Letter to the community: Update regarding Executive Order, thoughts on moving forward

The following email was sent today to the MIT community by President L. Rafael Reif.

To the members of the MIT community,

First, an update:

I was hoping to write to you today with some uplifting news. Yet, as I write, we continue to push hard to bring back to MIT those members of our community, including two undergraduates, who were barred from the US because of the January 27 Executive Order on immigration. We are working personally with each of the affected individuals we are aware of. If you know of others who are directly affected, please inform us immediately so we can try to help:

International Students Office, David Elwell
International Scholars Office, Penny Rosser

Over and over since the order was issued, I have been moved by the outpouring of support from hundreds across our community. I could not be more proud, and I am certain that you join me in thanking everyone inside and outside of MIT whose extraordinary efforts have helped us address this difficult situation. We hope we can welcome everyone back to MIT very soon.

MIT, the nation and the world
I found the events of the past few days deeply disturbing. The difficulty we have encountered in seeking to help the individuals from our community heightens our overall sense of concern. I would like to reflect on the situation we find ourselves in, as an institution and as a country.

MIT is profoundly American. The Institute was founded deliberately to accelerate the nation’s industrial revolution. With classic American ingenuity and drive, our graduates have invented fundamental technologies, launched new industries and created millions of American jobs. Our history of national service stretches back to World War I; especially through the work of Lincoln Lab, we are engaged every day in keeping America safe. We embody the American passion for boldness, big ideas, hard work and hands-on problem-solving. Our students come to us from every faith, culture and background and from all fifty states. And, like other institutions rooted in science and engineering, we are proud that, for many of our students, MIT supplies their ladder to the middle class, and sometimes beyond. We are as American as the flag on the Moon.

At the same time, and without the slightest sense of contradiction, MIT is profoundly global. Like the United States, and thanks to the United States, MIT gains tremendous strength by being a magnet for talent from around the world. More than 40% of our faculty, 40% of our graduate students and 10% of our undergraduates are international. Faculty, students, post-docs and staff from 134 other nations join us here because they love our mission, our values and our community. And – as I have – a great many stay in this country for life, repaying the American promise of freedom with their energy and their ideas. Together, through teaching, research and innovation, MIT's magnificently global, absolutely American community pursues its mission of service to the nation and the world.

What the moment demands of us
The Executive Order on Friday appeared to me a stunning violation of our deepest American values, the values of a nation of immigrants: fairness, equality, openness, generosity, courage. The Statue of Liberty is the “Mother of Exiles”; how can we slam the door on desperate refugees? Religious liberty is a founding American value; how can our government discriminate against people of any religion? In a nation made rich by immigrants, why would we signal to the world that we no longer welcome new talent? In a nation of laws, how can we reject students and others who have established legal rights to be here? And if we accept this injustice, where will it end? Which group will be singled out for suspicion tomorrow?

On Sunday, many members of our campus community joined a protest in Boston to make plain their rejection of these policies and their support for our Muslim friends and colleagues. As an immigrant and the child of refugees, I join them, with deep feeling, in believing that the policies announced Friday tear at the very fabric of our society.

I encourage anyone who shares that view to work constructively to improve the situation. Institutionally, though we may not be vocal in every instance, you can be confident we are paying attention; as we strive to protect our community, sustain our mission and advance our shared values, we will speak and act when and where we judge we can be most effective.

Yet I would like us to think seriously about the fact that both within the MIT community and the nation at large, there are people of goodwill who see the measures in the Executive Order as a reasonable path to make the country safer. We would all like our nation to be safe. I am convinced that the Executive Order will make us less safe. Yet all of us, across the spectrum of opinion, are Americans.

In this heated moment, I urge every one of us to avoid with all our might the forces that are driving America into two camps. If we love America, and if we believe in America, we cannot allow those divisions to grow worse. We need to imagine a shared future together, if we hope to have one. I am certain our community can help work on this great problem, too, by starting right here at home.

Sincerely,

L. Rafael Reif

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Explained: Greenhouse gases

When hearing the words “greenhouse gas,” most people think immediately of carbon dioxide. This is indeed the greenhouse gas that is currently producing the greatest impact on the Earth’s rapidly changing climate. But it is far from the only one making its mark, and for mitigating climate change it’s important to be able to compare the effects of the various gases that contribute to warming the planet.

But that’s not easy to do.

