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).

Talking about the Higgs Boson - Sixty Symbols

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

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Cosmology Results from Planck Tomorrow

The Planck satellite, a European cosmic microwave background observatory, was launched in 2009 and is finally ready to release its first set of cosmology results. (It has already released findings on galaxies and dust and so forth — what early-universe cosmologists call “foregrounds” and others call “my life’s work.”) They will be showing us the highest-precision all-sky map of the microwave background ever made. The announcement starts at 10 a.m. Paris time, which works out to 2 a.m. Los Angeles time. Don’t expect me to be live-blogging.

So what should we be looking for? Typically an experiment like this isn’t just a fishing expedition; scientists have a pretty clear idea of what questions they would like answered, and what discoveries they might be able to make. Nature is always capable of surprising us, of course. There are some very useful posts on this question by Renee Hlozek and Shaun Hotchkiss. (I hope everyone reading those posts will take a moment to appreciate how wonderful it is that we live in an era where real experts can chime in directly on important scientific questions.)

A CMB map contains an enormous amount of information, especially if you are measuring the polarization as well as the temperature at each point. My understanding is that this edition of the Planck results will not include polarization, but that will be coming some day down the road. (And Max Tegmark’s $100 is safe for another few months.) Nevertheless, a lot of the interesting information boils down to the “power spectrum,” which tells us how strongly the temperature varies on different angular scales. Of course, there are a few observables that go beyond the power spectrum, and those are some of the most interesting ones.

Here are some of the major things cosmologists might want to learn from the CMB temperature anisotropies:

  • Did the original perturbations we inherited from the early universe have the same amplitude on all scales, or were the slightly different?
  • What are the best fits for cosmological parameters such as the density of dark matter and dark energy, the numbers and masses of neutrinos, and the Hubble constant? Or even spatial curvature?
  • Are there persistent “anomalies” that can’t be easily accounted for by a simple theory of primordial perturbations? For example, do the anisotropies somehow define a preferred axis in space?
  • Are the perturbations completely random — “Gaussian” — or are there hints of primordial non-Gaussianity, which might help pin down specific models of inflation?

I suspect it would be wise to keep expectations low for Earth-shattering (or universe-shattering) discoveries here, although I’d certainly welcome a surprise. The amplitude of the primordial perturbations has already been nailed down fairly well, by the Atacama Cosmology Telescope as well as by the South Pole Telescope that I blogged about. From Renee’s post, here is a graph of the data from the WMAP satellite as well as ACT and SPT, which as you can see are pretty compatible with each other as well as with the theoretical prediction. We might get a more definite finding that the amplitudes aren’t strictly the same at all scales, which would be good news for proponents of inflation.

wmap9+spt+act

We definitely hope to get more precise measurements of cosmological parameters, especially the number of neutrino species and their masses. Evidence from particle physics experiments here on the ground is inconclusive when it comes to the number of neutrino species — very recent results from the MiniBooNE experiment seem to point in the direction of sterile neutrinos that don’t feel the weak interactions. If such neutrinos are produced in the early universe, they could have an effect on the CMB anisotropies. Obviously any definitive statement that there were more than three kinds of neutrinos would be huge news. The other hope for groundbreaking news would be the discovery of nonzero spatial curvature, but nobody really expects that.

As far as anomalies are concerned, Planck has a very different scanning strategy than WMAP had, so it’s possible that it will squelch some people’s favorite anomalies. But there is the problem of cosmic variance (in the original sense) — on very large scales, there is a limited number of modes we can measure, since we only get one universe. If large-scale fluctuations just happen to be statistically anomalous, it might be very difficult to ever decide whether it’s an accident or the sign of new physics.

The search for non-Gaussianities (correlations between fluctuations on different scales) is possibly the most interesting thing we should be looking at in the current release. If inflation is right, you may or may not see deviations from perfectly Gaussian behavior, depending on the kind of inflation we’re talking about. Roughly speaking, we expect perturbations to be Gaussian in simple models of inflation with ordinary dynamics of a single scalar field, but adding bells and whistles to your inflationary model can introduce some non-Gaussianities. So it’s not really evidence for or against inflation, but limits the model space if inflation is the right answer.

