# Audio of SIAM talk

Here is an audio recording synchronized to slides of my talk a week and a half ago in Pittsburgh. I noticed some places where I said the wrong thing such as conflating neuron with synapse.  I also did not explain the learning part very well. I should point out that we are not applying a control to the network.  We train a set of weights so that given some initial condition, the neuron firing rates follow a specified target pattern. I also made a joke that implied that the Recursive Least Squares algorithm dates to 1972. That is not correct. It goes back much further back than that. I also take a pot shot at physicists. It was meant as a joke of course and describes many of my own papers.

# Talk at Maryland

I gave a talk at the Center for Scientific Computing and Mathematical Modeling at the University of Maryland today.  My slides are here.  I apologize for the excessive number of pages but I had to render each build in my slides, otherwise many would be unreadable.  A summary of the work and links to other talks and papers can be found here.

# Gravitational waves detected

You have probably heard the news that gravitational waves have finally been directly detected. The Times has a nice summary. Also see Steve Hsu. Here is an interview with one of the founders, Rainer Weiss. I remember Weiss talking about LIGO back when I was a graduate student at MIT. It’s nice to see that he finally succeeded.

# The problem with sci fi movies

I, like many people, enjoy science fiction films. The biggest problem I find in these fictional universes is not that sounds can propagate through space, people can travel at the speed of light with no relativistic effects then decelerate to a stop in a few seconds and not even be knocked to the floor, be able to generate artificial gravity everywhere, have power sources that rarely need refueling, and so forth. I accept that these are convenient plot devices that keep the story moving forward. Although I do have to say that successful films like 2001: A Space Odyssey and more recently Interstellar and The Martian show that trying to be faithful to science can often provide an even better plot device. I am still impressed by the special effects in 2001 and the amazing attention to detail of director Stanley Kubrick, e.g. near the beginning of the movie when they are on the rotating space station you can see the subtle curvature of the floor inside the rim. I hope the success of these movies lead to more realistic science fiction and even realistic action movies where the violence is realistically portrayed – people can’t be hit by a brick and then get up.

No, the thing that most irks me about science fiction movies is that the film makers either refuse or are too lazy to make their universes self-consistent. This list is in no particular order and is by no means exhaustive.

1. Why do storm troopers in Star Wars movies wear plastic suits if they don’t protect them from anything?
2. In an age with extremely powerful computers and communication devices, why should various control systems only be accessed at specific locations in a building or space craft. Do you really need to go to the engine room to fix the engine? Haven’t they progressed beyond a WWII aircraft carrier?
3. Why are weapons in the future so bad? Why do people ever miss? There is self-aiming, self-guided bullet technology now and in a future universe with flying cars no one has thought of making this? This also goes for space crafts still engaging in dog fights like the Battle of Britain in 1940.
4. In the Avenger movies, Iron Man Tony Stark invents a fusion reactor that can fit in his chest and power a flying suit for at least the duration of the movie without ever refueling. Shouldn’t this have transformed the world? This could solve global warming if not end global poverty. Even if he is not making the invention public shouldn’t the rest of the world be working on this?
5. In the Hunger Games series they have technology to make mutant animals and plants so why is there hunger? They have a ban on GMO’s for food? Why do they still need coal mining or at least need people to do it?
6. My very first blog post was about the thermodynamic impossibility of the premise of the Matrix movies. Stupid premises seem to be a major problem with the Warchowski sibbling’s films that I have seen. They have this pretense for being intellectual and try to infuse their films with a social consciousness but unfortunately fail. The theme in both the Matrix and the more recent film Jupiter Ascending (JA) is that there is an evil future society that treats humans as commodities – as energy in the Matrix and as a source for an immortal elixir in JA. That could be fine if in JA there was something mystical about humans that could not be reproduced elsewhere but what the Warchowskis do instead is try to infuse some science in it so it is not magic. There is a proto-human race that caused the dinosaurs on earth to go extinct so that humans could arise and then waited 65 million years before they could harvest them for the elixir. That was the easiest way to create a farm for humans? A second premise is that the heroine of the movie is an exact genetic replica of a former Queen who owns earth and who bequeathed her wealth to anyone who is a genetic replica. Again, the Warchowskis forgot to do their math. The probability of an exact genetic replica coming from chance, which is what they insisted on, would be at most 1 in $2^{10,000,000}$ (if differences are only biallelic common variants), which is unimaginably small. The proto-humans are also billions of years old but have not evolved in any way over that time even though squirrel-like creatures turned into humans in 65 million years on earth.
7. Even in the movie Interstellar, there is a future race of humans that have the technology to tame a black hole and send messages to the past but they can’t send back instructions for making crops that will grow on earth?

I appreciate that some of these movies are not about science or the future but remakes of old western, adventure, or war movies. However, some are really trying to portray a possible future. If that is the case then some amount of self-consistency is necessary to make the story compelling. One very possible future that I don’t see being explored in popular movies is that unlike dystopian futures where there is a return to feudalism and people are exploited by evil overlords or capitalists, a real problem we may face is that people will become obsolete. People should make movies about what a world where machines can replace almost everything people do would look like. In fact a better premise for the Matrix is that we chose to live in a big simulacrum and a subset of us rebelled. Now that would be an interesting movie.

# Are we in a fusion renaissance?

Fusion is a potentially unlimited source of non-carbon emitting energy. It requires the mashing together of small nuclei such as deuterium and tritium to make another nucleus and a lot of leftover energy. The problem is that nuclei do not want to be mashed together and thus to achieve fusion you need something to confine high energy nuclei for a long enough time. Currently, there are only two methods that have successfully demonstrated fusion: 1) gravitational confinement as in the center of a star, and 2) inertial confinement as in a nuclear bomb. In order to get nuclei at high enough energy to overcome the energy barrier for a fusion reaction, electrons can no longer be bound to nuclei to form atoms. A gas of quasi-neutral hot nuclei and electrons is called a plasma and has often been dubbed the fourth state of matter. Hence, the physics of fusion is mostly the physics of plasmas.