Greenhouse gases vary in not only their sources and the measures needed to control them, but also in how intensely they trap solar heat, how long they last once they’re in the atmosphere, and how they react with other gases and ultimately get flushed out of the air. The differences make it impossible to do the very thing researchers and policymakers want most to do: come up with a simple conversion factor to allow exact comparisons among them.

Let’s take a look at the most extreme case: chlorofluorocarbons (CFCs). Compared to carbon dioxide, CFCs can produce more than 10,000 times as much warming, pound for pound, once they are in the air. Fortunately, CFCs were banned by an international agreement called the Montreal Protocol in 1987 — not because of their dramatic warming potential, although that was a secondary reason recognized at the time, but because they were found to be the primary cause of the rapidly escalating destruction of the Earth’s ozone layer, which protects the planet from dangerous, cancer-causing levels of ultraviolet radiation.

Out of the picture

CFCs “would be a major player by now” in contributing to global warming if they hadn’t been phased out, says Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT. By now, if they were still being used at the same rate as before the phaseout, CFCs would be contributing about one-third as much to the Earth’s greenhouse effect as carbon dioxide, which remains by far the biggest contributor, she says.

For comparison, she says, the Kyoto Protocol (now superceded by the Paris Agreement of 2015), which called for a series of measures to reduce greenhouse gas emissions around the world, produced a total reduction of about 2 gigatons of “carbon equivalent” emissions per year, while the phaseout of CFCs has already eliminated five times as much — an estimated 10 gigatons of carbon equivalent gas per year.

Today, the number-two producer of human-caused greenhouse effects is methane, the main constituent of natural gas. When initially released, methane is about 100 times more potent than carbon dioxide, but its lifetime in the atmosphere is much shorter — about a decade, unlike carbon dioxide’s residence time of centuries. When averaged over a 20-year period, methane’s “greenhouse gas equivalency” is about 72 times that of carbon dioxide, but when looked at on a timescale of 100 years, that equivalency drops to just 25 times.

Methane comes from multiple sources, some of which are relatively hard to measure. For example, leakage from natural gas wells, storage facilities, and distribution systems is a significant source. But because such leaks are highly variable and depend on factors such as well construction methods and maintenance systems for infrastructure — which in some cases are proprietary information — there has been a great deal of controversy over the extent of such leaks. Other sources, such as emissions related to wetlands, deforestation, and cattle, are difficult to measure accurately.

Accounting for dynamics

Jessika Trancik, the Atlantic Richfield Career Development Associate Professor in Energy Studies at MIT’s Institute for Data, Systems, and Society, says that because of the very different dynamics of methane in the atmosphere compared to carbon dioxide, it can be misleading to rely on the conventional single-factor comparisons that are often used. Instead, she and collaborators suggested in a 2014 research paper — and further expanded on the idea in 2016 — that a measure of the relative effects of different gases based on specific climate mitigation goals should be used, for example where the time horizon for the comparison is based on a specific stabilization goal.

The usual way of comparing greenhouse gases is through a single conversion factor, called the global warming potential, which uses a somewhat arbitrarily chosen time horizon of 100 years. For methane, this is usually given as a factor of 25 (that is, methane is 25 times more potent than carbon dioxide). But Trancik suggests that it is more meaningful to use “goal-inspired metrics,” which incorporate the different residence times of different gases over a time span that depends on when the emissions occur relative to a mitigation goal: an instantaneous climate impact (ICI) and a cumulative climate impact (CCI). She says that how much weight to give the different factors “comes down to how much you care about the rate of change in the short term, as opposed to the equilibrium state” that the climate will ultimately settle in to — which may not be reached for centuries.

Solomon’s research has recently shown that some of the effects of greenhouse gases can persist for centuries, even after the gases that initially triggered those changes are no longer being emitted at all. Specifically, the expansion of water as it warms, combined with the melting of polar and glacier ice, can lead to significant sea-level rise that would last for centuries even if all new greenhouse gas emissions were stopped altogether. That’s because these gases will remain in the atmosphere and continue to trap heat long after their sources are eliminated — a fact that’s sometimes overlooked in discussions of mitigating climate change. If all carbon dioxide emissions were eliminated by 2050, Solomon and her co-authors found, as much as half of the emissions would still be in the air 750 years later, and still warming the planet.

“There’s no question that carbon dioxide is the biggest contributor to human-caused climate change,” Trancik says, “so that’s the big focus of mitigation efforts. But there are a number of others that are also significant. These non-carbon dioxide emissions often come from some sort of leakage in the supply system, unlike the direct emissions of carbon dioxide that result from combusting carbon-containing fossil fuels. There are opportunities to clean these systems up to reduce leakage, though it’s not always easy.”

