## The Most Beautiful Equations in Applied Mathematics

By Nick Higham

The BBC Earth website has just published a selection of short articles on beautiful mathematical equations and is asking readers to vote for their favourite.

I wondered if we had included these equations in The Princeton Companion to
Applied Mathematics
(PCAM), specifically in Part III: Equations, Laws, and Functions of Applied Mathematics. We had indeed included the ones most
relevant to applied mathematics. Here are those equations, with links to the
BBC articles.

• The wave equation (which quotes PCAM author Ian Stewart). PCAM has a short
article by Paul Martin of the same title (III.31), and the wave equation
appears throughout the book.
• Einstein’s field equation. PCAM has a 2-page article Einstein’s Field
Equations
(note the plural), by Malcolm MacCallum (article III.10).
• The Euler-Lagrange equation. PCAM article III.12 by Paul Glendinning is about
these equations, and more appears in other articles, especially The
Calculus of Variations
(IV.6), by Irene Fonseca and Giovanni Leoni.
• The Dirac equation. A 3-page PCAM article by Mark Dennis (III.9) describes
this equation and its quantum mechanics roots.
• The logistic map. PCAM article The logistic equation (III.19), by Paul
Glendinning treats this equation, in both differential and difference forms.
It occurs in several places in the book.
• Bayes’ theorem. This theorem appears in the PCAM article Bayesian Inference in Applied Mathematics (V.11), by Des Higham, and in other articles employing
Bayesian methods.

A natural equation is: Are there other worthy equations that are the
subject of articles in Part III of PCAM that have not been included in the BBC
list? Yes! Here are some examples (assuming that only single equations are
allowed, which rules out the Cauchy-Riemann equations, for example).

• The Black-Scholes equation.
• The diffusion (or heat) equation.
• Laplace’s equation.
• The Riccati equation.
• Schrödinger’s equation.

Check out the Princeton Companion to Applied Math here.

## Solving last week’s L.A. Math challenge

We’re back with the conclusion to last week’s LA Math challenge, The Case of the Vanishing Greenbacks, (taken from chapter 2 of the book). After the conclusion of the story, we’ll talk a little more with the author, Jim Stein. Don’t forget to check out the fantastic trailer for LA Math here.

Forty‑eight hours later I was bleary‑eyed from lack of sleep. I had made no discernible progress. As far as I could tell, both Stevens and Blaisdell were completely on the up‑and‑up.   Either I was losing my touch, or one (or both) of them were wasting their talents, doctoring books for penny‑ante amounts.   Then I remembered the envelope Pete had sealed. Maybe he’d actually seen something that I hadn’t.

I went over to the main house, to find Pete hunkered down happily watching a baseball game. I waited for a commercial break, and then managed to get his attention.

“I’m ready to take a look in the envelope, Pete.”

“Have you figured out who the guilty party is?”

“Frankly, no. To be honest, it’s got me stumped.” I moved to the mantel and unsealed the envelope. The writing was on the other side of the piece of paper. I turned it over. The name Pete had written on it was “Garrett Ryan and the City Council”!

I nearly dropped the piece of paper. Whatever I had been expecting, it certainly wasn’t this. “What in heaven’s name makes you think Ryan and the City Council embezzled the money, Pete?”

“I didn’t say I thought they did. I just think they’re responsible for the missing funds.”

I shook my head. “I don’t get it. How can they be responsible for the missing funds if they didn’t embezzle them?”

“They’re probably just guilty of innumeracy. It’s pretty common.”

“I give up. What’s innumeracy?”

“Innumeracy is the arithmetical equivalent of illiteracy. In this instance, it consists of failing to realize how percentages behave.” A pitching change was taking place, so Pete turned back to me. “An increase in 20% of the tax base will not compensate for a reduction of 20% in each individual’s taxes.   Percentages involve multiplication and division, not addition and subtraction. A gain of 20 dollars will compensate for a loss of 20 dollars, but that’s because you’re dealing with adding and subtracting. It’s not the same with percentages, because the base upon which you figure the percentages varies from calculation to calculation.”

“You may be right, Pete, but how can we tell?”

Pete grabbed a calculator. “Didn’t you say that each faction was out \$198,000?”

I checked my figures. “Yeah, that’s the amount.”

Pete punched a few numbers into the calculator. “Call Ryan and see if there were 99,000 taxpayers in the last census. If there were, I’ll show you where the money went.”

I got on the phone to Ryan the next morning. He confirmed that the tax base in the previous census was indeed 99,000. I told Pete that it looked like he had been right, but I wanted to see the numbers to prove it.

Pete got out a piece of paper. “I think you can see where the money went if you simply do a little multiplication. The taxes collected in the previous census were \$100 for each of 99,000 individuals, or \$9,900,000. An increase of 20% in the population results in 118,800 individuals. If each pays \$80 (that’s the 20% reduction from \$100), the total taxes collected will be \$9,504,000, or \$396,000 less than was collected after the previous census. Half of \$396,000 is \$198,000.”

I was convinced. “There are going to be some awfully red faces down in Linda Vista. I’d like to see the press conference when they finally announce it.” I went back to the guesthouse, called Allen, and filled him in. He was delighted, and said that the check would be in the mail.   As I’ve said before, when Allen says it, he means it. Another advantage of having Allen make the arrangements is that I didn’t have to worry about collecting the fee, which is something I’ve never been very good at.

I wondered exactly how they were going to break the news to the citizens of Linda Vista that they had to pony up another \$396,000, but as it was only about \$3.34 per taxpayer I didn’t think they’d have too much trouble. Thanks to a combination of Ryan’s frugality and population increase, the tax assessment would still be lower than it was after the previous census, and how many government agencies do you know that actually reduce taxes? I quickly calculated that if they assessed everyone \$3.42 they could not only cover the shortage, but Allen’s fee as well. I considered suggesting it to Ryan, but then I thought that Ryan probably wasn’t real interested in hearing from someone who had made him look like a bungler.

My conscience was bothering me, and I don’t like that. I thought about it, and finally came up with a compromise I found acceptable. I went back to the main house.

Pete was watching another baseball game. The Dodgers fouled up an attempted squeeze into an inning‑ending double play. Pete groaned. “It could be a long season,” he sighed.

“It’s early in the year.” I handed him a piece of paper. “Maybe this will console you.”

“What’s this?” He was examining my check for \$1,750. “Your rent’s paid up.”

“It’s not for the rent, Pete. It’s your share of my fee.”

“Fee? What fee?”

“That embezzling case in Orange County. It was worth \$3,500 to me to come up with the correct answer. I feel you’re entitled to half of it. You crunched the numbers, but I had the contacts and did the legwork.”

Pete looked at the check. “It seems like a lot of money for very little work. Tell you what. I’ll take \$250, and credit the rest towards your rent.”

A landlord with a conscience! Maybe I should notify the Guinness Book of Records. “Seems more than fair to me.”

Pete tucked the check in the pocket of his shirt. “Tell me, Freddy, is it always this easy, doing investigations?”