My PhD work was in plasma physics and although my thesis ultimately dealt with chaos in nonlinear partial differential equations, my early projects were tangentially related to fusion. At that time there were two approaches to attaining fusion, one was to try to do controlled inertial confinement by using massive lasers to implode a tiny pellet of fuel and the second was to use magnetic confinement in a tokamak reactor. Government sponsored research has been focused almost exclusively on these two approaches for the past forty years. There is a huge laser fusion lab at Livermore and an even bigger global project for magnetic confinement fusion in Cadarache France, called ITER. As of today, neither has proven that they will ever be viable sources of energy although there is evidence of break even where the reactors produce more energy than is put in.

However, these approaches may not ultimately be viable and there really has not been much research funding to pursue alternative strategies. This recent New York Times article reports on a set of privately funded efforts to achieve fusion backed by some big names in technology including Paul Allen, Jeff Bezos and Peter Thiel. Although there is well deserved skepticism for the success of these companies,  (I’m sure my thesis advisor Abe Bers would have had some insightful things to say about them), the time may be ripe for new approaches. In an impressive talk I heard many years ago, roboticist Rodney Brooks remarked that Moore’s Law has allowed robotics to finally be widely available because you could use software to compensate for hardware. Instead of requiring cost prohibitive high precision motors, you could use cheap ones and use software to control them. The hybrid car is only possible because of the software to decide when to use the electric motor and when to use the gas engine. The same idea may also apply to fusion. Fusion is so difficult because plasmas are inherently unstable. Most of the past effort has been geared towards designing physical systems to contain them. However, I can now imagine using software instead.

Finally, government attempts have mostly focused on using a Deuterium-Tritium fusion reaction because it has the highest yield. The problem with this reaction is that it produces a neutron, which then destroys the reactor. However, there are reactions that do not produce neutrons (see here). Abe used to joke that that we could mine the moon for Helium 3 to use in a Deuterium-Helium 3 reactor. So, although we may never have viable fusion on earth, it could be a source of energy on Elon Musk’s moon base, although solar would probably be a lot cheaper.

# Abraham Bers, 1930 – 2015

I was saddened to hear that my PhD thesis advisor at MIT, Professor Abraham Bers, passed away last week at the age of 85. Abe was a fantastic physicist and mentor. He will be dearly missed by his many students. I showed up at MIT in the fall of 1986 with the intent of doing experimental particle physics. I took Abe’s plasma physics course as a breadth requirement for my degree. When I began, I didn’t know what a plasma was but by the end of the term I had joined his group. Abe was one of the best teachers I have ever had. His lectures exemplified his extremely clear and insightful mind. I still consult the notes from his classes from time to time.

Abe also had a great skill in finding the right problem for students. I struggled to get started doing research but one day Abe came to my desk with this old Russian book and showed me a figure. He said that it didn’t make sense according to the current theory and asked me to see if I could understand it. Somehow, this lit a spark in me and pursuing that little puzzle resulted in my first three papers. However, Abe also realized, even before I did I think, that I actually liked applied math better than physics. Thus, after finishing these papers and building some command in the field, he suggested that I completely switch my focus to nonlinear dynamics and chaos, which was very hot at the time. This turned out to be the perfect thing for me and it also made me realize that I could always change fields. I have never been afraid of going outside of my comfort zone since. I am always thankful for the excellent training I received at MIT.

The most eventful experience of those days was our weekly group meetings. These were famous no holds barred affairs where the job of the audience was to try to tear down everything the presenter said. I would prepare for a week to get ready when it was my turn. I couldn’t even get through the first slide my first time but by the time I graduated, nothing could faze me. Although the arguments could get quite heated at times, Abe never lost his cool. He would also come to my office after a particularly bad presentation to cheer me up. I don’t ever have any stress when giving talks or speaking in public now because I know that there could never be a sharper or tougher audience than Abe.

To me, Abe will always represent the gentleman scholar to which I’ve always aspired. He was always impeccably dressed with his tweed jacket, Burberry trench coat, and trademark bow tie. Well before good coffee became de rigueur in the US, Abe was a connoisseur and kept his coffee in a freezer in his office. He led a balanced life. He took work very seriously but also made sure to have time for his family and other pursuits. I visited him at MIT a few years ago and he was just as excited about what he was doing then as he was when I was a graduate student. Although he is gone, he will not be forgotten. The book he had been working on, Plasma Waves and Fusion, will be published this fall. I will be sure to get a copy as soon as it comes out.

2015-9-16: Here is a link to his MIT obituary.

# Hopfield on the difference between physics and biology

Here is a short essay by theoretical physicist John Hopfield of the Hopfield net and kinetic proofreading fame among many other things (hat tip to Steve Hsu). I think much of the hostility of biologists towards physicists and mathematicians that Hopfield talks about have dissipated over the past 40 years, especially amongst the younger set. In fact these days, a good share of Cell, Science, and Nature papers have some computational or mathematical component. However, the trend is towards brute force big data type analysis rather than the simple elegant conceptual advances that Hopfield was famous for. In the essay, Hopfield gives several anecdotes and summarizes them with pithy words of advice. The one that everyone should really heed and one I try to always follow is “Do your best to make falsifiable predictions. They are the distinction between physics and ‘Just So Stories.’”