Capping a Big Week for Astronomy

By Sean Carroll | August 24, 2006 5:21 pm

Friday afternoon I’ll be on NPR’s Science Friday to talk about the recent dark matter results. Nothing that regular readers haven’t heard already, I suspect.

(Update: the audio files are on the right-hand side of this page. At least the mp3 file seems to be working. It was a short-but-sweet segment.)

We’ll share the show with an update on Pluto’s status. A quick query of Google News reveals that there have been about ten times more stories about Pluto than about dark matter. This despite the fact that the Bullet Cluster data have taught us something profound about the constituents and forces of our universe, while the “planet” business has taught us about the vote of a committee on what to call stuff. Why is that?

Dark Matter Motivational Poster

(Motivational poster generator found via La Blonde Parisienne.)

CATEGORIZED UNDER: Science and the Media
  • twaters

    Probably because we can only beat Turkey when it comes to taking science seriously

  • mollishka

    Oh wow. I’m totally not a poster person, but I…. I want that poster. I will need to have a talk with our color printer….

  • Lee

    A “decision” on whether or not Pluto is a planet is a simple story; on the other hand, any story about dark matter, no matter the significance, is so relatively complex that several things are necessary to make it understandable: a smart science writer or broadcaster with a wide audience who knows the significance of this story; an ability on his or her part to make the story intelligible to a wide audience (and as good as your blog entry on this the other day was, it would have to be a lot shorter to fit into the average newspaper), and an intelligent, educated audience that would take the time to read the entire article and gain a bit of understanding. Unfortunately, even if you can assume the first two, the last is tough. I think a lot of people are interested in this story because they still confuse astronomy with astrology.

  • Elliot


    Point taken. Remember however George Bush was elected president here. Lesson: People like simple messages that they can relate to not complex “intellectual” stuff they don’t understand.

    Is this the way things should be. Hell no. But its the way they are.


  • Cynthia

    Simply bad astronomy: Pluto eclipses dark matter

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  • jay

    Humans are political animals. They like to vote or like to talk about votes. Even if you nailed down something profound, you don’t get much attention if it doesn’t have anything to be dramatized or politicized. Look at the recent flurry of media attention about Perelman’s proof of Poincare’s conjecture. In this week’s issue of New Yorker Sylvia Nasar, the author of “A Beautiful Mind”, even introduced a ugly, manipulative, power-craving (of course Chinese) mathematician to contrast with pure-minded unworldly Grisha Perelman. How dramatic it is! 😉

    Sean, if you are unable to dramatize the recent finding about dark matter, forget about people’s not getting the importance of the discovery. “What do you care what other people hype about?” You tell listeners what you think a profound discovery, then a handful of them might be inspired to become budding astrophysicists who will carry the torches down the generations. Isn’t that enough for you or for all humanity?

    By the way, I will be happy to be among listeners (of course via ipod).

  • weaklens

    Hi Sean,

    The main result of the dark matter paper was actually published in ApJ
    about two years ago.
    The new paper (the short one, not the long one with strong lensing
    results) only increases the significance of the result by adding more

    It’s a bit sad to see that many people become aware of about this important
    result only when it goes press released.

  • George Musser

    For most people most of the time, scientific research is little more than received wisdom. But the question of defining “planet” has been a debate in which they could meaningfully participate. A lot of people gave thought to scientific issues. They learned something. I think that is to be celebrated.


  • jamie

    Rather than being upset by dark matter’s being upstaged by Pluto, I find it heartening that the general public takes so much interest in the Pluto matter at all. Both dark matter and Pluto are, admittedly, topics that have almost no relevance to most people’s daily lives.

    As Lee mentioned, the concept of dark matter is not easy to understand without sufficient background, and as jay mentioned, humans are political (social) animals; part of the reason the planets arouse so much public affection is because they’re not only easy to understand, we’ve also anthropomorphized them to some extent, giving them gods’ names and personalities. We learn about them in second grade, not in college.

    People love SETI because of the notion of there being sentient creatures similar to ourselves somewhere out there; apart from the planets and SETI, astronomy primarily interests people via pretty pictures. Aesthetics do not take a background in physics to “get.”

    Let’s not be too elitist about this matter (hah, a pun). Just think of how many people have similar affections for dinosaurs, zoo animals, volcanoes, earthquakes, other natural disasters, sharks, fast or fantastic vehicles, aeroplanes, rockets. Just remember how so many people know nothing about ancient Egypt except — mummies and pyramids!