I summoned up a wry laugh. “You’ve got to be kidding. So far, I’ve asked you two questions that just turned out to be right down your alley. I’ve sometimes spent months on a case, and come up dry. That can make the bottom line look pretty sick. What’s it like in your line of work?”

“I don’t really have a line of work. I have this house and some money in the bank. I can rent out the guesthouse and make enough to live on. People know I’m pretty good at certain problems, and sometimes they hire me. If it looks like it might be interesting, I’ll work on it.” He paused. “Of course, if they offer me a ridiculous amount of money, I’ll work on it even if it’s not interesting. Hey, we’re in a recession.”

“I’ll keep that in mind.”   I turned to leave the room. Pete’s voice stopped me.

“Haven’t you forgotten something?”

I turned around. “I give up. What?”

“We had a bet. You owe me five bucks.”

I fished a five out of my wallet and handed it over. He nodded with satisfaction as he stuffed it in the same pocket as the check, and then turned his attention back to the game.

What made you include this particular idea in the book?

JS: The story features one of the most common misunderstandings about percentages.  There are innumerable mistakes made because people assume that percentages work the same way as regular quantities.  But they don’t — if a store lowers the cost of an item by 30% and then by another 20%, the cost of the item hasn’t been lowered by 50% — although many people make the mistake of assuming that it has.  I’m hoping that the story is sufficiently memorable that if a reader is confronted by a 30% discount followed by a 20% discount, they’ll think “Wasn’t there something like that in The Case of the Vanishing Greenbacks?

There are 14 stories in the book, and each features a mathematical point, injected into the story in a similar fashion as the one above.  I think the stories are fun to read, and if someone reads the book and remembers just a few of the points, well, I’ve done a whole lot better than when I was teaching liberal arts math the way it is usually done.

James D. Stein is emeritus professor in the Department of Mathematics at California State University, Long Beach. His books include LA Math, Cosmic Numbers (Basic) and How Math Explains the World (Smithsonian).

## Try your hand at solving an L.A. Math mystery

If you caught the rather incredible trailer for L.A. Math, you know it’s not your typical scholarly math book. Romance, crime, and mathematics don’t often go hand in hand, but emeritus professor in the Department of Mathematics at California State University Jim Stein cooked up the idea for an unconventional literary math book that would speak to students in his liberal arts math class. The end result is an entertaining, backdoor approach to practical mathematics knowledge, ranging from percentages and probability to set theory, statistics, and the mathematics of elections. Recently, Stein spoke to us about writing L.A. Math. Not only that, he left us with a mathematical mystery to solve.

L.A. Math is definitely an unusual book.  Brian Clegg described it by saying “It’s as if Ellery Queen, with the help of P. G. Wodehouse, spiced up a collection of detective tales with a generous handful of practical mathematics.”  How did you happen to write it?

JS: I absolutely loved it when he described it that way, because I was brought up on Ellery Queen.  For younger readers, Ellery Queen was one of the greatest literary detectives of the first half of the twentieth century, specializing in classic Sherlock Holmes type cases.  The Ellery Queen stories were written by the team of Manfred Dannay and Frederick Lee — and my mother actually dated one of them!

The two other mystery writers who influenced me were Agatha Christie and Rex Stout.  Rex Stout wrote a series featuring Nero Wolfe and Archie Goodwin; the books are presumably written by Archie Goodwin describing their cases, so I used that as the model for Freddy Carmichael.  The relationship between Archie and Nero also served, somewhat, as a parallel for the relationship between Freddy and Pete.  Nero and Pete both have addictions — Nero wants to spend his time eating elaborate cuisine and raising orchids, and Pete wants to spend his time watching and betting on sports.  It’s up to Archie and Freddy to prod them into taking cases.

How does Agatha Christie enter the picture?

JS: I’d taught liberal arts mathematics — math for poets — maybe ten times with temporary success but no retention.  Students would learn what was necessary to pass the course, and a year later they’d forgotten all of it.  That’s not surprising, because the typical liberal arts math course has no context that’s relevant for them.  They’re not math-oriented.  I know I had several history courses discussing the Battle of Azincourt, but I don’t remember anything about it because it has no context for me.

Agatha Christie’s best-known detective is Hercule Poirot, and one day I was in a library reading a collection of short stories she had written entitled The Labors of Hercules.  Christie had a background in the classics, and did something absolutely brilliant — she constructed a series of twelve detective stories featuring Hercule Poirot, each of which was modeled, in one way or another, around the Twelve Labors of Hercules in classical mythology.  I thought to myself — why don’t I do something like that for topics in liberal arts math?  Maybe the students would remember a few of the ideas because they’d have the context of a story from which to remember it.

Could you give an example?

JS: How about this?  Why don’t we take a story from the book, and present it the way Ellery Queen would have.  Ellery Queen always played fair with the reader, giving him or her all the clues, and after all the clues had been presented, EQ would write a paragraph entitled “Challenge to the Reader”.  EQ would tell the reader “Now you have all the clues.  Can you figure out whodunit?” — or words to that effect.

OK, here’s what we’ll do.  We’ll take The Case of the Vanishing Greenbacks, Chapter 2 in L.A. Math, and present the story up to the crucial point.  Then we’ll let the reader try to figure out whodunit, and finish the story next week.

Chapter 2 – The Case of the Vanishing Greenbacks

The phone rang just as I stepped out of the shower. It was Allen.

“Freddy, are you available for an embezzlement case?”

My biggest success had been in an embezzlement case involving a Wall Street firm specializing in bond trading. Allen had given me a whopping bonus for that one, which was one of the reasons I could afford to take it easy in L.A. I had done well in a couple of other similar cases, and had gotten the reputation of being the go-to guy in embezzlement cases. It never hurts to have a reputation for being good at something. Besides, you don’t see many guys in my line of work who can read balance sheets.

I’ve always felt it’s important to keep the cash flow positive, and the truth was that I was available for a jaywalking case if it would help the aforementioned cash flow. But it never hurts to play a little hard-to-get.

“I can probably clear my calendar if it looks interesting.”

Allen paused for a moment, either to collect his thoughts or to take a bite of one of those big greasy pastrami sandwiches he loves. “I’m pretty sure you’ll find it interesting. It’s stumped some people in L.A., and I told them I had a good man out there. BTW, that’s you.”

It’s nice to be well thought of – especially by someone in a position to send you business. I knew that Allen’s firm, though headquartered in New York, had arrangements with other firms in other cities. I didn’t really care about the details as long as the check cleared – which it always had.

“I’m certainly willing to listen. What’s the arrangement?”

“Consulting and contingency fee. Fifty‑fifty split.”

That was our usual arrangement. Burkitt Investigations got a guaranteed fee, plus a bonus for solving the case. Allen and I split it down the middle.

“OK, Allen, fill me in.”

“Ever heard of Linda Vista, Freddy?”

Temporary blank. Movie star? Socialite? Then I had it. Linda Vista was a town somewhere in Orange County with a big art community.

