Last month we mentioned a paper on the arxiv that made a provocative claim: evidence from the dynamics of stars above the galactic disk indicates that there is essentially no dark matter in the vicinity of the Sun. I am not an expert on galactic dynamics, but nevertheless I and others were immediately skeptical, especially since there is overwhelming evidence for the existence of dark matter from other measurements. Skeptics, of course, happily piled on. But this isn’t an area where one opinion or the other matters very much — better data and better analysis is what matters.

Now we have a better analysis, from people who are experts: Jo Bovy and Scott Tremaine have a paper in which they examine the claim closely. They find it wanting. This was pointed out here in a comment by Ben; Jester and Peter Coles also have useful blog posts up about it.

Short version: the original authors made assumptions about the distribution of velocities of the stars they were looking at, and those assumptions are known to be wrong. Using a better model (i.e., one more compatible with known data), Bovy and Tremaine show that the observations are perfectly consistent with the conventionally-assumed dark matter density. The good news is that they are actually able to use this technique to get a more precise measurement of that density than was previously available. It’s a rare scientific lemon that can’t be turned into at least a little bit of lemonade.

I’m not sure why people get so emotional about dark matter. The original paper here by Bidin et al. was accompanied by a dramatic press release from the European Southern Observatory. I am known as a “dark matter supporter,” but I have no personal investment; I think it would be much cooler if something crazy were going on with gravity. But that’s not what the data indicate. It’s just some new particle we haven’t yet made in the lab, hardly the end of the world.

The price of university textbooks (not to mention scholarly journals) is like the weather: everyone complains about it, but nobody does anything about it. My own graduate textbook in GR hovers around $100, but I’d be happier if it were half that price or less. But the real scam is not with niche-market graduate textbooks, which move small volumes and therefore have at least some justification for their prices (and which often serve as useful references for years down the road) — it’s with the large-volume introductory textbooks that students are forced to buy.

But that might be about to change. We’re very happy to have Marc Sher, a particle theorist at William and Mary, explain an interesting new initiative that hopes to provide a much lower-cost alternative to the mainstream publishers.

(Update: I changed the title from “Open Textbook” to “Nonprofit Textbook,” since “Open” has certain technical connotations that might not apply here. The confusion is mine, not Marc’s.)

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The textbook publishers’ price-gouging monopoly may be ending.

For decades, college students have been exploited by publishers of introductory textbooks. The publishers charge about $200 for a textbook, and then every 3-4 years they make some minor cosmetic changes, reorder some of the problems, add a few new problems, and call it a “new edition”. They then take the previous edition out of print. The purpose, of course, is to destroy the used book market and to continue charging students exorbitant amounts of money.

The Gates and Hewlett Foundations have apparently decided to help provide an alternative to this monopoly. The course I teach is “Physics for Life-Scientists”, which typically uses algebra-based textbooks, often entitled “College Physics.” For much of the late 1990′s, I used a book by Peter Urone. It was an excellent book with many biological applications. Unfortunately, after the second edition, it went out of print. Urone obtained the rights to the textbook from the publisher and has given it to a nonprofit group called OpenStax College, which, working with collaborators across the country has significantly revised the work and has produced a third edition. They have just begun putting this edition online (ePub for mobile and PDF), completely free of charge. The entire 1200 page book will be online within a month. People can access it without charge, or the company will print it for the cost of printing (approximately $40/book). Several online homework companies, such as Sapling Learning and Webassign, will include this book in their coverage.

OpenStax College Physics’ textbook is terrific, and with this free book available online, there will be enormous pressure on faculty to use it rather than a $200 textbook. OpenStax College plans to produce many other introductory textbooks, including sociology and biology textbooks. As a nonprofit they are sustained by philanthropy, through partnerships, and print sales, though the price for the print book is also very low.

Many of the details are at a website that has been set up at http://openstaxcollege.org/, and the book can be downloaded at http://openstaxcollege.org/textbooks/college-physics/download?type=pdf. As of the end of last week, 11 of the first 16 chapters had been uploaded, and the rest will follow shortly. If you teach an algebra-based physics course, please look at this textbook; it isn’t too late to use it for the fall semester. An instructor can just give the students the URL in the syllabus. If you don’t teach such a course, please show this announcement to someone who does. Of course, students will find out about the book as well, and will certainly inform their instructors. The monopoly may be ending, and students could save billions of dollars. For decades, the outrageous practices of textbook publishers have not been challenged by serious competition. This is serious competition. OpenStax College as a nonprofit and foundation supported entity does not have a sales force, so word of mouth is the way to go: Tell everyone!