    Fine, so people are drawn by simple things. Personally, although I know dark matter, I don’t know a jot about Egypt except mummies, nothing about old France except Napoleon, not a damn about music except that Bach and Beethoven once existed and their music strikes me at the core of my soul. I can’t diagram a sentence or analyze a novel, though I love to read. I’m sure that must frustrate somebody somewhere.

    Let us use what does draw people, and encourage them onward to a deeper and more satisfying understanding, if they are so inclined. Frankly, I think it’s great that so many people stop me at parties or at the grocery store and ask excited questions about planets, asteroids, and Kuiper belt objects.

  • Allyson


    I am a bit fortunate in that while I know little about science, I know enough physicists to be able to interpret things like this for me in ways I can understand…sometimes through drawings and interpretive dance. It doesn’t make me stupid, which is what I’m gathering from Elliot’s post, which seems to conflate ignorance with stupidity. If one has never seen or heard of an elephant, it isn’t useful to give him/her a discertation on the cruelty behind the ivory trade without first giving the person the information needed to understand that ivory comes from an animal called an elephant. And perhaps showing the person a film, photograph, and drawing of said elephant.

    The person isn’t necessarily stupid for not knowing what an elephant is if the information is out of reach.

    This is sort of how I feel about subjects like Dark Matter. I’d never heard of it until recently, and even then, it was presented to me as ivory, a piece of a greater thing I didn’t know existed. It’s not my fault, I’m not a Bush-voter or a moron, I’m just an average schmo occasionally wonderstruck by the universe and the stuff that floats through it. I’d like to know more, but it’s rare that the information is presented to me in a way I can grasp.

    It’s like asking me to picture the elephant after a bomb was placed in its belly, and figure out what it might all look like from the bits and pieces I can pull out of nearby shrubs.

    I need to know what the big picture is in simple, elegant terms that draw on what is already familiar to create an understanding, and then we can go from there.

    I’m getting a sense that the common belief is that people don’t care about discoveries like this because they’re stupid. But I think it’s more of a case that people don’t know about these discoveries because the information is presented in a way that assumes the reader is already knowledgeable in physics or astronomy. And so it’s out of reach and sounds like gibberish. I didn’t take a science class any more advanced than what a lot of you probably learned in the eighth grade. I still loved Cosmos, you know? But I’m still curious enough to try and pick up as much of an understanding as I can from the remains of the exploding elephant.

    There was a point in there, I swear. I think the point is, I am offended! Very offended! And I demand reparations for my people. I think.

  • jamie

    By the way, check out this article for further insight into why people like Pluto and not dark matter.

    Ex-Planet’s Fans Voice Dismay and Sorrow – New York Times

    Choice quote:

    Pluto, we hardly knew you. Indeed, across the country, and presumably the universe, the news that Pluto was no longer considered a full planet was met with a mix of surprise and shrugs, even as people struggled to eulogize a cosmic entity that most know very little about except its size (small), its distance from Earth (great) and its weather (terrible).

    The main effect, in fact, seemed to be to mystify further a populace that already seemed almost universally confused about the former planet.

    “I think its probably a star,” said Nick Sbicca, 22, who was visiting the Exploratorium, the children’s science center, on Thursday. “I really don’t know. But I think there’s definitely more than eight planets.”

    Sure enough, the kids quoted in the article know more about Pluto than the adults do. And you know what? It simply doesn’t matter that Mr. Sbicca thinks Pluto is a star, as far as facts go. What it may signal is what we really ought to worry about: a public that finds it difficult to comprehend and evaluate statements and arguments regarding logic and policy, not only in science but in many other arenas. That is a far larger problem than whether they care about dark matter. All the more encouragement toward knowledge and understanding is necessary.

  • jamie

    cheers to Allyson, who hits the nail on the head. We need more Carl Sagans. Anyone want to volunteer for the job? And yet, unfortunately, within academia and the scientific community we tend to denigrate those who pursue public education rather than research; they are not “serious” enough. Education is “fluffy.” But public education is a very serious matter.

  • Sean

    There seems to be an awful lot of point-missing going on here. I’m very happy that the Pluto discussion got people talking about astronomy; who wouldn’t be? But the news hook wasn’t new science, it was a vote taken by an assemblage of old men in Prague. That’s fine — but it wasn’t really made clear in any of the news stories I read. The dark matter stuff is huge news, truly a deep insight into the nature of our universe. And not in any sense overly complicated or beyond the grasp of non-experts — in fact it was quite straightforward, easily explainable in under a minute, and illustrated with gorgeous pictures. You don’t think that such a story could have been an even better hook to get people excited about astronomy? Really? Who is being the elitist here? The truth is, people will be interested and excited if we (scientists, journalists, knowledgeable amateurs) make the effort to explain what’s going on and respect their intelligence enough to give them the good stuff.