Let’s offer early congratulations to the Planck team, who have certainly worked incredibly hard to get to this point.

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What “The God Particle” Hath Wrought

You’ve doubtless heard the joke: We can’t call the Higgs boson the “God Particle” any more, because now we have tangible evidence that it exists.

But the label “God Particle,” attached to the poor unsuspecting Higgs boson by Leon Lederman and Dick Teresi, continues to wreak havoc on physicists’ attempts to clearly explain what is going on. Last week’s announcements from CERN that the new particle discovered last July is looking more and more like the Higgs predicted by the Standard Model generated stories like this one, from CBS news:

The Higgs boson is often called “the God particle” because it’s said to be what caused the “Big Bang” that created our universe many years ago. The nickname caught on so quickly (even though scientists and clergy alike do not care for it) partly because it’s a great explanation of what it’s supposed to do — the Higgs boson is what joins everything and gives it matter.

That might be the worst paragraph I’ve ever read about the Higgs boson, and I’ve read quite a few. (H/t Faye Flam.) Originally I thought the journalist was just making things up, but it turns out that it’s Michio Kaku’s fault. (H/t Matt Strassler on Facebook.) There is a video linked to the article, in which Kaku says that the Higgs helped cause the Big Bang, and that’s why it’s called the God Particle. Another example where it would have been tempting to rag on sloppy popular journalism, where actually it’s a supposed scientist who is largely to blame. (Although the above paragraph is also wrong about things it should be easy to get right.)

For the record, the Higgs had nothing whatsoever to do with causing the Big Bang. (Kaku tries to link it to inflation, but they’re not related.) It also doesn’t “join everything,” whatever that means. It does give mass to elementary particles like electrons and quarks, which isn’t the same as giving “matter” (since that kind of doesn’t make any sense), and besides which it doesn’t give mass to protons and neutrons and therefore most of the mass in ordinary objects.

The “God Particle” label, despite being very catchy and therefore leading to more publicity than most elementary particles manage to muster, has done more harm than good for the public understanding of science. Non-experts, hearing that physicists have named something after God, might actually think they were being serious. Imagine that.

[Update: Matt Strassler adds his take.]

It’s not going away any time soon. Leon Lederman and Chris Hill have a sequel to the original book coming out, Beyond the God Particle, due later this year. I’m sure the book will be great at explaining the physics, and I’m equally sure the title will generate a lot more confusion. Get your disclaimers ready!

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More Messy Dark Matter

Longtime readers know that I’m fascinated by the possibility that dark matter is “interesting.” Of course dark matter is by its very nature interesting, but I’m referring to the idea that the dark matter isn’t simply a single neutral particle with a negligible rate of interaction in the current universe, but rather a set of one or more kinds of particles with some noticeable forces acting between them. Friends of mine and I have investigated the idea of dark photons — dark matter being charged under a new “dark force” resembling ordinary electromagnetism. The next obvious step is dark atoms — two different kinds of charged dark particles that can join together in atom-like bound states. These ideas, it turns out, are fairly compatible with what we know about the dynamics of dark matter in the real universe.

Now a new paper by JiJi Fan, Andrey Katz, Lisa Randall, and Matthew Reece examines the particle physics and astrophysical consequences of a somewhat more elaborate version of this idea, which they call “Partially Interacting Dark Matter.” The idea is that most of the dark matter is vanilla and boring, but some fraction of it is atom-like. This has interesting implications for galaxies and small-scale structure. Here’s the abstract:

