## No greens for crimson

A few weeks ago, Nobel Laureate Al Gore came to visit our campus to officially inaugurate the new initiative to make Harvard University environmentally friendly. The following banner can now be seen everywhere around the university.

Crimson is a reference to the university colors and sports teams, The Crimsons.

Not too long ago we got an email from the president of the university announcing how, thanks to the economic disaster, things were going to get ugly here. Harvard’s endowment has been managed very conservatively and successfully through its history, making it the richest university, attracting people like me to do do research. About \$\$frac{1}{3}\$\$ of the employees here get paid from the profits generated from the investments of this endowment. With the market crash, there is now place to make money, no matter how safe you play it.

Yep, no greens for crimson.

The news hit the main media of how big the losses have been. And they have been big.

Harvard Endowment Fell 22 Percent in Four Months

Harvard’s endowment—the largest in higher education—fell 22 percent in four months from its June 30 value of \$36.9 billion, marking the endowment’s largest decline in modern history, University officials announced yesterday.

The precipitous drop will require Harvard’s faculties to take a “hard look at hiring, staffing levels, and compensation,” wrote University President Drew G. Faust and Executive Vice President Edward C. Forst ’82 in a letter informing the deans of Harvard’s losses.

What is the impact that these news will have on my fellowship? I don’t know.

## A Stochastic Goodbye to Ito

Mathematician Kiyoshi Ito died at the young age of 93 this past month. Ito was the inventor of calculus for stochastic processes, known as the Ito Calculus.

Calculus, as invented by Isaac Newton and Gottfried Leibniz, studied the rate of change of nice smooth variables, \$\$x\$\$ in terms of their differentials, infinitesimal quantities described by \$\$dx\$\$. To properly define a Leibniz differential, the variable \$\$x\$\$ must be nicely behaved. Words that are often associated with nice variables are smooth, differentiable and/or continuous.

This limited the scope of applications of calculus. In particular, it does not apply to a random process. A random process, such as rolling a dice, is not nicely behaved, each roll of the dice being very different from the one before, its values literally jumping around a lot. A processes given by probabilistic, random, rules is called a stochastic processes.

My favorite stochastic process is the random walk, and is defined as follows.

Imagine a drunk guy, who can either take a step forward or backwards. Each direction has an equal probability, so you can think of the drunk guy carrying out a random walk, where the direction of each step is determined by a coin toss, heads giving a step forward while tail signifying a step backwards.

This class of problems are very common in statistical physics, finance and biology. The difficulty with doing calculations of stochastic processes is that the variables are not nice, and thus their differentials are not well defined.

Ito invented his own type of differential for exactly this purpose. Although the rules he computed were inspired by traditional calculus, they are on a different class of their own. It’s impact is so broad that is difficult to think of a field with a component of applied math where Ito calculus does not play a role.

New York Times has the story.

\$\$langle mbox{Ito} rangle = 46.5 \$\$

## A solution to a fishy affair

Previously, on Minus Two Fish:
P.A.M. Dirac was presented with a puzzle.

Three fishermen come back from the sea. Each collapses in their respective tent. Fisherman #1 wakes up and decides to get his share of the catch. He counts the fish, realizes it is not a number divisible by three, throws away one fish to the sea correcting the situation, and takes a third of the remaining fish into his tent. Fisherman #2 wakes up later and also decides he is going to get his share of the catch. Fisherman #2 wants a third of the fish he sees. It is not a multiple of three, but he throws away one fish and takes a third of the fish and goes to sleep. Fisherman #3 wakes up after, and does the same: he throws away one fish, takes a third of the fish, and goes into his tent.
What is the smallest number of fish for which this would happen?

The real solution was not revealed, until now.

[Dirac’s Fish Puzzle Solution Spoiler Warning]

The want to find what is the smallest number of fish \$\$f\$\$ at the beginning.

\$\$f-1\$\$ is the number of fish after Fisherman #1 throws away one. \$\$left(f-1right)frac{1}{3}\$\$ is the number of fish that Fisherman #1 takes for himself, leaving only \$\$left(f-1right)frac{2}{3}\$\$. \$\$(f-1)frac{2}{3}-1\$\$ is the number of fish after Fisherman #2 throws away one. \$\$left( left(f-1right)frac{2}{3}-1right)frac{2}{3}\$\$ is the number of fish that Fisherman #2 leaves after he takes his share. \$\$left( left( f-1 right) frac{2}{3} -1 right)frac{2}{3}-1 \$\$ is the number of fish after Fisherman #3 throws away one. \$\$left(left(left(f-1right)frac{2}{3}-1right)frac{2}{3}-1right)frac{2}{3}\$\$ is the number of fish that Fisherman #3 leaves after he takes his share.

The last number must be an integer \$\$i\$\$, as it is implicit that only a whole number fish are left.
\$\$i=(((f-1)frac{2}{3}-1)frac{2}{3}-1)frac{2}{3}=ffrac{8}{27}-frac{38}{27}\$\$. Solving for \$\$f\$\$,
\$\$f=ifrac{27}{8}+frac{38}{8}\$\$.