Also, she says, “there’s a challenge in understanding the atmospheric lifetimes of all these greenhouse gases and how the radiative forcing changes as the concentration changes. There are interactive effects that change the radiative efficiencies of all these gases.”

Gases are not the only contributors to the greenhouse effect: Black carbon, otherwise known as soot, as well as some other particulate matter can also play a role. But such materials have even shorter residence times, typically just days or weeks, as they tend to be flushed out of the air by the next rainfall.

Which brings us to the biggest greenhouse gas of all: water vapor. There’s no doubt that water vapor is responsible for more greenhouse warming than any other atmospheric constituent. But water vapor’s behavior depends on the climate, so it is not a driver of climate change but rather an amplifying feedback, since the water cycle is a constant part of the atmospheric circulation. As the air gets warmer, it can hold more water vapor, so a warming climate leads to more vapor in the air, providing a feedback effect — and potentially leading to dramatic changes in rainfall patterns. But, water vapor only stays around until the next rainfall. “Water vapor is a slave to the climate system, it’s not a master,” Solomon says.

So when it comes to changing the planet’s climate, carbon dioxide really is the number one factor — and will be so for the foreseeable future, even if all emissions were to stop right now. Much of the carbon dioxide emitted over the last century will still be there centuries in the future — and will still be warming the planet and causing sea level to rise. “Some of our carbon dioxide will still be there in 1,000 years,” Solomon says. So for all practical purposes, she says, on a human timescale, carbon dioxide emitted into the air leads to “the irreversibility of carbon dioxide-induced warming.”

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Optimizing code

Compilers are programs that convert computer code written in high-level languages intelligible to humans into low-level instructions executable by machines.

But there’s more than one way to implement a given computation, and modern compilers extensively analyze the code they process, trying to deduce the implementations that will maximize the efficiency of the resulting software.

Code explicitly written to take advantage of parallel computing, however, usually loses the benefit of compilers’ optimization strategies. That’s because managing parallel execution requires a lot of extra code, and existing compilers add it before the optimizations occur. The optimizers aren’t sure how to interpret the new code, so they don’t try to improve its performance.

At the Association for Computing Machinery’s Symposium on Principles and Practice of Parallel Programming next week, researchers from MIT’s Computer Science and Artificial Intelligence Laboratory will present a new variation on a popular open-source compiler that optimizes before adding the code necessary for parallel execution.

As a consequence, says Charles E. Leiserson, the Edwin Sibley Webster Professor in Electrical Engineering and Computer Science at MIT and a coauthor on the new paper, the compiler “now optimizes parallel code better than any commercial or open-source compiler, and it also compiles where some of these other compilers don’t.”

That improvement comes purely from optimization strategies that were already part of the compiler the researchers modified, which was designed to compile conventional, serial programs. The researchers’ approach should also make it much more straightforward to add optimizations specifically tailored to parallel programs. And that will be crucial as computer chips add more and more "cores," or parallel processing units, in the years ahead.

The idea of optimizing before adding the extra code required by parallel processing has been around for decades. But “compiler developers were skeptical that this could be done,” Leiserson says.

“Everybody said it was going to be too hard, that you’d have to change the whole compiler. And these guys,” he says, referring to Tao B. Schardl, a postdoc in Leiserson’s group, and William S. Moses, an undergraduate double major in electrical engineering and computer science and physics, “basically showed that conventional wisdom to be flat-out wrong. The big surprise was that this didn’t require rewriting the 80-plus compiler passes that do either analysis or optimization. T.B. and Billy did it by modifying 6,000 lines of a 4-million-line code base.”

Schardl, who earned his PhD in electrical engineering and computer science (EECS) from MIT, with Leiserson as his advisor, before rejoining Leiserson’s group as a postdoc, and Moses, who will graduate next spring after only three years, with a master’s in EECS to boot, share authorship on the paper with Leiserson.

Forks and joins

A typical compiler has three components: the front end, which is tailored to a specific programming language; the back end, which is tailored to a specific chip design; and what computer scientists oxymoronically call the middle end, which uses an “intermediate representation,” compatible with many different front and back ends, to describe computations. In a standard, serial compiler, optimization happens in the middle end.

The researchers’ chief innovation is an intermediate representation that employs a so-called fork-join model of parallelism: At various points, a program may fork, or branch out into operations that can be performed in parallel; later, the branches join back together, and the program executes serially until the next fork.