For those of you not up on California politics, Orange County is a bastion of conservatism. You have Orange County to thank, or blame, for Richard Nixon and Ronald Reagan. But Linda Vista, which my fragmentary Spanish translates as “pretty view”, was different from your basic Orange County bastion.

The vista in Linda Vista was sufficiently linda that it had attracted a thriving artistic community.   There were plenty of artists in Linda Vista, and most of them were liberals.

As a result, Linda Vista was highly polarized. The moderates were few and far between. On the left, you had the artists, with their funky bungalows and workshops. On the right, you had the stockbrokers and real-estate moguls, living in gated communities so they wouldn’t have to have any contact with the riff-raff, except for the tradesmen delivering or repairing stuff. However, there were enough artists and hangers-on to acquire political clout – after all, it’s still one man-one vote in a democracy, rather than one dollar-one vote. Pitched battles had raged over practically every issue from A (abortion) to Z (zoning), and many of these battles had made state and even national news.

That’s all I knew about Linda Vista, other than not to try to drive down there at rush hour, which turned one hour on the 405 to more than twice that. The obvious question was: what kind of a contingency case had they got? So I asked it.

Allen filled me in. “The city is out a bunch of bucks, and each side is accusing the other of fraud and embezzlement. Because of the split in the political situation, the City Manager gave half the budget to the conservatives, and the other half to the liberals, letting each determine how to spend its half. Both sides claim to have been shortchanged.”

Allen paused to catch his breath. “I’ve got a friend who works in the City Manager’s office. I told him I had a good man out there who’d done a lot of first‑class work in embezzlement cases. Want to take a look at it?”

“Sure. How much time should I put in before I throw in the towel?” In other words, how much is the consulting fee?

“As much as you like.” In other words, since Allen’s meter wasn’t running, feel free to burn some midnight oil. “The consulting fee is \$3,000, upped to ten if you figure it out and get proof.” You don’t have to be an expert at division to realize that I was guaranteed a minimum of \$1,500 for the time I put in, and \$5,000 if I doped it out. You also don’t have to be an expert at division to realize that Allen was getting the same amount for making a phone call. I decided to be reincarnated as an employer rather than an employee.

Allen gave me a brief description of the protagonists, and I spent a good portion of the evening with a pot of coffee and my computer, getting some background information on them. I’ll say one thing for the Information Age; it’s a lot easier to run a background check on people than it used to be. What with search engines and social networks, you save a lot on gas money and shoe leather.

The next morning I waited until after rush hour, and made the trek to Linda Vista. The City Hall was located in a section of town where the vista was a long way from linda, unless strip malls filled with 7‑11s and fast-food stores constitute your idea of attractive scenery. I found a place to park, straightened my coat and tie, and prepared for the interviews.

I was scheduled to have three of them. I had been hoping to arrange for longer interviews, but everyone’s in a rush nowadays, and I was getting a quarter-hour with each, tops. They’d all been interviewed previously – Allen had mentioned that this case had stumped others – and people are generally less than enthusiastic about being asked the same questions again. And again. The first interview was with Everett Blaisdell, conservative city councilman, who would explain why the conservatives happened to be short. The next was with Melanie Stevens, liberal city councilwoman, ditto. The last interview would be with Garrett Ryan, City Manager.

I have a bad habit. My opinion of members of groups tends to be formed by the members of those groups that I have seen before. Consequently, I was expecting the conservative Everett Blaisdell to look like a typical paunchy southern senator with big jowls. So I was a little surprised to discover that Everett Blaisdell was a forty-ish African-American who looked like he had spent years twenty through thirty as an NBA point guard.

He got right down to business. “I want you to know,” he barked, “that everything that we have done with our budget allocation has been strictly by the book. Our expenses have been completely documented.” He handed me a folder full of ledger sheets and photos of checks, which I glanced at and stashed in my briefcase.

Blaisdell was clearly angry. “The business community is the heart of Linda Vista, and it is ridiculous to suggest that it would act in a manner detrimental to its citizens. We are \$198,000 short in our budget.”

You don’t expect NBA point guards to get out of breath too easily, considering the time they have to go up and down the court, but maybe Blaisdell wasn’t in shape. He paused, giving me a chance to get a question in edgewise. “Just what do you think has happened, Mr. Blaisdell?” I inquired mildly.

“I know what has happened. Melanie Stevens and her radical crowd have managed to get hold of that money. They want \$200,000 to fund a work of so‑called art which I, and every right‑thinking citizen of Linda Vista, find totally offensive. It’s mighty suspicious that the missing funds, \$198,000, almost precisely cover the projected cost of the statue.”

I was curious. “If you don’t mind my asking, exactly what is this statue?”

Blaisdell’s blood pressure was going up. “They are going to build a scale replica of the Statue of Liberty and submerge it in Coca‑Cola. You may know that Coca‑Cola is acidic, and it will eventually dissolve metal. They say that this so‑called dynamic representational art represents the destruction of our civil liberties by over‑commercialization. Well, let me tell you, we’ll fight it.”

He looked at his watch. “Sorry, I’ve got another appointment. When you find out what those scum have done with the money, let me know.” He walked me to his door.

It took a few minutes to locate Melanie Stevens’ office, as it was in a different wing of the building, possibly to minimize confrontations between her and Blaisdell. It was a bad day for stereotypes. My mental picture of Melanie Stevens, ultra‑liberal, was that of a long-haired hippie refugee from the ’60s. The real Melanie Stevens was a pert gray‑haired grandmother who looked like she had been interrupted while baking cookies for her grandchildren. She, too, was evidently on a tight schedule, for she said, “Sorry, I can only give you about ten minutes, but I’ve made copies of all our expenses.” More ledger sheets and photos of checks went into my briefcase.

“Let me tell you, Mr. Carmichael, that we could have used that \$198,000. We planned to use it for a free clinic. I know exactly what has happened. Blaisdell has doctored the books. I’m sure glad that Ryan had the guts to ask you to look into it.”

“Blaisdell seems to think that your people are responsible for the missing funds,” I observed.

She snorted. “That’s just typical of what they do. Whenever they’re in the wrong, they lie and accuse the other side of lying. They rip off the community, and channel money into PACs. Political action committees. Or worse. Blaisdell knows he faces a stiff battle for re-election, and I wouldn’t be the least bit surprised to find that money turning up in his campaign fund.”

“He seems to think that you are going to use the funds for an art project, rather than a free clinic,” I remarked.

“He’s just blowing smoke. He knows quite well that the statue will be funded through private subscription.” She looked at her watch. “Let me know when you pin the loss on them.”

I left Stevens’ office for the last interview, with Garrett Ryan, whose anxious expression made it clear that he was not a happy camper. “Have you got any ideas yet?” he asked.

I shook my head. “I’ve just talked to Blaisdell and Stevens. They’ve each handed me files containing what they consider to be complete documentation. They’ve each given me a story asserting their own innocence, and blaming the other. I take it that the missing amount is \$198,000?”

