## Diary — July 2015

#### July 1, 2015

THE OLDEST ONE

This is a tarsier, apparently filmed by Michael Bowers. There are several kinds of tarsiers. All of them live in Southeast Asia — mainly the Philippines, Sulawesi, Borneo, and Sumatra. But tarsiers used to live in many other places too.

They are, in fact, the oldest known primates that survive today! Fossils show that they've been around for the past 45 million years. The ancestors of tarsiers branched off from the ancestors of lemurs about 83 million years ago, considerably before the dinosaurs went extinct!

This particular guy is a spectral tarsier. I guess that 'spectral' here means 'like a ghost, or specter' rather than 'like the colors in a rainbow'. Probably their eyes look spooky at night when they reflect light.

The spectral tarsier lives on Selayar, an island off the larger island of Sulawesi, in Indonesia. It's less specialized than some other species of tarsiers: it doesn't have adhesive toes, for example. Its Latin name is Tarsier spectrum or sometimes Tarsier tarsier, since some consider it the prototype of all tarsiers.

#### July 2, 2015

It's fun to explore the tree of life at http://www.onezoom.org.

It only has organisms that are alive today, and not all of those. But still, it's fun to see how your favorites are related!

One nice feature is that you can see when branches happened. And at first I was shocked by how new so many mammals' branches are.

To set the stage, remember that an asteroid hit the Earth and a lot of dinosaurs went extinct 65 million years ago. About 24 million years ago, the Earth cooled enough that Antarctica becomes covered with ice. This cooling trend also created the great grasslands of the world! Humans split off from other apes about 5 million years ago: we are creatures of the grasslands. The glacial cycles began just 2.5 million years ago... and Homo erectus is first known to have tamed fire 1.4 million years ago.

Now compare this: the cats branched off from hyenas about 40 million years ago. Cheetahs branched off from other cats only 17 million years ago. That makes sense: we couldn't have cheetahs without grasslands! But bobcats and lynxes branched off only 11 million years ago... and tigers just 6 million years ago!

So tigers are almost as new as us! And the modern lion, Panthera leo, is even newer. It showed up just 1 million years old, after we tamed fire.

This changed my views a bit: I tended to think of humanity as the "new kid on the block". And okay, it's true that Homo sapiens is just 250,000 years old. But we had relatives making stone tools and fires for a lot longer!

Here's another fact that forced me to straighten out my mental chronology: the University of Oxford is older than the Aztec empire! Teaching started in Oxford as early as 1096, and the University was officially founded in 1249. On the other hand, we can say the Aztec empire officially started with the founding in Tenochtitlan in 1325.

And that, in turn, might explain why cell phones don't work very well here in Oxford. But I digress. Check out the tree of life, here:

#### July 3, 2015

This field of dunes lies on the floor of an old crater in Noachis Terra. That's one of the oldest places on Mars, scarred with many craters, with rocks up to 4 billion years old. It's in the southern hemisphere, near the giant impact basin called Hellas, which is 2.5 times deeper than the Grand Canyon and 2000 kilometers across!

This is a 'false color' photograph - you'd need to see infrared light to see that the dunes are very different than the rock below.

These are barchans, dunes with a gentle slope on the upwind side and a much steeper slope on the downwind side where horns or a notch can form. If you know this, you can see the wind is blowing from the southwest.

It's actually a bit of a puzzle where the sand in these dunes came from! Here's a paper on this subject:

The image is from a great series of photos taken by the HIRISE satellite, which orbits Mars and takes high resolution images:

#### July 4, 2015

THE STRUGGLING PHYSICIST

How does a physicist rationalize the fact that all her/his life's work may turn out to be meaningless? A physicist may chase a particular theory/phenomenon all his life solely because he is in love with the subject. However, knowing the history of science, his work may get trashed anytime. How does a physicist still motivate oneself?
I replied:

One is optimism bias: the belief that one is likely to succeed where others have failed. It's widespread, but I suspect it's even more common among people who work on high-risk projects - like trying to market a new invention, or trying to figure out new fundamental laws of physics. People who are not optimistic are unlikely to succeed in physics.

