Posts Tagged ‘Physics’
“It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.”*…
Einstein fought to save our everyday notion of reality from the strangeness of quantum mechanics. But, as Charlie Wood reports, those who set out to aid him keep poking holes in his argument…
One of a human’s earliest developmental milestones is an understanding of object permanence. It generally takes less than a year for a baby to realize that when an adult hides their face behind their hands in a game of peek-a-boo, they don’t cease to exist. There’s more to the world around us than what we perceive.
This suggests — or at least, it suggested to Albert Einstein — that the world is “real,” in the sense that things in the world have properties that are intrinsically true no matter what anyone thinks. A red billiard ball is red, even in the dark, and even if no one is checking its color. The redness is a property belonging to the ball, not to some device measuring the ball, and not to the mind of some person operating the measuring device.
Yet quantum mechanics, a thoroughly validated theory of how the world works, seems to suggest otherwise. The theory’s math assigns redness to the billiard ball at the moment you measure it. Before then, the theory gives you only a set of probabilities telling you what color the ball might be. Key founders of quantum mechanics suggested that this math reflects the nature of reality — that in some sense, a single, objective reality doesn’t really exist.
In 1935, Einstein rebelled against this surreal reading of quantum theory, proposing one of the 20th century’s most famous thought experiments. But his rebellion was doomed. In 1964, the physicist John Stewart Bell showed with a thought experiment of his own that reality had to be stranger than Einstein assumed. Subsequent work would put Bell’s thought experiment to the test — and prove him right.
Then, 50 years after Bell, Matthew Pusey, at the time a graduate student at Imperial College London, took on what remained of Einstein’s notion of reality and — without originally intending to — delivered the killing blow.
The paradigm-shifting theorem became known as PBR, for Pusey and his academic accomplices, Jonathan Barrett and Terry Rudolph. Since the publication of PBR in 2012, many theorists have come to accept that it rules out our most commonsense understanding of reality.
“From the moment [PBR] came out, people knew it would be a landmark,” said Jacques Pienaar, a physicist now at the Federal University of Rio de Janeiro in Brazil.
At the time, Pienaar, like Pusey, had been walking in Einstein’s footsteps, dabbling in theories designed to show that objective reality exists and that quantum mechanics merely describes our incomplete knowledge of it. But when the PBR theorem appeared, Pienaar remembers thinking, “That’s it. The program’s dead.”
This is the story of how Einstein, Bell, and finally Pusey and his collaborators killed reality as we know it. In three theorems, they proved that quantum mechanics is incompatible with the world we perceive. And since experiment after experiment — including a recent realization of PBR — has established that quantum mechanics is the law of the land, something about reality has to go.
The question that remains is: How much do we have to give up?…
[Wood recounts the fascinating history of attempts to grapple with the issue, which have, cumulatively, strengthened the conclusions (and thus implications) of PBR. As to those implications, he concludes…]
… Many physicists have taken PBR to mean that the quantum state must be real — an objective property living in particles, people, and planets. If so, impossible-seeming events like collapse must also have some physical correlate. This stance amounts to taking the extreme path of Bohmian mechanics and other “realist” interpretations. As Pusey pithily puts it, PBR guarantees that “if anything is real, the quantum state is real.”
But to conclude that the quantum state is definitely real is to misunderstand the PBR theorem, because PBR also leaves open the other extreme path: It could be, as the Copenhagenists have steadfastly maintained since the days of Bohr, that in some sense nothing is real, including the quantum state. It’s perfectly possible that the quantum state lives in our minds and has no direct connection to an objective reality. In this case, the redness of the billiard ball would be inextricably linked with the act of observing it — precisely the state of affairs that so deeply offended Einstein. “Do you really believe the moon is not there when you are not looking at it?” Einstein once famously pressed his colleague Abraham Pais.
PBR doesn’t give us the answer. What it does do is end a century of bargaining with quantum mechanics. By ruling out the possibility that reality is real while the wave function is not, PBR requires that physicists either fully embrace the notion of an objective but entirely surreal reality, or fully reject objective reality altogether. “Do you bite the bullet, or do you try and dodge the bullet?” Pusey said.
Pienaar was one of the few physicists who were still playing around with middle-of-the-road theories, though with waning interest. PBR contributed to his choice to give up on objective reality once and for all. He switched to a modern offshoot of Copenhagenism known as QBism.
QBism asserts that the world itself may exist, but quantum mechanics can’t describe it. All the theory can really do is capture our relationship to — and subjective experience of — the world. “You need two to tango,” Pienaar said. “Without two systems, there’s no relation. And reality is nothing but relations.”