In the current version of the compiler, the front end is tailored to a fork-join language called Cilk, pronounced “silk” but spelled with a C because it extends the C programming language. Cilk was a particularly congenial choice because it was developed by Leiserson’s group — although its commercial implementation is now owned and maintained by Intel. But the researchers might just as well have built a front end tailored to the popular OpenMP or any other fork-join language.

Cilk adds just two commands to C: “spawn,” which initiates a fork, and “sync,” which initiates a join. That makes things easy for programmers writing in Cilk but a lot harder for Cilk’s developers.

With Cilk, as with other fork-join languages, the responsibility of dividing computations among cores falls to a management program called a runtime. A program written in Cilk, however, must explicitly tell the runtime when to check on the progress of computations and rebalance cores’ assignments. To spare programmers from having to track all those runtime invocations themselves, Cilk, like other fork-join languages, leaves them to the compiler.

All previous compilers for fork-join languages are adaptations of serial compilers and add the runtime invocations in the front end, before translating a program into an intermediate representation, and thus before optimization. In their paper, the researchers give an example of what that entails. Seven concise lines of Cilk code, which compute a specified term in the Fibonacci series, require the compiler to add another 17 lines of runtime invocations. The middle end, designed for serial code, has no idea what to make of those extra 17 lines and throws up its hands.

The only alternative to adding the runtime invocations in the front end, however, seemed to be rewriting all the middle-end optimization algorithms to accommodate the fork-join model. And to many — including Leiserson, when his group was designing its first Cilk compilers — that seemed too daunting.

Schardl and Moses’s chief insight was that injecting just a little bit of serialism into the fork-join model would make it much more intelligible to existing compilers’ optimization algorithms. Where Cilk adds two basic commands to C, the MIT researchers’ intermediate representation adds three to a compiler’s middle end: detach, reattach, and sync.

The detach command is essentially the equivalent of Cilk’s spawn command. But reattach commands specify the order in which the results of parallel tasks must be recombined. That simple adjustment makes fork-join code look enough like serial code that many of a serial compiler’s optimization algorithms will work on it without modification, while the rest need only minor alterations.

Indeed, of the new code that Schardl and Moses wrote, more than half was the addition of runtime invocations, which existing fork-join compilers add in the front end, anyway. Another 900 lines were required just to define the new commands, detach, reattach, and sync. Only about 2,000 lines of code were actual modifications of analysis and optimization algorithms.

Payoff

To test their system, the researchers built two different versions of the popular open-source compiler LLVM. In one, they left the middle end alone but modified the front end to add Cilk runtime invocations; in the other, they left the front end alone but implemented their fork-join intermediate representation in the middle end, adding the runtime invocations only after optimization.

Then they compiled 20 Cilk programs on both. For 17 of the 20 programs, the compiler using the new intermediate representation yielded more efficient software, with gains of 10 to 25 percent for a third of them. On the programs where the new compiler yielded less efficient software, the falloff was less than 2 percent.

“For the last 10 years, all machines have had multicores in them,” says Guy Blelloch, a professor of computer science at Carnegie Mellon University. “Before that, there was a huge amount of work on infrastructure for sequential compilers and sequential debuggers and everything. When multicore hit, the easiest thing to do was just to add libraries [of reusable blocks of code] on top of existing infrastructure. The next step was to have the front end of the compiler put the library calls in for you.”

“What Charles and his students have been doing is actually putting it deep down into the compiler so that the compiler can do optimization on the things that have to do with parallelism,” Blelloch says. “That’s a needed step. It should have been done many years ago. It’s not clear at this point how much benefit you’ll gain, but presumably you could do a lot of optimizations that weren’t possible.”

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Letter to the community: Update regarding Executive Order, noon rally in Lobby 7

The following email was sent today to the MIT community by Provost Martin A. Schmidt, Chancellor Cynthia Barnhart, and Vice President for Research Maria T. Zuber. 

To the members of the MIT community:
 
Yesterday afternoon, we wrote to you about President Trump's executive order restricting people from seven countries from entering the United States. We write now with an important update and with new guidance to directly affected members of the MIT community.
 
Update

Early this morning, the Massachusetts federal district court issued a temporary order that restrains the government from enforcing the Executive Order to detain or remove holders of a valid visa or green card who travel from the seven countries to the US through Logan Airport. This order is in effect for the next 7 days.
 
The seven affected countries are: Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen.
 
