In 1981, many of the world’s leading cosmologists gathered at the Pontifical Academy of Sciences, a vestige of the coupled lineages of science and theology located in an elegant villa in the gardens of the Vatican. Stephen Hawking chose the august setting to present what he would later regard as his most important idea: a proposal about how the universe could have arisen from nothing.
Before Hawking’s talk, all cosmological origin stories, scientific or theological, had invited the rejoinder, “What happened before that?” The Big Bang theory, for instance — pioneered 50 years before Hawking’s lecture by the Belgian physicist and Catholic priest Georges Lemaître, who later served as president of the Vatican’s academy of sciences — rewinds the expansion of the universe back to a hot, dense bundle of energy. But where did the initial energy come from?
The Big Bang theory had other problems. Physicists understood that an expanding bundle of energy would grow into a crumpled mess rather than the huge, smooth cosmos that modern astronomers observe. In 1980, the year before Hawking’s talk, the cosmologist Alan Guth realized that the Big Bang’s problems could be fixed with an add-on: an initial, exponential growth spurt known as cosmic inflation, which would have rendered the universe huge, smooth and flat before gravity had a chance to wreck it. Inflation quickly became the leading theory of our cosmic origins. Yet the issue of initial conditions remained: What was the source of the minuscule patch that allegedly ballooned into our cosmos, and of the potential energy that inflated it?
Hawking, in his brilliance, saw a way to end the interminable groping backward in time: He proposed that there’s no end, or beginning, at all. According to the record of the Vatican conference, the Cambridge physicist, then 39 and still able to speak with his own voice, told the crowd, “There ought to be something very special about the boundary conditions of the universe, and what can be more special than the condition that there is no boundary?”
The “no-boundary proposal,” which Hawking and his frequent collaborator, James Hartle, fully formulated in a 1983 paper, envisions the cosmos having the shape of a shuttlecock. Just as a shuttlecock has a diameter of zero at its bottommost point and gradually widens on the way up, the universe, according to the no-boundary proposal, smoothly expanded from a point of zero size. Hartle and Hawking derived a formula describing the whole shuttlecock — the so-called “wave function of the universe” that encompasses the entire past, present and future at once — making moot all contemplation of seeds of creation, a creator, or any transition from a time before.
“Asking what came before the Big Bang is meaningless, according to the no-boundary proposal, because there is no notion of time available to refer to,” Hawking said in another lecture at the Pontifical Academy in 2016, a year and a half before his death. “It would be like asking what lies south of the South Pole.” [Continue reading…]
Physicists debate Stephen Hawking’s idea that the universe had no beginning
A bizarre form of water may exist all over the universe
Recently at the Laboratory for Laser Energetics in Brighton, New York, one of the world’s most powerful lasers blasted a droplet of water, creating a shock wave that raised the water’s pressure to millions of atmospheres and its temperature to thousands of degrees. X-rays that beamed through the droplet in the same fraction of a second offered humanity’s first glimpse of water under those extreme conditions.
The X-rays revealed that the water inside the shock wave didn’t become a superheated liquid or gas. Paradoxically — but just as physicists squinting at screens in an adjacent room had expected — the atoms froze solid, forming crystalline ice.
“You hear the shot,” said Marius Millot of Lawrence Livermore National Laboratory in California, and “right away you see that something interesting was happening.” Millot co-led the experiment with Federica Coppari, also of Lawrence Livermore.
The findings, published today in Nature, confirm the existence of “superionic ice,” a new phase of water with bizarre properties. Unlike the familiar ice found in your freezer or at the north pole, superionic ice is black and hot. A cube of it would weigh four times as much as a normal one. It was first theoretically predicted more than 30 years ago, and although it has never been seen until now, scientists think it might be among the most abundant forms of water in the universe. [Continue reading…]
Mystery of the universe’s expansion rate widens with new Hubble data
Astronomers using NASA’s Hubble Space Telescope say they have crossed an important threshold in revealing a discrepancy between the two key techniques for measuring the universe’s expansion rate. The recent study strengthens the case that new theories may be needed to explain the forces that have shaped the cosmos.