Double-Disk Dark Matter
JiJi Fan, Andrey Katz, Lisa Randall, Matthew Reece

Based on observational tests and constraints on halo structure, dark matter is generally taken to be cold and essentially collisionless. On the other hand, given the large number of particles and forces in the visible world, a more complex dark sector could be a reasonable or even likely possibility. This hypothesis leads to testable consequences, perhaps portending the discovery of a rich hidden world neighboring our own. We consider a scenario that readily satisfies current bounds that we call Partially Interacting Dark Matter (PIDM). This scenario contains self-interacting dark matter, but it is not the dominant component. Even if PIDM contains only a fraction of the net dark matter density, comparable to the baryonic fraction, the subdominant component’s interactions can lead to interesting and potentially observable consequences. Our primary focus will be the special case of Double-Disk Dark Matter (DDDM), in which self-interactions allow the dark matter to lose enough energy to lead to dynamics similar to those in the baryonic sector. We explore a simple model in which DDDM can cool efficiently and form a disk within galaxies, and we evaluate some of the possible observational signatures. The most prominent signal of such a scenario could be an enhanced indirect detection signature with a distinctive spatial distribution. Even though subdominant, the enhanced density at the center of the galaxy and possibly throughout the plane of the galaxy can lead to large boost factors, and could even explain a signature as large as the 130 GeV Fermi line. Such scenarios also predict additional dark radiation degrees of freedom that could soon be detectable and would influence the interpretation of future data, such as that from Planck and from the Gaia satellite. We consider this to be the first step toward exploring a rich array of new possibilities for dark matter dynamics.

Most investigations of dark matter indicate that it is spread much more tenuously through the universe than ordinary matter, which tends to clump together. The basic idea is illustrated in this artist’s conception of the dark matter halo associated with our Milky Way galaxy and its Magellanic Cloud satellites. (Update: oops, reading comprehension failure on my part. This is an artist’s conception of hot gas around the Milky Way, not dark matter, as Peter Edmonds pointed out on Twitter. But they look similar!)

halo-580x472

There is a straightforward explanation for this behavior: ordinary matter feels the electromagnetic interaction, so atoms can bump into each other and release energy by radiating photons, which lets them “cool” and settle down into relatively dense clumps (like galaxies and even stars). Standard dark matter particles have very weak interactions indeed, so when they fall into a gravitational potential well they just zip through the other side without cooling, giving the dark matter distribution a much puffier profile.

Here Fan et al. are suggesting that part of the dark matter could form atoms and cool, allowing it to clump more efficiently in the centers of galaxies. This could lead to more frequent dark-matter annihilations than we would otherwise expect, which might be suggested by some tantalizing observational results (although that’s fairly tentative).

It’s fun to think about, although we’re far away from drawing any firm conclusions at the moment. But we won’t know how to test these ideas observationally unless we work out their predictions theoretically. It’s a complicated universe, we need to be prepared.

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Science, Morality, Possible Worlds, Scientism, and Ways of Knowing

The relationship between science and morality popped up again on some of the blogs I regularly read, but real life getting in the way has prevented me from responding until now. Here’s Michael Shermer, Eric MacDonald, Massimo Pigliucci, and Jerry Coyne. I’ve spoken about this stuff more than anyone wants to hear (1, 2, 3, 4, 5, 6), but perhaps the wisdom that comes with advancing age has helped me boil the point down to the essence more effectively.

Morality will never be reduced to science, nor subsumed into the greater scientific project. It will increasingly make use of scientific discoveries, but it is fundamentally a separate endeavor; there will always be something necessary to get morality off the ground that simply isn’t part of science.

Here are some statements that are solidly part of science:

  • The universe is expanding.
  • Oxygen is delivered to the body by circulating blood.
  • The Sun will run out of nuclear fuel in several billion years.

What makes these statements scientific? I would say two things (admitting that we are glossing over many subtle points here, but trying to remain focused on the big picture).

  1. They could be false. That is, we can imagine possible worlds in which these statements were not true. We couldn’t decide on their truth just by thinking about them.
  2. They can, in principle if not in practice, be evaluated empirically — by doing the right experiments or collecting the right observations.

Of course we need to assume that all the appropriate definitions of the terms we are using have been established. Note that a statement doesn’t have to be true to be scientific; “The universe is contracting” is equally scientific as “The universe is expanding.” Finally, the “in principle if not in practice” is crucial. We can’t actually collect the data that shows directly that the Sun is out of nuclear fuel several billion years from now, at least not at the moment. But it is clear what form those data would take, and that’s all we really need. More realistically, the statement is implied by a theoretical superstructure that can itself be tested directly in the here-and-now.

Here are some statements that are not scientific.

  • 1+1=2.
  • Hamlet was really crazy, he wasn’t just faking it.
  • Chunky Monkey is the best possible ice cream.