  • John S Costello

    I’ve watched the animation and looked at those pictures, but seeing the motivational poster something struck me: most of the visible mass is supposed in those gas clouds! All those galaxies? Pipsqueaks, comparatively.

    That’s somewhat hard to believe, that most of the mass is in a relatively unformed state. Is that usual? Is the Milky Way sitting inside a massive cloud of gas that we just don’t see?

  • Eugene

    We lost Pluto?


  • jamie


    Knowing that Pluto has been demoted requires only that you understand that all your life there have been nine planets, nine little worlds in our own corner of the universe, and now there are only eight because one is so small that it “doesn’t count.” Heck, you don’t even have to be able to read the news to understand. This is new science to Joe or Jane simply because it is a change to what they have known. And if three thousand scientists are discussing it, it must be important.

    Understanding dark matter requires background. Most journalists are not equipped to explain dark matter, even on a basic level. And they are relatively educated. Plus, many scientists are abominable writers. (Fortunately you seem to do a pretty good job.)

    In other words: dark matter exists. Uh, well, great. What’s that and why should I care? What do you mean, it’s an insight? Never heard of it. Heck, I don’t really even know what the Big Bang is. I heard scientists think the Earth got randomly exploded into existence. But, but, My Very Educated Mother Just Showed Us Nine Planets! Oh, well, Eight now, but that messes up the mnemonic.

    I think you are overestimating not the average person’s intelligence, necessarily, but their body of prior knowledge. The dark matter stuff can be understood on a basic level only if you have a basic grasp of a handful of other things. And its profundity can really only be felt if one has been following the story for some time. One in five American adults does not even know that the Earth goes round the Sun.

    Of course, this is a damn shame! Of course, more people would be interested if we did a better job of conveying both information and enthusiasm! But I think that even the best, simplest exposition on dark matter would not reach as many Americans as Pluto does.

    Perhaps a more interesting question is how dark matter and Pluto are being covered in the popular press in Swedish and Japanese, and whether their journalists are able to appropriately cover both issues.

  • Malte

    The tabloids covered both Pluto (Aftonbladet and Expressen) and the dark matter discovery (though only with a short news agency reports, like this one in Expressen).

    Broadsheet Dagens Nyheter, thanks to blogger-turned-journalist Malin Sandström, covered both (Pluto with a series of reports like this one here and one on dark matter) quite nicely.

    More interesting would be to hear from places like Iran (where amateur astronomy is huge), or other places where science really is still popular (Uganda I think).

  • PK

    I think the NPR public is not quite the same as the Discovery Channel public, and many listeners might already have heard of dark matter. Sure, they will remember foremost that Pluto is no longer a planet, but a story about clusters of galaxies moving through each other and heating up interstellar gas will probably also excite a lot of people.

  • GB

    “A quick query of Google News reveals that there have been about ten times more stories about Pluto than about dark matter.”

    I think there is a misinterpretation here. The above information is not an idication of how much people are interested or care about Pluto vs DM, it is an indication of how much journalists believe that people will be interested or care or be impressed about Pluto vs DM, plus their ability to write for the one or the other subject.

    As to why they have this impression, perhaps they think that Pluto demoted is more gossipy. No doubt some smart aleck will have tied it up with American Idol.

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  • Malte

    GB says: The above information is not an idication of how much people are interested or care about Pluto vs DM, it is an indication of how much journalists believe that people will be interested or care or be impressed about Pluto vs DM, plus their ability to write for the one or the other subject.

    With my journalistic hat on, the Pluto story has been far, far more fun to follow and write about than the Bullet cluster result. The IAU did marvellous pictures to accompany the original resolution (and I really didn’t expect them to do this well at all), then the drama just got better and better as the week went on. Plenty of interest, and plenty of astrophysics if you wanted that too.

    The DM result is, well, another very nice DM result with some pretty pictures. But I think we’d need a dark matter particle identified and/or the whole lot excluded for it to have beaten the planets this week.

    And to be honest, ‘we don’t know what 25% of the universe is made of’ is still worse publicity for astronomers than ‘we can decide what’s a planet and what’s not’.

  • Elliot


    I think you misinterpreted my comment. I was not implying that people were stupid at all. I think that given the enormous expansion of available information over the last 100 years, it is impossible to know everything about everything. I think it is human nature to want the “readers digest” version of stuff that is outside your realm of expertise. Simple is easier than complex.

    I know some very smart people who voted for George Bush by the way. ;(


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  • George Musser

    There seems to be an awful lot of point-missing going on here. I’m very happy that the Pluto discussion got people talking about astronomy; who wouldn’t be? But the news hook wasn’t new science, it was a vote taken by an assemblage of old men in Prague.

    Sean, it is one thing to miss a point and another to disagree with it!

    The Pluto debate has been participatory science in a way dark matter cannot be. When nonspecialists read about dark matter, they can ask questions, they can think about it, they can grasp it, but in the end, they have to take astronomers’ word. But when they read about Pluto, they can have an opinion and lay out an argument that is the equal of any experts’.

    By the way, the planet definition is as much “new science” as the 1E0657 result. Both involve the latest developments in a decades-old discussion. The planet debate has been driven by discoveries in the Kuiper Belt and extrasolar systems (although the definition was ultimately restricted to the solar system). Indeed, Pluto was discovered around the same time that dark matter was!


  • Richard E[asther].

    It is indeed a good week for astronomy, in the sense that any exposure is good exposure.

    My feeling is that dark matter is not *that* hard to explain. My favorite analogy is that galaxies are like the Rockefeller Center Christmas tree. From a distance all you can see are the twinkling lights. If you had never seen a Christmas tree before you would wonder what was holding them up. Dark matter provides the “tree” that holds the galaxies and galaxy clusters together, but what we *see* is just the twinkling lights.

    It is certainly true that dark matter gives us yet another nasty surprise, at least for those who don’t like to think that baryons – the stuff that people and planets are made from — are a minor ingredient of the universe. But those surprises have been going on since Copernicus.

    It is also true that we would like to know what dark mattter is actually made of – but there is nothing about it that is wildly at odds with our understanding of particle physics. Indeed in many models, including supersymmetric ones, a stable, weakly interacting TeV mass particle is entirely natural. Moreover, the dark matter parameter space can be probed by direct detection experiments and by the LHC, so these models are testable experimentally, it is just that the experiments have not yet been performed.

    Further, simple models of dark matter *predict* the acoustic peaks in the CMB and weak lensing. It is not often phrased that way, but both these predictions have been spectacularly confirmed. Conversely something like MOND needs a different component for each of these effects, which is why it is such a horrible lash-up — and it would never have predicted the acoustic peaks before they were actually seen. My feeling is that is important to emphasise that there are multiple independent sources of evidence for dark matter, and it is by far the simplest known explanation for the large scale dynamics of matter in the universe — it is not “preposterous”, or an ad hoc addition we added to explain away a couple of embarrassing observations.

    As a thought experiment, imagine your reaction if these observations had agreed with MOND, and not with standard dark matter. My guess is that anyone who works on this stuff would be far more surprised about that than we are about this data.

  • Sean

    George — my point (which you are welcome to disagree with) is that the planet definition is not about new science at all. It’s a human-interest story, about the most convenient way to deploy certain words. You can use it as an excuse to talk about interesting science questions, which is fine; but you could also use an actual new science result to talk about interesting science questions, which is even better.

    About the relative participatory possibilities of the two subjects, we apparently do disagree. I think the dark matter story is just as understandable and participatory (and far more significant) than the planet story, if we responsible parties just do our job to make it so.

  • Richard E[asther].

    PS — in the above post I did not mean to imply that the *full* dark matter parameter space can be probed by direct detection or the LHC. But we can certainly take some very big bites out of it in the next decade.

  • Richard E[asther].

    But my point (which you are welcome to disagree with) is that the planet definition is not about new science at all.

    I should be finishing a paper, writing a talk and polishing a grant proposal… But why not post to CV as well :-)

    The strict question of “what is a planet?” is arguably a matter of semantics, rather than science. However, the question has arised because of new discoveries about our solar system — that there is likely a large number of Kuiper Belt Objects, and some of these things are fairly big, and Pluto is a lot smaller than we first realized. On the theoretical level, there is a lot of fascinating work being done on the stability and long term evolution of solar systems (driven in part by the discovery of “hot Jupiters” in extra-solar systems, I think), and that also has an impact of how we view the classical planets.

    For what its worth, I told my son (who is almost 5) that Pluto was not a planet, and took it in his stride, and it is perhaps more important to stress science as a work in progress rather than something akin to a revealed truth….

    FWIW, it often strikes me that kindergarten level books on “space” contain much information that is relatively new — and anything that filters down to this level is bedrock discovery, rather than a refinement of what we already knew, so astronomy has always been “changing”.