On local TV last night, I somehow got reporter Dave Malkoff to take a stab at explaining quantum field theory: the world is made of fields, but we only notice the ripples within them, which we see as particles. Something about Angelina Jolie in there at the end as well.

It’s well known that all of our evidence for dark matter (and dark energy too, but that’s not the subject here) at the present time is indirect: it comes from observing the gravitational influence of the hypothetical stuff, not from detecting it “directly” (i.e., using some interaction other than gravitational). So it’s natural to ask whether we can do away with dark matter by positing some modification of the behavior of gravity; I’ve certainly wondered that myself.

And it may very well turn out that the behavior of gravity on large scales does not precisely match the prediction of ordinary general relativity. Nevertheless, I think that by now we’ve accumulated enough data to conclude that the universe cannot be explained solely by modifying gravity; there is ample evidence of gravitational forces pointing in directions where there isn’t any (ordinary) “stuff” to create them, leading us to accept the existence of some form of dark matter. About a year ago I put up a post that explained this point of view, and took aim in particular at the popular framework known as MOND.

This led to some good discussion in the comments, and also to a behind-the-scenes email exchange between Rainer Plaga, Stacy McGaugh, and me. It’s a bit of old news, but I thought there would still be some interest in our discussion, so (with permission) I’m posting our emails here. Seeing how the sausage is made, as it were. It’s a bit of a long read, sorry about that.

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“Atheism” is a fine word, and I’m happy to describe myself as an atheist. God is an idea that has consequences, and those consequences don’t accord with the world we experience any better than countless other ideas we’ve given up on. But given a choice I would always describe myself first as a “naturalist” — someone who believes that there is only one realm of reality, the material world, which obeys natural laws, and that we human beings are part of it. “Atheism” is ultimately about rejecting a certain idea, while “naturalism” is about a positive acceptance of a comprehensive worldview. Naturalists have a lot more work to do than simply rejecting God; they bear the responsibility of understanding how to live a meaningful life in a universe without built-in purpose.

Which is why I devoted my opening statement at “The Great Debate” a few weeks ago to presenting the positive case for naturalism, rather than just arguing against the idea of God. And I tried to do so in terms that would be comprehensible to people who disagreed with me — at least that was the goal, you can judge for yourself whether I actually succeeded.

So here I’ve excerpted that opening ten-minute statement from the two-hour debate I had with Michael Shermer, Dinesh D’Souza, and Ian Hutchinson. I figure there must be people out there who might possibly be willing to watch a ten-minute video (or watch for one minute before changing the channel) but who wouldn’t even press “play” on the full version. This is the best I can do in ten minutes to sum up the progress in human understanding that has led us to reject the supernatural and accept that the natural world is all there is. And I did manage to work in Princess Elisabeth of Bohemia.

I am curious as to how the pitch goes over (given the constraints of time and the medium), so constructive criticism is appreciated.

Mostly I’m holed up at home these days, pounding out paragraph after paragraph about the LHC and the Higgs boson. But even the most dedicated author needs a sanity break, and mine is coming tonight, in the form of The Avengers. I won’t bore you with an explanation of what the movie is about, as 99% of the potential audience has pre-decided on geeky enthusiasm and/or hipster disdain (or both!). But I will take the opportunity to post a clip featuring everybody’s favorite Marvel character: Agent Phil Coulson of SHIELD. (And one of those leather-clad superheroes people seem to like so much.)

In case you can’t get enough, Clark Gregg has collected all his favorite Agent Coulson moments. (Just ask the professional screenwriters: “I’m sure avengers is great, but the only marvel movie i’d truly kill or die to see is Read the rest of this entry »

I should have advertised this ahead of time, but even though I’m late to it, I wanted to mention that the Philadelphia Science Festival was going on all last week. It’s been great to see science taking its rightful place among the other cultural attractions of Philadelphia, and in particular, it was nice that astronomy was prominently featured.

Penn’s School of Arts and Sciences has been posting about our involvement on its facebook page, where you can see my colleague Gary Bernstein delivering a lecture on planets at Astronomy Night

and attendees observing planets in Perelman Quadrangle.

We are very close to the end of the semester here at Penn, and the last couple of weeks have been the usual flurry of activity as teaching comes to an end, exam period begins, and a few late semester/early summer meetings all take place at the same time.

A week or so ago, I spent a couple of days back at Syracuse University, where I was a faculty member for quite a few years. I was there primarily to participate in a special event that preceded the East Coast Gravity Meeting being held there on the following weekend. The event was a celebration – GoldbergFest – of the career of Josh Goldberg, a good personal friend, and an eminent relativist at Syracuse, who has been an emeritus professor there for many years now.

