “Priceless” “interesting” “talented, bright” “fascinating”

  4. Sean Carroll says:

    Vince, thanks for the catch. Much longer than Sixty Seconds!

  5. zoidberg says:


    Have you read Thomas Pynchon’s “Against the Day”?

  6. Jay says:

    “Planck says that dark matter makes up 26% of the universe, while the best-fit WMAP number from a few years ago was 23%. This led me to joke on Twitter that we needed a model in which the dark matter density was rapidly increasing.”

    Let’s hope Rupert Sheldrake isn’t following you on Twitter.

  7. Tony Rtz says:

    No need to swear! I get your point. Holy have a cow.

  8. Marshall Eubanks says:

    “Planck says that dark matter makes up 26% of the universe, while the best-fit WMAP number from a few years ago was 23%. This led me to joke on Twitter that we needed a model in which the dark matter density was rapidly increasing.”

    Better watch out – in that model the universe would be completely dark matter in about 2 centuries, assuming that it stays at closure density. After that, the cosmological constant would have to change sign, which I guess would please some string theorists.

  9. James Goetz says:

    Well, if dark energy is constantly increasing, then why not an increase of dark matter? :-)

  10. David Yerle says:

    Am I the only one who gets disappointed after each single big announcement in physics? Where are the cosmic strings and all the super-exciting stuff we were hoping to see? I don’t think I can bear another “yes, well, the data fits our current models” anymore. I need some novelty. Something unexpected.
    Come on, universe. You can do better.

  11. Brett says:

    Something unexpected was that the universe doesn’t appear to be evenly distributed and it’s not an instrumental error. There is a large cold spot and the “axis of evil”. So both inflation theorists and fractal cosmologists on the fringe are pretty happy.

  12. David says:

    I am a scientist but not a physicist but find this stuff really interesting. Can I ask what may be a silly question. General Relativity is premised on the universe being homogeneous and isotropic on very large scales. Do these results which show non homogeneity isotropy impact on GR?

  13. Oliver says:


    General Relativity does not require a homogeneous and isotropic Universe. The solution to the Einstein equations that cosmologists use to model the universe assumes a homogeneous and isotropic spacetime ( http://en.wikipedia.org/wiki/Friedmann-Lema%C3%AEtre-Robertson-Walker_metric ), but there are other cosmological solutions as well, for example: http://en.wikipedia.org/wiki/Mixmaster_universe

  14. David says:

    Oliver thanks for this. If I could ask one more question which I am sure other people will address. Does the data help in any way to answer the horizon problem and provide answers to the alternative models of inflation?

  15. Plato Hagel says:

    Ed Copeland has a nice video that one might enjoy concerning Planck predated info.

  16. David Lau says:

    Great video. Sean, I tweeted you on last week about the errors on pp294 in your new book, the appendix on particle zoo for fermions. It is just a minor print error, and it’s not all that critical. I finally finished reading the book. Took me a while as I have been busy.

  17. Ned Wright says:

    Actually the dark matter density has changed rather little. But the Hubble
    constant is down, so the critical density is down by the square of H0.
    So the cold dark matter density went from 2.17 +/- 0.04 yoctograms per cubic meter in the WMAP9 analysis to 2.23 +/- 0.032 yoctograms per cubic meter in the Planck analysis, which is only a small change (<3%) and in the noise.

    The dark energy density changed more, from 3607 +/- 144 eV/cc in WMAP9 to 3352 +/- 125 eV/cc in Planck, which is 7% change, but still in the noise.

  18. martenvandijk says:

    “Lopsided”: seems quod erat expectandum to me as time is slower/faster where mass is more/less abundant and therefore histories of events did unfold slower/faster into directions where mass was more /less abundant.

  19. Tony Rz says:

    A perfectly mysterious Universe!! Just what all the Theorists would desire. As time goes on it will become more so.

  20. Gizelle Janine says:

  21. BobC says:

    Hi Sean,

    I was reviewing the latest Higgs boson/mechanism details, got into a Wikipedia link-a-thon, and finally (and quite logically, for once) wound up here: Unanswered Questions in Physics

    Is the list complete, in your view? Which of the above are most closely related to your own research? If you were to rank them by personal interest/fascination, how would they be ordered?

  22. Tony Rz says:

    I hope everyone had a happy Easter!!

  23. Anton Szautner says:

    Just saw the NASA news conference announcing the AMS results…

    Not a single graphic of the spectrum was offered to SHOW anything described.