    For example, Pluto itself was discovered in 1930, close-up pictures of the planets were only obtained in the 1960s and 70s, the “great debate” on the nature of galaxies was only settled in the 1920s, and many of these books talk about the big bang, which was only widely accepted after the discovery of the CMB (although the expanding universe dates back to the 1920s.) I am too young to remember any of these discoveries as they occurred, but almost all of them fall within my father’s lifetime.

  • George Musser

    Well, as you know, Sean, I do think that definitions are part of science, but anyway, let me try to move the discussion forward by seeking ways to make dark matter participatory. Suppose I wanted to publish an Amateur Scientist project, “How you, too, can see dark matter”. It has to be do-able with instruments and resources amateurs could be reasonably expected to have. Ideally, it wouldn’t require any instruments at all — just careful thinking about an easy-to-make observation, much as you could deduce the big bang (or at least a finite cosmic age) from the darkness of the night sky.

    How would you do it? Do the teachers already have such a lab project?


  • Allyson

    I think the dark matter story is just as understandable and participatory (and far more significant) than the planet story, if we responsible parties just do our job to make it so.

    Which is the point I lost when discussing exploding elephants. Dark Matter certainly sounds sexy, but if you asked me about it two weeks ago I would have been the rube on the street asking, “isn’t that the stuff in the containment thingy on Next Generation that was always about to blow?”

    CV is a blog by physicists, talking to other scientists, mostly, so I don’t expect the ideas here to be presented in a way I can easily get them, but get enough of it to be intrigued to ask questions. For which I am grateful, BTW. Though, Joanne’s rat issue was a most entertaining read. I’m rooting for the tomatoes.

    Like you said, as a responsible party it is your job to tell me what dark matter is, why it’s special, and what it does to further our understanding of how the cosmos works. Tell me why it’s important, in language you’d use over beers in a sticky-floor tavern. Maybe not here, since it would bore the regular audience, but it seems that it’s frustrating enough to all of you sciencesmart people that you have to find a way to present this to the public. I mean, why not pitch a story like this to Discovery Channel? Just hope for a time slot during Shark Week. I think you all need agents. Or a PR rep.

    I think you misinterpreted my comment. I was not implying that people were stupid at all. I think that given the enormous expansion of available information over the last 100 years, it is impossible to know everything about everything.

    Thanks for the clarification. I can still get reparations, though, right?

  • Sean

    I think I didn’t understand what you meant by “participatory” — I was thinking of participating in the discussion, not in taking data. (And I’m not sure why deducing the finiteness of the universe from the darkness of the night sky is all that different from deducing the existence of dark matter from the images of the bullet cluster.) Obviously nobody is going to set up a telescope in their back yard and collect evidence for dark matter. On the other hand, I sincerely doubt that the 5,000 stories about Pluto were aimed at people who were going to look for the thing themselves, either.

    But if you wanted to get at the spirit of dark matter, I would use tides. Either collect data about the rise and fall of tides directly, for folks lucky enough to be close to the water, or just download an appropriate data set from some web page. From that, and the hypothesis that the tides are due to the gravitational influence of some celestial object, deduce what we can about it. Not only could you detect the Moon (which, admittedly, is not made of dark matter, but the spirit is the same), but you could figure out its distance and perhaps even its mass, given some assumptions. If you were careful you could even detect the Sun! (Jupiter, sadly, is out of reach.) We don’t want to ask people to do Fourier transforms, but you could have a simple program (e.g. a Java applet) that let them subtract off sine waves by hand, and use trial and error. If you were ambitious, you could even take into account uncertainties in the data, and use that to put upper limits on the existence of a heretofore unsuspected dark-matter satellite orbiting the Earth. Or you could just synthesize fake data for hypothetical planetary systems, and challenge people to detect as many celestial bodies as they could, using nothing but gravity.

    Again, I’m not sure that “participatory” in this sense is the most important point. But there’s no reason why everyone can’t understand why we believe in dark matter, and what the new observations are teaching us.

  • George Musser

    …there’s no reason why everyone can’t understand why we believe in dark matter, and what the new observations are teaching us.

    Absolutely. I’m just wondering whether we can go one step further. Tides are a good analogy: by monitoring ocean tides, you could deduce the presence of the moon. But that’s only an analogy. What is the simplest possible observation you can make to get at honest-to-god missing matter?

    I’ve given students galaxy rotation curves, and I suppose you might also ask them to compare x-ray and optical images of clusters.