And yet, some physicists remain unsatisfied with the two extreme options: a surreal reality or no reality. So they are beginning to pick at the fine print on the technical definition of reality. “Maybe the correct way of thinking about a state of reality is something a bit more woolly, that doesn’t quite fit into this straitjacket,” Pusey said.
In this spirit, Hardy questions whether reality needs to necessarily have a single, objective state at every given moment. Perhaps states could somehow spread out across multiple moments. He doesn’t yet have a fully fleshed-out proposal, but his goal is to come up with a deeper, more general notion of reality that is still recognizable.
If underdogs like Hardy succeed in saving some notion of reality, it won’t quite be the one Einstein wanted; Bell and PBR guarantee that. But it may yet turn out to be the sort of reality Einstein needed, one that makes enough intuitive sense to win the hearts and minds of physicists, especially those fatigued from a lifetime of labyrinthine debates about what is real. “It needs to have the ring of truth, so that when people see it, they can’t unsee it,” Schmid said.
Curiouser and curiouser: “A Strange Quantum Theorem Has Killed Einstein’s Reality,” from @walkingthedot.bsky.social in @quantamagazine.org.
* Niels Bohr, who also famously– and relevantly– observed: “Those who are not shocked when they first come across quantum theory cannot possibly have understood it.”
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As we get real, we might recall that it was on this date in 1974 that the discovery of the “charmed quark” subatomic particle was announced simultaneously by the two American experimental groups responsible: an MIT group at Brookhaven National Laboratory, and a SLAC-Berkeley group at the Stanford Linear accelerator center.
The existence of the charm quark was first predicted by James Bjorken and Sheldon Glashow in 1964. The new particle, made up of a charm quark and its antimatter opposite, anti-charm, was the fourth quark to be indentified; with a mass of 3095 MeV (or 1.27±0.02 GeV/c2), it had a lifetime about 1000 times longer than that of other particles of comparable mass. Its announcement set the world of high energy physics on fire and is now known in the physics community as “the November revolution.”
For their photo-finish discoveries, the scientists leading those groups, Samuel Ting and Burton Richter, were awarded the Nobel Prize in Physics in 1976.
“In our world of big names, curiously, our true heroes tend to be anonymous”*…
Your correspondent is headed off-line for a few days, so (R)D will be off until Monday, October 19, when (airline performance permitting) regular service should resume…
Billions of computers and phones run on code looked after by a handful of mostly-volunteer people. On his lovely site sheets.works, Akash Wadhwani introduces us to some of those generous souls…
People post [the comic above] whenever something breaks. The tower is labelled “all modern digital infrastructure” and it stands on one small block, “a project some random person in Nebraska has been thanklessly maintaining since 2003”.
We wanted to know how close to true it is. We downloaded the full history of 23 pieces of software that phones, browsers and servers depend on, and counted everyone who made ten or more changes to each one between October 2025 and October 2026. Then we listed what is actually installed on an Android phone, an iPhone and a Windows PC…
Wadhwani opens with the story of Paul Eggert…
Your alarm, a boarding pass, a meeting in another country, the day your salary lands: anything on your phone that shows a time has to know where you are. Underneath sit every Android phone, every iPhone and most of the servers on the internet.
They all get local time from one text file, the time zone database, which holds every clock rule a government has ever announced. Paul Eggert, a lecturer at UCLA, keeps that file up to date in his spare time [and has since 2012].
4,000,000,000 Android phones and iPhones use his file. We didn’t count servers, Macs or laptops, which would push the number higher.
On 29 September Paul put out version 2026e of the file. The first line of its notes says that Manitoba moves to permanent -05 on 31 October, which tells phones in Winnipeg not to set their clocks back on 1 November, and it was typed in by two volunteers a month ahead…
Read on for 22 other tales of extraordinary generosity: “The people holding up the internet.”
* Daniel J. Boorstin, The Image: A Guide to Pseudo-events in America
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As we give thanks, we might spare a thought for a man who, if not un-sung, has been at least under-sung: Walter M. Elsasser; he died on this date in 1991. A physicist, he contributed to science across several disciplines. In atomic physics, he interpreted electron scattering. In geophysics, during the 1940’s, he provided insight into radiative heat transfer in the Earth’s atmosphere, and developed the currently-accepted dynamo theory to explain the origin and properties of the Earth’s magnetic field. And he pioneered study of the magnetic orientation of minerals in rocks to reveal the Earth’s history of its magnetic field.