New guidance from MIT

If you are a directly affected member of the MIT community who is currently traveling outside the United States and you wish to return to campus, we encourage you to fly back to Boston--directly to Logan Airport--as as soon as possible, and before February 4.
 
The MIT administration is helping members of our community who we know to be traveling, including connecting them to legal resources.
 
If you are from one of the seven affected countries and are not already in touch with us, please reach out. You can email David Elwell, Associate Dean and Director of the International Students Office, or Penny Rosser, Director of the International Scholars Office. We will do what we can to help you get back to campus.
 
Noontime rally

Students have organized a gathering in Lobby 7 for today at noon, ahead of a rally in Copley Square opposing the executive order. Faculty chair Krishna Rajagopal has emailed all faculty inviting them to attend: with this note, we invite the broader MIT community to join in a show of support for MIT’s values.
 
We will send further updates as necessary.
 
Sincerely,
Martin A. Schmidt
Cynthia Barnhart
Maria T. Zuber

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Letter regarding Executive Order affecting international students and scholars

The following email was sent today to the MIT community by Provost Martin A. Schmidt, Chancellor Cynthia Barnhart, and Vice President for Research Maria T. Zuber. 

To the members of the MIT community:
 
The Executive Order President Trump signed yesterday restricting individuals from seven countries from entering the United States is already having an impact on members of our community.
 
While we are very troubled by this situation, our first concern is for those of our international students and scholars who are directly affected. We are working closely with them to offer every support we can.
 
We are also keeping close watch on the overall situation and exploring the best options to help and respond.
 
If you have specific questions, please contact David Elwell, associate dean and director of the International Students Office (elwell@mit.edu) or Penny Rosser, director of the International Scholars Office (pennysun@mit.edu).
 
Sincerely,
Martin A. Schmidt
Cynthia Barnhart
Maria T. Zuber

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Fadel Adib joins Media Lab faculty

Fadel Adib SM '13, PhD '16 has been appointed an assistant professor in the Program in Media Arts and Sciences at the MIT Media Lab, where he leads the new Signal Kinetics research group. His group’s mission is to explore and develop new technologies that can extend human and computer abilities in communication, sensing, and actuation.

Adib comes to the lab from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL), where he received his PhD and master’s degrees in electrical engineering and computer science, supervised by MIT professor of electrical engineering and computer science Dina Katabi. Adib’s doctoral thesis, "Wireless Systems that Extend Our Senses," demonstrates that wireless signals can be used as sensing tools to learn about the environment, thus enabling us to see through walls, track human gestures, and monitor human vital signs from a distance. His master’s thesis, "See Through Walls with Wifi," won the best master’s thesis award in computer science at MIT in 2013. He earned his bachelor’s degree in computer and communications engineering from the American University of Beirut, in Lebanon, the country of his birth, where he graduated with the highest GPA in the university's digitally-recorded history.

“We can get your locations, we can get your gestures, we can get your breathing,” Adib said at a Media Lab event in October 2016. “And we can even get your heart rate—all without putting any sensor on your body. This is exactly what our research is about.” Signal Kinetics researchers tap into the invisible signals that surround us — from WiFi to brain waves. The aim is to uncover, analyze, and engineer these natural and human-made networks, drawing on tools from computer networks, signal processing, machine learning, and hardware design.

“We are living in a sea of radio waves,” Adib told the lab audience. “As our bodies move, we modulate these radio waves, similar to how you create waves when you move around in a pool of water. While we cannot see these with our naked eye, we can extract them and we can build intelligence in the environment to enable a large number of applications and extend our senses using wireless technology.” The technology is applicable to a broad range of needs: from monitoring an infant’s breathing or an elderly person who has fallen, to determining whether someone has sleep apnea, to detecting survivors in a burning building. The group’s research also has potential applications for gaming and filmmaking.

In 2015, Forbes magazine selected Adib among the 30 Under 30 Who Are Moving the World in Enterprise Technology. In 2014, MIT Technology Review chose him as one of the world’s 35 top innovators under the age of 35. His research has been identified as one of the 50 ways MIT has transformed computer science over the past 50 years.

“Fadel’s work in wireless sensing is groundbreaking and opens up all sorts of new opportunities,” says the Media Lab’s Pattie Maes, the Alex W. Dreyfoos Professor of Media Technology and academic head of the Program in Media Arts and Sciences. “I can’t wait to see what impact his presence in the lab will have on many of the research topics that we focus on, including Smart Cities, Responsive Environments, Extreme Bionics, Extended Intelligence, Tools for Health and Wellbeing, and more.”

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