The first statement kind of looks sciencey; it’s part of math. But you don’t need to do any experiments to evaluate whether it’s true. It can’t help but be true, once the terms are understood; there are no possible worlds out there in which 1+1=3, in the conventional definition of those symbols. So it’s math, or logic, or philosophy; but it’s not science.

The second statement is again not science because there is no data we could conceivably collect that would judge its truthfulness, but in a different way. You might think that we just need to collect more data about Hamlet’s mental state, but that’s going down the wrong path; there is no such data, because Hamlet is a fictional character. The words of the play are all the data that exist or ever will exist. You might also suggest that in principle we could collect data relevant to Shakespeare’s mental state, perhaps some notes of his establishing that he always thought Hamlet was just faking. But that only bears on the question “Did Shakespeare think of Hamlet as really crazy?” (which is scientific), not “Was Hamlet really crazy?” (not).

The ice cream question is the one that is closest to the issue of morality. Again, one might suggest that all we need to do is collect neurological data relevant to the functioning of pleasure centers in the brain when one eats different kinds of ice cream, and decide which does the best job. But that’s the question “What effect do different flavors of ice cream have on the brain?” (which is scientific), not “What flavor of ice cream is the best?” (not). To answer the latter question, we would have to know how to translate “the best ice cream” into specific actions in human brains. We can (and do) discuss how that might be done, but deciding which translation is right is — you guessed it — not a scientific question. If I like creamy New-England-style ice cream, and you prefer something more gelato-y, neither one of us is wrong in the sense that it is wrong to say that the universe is contracting. Even if you collect data and show beyond a reasonable doubt that New York Super Fudge Chunk lights up my brain more effectively in every conceivable way than Chunky Monkey does, I’m still not “wrong” to prefer the latter. It’s a judgment, not a statement about empirically measurable features of reality. We can talk about how we should relate such judgments to reality — and we do! — but that talk doesn’t itself lie within the purview of science. It’s aesthetics, or taste, or philosophy.

And that’s okay. There are many kinds of questions, moral ones among them, that have a scientific component but cannot ultimately be reduced to science. Consider a statement of the form

  • We should work to maximize the well-being of conscious creatures.

This is not a scientific statement. To convince me otherwise would be straightforward enough. Simply delineate what the worlds would be like in which that statement is true, and the worlds in which it is not true, and then tell me what data we need to collect to decide which kind of world we live in. Obviously this is absurd. Science is relevant to morality, and we should ground our moral conversations on correct ideas about the physical world rather than incorrect ones, but deciding the truth of moral claims is always going to involve something other than simply doing science.

I don’t like using the word “scientism” to label the unfortunate desire on the part of some people to hope that every interesting question can be reduced to science, because the folks who do like using it are often people whose side I’m really not on. Nevertheless, there is a real mistake that can be sensibly labeled “scientism.” Likewise, I generally take the phrase “ways of knowing” as a sign that I can stop listening and start checking Twitter on my iPhone, no matter which side of the debate the speaker is on. Are mathematics, literary criticism, aesthetics, and morality “other ways of knowing”? It would be hard for me to care less. They are different areas of thinking and judging than science is, that’s for sure. If you really want to call them “ways of knowing,” you should work hard to make the distinctions clear — they are not ways of making statements about what happens in the world, which is an empirical endeavor.

Grumbling aside, it’s always a long-term good when smart people come from very different perspectives to hash out difficult issues in a changing intellectual landscape. There are real moral questions that confront us every day, and as a society we’re still burdened with a slapdash pre-rational way of answering them. I look forward to the day when there is a consensus theory of secular moral philosophy that forms a basis for democratic discourse, and we’re teaching fifth-graders how to cope with trolley problems.

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Spoiler Alert: One Day We Will All Die

Not on the same day, of course. At least, I hope not.

Philosophers Katarzyna de Lazari-Radek and Peter Singer have started a project called Help! My Child is a Philosopher! All children are, of course, just as all children are scientists. The issue is to nurture children’s natural curiosity, rather than let it be squelched.

