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?
(Motivational poster generator found via La Blonde Parisienne.)
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.
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.
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.
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.
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?
George
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.
Thanks for the clarification. I can still get reparations, though, right?
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.
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.
George
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.
‘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.
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.
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?
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.
#37:
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.
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… ;^)
Sean,
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.
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
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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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!
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.
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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Allyson,
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.
Joe, my post was in response to:
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.