    I don’t care about whether or not AMS was a good idea, how many people worked so hard over such a long time on it, and so on. All of that is properly splendid and impressive. Nobody doubts how hard it was to get that thing up and where it now observes.

    Its there already and collecting data, and Dr. Ting has announced that about a tenth of the data has indicated a signal worthy for publication.

    Good! Magnificent! Outstanding!

    So where are the visuals that back up what Professor Ting and the rest of the panel say – any data to show (pictures of the experiment attached to the ISS isn’t enough).

    Not there – besides verbal description offered by Ting with hand motions.

    And that within the context of one response by him that science cannot be conducted upon preconceptions.

    That was an example of how not to perform a press conference – the worst since the claim for arsenic metabolism – evidently they didn’t learn from that.

    This press conference seemed to go downhill rapidly after the opening remarks; the fellow on the right side of the panel smirking the whole time as if he held some sordid secret (though he offered a short statement that ‘contributed’ to the agancy line…’um, okay?… okay?…okay?’)

    Man that was hard to watch.

    There’s something very wrong there, and bureaucracy – as well has personal responsibility and honesty – no doubt has a hand in it.

  24. Marshall Eubanks says:

    There is a nice graph + discussion here :


    and the actual paper is here (paywalled, alas)


  25. Marshall Eubanks says:

    Oh, now I see it is available for free


    Lots ‘o graphs…

  26. Bob Iles says:

    Say, Prof. Carroll, do you realize that you’ve been libeled on TED? There’s a coupla crackpot cranks whose lectures got kicked off the main TED menu & they’re quite upset about it. They accuse you of just “copying Wikipedia” in some kind of rebuttal you made on the speed of light. I don’t remember all the details but here’s the URL for the discussion: http://blog.ted.com/2013/03/14/open-for-discussion-graham-hancock-and-rupert-sheldrake/

  27. @Bob Iles,

    while you can find the TedX talks a ‘little out there’ I think ‘coupla crackpot cranks’ oversimplifies a little. Wikipedia has this on Rupert Sheldrake (a singleton of the “coupla'”):

    …. He obtained a scholarship to study Biology at Clare College, Cambridge. He specialized in biochemistry, graduated with double-first-class honours, and won the University Botany Prize. He won a Frank Knox fellowship to study philosophy and history at Harvard University at around the time Thomas Kuhn’s The Structure of Scientific Revolutions (1962) was published, which he writes informed his view on the extent to which the mechanistic theory of life is just a paradigm. He returned to Cambridge, where he obtained his Ph.D. in biochemistry ….

    Clearly a smart guy whether right or wrong … and perhaps Prof Carroll can set me straight, but one of the bushes Sheldrake was shaking in his talk was the tree of universal constants. It is my understanding that, putting whatever happened to C between 1928 and 1945 aside, there is indeed a lot of questioning as to when, and if, certain cosmological constants became constant (and, all punning aside, certainly the Cosmological Constant is anything but).


  28. halooza says:

    I don’t understand the argument over a recorded changing speed of light between the late 18th century and today. Or even the 20s and 40s. Technology improved…therefore…our ability to accurately measure the speed of light improved. We noticed errors in our earlier experiments and fixed them. I thought this would be common sense.

    Hey, did you know that the speed of electricity has been getting faster and faster?! A steady trend in the speed of electricity can be observed when looking at the data. Every 18 months, IT DOUBLES! My new iphone and my new computer are twice as fast as my old ones, therefore, the speed of electricity must increasing over time.

  29. Sean Carroll says:

    Bob, if I wrote a careful reply every time a crackpot said something wrong about me, I wouldn’t get anything else done. :)

    There are many respectable scientists (including me, or at least “as well as me”) who study the possibility that physical parameters vary with time, both theoretically and experimentally. For the most part they understand the concept of error bars, as well as how different parameters are related to each other, neither of which Sheldrake has any clue about. Life is too short.

    Alan, if you think that winning an undergraduate prize in botany is good evidence that someone is not a crackpot when talking about physics, you need to raise your standards a bit.

  30. Bob Iles says:

    Thanks for your reply, Prof. Carroll. It certainly entered my mind as well that you wouldn’t have time to respond to every crackpot. :) I just wanted to let you know that this libel was out there, in case you hadn’t been aware of it. And I agree about the botany prize. In fact, as soon as I saw that his Ph.D. was in biochem., I started to wonder what the heck he thought he was doing pontificating about physics!

  31. MKS says:


    do you think there could be dark matter life?