Posts Tagged ‘Max Planck’
“What happens when you get to the end of things?”*…
Charlie Wood introduces a remarkable new collection in Quanta…
A couple of years ago, I was chatting about black holes with Dan Harlow of the Massachusetts Institute of Technology when he made a casual comment that left a deep impression on me. I asked if some new work he’d been doing strengthened the case that space-time was “emergent.” Without missing a beat he replied, “Sure, if it needed strengthening.”
Harlow isn’t the only physicist with serious doubts about what reality is made of. For more than a decade now, Nima Arkani-Hamed of the Institute for Advanced Study has been delivering a polished lecture arguing that space-time is “doomed.” Time and again, I’ve heard theorists in high-energy physics make similar-sounding statements, and I’ve always been struck by their confidence. We don’t have the faintest idea what the next theory of physics will look like, whether it will involve strings, loops, triangles or something entirely new that no one has thought to propose. And yet so many theorists seem rather convinced that whatever it will be, it won’t involve space or time.
Why? What does that statement mean? What would it look like to do physics without referring to space or time? I’ve spent most of this year trying to find out. The results have just been published in “The Unraveling of Space-Time,” a massive package that includes articles, videos and interactive animations from me and my colleagues Mark Belan, Emily Buder, Amanda Gefter and Joseph Howlett.
Over the course of more than 40 interviews with nearly 30 physicists, I learned that there are many ways to define emergent space-time. But at the most basic level, “emergent space-time” means that space and time are the outputs of a theory instead of the inputs. A classic analogy is heat. To explain why a teacup cools, scientists of the 1700s put heat into their theory of the world as a substance that repels itself and naturally spreads out. But this “caloric theory” was ultimately replaced by thermodynamics, a theory where a primary input is molecules that buzz around with some energy. As molecules crash into each other, their energy spreads, and we now recognize this process as the origin of heat transfer. Heat is an output — a prediction — of thermodynamics. It is an emergent phenomenon.
Space-time is the ultimate input. If physics is largely about predicting what happens where and when, you need a stage upon which things can happen. Albert Einstein became a household name for revealing that this stage acts like a fabric that bends in ways we experience as gravity. He described in spectacular detail how space-time behaves, much as 19th-century scientists described how heat behaves with caloric theory. The idea that space-time is emergent is the idea that space-time will eventually go the way of heat, water, air and so many other substances before it; we will someday understand it to be the inevitable consequence of the behavior of simpler entities. Call them the “atoms” of space-time.This week’s series explores the mind-bending notion of emergent space-time from a number of angles. There is, of course, the why of it all. This mostly boils down to the strange things that happen when Einstein’s theory of space-time collides with quantum mechanics, the theory of the subatomic world. When we combine features from both theories, we see that any experiment that tries to probe reality a little too closely will get thwarted by the appearance of a black hole, an enigma that undermines the familiar picture of space-time in its own way.
For this and other reasons, physicists are pushing to escape our familiar space-time, often referred to as the “bulk,” in search of alien environments conducive to new ways of doing physics.
Where else might one do physics, if not in the bulk? A few ideas are being developed, including one that goes by the name of holography. This is roughly the idea that any gravitational system — even the entire universe — can have an alternative description as a collection of quantum particles moving around a flat surface. From these gravity-free surfaces, a bulk world with gravity somehow pops out. It’s a remarkable theoretical claim, and over the past few years, holographers have developed a suite of tools that have helped them decode the bulk from the behavior of these surface particles.Another research program, spearheaded by Arkani-Hamed, has even more ambitious aims — getting both space-time and quantum mechanics as outputs from even more alien inputs. His group has recently developed an entirely new language for making predictions, one that makes no reference to space-time. Instead, it uses only geometric shapes and primitive counting tasks.
Is space-time, at least in its current form, definitely doomed? The idea tortured one of the pioneers of gravitational theory, John Wheeler. And today, the end of space-time is even more widely accepted. Most of the theorists I spoke with struggled to think of colleagues in the quantum gravity community who would defend space-time as a fundamental ingredient of reality. However, some researchers are pursuing alternatives. I spoke at length with Latham Boyle about patterns in particle physics that have led him and his collaborators to the more conservative notion that space-time might come in two “sheets.”
The various proposals under development are unlikely to see experimental tests this century, so a conclusive answer doesn’t seem near. But if it were someday established that space-time does break down, what would that mean for us?
On a practical level, not much. Einstein’s fabric of space-time is so sturdy that little short of a black hole would put a noticeable dent in it. But at a conceptual level, it’s hard to imagine a more dramatic rethinking of reality. When Democritus suggested that matter emerges from tiny barbed “atoms” more than 2,000 years ago, he couldn’t possibly have foreseen that parts of his proposal would ultimately be realized in the form of quantum theory — a framework asserting that reality is an ocean of overlapping waves of possibility that resolve into fixed objects only in certain situations.
