“Big Bang to Little Swoosh” (NYTimes.com)

MIT Prof. Max Tegmark wrote about the discovery of gravitational waves, “the holy grail of cosmology,” in an opinion piece in the New York Times:

The shock waves are still reverberating from the bombshell announcement of the discovery of cosmology’s holy grail: telltale signature of ripples in the very fabric of space generated as it “inflated” during our cosmic origins.

I think that if this discovery holds up, it will go down as one of the greatest in the history of science. It teaches us humans that we need to think big, because we are the masters of underestimation. Again and again we have underestimated not only the size of our cosmos, discovering that everything we thought existed was merely a small part of a much grander structure (a planet, a solar system, a galaxy, a universe, and maybe even a multiverse), but we have also repeatedly underestimated the power of our human minds to understand our cosmos.

He goes on to talk more about the discovery, and ends with this optimistic thought: “…although we humans may be small, the power of our minds to figure things out has superseded our ancestors’ wildest dreams.”

Read the entire article here. You can learn more about cosmology on OCW in the following courses:

8.942 Cosmology
8.224 Exploring Black Holes: General Relativity & Astrophysics
      Video Lecture 10: The Universe and Three Examples
      Video Lecture 13: Cosmic Structure Formation; From Inflation to Galaxies
8.286 The Early Universe

Climate Change and Sustainability Courses in OCW


Earth seen from Apollo 17.

MIT is home to many groups and individuals who are working to better understand the science, economics, and politics of global climate change and sustainability. We are proud to represent some of their work on OCW. In honor of Earth Day, here’s a hand-picked selection of OCW’s best courses on these topics, organized around four themes: science foundations, new technology and engineering solutions, the continuum of economics-business-policy-politics, and perspectives from the humanities.

Science Foundations

Technology and Engineering Solutions

Economics, Business, Planning, & Politics

Humanities Perspectives

Other Course Lists

If OCW courses have helped you make a difference — like these Haitian solar energy entrepreneurs and a polar research scientist — we’d love to hear about it.  Please send us your feedback!

Michael Greenstone on the experimental method in environmental economics (MIT News)

This power station smokestack in Pittsburgh was fit with a $42 million wet scrubber to minimize emissions.

This power station smokestack in Pittsburgh was fit with a $42 million wet scrubber to minimize emissions. (Image from archives.gov)

Next week – April 22, 2014 – is the 45th anniversary of the first Earth Day. Debates continue about the costs and benefits of anti-pollution regulation: what actions are most appropriate, and most effective? Environmental economists like MIT’s Michael Greenstone are finding new insights that should help us come to better decisions.

3 Questions: Michael Greenstone on the experimental method in environmental economics
MIT economist makes the case for new quasi-experiments as a way of studying environmental issues.

Peter Dizikes | MIT News Office
April 17, 2014

How can scholars get traction on environmental problems, particularly those relating to pollution? In an essay appearing in this week’s issue of the journal Science, MIT economist Michael Greenstone, along with co-authors Francesca Dominici and Cass Sunstein of Harvard University, make the case for “quasi-experiments,” or “natural experiments,” which have gained prominence in other domains of the social sciences. Environmental economics, they suggest, can rely increasingly on quasi-experiments to sharpen its conclusions about which kinds of environmental action are most cost-effective. Greenstone sat down with MIT News to discuss the subject.

Q. Why should quasi-experiments be in the environmental economics toolbox?

A. The single best way to learn about the world is through randomized controlled trials (RCTs). Now, some problems are not directly amenable to RCTs. In the case of climate change, we don’t have a second planet to randomly assign climate change to, or not. And that means to learn about a lot of environmental problems, such as climate change or air quality, we have to turn to other methods.

The conventional approach to doing that has been to rely on comparisons of places that are more polluted to places that are less polluted. [But] places that are more polluted might have other things that are different about them, besides the pollution. In this paper we have highlighted a potential solution, the use of quasi-experimental evaluation techniques, which mimic some of the features of an experiment, in the sense that there is a group that receives the treatment and a [very similar] group that doesn’t. But [this] is based on nature or politics or some other accident, rather than being done through random assignment.

In the case of environmental questions, there has been great progress in the last 10 to 15 years applying quasi-experiments to environmental questions. This same revolution has been occurring in other fields — labor economics, development economics, public finance, statistics, and criminology. This “credibility revolution,” as some people refer to it, tries to move beyond simple comparisons. Read more…

Learn more in OCW, with Professor Greenstone’s 14.475 Environmental Economics and Government Responses to Market Failure. For an overview of environmental economics, see 14.42 Environmental Policy and Economics. And for more on the randomized quasi-experiment methodology, see Abdul Latif Jameel Poverty Action Lab Executive Training: Evaluating Social Programs 2009.


Earth-Sized Exoplanet is “Just Right”

Goldilocks likes her porridge not too hot, not too cold, but just right. Planets, too, can be “just right” if they’re not too close to their star, but not too far away. The “just right” zone is called the habitable zone, or the Goldilocks zone.