Josh began as a graduate student at Syracuse in the early 1950′s, working on conservation laws in General Relativity (GR) and on canonical quantization. At the time Syracuse had one of the few well-known relativity groups in the world, led by Peter Bergmann, and an impressive group of young people were trained under him, and later under Josh, as students and postdocs; people like Ted Newman, Ray Sachs, Art Komar, Roger Penrose, and many others. I’m certainly no expert on the precise history of the Syracuse group, but fortunately, as part of a special issue of General Relativity and Gravitation dedicated to Josh, to which I was honored to also contribute, Ted Newman describes it wonderfully. The Fest was a lovely event. I enjoyed the other speakers’ talks – John Stachel, Rafael Sorkin and Peter Saulson, and Ted Newman’s hilarious and touching after dinner speech, and the reminiscences of the other people at the dinner made for what I hope Josh thought was a wonderful day.

Over the next two days quite a few of our students and postdocs from Penn gave talks at the East Coast Gravity Meeting, and I was delighted to hear that our very own Godfrey Miller won the award for the best student presentation.

Returning To Penn, I just about had enough time to finish putting together the take-home final exam for my graduate General Relativity course, before heading off to NYU on Wednesday with our whole group for our semesterly joint meeting. We were joined, as usual, by a nice crowd from Columbia and Case Western for a day of talks and discussion. I always find these meetings to be incredibly useful scientifically, because the group is so interactive, boisterous and interested in the material, while being such warm and friendly hosts. It makes for an enjoyable day every time. Beyond the obvious exchange of ideas, these meetings also provide an opportunity for our students to get used to giving talks on their work. This time my student – Garrett Goon – and one of my colleague Justin Khoury’s students – Austin Joyce – gave our student talks, leading to some healthy discussion Wess-Zumino terms in new field theories and conformal cosmology, respectively. Both did a terrific job, although they’re becoming old pros at this point, rather than beginning students in need of practice.

To close out last week, Greg Gabadadze from NYU came down on Friday so that we could try to finish up some details in a project that is close to completion, before we start dispersing for various summer conferences. I’ll discuss these soon, I expect.

Today my final exam will be turned in and grading starts, an old friend is delivering a seminar in our group, and Sean’s student Kim Boddy arrives for a week so that the three of us can try to finish up a paper. The end of the semester always seems to go this way. While all these things are fun, life becomes excessively hectic for two weeks, and then travel begins.

Some of you may have been following a tiny brouhaha (“kerfuffle” is so overused, don’t you think?) that has sprung up around the question of why the universe exists. You can’t say we think small around here.

First Lawrence Krauss came out with a new book, A Universe From Nothing: Why There Is Something Rather Than Nothing (based in part on a popular YouTube lecture), which addresses this question from the point of view of a modern cosmologist. Then David Albert, speaking as a modern philosopher of science, came out with quite a negative review of the book in the New York Times. And discussion has gone back and forth since then: here’s Jerry Coyne (mostly siding with Albert), the Rutgers Philosophy of Cosmology blog (with interesting voices in the comments), a long interview with Krauss in the Atlantic, comments by Massimo Pigliucci, and another response by Krauss on the Scientific American site.

I’ve been meaning to chime in, for personal as well as scientific reasons. I do work on the origin of the universe, after all, and both Lawrence and David are friends of the blog (and of me): Lawrence was our first guest-blogger, and David and I did Bloggingheads dialogues here and here.

Executive summary

This is going to be kind of long, so here’s the upshot. Very roughly, there are two different kinds of questions lurking around the issue of “Why is there something rather than nothing?” One question is, within some framework of physical laws that is flexible enough to allow for the possible existence of either “stuff” or “no stuff” (where “stuff” might include space and time itself), why does the actual manifestation of reality seem to feature all this stuff? The other is, why do we have this particular framework of physical law, or even something called “physical law” at all? Lawrence (again, roughly) addresses the first question, and David cares about the second, and both sides expend a lot of energy insisting that their question is the “right” one rather than just admitting they are different questions. Nothing about modern physics explains why we have these laws rather than some totally different laws, although physicists sometimes talk that way — a mistake they might be able to avoid if they took philosophers more seriously. Then the discussion quickly degrades into name-calling and point-missing, which is unfortunate because these are smart people who agree about 95% of the interesting issues, and the chance for productive engagement diminishes considerably with each installment.

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Jorge Cham visits CERN, and comes back with tales of particles and mass.