(This does not imply that people who are optimistic are likely to succeed.)

Another answer: it's easy to keep thinking one will succeed in theoretical physics, compared to business, because there are few definitive signs of failure except for making an experimental prediction and having it fail when tested. You'll notice that string theory and loop quantum gravity, two popular theories of physics, make no definitive testable predictions at this time. That is, there's no experiment we could do now that would definitively disprove these theories. So, no matter what experiments are done, people can continue to work on these theories and feel their work will succeed someday.

Furthermore, physics can lead to interesting and important mathematics even if it's wrong or untestable by experiment! String theory, in particular, has been incredibly successful as a source of mathematical ideas. So, if one is content with that, one can remain happy.

Finally, if one loves doing something and manages to get paid to do it, it's hard to stop. And as one grows up and matures, one may realize that there's more to life than succeeding in an ambitious dream. If one has the opportunity to be part of a noble tradition, if one has the opportunity to teach students to continue this tradition, one should consider oneself lucky.

Nonetheless, I stopped working on quantum gravity back around 2008, and I'm very happy I did. I explained why here:

#### July 9, 2015

Climate scientists have been working hard to understand global warming. But they have a lot to deal with. First: hacking, lawsuits and death threats. And second: the stress of trying to stay objective and scientific when you discover scary things.

Jason Box is studying how Petermann Glacier, in Greenland, is melting. He caused a stir when he read a colleague's remarks about newly discovered plumes of methane bubbling up through the Arctic ocean. He tweeted:

If even a small fraction of Arctic sea floor carbon is released to the atmosphere, we're f'd.

His remark quickly got amplified and distorted, with headlines blaring:

CLIMATOLOGIST: METHANE PLUMES FROM THE ARCTIC MEAN WE'RE SCREWED

Notice this is not what he said. He said if. In fact, it seems that human-produced carbon dioxide will be much more important for global warning than Arctic methane release, at least for the rest of this century. A few centuries down the line, if we don't get a handle on this problem, then it could get scary.

But when it comes to emotions, the issue tends to boil down to: "are we fucked?"

Gavin Schmidt, one of the climate scientists whose emails got hacked, had this reaction:

"I don't agree. I don't think we're fucked. There is time to build sustainable solutions to a lot of these things. You don't have to close down all the coal-powered stations tomorrow. You can transition. It sounds cute to say, 'Oh, we're fucked and there's nothing we can do,' but it's a bit of a nihilistic attitude. We always have the choice. We can continue to make worse decisions, or we can try to make ever better decisions. 'Oh, we're fucked! Just give up now, just kill me now,' that's just stupid."

This is from an interview with John H. Richardson in Esquire. Richardson probed him a bit, and that's when it gets interesting:

"The methane thing is actually something I work on a lot, and most of the headlines are crap. There's no actual evidence that anything dramatically different is going on in the Arctic, other than the fact that it's melting pretty much everywhere."

But climate change happens gradually and we've already gone up almost 1 degree centigrade and seen eight inches of ocean rise. Barring unthinkably radical change, we'll hit 2 degrees in thirty or forty years and that's been described as a catastrophe — melting ice, rising waters, drought, famine, and massive economic turmoil. And many scientists now think we're on track to 4 or 5 degrees — even Shell oil said that it anticipates a world 4 degrees hotter because it doesn't see "governments taking the steps now that are consistent with the 2 degrees C scenario." That would mean a world racked by economic and social and environmental collapse.

"Oh yeah," Schmidt says, almost casually. "The business-as-usual world that we project is really a totally different planet. There's going to be huge dislocations if that comes about."

But things can change much quicker than people think, he says. Look at attitudes on gay marriage.

And the glaciers?

"The glaciers are going to melt, they're all going to melt," he says. "But my reaction to Jason Box's comments is — what is the point of saying that? It doesn't help anybody."

As it happens, Schmidt was the first winner of the Climate Communication Prize from the American Geophysical Union, and various recent studies in the growing field of climate communications find that frank talk about the grim realities turns people off — it's simply too much to take in. But strategy is one thing and truth is another. Aren't those glaciers water sources for hundreds of millions of people?

