Two PUP Books Longlisted for the 2018 AAAS/Subaru SB&F Prizes

We are delighted that Monarchs and Milkweed by Anurag Agrawal and Welcome to the Universe by Neil DeGrasse Tyson, Michael Strauss, and J. Richard Gott have been longlisted for the AAAS/Subaru SB&F Prizes for Excellence in Science Books!

The Prizes celebrate outstanding science writing and illustration for children and young adults and are meant to encourage the writing and publishing of high-quality science books for all ages. AAAS believes that, through good science books, this generation, and the next, will have a better understanding and appreciation of science.

Agrawal

Welcome to the Universe

Steven S. Gubser: Thunder and Lightning from Neutron Star mergers

As of late 2015, we have a new way of probing the cosmos: gravitational radiation. Thanks to LIGO (the Laser Interferometer Gravitational-wave Observatory) and its new sibling Virgo (a similar interferometer in Italy), we can now “hear” the thumps and chirps of colliding massive objects in the universe. Not for nothing has this soundtrack been described by LIGO scientists as “the music of the cosmos.” This music is at a frequency easily discerned by human hearing, from somewhat under a hundred hertz to several hundred hertz. Moreover, gravitational radiation, like sound, is wholly different from light. It is possible for heavy dark objects like black holes to produce mighty gravitational thumps without at the same time emitting any significant amount of light. Indeed, the first observations of gravitational waves came from black hole merger events whose total power briefly exceeded the light from all stars in the known universe. But we didn’t observe any light from these events at all, because almost all their power went into gravitational radiation.

In August 2017, LIGO and Virgo observed a collision of neutron stars which did produce observable light, notably in the form of gamma rays. Think of it as cosmic thunder and lightning, where the thunder is the gravitational waves and the lightning is the gamma rays. When we see a flash of ordinary lightning, we can count a few seconds until we hear the thunder. Knowing that sound travels one mile in about five seconds, we can reckon how distant the event is. The reason this method works is that light travels much faster than sound, so we can think of the transmission of light as instantaneous for purposes of our estimate.

Things are very different for the neutron star collision, in that the event took place about 130 million light years away, but the thunder and lightning arrived on earth pretty much simultaneously. To be precise, the thunder was first: LIGO and Virgo heard a basso rumble rising to a characteristic “whoop,” and just 1.7 seconds later, the Fermi and INTEGRAL experiments observed gamma ray bursts from a source whose location was consistent with the LIGO and Virgo observations. The production of gamma rays from merging neutron stars is not a simple process, so it’s not clear to me whether we can pin that 1.7 seconds down as a delay precisely due to the astrophysical production mechanisms; but at least we can say with some confidence that the propagation time of light and gravity waves are the same to within a few seconds over 130 million light years. From a certain point of view, that amounts to one of the most precise measurements in physics: the ratio of the speed of light to the speed of gravity equals 1, correct to about 14 decimal places or better.

The whole story adds up much more easily when we remember that gravitational waves are not sound at all. In fact, they’re nothing like ordinary sound, which is a longitudinal wave in air, where individual air molecules are swept forward and backward just a little as the sound waves pass them by. Gravitational waves instead involve transverse disturbances of spacetime, where space is stretched in one direction and squeezed in another—but both of those stretch-squeeze directions are at right angles to the direction of the wave. Light has a similar transverse quality: It is made up of electric and magnetic fields, again in directions that are at right angles to the direction in which the light travels. It turns out that a deep principle underlying both Maxwell’s electromagnetism and Einstein’s general relativity forces light and gravitational waves to be transverse. This principle is called gauge symmetry, and it also guarantees that photons and gravitons are massless, which implies in turn that they travel at the same speed regardless of wavelength.

It’s possible to have transverse sound waves: For instance, shearing waves in crystals are a form of sound. They typically travel at a different speed from longitudinal sound waves. No principle of gauge symmetry forbids longitudinal sound waves, and indeed they can be directly observed, along with their transverse cousins, in ordinary materials like metals. The gauge symmetries that forbid longitudinal light waves and longitudinal gravity waves are abstract, but a useful first cut at the idea is that there is extra information in electromagnetism and in gravity, kind of like an error-correcting code. A much more modest form of symmetry is enough to characterize the behavior of ordinary sound waves: It suffices to note that air (at macroscopic scales) is a uniform medium, so that nothing changes in a volume of air if we displace all of it by a constant distance.

In short, Maxwell’s and Einstein’s theories have a feeling of being overbuilt to guarantee a constant speed of propagation. And they cannot coexist peacefully as theories unless these speeds are identical. As we continue Einstein’s hunt for a unified theory combining electromagnetism and gravity, this highly symmetrical, overbuilt quality is one of our biggest clues.

The transverse nature of gravitational waves is immediately relevant to the latest LIGO / Virgo detection. It is responsible for the existence of blind spots in each of the three detectors (LIGO Hanford, LIGO Livingston, and Virgo). It seems like blind spots would be bad, but they actually turned out to be pretty convenient: The signal at Virgo was relatively weak, indicating that the direction of the source was close to one of its blind spots. This helped localize the event, and localizing the event helped astronomers home in on it with telescopes. Gamma rays were just the first non-gravitational signal observed: the subsequent light-show from the death throes of the merging neutron stars promises to challenge and improve our understanding of the complex astrophysical processes involved. And the combination of gravitational and electromagnetic observations will surely be a driver of new discoveries in years and decades to come.

 

BlackSteven S. Gubser is professor of physics at Princeton University and the author of The Little Book of String TheoryFrans Pretorius is professor of physics at Princeton. They both live in Princeton, New Jersey. They are the authors of The Little Book of Black Holes.