On their forum they shared an anecdote from Daniel Ogilvie:

“When one of my daughters was four years old, she came charging out of her bedroom and down the staircase well after she would normally have been asleep. She was crying. She stood before her mother and me and through her sobs announced that she did not want to be a thing that dies. I was astonished by her announcement. Clearly she was calling out for help. It occurred to me to tell her to shut up and go back to bed. I had enough sense not to act on that impulse and was relieved when my wife responded, “Don’t worry dear, you have a long life ahead of you” and gave her a hug. The words worked wonders. Her emotional pain subsided and she was sound asleep in 15-minutes.”

I had precisely the same experience as a kid myself; one of my earliest childhood memories is of lying in bed and crying at the realization that my grandmother and everyone else I knew was someday going to die. (Apparently it’s a somewhat-common occurrence?)

The fear of death doesn’t go away for most of us, and it’s one of the major motivating factors for people choosing to believe in the supernatural. (Ricky Gervais’s underappreciated movie The Invention of Lying does a great job with this theme.) Even I will admit that the shortness of our lives here on Earth is one of the least attractive parts of a naturalistic worldview. That’s not an argument against it, of course; when we want something to be true, we should take that as a reason to be extra suspicious, not as a justification for believing it. But accepting it is crucially important for constructing a meaningful life in the real world. Might as well start young.

This is not a dress rehearsal, this is the performance. Make it count.

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Brain-to-Brain Communication

Over at Nature, Ed Yong reports on a new study by Miguel Pais-Vieira and collaborators, in which mental activity in the brain of a rat living in Brazil is communicated directly to the brain of a rat living in North Carolina, which responds accordingly (sometimes; at least greater than by chance). Ed was able to find another researcher to give the mandatory curmudgeonly response, comparing the work to a “poor Hollywood science-fiction script.” To which the rest of us respond: we want to see that movie!

This isn’t my bailiwick, obviously, so check out Ed’s article or the original paper. The basic idea is that the Brazil rat sees a light, and presses a lever that it has been trained to when that light goes on. An implant records activity in the rat’s motor cortex (in charge of pressing levers), which is then encoded and sent to the North Carolina rat, which presses the corresponding lever itself. At least, about 64% of the time. Which is a pretty noisy signal, but a signal nonetheless.

Direct mental communication won’t be replacing email any time soon. But unlike our skeptical commentator, I think experiments like this are important. They prod people’s minds in the direction of thinking about what might someday be possible.

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Explaining Time to Kids

Don’t forget that the deadline for this year’s Flame Challenge is coming up. Your mission: to explain “Time” to a group of 11-year-olds, who will be sternly judging your work. Get your submissions in by March 1, either video or written (less than 300 words).

Here’s my attempt. (Just given the likely number of entries, winning seems like a long shot, so I don’t mind encouraging other submissions or giving away all my best lines.) 300 words is hard, and aiming squarely at 11-year-olds who are judging a bunch of submissions is also no easy feat. But it’s good practice. I personally first fell in love with science when I was 10, so 11-year-olds are a great audience to aim at.

Admittedly the definitions I propose below could be accused of being circular, but without using technical jargon I think it’s appropriate to aim for intuitive understanding rather than perfect rigor.


Time is not hard to understand! How time works can be tricky, but time itself isn’t that mysterious.

We live in a world full of stuff. Chairs, trees, planets, stars, all kinds of things. This stuff is spread throughout space–everything has a location somewhere or another. And all this stuff, at various positions in space, happens over and over again, slightly differently each time. Things move, age, transform. Planets orbit stars, animals eat and sleep, people play and fight and think and learn. The universe doesn’t sit still.

Time is the label we stick on different moments in the life of the world. There is the universe at 2 p.m. July 1st 2013, the universe at 2:01 p.m., and so on. Just like a page number tells you where you are in a book, time tells you when you are in the universe. Moments of time are pages in the book of the universe.

We can measure time using clocks and calendars—things that repeat themselves in a predictable way. Every time the Earth revolves around the Sun, it rotates around its axis about 365 times. Every time the little hand goes around a clock dial, we can be sure the big hand goes around twelve times.

Time gets mysterious when we think about past, present, and future. We can remember what happened yesterday, but we can’t remember tomorrow. It seems obvious, but why is it true? Why does everyone – everyone! – get born young, and then grow old? We can choose what to do next in our lives, but we can’t un-choose events in the past, things that have already happened. The past is in the books, but the future remains to be shaped. Let’s hope we choose wisely!

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