"Particularly in the Indian subcontinent, that's a real issue," he says. "There's going to be dislocation there, no question."

And the rising oceans? Bangladesh is almost underwater now. Do a hundred million people have to move?

"Well, yeah. Under business as usual. But I don't think we're fucked."

Resource wars, starvation, mass migrations...

"Bad things are going to happen. What can you do as a person? You write stories. I do science. You don't run around saying, 'We're fucked! We're fucked! We're fucked!' It doesn't — it doesn't incentivize anybody to do anything."

So you see, Schmidt had made up his mind to be determinedly optimistic, because he thinks that's the right approach. And maybe he's right. But it's not easy.

Jason Box doesn't actually run around saying "we're fucked". Here's what he says:

"There's a lot that's scary," he says, running down the list.the melting sea ice, the slowing of the conveyor belt. Only in the last few years were they able to conclude that Greenland is warmer than it was in the twenties, and the unpublished data looks very hockey-stick-ish. He figures there's a 50 percent chance we're already committed to going beyond 2 degrees centigrade and agrees with the growing consensus that the business-as-usual trajectory is 4 or 5 degrees. "It's, um... bad. Really nasty."

The big question is, What amount of warming puts Greenland into irreversible loss? That's what will destroy all the coastal cities on earth. The answer is between 2 and 3 degrees. "Then it just thins and thins enough and you can't regrow it without an ice age. And a small fraction of that is already a huge problem.Florida's already installing all these expensive pumps."

and:
"It's unethical to bankrupt the environment of this planet," he says. "That's a tragedy, right?" Even now, he insists, the horror of what is happening rarely touches him on an emotional level... although it has been hitting him more often recently. "But I-I-I'm not letting it get to me. If I spend my energy on despair, I won't be thinking about opportunities to minimize the problem."

You should read the whole article:

Thanks to Rasha Kamel and Jenny Meyer for bringing this story to my attention! I find it fascinating because I notice myself tending to study beautiful mathematics as a way to stay happy — even though I feel I should be doing something about global warming. I'm actually trying to combine the two. But even if I can't, maybe I need to keep doing some math for purely emotional reasons.

#### July 18, 2015

This summer I'm working at the Centre for Quantum Technologies in Singapore again. But I spent the last week at Quantum Physics and Logic, an annual conference at Oxford.

I'm mainly studying networks in engineering, biology and chemistry, but a lot of the math I use comes from my my old favorite subject: quantum physics. So, it was great to see the latest things my friends and their students are doing now.

The prize-winning student paper was written by Amar Hadzihasanovic, from the computer science department at Oxford. Yes, computer science! That's because quantum computers and quantum cryptography are hot topics now.

To explain a bit about Hadzihasanovic's paper, I have to start with Schrödinger's cat, a thought experiment in which you put a cat into a quantum superposition of two dramatically different states: one live, one dead. Nobody has actually done this, but people have tried to see how close they can get.

Physicists have succeeded in making light in a quantum superposition of two dramatically different states. In classical mechanics we think of light as a wave. In a so-called cat state, we have light in a superposition of states where the peaks and valleys of this wave are in different places.

Another kind of cat state involves a bunch of particles that can have spin pointing up or down. For example, if you have 3 of these particles, you can make a state

↑↑↑ + ↓↓↓

It takes work to do it, though — and more work to check that you've succeeded!

The first success came in 1998, by a team of experimentalists led by Anton Zeilinger. So, this particular kind of cat state is usually called a Greene-Horn-Zeilenger state or 'GHZ state' for short.

What's interesting about the GHZ state is that if you look at any two of the particles, you don't see the spooky quantum effect called entanglement. Only all three particles taken together are entangled. It's like the Borromean rings, three rings that are linked even though no two are linked to each other.

Another interesting state of 3 particles is called the 'W state':

↑↓↓ + ↓↑↓ + ↓↓↑

In this state, unlike the GHZ state, you can see entanglement by looking at any two particles.

In fact, there's a classification of states of 3 particles that can have spin up or down, and besides the boring unentangled state

↑↑↑

the only other possibilities &emdash; apart from various inessential changes, like turning up to down &emdash; are the GHZ state and the W state.

This is why the GHZ state and W state are so important: they're fundamental building blocks of quantum entanglement, just one step more complicated than the all-important 'Bell state'

↑↓ + ↓↑

for two particles.

What Amar Hadzihasanovic did is give a complete description of what you can do with the GHZ and W states, in terms of diagrams. He explained how to use pictures to design states of more particles from these building blocks. And he found a complete set of rules to tell when two pictures describe the same state!

You can see these pictures here:

Since this paper he's been working to make the rules simpler and more beautiful. There's a lot of cool math here.

The Steve Cundiff group at Marburg University is doing research on cat states of light, and the picture here comes from a page on his work:

For more, see:

#### July 20, 2015

Last week a team at CERN says they might have seen some pentaquarks! Physicists have been looking for them. Back in 2005 Japanese researchers claimed they saw some, but this was later discredited. I hope this new claim holds up.

What's a pentaquark? It's not really 5 quarks. It's actually 4 quarks and an antiquark, all held together by exchanging other particles called gluons.

Let's start with something easier: a neutron, as shown here. A neutron consists of 3 quarks: one up quark and two down quarks. They're actually zipping around like mad in a blurry quantum way, but this movie simplifies things.

Besides coming in various kinds, like up and down, quarks have an easily changeable property called color. This is nothing like ordinary color — but color serves as a convenient metaphor, and physicists occasionally have a sense of humor, so that's what they called it.

There's a lot of math underlying this story, but let's sweep that under the carpet and talk about color in simple terms, so you can explain pentaquarks to your children and parents.

Quarks can be in 3 different colors, called 'red', 'green' and 'blue'. But they can only stick together and form a somewhat stable particle if all three colors add up and cancel out to give something 'white'. So, protons and neutrons are made of 3 quarks.

The quarks stick together by exchanging gluons, which have subtler colors like 'red-antigreen' and 'green-antiblue'.

If you watch this movie of a neutron, you'll see a red quark emit a red-antigreen gluon and turn green. This red-antigreen gluon is then absorbed by a green quark, turning it red. Color is conserved like this! The total color of the neutron remains white.

You can't build something white out of just a single quark, so we never see lone quarks in nature. The closest you can come is at insanely high temperatures when everything is shaking around like mad and you get a quark-gluon plasma. I'm talking temperatures of several trillion degrees Celsius! People have gotten this to happen at places like the Relativistic Heavy Ion Collider on Long Island, New York.

You also never see a particle built of just 2 quarks. Again, the reason is that it can't be white.

But you can get particles built of a quark and an antiquark — their colors can cancel.

You can't build a particle out of 4 quarks, because the colors can't cancel.

But you can do 3 quarks together with an extra quark and antiquark! And that's called — somewhat misleadingly — a pentaquark.

Here's the paper:

• LHCb collaboration: R. Aaij, B. Adeva, M. Adinolfi, A. Affolder, Z. Ajaltouni, S. Akar, J. Albrecht, F. Alessio, M. Alexander, S. Ali, G. Alkhazov, P. Alvarez Cartelle, A.A. Alves Jr, S. Amato, S. Amerio, Y. Amhis, L. An, L. Anderlini, J. Anderson, G. Andreassi, M. Andreotti, J.E. Andrews, R.B. Appleby, O. Aquines Gutierrez, F. Archilli, P. d'Argent, A. Artamonov, M. Artuso, E. Aslanides, G. Auriemma, M. Baalouch, S. Bachmann, J.J. Back, A. Badalov, C. Baesso, W. Baldini, R.J. Barlow, C. Barschel, S. Barsuk, W. Barter, V. Batozskaya, V. Battista, A. Bay, L. Beaucourt, J. Beddow, F. Bedeschi, I. Bediaga, L.J. Bel, V. Bellee, N. Belloli, I. Belyaev, E. Ben-Haim, G. Bencivenni, S. Benson, J. Benton, A. Berezhnoy, R. Bernet, A. Bertolin, M.-O. Bettler, M. van Beuzekom, A. Bien, S. Bifani and 662 other authors, Observation of $$J/\psi p$$ resonances consistent with pentaquark states in $$\Lambda^0_b \to J/K^-p$$ decays.