Now it was Ryan’s turn to shake his head. “No, each side says that it is missing \$198,000. Quite a coincidence. And I’ll tell you, Mr. Carmichael, despite the animosity between them, I think that they are both honorable individuals. I find it difficult to believe that either would rip the city off.”

I focused on Ryan’s coincidence. “It’s funny that they are both short exactly the same amount. Perhaps you could tell me a little more about the budgetary process.”

“It’s really quite simple. Each resident of Linda Vista is taxed a fixed amount. Any complicated tax scheme would just result in a full employment act for accountants. The previous census resulted in a \$100 assessment per individual. The population of Linda Vista increased by 20% since the last census. We didn’t need any increase in operating expenditures; under my guidance we’ve done a fiscally conservative and frugal job of running the city. As a result, the Council voted to reduce everybody’s taxes by 20%. Needless to say, this was a very popular move.”

“I’ll bet it was. Did everyone pay their taxes, Mr. Ryan?”

“Everybody. We’re very proud of that ‑‑ a 100% collection rate. Despite what you may have heard, the citizens of Linda Vista are very civic‑minded. Liberals and conservatives alike.”

I’ve spent enough time with balance sheets to know that accuracy is extremely important. “Was this population increase exactly 20%, or is that merely an approximate figure?”

Ryan consulted a sheet of paper. “Exactly 20%. I have a sheet of printout that gives information to four decimal places, so I can be quite sure of that.”

Just then a phone rang. Ryan picked it up, and engaged in some political doubletalk. After a few minutes he replaced the receiver. “Sorry, Mr. Carmichael. I’m behind schedule. Let me know if you make any progress.”   We shook hands, and I left.

A couple of hours later, I got home, having stopped for a bite but still avoiding rush-hour traffic. Pete noticed my presence, and asked, “So how’d things go in Linda Vista, Freddy?”

He nodded. I took about fifteen minutes to describe the problem and the cast of characters. “It looks like I’ll have to spend a day or so looking over the books.”

Pete shook his head. “It seems pretty clear to me.”

I’d seen it before — everybody’s a detective. Amateurs always think they know who the guilty party is, because it fits in with their preconceptions. I didn’t know whether Pete had cast Blaisdell in the role of a political fat-cat out to line his campaign war chest, or whether he was a conservative who saw Melanie Stevens as a radical troublemaker. Anyway, you’ve got to learn not to jump to conclusions in my line of work.

“You can’t do it like that, Pete. You’ve got to trace down the paper trails. I’ve done this lots of times.”

Pete grabbed a piece of paper, scribbled something on it, and sealed it in an envelope. “Five dollars will get you twenty that the name of the guilty party is inside this envelope.”

Pete needed taking down a peg. Maybe two pegs. Besides, I liked getting four‑to‑one odds on what was obviously an even‑ money proposition. “You’ve got a bet,” I said. We wrote our names on the envelope, and Pete put it on the table next to the HDTV.

“Whenever you’re ready, we’ll unseal the envelope.” I headed back to the guesthouse for a session with the books.

Challenge to the Reader: You have all the clues. Can you name the party responsible for the missing greenbacks? We’ll give you until the next blog to figure it out, when we’ll present the conclusion to the story.

## Anna Frebel on the search for the oldest stars

Astronomers study the oldest observable stars in the universe in much the same way that archaeologists study ancient artifacts on Earth. Stellar archaeologist Anna Frebel is credited with discovering several of the oldest and most primitive stars, and her book, Searching for the Oldest Stars is a gripping firsthand account of her work. Recently she took the time to answer some questions:

What is your main research topic and what is stellar archaeology?

AF: My work is broadly centered on finding the oldest stars in the universe and using them to explore how the first stars and the first galaxies formed soon after the Big Bang. This works because these ancient stars are about 13 billion years old and they are still shining. The universe itself, by comparison, is 13.8 billion years old. I find these ancient stars in the outskirts of the Milky Way galaxy, using a large telescope. I’m also researching how the chemical elements heavier than hydrogen and helium were first created in those early stars, which ultimately allowed Earth to form and to bring about life in the universe.

AF: I have been fortunate enough to discover several “record holding stars”. In 2007, I found a 13.2 billion year-old star, which is incredibly old. This followed the 2005 discovery of the chemically most primitive star – a star of the second generation of stars to have formed in the universe. Since then, I have analyzed some incredible ancient stars in dwarf galaxies that orbit the Milky Way galaxy, and together with my team, we have recently beaten said 2005 record, which was enormously exciting.

Why do people say we are made from stardust?

AF: We humans are made from all sorts of different chemical elements, mostly carbon. We breathe oxygen and nitrogen, we wear silver and gold jewelry. All these elements were once, atom by atom, created inside different kinds of stars and their supernova explosions over the course of billions of years. Studying this evolution of the chemical elements in the universe with the help of ancient stars means that I’m literally studying the cosmic origins of the building blocks of life. So we really are closely connected with the universe, far more than we realize.

How did you decide to become a scientist?

AF: From a young age I knew I wanted to study stars. They were just so fascinating to me, these big spheres of gas, fusing new elements to gain energy to shine for eons in the sky. Fortunately, I received good advice during high school on how to become an astronomer. After studying physics until 2002, I turned to astronomy and the rest is history. Today, I take pride in sharing my story with young people and the general public by telling them what astronomers do on a daily basis, and how scientific results are achieved. I am passionate about conveying the importance of science literacy to the young and the young at heart while inspiring them with the beauty and mystery of the cosmos.

What kind of telescope is used for your astronomical observations?

AF: Astronomers use all kinds of different telescopes on Earth as well as from space to peer deep into the cosmos. It depends on the type of project and the brightness of the objects which telescope is best suited. Space observations are being carried out remotely, whereas ground-based observations are still done by the astronomer who has to travel to the telescope. More and more telescopes are becoming automated to enable remote controlled “office observing”.

Anna Frebel in front of the 6.5m Magellan Telescope in Chile.

Are you traveling to any telescopes?

AF: Yes, I regularly fly to Chile to the Magellan Telescopes to carry out my observations. These are some of the largest telescopes in the world and the dark night sky in the Southern Hemisphere is terrific for studying the cosmos. It’s the favorite part of my job and I love discovering new facts about the universe through these observations!

What does it mean when you say you’re going observing?

AF: To use the telescopes, you have to fly to Chile. First to Santiago, then to La Serena and from there is a 2-3h drive up the mountains of the Atacama Desert where the telescopes are. There are guest rooms there for the observers to sleep during the day and the observatory chefs are cooking delicious meals for everyone. Dinner is eaten together by all observers, including the technical staff. It’s a little community with the sole purposes of caring for the telescopes and obtaining exquisite astronomical observations all night long of a breathtaking sky.

What does a typical night at the telescope look like?