  • Sean

    If you want to give them astronomical data and ask them to infer the properties of dark matter, there are many good possibilities: rotation curves, but also cluster velocity dispersions (using the virial theorem), gravitational-lensing maps, X-ray profiles, not to mention light-element abundances and CMB anisotropies. Probably the cluster velocities is the most straightforward thing; that’s what Zwicky did, and you can teach a little about potential and kinetic energy.

  • missVolare

    ‘Obviously nobody is going to set up a telescope in their back yard and collect evidence for dark matter. On the other hand, I sincerely doubt that the 5,000 stories about Pluto were aimed at people who were going to look for the thing themselves, either.’

    Excellent point. But i would like to detect some!

    I’d like to use a bunch of old film, now that it’s obsolete, and ask the Church of Scientology if we can use their underground bunker to leave it in layers for 22,552 years, and then check if any gravitons leave a trace. Or maybe it would work better using the Time of the Long Now facilities…

    Okay, seriously, what you are describing is akin to asking people to believe in indeterminancy and god’s comic gambler, with hardly any of the usual hooks onwhich to hang complicated ideas. It’s difficult enough to consider the pertinance of a silly ball of rocky ice somewhere WAY out there, not to mention invisible minute particules that supposedly hold a secret (a secret!) we must quantify to understand life, the universe, and everything. I barely have time to finish the laundry, let alone devote the time to the necessary reading and research to get conversant with these ideas.

    Change happens like a shockwave, and the grasping of the shadow of reality will resonate through time, but it hasn’t been translated into concrete-enough terms to be clear to the layman. The ability to think abstractly has been seriously degraded and trivialized, discouraged and denied; we can argue about causes/effects, but the very basis of rationality, not just reality, is in dispute (emergent recapitulation of human history anyone?).

    ‘But if you wanted to get at the spirit of dark matter, I would use tides. Either collect data about the rise and fall of tides directly, for folks lucky enough to be close to the water, or just download an appropriate data set from some web page. From that, and the hypothesis that the tides are due to the gravitational influence of some celestial object…’

    It’s interesting, characterizing darkmatter as a ‘spirit.’ This is an important issue, and i wish i could devote more time/attention. The tides are such an easy way to explain things, yes, but how then can MsAverage be introduced to ideas that require such faith to accept? Or require mathematics even! I admit, path integrals are one thing, but so far no one has actually put Schrodinger (excuse no umlaut) to the test…at least in this version of collapsed wave function.

    Thank you to all for such erudite discussion: i really love these internets tubes.

  • CapitalistImperialistPig

    I say we Pluto fans get even by voting down dark matter! For one thing, it’s hard to directly detect, and for another it sounds vaguely racist. Moreover, it doesn’t even seem to be able to clear its local galaxy, much less lie in the galactic plane.

  • CapitalistImperialistPig

    On a slightly more serious note, do we know anything about the temperature of dark matter? Does it seem to be in any kind of thermal equilibrium?

  • Lindsay Beyerstein

    As a philosopher, I would like to think that the popular fascination over Pluto is due to the average internet reader’s preoccupation with Frege and the de re/de dictu distinction as it relates to necessary and contingent truths. We all look like schmucks now that it’s neither necessarily nor contingently true that nine is the number of planets in the solar system.

  • Malte

    Well there’s a conference paper by Gerry Gilmore et al which includes their measurement of the velocity dispersion in DM in DM-dominated dwarf galaxies, and the BBC article that (strangely) preceded it.

  • dnna

    If it were up to people voting and popular stories, the earth would still be the center of the universe and all you astronomer hertics would be burned at the stake… ;^)

  • AndyS


    Quite by accident I turned on my radio the other day just as you were being introduced. You were just fabulous. Explaining a topic like dark matter and how you obtain evidence of it by observing galaxies coliding — and doing this on the radio (!) without any visuals — well, you did a masterful job of it. (You also have a great voice for the radio.) After your segment was over, I ran to my wife to tell her how lucky I was to hear “Sean Carroll, you know, that guy whose blog I’ve been reading all this time.”

    So here’s the connection between that experience and your current post:

    My wife is pretty smart, well-educated, interested in science, and very curious about the world. But she really doesn’t give a hoot about dark matter. In fact, the effect of my telling her about it is much like the effect of baryonic matter on dark matter. She listens because she loves me and likes to hear about the things that I find intriguing.

    When someone says “ordinary matter (every particle ever detected in any experiment) constitutes only about 5% of the energy of the universe” the vast majority of humanity responses, quite rightly, “so what?” I suspect the same was true when Copernicus and Galileo talked about the heliocentrism, except back then some might have added “you know you could get in trouble if you say that to loudly.” At least the addendum isn’t needed today.