Now, \$\$i\$\$ must be a small integer. The easiest way to explain the solution is by trial and error. So, try \$\$i=1\$\$, and you will see \$\$f\$\$ is not an integer. Try \$\$i=2\$\$, \$\$i=3\$\$ … still \$\$f\$\$ is not an integer. Until you reach \$\$i=6\$\$, where \$\$f=25\$\$.
So, the smallest number of fish \$\$f\$\$ is 25.
Also, try in the equation to plug in \$\$f=-2\$\$, Dirac’s solution and you will see \$\$i=-2\$\$. That is why it is so weird, Dirac assumes that there are negative fish to start, and negative fish at the end.

This solution permits for infinite number of fishermen to come and throw away \$\$1\$\$ fish and take \$\$frac{1}{3}\$\$ of the remaining fish as the number of fish at the end is the same as the beginning.

## Baby’s first physics book

###### Here are Paul Dirac and Enrico Fermi. They can do lots of things!

How can I jump start my toddler’s career as a theoretical physicist?, I get asked often. I knew only one way how to answer, a way following the Talmudic tradition, answering with another question: Why?.

But, finally, the resource everyone has been looking for is available for sale, online.

Baby’s first physics book – Pat Schrodinger’s Kitty

This is the perfect gift for the nerdy babies in your life. With seven colorfully illustrated activities that will delight any infant who is interested in exploring theoretical physics.

## But as Deepak Chopra taught us…

The Quantum word has been abused by all sorts of new age movements.

Quantum Healing. Quantum Psychology. Quantum Love.

Nobody explains this phenomenon better than Professor Farnsworth from Futurama.

http://vimeo.com/moogaloop.swf?clip_id=2312258&server=vimeo.com&show_title=1&show_byline=1&show_portrait=0&color=&fullscreen=1

But as Deepak Chopra taught us, quantum physics means that anything can happen at anytime and for no reason. Also, eat plenty of oatmeal, and animals never had a war! Who is the real animal?
-Prof. Hubert J. Farnsworth

## Imagine a molecule. Now Imagine a quantum computer solving it.

###### ##### A quantum circuit, a molecular spectra, a molecule: will they ever have a threesome?

So, we have the periodic table. We know that atoms combine into molecules depending on their energy spectrum, its energy levels. We know quantum physics, the theory that reigns in the atomic regime.We know math. We know quite a lot, actually.

So, we want to create new chemicals. Having new materials would give us new technologies, having new molecules would provide us with new medicines, saving millions of lives.

How come it is so hard to use what we know to get what we want?

The problem is that atoms have many electrons, and you have to calculate the equations for each electron. But, electrons interact with other, the solution of the equations of one depend on the solutions of the equations of the other. The solutions are interconnected, coupled. This is know as the many body problem. This makes solving the equations very hard.

Although we know what to do to calculate the energy of a complicated molecule, we can’t actually do it. It takes too long, even for a computer. Computers get faster every year, but they don’t get fast fast enough for the problem. Making the molecule just a bit more complicated demands us to have a computer much much much more powerful than for one a bit simpler. In other words, the problem of solving the energy of a molecule doesn’t “scale” well.

Enter quantum computers.

Unlike a conventional computer, Aspuru-Guzik and his colleagues say, a quantum computer could complete the steps necessary to simulate a chemical reaction in a time that doesn’t increase exponentially with the reaction’s complexity.

What is a quantum computer? How is it different from other computers? What tricks can it do to solve chemical reactions faster than a normal computer?

This blog is about those questions and more. Stay tuned.

## A fishy affair

The nobel laurate in physics, extreme weirdo, inventor of the delta function (\$\$delta\$\$) and my own personal hero Paul Adrien Maurice Dirac was presented with the following puzzle:

Three fishermen come back from the sea, celebrating the catch of the day.  They land their boat and set up camp. After much drinking (rum?), each collapses in their respective tent. Fisherman #1 wakes up and, after relieving himself, decides to get his share of the catch. He counts the fish, realizes it is not a number divisible by three, throws away one fish to the sea correcting the situation, and takes a third of the remaining fish into his tent. Fisherman #2 wakes up later, goes to pee too, and also decides he is going to get his share of the catch. Unaware that Fisherman #1 already took his part, Fisherman #2 wants a third of the fish he sees. It is not a multiple of three, but he throws away one fish and takes a third of the fish and goes to sleep. Fisherman #3 wakes up after, and does the same: he throws away one fish, takes a third of the fish, and goes into his tent.

What is the smallest number of fish for which this would happen?

I’m not going to spoil the puzzle by revealing the regular answer, but I can tell you Dirac’s answer.  A weird answer, but correct nevertheless.

##### Dirac prefered to sleep on his left side.

Dirac’s answer was minus two fish.