It's not unusual to have lots of authors on these papers, but it's rather unusual to list them in alphabetical order. I like that system, especially since it usually puts me near the front.

In case you're wondering, the theory behind all this is quantum chromodynamics, which is based on quantum field theory, in particular Yang-Mills theory, and on the representation theory of the group SU(3).

It is conjectured but not yet proved that quantum chromodynamics is mathematically consistent and that stable particles must all be 'white', that is, transform in the trivial representation of $$\mathrm{SU}(3)$$. We describe quarks using the fundamental representation of $$\mathrm{SU}(3)$$ on $$\mathbb{C}^3$$, which has 3 basis vectors whimsically called red, blue and green. We describe antiquarks using the dual representation, which has 3 basis vectors called anti-red, anti-blue and anti-green. We describe gluons using the adjoint representation, which has basis vectors like red-antiblue.

If you want to carry the color analogy even further, you can call anti-red, anti-blue and anti-green 'cyan', 'yellow' and 'magenta'. However, you need to be careful. Cyan, yellow and magenta do not combine to form 'black'. They form 'antiwhite', but antiwhite is white - that's what the math says, and the math is more fundamental than the cute analogy to colors.

Also, gluons only come in 8 colors, not 9.

Puzzle 1: Why? If you know some math you may know $$\mathrm{SU}(3)$$ is 8-dimensional so we can't get 9, but try to explain the story in terms of colors.

Puzzle 2: If you build particles using only quarks, not antiquarks, could you build something white with 4 quarks? How about 5? How about 6? What's the rule?

The animated gif was made by Qashqaiilove.

#### July 21, 2015

It's 1 meter long and it weighs 150 kilos. When it crawls on land to lay its eggs, a green sea turtle looks clumsy and awkward. But in its true home — the sea — it's beautiful and graceful!

And here's some good news. Back in the 1980s, when scientists first started counting the nests of green sea turtles in one area in Florida, they found fewer than 40 nests. Now they count almost 12,000!

We can thank the Endangered Species Act, which brought sea turtles under protection in 1978. We can also thank state laws discouraging development on Florida beaches — and the Archie Carr National Wildlife Refuge, which was established in 1991.

Endangered species can bounce back! Animals like nothing better than to breed, after all.

Sea turtles have been around since the late Triassic Period, 245 million years ago. During the Mesozoic Era turtles went back and forth between land and sea. But modern sea turtles, with flippers instead of claws, evolved about 120 million years ago, during the Cretaceous Period. They survived the extinction of the dinosaurs — and with a bit of luck, they'll survive us.

For more, listen to this story:

The picture is from here:
For more on the green sea turtle, Chelonia mydas, read this:

#### July 30, 2015

We've just arrived in Yogyakarta today — that's a city in Java — and look what my wife Lisa has gotten us into:

These are Indonesian reporters interviewing her near the sultan's palace. She had just won a race where she had to walk 50 meters wearing a mask like the head of a monkey. The mask covers your whole head, with no eye holes, so it prevents you from seeing. You need to go between two banyan trees and cross the finish line without veering off the track.

Most of the contestants were Indonesian high school kids, so the reporters were interested to see an American woman try this — and win!

A few years ago another American woman, Della Bradt, wrote:

In the middle of the square are two giant banyan trees. There is a challenge associated with these trees that we've been itching to try since day one. You have to start from 50 meters away from the trees and you are blindfolded. Then you are spun around 3 times to the right and 3 times to the left. Once you are oriented towards the trees, you have to walk in a straight line through the middle of them moving from North to South. While the opening between the trees is very wide, it's extremely difficult to accomplish. I actually failed a spectacular 3 times in a row. Each time I veered in the opposite direction of the trees. While 2 people in our group made it, most people weren't able to. It is said that those who make it through will have success and good fortune in their lives.