    Most people — and probably most journalists — have never looked through a telescope, understand higher math as what happens when you add a column of numbers after smoking a joint, and think the Hubble space telescope has some connection to The Way We Were.

    In spite of that, I think many people would join me in thanking you for your wonderful post Dark Matter Exists; it was the only material I found that explained the topic at the level I required. So, thanks! Keep up the good work.

  • Sylas

    Just to cheer you all up… I am active on a Christian discussion board, though I am not actually a Christian myself. We have a forum set aside for issues related to science. In this forum, we had two threads about Pluto’s demotion, which picked up 16 and 10 replies respectively. We had one thread on the dark matter discovery, which picked up 31 relies. We linked to Sean’s “Dark Matter Exists” blog article as well.

    There was an earlier thread about Charon, Ceres and Sedna being mooted as planets, with more in the wings; that thread now has 13 replies. But there is also a thread on Big Bang cosmology, which gets pretty technical in places, and had been discussing dark matter and alternatives like MOND when the news broke. The thread has 38 replies, and the reports of the bullet cluster came out just in time to make a great followup in there as well.

    Moral of the story… dark matter is outside most people’s normal interests; but it can still capture the imagination. A few enthusiasts talking about it can help foster a wider interest. Pluto is easier to grasp; but there is also some interest — and confusion — on what the heck dark matter and expanding space and dark energy and cosmic radiation and so on are all about.

    It’s great to hear about folks making it more accessible!

    Cheers — Sylas

  • Amara

    While on travel (Helsinki) for a Europlanet workshop, this week I received some email from friends who are scientists (most non-planetary) and nonscientists, with this one being the ripest to open the science education door for two generations:

    “And may I just add here that now I’m really confused — 8 planets and 4 dwarfs??? I just taught my kids about 12 planets a couple of days ago!”

    Where one can answer to the kids:

    There is a protest about the decision in motion, since less than 5 percent of the astronomical community voted at the Prague IAU for a definition of ‘planet’ that uses dynamics (location) rather than intrinsic properties to decide if an object is or is not a planet. So Pluto-supporters should not give up hope yet, a more democratic vote could be taken. Think of how active and dynamic is the solar system; gravity’s forces can give surprising results with some objects being trapped in some places (resonances) and bouncing other objects around, and sometimes even the smallest solar system bodies can sculpt the positions of the other bodies that we see. The astronomers are discovering new solar system objects all of the time that are larger than Pluto, but sometimes they need time to learn how those new objects could be at the location that they are. And because they are so far away, the astronomers don’t know yet their shape and other basic properties such as their mass or of what material those bodies are made. Because astronomers are people like you and me, they have heated discussions about it because they have different explanations . But in the end those disagreements are usually resolved when they have more data from the new instruments that they are building.

    If you can explain this to your kids, then it would make the discussion more interesting and fun. It can also open the door to other science topics like.. gravity. I’m sure that Sean could bootstrap from any popular science topic involving gravity to quickly jump into the dark matter topic.

    From this link, you can see how the Pluto topic has grabbed the public imagination. Just like when comet Shoemaker-Levy9 crashed into Jupiter, here we have a hot science topic. I say seize _any_ opportunity to support the public’s interest in science. If you find that precious tidbit, use it for all its worth, because the public’s attention span for science is usually short. Once you have hooked them, then go to topics that are more difficult to explain (and the science popularizers can learn at the same time what works well to hook the public’s interest for future efforts).

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  • Sean

    AndyS (and others), thanks very much for your kind words, it’s always nice to hear that people enjoy what you’re doing. As JoAnne keeps hinting, flattery will get you everywhere!

  • Joe

    One reason people are not interested in dark matter or science in general with the exception of the recent Pluto debate is that people don’t like to be made to feel stupid. They also are not very hip to being mocked, ridiculed, and sorting through a field of scorn that is denser than the dark matter in question.

    Read the article in the New York Times that is linked in these comments. Let’s do our best to make these people, or similar people like them, feel stupid because they do not know what we know (although this really isn’t important since we all know that the blunt foreheads among us don’t read such sophisticated writing as that present in the New York Times!)

    The article also points out that these people who care about Pluto don’t know jack about Pluto; It’s far away, it’s cold, it’s small. Now honestly I don’t know much more about Pluto except for more than a few basics like that it’s a slush ball and if one moon is called Charon another should be called Acheron. That info really makes a big difference in my life on those deep nights when I’m wondering where my life is going.