A brief recap: The universe is getting bigger every second. The space between galaxies is stretching, like dough rising in the oven. But how fast is the universe expanding? As Hubble and other telescopes seek to answer this question, they have run into an intriguing difference between what scientists predict and what they observe.
Hubble measurements suggest a faster expansion rate in the modern universe than expected, based on how the universe appeared more than 13 billion years ago. These measurements of the early universe come from the European Space Agency’s Planck satellite. This discrepancy has been identified in scientific papers over the last several years, but it has been unclear whether differences in measurement techniques are to blame, or whether the difference could result from unlucky measurements.
The latest Hubble data lower the possibility that the discrepancy is only a fluke to 1 in 100,000. This is a significant gain from an earlier estimate, less than a year ago, of a chance of 1 in 3,000.
These most precise Hubble measurements to date bolster the idea that new physics may be needed to explain the mismatch. [Continue reading…]
Experiments that make quantum mechanics directly visible to the human eye
I spent a lot of time in the dark in graduate school. Not just because I was learning the field of quantum optics – where we usually deal with one particle of light or photon at a time – but because my research used my own eyes as a measurement tool. I was studying how humans perceive the smallest amounts of light, and I was the first test subject every time.
I conducted these experiments in a closet-sized room on the eighth floor of the psychology department at the University of Illinois, working alongside my graduate advisor, Paul Kwiat, and psychologist Ranxiao Frances Wang. The space was equipped with special blackout curtains and a sealed door to achieve total darkness. For six years, I spent countless hours in that room, sitting in an uncomfortable chair with my head supported in a chin rest, focusing on dim, red crosshairs, and waiting for tiny flashes delivered by the most precise light source ever built for human vision research. My goal was to quantify how I (and other volunteer observers) perceived flashes of light from a few hundred photons down to just one photon.
As individual particles of light, photons belong to the world of quantum mechanics – a place that can seem totally unlike the Universe we know. Physics professors tell students with a straight face that an electron can be in two places at once (quantum superposition), or that a measurement on one photon can instantly affect another, far-away photon with no physical connection (quantum entanglement). Maybe we accept these incredible ideas so casually because we usually don’t have to integrate them into our daily existence. An electron can be in two places at once; a soccer ball cannot.
But photons are quantum particles that human beings can, in fact, directly perceive. Experiments with single photons could force the quantum world to become visible, and we don’t have to wait around – several tests are possible with today’s technology. The eye is a unique biological measurement device, and deploying it opens up exciting areas of research where we truly don’t know what we might find. Studying what we see when photons are in a superposition state could contribute to our understanding of the boundary between the quantum and classical worlds, while a human observer might even participate in a test of the strangest consequences of quantum entanglement. [Continue reading…]
The interplay that brings together order and disorder
Planets, stars, life, even the direction of time all depend on disorder. And we human beings as well. Especially if, along with disorder, we group together such concepts as randomness, novelty, spontaneity, free will and unpredictability. We might put all of these ideas in the same psychic basket. Within the oppositional category of order, we can gather together notions such as systems, law, reason, rationality, pattern, predictability. While the different clusters of concepts are not mirror images of one another, like twilight and dawn, they have much in common.
Our primeval attraction to both order and disorder shows up in modern aesthetics. We like symmetry and pattern, but we also relish a bit of asymmetry. The British art historian Ernst Gombrich believed that, although human beings have a deep psychological attraction to order, perfect order in art is uninteresting. ‘However we analyse the difference between the regular and the irregular,’ he wrote in The Sense of Order (1979), ‘we must ultimately be able to account for the most basic fact of aesthetic experience, the fact that delight lies somewhere between boredom and confusion.’ Too much order, we lose interest. Too much disorder, and there’s nothing to be interested in. My wife, a painter, always puts a splash of colour in the corner of her canvas, off balance, to make the painting more appealing. Evidently, our visual sweet-spot lies somewhere between boredom and confusion, predictability and newness.