Steven S. Gubser & Frans Pretorius: The Little Book of Black Holes

Black holes, predicted by Albert Einstein’s general theory of relativity more than a century ago, have long intrigued scientists and the public with their bizarre and fantastical properties. Although Einstein understood that black holes were mathematical solutions to his equations, he never accepted their physical reality—a viewpoint many shared. This all changed in the 1960s and 1970s, when a deeper conceptual understanding of black holes developed just as new observations revealed the existence of quasars and X-ray binary star systems, whose mysterious properties could be explained by the presence of black holes. Black holes have since been the subject of intense research—and the physics governing how they behave and affect their surroundings is stranger and more mind-bending than any fiction. The Little Book of Black Holes by Steven S. Gubser and Frans Pretorius takes readers deep into the mysterious heart of the subject, offering rare clarity of insight into the physics that makes black holes simple yet destructive manifestations of geometric destiny. Read on to learn a bit more about black holes and what inspired the authors to write this book.

Your book tells the story of black holes from a physics perspective. What are black holes, really? What’s inside?

Black holes are regions of spacetime from which nothing can escape, not even light. In our book, we try to live up to our title by getting quickly to the heart of the subject, explaining in non-technical terms what black holes are and how we use Einstein’s theory of relativity to understand them. What’s inside black holes is a great mystery. Taken at face value, general relativity says spacetime inside a black hole collapses in on itself, so violently that singularities form. We need something more than Einstein’s theory of relativity to understand what these singularities mean. Hawking showed that quantum effects cause black holes to radiate very faintly. That radiation is linked with quantum fluctuations inside the black hole. But it’s a matter of ongoing debate whether these fluctuations are a key to resolving the puzzle of the singularity, or whether some more drastic theory is needed.

How sure are we that black holes exist?

A lot more certain than we were a few years ago. In September 2015, the LIGO experiment detected gravitational waves from the collision of two black holes, each one about thirty times the mass of the sun. Everything about that detection fit our expectations based on Einstein’s theories, so it’s hard to escape the conclusion that there really are black holes out there. In fact, before the LIGO detection we were already pretty sure that black holes exist. Matter swirling around gigantic black holes at the core of distant galaxies form the brightest objects in the Universe. They’re called quasars, and the only reason they’re dim in our sight is that they’re so far away, literally across the Universe. Similar effects around smaller black holes generate X-rays that we can detect relatively nearby, mere thousands of light years away from us. And we have good evidence that there is a large black hole at the center of the Milky Way.

Can you talk a bit about the formation of black holes?

Black holes with mass comparable to the sun can form when big stars run out of fuel and collapse in on themselves. Ordinarily, gravity is the weakest force, but when too much matter comes together, no force conceivable can hold it up against the pull of gravity. In a sense, even spacetime collapses when a black hole forms, and the result is a black hole geometry: an endless inward cascade of nothing into nothing. All the pyrotechnics that we see in distant quasars and some nearby X-ray sources comes from matter rubbing against itself as it follows this inward cascade.

How have black holes become so interesting to non-specialists? How have they been glorified in popular culture?

There’s so much poetry in black hole physics. Black hole horizons are where time stands still—literally! Black holes are the darkest things that exist in Nature, formed from the ultimate ashes of used-up stars. But they create brilliant light in the process of devouring yet more matter. The LIGO detection was based on a black hole collision that shook the Universe, with a peak power greater than all stars combined; yet we wouldn’t even have noticed it here on earth without the most exquisitely sensitive detector of spacetime distortions ever built. Strangest of all, when stripped of surrounding matter, black holes are nothing but empty space. Their emptiness is actually what makes them easy to understand mathematically. Only deep inside the horizon does the emptiness end in a terrible, singular core (we think). Horrendous as this sounds, black holes could also be doorways into wormholes connecting distant parts of the Universe. But before packing our bags for a trip from Deep Space Nine to the Gamma Quadrant, we’ve got to read the fine print: as far as we know, it’s impossible to make a traversable wormhole.

What inspired you to write this book? Was there a point in life where your interest in this topic was piqued?

We both feel extremely fortunate to have had great mentors, including Igor Klebanov, Curt Callan, Werner Israel, Matthew Choptuik, and Kip Thorne who gave us a lot of insight into black holes and general relativity. And we owe a big shout-out to our editor, Ingrid Gnerlich, who suggested that we write this book.

GubserSteven S. Gubser is professor of physics at Princeton University and the author of The Little Book of String Theory. Frans Pretorius is professor of physics at Princeton.

Kip Thorne & Roger Blandford on Modern Classical Physics

PhysicsThis first-year, graduate-level text and reference book covers the fundamental concepts and twenty-first-century applications of six major areas of classical physics that every masters- or PhD-level physicist should be exposed to, but often isn’t: statistical physics, optics (waves of all sorts), elastodynamics, fluid mechanics, plasma physics, and special and general relativity and cosmology. Growing out of a full-year course that the eminent researchers Kip S. Thorne, winner of the 2017 Nobel Prize in Physics, and Roger D. Blandford taught at Caltech for almost three decades, this book is designed to broaden the training of physicists. Its six main topical sections are also designed so they can be used in separate courses, and the book provides an invaluable reference for researchers.

This book emerged from a course you both began teaching nearly 4 decades ago. What drove you to create the course, and ultimately to write this book?

KST: We were unhappy with the narrowness of physics graduate education in the United States. We believed that every masters-level or PhD physicist should be familiar with the basic concepts of all the major branches of classical physics and should have some experience applying them to real world phenomena. But there was no obvious route to achieve this, so we created our course.

RDB: Of course we had much encouragement from colleagues who helped us teach it and students who gave us invaluable feedback on the content.

The title indicates that the book is a “modern” approach to classical physics (which emphasizes physical phenomena at macroscopic scales). What specifically is “modern” in your book’s approach to this subject?

KST: Classical-physics ideas and tools are used extensively today in research areas as diverse as astrophysics, high-precision experimental physics, optical physics, biophysics, controlled fusion, aerodynamics, computer simulations, etc. Our book draws applications from all these modern topics and many more. Also, these modern applications have led to powerful new viewpoints on the fundamental concepts of classical physics, viewpoints that we elucidate—for example, quantum mechanical viewpoints and language for purely classical mode-mode coupling in nonlinear optics and in nonlinear plasma physics.

Why do you feel that it is so important for readers to become more familiar with classical physics, beyond what they may have been introduced to already?