    I fit into the category of the 1 out of 4 or 5 Americans that don’t know the earth goes around the sun. I stumbled on this site looking for a better (hopefully graphical) way to explain reference frames to my son — which is exactly tied to Pluto as we discuss conceptualization and what has and hasn’t changed with the recategorization of Pluto. He didn’t like the idea a few weeks ago that we might wind up with over a hundred planets (what’s so special about that?) but dislikes the new proposal even more. Of course he knows it’s just a name, but then he asks the question, he is only 10, that if it is really just a convention, can’t the scientists just build the definition around the nine planets as they are? Of course they could, but the audacity of thinking that the input of the masses of morons should have anything to suggest to science? Science shall bring the stone tablets to the masses.

    Now Pluto has also given a way for me to introduce him to paradoxical statements, as when I tell him that the moral of the Pluto debacle is that you should never listen to someone who tells you they know what they are talking about, and the more authoritatively the more so.

    A couple of reasons that Pluto is more interesting than Dark Matter:

    1. People are interested in Pluto partly because it represents the “edge” of our solar system.
    2. Children like Pluto because it is small, like themselves, relative to the big balls of the neighborhood.
    3. It represents the hubris of science being knocked of its pedestal.
    4. It is relevant in these days where we are not sure what to believe in what we hear from those people who have set themselves up as “priests” governing the world; the politicians, the filthy rich, and academia.

    BTW, I enjoyed the article on Dark Matter and this post is NOT directed toward that or all the comments (although some do qualify and the author(s) probably aren’t even aware), but honestly I found the gravitational lens very interesting. I never knew that.

  • Allyson

    There’s a bit about Pluto at the NASA Kids site, and that may be helpful.

    Anyone here up to the task of writing about the Dark Matter discovery for kids? I found an explanation from 2003.

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  • Joe


    I am, perhaps in error, assuming that the link to Pluto for kids was in response to my post. If so I appreciate it, but that really wasn’t my point. My point was more along the lines of your earlier comment regarding the element of disrespect often given to individuals who are not “into” science in neglecting what knowledge the individual may have, be it from formal education and career or from simply life experiences.

    I don’t need to know one more bit of information about Pluto and neither does my son — it means nothing in either of our lives and effects us in no significant way. That does not mean either of us shouldn’t know more about Pluto proper or about Pluto indirectly or that more information would not be nice. However, a better understanding of the manner in ways conceptualization and/or categorization effects our understanding and development of ideas is much more important and something that one should always diligently be on lookout for a greater understanding of.

    The problem is that the question is why don’t people care about dark matter or science in general, then we use science to make people feel stupid or to laugh at them. That’s why if I’m ever asked a question on a poll that’s getting at if I know the earth orbits around the sun I will answer incorrectly; the ignorance of asking a question like that is much worse than the ignorance of not knowing the “correct” answer.

    If we think there is some super duper special reason why scientific knowledge is generally better than the knowledge of history or mythology or art we have turned science into a religion and as a religion it really sucks. Looking at the applied results of science in Lebanon and Iraq (and everywhere else) maybe we should not laugh at the person who doesn’t know or care about Pluto and dark energy but at the person who doesn’t have a significant understanding of Gandhi.

    The problem isn’t a lack of understanding or appreciation of science. The problem is the misanthropy that underlies the two political parties in the United States and is used to keep citizens at odds with each other instead of focusing on the blatant incompetence of BOTH parties and thus the true causes of the lack of understanding or appreciation of science. Peace.

  • Allyson

    Joe, my post was in response to:

    I stumbled on this site looking for a better (hopefully graphical) way to explain reference frames to my son — which is exactly tied to Pluto as we discuss conceptualization and what has and hasn’t changed with the recategorization of Pluto.

    I thought that it would be a good starting point for your little boy since you were looking for info on Pluto. But from your response it looks like you found whatever info you needed.

  • bittergradstudent

    I want that poster.

    I want it in my office

    and I want it in my apartment

  • AstroChild

    I am a high school jounralist and aspiring astronomy student in po-dunk Wyoming.

    I agree with previous statements that the Pluto story is printed more because its easier to write. It’s also because anyone who doesn’t know what Pluto is wouldn’t be reading a paper, whereas, a lot more people didn’t even know dark matter was yet to be “discovered” or proven. It becomes a matter of what people will read. It doesn’t help that many people still believe astronomy is not useful to anyone on Earth and some mistake it for astrology.

    I am excited about this discovery, as I know all of you are, too. So let us put up that poster, celebrating with those who understand it and telling the story to people who look at it with an questioning look.

    Long live truth and the scientists who pursue it.


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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] .


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