Human beings have a conflicted relationship to this order-disorder nexus. We are alternately attracted from one to the other. We admire principles and laws and order. We embrace reasons and causes. We seek predictability. Some of the time. On other occasions, we value spontaneity, unpredictability, novelty, unconstrained personal freedom. We love the structure of Western classical music, as well as the free-wheeling runs or improvised rhythms of jazz. We are drawn to the symmetry of a snowflake, but we also revel in the amorphous shape of a high-riding cloud. We appreciate the regular features of pure-bred animals, while we’re also fascinated by hybrids and mongrels. We might respect those who manage to live sensibly and lead upright lives. But we also esteem the mavericks who break the mould, and we celebrate the wild, the unbridled and the unpredictable in ourselves. We are a strange and contradictory animal, we human beings. And we inhabit a cosmos equally strange. [Continue reading…]
A quantum experiment suggests there’s no such thing as objective reality
MIT Technology Review reports:
Back in 1961, the Nobel Prize–winning physicist Eugene Wigner outlined a thought experiment that demonstrated one of the lesser-known paradoxes of quantum mechanics. The experiment shows how the strange nature of the universe allows two observers—say, Wigner and Wigner’s friend—to experience different realities.
Since then, physicists have used the “Wigner’s Friend” thought experiment to explore the nature of measurement and to argue over whether objective facts can exist. That’s important because scientists carry out experiments to establish objective facts. But if they experience different realities, the argument goes, how can they agree on what these facts might be?
That’s provided some entertaining fodder for after-dinner conversation, but Wigner’s thought experiment has never been more than that—just a thought experiment.
Last year, however, physicists noticed that recent advances in quantum technologies have made it possible to reproduce the Wigner’s Friend test in a real experiment. In other words, it ought to be possible to create different realities and compare them in the lab to find out whether they can be reconciled.
And today, Massimiliano Proietti at Heriot-Watt University in Edinburgh and a few colleagues say they have performed this experiment for the first time: they have created different realities and compared them. Their conclusion is that Wigner was correct—these realities can be made irreconcilable so that it is impossible to agree on objective facts about an experiment. [Continue reading…]
Inside the struggle to define life
All the brain cells of life on Earth still cannot explain life on Earth. Its most intelligent species has uncovered the building blocks of matter, read countless genomes and watched spacetime quiver as black holes collide. It understands much of how living creatures work, but not how they came to be. There is no agreement, even, on what life is.
The conundrum of life is so fundamental that to solve it would rank among the most important achievements of the human mind. But for all scientists’ efforts – and there have been plenty – the big questions remain. If biology is defined as the study of life, on this it has failed to deliver.
But enlightenment may come from another direction. Rather than biology, some scientists are now looking to physics for answers, in particular the physics of information. Buried in the rules that shape information lie the secrets of life and perhaps even the reason for our existence.
That, at least, is the bold proposal from Paul Davies, a prominent physicist who explores the idea in his forthcoming book, The Demon in the Machine. Published next week, it continues a theme of thinking that landed Davies the $1m Templeton prize for contributions to religious thought and inquiry.
As director of the Beyond Center for Fundamental Concepts in Science at Arizona State University, Davies is well placed to spot the next wave that will crash over science. What he sees on the horizon is a revolution that brings physics and biology together through the common science of information.
“The basic hypothesis is this,” Davies says. “We have fundamental laws of information that bring life into being from an incoherent mish-mash of chemicals. The remarkable properties we associate with life are not going to come about by accident.”
The proposal takes some unpacking. Davies believes that the laws of nature as we know them today are insufficient to explain what life is and how it came about. We need to find new laws, he says, or at least new principles, which describe how information courses around living creatures. Those rules may not only nail down what life is, but actively favour its emergence. [Continue reading…]
Emergence: How complex wholes arise from simple parts
You could spend a lifetime studying an individual water molecule and never deduce the precise hardness or slipperiness of ice. Watch a lone ant under a microscope for as long as you like, and you still couldn’t predict that thousands of them might collaboratively build bridges with their bodies to span gaps. Scrutinize the birds in a flock or the fish in a school and you wouldn’t find one that’s orchestrating the movements of all the others.
