Posts Tagged ‘Physics’
“The universe is under no obligation to make sense to you”*…
Still, we try… In a consideration of three new books, the estimable Sean Carroll brings us up to date on the state of play…
Should scientists be embarrassed that they can’t settle on a definition for the Big Bang? The cosmologist Will Kinney describes it as the “physical theory of the hot infant universe,” while Wikipedia goes for the more elaborate “a physical theory that describes how the universe expanded from an initial state of high density and temperature.” The first refers only to early times, while the latter seems to extend to subsequent times as well. The physicist and science writer Tony Rothman offers the pithier “the universe’s origin,” the theoretical physicist Thomas Hertog suggests that it is the “primeval state” of cosmic history, and a NASA website gives us “the idea that the universe began as just a single point.” These seem to refer to one moment at the start of things, rather than the universe’s life since then.
All of these sources (except NASA, unfortunately) capture something correct. The confusion stems both from the inherent ambiguity of using ordinary language to describe novel scientific concepts and from the state of modern cosmology itself. Cosmology is the study of the universe on the largest scales. So it ignores details of stars and planets, focusing on galaxies and even bigger structures, up to the universe as a whole. Modern cosmology is only about a century old, as it wasn’t until the 1920s that astronomers determined that our own Milky Way is just one of a large number of galaxies and the origin and evolution of them all could be studied together. And it wasn’t until the 1990s that the field matured into the one that exists today, featuring precision measurements and ultralarge datasets.
Dealing as it does with some of the most profound questions about the nature of the cosmos, cosmological research has always involved a vigorous give-and-take between rampant speculation and unanticipated discoveries. Its practitioners have long been fond of spinning purportedly inviolate physical principles from their personal intuitions about how reality should work. But cosmology remains an empirical science—a cherished belief can be quickly swept away by a solid measurement.
The present moment in the science of cosmology is one of consolidation, as we have successfully incorporated the lessons of some impressive discoveries made near the turn of the twenty-first century. Yet crucially important questions remain unanswered, especially about what exactly happened at the onset of the expanding space that evolved into our contemporary universe. It is therefore a good time for books that take stock of where we are and what might come next, and that illustrate which puzzles modern physicists choose to take seriously.
This much we know: we live in a galaxy, the Milky Way, containing around 200 billion stars. There are something like a trillion galaxies in our observable universe, distributed almost uniformly through space. Stars and galaxies condensed out of an originally nearly smooth distribution of matter. Distant galaxies are moving apart from one another. Extrapolating backward, we reach a hot, densely packed configuration about 13.8 billion years ago. We can observe the remnants of this early period in nearly uniform cosmic background radiation coming from every direction in the sky.
The Big Bang model is precisely this general picture, of a universe that expands and cools out of a smooth, hot primordial state. It is well understood and almost universally accepted among modern cosmologists. The Big Bang event is a hypothetical moment when the whole thing might have started, at which the temperature and density are supposed to have been literally infinite—a “singularity,” in physics parlance. This is why the NASA definition above is unambiguously wrong: the Big Bang event has nothing to do with “a single point” in space—it refers to a moment in time.
Nobody knows whether there actually was such an event. To be honest, there probably wasn’t. Einstein’s theory of general relativity predicts that such a singularity would have happened, but most physicists think this signals a breakdown in the theory rather than being an accurate description of the physical world. A prediction of infinitely big physical quantities is apt to be a sign that we don’t have the right theoretical understanding…
[Starting with Einstein’s unification of space-time in 1905, Carroll explains the implications of quantum theory, in particular on the question of the expansion of the universe. Using the three (very different, but complementary) books under consideration, he unpacks the issues and demonstrates the way in which scientific theories about the origin of the universe often involve a vigorous give-and-take between speculation and discovery…]
… Taken together, these three books provide an illuminating view of the state of modern cosmology. There are established results, laudable efforts to connect promising hypotheses to a flood of incoming data, and brave speculations about the physical and metaphysical unknown. They are all notably well written for the genre and will keep readers entertained as they are educated. We can marvel at both how much scientists have learned about the universe and how much we have yet to understand.
The state of cosmology (and a look at science at work): “A First Time for Everything,” from @seanmcarroll.bsky.social in @nybooks.com.
* Neil deGrasse Tyson
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As we wrestle with reality, we might spare a thought for a major (if, in the end, incorrect) character in tale that Carroll tells: Fred Hoyle; he died on this date in 2001. A prominent astronomer, he formulated the theory of stellar nucleosynthesis. But he is rather better remembered for his controversial stances on other scientific matters—in particular his rejection of the (as Carroll observes, now widely-accepted) “Big Bang” theory– a term he coined, derisively, in an episode of his immensely-popular series The Nature of the Universe on BBC radio– and his promotion of panspermia as the source of life on Earth (or maybe the traffic was in the other direction?).
“Anyone not shocked by quantum mechanics has not yet understood it”*…
In the summer of 1925, a young Werner Heisenberg retreated to Helgoland in the North Sea and reemerged with the first full-fledged version of quantum mechanics. A century later, the theory’s meaning remains unsettled. Charlie Wood joined a group of physicists in Helgoland to take stock of the theory on its centennial…
Happy 100th birthday, quantum mechanics!” a physicist bellowed into a microphone one evening in June, and the cavernous banquet hall of Hamburg’s Hotel Atlantic erupted into cheers and applause. Some 300 quantum physicists had traveled from around the world to attend the opening reception of a six-day conference marking the centennial of the most successful theory in physics. The crowd included well-known pioneers of quantum computing and quantum cryptography, and four Nobel Prize winners.
“I feel like I’m at Woodstock,” Daniel Burgarth of the University of Erlangen-Nuremberg in Germany told me. “It’s my only chance to see them all in one place.”
One hundred years to the month had passed since a 23-year-old postdoc named Werner Heisenberg was driven by a case of hay fever to Helgoland, a barren, windswept island in the North Sea. There, Heisenberg completed a calculation that would become the heart of quantum mechanics, a radical new theory of the atomic and subatomic world.
The theory remains radical.
Before quantum mechanics hit the scene, “classical” physics theories dealt directly with the stuff of the world and its properties: the orbits of planets, say, and the speeds of pendulums. Quantum mechanics deals in something more abstract: possibilities. It predicts the chances that we’ll observe an atom doing this or that, or being here or there. It gives the impression that particles can engage in multiple possible behaviors at once, that they have no fixed reality. So physicists have spent the last century grappling with questions like: What is real? And where does our reality come from?…
Wood recounts the genesis and development of the theory and considers some of the vexing questions that remain: e.g., the many-world interpretation, the place (?) of gravity in the theory, et al. He concludes with a quote from Robert Spekkens, a physicist at the Perimeter Institute (whose work illustrates Lawrence Krause‘s observation that “At the heart of quantum mechanics is a rule that sometimes governs politicians or CEOs – as long as no one is watching, anything goes”): “We’re privileged to live at a time when the great prize of making sense of quantum theory is still there for the taking.”
Eminently worth reading in full: “‘It’s a Mess’: A Brain-Bending Trip to Quantum Theory’s 100th Birthday Party” from @walkingthedot.bsky.social in @quantamagazine.bsky.social.
See also: “Physicists Can’t Agree on What Quantum Mechanics Says about Reality“
* Niels Bohr
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As we wrestle with reality, we might send relativistic birthday greetings to one of quantum theory’s pioneers, Erwin Schrödinger; he was born on this date in 1887. A physicist, Schrödinger took Louis de Broglie‘s concept of atomic particles as having wave-like properties, and modified the earlier Bohr model of the atom to accommodate the wave nature of the electrons, which he instantiated in the Schrödinger equation, which provides a way to calculate the wave function of a system and how it changes dynamically in time. It was the basis of the work that earned him the Nobel Prize in 1933. And he coined the term “quantum entanglement” in 1935.
But surely Schrödinger is most widely known for creating the thought experiment we all know as “Schrödinger’s Cat” (and here).
“The story of the events and the people who, over centuries, came together to bring us in from the cold and to wrap us in a warm blanket of technology is a matter of vital importance, since more and more of that technology infiltrates every aspect of our lives”*…
From Étienne Fortier-Dubois, the Historical Tech Tree, “a timeline to visualize the full history of all major technologies (or 1,780 of them, at least), from 3.3 million years ago to today. More importantly, it also contains more than 2,000 connections between them: prerequisites, improvements, inspirations: anything that allows you to understand how one thing led to another”…
The historical tech tree is a project by Étienne Fortier-Dubois to visualize the entire history of technologies, inventions, and (some) discoveries, from prehistory to today. Unlike other visualizations of the sort, the tree emphasizes the connections between technologies: prerequisites, improvements, inspirations, and so on.
These connections allow viewers to understand how technologies came about, at least to some degree, thus revealing the entire history in more detail than a simple timeline, and with more breadth than most historical narratives. The goal is not to predict future technology, except in the weak sense that knowing history can help form a better model of the world. Rather, the point of the tree is to create an easy way to explore the history of technology, discover unexpected patterns and connections, and generally make the complexity of modern tech feel less daunting….
How one thing led to another: “Historical Tech Tree.”
See also: “Introducing the Historical Tech Tree.”
* “The story of the events and the people who, over centuries, came together to bring us in from the cold and to wrap us in a warm blanket of technology is a matter of vital importance, since more and more of that technology infiltrates every aspect of our lives. It’s become a life-support system without which we can’t survive. And yet, how much of it do we understand?”- James Burke, in the first episode of Connections.
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As we ponder progress, we might recall that it was on this date in 1633, following an Inquisition, that the Holy Office in Rome forced Galileo Galilei to recant his view that the Sun, not the Earth, is the center of the Universe in the form in which he presented it. Gaileo had used a telescope (1603 on the Timeline) to reach his (correct) conclusion.
He refused to recant, and put under house arrest, where he effectively remained for the rest of his life. He dedicated his time in restriction to one of his finest works, Two New Sciences, in which he summarised work he had done some forty years earlier, on the two sciences now called kinematics and strength of materials, and published in Holland to avoid the censor. As a result of this work– highly praised by Albert Einstein– Galileo is often called the “father of modern physics.”
“Form follows function – that has been misunderstood. Form and function should be one, joined in a spiritual union”*…
In the quote above, Frank Lloyd Wright was glossing his mentor, Louis Sullivan… He might have been alluding to the work of L. Mahadevan. In a conversation with Steven Strogatz, Mahadeven explains how complex biological forms and behaviors– from brain folds to insect architecture– emerge through the interplay of physical forces, environment and embodiment…
What links a Möbius strip, brain folds and termite mounds? The answer is Harvard University’s L. Mahadevan, whose career has been devoted to using mathematics and physics to explore the form and function of common phenomena.
Mahadevan, or Maha to his friends and colleagues, has long been fascinated by questions one wouldn’t normally ask — from the equilibrium shape of inert objects like a Möbius strip, to the complex factors that drive biological systems like morphogenesis or social insect colonies…
… Mahadevan tells Steven Strogatz what inspires him to tackle these questions, and how gels, gypsum and LED lights can help uncover form and function in biological systems. He also offers some provocative thoughts about how noisy random processes might underlie our intuitions about geometry…
… STROGATZ: I feel like it’s relevant for our discussion today because it seems like you’ve been interested in this interplay between shape and force, certainly from your early work and it looks like you’re still thinking about it these days.
MAHADEVAN: Partly, yes. I would say a lot of what I am trying to do nowadays is more biologically motivated and inspired. But flow, shape and increasingly now thinking about sentient systems, understanding how we learn what we learn. I’m very much interested in embodiment as a way in which sentient organisms find their way and function in the world… and particularly with social insects, but a little bit with humans as well…
“Does Form Really Shape Function?” It’s so much more interesting than that… @stevenstrogatz.com and @quantamagazine.bsky.social.
(Image above: source)
* Frank Lloyd Wright
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As we blend, we might recall that it was on this date in 1987 that Ben & Jerry’s Ice Cream introduced a new flavor, Cherry Garcia.
“Gravity. It’s not just a good idea; it’s the law!”*…
… But what is gravity? George Musser unpacks a new argument that explores how the growth of disorder could cause massive objects to move toward one another– one that has left some physicists interested, and some skeptical…
Isaac Newton was never entirely happy with his law of universal gravitation. For decades after publishing it in 1687, he sought to understand how, exactly, two objects were able to pull on each other from afar. He and others came up with several mechanical models, in which gravity was not a pull, but a push. For example, space might be filled with unseen particles that bombard the objects on all sides. The object on the left absorbs the particles coming from the left, the one on the right absorbs those coming from the right, and the net effect is to push them together.
Those theories never quite worked, and Albert Einstein eventually provided a deeper explanation of gravity as a distortion of space and time. But Einstein’s account, called general relativity, created its own puzzles, and he himself recognized that it could not be the final word. So the idea that gravity is a collective effect — not a fundamental force, but the outcome of swarm behavior on a finer scale — still compels physicists.
Earlier this year, a team of theoretical physicists put forward what might be considered a modern version of those 17th-century mechanical models. “There’s some kind of gas or some thermal system out there that we can’t see directly,” said Daniel Carney of Lawrence Berkeley National Laboratory, who led the effort. “But it’s randomly interacting with masses in some way, such that on average you see all the normal gravity things that you know about: The Earth orbits the sun, and so forth.”
This project is one of the many ways that physicists have sought to understand gravity, and perhaps the bendy space-time continuum itself, as emergent from deeper, more microscopic physics. Carney’s line of thinking, known as entropic gravity, pegs that deeper physics as essentially just the physics of heat. It says gravity results from the same random jiggling and mixing up of particles — and the attendant rise of entropy, loosely defined as disorder — that governs steam boilers, car engines and refrigerators.
Attempts at modeling gravity as a consequence of rising entropy have cropped up now and again for several decades. Entropic gravity is very much a minority view. But it’s one that won’t die, and even detractors are loath to dismiss it altogether. The new model has the virtue of being experimentally testable — a rarity when it comes to theories about the mysterious underpinnings of the universal attraction…
[Musser explains the hypothesis, traces is origin, and reviews other scientists’ reactions, and traces possible approaches to testing it…]
… if this long-shot theory does work out, physicists will need to update the artist Gerry Mooney’s famous gravity poster, which reads: “Gravity. It isn’t just a good idea. It’s the law.” Perhaps gravity is not, in fact, a law, just a statistical tendency…
“Is Gravity Just Entropy Rising? Long-Shot Idea Gets Another Look” from @georgemusser.com in @quantamagazine.bsky.social.
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As we fumble with forces, we might send insightful birthday greetings to a man who encourages us to see in different ways, M. C. Escher; he was born on this date in 1898. A graphic artist inspired by mathematics, he created woodcuts, lithographs, and mezzotints, that— while largely ignored by the art world in his lifetime, have become widely celebrated. He’s been recognized as an heir to Parmigianino, Hogarth, and Piranesi.
His work features mathematical objects and operations including impossible objects, explorations of infinity, reflection, symmetry, perspective, truncated and stellated polyhedra, hyperbolic geometry, and tessellations. And though Escher believed he had no mathematical ability, he interacted with the mathematicians George Pólya, Roger Penrose, and Donald Coxeter, and the crystallographer Friedrich Haag, and conducted his own research into tessellation.
For more on (and more examples of) Escher’s work, see here.
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