KST: In their undergraduate and graduate level education, most physicists have been exposed to classical mechanics, electromagnetic theory, elementary thermodynamics, and little classical physics beyond this. But in their subsequent careers, most physicists discover that they need an understanding of other areas of classical physics (and this book is a vehicle for that).

In many cases they may not even be aware of their need. They encounter problems in their research or in R&D where powerful solutions could be imported from other areas of classical physics, if only they were aware of those other areas. An example from my career: in the 1970s, when trying to understand recoil of a binary star as it emits gravitational waves, I, like many relativity physicists before me, got terribly confused. Then my graduate student, Bill Burke—who was more broadly educated than I—said “we can resolve the confusion by adopting techniques that are used to analyze boundary layers in fluid flows around bodies with complicated shapes.” Those techniques (matched asymptotic expansions), indeed, did the job, and through Bill, they were imported from fluid mechanics into relativity.

RDB: Yes. To give a second example, when I was thinking about ways to accelerate cosmic rays, I recalled graduate lectures on stellar dynamics and found just the tools I needed.

You also mention in the book that geometry is a deep theme and important connector of ideas. Could you explain your perspective, and how geometry is used thematically throughout the book?

KST: The essential point is that, although coordinates are a powerful, and sometimes essential, tool in many calculations, the fundamental laws of physics can be expressed without the aid of coordinates; and, indeed, their coordinate-free expressions are generally elegant and exceedingly powerful. By learning to think about the laws in coordinate-free (geometric) language, a physicist acquires great power. For example, when one searches for new physical laws, requiring that they be geometric (coordinate-free) constrains enormously the forms that they may take. And in many practical computations (for example, of the relativistic Doppler shift), a geometric route to the solution can be faster and much more insightful than one that uses coordinates. Our book is infused with this.

RDB: We are especially keen on presenting these fundamental laws in a manner which makes explicit the geometrically formulated conservation laws for mass, momentum, energy, etc. It turns out that this is often a good starting point when one wants to solve these equations numerically. But ultimately, a coordinate system must be introduced to execute the calculations and interpret the output.

One of the areas of application that you cover in the book is cosmology, an area of research that has undergone a revolution over the past few decades. What are some of the most transformative discoveries in the field’s recent history? How does classical physics serve to underpin our modern understanding of how the universe formed and is evolving? What are some of the mysteries that continue to challenge scientists in the field of cosmology?   

RDB: There have indeed been great strides in understanding the large scale structure and evolution of the universe, and there is good observational support for a comparatively simple description. Cosmologists have found that 26 percent of the energy density in the contemporary, smoothed-out universe is in the form of “dark matter,” which only seems to interact through its gravity. Meanwhile, 69 percent is associated with a “cosmological constant,” as first introduced by Einstein and which causes the universe to accelerate. The remaining five percent is the normal baryonic matter which we once thought accounted for essentially all of the universe. The actual structure that we observe appears to be derived from almost scale-free statistically simple, random fluctuations just as expected from an early time known as inflation. Fleshing out the details of this description is almost entirely an exercise in classical physics. Even if this description is validated by future observations, much remains to be understood, including the nature of dark matter and the cosmological constant, what fixes the normal matter density, and the great metaphysical question of what lies beyond the spacetime neighborhood that we can observe directly.

KST: Remarkably, in fleshing out the details in the last chapter of our book, we utilize classical-physics concepts and results from every one of the other chapters. ALL of classical physics feeds into cosmology!

The revolution in cosmology that you describe depends upon many very detailed observations using telescopes operating throughout the entire electromagnetic spectrum and beyond. How do you deal with this in the book?

RDB: We make no attempt to describe the rich observational and experimental evidence, referring the reader to many excellent texts on cosmology that describe these in detail. However, we do describe some of the principles that underlie the design and operation of the radio and optical telescopes that bring us cosmological data.

There is has also been a lot of excitement regarding the recent observation by LIGO of gravitational waves caused by merging black holes. How is this subject covered in the book, and how, briefly, are some of the concepts of classical physics elucidated in your description of this cutting-edge research area?   

KST: LIGO’s gravitational wave detectors rely on an amazingly wide range of classical physics concepts and tools, so time and again we draw on LIGO for illustrations. The theory of random processes, spectral densities, the fluctuation-dissipation theorem, the Fokker-Planck equation; shot noise, thermal noise, thermoelastic noise, optimal filters for extracting weak signals from noise; paraxial optics, Gaussian beams, the theory of coherence, squeezed light, interferometry, laser physics; the interaction of gravitational waves with light and with matter; the subtle issue of the conservation or non conservation of energy in general relativity—all these and more are illustrated by LIGO in our book.

What are some of the classical physics phenomena in every day life that you are surprised more people do not fully understand—whether they are lay people, students, or scientists?

KST: Does water going down a drain really have a strong preference for clockwise in the northern hemisphere and counterclockwise in the south? How strong? What happens as you cross the equator? How are ocean waves produced? Why do stars twinkle in the night sky, and why doesn’t Jupiter twinkle? How does a hologram work? How much can solid objects be stretched before they break, and why are there such huge differences from one type of solid (for example thin wire) to another (a rubber band)?

RDB: I agree and have to add that I am regularly humbled by some every day phenomenon that I cannot explain or for which I have carried around for years a fallacious explanation. There is, rightly, a lot of focus right now on climate change, energy, hurricanes, earthquakes, and so on. We hear about them every day. We physicists need to shore up our understanding and do a better job of communicating this.

Do you believe that some of your intended readers might be surprised to discover the deep relevance of classical physics to certain subject areas?

KST: In subjects that physicists think of as purely quantum, classical ideas and classical computational techniques can often be powerful. Condensed matter physics is an excellent example—and accordingly, our book includes a huge number of condensed-matter topics. Examples are Bose-Einstein condensates, the van der Waals gas, and the Ising model for ferromagnetism.

RDB: Conversely, quantum mechanical techniques are often used to simplify purely classical problems, for example in optics.

Writing a book is always an intellectual journey. In the preparation of this tremendously wide-ranging book, what were some of the most interesting things you learned along the way?

KST: How very rich and fascinating is the world of classical physics—far more so than we thought in 1980 when we embarked on this venture. And then there are the new inventions, discoveries, and phenomena that did not exist in 1980 but were so important or mind-boggling that we could not resist including them in our book. For example, optical-frequency combs and the phase-locked lasers that underlie them, Bose-Einstein condensates, the collapse of the World Trade Center buildings on 9/11/01, the discovery of gravitational waves and the techniques that made it possible, laser fusion, and our view of the universe at large.

Kip S. Thorne is the Feynman Professor Emeritus of Theoretical Physics at Caltech. His books include Gravitation and Black Holes and Time Warps. Roger D. Blandford is the Luke Blossom Professor of Physics and the founding director of the Kavli Institute of Particle Astrophysics and Cosmology at Stanford University. Both are members of the National Academy of Sciences.

 

Michael Strauss: America’s Eclipse

Welcome to the UniverseOn Monday, August 21, people all across the United States will witness one of the rarest and most spectacular of all astronomical phenomena: a total solar eclipse. This occurs when the position of the Moon and the Sun in the sky align perfectly, such that the Moon’s shadow falls onto a specific point on the Earth’s surface. If you are lucky enough to be standing in the shadow, you will see the Sun’s light completely blocked by the Moon: the sky will become dark, and the stars and planets will become visible. But because the apparent sizes of the Moon and the Sun are almost the same, and because everything is in motion—the Moon orbits Earth, and Earth rotates around its axis and orbits the Sun—the Moon’s shadow moves quickly.  During the eclipse, the Moon’s shadow will cross the United States at a speed of 1800 miles per hour, taking about 90 minutes to travel from the Pacific Coast in Oregon to touch the Atlantic in South Carolina.  This means that totality, the time when the Sun’s disk is completely covered as seen from any given spot along the eclipse path, is very brief: 2 minutes and 40 seconds at best.

If you are standing along the eclipse path, it takes about 2.5 hours for the Moon to pass across the Sun.  That is, you will see the disk of the Sun eaten away, becoming an ever-narrowing crescent. During this time, you can only look at the Sun with eclipse glasses (make sure they are from a reputable company!), which block the vast majority of the light from the Sun.  It is also fun to look at the dappled shadows underneath a leafy tree; if you look closely, you’ll see that the individual spots of light are all crescent-shaped. A bit more than an hour after the Moon begins to cover the Sun, you reach the point of totality, and the sky becomes dark. It is now safe to remove your eclipse glasses.

Experiencing a few minutes of darkness in the middle of the day is pretty cool. But what makes the eclipse really special is that with the light of the Sun’s disk blocked out, the faint outer atmosphere of the Sun, its corona, becomes visible to the naked eye. The corona consists of tenuous gas extending over millions of miles, with a temperature of a few million degrees. It is shaped by the complex magnetic field of the Sun, and may exhibit a complex arrangement of loops and filaments: indeed, observations of the solar corona during eclipses have been one of the principal ways in which astronomers have learned about its magnetic field. The sight is awe-inspiring; those who have experienced it say that it is as a life-changing experience.

As the Moon starts to move off the disk, the full brightness of the Sun becomes visible again, and you must put your eclipse glasses back on to protect your eyes. The Sun now appears as a narrow and ever-widening crescent. A bit more than an hour later, the Sun’s disk is completely uncovered.

The shadow of the Moon will be about 70 miles in diameter at any given time. That means that if you are not standing in that 70-mile-wide path as the shadow crosses the country, you will only see a partial solar eclipse, in which you will see the Sun appearing as a crescent.  Again, be sure to wear eclipse glasses to look at the Sun!

Solar eclipses happen roughly once or twice a year somewhere on Earth’s surface, but because  of the narrowness of the eclipse path, the number of people standing in the path is usually relatively small. This one, crossing the entire continental US, is special in this regard: tens of millions of people live within a few hours of the eclipse path. This promises to be the most widely seen and recorded eclipse in history! I have never seen a total eclipse of the Sun before, and am very excited to be traveling with my family to Oregon, where we have our fingers crossed for good weather. So, to all those who have the opportunity to stand in the Moon’s shadow, get yourself a pair of eclipse glasses, and prepare yourself to be awed.

Michael A. Strauss is professor of astrophysics at Princeton University. He is the coauthor (with Neil deGrasse Tyson and J. Richard Gott) of Welcome to the Universe: An Astrophysical Tour.

Anna Frebel: Solar Eclipse 2017

Next Monday, the U.S. will witness an absolutely breathtaking natural spectacle. One worthy of many tweets as it is of the astronomical kind—quite literally. I’m talking about the upcoming total solar eclipse where, for a short couple of minutes, the Moon will move directly into our line of sight to perfectly eclipse the Sun.

During the so-called “totality,” when the Sun is fully covered, everything around you will take on twilight colors. It will get cooler, the birds will become quieter, and you’ll get this eerie feeling that something is funny is going on. No wonder that in ancient times, people thought the world would end during such an event.

I have witnessed this twice before. 1999 in Munich, Germany, and 2002 in Ceduna, Australia. Like so many others, I traveled there with great anticipation to see the Sun disappear on us. In both cases, however, it was cloudy for hours before totality which caused frustration and even anxiety in the crowd. But nature happened to be kind. A few minutes before totality, the clouds parted to let us catch a glimpse. We experienced how the disk of the Sun finally fully vanished just after seeing the last little rays of light peeking through that produced a famous “diamond ring” image. We could also see the glowing corona surrounding the black Sun. All the while, nature around us transformed into what felt like a cool and breezy late summer evening. A few minutes later, everything was back to normal and the clouds covered it all once again like nothing had ever happened. The exact same cloud scenario happened both times—how lucky was that?

As for next Monday, I sincerely hope the clouds will stay home. I know so many folks who will travel from far and wide into the totality zone to experience this “Great American Eclipse.” It is actually fairly narrow, only about 100 miles wide, but stretches diagonally across the entire U.S.. For many, this will be a once in a lifetime opportunity to see such a rare event and I’m sure this experience will stay with them for years to come. It sure did for me.

I will actually not travel into the totality zone. Instead, I’ll be watching and talking about the partial eclipse that we can see up here in Massachusetts with my three year old son and his preschool class. A partial eclipse lasts for a couple of hours and occurs when the alignment between Earth, Moon, and Sun is just a bit “off.” Generally, this can happen when these three bodies are indeed not going to perfectly align. Or, when a person on Earth is close but not right in the totality zone, it causes a misalignment between the observer, the Moon, and the Sun. In both cases, the Sun is not going to get fully covered. Nevertheless, it is still a marvelous event and great for children and anyone interested to learn about solar eclipses and astronomy. And luckily enough, everyone in the U.S., Canada, and Mexico can watch a partial eclipse, no matter where you are located.

Solar eclipses don’t happen randomly. There are part of long lasting cycles that stem from the motion of the Moon around the Earth and the alignment of its orbit with respect to the Sun. This eclipse is part of the famous Saros cycle 145, and so was the 1999 eclipse I saw in Munich. It produces eclipses every 18 years, 11 days and 8h. Subsequent Saros eclipses are visible from different parts of the globe.The extra 8 hours in the cycle mean that from one eclipse to the next, the Earth must rotate an additional ~8 hours or ~120º. Hence, this eclipse is ~120º westward from continental Europe which is the continental U.S.. The next one will be visible from China in 2035. Each of the many Saros series typically lasts 12 to 13 centuries. Series 145 began in 1639 and will end in 3009 after 77 eclipses.

There are 4 to 6 total eclipses every year but not all are visible on land. Actually, from about any given point on Earth, once every 150 years an eclipse is visible. Now, it’s our turn. So if you’re not already traveling into the totality zone, make sure you still watch the partial eclipse—never without eclipse glasses, though, partial or total eclipse alike! Looking into the Sun causes serious longterm damage to your eyes but also your camera. So equip your camera with glasses, too! Alternatively, you can just watch the Sun’s shadow on a wall to observe how the Sun gets eaten away piece by piece by the incoming Moon. Ask your work if you can take a few minutes off. It’s a worthy cause. Actually, a well-timed bathroom break is almost long enough to catch totality or a glimpse of partial coverage. Eclipses are simply too rare and too beautiful to miss!

Get your eclipse glasses, rearrange your schedule (just a little bit), and make sure your kids or grandkids, friends and neighbors are seeing it too. Because, actually, the tides of the oceans on Earth are slowing down Earth’s rotation which make the Moon spiral outward and away from us by 1 inch per year. This means that the Moon will appear smaller and smaller with time, and in the far future, there won’t be any total eclipses possible anymore.

FrebelAnna Frebel is the Silverman (1968) Family Career Development Assistant Professor in the Department of Physics at the Massachusetts Institute of Technology. She has received numerous international honors and awards for her discoveries and analyses of the oldest stars. She is the author of Searching for the Oldest Stars: Ancient Relics from the Early Universe.

Welcome to the Universe microsite receives a Webby

We’re pleased to announce that the accompanying microsite to Welcome to the Universe by Neil DeGrasse Tyson, Michael A. Strauss, and J. Richard Gott has won a People’s Choice Webby in the Best Use of Animation or Motion Graphics category. Congratulations to Eastern Standard, the web designer, on a beautifully designed site.

Winning a Webby is especially gratifying because it honors how much fun we had making the site. We knew we wanted an unconventional approach that would mirror both the complexity and accessibility of the book it was meant to promote. Our wonderful in-house team and creative partners, Eastern Standard took on this challenge, and we are so happy with the results.
—Maria Lindenfeldar, Creative Director, Princeton University Press 

Creating this microsite was a wonderful experiment for us at Princeton University Press.  We wanted to explore how we, as a publisher, could present one of our major books to the public in a compelling way in the digital environment.  Ideally, we had a vision of creating a simple site with intuitive navigation that would give readers an inviting mini-tour through the topics of the book, Welcome to the Universe, by Neil deGrasse Tyson, Michael Strauss, and Richard Gott.  The animation was meant to be subtle, but meaningful, and to gently encourage user interaction, so that the focus would always remain immersing the reader in the content of the book – what we feel is the most interesting part!  We were very happy with how it turned out and now all the more thrilled and honored that the site was chosen for a Webby!
—Ingrid Gnerlich, Science Publisher, Princeton University Press

Celebration of Science: A reading list

This Earth Day 2017, Princeton University Press is celebrating science in all its forms. From ecology to psychology, astronomy to earth sciences, we are proud to publish books at the highest standards of scholarship, bringing the best work of scientists to a global audience. We all benefit when scientists are given the space to conduct their research and push the boundaries of the human store of knowledge further. Read on for a list of essential reading from some of the esteemed scientists who have published with Princeton University Press.

The Usefulness of Useless Knowledge
Abraham Flexner and Robbert Dijkgraaf

Use

The Serengeti Rules
Sean B. Carroll

Carroll

Honeybee Democracy
Thomas D. Seeley

Seeley

Silent Sparks
Sara Lewis

Lewis

Where the River Flows
Sean W. Fleming

Fleming

How to Clone a Mammoth
Beth Shapiro

Shapiro

The Future of the Brain
Gary Marcus & Jeremy Freeman

Brain

Searching for the Oldest Stars
Anna Frebel

Frebel

Climate Shock
Gernot Wagner & Martin L. Weitzman

Climate

Welcome to the Universe
Neil DeGrasse Tyson, Michael A. Strauss, and J. Richard Gott

Universe

The New Ecology
Oswald J. Schmitz

Schmitz

Welcome to the Universe microsite nominated for a Webby

We’re thrilled to announce that the microsite for Welcome to the Universe by Neil DeGrasse Tyson, Michael A. Strauss, and J. Richard Gott, designed by Eastern Standard, has been nominated for a Webby in the Best Use of Animation or Motion Graphics category. Be sure to check it out and vote for the best of the internet!

webby

 

J. Richard Gott: What’s the Value of Pi in Your Universe?

Carl Sagan’s sci-fi novel Contact famously introduced wormholes for rapid transit between the stars. Carl had asked his friend Kip Thorne to tell him if the physics of wormholes was tenable and this led Thorne and his colleagues to investigate their properties. They found that traversable wormholes required exotic matter to prop them open and that, by moving the wormhole mouths one could find general relativity solutions allowing time travel to the past. A quantum state called the Casimir vacuum whose effects have been observed experimentally, could provide the exotic matter. To learn whether such time machines could be constructible in principle, we may have to master the laws of quantum gravity, which govern how gravity behaves on microscopic scales. It’s one of the reasons physicists find these solutions so interesting.

But in Contact there is lurking yet another fantastic sci-fi idea, which gets less publicity because it was not included in the movie version. In the book, the protagonist finds out from the extraterrestrials that the system of wormholes throughout the galaxy was not built by them, but by the long gone “old ones” who could manipulate not only the laws of physics but also the laws of mathematics! And they left a secret message in the digits of pi. In his movie Pi, Darren Aronofsky showed a man driven crazy by his search for hidden meanings in the digits of pi.

This opens the question: could pi have been something else? And if so, does pi depend on the laws of physics? Galileo said: “Philosophy is written in this grand book…. I mean the universe … which stands continually open to our gaze…. It is written in the language of mathematics.” The universe is written in the language of mathematics. Nobel laureate Eugene Wigner famously spoke of the “unreasonable effectiveness of mathematics” in explaining physics. Many philosophers take the Platonic view that mathematics would exist even the universe did not. And cosmologist Max Tegmark goes so far as to say that the universe actually is mathematics.

Yet maybe it is the other way around. The laws of physics are just the laws by which matter behaves. They determine the nature of our universe. Maybe humans have simply developed the mathematics appropriate for describing our universe, and so of course it fits with what we see. The mathematician Leopold Kronecker said, “God created the integers, all the rest is the work of man.” Are the laws of mathematics discovered by us in the same way as we discover the laws of physics? And are the laws of mathematics we discover just those which would have occurred to creatures living in a universe with physics like ours? In our universe, physics produces individual identical particles: all electrons are the same for example. We know about integers because there are things that look the same (like apples) for us to count. If you were some strange creature in a fractal universe containing only one object—yourself—and you thought only recursively, you might not ever think of counting anything and would never discover integers.

What about π = 3.14159265.…? Might it have a different value in a different universe? In our universe we have a fundamental physical dimensionless constant, the fine structure constant α which is related to the square of the value of the electric charge of the proton in natural geometrical Planck units (where the speed of light is 1 and the reduced Planck constant is 1 and Newton’s gravitational constant is 1). Now 1/α = 137.035999… Some physicists hope that one day we may have a mathematical formula for 1/α using mathematical constants such as π and e. If a theory for the fine structure constant could be developed giving a value in agreement with observations but allowing it to be calculated uniquely from pure mathematics, and if more and more digits of the constant were discovered experimentally fulfilling its prediction, it would certainly merit a Nobel Prize. But many physicists feel that no such magic formula will ever be discovered. Inflation may produce an infinite number of bubble universes, each with different laws of physics. Different universes bubbling out of an original inflating sea could have different values of 1/α. As Martin Rees has said, the laws of physics we know may be just local bylaws in an infinite multiverse of universes. String theory, if correct, may eventually give us a probability distribution for 1/α and we may find that our universe is just somewhere in the predicted middle 95% of the distribution, for example. Maybe there could be different universes with different values of π.

Let’s consider one possible example: taxicab geometry. This was invented by Hermann Minkowski. Now this brilliant mathematician also invented the geometrical interpretation of time as a fourth dimension based on Einstein’s theory of special relativity, so his taxicab geometry merits a serious look. Imagine a city with a checkerboard pattern of equal-sized square blocks. Suppose you wanted to take a taxicab to a location 3 blocks east, and 1 block north of your location, the shortest total distance you would have to travel to get there is 4 blocks. Your taxi has to travel along the streets, it does not get to travel as the crow flies. You could go 1 block east, then 1 block north then 2 blocks east, and still get to your destination, but the total distance you traveled would also be 4 blocks. The distance to your destination would be ds = |dx| + |dy|, where |dx| is the absolute value of the difference in x coordinates and |dy| is the absolute value of the difference in y coordinates. This is not the Euclidean formula. We are not in Kansas anymore! The set of points equidistant from the origin is a set of dots in a diamond shape. See diagram.

Gott

Image showing an intuitive explanation of why circles in taxicab geometry look like diamonds. Wikipedia.

Now if the blocks were smaller, there would be more dots, still in a diamond shape. In the limit where the size of the blocks had shrunk to zero, one would have a smooth diamond shape as shown in the bottom section of the diagram. The set of points equidistant from the origin has a name—a “circle!” If the circle has a radius of 1 unit, the distance along one side of its diamond shape is 2 units: going from the East vertex of the diamond to the North vertex of the diamond along the diagonal requires you to change the x coordinate by 1 unit and the y coordinate by 1 unit, making the distance along one side of the diagonal equal to 2 units (ds = |dx| + |dy| = 1 + 1 units = 2 units). The diamond shape has 4 sides so the circumference of the diamond is 8 units. The diameter of the circle is twice the radius, and therefore 2 units. In the taxicab universe π = C/d = C/2r = 8/2 = 4. If different laws of physics dictate different laws of geometry, you can change the value of π.

This taxicab geometry applies in the classic etch-a-sketch toy (Look it up on google, if you have never seen one). It has a white screen, and an internal stylus that draws a black line, directed by horizontal and vertical control knobs. If you want to draw a vertical line, you turn the vertical knob. If you want to draw a horizontal line you turn the horizontal knob. If you want to draw a diagonal line, you must simultaneously turn both knobs smoothly. If the distance between two points is defined by the minimal amount of total turning of the two knobs required to get from one point to the other, then that is the “taxicab” distance between the two points. In Euclidean geometry there is one shortest line between two points: a straight line between them. In taxicab geometry there can be many different, equally short, broken lines (taxicab routes) connecting two points. Taxicab geometry does not obey the axioms of Euclidean geometry and therefore does not have the same theorems as Euclidean geometry. And π is 4.

Mathematician and computer scientist John von Neumann invented a cellular automaton universe that obeys taxicab geometry. It starts with an infinite checkerboard of pixels. Pixels can be either black or white. The state of a pixel at time step t = n + 1 depends only on the state of its 4 neighbors (with which it shares a side: north, south, east, west of it) on the previous time step t = n. Causal, physical effects move like a taxicab. If the pixels are microscopic, we get a taxicab geometry. Here is a simple law of physics for this universe: a pixel stays in the same state, unless it is surrounded by an odd number of black pixels, in which case it switches to the opposite state on the next time step. Start with a white universe with only 1 black pixel at the origin. In the next time step it remains black while its 4 neighbors also become black. There is now a black cross of 5 pixels at the center. It has given birth to 4 black pixels like itself. Come back later and there will be 25 black pixels in a cross-shaped pattern of 5 cross-shaped patterns.

Come back still later and you can find 125 black pixels in 5 cross-shaped patterns (of 5 cross-shaped patterns). All these new black pixels lie inside a diamond-shaped region whose radius grows larger by one pixel per time step. In our universe, drop a rock in a pond, and a circular ripple spreads out. In the von Neumann universe, causal effects spread out in a diamond-shaped pattern.

If by “life” you mean a pattern able to reproduce itself, then this universe is luxuriant with life. Draw any pattern (say a drawing of a bicycle) in black pixels and at a later time you will find 5 bicycles, and then 25 bicycles, and 125 bicycles, etc. The laws of physics in this universe cause any object to copy itself. If you object that this is just a video game, I must tell you that some physicists seriously entertain the idea that we are living in an elaborate video game right now with quantum fuzziness at small scales providing the proof of microscopic “pixelization” at small scales.

Mathematicians in the von Neumann universe would know π = 4 (Or, if we had a taxicab universe with triangular pixels filling the plane, causal effects could spread out along three axes instead of two and a circle would look like a hexagon, giving π = 3.). In 1932, Stanislaw Golab showed that if we were clever enough in the way distances were measured in different directions, we could design laws of physics so that π might be anything we wanted from a low of 3 to a high of 4.

Back to the inhabitants of the von Neumann universe who think π = 4. Might they be familiar with number we know and love, 3.14159265…? They might:

3.14159265… = 4 {(1/1) – (1/3) + (1/5) – (1/7) + (1/9) + …} (Leibnitz)

If they were familiar with integers, they might be able to discover 3.14159265… But maybe the only integers they know are 1, 5, 25, 125, … and 4 of course. They would know that 5 = SQRT(25), so they would know what a square root was. In this case they could still find a formula for

3.14159265. . . =
SQRT(4) {SQRT(4)/SQRT(SQRT(4))}{SQRT(4)/SQRT(SQRT(4) + SQRT(SQRT(4)))}{SQRT(4)/ SQRT(SQRT(4) + SQRT(SQRT(4) + SQRT(SQRT(4))))} …

This infinite product involving only the integer 4 derives from one found by Vieta in 1594.

There are indeed many formulas equal to our old friend 3.14159265… including a spectacular one found by the renowned mathematician Ramanujan. Though every real number can be represented by such infinite series, products and continued fractions, these are particularly simple. So 3.14159265… does seem to have a special intimate relationship with integers, independent of geometry. If physics creates individual objects that can be counted, it seems difficult to avoid learning about 3.14159265… eventually—“If God made the integers,” as Kronecker suggested. So 3.14159265… appears not to be a random real number and we are still left with the mystery of the unreasonable effectiveness of mathematics in explaining the physics we see in our universe. We are also left with the mystery of why the universe is as comprehensible as it is. Why should we lowly carbon life forms be capable of finding out as much about how the universe works as we have done? Having the ability as intelligent observers to ask questions about the universe seems to come with the ability to actually answer some of them. That’s remarkable.

UniverseGottJ. Richard Gott is professor of astrophysics at Princeton University. His books include The Cosmic Web: Mysterious Architecture of the Universe. He is the coauthor of Welcome to the Universe: An Astrophysical Tour with Neil DeGrasse Tyson and Michael A. Strauss.

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Welcome to the Universe is a personal guided tour of the cosmos by three of today’s leading astrophysicists: Neil deGrasse Tyson, Michael A. Strauss, and J. Richard Gott. Breathtaking in scope and stunningly illustrated throughout, this book is for those who hunger for insights into our evolving universe that only world-class astrophysicists can provide.

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In Fashion, Faith, and Fantasy in the New Physics of the Universe, acclaimed physicist and bestselling author Roger Penrose argues that fashion, faith, and fantasy, while sometimes productive and even essential in physics, may be leading today’s researchers astray in three of the field’s most important areas—string theory, quantum mechanics, and cosmology.

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An accessible blend of narrative history and science, Strange Glow describes mankind’s extraordinary, thorny relationship with radiation, including the hard-won lessons of how radiation helps and harms our health. Timothy Jorgensen explores how our knowledge of and experiences with radiation in the last century can lead us to smarter personal decisions about radiation exposures today.

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Exclusive interview with Neil deGrasse Tyson, Michael A. Strauss, and J. Richard Gott on their NYT bestseller, Welcome to the Universe

UniverseWe’re thrilled to announce that Welcome to the Universe, a guided tour of the cosmos by three of today’s leading astrophysicists, recently made the New York Times extended bestseller list in science. Inspired by the enormously popular introductory astronomy course that Neil deGrasse Tyson, Michael A. Strauss, and J. Richard Gott taught together at Princeton, this book covers it all—from planets, stars, and galaxies to black holes, wormholes, and time travel. The authors introduce some of the hot topics in astrophysics in today’s Q&A:


What is the Cosmic Perspective?

NDT: A view bigger than your own that offers a humbling, yet enlightening, and occasionally empowering outlook on our place as humans in time, space, on Earth and in the Universe. We devote many pages of Welcome to the Universe to establishing our place in the cosmos – not only declarations of that place, but also the reasons and the foundations for how we have come to learn how we fit in that place. When armed with a cosmic perspective, many earthly problems seem small, yet you cultivate a new sense of belonging to the universe. You are, in fact, a participant in the great unfolding of cosmic events.

What are some of the takeaways from the book?

NDT: If you read the entire book, and if we have succeeded as authors, then you should walk away with a deep sense of the operations of nature, and an appreciation for the size and scale of the universe; how and why planets form; how and why we search for planets orbiting around other stars, and alien life that may thrive upon them; how and why stars are born, live out their lives and die; what galaxies are and why they are the largest organizations of stars in the universe; the large scale structure of galaxies and space-time; the origins and future of the universe, Einstein’s relativity, black holes, and gravitational waves; and time travel. If that’s not enough, you will also learn about some of the continued unsolved mysteries in our field, such as dark matter, dark energy, and multiverses.

This book has more equations than do most popular books about astrophysics.  Was that a deliberate decision?

MAS: Yes.  The book’s subtitle is “An Astrophysical Tour,” and one of our goals in writing it was to show how observations, the laws of physics, and some high school mathematics can combine to yield the amazing discoveries of modern astrophysics: A Big Bang that happened 13.8 billion years ago (we show you how that number is determined), the dominant role dark matter has in the properties of galaxies (we tell you how we came to that conclusion), even the fact that some planets orbiting other stars have conditions conducive for liquid water to exist on their surface, thought to be a necessary prerequisite for life. Our goal is not just to present the wonders of the universe to the reader, but to have the reader understand how we have determined what we know, and where the remaining uncertainties (and there are plenty of them!) lie.

So your emphasis is on astrophysics as a quantitative science, a branch of physics?

MAS:  Yes.  We introduce the necessary physics concepts as we go: we do not expect the reader to know this physics before they read the book.  But astrophysicists are famous (perhaps notorious!) for rough calculations, “to astrophysical accuracy.”  We also lead the reader through some examples of such rough calculations, where we aim to get an answer to “an order of magnitude.”  That is, we’re delighted if we get an estimate that’s correct to within a factor of 2, or so.  Such calculations are useful in everyday life, helping us discriminate the nonsensical from the factual in the numerical world in which we live.

Can you give an example?

MAS: Most people in everyday discourse don’t think much about the distinction between “million,” “billion,” “trillion,” and so on, hearing them all as “a really big number,” with not much difference between them.  It is actually a real problem, and the difference between Federal budget items causing millions vs. billions of dollars is of course huge.  Our politicians and the media are confusing these all the time.  We hope that the readers of this book will come away with a renewed sense of how to think about numbers, big and small, and see whether the numbers they read about in the media make sense.

Is time travel possible?

JRG: In 1905 Einstein proved that time travel to the future is possible. Get on a rocket and travel out to the star Betelgeuse 500 light-years away and return at a speed of 99.995 % the speed of light and you will age only 10 years, but when you get back it will be the year 3016 on Earth. Even though we have not gone that fast or far, we still have time travelers among us today. Our greatest time traveler to date is the Russian cosmonaut Gennady Padalka, who by virtue of traveling at high speed in low Earth orbit for 879 days aged 1/44 of a second less than if he had stayed home. Thus, when he returned, he found Earth to be 1/44 of a second to the future of where he expected it to be. He has time traveled 1/44 of a second to the future. An astronaut traveling to the planet Mercury, living there for 30 years, and returning to Earth, would time travel into the future by 22 seconds. Einstein’s equations of general relativity, his theory of curved spacetime to explain gravity, have solutions that are sufficiently twisted to allow time travel to the past. Wormholes and moving cosmic strings are two examples. The time traveler can loop back to visit an event in his own past. Such a time machine cannot be used to journey back in time before it was created. Thus, if some supercivilization were to create one by twisting spacetime in the year 3000, they might use it to go from 3002 back to 3001, but they couldn’t use it go back to 2016, because that is before the time loop was created. To understand whether such time machines can be realized, we may need to understand how gravity works on microscopic scales, which will require us to develop a theory of quantum gravity. Places to look for naturally occurring time machines would be in the interiors of rotating black holes and at the very beginning of the universe, where spacetime is strongly curved.

Do we live in a multiverse?

JRG: A multiverse seems to be a natural consequence of the theory of inflation. Inflation explains beautifully the pattern of slightly hotter and colder spots we see in the Cosmic Microwave Background Radiation. It explains why the universe is so large and why it is as smooth as it is and still has enough variations in density to allow gravity to grow these into galaxies and clusters of galaxies by the present epoch. It also explains why the geometry of the universe at the present epoch is approximately Euclidean. Inflation is a period of hyperactive accelerated expansion occurring at the beginning of our universe. It is powered by a large vacuum energy density and negative pressure permeating empty space that is gravitationally repulsive. The universe doubles in size about every 3 10-38 seconds. With this rate of doubling, it very quickly grows to enormous size: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024… That explains why the universe is so large. When the high density vacuum state decays, it doesn’t do so all at once. Like water boiling in a pot, it does not turn into steam all at once, but should form bubbles. Each expanding bubble makes a universe. The inflationary sea should expand forever, creating an infinite number of bubble universes, ours being one of them. Other distant bubble universes are so far away, and the space between us and them is expanding so fast, that light from them may never reach us. Nevertheless, multiple universes seem a nearly inevitable consequence of inflation.

What discovery about the universe surprises or inspires you the most?

JRG: Perhaps the most amazing thing about the universe is that it is comprehensible to intelligent, carbon-based life forms like ourselves. We have been able to discover how old the universe is (13.8 billion years) and figure out many of the laws by which it operates. The object of this book is to make the universe comprehensible to our readers.

Don’t miss this C-Span video on the book, in which the authors answer questions about the universe, including how it began and the likelihood of intelligent life elsewhere.

Neil deGrasse Tyson is director of the Hayden Planetarium at the American Museum of Natural History. He is the author of many books, including Space Chronicles: Facing the Ultimate Frontier, and the host of the Emmy Award–winning documentary Cosmos: A Spacetime Odyssey. Michael A. Strauss is professor of astrophysics at Princeton University. J. Richard Gott is professor of astrophysics at Princeton University. His books include The Cosmic Web: Mysterious Architecture of the Universe (Princeton).