Blogs / Cosmic Variance

In the long-standing CV tradition of love for cured pork products, may we suggest the giant bag of pre-cooked bacon from Costco?

Our holiday season is filled with the joyful noise of loved ones asking “Would you like some bacon with that?”

Having recently slogged through grading an enormous pile of graduate-level problem sets, I am compelled to share one of the most useful tricks I learned in graduate school.

Make your integrals dimensionless.

This probably seems silly to the theoretical physicists in the audience, who have a habit of changing variables and units to the point where everything is dimensionless and equals one. However, in astrophysics, you frequently are integrating over real physical quantities (numbers of photons, masses of stars, luminosities of galaxies, etc) that still have units attached. While students typically do an admirable job of setting up the necessary integrals, they frequently go off the rails when actually evaluating the integrals, as they valiantly try to propagate all those extra factors.

Here’s an example of what I mean. Suppose you want to calculate some sort of rate constant for photoionization, that when multiplied by the density of atoms, will give you the rate of photo-ionizations per volume. These sorts of rates are always density times velocity times cross section:

For a Planck spectrum of photons and a typical energy-dependent cross section above some threshold

which becomes

This integral looks like a rough customer. You can pull some factors out front, but you’re still left with that unpleasant business in the exponential. You’re also using an integrating variable that has units, making it a bit tougher to check the dimensions of your answer to make sure it’s sensible.

Instead, if you force the variable you’re integrating over to be dimensionless:

the integral reduces to something that you can start to wrap your brain around:

Now you have the business end of the integral out front, where you can check the units and the scaling of the answer to see if it makes sense. The integral is also something that is far simpler to evaluate (although in this case, it’s actually not a trivial integration, but at least you can recognize that early and plan on how to deal with it). If you’re in a situation where you have to integrate by parts, the dimensionless integral will save you a world of pain. Even if you make a mistake in evaluating the integral, you’re usually only off by a simple multiplicative factor like pi, or 2. All these things are good.

I have been buying things, banking, booking reservations, and all sorts of other transactions on the Internet for 13 years now. I don’t know how many times I have given out my credit card number, and lots of other personal information, trusting that it would be respected. Until now, it always has been. Obviously Internet commerce has thrived, and formed an important part of our economy.

But, as our department’s computer support person said recently, “the road ahead is filled with marauders”. Heh. Not just the road ahead…

It all started last January when I was interested in getting a home equity line of credit to do our landscaping project this year. Some of the places I wanted to apply to a specified minimum credit scores – I wanted to know mine. So, I Googled “free credit report” and got a list. I confess I don’t remember which one I went to. I do remember though that in order to get my free credit report at a certain point I had to enter my credit card number and authorize a one dollar payment. I was very careful to not sign up for any of the subscriptions or services that kept popping up as I clicked my way to my free credit report.

Eventually, I did get my free credit report, my score was great, and a few weeks later and got a really great deal on a home equity line of credit.

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It’s usually not a good idea to have one of your parents call the department on your behalf.

And if you have the kind of parent who does this without your asking, you have my condolences.

It’s September, and a young person’s fancy naturally turns to applying to grad school/postdocs/faculty jobs. And in this day and age, questions inevitably arise: Are they going to google me? What will they find? Followed immediately by: Should I have my own web page (if I don’t already)? And what should be on it?

Roughly speaking, as you climb up the academic ladder, the scrutiny one undergoes becomes increasingly close. If you are in high school and applying to colleges, I would be extremely surprised if any admissions committee googled you — there are just too many of you, frankly. Mostly this also holds for undergrads applying to grad school. At least, that’s the situation among theorists; for experimentalists, who might be joining a specific lab on day one, the number might be smaller and the individual attention correspondingly greater. By the time you apply for faculty jobs, the numbers are very small, and nobody gets an offer without being poked and prodded in person, and having their CV examined under a microscope. In that case, the web page is (almost) beside the point, as they’ve seen you up close and personal.

It’s for postdoc applications, then, that the googling question becomes most relevant. Remember that most research groups have relatively few postdocs, so they take the selection process very seriously — mistakes can be costly. But in many cases the decision-making timescale is sufficiently short that they don’t have the luxury of seeing each candidate in person. So I would say: yes, at many places where you apply for postdocs, they will be googling you to glean information that might not show up on a formal application. That is especially true if you’re applying to individual professors or groups (rather than wider-ranging fellowships), and also if the relevant decision-makers are younger.

So: if they do google you, what will they find? You can see how it might make sense to put up your own web page: that way you have some influence over their first impressions of you. There is a systematic issue, of course, that some names are more easily googleable than others, but we won’t address that here. If you do have a web page, you can simply include the URL in your CV, so they will have it in front of them.

If you do decide to have a web page, what should it look like? There is an overarching principle at work here: the Web is World-Wide. That is, everything you put on your page can be viewed (ordinarily) by everyone. You can’t put stuff up that “is only meant for your friends,” and then be surprised when it is examined by prospective employers. If you have pictures or stories that are in any way private — keep them private!