AF: All preparations for the night happen during the afternoon while it’s still light outside. After sunset, I usually choose the first targets from my list, which I begin to observe soon after dark. Each star is observed for 10-30 minutes. We immediately inspect each observation and then decide on the fly whether we need more data or not. If we have found an interesting old star we may choose to immediately observe it for a few more hours.

Did anything ever go wrong at the telescopes?

AF: Of course! Mostly when it’s cloudy because then we can’t observe any starlight. This can be very frustrating because it can mean that we have to come back to the telescope a year later to try again. Clouds spell bad luck. Other times, the air layers above the telescope are often not as smooth as is required. This makes the stars twinkle and appear less sharp, which means less good data and longer exposure times. And sometimes there are technical problems with the telescope too.

How do you get your telescope time? Can I go to your telescope and observe, too?

AF: To obtain telescope time, astronomers have to submit a proposal to a committee that selects the best projects and awards them the time. The proposal contains a detailed description of the project and the technical details on what information is being sought. Telescope use is restricted to professional astronomers because of the considerable expense. The cost is about USD 50,000 to 100,000 per night, depending on the telescope, and often paid by various institutions and universities who jointly operate observatories. While this is a lot of money, it’s actually not that much in comparison to many other research facilities.

Are there any special moments at the telescope that you remember in particular?

AF: Yes, going observing is always magical and memorable. Of course I particularly remember big discoveries and the excited nervousness of checking and checking whether we didn’t make a mistake and that the discovery was really what it appeared to be. Then, there have been the frustrating moments of sitting at the telescopes for nights on end listening to the rain and flying home empty-handed. I have been there when severe technical problems and even a bush fire prevented observing during clear nights. But I always associate observing with the most colorful sunsets, the calm and peaceful atmosphere up in the mountains, and of course the sleepless but exciting nights.

Anna Frebel is the Silverman (1968) Family Career Development Assistant Professor in the Department of Physics at the Massachusetts Institute of Technology. She is author of Searching for the Oldest Stars, and has received numerous international honors and awards for her discoveries and analyses of the oldest stars. She lives in Cambridge, Massachusetts.

## New Physics & Astrophysics Catalog

We invite you to browse our Physics & Astrophysics 2016 catalog:

 Check out Doing Global Science, an introductory guide to responsible science in our globalized society. Written by a committee of leading scientists from all over the world, this text is required reading for anyone involved in scientific inquiry. Modern Classical Physics is a graduate-level text and reference book for first-year students that covers statistical physics, optics, elastodynamics, fluid mechanics, plasma physics, and special and general relativity and cosmology. A. Zee has contributed another new title to our In a Nutshell series entitled Group Theory in a Nutshell for Physicists. He takes all the nuts and bolts of a mathematical subject and makes it accessible for physicists. PUP is also publishing the second edition of Astrophysics in a Nutshell by Dan Maoz this season, a work that has become a standard text in courses on astrophysics.

If you would like updates of new titles emailed to you, subscribe to our newsletter.

Finally, PUP will be at the American Physical Society March Meeting in Baltimore from March 14 to March 18.

## Lynn Gamwell on math and the visual arts’ shared cultural history

Mathematicians and artists have historically shared a common interest: inquiry and comprehension of the intricacies of the world around them, whether through numerical or aesthetic design. Illustrating the relationship between math and art from antiquity to present day, Lynn Gamwells Mathematics and Art highlights the significant impact these two linked worlds have on one another. Gamwell recently took the time to answer some questions about her book. Examining the modern disciplines of art and math, she reveals the profound philosophy of self-reflection that these two cultural and intellectual pursuits share. Don’t forget to check out the stunning slideshow following the Q&A.

What’s the basic idea of your book?

LG: I started with the assumption that how people understand reality relates directly to the concepts of mathematics that develop in their culture. Mathematics is a search for patterns, and artists, in turn, create visualizations of the patterns discovered in their time. So I describe a general history of mathematics and the related artwork.

Since you begin in Stone Age times, your book covers over 5000 years. Is there a historical focus to the book?

LG: Yes, there are 13 chapters, and the first gives the background up to around 1800 AD. The other 12 chapters are on the modern and contemporary eras, although I occasionally dip back into pre-modern times to give the background of a topic. A central question that drove my exploration of the modern era was: where did abstract, non-objective art come from? Between around 1890 and 1915, many artists stopped depicting people and landscapes and start using pure color and form as the vocabulary of their art. Why? I argue that modern art is an expression of the scientific worldview. Beginning in the late nineteenth century and continuing today, researchers describe bacteria, cells, radiation, and pulsars that are invisible to the unaided eye, as well as mathematical patterns in nature.

Can you give a few examples of the relation of math and art?

LG: Italian Renaissance artists, such as Leonardo da Vinci, constructed the space in paintings such as The Last Supper using linear perspective, which is a geometric projection invented in the 1430s by the architect Filippo Brunelleschi. In the twentieth century, Swiss Constructivists such as Karl Gerstner created symmetrical patterns based on the mathematics of group theory, which measures the amount of symmetry in a system, such as atoms and sub-atomic particles. The contemporary America artist Jim Sanborn uses topology, which is the projection of geometric shapes onto surfaces that are stretched and distorted. For example in photographs of cliffs in Ireland, Jim first projected concentric circles onto the rocks and then took the photograph with a long exposure at moonrise. These artists are, of course, interested in many other things besides mathematics; aesthetic issues are their primary focus.

The examples you give are artists who are inspired by math; are mathematicians ever influenced by art?

LG: Mathematics are rarely inspired by a particular piece of art (since most artists use elementary arithmetic and geometry), but rather they aspire to include in their proofs general aesthetic qualities, such as purity, simplicity, and elegance.

You mention Leonardo da Vinci; didn’t he use the Golden Ration?

LG: No. It is a common misconception that a ratio described by Euclid as “mean and extreme ratio” has been used by artists throughout history because it holds the key to beautiful proportions. This myth was begun in the early nineteenth century by a German scholar who called Euclid’s ratio “golden.” The myth took a tenacious hold on Western intellectuals because, as science was beginning to take them off their privileged pedestal, it assured them that all beauty is based on a ratio embodied in human anatomy. There is no science supporting this claim.

Your book is a global history; did you find that there is a difference between math in the East and West?

LG: Yes, because a culture’s understanding of mathematics is based in its understanding of reality. In antiquity, Eastern mathematics in based in Taoism, the view that nature is composed of myriad parts that came together by self-assembly into a harmonious whole. Thus Chinese mathematicians discerned patterns in numbers, such as the Luoshu (magic square), in which numbers in the rows, columns, and diagonals have the same sum (the harmonious whole). On the other hand, Western cultures believed that a divine person (The Egyptian sun-god Ra, the God of Abraham, Plato’s carpenter) had imposed order on formless chaos. Thus Westerners went looking for this order, and they found it in the movement of the stars (the Babylonian zodiac), and the planets (Kepler’s Laws of Planetary Motion). Although there was a difference between Eastern and Western math when there was little contact, in today’s culture there is one global math.

