### Tony Phillips' Take Math Digest Reviews Blog on Math Blogs

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# Tony Phillips' Take on Math in the MediaA monthly survey of math news

## "Space Race Math Whizzes"

A quote from the trailer for the movie, due out next January: "I need a mathematician ... that can look beyond the numbers ... find math that doesn't yet exist ... before the Russians plant a flag on the damn Moon."

## Math and the brain

"How is it possible that some individuals struggle to calculate a tip, whereas others find solutions to complex, ancient mathematical problems? Although some have argued that language provides the basis for highlevel mathematical expertise, others have contended that such mathematical abilities are linked to nonverbal processes that underpin the processing of magnitude and space. In PNAS, Amalric and Dehaene report data that significantly advance our understanding of the origins of high-level mathematical abilities." That quote is from the commentary by Daniel Ansari (Psychology, University of Western Ontario) on a report by Marie Amalric and Stephane Dehaene in that same issue (May 3, 2016) of Proc Natl Acad Sci USA.

Amalric and Dehaene's paper is "Origins of the brain networks for advanced mathematics in expert mathematicians." They conducted extensive fMRI studies on 30 subjects, (fifteen of them were professional mathematicians, while the other fifteen "had the same education level but had specialized in humanities and had never received any mathematical courses since high school"), scanning them "as they evaluated the truth of advanced mathematical and nonmathematical statements." Their experiments lead them to three main conclusions:

• In professional mathematicians only, mathematical statements activated the same set of specific areas of the brain. This was independent of whether the statements involved algebra, analysis, topology or geometry.
• Those areas did not include areas related to language and to "general-knowledge semantics."
• "mathematical judgments were related to an amplification of brain activity at sites that are activated by numbers and formulas in nonmathematicians."

This figure is part of their evidence for the third point. It shows fMRI-detected activation in two different slices of the brain: the red areas are characteristic of professional mathematicians doing their mathematics. The green and blue areas are characteristic of educated people responding to Arabic numerals or to single-digit calculations. The yellow shows the impressive overlap.

One of the images from Amalric and Dehaene, PNAS 113:4909-4917. Colored areas are those which showed greatest contrast: RED, among mathematicians, contrast between activation caused by mathematical versus non-mathematical statements. GREEN, in the entire population, contrast between activation caused by Arabic numerals versus all other visual stimuli. BLUE, again in the entire population, contrast between activation caused by single-digit calculation versus sentence processing. YELLOW, the intersection of the three activation maps.

Ansari predicts that this work, along with follow-up studies, will lead us to "better understand the complex mechanisms that allow some to understand a level of mathematical complexity that is elusive to the majority of humankind." But on a less rarefied level, this work has clear implications for the theory and practice of mathematical education.

## Induction in Britain

Daniel S. Silver contributed "Mathematical Induction and the Nature of British Miracles" to American Scientist, September-October 2016. He distinguishes between the name "mathematical induction" (which seems to be due to Augustus de Morgan, 1838) and the practice, which as he explains, can already be detected in Euclid's proof that there are infinitely many primes. He also shows how the looser meaning of induction: a mental procedure that goes from a finite number of examples to a law, could potentially lead to mathematical disaster in the wrong hands.

Silver places the cristallization of the notion of mathematical induction in Britain in the context of the tension between the British and Continental schools (left over from the Newton-Leibniz controversy) and the tension between the traditional frame of mind and the new ideas that would find their epitome in the works of Darwin. The article has many delicious bits of British mathematical history, like Cayley's "proof" of what is known as the Cayley-Hamilton Theorem: he works it out for $2\times 2$ matrices and then says "I have verified the theorem, in the next simplest case, of a matrix of order 3... but I have not thought it necessary to undertake the labour of a formal proof of the theorem in the general case of a matrix of any degree." And the wonderful rejection letter sent in 1821 by Sir David Brewster, editor of the Edinburgh Journal of Science, to Charles Babbage, who had proposed a series of papers including one on induction: "The subjects you propose for a series of Mathematical and Metaphysical Essays are so very profound, that there is perhaps not a single subscriber to our Journal who could follow them."

## Andrew Hacker on NPR

Andrew Hacker continues to get high-level media coverage. He was Ira Flatow's guest on "Science Friday," August 28, 2016. The segment, "How Much Math Should Everyone Know?" along with a printed-out summary by NPR's Julia Franz, is available online. There were two other guests.

• Maria Droujkova ("is a founder of Natural Math, and has taught basic calculus concepts to 5-year-olds. ... For Droujkova, high-level math is important, and what it could use in American classrooms is an injection of childlike wonder.")
• Pamela Webster Harris (UT Austin) hates "rote memorization" and believes in teaching "chunking": if a student doesn't know $6\times 7$ "then I might ask them, 'Do you know three sevens?' And if a kid knows three sevens is 21 and I need six sevens, then I just need to double 21, which is 42." Back to Franz: "Harris argues that 'chunking' like this quickly leads children to higher math by showing that a complicated figure can be built from easier-to-digest composite figures. Students who learn these concepts early on, she says, may get more out of courses like algebra and calculus when they reach them."
• Hacker (who keeps talking about inflicting math): "I'm going to leave it to those who are in mathematics to work out the ways to make their subject interesting and exciting so students want to take it. All that I ask is that alternatives, other options, be offered instead of putting all of us on the road to calculus."

Tony Phillips
Stony Brook University
tony at math.sunysb.edu

Math Digest includes posts throughout each month, with summaries of math stories and unique insights (and occasionally videos, interviews and podcasts) on math-related topics recently covered by the media.

Recently posted:

On envy-free cake cutting, by Rachel Crowell

It is possible to divide a cake among a group of people in an "envy-free" way, according to two young computer scientists who recently published their results. Simon Mackenzie (a 27-year-old postdoctoral researcher at Carnegie Mellon University) and Haris Aziz (a 35-year-old computer scientist at the University of New South Wales and Data 61, an Australian data research group) make up the team. Envy-free cake cutting isn’t just about dividing the cake into slices that are each the same size. Envy-free cake cutting incorporates the notion of dividing a cake that has different features among people who value those features differently. This concept applies to other real-world situations where a continuous object--such as a tract of farm land--needs to be divided among people who assign different values to the varied features. For example, one person might want a tract of land that has a lot of trees but the most important feature to another person could be an abundance of wildflowers.

Since Biblical times, the rule for making such a division fair has been to let one person decide where the division should be and let the other person decide which piece of the divided object they want. In the case of a cake, one person would cut the cake and the other person would choose which piece they wanted. This works for two people but until Aziz and Mackenzie’s algorithm, it was thought that it would not be possible to develop a bounded, envy-free algorithm for dividing a cake among n people. The pair changed that by building on a procedure for envy-free cake cutting among three people that was independently devised by mathematicians John Selfridge and John Conway in 1960. Image: Helena Jacoba, Creative Commons 2.0, Wikimedia .

See "How to Cut Cake Fairly and Finally Eat It Too," by Erica Klarreich, Quanta Magazine, 6 October 2016.

--- Rachel Crowell

Also now on Math Digest: math and credit scores, Sophie Bryant, modeling crime, and more.

#### More . . .

Reviews: Books, plays and films about mathematics

Citations for reviews of books, plays, movies and television shows that are related to mathematics (but are not aimed solely at the professional mathematician). The alphabetical list includes links to the sources of reviews posted online, and covers reviews published in magazines, science journals and newspapers since 1996