A team of scientists have found an exoplanet, a planet outside of our solar system, in the Goldilocks zone of its star. This exoplanet, named Kepler-186, is roughly the same size as Earth. These two qualities make Kepler-186 one of the most Earth-like planets yet discovered!

A comparison of Earth and Kepler-186f

A comparison of the sizes and orbits of Earth and Kepler-186f. Image by  NASA Ames/SETI Institute/JPL-Caltech.

Update: Prof. Sara Seager, who was not involved in the study, weighs in on the discovery of Kepler-186f:

Sounds like a great planet to visit, if we could figure out how to travel there!

Personally I find it simply awesome that we live in a time when finding potentially habitable planets is common, and the method to find them is standardized. Kepler has [found] a handful of such planets and this is the smallest one.

In reality we cannot know if the planet is actually habitable. We need to get a sense of the atmosphere and its greenhouse effect.

You can learn more about exoplanets in Prof. Sara Seager‘s course 12.425 Extrasolar Planets: Physics and Detection Techniques on OCW.

Robert Talbert – Getting off on the right foot in an inverted calculus class (Chronicle of Higher Ed)

Here’s an excerpt from the  sixth post in from Robert Talbert’s excellent series on flipping his calculus class:

Getting off on the right foot in an inverted calculus class

In the previous post about the flipped/inverted calculus class, we looked at getting student buy-in for the flipped concept, so that when they are asked to do Guided Practice and other such assignments, they won’t rebel (much). When you hear people talk about the flipped classroom, much of the time the emphasis is on what happens before class – the videos, how to get students to do the reading, and so on. But the real magic is what happens in class when students come, prepared with some basic knowledge they’ve acquired for themselves, and put it to work with their peers on hard problems.

But before this happens, there’s an oddly complex buffer zone that students and instructors have to cross, and that’s the time when students arrive at the class meeting. Really? you are thinking. How can arrival to class be such a complicated thing? They show up, you get to work, right? Well – not so fast. There are of number of things you have to get right in this period at the beginning of class. Read more.


Excitons observed in action for the first time (MIT News)

Insights generated by this new imaging technique could lead to significant advances in electronics, and deeper understanding about energy-transfer processes like photosynthesis.

Excitons observed in action for the first time
Technique developed at MIT reveals the motion of energy-carrying quasiparticles in solid material.

David L. Chandler | MIT News Office
April 16, 2014

A quasiparticle called an exciton — responsible for the transfer of energy within devices such as solar cells, LEDs, and semiconductor circuits — has been understood theoretically for decades. But exciton movement within materials has never been directly observed.

Now scientists at MIT and the City College of New York have achieved that feat, imaging excitons’ motions directly. This could enable research leading to significant advances in electronics, they say, as well as a better understanding of natural energy-transfer processes, such as photosynthesis.

The research is described this week in the journal Nature Communications, in a paper co-authored by MIT postdocs Gleb Akselrod and Parag Deotare, professors Vladimir Bulovic and Marc Baldo, and four others.

“This is the first direct observation of exciton diffusion processes,” Bulovic says, “showing that crystal structure can dramatically affect the diffusion process.”

“Excitons are at the heart of devices that are relevant to modern technology,” Akselrod explains: The particles determine how energy moves at the nanoscale. “The efficiency of devices such as photovoltaics and LEDs depends on how well excitons move within the material,” he adds. Read more…

Learn more about the exciton and related phenomena in these OCW courses:

A molecular approach to solar power (MIT News)

Diagram of molecules going through solar-induced charge-discharge cycle, with heat released.

The working cycle of a solar thermal fuel, using azobenzene as an example. (Courtesy of Jeff Grossman.)

A molecular approach to solar power
Switchable material could harness the power of the sun — even when it’s not shining.

David L. Chandler | MIT News Office
April 13, 2014

It’s an obvious truism, but one that may soon be outdated: The problem with solar power is that sometimes the sun doesn’t shine.

Now a team at MIT and Harvard University has come up with an ingenious workaround — a material that can absorb the sun’s heat and store that energy in chemical form, ready to be released again on demand.

This solution is no solar-energy panacea: While it could produce electricity, it would be inefficient at doing so. But for applications where heat is the desired output — whether for heating buildings, cooking, or powering heat-based industrial processes — this could provide an opportunity for the expansion of solar power into new realms.

“It could change the game, since it makes the sun’s energy, in the form of heat, storable and distributable,” says Jeffrey Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering at MIT, who is a co-author of a paper describing the new process in the journal Nature Chemistry. Timothy Kucharski, a postdoc at MIT and Harvard, is the paper’s lead author.

The principle is simple: Some molecules, known as photoswitches, can assume either of two different shapes, as if they had a hinge in the middle. Exposing them to sunlight causes them to absorb energy and jump from one configuration to the other, which is then stable for long periods of time.

But these photoswitches can be triggered to return to the other configuration by applying a small jolt of heat, light, or electricity — and when they relax, they give off heat. In effect, they behave as rechargeable thermal batteries: taking in energy from the sun, storing it indefinitely, and then releasing it on demand.

Read more…

See Prof. Grossman teach about this new class of solar materials, in this lecture video from his OCW course 3.021J Introduction to Modeling and Simulation: