Martin Rees on On The Future

Humanity has reached a critical moment. Our world is unsettled and rapidly changing, and we face existential risks over the next century. Various prospects for the future—good and bad—are possible. Yet our approach to the future is characterized by short-term thinking, polarizing debates, alarmist rhetoric, and pessimism. In this short, exhilarating book, renowned scientist and bestselling author Martin Rees argues that humanity’s future depends on our taking a very different approach to thinking about and planning for tomorrow. Rich with fascinating insights into cutting-edge science and technology, this book will captivate anyone who wants to understand the critical issues that will define the future of humanity on Earth and beyond.

Are you an optimist?

I am writing this book as a citizen, and as an anxious member of the human species. One of its unifying themes is that humanity’s flourishing depends on how wisely science and technology are deployed. Our lives, our health, and our environment can benefit still more from further advances in biotech, cybertech, robotics, and AI. There seems no scientific impediment to achieving a sustainable and secure world, where all enjoy a lifestyle better than those in the ‘west’ do today (albeit using less energy and eating less meat). To that extent, I am a techno-optimist. But what actually happens depends on politics and ethical choices.

Our ever more interconnected world is exposed to new vulnerabilities. Even within the next decade or two, robotics will disrupt working patterns, national economies, and international relations. A growing and more demanding population puts the natural environment under strain; peoples’ actions could trigger dangerous climate change and mass extinctions if ‘tipping points’ are crossed—outcomes that would bequeath a depleted and impoverished world to future generations. But to reduce these risks, we need to enhance our understanding of nature and deploy appropriate technology (zero-carbon energy, for instance) more urgently. Risks and ethical dilemmas can be minimized by a culture of ‘responsible innovation’, especially in fields like biotech, advanced AI and geoengineering; and we’ll need to confront new ethical issues—‘designer babies’, blurring of the line between life and death, and so forth—guided by priorities and values that science itself can’t provide.

Is there a moral imperative as well?

There has plainly been a welcome improvement in most people’s lives and life-chances—in education, health, and lifespan. This is owed to technology. However, it’s surely a depressing indictment of current morality that the gulf between the way the world is and the way it could be is wider than it ever was. The lives of medieval people may have been miserable compared to ours, but there was little that could have been done to improve them. In contrast, the plight of the ‘bottom billion’ in today’s world could be transformed by redistributing the wealth of the thousand richest people on the planet. Failure to respond to this humanitarian imperative, which nations have the power to remedy—surely casts doubt on any claims of institutional moral progress. That’s why I can’t go along with the ‘new optimists’ who promote a rosy view of the future, enthusing about improvements in our moral sensitivities as well as in our material progress. I don’t share their hope in markets and enlightenment.

A benign society should, at the very least, require trust between individuals and their institutions. I worry that we are moving further from this ideal for two reasons: firstly, those we routinely have to deal with are increasingly remote and depersonalised; and secondly, modern life is more vulnerable to disruption—‘hackers’ or dissidents can trigger incidents that cascade globally. Such trends necessitate burgeoning security measures. These are already irritants in our everyday life—security guards, elaborate passwords, airport searches and so forth—but they are likely to become ever more vexatious. Innovations like blockchain could offer protocols that render the entire internet more secure. But their current applications—allowing an economy based on cryptocurrencies to function independently of traditional financial institutions—seem damaging rather than benign. It’s depressing to realize how much of the economy is dedicated to activities that would be superfluous if we felt we could trust each other. (It would be a worthwhile exercise if some economist could quantify this.)

But what about politics? 

In an era where we are all becoming interconnected, where the disadvantaged are aware of their predicament, and where migration is easy, it’s hard to be optimistic about a peaceful world if a chasm persists, as deep as it is today’s geopolitics, between the welfare levels and life-chances in different regions. It’s specially disquieting if advances in genetics and medicine that can enhance human lives are available to a privileged few, and portend more fundamental forms of inequality. Harmonious geopolitics would require a global distribution of wealth that’s perceived as fair—with far less inequality between rich and poor nations. And even without being utopian it’s surely a moral imperative (as well as in the self-interest of fortunate nations) to push towards this goal. Sadly, we downplay what’s happening even now in far-away countries. And we discount too heavily the problems we’ll leave for new generations. Governments need to prioritise projects that are long-term in a political perspectives, even if a mere instant in the history of our planet.

Will super intelligent AI out-think humans?

We are of course already being aided by computational power. In the ‘virtual world’ inside a computer astronomers can mimic galaxy formation; meteorologists can simulate the atmosphere. As computer power grows, these ‘virtual’ experiments become more realistic and useful. And AI will make discoveries that have eluded unaided human brains. For example, there is a continuing quest to find the ‘recipe’ for a superconductor that works at ordinary room temperatures. This quest involves a lot of ‘trial and error’, because nobody fully understands what makes the electrical resistance disappear more readily in some materials than in others. But it’s becoming possible to calculate the properties of materials, so fast that millions of alternatives can be computed, far more quickly than actual experiments could be done. Suppose that a machine came up with a novel and successful recipe. It would have achieved something that would get a scientist a Nobel prize. It would have behaved as though it had insight and imagination within its rather specialized universe—just as Deep Mind’s Alpha Go flummoxed and impressed human champions with some of its moves. Likewise, searches for the optimal chemical composition for new drugs will increasingly be done by computers rather than by real experiments.

Equally important is the capability to ‘crunch’ huge data-sets. As an example from genetics, qualities like intelligence and height are determined by combinations of genes. To identify these combinations would require a machine fast enough to scan huge samples of genomes to identify small correlations. Similar procedures are used by financial traders in seeking out market trends, and responding rapidly to them, so that their investors can top-slice funds from the rest of us.

Should humans spread beyond Earth?

The practical case for sending people into space gets weaker as robots improve. So the only manned ventures (except for those motivated by national prestige) will be high-risk, cut price, and privately sponsored—undertaken by thrill-seekers prepared even to accept one-way tickets. They’re the people who will venture to Mars. But there won’t be mass emigration: Mars is far less comfortable than the South Pole or the ocean bed. It’s a dangerous delusion to think that space offers an escape from Earth’s problems. We’ve got to solve these here. Coping with climate change may seem daunting, but it’s a doddle compared to terraforming Mars. There’s no ‘Planet B’ for ordinary risk-averse people.

But I think (and hope) that there will be bases on Mars by 2100. Moreover we (and our progeny here on Earth) should cheer on the brave adventurers who go there. The space environment is inherently hostile for humans, so, precisely because they will be ill-adapted to their new habitat, the pioneer explorers will have a more compelling incentive than those of us on Earth to redesign themselves. They’ll harness the super-powerful genetic and cyborg technologies that will be developed in coming decades. These techniques will, one hopes, be heavily regulated on Earth; but ‘settlers’ on Mars will be far beyond the clutches of the regulators. This might be the first step towards divergence into a new species. So it’s these spacefaring adventurers, not those of us comfortably adapted to life on Earth, who will spearhead the post-human era. If they become cyborgs, they won’t need an atmosphere, and may prefer zero-g—perhaps even spreading among the stars.

Is there ‘intelligence’ out there already?

Perhaps we’ll one day find evidence of alien intelligence. On the other hand, our Earth may be unique and the searches may fail. This would disappoint the searchers. But it would have an upside for humanity’s long-term resonance. Our solar system is barely middle aged and if humans avoid self-destruction within the next century, the post-human era beckons. Intelligence from Earth could spread through the entire Galaxy, evolving into a teeming complexity far beyond what we can even conceive. If so, our tiny planet—this pale blue dot floating in space—could be the most important place in the entire cosmos.

What about God?

I don’t believe in any religious dogmas, but I share a sense of mystery and wonder with many who do. And I deplore the so called ‘new atheists’—small-time Bertrand Russell’s recycling his arguments—who attack religion. Hard-line atheists must surely be aware of ‘religious’ people who are manifestly neither unintelligent nor naïve, though they make minimal attempts to understand them by attacking mainstream religion, rather than striving for peaceful coexistence with it; they weaken the alliance against fundamentalism and fanaticism. They also weaken science. If a young Muslim or evangelical Christian is told at school that they can’t have their God and accept evolution, they will opt for their God and be lost to science. When so much divides us, and change is disturbingly fast, religion offers bonding within a community. And its heritage, linking its adherents with past generations, should strengthen our motivation not to leave a degraded world for generations yet to come.

Do scientists have special obligations?

It’s a main theme of my book that our entire future depends on making wise choices about how to apply science. These choices shouldn’t be made just by scientists: they matter to us all and should be the outcome of wide public debate. But for that to happen, we all need enough ‘feel’ for the key ideas of science, and enough numeracy to assess hazards, probabilities and risks—so as not to be bamboozled by experts, or credulous of populist sloganising. Moreover, quite apart from their practical use, these ideas should be part of our common culture. More than that, science is the one culture that’s truly global. It should transcend all barriers of nationality. And it should straddle all faiths too.

I think all scientists should divert some of their efforts towards public policy—and engage with government, business, and campaigning bodies. And of course the challenges are global. Coping with potential shortage of resources—and transitioning to low carbon energy—can’t be solved by each nation separately.

The trouble is that even the best politicians focus mainly on the urgent and parochial—and getting reelected. This is an endemic frustration for those who’ve been official scientific advisors in governments. To attract politicians’ attention you must get headlined in the press, and fill their inboxes. So scientists can have more leverage indirectly—by campaigning, so that the public and the media amplify their voice. Rachel Carson and Carl Sagan, for instance, were preeminent exemplars of the concerned scientist—with immense influence through their writings, lectures and campaigns, even before the age of social media and tweets

Science is a universal culture, spanning all nations and faiths. So scientists confront fewer impediments on straddling political divides.

Does being an astronomer influence your attitude toward the future?

Yes, I think it makes me specially mindful of the longterm future. Let me explain this. The stupendous timespans of the evolutionary past are now part of common culture (maybe not in Kentucky, or in parts of the Muslim world). But most people still somehow think we humans are necessarily the culmination of the evolutionary tree. That hardly seems credible to an astronomer—indeed, we could still be nearer the beginning than the end. Our Sun formed 4.5 billion years ago, but it’s got 6 billion more before the fuel runs out. It then flares up, engulfing the inner planets. And the expanding universe will continue—perhaps forever. Any creatures witnessing the Sun’s demise won’t be human—they could be as different from us as we are from slime mold. Posthuman evolution—here on Earth and far beyond—could be as prolonged as the evolution that’s led to us, and even more wonderful. And of course this evolution will be faster than Darwinian: it happens on a technological timescale, driven by advances in genetics and AI.

But (a final thought) even in the context of a timeline that extends billions of years into the future, as well as into the past. this century is special. It’s the first where one species—ours—has our planet’s future in its hands. Our creative intelligence could inaugurate billions of years of posthuman evolution even more marvelous than what’s led to us. On the other hand, humans could trigger bio, cyber, or environmental catastrophes that foreclose all such potentialities. Our Earth, this ‘pale blue dot’ in the cosmos, is a special place. It may be a unique place. And we’re its stewards at a specially crucial era—the anthropocene. That’s a key message for us all, whether or not we’re astronomers, and a motivation for my book.

Martin Rees is Astronomer Royal, and has been Master of Trinity College and Director of the Institute of Astronomy at Cambridge University. As a member of the UK’s House of Lords and former President of the Royal Society, he is much involved in international science and issues of technological risk. His books include Our Cosmic HabitatJust Six Numbers, and Our Final Hour (published in the UK as Our Final Century). He lives in Cambridge, UK.

A Big Deal: Organic Molecules Found on Mars

by David Weintraub

MarsIn 1976, both Viking 1 and Viking 2 touched down on the surface of Mars. Both landed on vast, flat plains, chosen because they were ideal locations for landing safely. Perhaps the most important Viking experiment for assessing whether life could exist on Mars was the gas chromatograph and mass spectrometer (GCMS) instrument, built by a team led by Klaus Biermann of MIT. Ultimately, Biermann and his GCMS team reported a definitive answer: “No organic compounds were found at either of the two landing sites.” None, nada, zilch.

This scientific discovery had enormous importance for our understanding Mars. Summing up what we learned from the Viking missions in 1992, and in particular what we learned from the absence of any organics in the sampled Martian soil, a team of Viking scientists wrote, “The Viking findings established that there is no life at the two landing sites.” Furthermore, because these two sites were thought to be extremely representative of all of Mars, they concluded that this result “virtually guarantees that the Martian surface is lifeless everywhere.” 

If Mars is sterile, then SpaceX and NASA and Blue Origin and Mars One can all move forward with their efforts to land colonists on Mars in the near future. They needn’t wrestle with any ethical issues about contaminating Mars.

Fast forward a generation. In a paper published in Science last week, Jennifer Eigenbrode and her team, working with data collected by the Mars Science Laboratory (i.e., the Curiosity rover), report that they discovered organic molecules in Martian soil. The importance of this discovery for the possible existence of life on Mars is hard to overstate. The discovery of organics on Mars is a BIG deal.

Let’s be careful in discussing organic molecules. An organic molecule must contain at least one carbon atom and that carbon atom must be chemically bonded to a hydrogen atom. All life on Earth is built on a backbone (literally) of organic molecules (DNA). And life on Earth can produce organic molecules (for example, the methane that is produced in the stomachs of cows). But abiological processes can also make organic molecules. In fact, the universe is full of such molecules known as PAHs (polycyclic aromatic hydrocarbons), which are found in interstellar clouds and the atmospheres of red giant stars and which have absolutely nothing to do with life.

Repeat: the presence of organic molecules on Mars does not mean life has been found on Mars. The absence of organic molecules in the Martian soil, as discovered in the Viking experiments, however, almost certainly means “no life here.” 

Were the Viking scientists wrong? Yes, in part. Their conclusion that the plains of Mars are representative of every locale on Mars was an overreach. When assessing whether the environment on Mars might be hospitable to life, local matters. That conclusion shouldn’t surprise anyone. After all, we find significant differences on Earth between the amount and kinds of life in the Mojave Desert and the Amazon River basin. Why? Water.

The vast, flat plains of Mars are free of organics, but they are unlike Gale Crater. Gale Crater was once a lake, full of water and dissolved minerals. We know now that certain locations on Mars that were warm and wet for extended periods of time in the ancient past have preserved a record of the organic molecules that formed in those environments.

Could life have played a role in creating these molecules?  Maybe, but we don’t know, yet. We do know, however, where to keep looking. We do know where to send the next several generations of robots. We do know that we should build robotic explorers that can drill deep into the soil and explore caves in places similar to Gale Crater.

Abigail Allwood, working at NASA’s Jet Propulsion Laboratory, is building a detector called PIXL that will be sent to Mars on a rover mission that is scheduled for launch in 2020. PIXL will be able to make smart decisions, based on the chemistry of a rock, as to whether that rock sample might contain ancient, fossilized microbes. A later mission might retrieve Allwood’s PIXL specimens and bring them back to Earth for more sophisticated laboratory studies. With instruments like PIXL, we have a good chance of definitively answering the question, “Does Mars or did Mars ever have life?”

What does the presence of organic molecules in the Martian regolith mean, as discovered by Curiosity? Those molecules could mean that life is or once was present on Mars. Finding those molecules just raised the stakes in the search for life on Mars. The jury is still out, but the betting odds just changed.

Given all we currently know about Mars, should we be sending astronauts to Mars in the next decade? Do we have the right to contaminate Mars if is already home to native Martian microbes? These are important questions that are more relevant than ever. 

David A. Weintraub is professor of astronomy at Vanderbilt University. He is the author of Life on Mars: What to Know Before We GoReligions and Extraterrestrial Life: How Will We Deal with It?How Old Is the Universe?, and Is Pluto a Planet?: A Historical Journey through the Solar System. He lives in Nashville.

Life on Mars: Imagining Martians

If you had the chance to travel to Mars, would you take it?

Astronomer David A. Weintraub thinks it won’t be long before we are faced with this question not as a hypothetical, but as a real option. Based on the pace of research and the growing private interest in space exploration, humans might be considering trips to Mars before the next century.

In his new book Life on Mars: What to Know Before We Go, Weintraub argues that would-be colonizers of the red planet should first learn whether life already exists on Mars. Just as colonization of various parts of Earth has historically decimated human, animal, and plant populations, so, argues Weintraub, will human colonization of Mars dramatically affect and likely destroy any life that might already exist on Mars. Before we visit, we need to know what – and whom – we might be visiting.

While scientists have yet to determine whether life exists on the red planet, they agree that if Martians do exist, they probably aren’t little green men. So where does our popular idea of Martians come from? Artists and writers have been imagining and depicting Martian life in a variety of ways since long before space travel was a reality. Check out these descriptions of imagined Martian life from over one hundred years ago.

Cover of The Martian, by George du Maurier

In George du Maurier’s 1897 gothic science fiction story The Martian, Martians are described as furry amphibians who are highly skilled in metalworking and sculpting:

“Man in Mars is, it appears, a very different being from what he is here. He is amphibious, and descends from no monkey, but from a small animal that seems to be something between our seal and our sea-lion….

“His five senses are extraordinarily acute, even the sense of touch in his webbed fingers and toes….

“These exemplary Martians wear no clothes but the exquisite fur with which nature has endowed them, and which constitutes a part of their immense beauty….

“They feed exclusively on edible moss and roots and submarine seaweed, which they know how to grow and prepare and preserve. Except for heavy-winged bat-like birds, and big fish, which they have domesticated and use for their own purposes in an incredible manner (incarnating a portion of themselves and their consciousness at will in their bodies), they have cleared Mars of all useless and harmful and mutually destructive forms of animal life. A sorry fauna, the Martian—even at its best—and a flora beneath contempt, compared to ours.”

“How the Earth Men Learned the Martian Language,” from Edison’s Conquest of Mars by Garrett P. Serviss

In Garrett Serviss’s Edison’s Conquest of Mars (1898), on the other hand, Martians are huge creatures, two to three times as tall as a human:

“It is impossible for me to describe the appearance of this creature in terms that would be readily understood. Was he like a man? Yes and no. He possessed many human characteristics, but they were exaggerated and monstrous in scale and in detail. His head was of enormous size, and his huge projecting eyes gleamed with a strange fire of intelligence. His face was like a caricature, but not one to make the beholder laugh. Drawing himself up, he towered to a height of at least fifteen feet.”

Edwin Lester Arnold, in Lieut. Gullivar Jones: His Vacation, published in 1905, describes Martians instead as “graceful and slow,” with an “odor of friendly, slothful happiness about them”:

“They were the prettiest, daintiest folk ever eyes looked upon, well-formed and like to us as could be in the main, but slender and willowy, so dainty and light, both the men and the women, so pretty of cheek and hair, so mild of aspect, I felt, as I strode amongst them, I could have plucked them like flowers and bound them up in bunches with my belt. And yet somehow I liked them from the first minute; such a happy, careless, light-hearted race, again I say, never was seen before.” 

“The old man sat and talked with me for hours,” from A Princess of Mars by Edgar Rice Burroughs

And in Edgar Rice Burroughs’ A Princess of Mars, published in 1917, Martians are finally depicted as the little green men of the popular imagination:

“Five or six had already hatched and the grotesque caricatures which sat blinking in the sunlight were enough to cause me to doubt my sanity. They seemed mostly head, with little scrawny bodies, long necks and six legs, or, as I afterward learned, two legs and two arms, with an intermediary pair of limbs which could be used at will either as arms or legs. Their eyes were set at the extreme sides of their heads a trifle above the center and protruded in such a manner that they could be directed either forward or back and also independently of each other, thus permitting this queer animal to look in any direction, or in two directions at once, without the necessity of turning the head.

“The ears, which were slightly above the eyes and closer together, were small, cup-shaped antennae, protruding not more than an inch on these young specimens. Their noses were but longitudinal slits in the center of their faces, midway between their mouths and ears.

“There was no hair on their bodies, which were of a very light yellowish-green color. In the adults, as I was to learn quite soon, this color deepens to an olive green and is darker in the male than in the female. Further, the heads of the adults are not so out of proportion to their bodies as in the case of the young.”

To learn more about Martians in popular culture, the history of planetary astronomy, and the scientific search for life on Mars, read David Weintraub’s Life on Mars!

David Weintraub on Life on Mars: What to Know Before We Go

WeintraubDoes life exist on Mars? The question has captivated humans for centuries, but today it has taken on new urgency. NASA plans to send astronauts to Mars orbit by the 2030s. SpaceX wants to go by 2024, while Mars One wants to land a permanent settlement there in 2032. As we gear up for missions like these, we have a responsibility to think deeply about what kinds of life may already inhabit the plane—and whether we have the right to invite ourselves in. This book tells the complete story of the quest to answer one of the most tantalizing questions in astronomy. But it is more than a history. Life on Mars explains what we need to know before we go.

Why does Mars matter?

Are we alone in the universe? Earth might be an oasis of life, the only place in the universe where living beings of any kind exist. On the other hand, life might be as common across the universe as the hundreds of billions of stars and planets that populate it. Mars is the closest habitable world in the universe where we can begin to learn about extraterrestrial life. If life is common, if the genesis of life is possible given the right environment and the necessary elemental materials, some form of life might exist right next door, on Mars, and if life were discovered on Mars that is of an independent origin than life on Earth, we could safely predict that life is common throughout the universe. Such a discovery would be extraordinary. Mars Matters.

Haven’t we already discovered life on Mars?

Maybe. Maybe not. Some astronomers believe that evidence from NASA’s Viking Lander biology experiments strongly suggest the presence of past or present life on Mars. Other astronomers believe that evidence found in a meteorite from Mars is evidence of ancient life on Mars. Still others believe that methane gas discovered in the atmosphere of Mars is evidence for life on Mars today. However, no consensus exists. None of the data is definitive that would prove or disprove the hypothesis that Mars once harbored or still nurtures life. The jury is still out.

Could life on Mars and life on Earth be related?

Could be. In order for a meteorite to get knocked off Mars and arrive on Earth, several things must happen. First, an asteroid of significant size must hit the surface of Mars and some of the debris from that impact must be lofted off the surface intact and at high speed. The impact debris kicked off the surface then must drill a hole through the Martian atmosphere and emerge above the atmosphere with a high enough velocity (known as “escape velocity”) to escape the gravitational clutches of Mars. Then that object has to end up on an orbit that intersects with that of Earth. All of these things are improbable but possible. Have they actually happened?

A meteoritic breakthrough occurred in 1982, when the leader of the 1981–1982 U.S. search party looking for meteorites in Antarctica found a tiny, unusual-looking rock now known as ALH 81005, which showed mineralogical similarities to lunar rocks. By 1983, several teams of meteoriticists, working independently, had confirmed that this specimen was, without any doubt, a lunar meteorite. For the first time, we had evidence that meteorites can come from objects as large as our Moon.

Then, in 1985, a geochemist proved that the gases trapped inside air bubbles inside EETA 79001, another Antarctic meteorite, this one collected in 1979 in the Elephant Moraine region, were a perfect match to the gases found by NASA’s Viking lander in the atmosphere of Mars. Therefore, without any doubt, EETA 79001 itself was a piece of Mars. We now know of several dozen meteorites that are, without question, of Martian origin.

If a meteorite can travel from Mars to Earth (or vica versa), then life could be transported by this vehicle from one planet to the other.

Why should you care about microscopic Martians?

Do microscopic Martians matter? Yes. Microscopic Martians, if they exist, would be astoundingly important to our understanding of life in the universe. A second genesis, life that began completely independently of terrestrial origins, might have occurred on Mars. Even if life on Mars is limited to bacterial-sized beings, buried underground or hiding deep in a crevice where they are protected from dangerous ultraviolet radiation and cosmic rays and where they can find water, those beings would teach us something of enormous importance about the existence of life beyond Earth. Life on Mars that is independent of life on Earth would send us a clear message about exobiology: life could happen anywhere and everywhere that conditions allow. Alternatively, if we find microscopic life that is DNA-based, we also receive an enormously important message about exobiology and clues about our distant, evolutionary past: such a discovery would tell us that life is easily transported across interplanetary space. Once life gets started, it can spread, and thus, whether we are Martians or the Martians are us, we’re all related. Finally, if we discover that Mars is barren and sterile, without even microscopic Martians, we will know that we are more alone in the solar system and perhaps in the galaxy and universe than many of us currently think.

How Earth-like is Mars? And does that matter?

Mars is very nearly a twin of Earth. Like Earth, Mars is a small rocky planet with a solid surface and an atmosphere.  Mars orbits the Sun at a similar distance as Earth, where the amount of solar heating is sufficient, for at least part of every year, to allow the possibility of the existence of liquid water on at least parts of the surfaces of both planets. The length of the day and night of Mars — 24 hours, 39 minutes — is extremely similar to the day/night spin (24 hours) of Earth. The obliquity of Mars (the 25 degree tilt of Mars’ rotation axis with respect to the plane of its orbit around the Sun) is almost the same as the tilt of Earth (23.5 degrees). These tilts generate seasonal changes, and the seasonal changes of Mars are very similar to the seasons we find here on Earth. The polar caps on Mars, which are mostly water ice, closely resemble the ice caps on Earth. The thin Martian atmosphere behaves like the thicker atmosphere of Earth, with clouds, frost that condenses on the surface, and winds that blow across the surface of the planet. And Mars has large reservoirs of water, just like Earth.  Yes, differences exist. The mass of Mars is smaller than the mass of Earth; the density and composition of the Martian atmosphere are different from those of Earth; Earth has a strong magnetic field while Mars does not; Mars’ water is either frozen or buried deep beneath the surface, while most of Earth’s water is either frozen or liquid and is at or near the surface.  But if you’re looking for an Earth-like planet where Earth-like forms of life could thrive, Mars is a great place to look.

Why did you decide to write this book?  Why should someone read your book?

I think, without any doubt, that humanity will colonize Mars in the near future, perhaps within a decade, and most certainly by the end of the twenty first century. When we settle on Mars, we will contaminate Mars. If any life exists there today, we almost certainly will alter or destroy it in the same way that human and animal diseases have devastated the native species on every continent and island on Earth to which human explorers have extended their reach, putting life forms that have been isolated and protected from other life forms in harm’s way. After we place human colonies on Mars, we will lose the opportunity to discover, with certainty, whether Mars ever was or still is inhabited.

We have one chance to make these discoveries, and that is the present time before we colonize Mars. I think the knowledge we might gain about Mars and Martian life before we send colonists to the red planet is so unique and valuable that we humans should, collectively, debate whether the 2020s and 2030s are the right time to send the first wave of settlers to Mars. Perhaps we should wait just a bit longer, and let robotic exploration continue until the debate about life on Mars is settled. With this book, I hope to help trigger that public debate before it is too late.

David A. Weintraub is professor of astronomy at Vanderbilt University. He is the author of How Old Is the Universe? and Is Pluto a Planet?: A Historical Journey through the Solar System. He lives in Nashville.

Martin Rees: Stephen Hawking — An Appreciation

Soon after I enrolled as a graduate student at Cambridge University in 1964, I encountered a fellow student, two years ahead of me in his studies; he was unsteady on his feet and spoke with great difficulty. This was Stephen Hawking. He had recently been diagnosed with a degenerative disease, and it was thought that he might not survive long enough even to finish his PhD. But, amazingly, he lived on to the age of 76. Even mere survival would have been a medical marvel, but of course he didn’t just survive. He become one of the most famous scientists  in the world—acclaimed  as a world-leading researcher in mathematical physics, for his best-selling books about space, time, and the cosmos, and for his astonishing triumph over adversity.

Astronomers are used to large numbers. But few numbers could be as large as the odds I’d have given, back in 1964 when Stephen received his ‘death sentence,’ against witnessing this uniquely inspiring crescendo of achievement sustained for more than 50 years. Few, if any, of Einstein’s successors have done more to deepen our insights into gravity, space, and time.

Stephen went to school in St Albans, near London, and then to Oxford University. He was, by all accounts, a ‘laid back’ undergraduate, but his brilliance nonetheless earned him a first class degree in physics, and an ‘entry ticket’ to a research career in Cambridge. Within a few years of the onset of his disease he was wheelchair-bound, and his speech was an indistinct croak that could only be interpreted by those who knew him. But in other respects fortune had favored him. He married a family friend, Jane Wilde, who provided a supportive home life for him and their three children, Robert, Lucy, and Tim.

The 1960s were an exciting period in astronomy and cosmology: this was the decade when evidence began to emerge for black holes and the big bang. In Cambridge, Stephen  joined a lively research group. It was headed by Dennis Sciama, an enthusiastic and effective mentor who urged him to focus on the new mathematical concepts being developed by Roger Penrose, then at London University, which were initiating a renaissance in the study of Einstein’s theory of general relativity. Stephen mastered Penrose’s techniques and quickly came up with a succession of insights into the nature of black holes (then a very new idea),   along with new arguments that our universe had expanded from a ‘big bang.’ The latter work was done jointly with George Ellis, another of Sciama’s students, with whom Stephen wrote a monograph entitled The Large-Scale Structure of Space-Time. Especially important was the realization that the area of a black hole’s horizon (the ‘one-way membranes’ that shroud the interior of black holes, and from within which nothing can escape) could never decrease. The analogy with entropy (a measure of disorder, that likewise can never decrease) was developed further by the late Israeli theorist Jacob Bekenstein. In the subsequent decades, the observational support for these ideas  has strengthened—most spectacularly with the 2016 announcement of the detection of gravitational waves from colliding black holes.

Stephen was elected to the Royal Society, Britain’s main scientific academy, at the exceptionally early age of 32. He was by then so frail that most of us suspected that he could scale no further heights. But, for Stephen, this was still just the beginning. He worked in the same building as I did. I would often push his wheelchair into his office, and he would ask me to open an abstruse book on quantum theory—the science of atoms, not a subject that had hitherto much interested him. He would sit hunched motionless for hours—he couldn’t even to turn the pages without help. I wondered what was going through his mind, and if his powers were failing. But within a year he came up with his best-ever idea—encapsulated in an equation that he said he wanted on his memorial stone.

The great advances in science generally involve  discovering a link between phenomena that seemed hitherto conceptually unconnected: for instance, Isaac Newton famously realized that the force making an apple fall was the same as the force that held the moon and planets in their orbits. Stephen’s ‘eureka moment’ revealed a profound and unexpected  link between gravity and quantum theory: he predicted that black holes would not be completely black, but would radiate in a characteristic way. Bekenstein’s concept that black holes had ‘entropy’ was more than just an analogy. This radiation is only significant for black holes much less massive than stars—and none of these have been found. However, ‘Hawking radiation’ had very deep implications for mathematical physics—indeed one of the main achievements of string theory has been to corroborate his idea. It is still the focus of theoretical interest—a topic of debate and controversy more than 40 years after his discovery. Indeed the Harvard theorist, Andrew Strominger (with whom Stephen recently collaborated) said that this paper had caused ‘more sleepless nights among theoretical physicists than any paper in history.’ The key issue is whether information that is seemingly lost when objects fall into a black hole is in principle recoverable from the radiation when it evaporates. If it is not, this violates a deeply believed general physical principle. In 2013 he was one of the early winners of the Breakthrough Prize, worth 3 million dollars, which was intended to recognize theoretical work.

Cambridge was Stephen’s base throughout his career, and he became a familiar figure navigating his wheelchair around the city’s streets. By the end of the 1970s, he had advanced to one of the most distinguished posts in the University—the Lucasian Professorship of Mathematics, once held by Newton himself. He held this chair with distinction for 30 years; but reached the retiring age in 2009 and thereafter held a special research professorship. He travelled widely: he was an especially frequent visitor at Caltech, in Pasadena, California; and at Texas A&M University. He continued to seek new links between the very large (the cosmos) and the very small (atoms and quantum theory) and to gain deeper insights into the very beginning of our universe—addressing questions like ‘was our big bang the only one?’ He had a remarkable ability to figure things out in his head. But latterly he worked with students and colleagues who would write a formula on a blackboard; he would stare at it, and say whether he agreed with it, and perhaps what should come next.

In 1987, Stephen contracted pneumonia. He had to undergo a tracheotomy, which removed even the limited powers of speech he then possessed. It had been more than 10 years since he could write, or even  use a keyboard. Without speech, the only way he could communicate was by directing his eye towards  one of the letters of the alphabet on a big board in front of him.

But he was saved by technology. He still had the use of one hand; and a computer, controlled by a single lever, allowed him to spell out sentences. These were then declaimed by a speech synthesizer, with the androidal American accent that has since become his trademark. His lectures were, of course, pre-prepared, but conversation remained a struggle. Each word involved several presses of the lever, so even a sentence took several minutes. He learnt to economize with words. His comments were aphoristic or oracular, but often infused with wit. In his later years, he became too weak to control this machine effectively, even via facial muscles or eye movements, and his communication—to his immense frustration—became even slower.

At the time of his tracheotomy operation, he had a rough draft of a book, which he’d hoped would describe his ideas to a wide readership and earn something for his two eldest children, who were then of college age. On his recovery from pneumonia, he resumed work with the help of an editor. When the US edition of   A Brief History of Time appeared, the printers made some errors (a picture was upside down), and the publishers tried to recall the stock. To their amazement, all copies had already been sold. This was the first inkling that the book was destined for runaway success—four years on bestseller lists around the world.

The feature film The Theory of Everything (where he was superbly impersonated by Eddie Redmayne, in an Oscar-winning performance) portrayed  the human story behind his struggle. It surpassed most biopics in  representing the main characters so well that they themselves were happy with the portrayal (even though it understandably omitted and conflated key episodes in his scientific life). Even before this film, his life and work had featured in movies. In  an excellent TV docudrama made in 2004, he was played by Benedict Cumberbatch (In 2012 Cumberbatch spoke his words in a 4-part documentary The Grand Design made for the Discovery TV  Channel).

Why did he become such a ‘cult figure?’ The concept of an imprisoned mind roaming the cosmos plainly grabbed people’s imagination. If he had achieved equal distinction in (say) genetics rather than cosmology, his triumph of intellect against adversity probably wouldn’t have achieved the same resonance with a worldwide public.

The Theory of Everything conveyed with sensitivity how the need for support (first from a succession of students, but later requiring a team of nurses) strained his marriage to breaking point, especially when augmented by the pressure of his growing celebrity. Jane’s book, on which the film is based chronicles the 25 years during which, with amazing dedication, she underpinned his family life and his career.

This is where the film ends. But it left us only half way through Stephen’s adult life. After the split with Jane, Stephen married, in 1995, Elaine Mason, who had been one of his nurses, and whose former husband had designed Stephen’s speech synthesizer. But this partnership broke up within a decade. He was sustained, then and thereafter, by a team of helpers and personal assistants, as well as his family. His daughter Lucy has written books for children with her father as coauthor. His later theories were described, and beautifully illustrated, in other books such as Our Universe in a Nutshell and The Grand Design. These weren’t  bought by quite as many people as his first book—but probably more readers got to the end of them.

The success of A Brief History of Time catapulted Stephen to international stardom. He  featured in numerous TV programs; his lectures filled the Albert Hall, and similar venues in the US and Japan. He  featured in Star Trek and The Simpsons, and in numerous TV documentaries, as well as advertisements. He lectured at Clinton’s White House; he was back there more recently when President Obama presented him with the US Medal of Freedom, a very rare honor for any foreigner—and of course just one of the many awards he accumulated over his career (including Companion of Honor from the UK). In the summer of 2012, he reached perhaps his largest-ever audience when he had a star role at the opening ceremony of the London Paralympics.

His 60th birthday celebrations, in January 2002 , were a memorable occasion for all of us. Hundreds of leading scientists came from all over the world to honor and celebrate Stephen’s discoveries, and to spend a week discussing the latest theories on space, time, and the cosmos. But the celebrations weren’t just scientific—that wouldn’t have been Stephen’s style. Stephen was surrounded by his children and grandchildren; there was music and singing; there were ‘celebrities’ in attendance. And when the week’s events were all over, he celebrated with a trip in a hot air balloon.

It was amazing enough that Stephen reached the age of 60; few of us then thought that he would survive 16 more years. His 70th birthday was again marked by an international gathering of scientists in Cambridge, and also with some razzmatazz. So was his 75th birthday, though now shared by several million people via a livestream on the internet. He was in these last years plainly weakening. But he was still able to ‘deliver’ entertaining (and sometimes rather moving) lectures via his speech synthesizer and with the aid of skillfully prepared visuals.

Stephen continued, right until his last decade, to coauthor technical papers, and speak at premier international conferences—doubly remarkable in a subject where even healthy researchers tend to peak at an early age. Specially influential were his contributions to ‘cosmic inflation’—a theory that many believe describes the ultra-early phases of our expanding universe. A key issue is to understand the primordial seeds which eventually develop into galaxies. He proposed (as, independently, did the Russian theorist Viatcheslav Mukhanov) that these were quantum fluctuations—somewhat analogous to those involved in ‘Hawking radiation’ from black holes. He hosted an important meeting in 1982 where such ideas were thoroughly discussed. Subsequently, particularly with James Hartle and Thomas Hertog, he made further steps towards linking the two great theories of 20th century physics: the quantum theory of the microworld and Einstein’s theory of gravity and space-time.

He continued  to be an inveterate traveller—despite attempts to curb this as his respiration weakened. This wasn’t just to lecture. For instance, on a visit to Canada he was undeterred by having to go two miles down a mine-shaft to visit an underground laboratory where famous and delicate experiments had been done. And on a later trip, only a last-minute health setback prevented him from going to the Galapagos. All these travels—and indeed his everyday working life—involved an entourage of assistants and nurses. His fame, and the allure of his public appearances, gave him the resources for  nursing care, and protected him against the ‘does he take sugar?’ type of indignity that the disabled often suffer.

Stephen was far from being the archetype unworldly or nerdish scientist—his personality remained amazingly unwarped by his frustrations and handicaps. As well as his extensive travels, he enjoyed  trips to theatre or opera. He had robust common sense, and was ready to express forceful political opinions. However, a downside of his iconic status was that that his comments attracted exaggerated attention even on topics where he had  no special expertise—for instance philosophy, or the dangers from aliens or from intelligent machines. And he was sometimes involved in media events where his ‘script’ was written by the promoters of causes about which he may have been ambivalent.

But there was absolutely no gainsaying his lifelong commitment to campaigns for the disabled, and (just in the last few months) in support of the NHS—to which he acknowledged he owed so much. He was always, at the personal level, sensitive to the misfortunes of others. He recorded  that, when in hospital soon after his illness was first diagnosed, his depression was lifted when he compared his lot with a boy in the next bed who was dying of leukemia. And he was firmly aligned with other political campaigns and causes. When he visited Israel, he insisted on going also to the West Bank. Newspapers in 2006 showed remarkable pictures of him, in his wheelchair, surrounded  by fascinated and curious crowds in Ramallah.

Even more astonishing are the pictures of him ‘floating’ in the NASA aircraft  (the ‘vomit comet’) that allows passengers to experience weightlessness—he was manifestly overjoyed at escaping, albeit briefly, the clutches of the gravitational force he’d studied for decades and which had so cruelly imprisoned his body.

Tragedy struck Stephen Hawking when he was only 22. He was diagnosed with a deadly disease, and his  expectations dropped to zero. He himself said that everything that happened since then was a bonus. And what a triumph his life has been. His name will live in the annals of science; millions have had their cosmic horizons widened by his best-selling books; and even more, around the world, have been inspired by a unique example of achievement against all the odds—a manifestation of amazing will-power and determination.

Martin Rees is Astronomer Royal of Great Britain, a Fellow of Trinity College, Cambridge, a former director of the Cambridge Institute of Astronomy and author, most recently, of the bestselling Just Six Numbers: The Deep Forces That Shape the Universe. His forthcoming book, On the Future, will be available in October 2018.

Celebrate Pi Day with Books about Einstein

Pi Day is coming up! Mathematicians around the world celebrate on March 14th because the date represents the first three digits of π: 3.14.

In Princeton, Pi Day is a huge event even for the non-mathematicians among us, given that March 14 is also Albert Einstein’s birthday. Einstein was born on March 14, 1879, in Ulm, in the German Empire. He turns 139 this year! If you’re in the Princeton area and want to celebrate, check out some of the festivities happening around town:

Saturday, 3/10/18

  • Apple Pie Eating Contest, 9:00 a.m., McCaffrey’s (301 North Harrison Street). Arrive by 8:45 a.m. to participate.
  • Einstein in Princeton Guided Walking Tour, 10:00 a.m. Call Princeton Tour Company at (855) 743-1415 for details.
  • Einstein Look-A-Like Contest, 12:00 p.m., Nassau Inn. Arrive early to get a spot to watch this standing-room-only event!
  • Pi Recitation Contest, 1:30 p.m., Prince William Ballroom, Nassau Inn. Children ages 12 and younger may compete. Register by 1:15 p.m.
  • Pie Throwing Event, 3:14 p.m., Palmer Square. Proceeds to benefit the Princeton Educational Fund Teacher Mini-Grant Program.
  • Cupcake Decorating Competition, 4:00 p.m., House of Cupcakes (34 Witherspoon Street). The winner receives one free cupcake each month for the rest of the year.

Wednesday, 3/14/18

  • Princeton School Gardens Cooperative Fundraiser, 12:00 p.m. to 6:00 p.m., The Bent Spoon (35 Palmer Square West) and Lillipies (301 North Harrison Street). All proceeds from your afternoon treat will be donated to the Princeton School Gardens Cooperative.
  • Pi Day Pop Up Wedding/Vow Renewal Ceremonies, 3:14 p.m. to 6:00 p.m., Princeton Pi (84 Nassau Street). You must pre-register by contacting the Princeton Tour Company.

Not into crowds, or pie? You can also celebrate this multifaceted holiday by picking up one of PUP’s many books about Albert Einstein! In 1922, Princeton University Press published Einstein’s The Meaning of Relativity, his first book produced by an American publisher. Since then, we’ve published numerous works by and about Einstein.

The books and collections highlighted here celebrate not only his scientific accomplishments but also his personal reflections and his impact on present-day scholarship and technology. Check them out and learn about Einstein’s interpersonal relationships, his musings on travel, his theories of time, and his legacy for the 21st century.

Volume 15 of the Collected Papers of Albert Einstein, forthcoming in April 2018, covers one of the most thrilling two-year periods in twentieth-century physics, as matrix mechanics—developed chiefly by W. Heisenberg, M. Born, and P. Jordan—and wave mechanics—developed by E. Schrödinger—supplanted the earlier quantum theory. The almost one hundred writings by Einstein, of which a third have never been published, and the more than thirteen hundred letters show Einstein’s immense productivity and hectic pace of life.

Einstein quickly grasps the conceptual peculiarities involved in the new quantum mechanics, such as the difference between Schrödinger’s wave function and a field defined in spacetime, or the emerging statistical interpretation of both matrix and wave mechanics. Inspired by correspondence with G. Y. Rainich, he investigates with Jakob Grommer the problem of motion in general relativity, hoping for a hint at a new avenue to unified field theory.

Readers can access Volumes 1-14 of the Collected Papers of Albert Einstein online at The Digital Einstein Papers, an exciting new free, open-access website that brings the writings of the twentieth century’s most influential scientist to a wider audience than ever before. This unique, authoritative resource provides full public access to the complete transcribed, annotated, and translated contents of each print volume of the Collected Papers. The volumes are published by Princeton University Press, sponsored by the Hebrew University of Jerusalem, and supported by the California Institute of Technology. Volumes 1-14 of The Collected Papers cover the first forty-six years of Einstein’s life, up to and including the years immediately before the final formulation of new quantum mechanics. The contents of each new volume will be added to the website approximately eighteen months after print publication. Eventually, the website will provide access to all of Einstein’s writings and correspondence accompanied by scholarly annotation and apparatus, which are expected to fill thirty volumes.

The Travel Diaries of Albert Einstein is the first publication of Albert Einstein’s 1922 travel diary to the Far East and Middle East, regions that the renowned physicist had never visited before. Einstein’s lengthy itinerary consisted of stops in Hong Kong and Singapore, two brief stays in China, a six-week whirlwind lecture tour of Japan, a twelve-day tour of Palestine, and a three-week visit to Spain. This handsome edition makes available, for the first time, the complete journal that Einstein kept on this momentous journey.

The telegraphic-style diary entries—quirky, succinct, and at times irreverent—record Einstein’s musings on science, philosophy, art, and politics, as well as his immediate impressions and broader thoughts on such events as his inaugural lecture at the future site of the Hebrew University in Jerusalem, a garden party hosted by the Japanese Empress, an audience with the King of Spain, and meetings with other prominent colleagues and statesmen. Entries also contain passages that reveal Einstein’s stereotyping of members of various nations and raise questions about his attitudes on race. This beautiful edition features stunning facsimiles of the diary’s pages, accompanied by an English translation, an extensive historical introduction, numerous illustrations, and annotations. Supplementary materials include letters, postcards, speeches, and articles, a map of the voyage, a chronology, a bibliography, and an index.

Einstein would go on to keep a journal for all succeeding trips abroad, and this first volume of his travel diaries offers an initial, intimate glimpse into a brilliant mind encountering the great, wide world. 

More than fifty years after his death, Albert Einstein’s vital engagement with the world continues to inspire others, spurring conversations, projects, and research, in the sciences as well as the humanities. Einstein for the 21st Century shows us why he remains a figure of fascination.

In this wide-ranging collection, eminent artists, historians, scientists, and social scientists describe Einstein’s influence on their work, and consider his relevance for the future. Scientists discuss how Einstein’s vision continues to motivate them, whether in their quest for a fundamental description of nature or in their investigations in chaos theory; art scholars and artists explore his ties to modern aesthetics; a music historian probes Einstein’s musical tastes and relates them to his outlook in science; historians explore the interconnections between Einstein’s politics, physics, and philosophy; and other contributors examine his impact on the innovations of our time. Uniquely cross-disciplinary, Einstein for the 21st Century serves as a testament to his legacy and speaks to everyone with an interest in his work. 

The contributors are Leon Botstein, Lorraine Daston, E. L. Doctorow, Yehuda Elkana, Yaron Ezrahi, Michael L. Friedman, Jürg Fröhlich, Peter L. Galison, David Gross, Hanoch Gutfreund, Linda D. Henderson, Dudley Herschbach, Gerald Holton, Caroline Jones, Susan Neiman, Lisa Randall, Jürgen Renn, Matthew Ritchie, Silvan S. Schweber, and A. Douglas Stone.

On April 6, 1922, in Paris, Albert Einstein and Henri Bergson publicly debated the nature of time. Einstein considered Bergson’s theory of time to be a soft, psychological notion, irreconcilable with the quantitative realities of physics. Bergson, who gained fame as a philosopher by arguing that time should not be understood exclusively through the lens of science, criticized Einstein’s theory of time for being a metaphysics grafted on to science, one that ignored the intuitive aspects of time. Jimena Canales tells the remarkable story of how this explosive debate transformed our understanding of time and drove a rift between science and the humanities that persists today.

The Physicist and the Philosopher is a magisterial and revealing account that shows how scientific truth was placed on trial in a divided century marked by a new sense of time.

 

After completing the final version of his general theory of relativity in November 1915, Albert Einstein wrote a book about relativity for a popular audience. His intention was “to give an exact insight into the theory of relativity to those readers who, from a general scientific and philosophical point of view, are interested in the theory, but who are not conversant with the mathematical apparatus of theoretical physics.” The book remains one of the most lucid explanations of the special and general theories ever written.

This new edition features an authoritative English translation of the text along with an introduction and a reading companion by Hanoch Gutfreund and Jürgen Renn that examines the evolution of Einstein’s thinking and casts his ideas in a broader present-day context.

Published on the hundredth anniversary of general relativity, this handsome edition of Einstein’s famous book places the work in historical and intellectual context while providing invaluable insight into one of the greatest scientific minds of all time.

 

Browse Our 2018 Physics & Astrophysics Catalog

Our new Physics & Astrophysics catalog includes two new graduate-level textbooks from Kip S. Thorne, Co-Winner of the 2017 Noble Prize in Physics, as well as a look into the physics behind black holes.

If you plan on attending AAS 2018 in National Harbor, MD this weekend, please stop by Booth 1003 to see our full range of Physics and Astrophysics titles and more.

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 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.

Modern Classical Physics is a long-awaited, 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 Thorne and Roger 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.

First published in 1973, Gravitation is a landmark graduate-level textbook that presents Einstein’s general theory of relativity and offers a rigorous, full-year course on the physics of gravitation. Upon publication, Science called it “a pedagogic masterpiece,” and it has since become a classic, considered essential reading for every serious student and researcher in the field of relativity. This authoritative text has shaped the research of generations of physicists and astronomers, and the book continues to influence the way experts think about the subject.

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.