The book includes the diverse fields of art, philosophy, mathematics, and physics; what is your educational background?

LG: I have a BA in philosophy and a PhD in art history. I’m self-taught in the history of science and math.

At 576 pages, this is a long book with extensive endnotes and 500+ illustrations; how long did it take you?

LG: 12 years of research and writing, plus one year in production.

Did you make any discoveries about art that especially surprised you?

LG: Yes. When I started my research I thought that artists during the modern era (the twentieth- and twenty-first centuries) would have only a vague knowledge of the math of their times, because of the famed “two cultures” divide. But I found specific historical evidence (an artist’s essay, manifesto, interview, or letter), which demonstrated that the artist had direct knowledge of a particular piece of mathematics and had embodied it in his or her art. Examples include: Aleksandr Rodchenko, Henry Moore, Piet Mondrian, Max Bill, Dorothea Rockburne, as well as musicians, such as Arnold Schoenberg, and poets, such as T. S. Eliot and James Joyce. Again, I would stress that for such artists mathematics is a secondary interest at best, and they are concerned with materials, expressive content, and purely aesthetic issues.

Any surprising discoveries about math and science?

LG: Yes, here are two. Much of what is taught as physics is really philosophy (interpretation) of physical data. An example is the Copenhagen interpretation of quantum physics, which was taught as THE gospel truth from its announcement in 1927 to around 1960. In fact, there are other ways to interpret the same laboratory data, which were largely ignored. I’m used to such dogmatism in the art world, where artists and critics are known to proclaim what art IS, but I expected to find a more cool-headed rationalism in the laboratory. Alas, we’re all human beings, driven by our passions. Another example is the strong resistance to Platonism (the view that abstract objects exist outside time and space) in modern culture, even though Platonism is the view held by most working mathematicians (i.e., they believe they are discovering patterns not creating them). While doing research, I found myself viewed with suspicion of being a religious missionary (disguised as a scholar) because I gave a sympathetic reading of historical religious documents (in other words, I tried to describe reality from their point of view). In fact, my outlook is completely secular. I came to realize that many secularists are unable to separate Platonism from its long association with religious doctrine, which touches a nerve in certain otherwise dispassionate academics.

Are you planning another project? What are you going to do next?

LG: I’m going to take some time off and regroup. I’ve started to think about writing something for children.

Check out the slideshow highlighting just a few of the book’s stunning images:

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``` Eric J. Heller (American, b. 1946), Transport 2, ca. 2000. Digital print. Courtesy of the artist.Center of the Cat’s Eye Nebula (NGC 6543), 2004. NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA)Zodiac. Digital print, 2015. Umbra Studio, New York.Luoshu diagram, from Zhu Xi, Zhouyi (twelfth century AD), reproduced in Yitu mingbian (Clarification of the diagrams in the book of changes), by Hu Wei (1706 AD), chap. 1. Needham Research Institute, Cambridge, England.Tatsuo Miyajima, Keep Changing, Connect with Everything, Continue Forever, 1998. LED, IC, electric wire, plastic, aluminum panel, iron, 113 1/4 × 151 3/16 × 5 1/8 in. (288 × 384 × 13 cm). Museum of Contemporary Art, Tokyo, courtesy of the artist and SCAI The Bathhouse, Tokyo, Japan. Photo: Norihiro Ueno.Sylvie Donmoyer (French, b. 1959), Still Life with Magic Square, 2011. Oil on canvas, 26 × 20 in. (66 × 50.8 cm). Courtesy of the artist.Andrei Bely’s chart of the stress pattern in lines of verse, in Символизм (Symbolism; Moscow: Musaget, 1910), 260. Public domain.Andrea Mantegna (Italian, 1431–1506), The Adoration of the Magi, 1495–1500. Distemper on linen, 19 1/8 × 25 13/16 in. (54.6 × 70.7 cm). J. Paul Getty Museum, Los Angeles, inv. 85.PA.417. Photo: Courtesy of the Getty's Open Content ProgramJim Sanborn (American, b. 1945), Kilkee County Clare, Ireland, 1997. Large-format projection, digital print, 30 × 36 in. (76.2 × 91.4 cm). Courtesy of the artist.Force Fields diagrams, in James Clerk Maxwell, A Treatise on Electricity and Magnetism (Oxford: Clarendon Press, 1873). Public domain.Karl Gerstner (Swiss, b. 1930), Color Sound 66: Introversion, 1998. Nitrocellulose lacquers on phenolic resin panels, 46 3/4 × 46 3/4 in. (119 × 119 cm). Courtesy of the artist.Simon Thomas (British, b. 1960), Planeliner, 2005. Bead blasted stainless steel, 23 5/8 in. (60 cm) diam. × 2 1/4 in. (5.55 cm) high. Courtesy of the artist.Robert Bosch (American, b. 1963), Knot? 2006. Digital print, 34 × 34 in. (86.3 × 86.3 cm). Courtesy of the artist.Erik Demaine (Canadian-born American, b. 1981) and Martin Demaine (American, b. 1942), Untitled (0264), from the Earthtone Series, 2012. Mi-Teintes paper, 19 in. (48.2 cm) high. Courtesy of the artists.PlayPrev|NextFullscreen 123left right```

Lynn Gamwell is lecturer in the history of art, science, and mathematics at the School of Visual Arts in New York. She is the author of Exploring the Invisible: Art, Science, and the Spiritual (Princeton).

## The Digital Einstein Papers: An Open Access Story

A year ago in December, Princeton University Press rolled out an unprecedented open access initiative: the ongoing publication of Einstein’s massive written legacy comprising more than 30,000 unique documents. The Digital Einstein Papers, one of the most ambitious publishing projects ever undertaken, launched to widespread fanfare from the scientific, publishing, and tech communities, with enthusiastic coverage from The New York Times, (which hailed the papers as “the Dead Sea Scrolls of Physics”), to Inside Higher Ed, The Guardian, and far beyond. You can watch Diana Buchwald, editor of The Collected Papers of Albert Einstein, launch The Digital Einstein here.

A year out, what has the success looked like in terms of traffic? Ken Reed, Digital Production Manager at Princeton University Press takes us behind the scenes:

The Digital Einstein Papers site launched on 5 December 2014, and in the past year has had over 340,000 sessions, with over 3.2 million pageviews.

Site traffic has been worldwide, with the top five countries in order being the United States, Germany, India, Canada, and Brazil. The site is mobile optimized, especially for the iOS, which accounts for 50% of mobile traffic to the site. This is vital for global users, since by some accounts the mobile share of web traffic is now at 33% globally.

The Papers features advanced search technology and allows users to easily navigate between the original languages in which the texts were written and their English translation, as well as extensive supplementary material. But the Press is always looking to make technological improvements. In the past year, Princeton University Press has worked closely with the developer, Tizra, to monitor traffic and continually tweak display issues, especially around mobile devices. We have recently added a news tab, and the future will hold more enhancements to the site, including added functionality for the search results, and the addition of a chronological sort.