Nature is filled with such examples of complex behaviors that arise spontaneously from relatively simple elements. Researchers have even coined the term “emergence” to describe these puzzling manifestations of self-organization, which can seem, at first blush, inexplicable. Where does the extra injection of complex order suddenly come from?
Answers are starting to come into view. One is that these emergent phenomena can be understood only as collective behaviors — there is no way to make sense of them without looking at dozens, hundreds, thousands or more of the contributing elements en masse. These wholes are indeed greater than the sums of their parts.
Another is that even when the elements continue to follow the same rules of individual behavior, external considerations can change the collective outcome of their actions. For instance, ice doesn’t form at zero degrees Celsius because the water molecules suddenly become stickier to one another. Rather, the average kinetic energy of the molecules drops low enough for the repulsive and attractive forces among them to fall into a new, more springy balance. That liquid-to-solid transition is such a useful comparison for scientists studying emergence that they often characterize emergent phenomena as phase changes.
Our latest In Theory video on emergence explains more about how throngs of simple parts can self-organize into a more extraordinary whole:
The crisis inside the physics of time
Poets often think of time as a river, a free-flowing stream that carries us from the radiant morning of birth to the golden twilight of old age. It is the span that separates the delicate bud of spring from the lush flower of summer.
Physicists think of time in somewhat more practical terms. For them, time is a means of measuring change—an endless series of instants that, strung together like beads, turn an uncertain future into the present and the present into a definite past. The very concept of time allows researchers to calculate when a comet will round the sun or how a signal traverses a silicon chip. Each step in time provides a peek at the evolution of nature’s myriad phenomena.
In other words, time is a tool. In fact, it was the first scientific tool. Time can now be sliced into slivers as thin as one ten-trillionth of a second. But what is being sliced? Unlike mass and distance, time cannot be perceived by our physical senses. We don’t see, hear, smell, touch, or taste time. And yet we somehow measure it. As a cadre of theorists attempt to extend and refine the general theory of relativity, Einstein’s momentous law of gravitation, they have a problem with time. A big problem.
“It’s a crisis,” says mathematician John Baez, of the University of California at Riverside, “and the solution may take physics in a new direction.” Not the physics of our everyday world. Stopwatches, pendulums, and hydrogen maser clocks will continue to keep track of nature quite nicely here in our low-energy earthly environs. The crisis arises when physicists attempt to merge the macrocosm—the universe on its grandest scale—with the microcosm of subatomic particles. [Continue reading…]
Studying time is like holding a snowflake
In April, in the famous Faraday Theatre at the Royal Institution in London, Carlo Rovelli gave an hour-long lecture on the nature of time. A red thread spanned the stage, a metaphor for the Italian theoretical physicist’s subject. “Time is a long line,” he said. To the left lies the past—the dinosaurs, the big bang—and to the right, the future—the unknown. “We’re sort of here,” he said, hanging a carabiner on it, as a marker for the present.
Then he flipped the script. “I’m going to tell you that time is not like that,” he explained.
Rovelli went on to challenge our common-sense notion of time, starting with the idea that it ticks everywhere at a uniform rate. In fact, clocks tick slower when they are in a stronger gravitational field. When you move nearby clocks showing the same time into different fields—one in space, the other on Earth, say—and then bring them back together again, they will show different times. “It’s a fact,” Rovelli said, and it means “your head is older than your feet.” Also a non-starter is any shared sense of “now.” We don’t really share the present moment with anyone. “If I look at you, I see you now—well, but not really, because light takes time to come from you to me,” he said. “So I see you sort of a little bit in the past.” As a result, “now” means nothing beyond the temporal bubble “in which we can disregard the time it takes light to go back and forth.”