If the void itself emerges from something, that something will be at least as alien. Just as individual molecules don’t themselves have a well-defined notion of heat, the base level of reality could lack marquee features of our existence that we take for granted. Places. Times. The ability to influence only nearby objects. The requirement that causes precede effects. Physicists are already finding that these notions seem unlikely to be present in a more precise accounting of the world. They seem to be the approximate outputs of something stranger.“One of the most spectacular aspects of these new findings is the emergence of causality can only happen in the approximate description,” Elliott Gesteau, a quantum gravity researcher at the California Institute of Technology, told me over Zoom earlier this year. If there is gravity, he continued, “which is what we have in our world, then this causal structure is only approximate and must break down.”…
Are we on the verge of a new physics? “Why Space-Time Looks Doomed,” from @walkingthedot in @QuantaMagazine.
The full interactive collection is here, and eminently worth reading in full.
* John Wheeler
###
As we wrestle with reality, we might spare a thought for a physicist whose work helped move the questions we face forward– Max Karl Ernst Ludwig Planck; he died on this date in 1947. A theoretical physicist, he is best remembered as the originator of quantum theory. It was his discovery of energy quanta that won him the Nobel Prize in Physics in 1918.
“There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.”*…
Some observations are best considered “interesting, if true”; some, a la Karl Popper, “true, until false”… Consider this very recent paper in Nature…
Theories of scientific and technological change view discovery and invention as endogenous processes, wherein previous accumulated knowledge enables future progress by allowing researchers to, in Newton’s words, ‘stand on the shoulders of giants.’ Recent decades have witnessed exponential growth in the volume of new scientific and technological knowledge, thereby creating conditions that should be ripe for major advances. Yet contrary to this view, studies suggest that progress is slowing in several major fields. Here, we analyse these claims at scale across six decades, using data on 45 million papers and 3.9 million patents from six large-scale datasets, together with a new quantitative metric—the CD index—that characterizes how papers and patents change networks of citations in science and technology. We find that papers and patents are increasingly less likely to break with the past in ways that push science and technology in new directions. This pattern holds universally across fields and is robust across multiple different citation- and text-based metrics. Subsequently, we link this decline in disruptiveness to a narrowing in the use of previous knowledge, allowing us to reconcile the patterns we observe with the ‘shoulders of giants’ view. We find that the observed declines are unlikely to be driven by changes in the quality of published science, citation practices or field-specific factors. Overall, our results suggest that slowing rates of disruption may reflect a fundamental shift in the nature of science and technology.
The full paper: “Papers and patents are becoming less disruptive over time” @Nature
One notes that the quote above– from Lord Kelvin, at the turn of the twentieth century– immediately preceded a couple of decades in which physics was radically redefined and advanced by Planck, Einstein, Bohr, et al. (In fairness to Kelvin, consider this suggestion that his point was more subtle.) As we look forward, we might ponder the ways in which the reorganization of disciplines, the rise of research in other cultures (less constrained by the mores of “conventional” research), the use of AI, and/or some as yet unknown dynamic could challenge the phenomenon– “a narrowing in the use of previous knowledge”– to which the authors attribute diminishing disruption.
[Source of the image above]
* Lord Kelvin, in an address to the the Royal Institution in April of 1900
###
As we ponder progress, we might send advanced birthday greetings to Wilhelm Wien; he was born on this date in 1864. A physicist, his work helped move past Kelvin’s log-jam. In 1893, he used theories about heat and electromagnetism to deduce Wien’s displacement law, which calculates the emission of a blackbody (a surface that absorbs all radiant energy falling on it) at any temperature from the emission at any one reference temperature. His colleague Max Planck colaborated with Wien, then extended the thinking in what we now know as Planck’s law, which led to the development of quantum theory.
Wien received the 1911 Nobel Prize for his work on heat radiation.
Just before Kelvin’s speech (in 1898) Wien identified a positive particle equal in mass to the hydrogen atom– what we now know as a proton. Wien, in the techniques he used, laid the foundation of mass spectrometry.
“A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it”*…
A curious thing happened at the end of the 19th century and the dawning of the 20th. As European and American industries became increasingly confident in their methods of invention and production, scientists made discovery after discovery that shook their understanding of the physical world to the core. “Researchers in the 19th century had thought they would soon describe all known physical processes using the equations of Isaac Newton and James Clerk Maxwell,” Adam Mann writes at Wired. But “the new and unexpected observations were destroying this rosy outlook.
These observations included X-rays, the photoelectric effect, nuclear radiation and electrons; “leading physicists, such as Max Planck and Walter Nernst believed circumstances were dire enough to warrant an international symposium that could attempt to resolve the situation.” Those scientists could not have known that over a century later, we would still be staring at what physicist Dominic Walliman calls the “Chasm of Ignorance” at the edge of quantum theory. But they did initiate “the quantum revolution” in the first Solvay Council, in Brussels, named for wealthy chemist and organizer Ernest Solvay.
