Experiments that make quantum mechanics directly visible to the human eye

Rebecca Holmes writes:

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

Alan Lightman writes:

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

Ian Sample writes:

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

John Rennie writes:

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

Marcia Bartusiak writes:

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

Brian Gallagher writes:

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.”

 

Michio Kaku: Why there are higher dimensions

 

The peculiar numbers that could underlie the laws of nature

 

Natalie Wolchover writes:

In 2014, a graduate student at the University of Waterloo, Canada, named Cohl Furey rented a car and drove six hours south to Pennsylvania State University, eager to talk to a physics professor there named Murat Günaydin. Furey had figured out how to build on a finding of Günaydin’s from 40 years earlier — a largely forgotten result that supported a powerful suspicion about fundamental physics and its relationship to pure math.

The suspicion, harbored by many physicists and mathematicians over the decades but rarely actively pursued, is that the peculiar panoply of forces and particles that comprise reality spring logically from the properties of eight-dimensional numbers called “octonions.”

As numbers go, the familiar real numbers — those found on the number line, like 1, π and -83.777 — just get things started. Real numbers can be paired up in a particular way to form “complex numbers,” first studied in 16th-century Italy, that behave like coordinates on a 2-D plane. Adding, subtracting, multiplying and dividing is like translating and rotating positions around the plane. Complex numbers, suitably paired, form 4-D “quaternions,” discovered in 1843 by the Irish mathematician William Rowan Hamilton, who on the spot ecstatically chiseled the formula into Dublin’s Broome Bridge. John Graves, a lawyer friend of Hamilton’s, subsequently showed that pairs of quaternions make octonions: numbers that define coordinates in an abstract 8-D space.

There the game stops. Proof surfaced in 1898 that the reals, complex numbers, quaternions and octonions are the only kinds of numbers that can be added, subtracted, multiplied and divided. The first three of these “division algebras” would soon lay the mathematical foundation for 20th-century physics, with real numbers appearing ubiquitously, complex numbers providing the math of quantum mechanics, and quaternions underlying Albert Einstein’s special theory of relativity. This has led many researchers to wonder about the last and least-understood division algebra. Might the octonions hold secrets of the universe? [Continue reading…]

The Standard Model of particle physics: The absolutely amazing theory of almost everything

File 20180521 14978 36nv6i.jpg?ixlib=rb 1.1
How does our world work on a subatomic level?
Varsha Y S, CC BY-SA

By Glenn Starkman, Case Western Reserve University

The Standard Model. What dull name for the most accurate scientific theory known to human beings.

More than a quarter of the Nobel Prizes in physics of the last century are direct inputs to or direct results of the Standard Model. Yet its name suggests that if you can afford a few extra dollars a month you should buy the upgrade. As a theoretical physicist, I’d prefer The Absolutely Amazing Theory of Almost Everything. That’s what the Standard Model really is.

Many recall the excitement among scientists and media over the 2012 discovery of the Higgs boson. But that much-ballyhooed event didn’t come out of the blue – it capped a five-decade undefeated streak for the Standard Model. Every fundamental force but gravity is included in it. Every attempt to overturn it to demonstrate in the laboratory that it must be substantially reworked – and there have been many over the past 50 years – has failed.

In short, the Standard Model answers this question: What is everything made of, and how does it hold together?

[Read more…]