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A: Hey, what’s up? You’re looking a little anxious these days.

B: I know. We’re getting close to the romance deadline.

A: The romance deadline?

B: Yeah, in a couple of days I have to decide who I’ll be going out with for the next five years or so.

A: Oh, right, I forgot. Have you decided between boyfriend and girlfriend?

B: I’ve thought about it a lot, and I definitely want a girlfriend.

A: That’s cool. But don’t you worry that the standards are higher if you say you want a girlfriend? I’ve heard that boyfriends are much easier.

B: I heard that, too. But girls are what I’m really passionate about.

A: Couldn’t you just get a boyfriend first, and then switch if you don’t like it?

B: Some people try that, but it can be awkward. Better to just be honest about your intentions from the start.

A: Fair enough. So did you get any acceptances?

B: Yeah, two different women have agreed to date me. Cindy and Alyssa. But I have to choose one.

A: Hey, that’s great that you go two offers. Have you made a choice yet?

B: Well, I had coffee with Alyssa, and we really hit it off — she’s beautiful, and charming, and laughed at my jokes. I definitely think we would get along well over the next few years. I met Cindy, too; she’s a knockout, and clearly very talented, but there wasn’t as much of a spark there.

A: That can happen. So are you going to choose Alyssa?

B: I’m tempted, but the thing is — Cindy’s US News ranking is much higher.

A: Her what?

B: Every year, US News puts out rankings of boyfriends and girlfriends. Now, Alyssa is a solid top-20 girlfriend, but Cindy is top five! I’m really worried I’d be making a mistake by passing up the opportunity to go out with Cindy. Everyone has heard of her.

A: That sounds a little weird to me. How do they come up with these rankings?

B: Nobody knows, really. But everyone takes them very seriously. Still, I keep hoping that the NRC will update their boyfriend/girlfriend rankings soon. Those are supposed to be much more scientific.

A: NRC?

B: The National Romance Council.

A: But look, you seem to have really hit it off with Alyssa. Who cares that US News ranks Cindy higher? The concept of a “boyfriend/girlfriend ranking” just doesn’t make sense — what matters is how well you personally get along with them, not some pseudo-objective measure of excellence.

B: It’s easy to say that, but this is a big decision. I’m really worried that, ten years from now when I’m ready to get married, my prospective spouse is not going to be nearly as impressed that I went out with Alyssa than if I had gone out with Cindy.

A: Come on, it’s five years of your life that we’re talking about here. Your chances of eventually being happily married would seem to be a lot better if you choose someone you’re likely to be happy with right now.

B: You’re right, I know. Well, I hope Cindy won’t be disappointed. I don’t think she’s used to being turned down.

A: Don’t worry. I’m pretty sure she’ll get over it.

Today is Grad School Recruitment Day at Caltech, from which I surmise that there must be dozens of readers of this blog who are currently puzzling over where they might want to spend the next years of their lives. And hundreds of readers who went through this puzzling at one point themselves, or will face it in the future. So, since “work” is preventing me from blogging very much, here is a place to share stories and questions; we’ve previously given advice, but you can never get too much. (Professors, did you know that these students are talking about you behind your back on the internet? A brave new world etc.)

My grad school story: I was an astronomy major at Villanova as an undergrad, but knew that I really wanted to do physics. Nobody in my department was really qualified to give advice about grad schools in theoretical high energy physics or cosmology, but there was a big book put out by the AIP that listed programs and the people working in each specialty; not sure if the book still exists, or whether it’s been replaced by a website. So I applied to five different places, all top-notch; got into three, waitlisted at one, and rejected at one. (I had a not-completely-unheard-of profile: small undergrad school, great letters, good but not perfect grades and GRE’s, vague and untutored desire to unify all of theoretical physics.) I wanted to stay on the East Coast for personal reasons (= “girlfriend”). Sadly, the school that rejected me (Princeton) and wait-listed me (Harvard) were the ones on the East Coast that I had applied to. So I visited Harvard myself to plead my case; to no avail, of course (I wouldn’t recommend doing this — it won’t work and can annoy people), but I was told that if I could get an outside fellowship they would accept me. And then I did get an outside fellowship, from the NSF; but Harvard still wouldn’t accept me. Apparently that was a bit of a tactic. So I called up the astronomy department and asked if they would let me in. They were a bit surprised that physics wouldn’t accept me, given that I was free, but happily took me on. Which explains why I have no degrees in physics, even though all of my subsequent employment has been in physics departments.

Did it matter that I went to an astronomy department rather than a physics department where my interests would have been a more natural fit? Absolutely — I hung out with people who chatted about redshifts in their spare time, not with people who chatted about Feynman diagrams, and that lack of immersion in a crucial subject has undoubtedly been a handicap. But I was generally in a good situation (you can’t really complain about being at Harvard), and I made the most of it — took many physics classes, spent time talking to professors, wrote papers with other students and mathematicians as well as my advisor, went to MIT and ended up collaborating with people there as well. If you go to someplace that is decent enough to offer opportunities, it will be up to you to take the initiative and make your time there a success.

It’s about the time of year when prospective graduate students are making one of the most important decisions of their lives: where to go to grad school. So we really should give some advice about that, but happily we already have! And it still seems pretty relevant. Meanwhile, today I’m at the KITP in Santa Barbara, speaking on a panel on The Perils and Pitfalls of Speaking to the Press. (One in a series organized by the KITP’s Journalist in Residence.) So I have to give a short talk about that, and thought I could take advantage of the opportunity by turning it into a blog post.

Sadly, I eventually realized that I do not have a Grand Unified Theory of interactions between scientists and journalists. It is a complicated relationship, in which there is much overlap in objectives on both sides, but also undeniably some tensions here and there. Consider the following two anecdotes:

• My first direct interaction with the science press was as a grad student, when I was working with Edward Farhi and Alan Guth on whether it was possible to build a time machine out of cosmic strings (as proposed by Richard Gott). Our work was written up in Science News, and they did an extremely careful job — Ron Cowen interviewed us in depth, asked good questions, and the magazine even sent us a draft copy of the article to check for accuracy before it was printed. (That almost never happens, don’t expect it.) But when we saw it in print, an editor had helpfully inserted just one new sentence to make things more clear — explaining that open universes were ones that would expand forever. Except that we were working in the slightly unusual context of 3 spacetime dimensions, not the usual 4, and in that case open universes don’t really “expand” at all. Good intentions gone awry.
• I was once in the audience for a panel featuring David Kestenbaum, a science reporter for NPR. He played us a tape of a radio journalist talking to a scientist about the fear of avian flu spreading from the Bronx Zoo. The scientist babbled on at length about open systems and complex environment and disease vectors in a rapid-fire stream of utter incomprehensibility. The journalist stopped him for a second, and basically said “Look, cutting to the chase, does the zoo pose a danger?” The scientist said “No, absolutely not.” “Okay, could you say that directly?” “Sure, no problem.” And then the journalist asks the question again, to which the scientist — well, you can guess. A rapid-fire stream of dense jargon, in which the word “No” never appeared. Completely useless for the radio.

As far as the Very Big Picture is concerned, scientists and journalists are on the same side. We all want to tell interesting and true stories to a wide audience. But when it comes to specifics, aims and competencies often diverge. Understanding what each others’ goals and constraints are can definitely help to make for a better final product.

So here are some things that I, as a scientist, have figured out about what journalists want. At least I think I have figured them out; actual journalists are welcome to jump in and explain what they really want in their own words.

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Now that late January is upon us, a wave of graduate school admissions letters is soon to come crashing down upon undergraduates throughout the land. The process can be immensely frustrating to a student, as one often has little idea as to what magic ingredient is determining whether one is admitted or rejected from different schools. Having been involved in graduate admissions decisions for much of the last decade, I therefore thought I’d give a summary of how it’s done at UW Astronomy, so students can get a sense of where in the process their application might potentially go astray. My take will be different from other schools and other departments whose admissions committees may emphasize different strengths, but at least it’s one data point where few are available.

Details below the fold. Enter if you dare!
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Yesterday we went to see a chat with Alan Alda and KC Cole at USC’s Annenberg School for Communication, as advertised by Clifford here. Alda was apparently some kind of TV actor back in the day, but he is also quite the science aficionado — hosting Scientific American Frontiers on PBS, and originating the role of Richard Feynman in Peter Parnell’s play QED.

The most interesting story we heard was one that happened just the day before, when Alda and Cole visited with some students at USC’s engineering school. Apparently it was quite a day, beginning with short presentations by each of the students about the work they were doing. After the presentations, Alda led the students through a series of improvisation exercises from Viola Spolin’s classic workbook. After which, the students were asked to give their presentations again! Apparently (I have to take their word for it), the first time around the students were pretty darn good, but the second time they truly came to life.

Giving talks, or presenting ideas more generally, is one of the necessary skills of academic life that we usually presume one just picks up on street corners. The idea that, for example, college professors should learn how to teach classes would be an anathema to most actual college professors. But there is a lot of skill involved, and practice and learning can really make a difference. (The same would go for writing papers, or being an advisor, or a thousand other aspects of being a professor.)

My favorite part of the chat was Alda’s admonition to scientists to “Show the Love.” He was moved by the evident passion for their work exhibited by the students, but recognized that it didn’t always come through during scientific presentations. So here is some simple advice to young scientists giving talks: show the love! (Good advice to old scientists, too, but there’s no hope they would listen.) Let it be clear that you are absolutely fascinated by this work you are doing. You’re not in it for the money and fame, one presumes. Don’t look at a talk as a terrifying ordeal to be stoically survived; look at it as a chance to share some of your passion with other people who haven’t delved as deeply into the material as you have. I know we’re not supposed to use icky words like “love” in the rigorously austere corridors of professional physics, but this is a case where a little culture-changing wouldn’t hurt anybody.

And if you’re not all that passionate about what you’re doing — switch to doing something you really do love.

Update: Jennifer adds more words, plus an amusing cartoon, and an annoying poem.