Direct to video

I wrote up a little piece for the proceedings of a conference I went to over the summer. To go into self-deprecating mode, this is the sort of thing that a colleague of mine used to call a direct-to-video paper (this was in the pre-DVD era), because it doesn’t go through the same level of scrutiny as a refereed journal article.

The article has to do with how to separate a map of the polarization of the microwave background into two pieces called the E and B components.  Over the coming years, maps of microwave background polarization are likely to become more and more important in putting constraints on our theories of the early Universe.   A polarization map can be thought of as two maps lying on top of each other.  The B map is considerably weaker than the E map, and it contains information that’s much more useful than the E map, so cleanly splitting the map into the two pieces is going to be very important in extracting science from the data.  This article is an overview of some of the issues involved in this separation.  It contains an extension of some work I did a while ago on finding ways to do this separation more accurately and efficiently.

Not living up to the hype.

This blog is mentioned in a piece in the U.R. newsletter RichmondNow, which makes it all the more embarrassing that I haven’t posted anything to it for ages.

In case you’re desperately searching for blog posts to read, let me mention a couple of good ones by colleagues of mine.

Students who have to give talks on their research should really look at Bill Ross’s post on how to give a good math talk. Some of it’s math-specific, but most of it’s just good general advice. Many eminent scientists could benefit from following it.

Also, Matt Trawick’s blog has a lot of good stuff, including an explanation of what undergraduate research is all about.

Black holes in Slate

The online magazine Slate published a piece today explaining what happens to you if you fall into a black hole, and they had the good sense to consult me on it. Slate’s “Explainer” articles are also podcasted, so if you’re not into reading, you can listen to it instead.

The article pretty much gets things right. One minor quibble: the sentence

In fact, for all but the largest black holes, dissolution would happen before a person even crossed the event horizon, and it would take place in a matter of billionths of a second.

isn’t quite right: the “billionths of a second” number (which I think the author got from me) applies only to quite small black holes, not to “all but the largest” ones, and I think that even for stellar-mass black holes (which are much smaller than “the largest” ones) you’d make it across the horizon before being ripped apart by tidal forces. But those are pretty minor points; the main ideas are all right.

The motivation for this article is the possibility that the Large Hadron Collider will produce black holes. Short answer: It probably won’t, and even if it does, they’ll evaporate quickly rather than gobbling up the Earth. You really don’t need to worry about this.

Slate doesn’t do a lot of science reporting, but when they do it’s often pretty good. A recent article discussed one of the main things the LHC is actually expected to find, namely evidence for the Higgs mechanism. Unlike a lot of writing on the subject, this article actually tried to explain the fact that the Higgs mechanism won’t necessarily manifest itself as just a single new type of particle: it’s likely that something more complicated will be found. If so, that’ll be much more interesting than just finding a single Higgs particle.

Since I’ve been saying nice things about Slate, I want to end with one criticism of their science reporting: they still let Gregg Easterbrook write about science from time to time. Easterbrook’s done some good stuff over the years — in particular he was sharply and rightly critical of the space shuttle and space station long before that became fashionable, and he deserves credit for publicly and forthrightly changing his mind about global warming. (Also, I’ve heard his writing on the NFL is good, but I know nothing about that.) But as far as I’m concerned, anyone who defends the teaching of intelligent design in science classes forfeits all credibility as a science journalist. Yes, I’m intolerant and closed-minded about this. But I’m also right, so it’s OK.

Puzzles in the microwave background

The maps of the microwave background radiation made by the WMAP satellite have been incredibly important in our understanding of the Universe.  In most ways, the maps are amazingly consistent with the “standard model” of cosmology.  In this model the Universe is made of mostly dark energy and dark matter, and the structure we see around us grew out of tiny density variations imprinted during a period of inflation.

But there are a few puzzles in the WMAP observations, mainly having to do with large-scale patterns in the maps.  One of the puzzles is that large-angle correlations in the map are significantly weaker than expected.  U.R. rising junior Austin Bourdon and I have written a paper analyzing some possible explanations for this puzzle.  Our paper shows that a broad class of possible explanations can actually be ruled out, because they make the problem worse rather than better.  The class of explanations we rule out includes some “exotic” models that have been proposed in the literature recently, but it also includes some much more mundane possibilities, such as various non-cosmological contaminants in the data.

In addition to posting it on the web, we’ve submitted the paper for publication in the journal Physical Review D.  For any non-scientists who’ve read this far, the next step is that the paper will be sent out for review by experts, who will recommend for or against publication.  In the mean time, most people who care about this subject will see it on the web archive.


I’m spending this week in Paris, at a conference on Bolometric interferometry for the B mode search.  This is a narrowly focused workshop on a specific technique that may be used  for future measurements of the microwave background.  (That’s why its name is so completely esoteric.) For a number of years now,  I’ve been part of a collaboration trying to develop this technique.

This is the second conference I’ve been to in the past few weeks.  St. Louis was perfectly nice, but I have to say it’s nicer to be in Paris, weak dollar notwithstanding.


Apparently there’s a tradition here at the University of Richmond: when a faculty member gets tenured, he or she chooses a book for the library and writes a description of the importance of the book. The library inserts that description into the catalog, or into the book, or something like that.

Since I just got tenure, I had to choose a book to write about. After thinking about it for a while, I decided to go with Galileo’s Dialogue concerning the two chief world systems. Here’s the description I’m sending off to the library.

By the way, I really mean it when I say in here that the book is extremely readable. I can’t think of any other book that’s (a) anywhere near as important as this one and (b) actually fun to read. If you haven’t read it, check it out! (Although if you’re at UR, you’ll have to wait a week or so to get it out of the library, because I’ve got it at the moment.)

Anyway, here’s what I wrote:

The central idea of astrophysics is that the same laws of nature we discover in labs on Earth can be used throughout the Universe: there are not separate laws for heavenly bodies. It would be hard to overstate the importance of this insight to the emergence of modern science. Galileo did not invent this idea – like most really big ideas, this one cannot be attributed to any one person. But he deserves a large share of the credit for developing the idea and for persuasively and cogently championing it. Galileo is an all-too-rare figure among the giants of science: he wrote with clarity and even wit for an audience of non-specialists. He wrote in the common language, not in Latin, in a style that makes his work still readable and even enjoyable today.

Galileo has a lot in common with Einstein, so it is fitting that Einstein wrote the foreword to this English translation. In particular, Galileo's description of experiments performed below decks on a moving ship is the direct ancestor of Einstein's discovery of relativity, both in the scientific content of the ideas and in the ingenious use of thought experiments.

Einstein and me

I never met Einstein, which is not surprising, since he died over 20 years before I was born. [Update: Make that 12 years.  See Matt Trawick’s comment below.]  (The most famous physicists I have ever met, I think, are Eugene Wigner and John Wheeler, who are not exactly household names to non-scientists.) But back when I was in college I did get to know an old friend of Einstein’s pretty well.

Her name was Gabrielle Oppenheim, and she was about 95 when I knew her in the summer of 1988. Because her eyesight was very poor, she hired students to read the newspaper to her. This was a great job, which was passed on from student to student. I don’t remember how much it paid; I would have done it for nothing.

Mrs. Oppenheim told me lots of stories about Einstein. She first met him at a party in Brussels in 1911. Her husband pointed Einstein out and said, “That man will be one of the greatest physicists.” Mrs. Oppenheim’s response: “So I gave him one sandwich more.” (She later told this story to F. Murray Abraham in a Nova documentary, but I heard it first.)

She also said she was with Einstein in 1919 when he got the telegram from Sir Arthur Eddington, announcing that his observations of the bending of starlight had confirmed Einstein’s theory of general relativity. This was the event that made Einstein world-famous. But according to Mrs. Oppenheim, Einstein was much less excited about the result than the other people who were there at the time, because he had never doubted what the result would be.

She knew Einstein in Europe, but she spent much more time with him later in the U.S., when she and her husband had come to Princeton. (Her husband, Paul Oppenheim, was a philosopher.) Once, she and her husband were sailing with Einstein when the boat capsized. Her husband said, “Well, at least if we die with Einstein, we’ll be famous.”

She told me lots of other good stories. Once, she said, she was at a dinner party somewhere in Europe during World War I. A German army officer asked where she was from, and she told him she was Belgian. He replied that Germany would be invading Belgium soon. Mrs. Oppenheim said, “I was so offended by that, that I turned away and didn’t speak to him for the rest of the dinner.”

Mrs. Oppenheim told me way back then that I was “the scientist type”. Given that she hobnobbed with some of the greatest physicists of the 20th century (Bohr and others as well as Einstein), I figured she must know what she was talking about.