“Reverberations from this meeting are still felt to this day… though physics may still sometimes seem to be in crisis” writes Mann (in a 2011 article just months before the discovery of the Higgs boson). The inaugural meeting kicked off a series of conferences on physics and chemistry that have continued into the 21st century. Included in the proceedings were Planck, “often called the father of quantum mechanics,” Ernest Rutherford, who discovered the proton, and Heike Kamerlingh-Onnes, who discovered superconductivity.
Also present were mathematician Henri Poincaré, chemist Marie Curie, and a 32-year-old Albert Einstein, the second youngest member of the group. Einstein described the first Solvay conference (1911) in a letter to a friend as “the lamentations on the ruins of Jerusalem. Nothing positive came out of it.” The ruined “temple,” in this case, were the theories of classical physics, “which had dominated scientific thinking in the previous century.” Einstein understood the dismay, but found his colleagues to be irrationally stubborn and conservative…
For more– and a complete list of attendees in the photo above: ““The Most Intelligent Photo Ever Taken”: The 1927 Solvay Council Conference, Featuring Einstein, Bohr, Curie, Heisenberg, Schrödinger & More.”
* Max Planck (second from the left in the first row of the photo above)
###
As we ponder paradigms, we might send insightful birthday greetings to Edward Williams Morley; he was born on this date in 1838. A chemist who was first to precisely determine the atomic weight of oxygen, he is probably best remembered for his collaboration with the physicist Albert A. Michelson. In what we call the Michelson–Morley experiment (actually a number of experiments conducted between April and July in 1887), they attempted to detect the luminiferous aether, a supposed medium permeating space that was thought to be the carrier of light waves; their method was the very precise measurement of the speed of light (in various directions, and at different times of the year, as the Earth revolved in its orbit around the Sun). Michelson and Morley always found that the speed of light did not vary at all depending on the direction of measurement, or the position of the Earth in its orbit– the so-called “null result.”
Neither Morley nor Michelson ever considered that these null results disproved the hypothesis of the existence of “luminiferous aether.” But other scientists began to suspect that they did. Almost two decades later the results of the Michelson–Morley experiments supported Albert Einstein’s strong postulate (in 1905) that the speed of light is a constant in all inertial frames of reference as part of his Special Theory of Relativity.
“I’ve developed a new philosophy. I only dread one day at a time.”*…
Starting [last] month, the very talented Adam Koford, the creator of Laugh-Out-Loud Cats webcomic, started posting these wonderful bootleg Peanuts comics to his Twitter account, and continued almost every day since.
Loose and sketchy, they capture the essence of Charles Schultz’ Peanuts so well: sweet and sad, combining childlike wonder and existential dread. As he went on, they started evolving a unique style of their own, distinct from the Peanuts characters but still recognizable….
Via Andy Baio‘s wonderful site Waxy. The “Peanuts” panels are strewn through Adam’s Twitter feed; as a gift to us all, Baio collected a bunch of them into a Twitter “Moment.”
Enjoy… and don’t mention it to the Schultz estate.
* Charlie Brown
###
As we ruminate on reality, we might recall that today’s a relative-ly good day for it, as it was on this date in 1900 that German physicist Max Planck presented and published his study of the effect of radiation on a “black-body” substance (introducing what we’ve come to know as the Planck Postulate), and the quantum theory of modern physics– and for that matter, Twentieth Century modernity– were born.
Planck study demonstrated that in certain situations energy exhibits the characteristics of physical matter– something unthinkable at the time, when energy was thought to exist only in wave form– and suggested that energy exists in discrete packets, which he called “quanta”… thus laying the foundation on which he, Einstein, Bohr, Schrodinger, Dirac, and others built our modern understanding.
Max Planck
“There is a size at which dignity begins”*…
The spectrometer for the KATRIN experiment, as it works its way through the German town of Eggenstein-Leopoldshafen in 2006 en route to the nearby Karlsruhe Institute of Technology
Isaac Asimov dubbed neutrinos “ghost particles.” John Updike immortalized them in verse. They’ve been the subject of several Nobel Prize citations, because these weird tiny particles just keep surprising physicists. And now we have a much better idea of the upper limit of what their rest mass could be, thanks to the first results from the Karlsruhe Tritium Neutrino experiment (KATRIN) in Germany. Leaders from the experiment announced their results last week at a scientific conference in Japan and posted a preprint to the physics arXiv.
“Knowing the mass of the neutrino will allow scientists to answer fundamental questions in cosmology, astrophysics, and particle physics, such as how the universe evolved or what physics exists beyond the Standard Model,” said Hamish Robertson, a KATRIN scientist and professor emeritus of physics at the University of Washington…
Physicists get small: “Weighing in: Physicists cut upper limit on neutrino’s mass in half.”
* Thomas Hardy, “Two on a Tower”
###
As we step onto the scales, we might spare a thought for Max Karl Ernst Ludwig Planck; he died on this date in 1947. A theoretical physicist, he is best remembered as the originator of quantum theory. It was his discovery of energy quanta that won him the Nobel Prize in Physics in 1918.
You must be logged in to post a comment.