At present, the site presents 13 volumes published by the editors of the Einstein Papers Project, with a 14th slated to go online in 2016. Here is just a sampling of the included documents:

“My Projects for the Future” — In this high school French essay, a seventeen-year-old Einstein describes his future plans, writing that “young people especially like to contemplate bold projects.”

Einstein’s first job offer — Einstein graduated from university in 1900, but had great difficulty finding academic employment. He received this notice of his appointment as a technical clerk at the Swiss Patent Office in June 1902 and would later describe his time there as happy and productive.

“On the Electrodynamics of Moving Bodies” — Einstein’s 1905 paper on the special theory of relativity is a landmark in the development of modern physics.

Keep an eye on this exciting open access project as it evolves in 2016 and beyond. Explore for yourself here.

## New Mathematics Catalog

We invite you to browse our Mathematics 2016 catalog:

 In his forthcoming book, Roger Penrose makes the case that physicists are just as prone to be influenced by fashion, faith, and fantasy as anyone else. Sometimes, these forces can be positive, he argues, but they often lead researchers astray. Pick up a copy of Fashion, Faith, and Fantasy in the New Physics of the Universe to learn more. Interested in numbers? Then Summing It Up by mathematicians Avner Ash and Robert Gross is for you! Ash and Gross have written an accessible book about current mathematical research that can be enjoyed by those with a casual interest and college math majors alike. Paul J. Nahin explains how physics can be found in everyday situations in In Praise of Simple Physics. You’ll be surprised at how often you use it!

If you would like to be updated on new titles, subscribe to our newsletter.

Finally, if you’re going to be in Seattle for the Joint Mathematics Meeting from January 6 to January 9, visit PUP at booth #105 or follow it online using #JMM16.

## Introducing the mesmerizing new trailer for Mathematics and Art

Looking for a unique coffee table book for someone mathematically or artistically inclined? Mathematics and art are surprisingly similar disciplines, given their distinctively introspective, expressive natures. Even before antiquity, artists have attempted to render mathematical concepts in visual form, and the results have often been spectacular. In a stunning illustrated cultural history that one truly has to see to appreciate, Lynn Gamwell of the School of Visual Arts in New York explores artistic representations from the Enlightenment—including Greek, Islamic, and Asian mathematics—to the modern era, including Aleksandr Rodchenko’s monochrome paintings. Check out her piece on the Guardian’s Adventures in Numberland blog, and the trailer for Mathematics and Art, here:

## Romance, Crime, and… Mathematics? Presenting the new trailer for LA Math

LA Math by James D. Stein, emeritus professor in the Department of Mathematics at California State University, is full of A-listers and wannabes, lovers and lawyers, heroes and villains. And it’s also full of math—practical mathematics knowledge, ranging from percentages and probability to set theory, statistics, and the mathematics of elections. Check out the new trailer for this unconventional and highly readable book of mathematical short stories here:

## Andrew Robinson to talk on “Einstein in Oxford” at Christ Church

In late 1915, in Berlin, Albert Einstein announced the general theory of relativity: his greatest achievement. In 1931-33, he lectured on relativity in Oxford, receiving an honorary degree from the university and staying in rooms in Christ Church, before fleeing his home in Nazi Germany and settling in Princeton. How much is known about Einstein’s time in the city of dreaming spires? For the centenary of general relativity, Einstein biographer Andrew Robinson will give a talk on “Einstein in Oxford” at Christ Church, Oxford on December 3. Robinson, the author of Einstein: A Hundred Years of Relativity, will reflect on relativity, Einstein’s intriguing relationship with Oxford and the puzzle of his universal fame.

Ahead of his talk, Robinson shares some fascinating details about the historic visit:

# Einstein in Oxford

## By Andrew Robinson

My father was a physicist at Oxford’s Clarendon Laboratory for more than four decades, revered Einstein’s work and wrote a textbook on relativity. I was born, brought up and largely educated in Oxford. So I am naturally curious about Einstein’s relationship with the city.

When Einstein paid his first visit to England in 1921, The Times carried a two-sentence news item headlined “Professor Einstein at Oxford”. It read as follows: “Professor Einstein paid a private visit to Oxford University as the guest of Dr. Lindemann of Wadham College. A tour was made of the principal University buildings and the Professor returned to London in the evening.”

Einstein receiving an honorary degree at Oxford. Source: http://www.einsteingalerie.de/zubehoer/grafiken/portraet/doctor1931.jpg

Nothing further came of this Oxford visit for a decade. But the name of Einstein’s host in Oxford in 1921, the physicist Frederick Lindemann, proved to be very important. Though born in Germany in 1886, Lindemann was actually brought up in Britain and regarded himself as British. But he returned to Germany as a PhD student in Berlin. In 1911, when his Berlin supervisor, the future Nobel laureate Walther Nernst, organized a key scientific conference in Brussels—the first Solvay Congress—Nernst appointed his student Lindemann as one of the scientific secretaries of the conference. And it was at this historic conference—where the young Einstein lectured on quantum theory—that Lindemann first met him.

In 1919, Lindemann was elected Dr Lee’s professor of experimental philosophy (that is, physics) in Oxford, and began the much-needed rejuvenation of physics at the university, centred on the Clarendon Laboratory. The Dr Lee’s chair was attached to Wadham College, where Lindemann remained a fellow until his retirement. But in 1921 Lindemann was also elected, as was legally possible in those days, to a “studentship not on the governing body” at Christ Church, which had provided the endowment for the chair. This entitled Lindemann to rooms in Christ Church that were more spacious than Wadham could provide, and from 1922 for the rest of his life, until his death in 1957, ‘Prof’, as Lindemann was known, lived in Christ Church. He was living there when he became close to Winston Churchill in the mid-1920s and eventually acted as Churchill’s key scientific adviser during the Second World War.

In 1927, Lindemann made his first attempt to persuade Einstein to return to Oxford and give one or two lectures, on behalf of the newly established Rhodes Trust—without success. In 1930, he tried again. This time, Einstein agreed, then changed his mind. But Lindemann was determined. He saw Einstein in person in Berlin, and also worked on Mrs Einstein. Einstein agreed to give three lectures—one on relativity, the second on cosmological theory and the third on his much-discussed unified field theory—and to stay in Oxford for some weeks. A solicitous Lindemann assured Mrs. Einstein in a letter:

He can of course have as many meals as he likes alone in his rooms and I will endeavour to preserve him as much as possible from importunate invitations. I am taking steps to see that he can get some sailing, so that I hope he will not feel that he is wasting his time here altogether.

Einstein arrived in Oxford in early May 1931 and was given rooms in Christ Church on Tom Quad (now the Graduate Common Room) belonging to the classical scholar Robert Hamilton Dundas, who was away on a world tour in 1930-31. At a practical level, he was looked after by Lindemann’s indefatigable manservant and general factotum, James Harvey. Lindemann himself acted as Einstein’s mentor and guide, showing him the sights and introducing him to various friends and acquaintances. According to Lindemann, over the course of Einstein’s visit, he “threw himself into all the activities of Oxford science, attended the Colloquiums and meetings for discussion and proved so stimulating and thought-provoking that I am sure his visit will leave a permanent mark on the progress of our subject.”

His first Rhodes lecture was on 9 May. Entitled “The Theory of Relativity”, it drew a packed house in the Milner Hall of Rhodes House, with some people standing. But since the lecture included much mathematics and was also in German, it quickly went over the heads of most of the audience. Those whose maths was good enough to follow Einstein’s calculations, mostly lacked sufficient German to follow his words, while the German speakers certainly lacked sufficient maths.

By the time of the second lecture a week later, devoted to the recent notion of an expanding universe, there were somewhat fewer listeners. As The Times correspondent cautiously noted:

Once more he had an audience which, though not so large as for his first lecture, almost filled the hall. An analysis of the audience was interesting. Senior and junior members of the University were divided by a barrier. The senior members consisted chiefly of teachers in the faculties of Literae Humaniores, mathematics, natural science, and theology, all of whom are affected in some degree by the new theory. The junior members were drawn by considerations partly of science, partly of language, and partly of curiosity. The element of curiosity, however, was not so strong as for the previous lecture, and most of those present had a serious interest.… Two blackboards, plentifully sprinkled beforehand in the international language of mathematical symbol, served him for reference.

One of these Einstein blackboards was wiped by an over-zealous cleaner. Fortunately, the other one was rescued by one of the Oxford dons with a serious interest in relativity, who whisked it away to the Museum of the History of Science in Broad Street, where it today attracts much intrigued, if bemused, attention from visitors. (The wiped blackboard still exists, too, but lies ignominiously in the storeroom of the Museum.)

Just before the third lecture on 23 May, Einstein was awarded an honorary doctorate by the University at the Sheldonian Theatre. The Public Orator, presenting Einstein to the vice-chancellor in Latin, claimed that relativity, “which touched both science and philosophy, was specially acceptable to Oxonians … who had learnt from Heraclitus that you could not bathe in the same river twice”.

Then the audience in the Sheldonian—or at least those members strong enough to cope not only with Latin but also with Einstein’s German and his mathematics—proceeded to Rhodes House. After this lecture, Einstein remarked that the next time he had to lecture in Oxford, “the discourse should be in English delivered”. To which one of Lindemann’s friends was heard to murmur in German: “Bewahr!” But two years later, when Einstein gave the Herbert Spencer lecture in Oxford in 1933, “On the Method of Theoretical Physics”, he wisely spoke it in an excellent English version translated from his German by colleagues from Christ Church. This lecture included a piercing tribute to an Einstein hero, Galileo:

Conclusions obtained by purely rational processes are, so far as Reality is concerned, entirely empty. It was because he recognized this, and especially because he impressed it upon the scientific world, that Galileo became the father of modern physics and in fact of the whole of modern natural science.

However, Einstein also stated, controversially, his growing view—which would come to dominate his work in the United States—of the importance of mathematics over experiment in devising physical theories:

It is my conviction that purely mathematical construction enables us to discover the concepts and the laws connecting them which give us the key to the understanding of the phenomena of Nature. Experience can of course guide us in our choice of serviceable mathematical concepts; it cannot possibly be the source from which they are derived; experience of course remains the sole criterion of the serviceability of a mathematical construction for physics, but the truly creative principle resides in mathematics. In a certain sense, therefore, I hold it to be true that pure thought is competent to comprehend the real, as the ancients dreamed.

Undoubtedly, Einstein left a pleasant impression on the students (fellows) of Christ Church. The classicist Dundas—in whose rooms Einstein lived in 1931—was tickled to find a poem by Einstein written in German in his visitor’s book when he returned from his world tour, including the verse:

Grumble: Why’s this creature staying

With his pipe and piano playing?

Why should this barbarian roam?

Could he not have stopped at home?

While the economist Roy Harrod wrote in his biography of Lindemann that Einstein “was a charming person, and we entered into relations of easy intimacy with him.” Harrod recalled vividly that Einstein

divided his time between his mathematics and playing the violin; as one crossed the quad, one was privileged to hear the strains coming from his rooms. In our Governing Body I sat next to him; we had a green baize table-cloth; under cover of this he held a wad of paper on his knee, and I observed that all through our meetings his pencil was in incessant progress, covering sheet after sheet with equations.

On one occasion, Einstein turned up at the college’s entrance gate in a pony cart driven by a girl he had met over lunch at the house of some friends of Lindemann. Some of his admirers were waiting to help him out of the cart, but a big button from his Ulster had caught in the cart’s basket-work. His lady driver wanted to disentangle it and give it to Einstein, but the college porter said: ‘I wouldn’t worry, Miss. The gentleman will never miss it. He has one odd button on his coat already.” “Oh, in that case I shall keep it,” said the girl. “I shall probably never drive anyone so famous again!”

Andrew Robinson will give a talk on “Einstein in Oxford” at Christ Church, Oxford on 3 December 2015. He is the author of Einstein: A Hundred Years of Relativity, published by Princeton University Press in 2015, and Genius: A Very Short Introduction, published by Oxford University Press in 2011.

## J. P. Ostriker

J.P. Ostriker is an astrophysicist and the co-author of Heart of Darkness, which tells the saga of humankind’s quest to unravel the deepest secrets of the universe: dark matter and dark energy. Here is his story about how an Einstein thought experiment he encountered as a teenager changed his life.

When I was a high school student I drove my teachers crazy with incessant and insatiable curiosity about the natural world. Next to our pictures in the yearbook, one of the teachers had added a line for each student and for me it was “I thought of questions that have no reply.”

And for the questions that I had that my teachers could not or would not answer, I went to books. Einstein wrote several of these that were accessible to high school students, and they fascinated me. I remember a “thought experiment” presented in one of them: A scientist sets up an exquisite laboratory on a train and tests both Newton’s laws of mechanics and Maxwell’s laws of electricity and magnetism. And, hypothetically, one finds that both are correct to arbitrary precision.

Then the train begins to move and E shows that, since the laws transform differently with the velocity of the observer, they can no longer both be true! Therefore one (or both) theories must be false.

This amazed me. No experiment was necessary. Pure thought was all that was needed and any high school student who thought about it could have come to the same conclusion as Einstein, and could have invented special relativity to solve the problem! I thought that this was wonderful, truly wonderful. I resolved that I would pursue physics and think about simple and fundamental matters. It looked easy.

Well, needless to say it was not always easy, but it has always been fun. I’m thankful I had access to Einstein’s popular books when I was a teenager with more questions than answers.

Jeremiah P. Ostriker is professor of astrophysical sciences at Princeton University. He is author, with Simon Mitton, of Heart of Darkness: Unraveling the Mysteries of the Invisible Universe. His books include Formation of Structure in the Universe and Unsolved Problems in Astrophysics (Princeton).

Train tracks image from Shutterstock, copyright: phildaint