The last fifty years of his life were in large measure spent on biology, more particularly on Systems Biology: Elsasser worked toward a theory of organisms (an effort to establish the distinction between living and inanimate matter). His thinking is still at play in both Complex Systems Biology and Relational Biology.
“Merely fact-minded sciences make merely fact-minded people”*…
As we float awash in the debate over who/what is conscious (only humans? animals? plants? AI? everything?), we might take a moment to ponder the role of consciousness. For example, in science.
Harald A. Wiltsche argues that physicists, and scientists in general, attempt to paint an objective picture of reality. Consciousness, experience, and subjectivity are forcibly pushed out of the picture. Indeed, even where science is empirical, this empiricism rarely involves a consideration of human consciousness, but rather the readings of some mechanical measuring device, or some hypothetical abstracted sum of all perspectives – a God’s eye view or view from nowhere.
A phenomenologist of science, Wiltsche paints a different picture. Physics, even in the form of quantum mechanics, has its origins in the phenomenology of human consciousness. No matter how hard scientists try, it can never escape those origins, and to truly move forward, it must understand and embrace them…
Physics and phenomenology are usually taken to inhabit different worlds. Physics aims at a description of objective reality in mathematical terms. Phenomenology—the philosophical movement inaugurated by Edmund Husserl—is an a priori investigation into consciousness and into the ways things appear in experience. Physics deals with equations, invariants, and symmetries, aiming to represent reality minus observers; phenomenology seems to concern precisely what physics leaves out: subjectivity, consciousness, meaning. If the two meet at all, it is only in polite, but ultimately inconsequential, interdisciplinary dialogue.
My claim is that this picture is mistaken. Physics does not stand outside phenomenology. It presupposes the very structures phenomenology seeks to analyse—above all, the structured correlation between subject and object through which objectivity first becomes intelligible. The task, therefore, is not to unite two distant domains, but to recognize a relation that has been there from the beginning…
[Wiltsche makes his point first with reference to spacetime physics, then to quantum mechanics. He concludes…]
… The question, then, is no longer whether physics and phenomenology should be united. As physics confronts its own conceptual foundations, the challenge is to bring into view the structures phenomenology has analyzed since its inception—and to explore how they can illuminate the meaning of objectivity in modern theory.
Eminently worth reading in full.
Physics cannot escape its roots in phenomenology: “Consciousness is the hidden architecture behind fundamental and quantum physics” (or archived version here) from @haraldwiltsche.bsky.social in @iai.tv.
Bonus question: if Wiltsche is right that consciousness is essential to advancing our understanding of reality, and consciousness is something that other things, living and “inanimate,” (do or can) possess, what does that mean for our quest to understand realit(ies)?… Or does a question like this simply (albeit implicitly) affirm anthropocentrism? How will we know?
See also: “A physicist is just an atom’s way of looking at itself“
* Edmund Husserl
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As we contemplate consciousness, we might note that it was on this date in 1977, at the High Wyncombe Town Hall in England, that the Bunch of Stiffs tour kicked off. It featured Nick Lowe’s Last Chicken in the Shop, Elvis Costello and The Attractions, Ian Dury and the Blockheads, Wreckless Eric and The New Rockets, and Larry Wallis’ Psychedelic Rowdies– acts managed by Dave Robinson and Jake Riviera before they formed the Stiff Records label, which released a live album of the festivities in February of 1978.
“A physicist is just an atom’s way of looking at itself”*…
Encouraged by successes in understanding black holes, theoretical physicists are applying what they’ve learned to whole universes. As Matt von Hippel explains, what they’re finding has them questioning fundamental assumptions about how physics ought to be done…
Tinkering at their desks with the mathematics of quantum space and time, physicists have discovered a puzzling conundrum. The arcane rules of quantum theory and gravity let them imagine many different kinds of universes in precise detail, enabling powerful thought experiments that in recent years have addressed long-standing mysteries swirling around black holes.
But when a group of researchers examined a universe intriguingly like our own in 2019, they found a paradox: The theoretical universe seemed to admit only a single possible state. It appeared so simple that its contents could be described without conveying even a single bit of data, not even a choice of a zero or a one. This result clashed with the fact that this type of universe should be capable of hosting black holes, stars, planets — and people. Yet all those rich details were nowhere to be seen.
“We look around, and certainly the world seems more complex than that,” said Rob Myers, a theoretical physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, who has not been directly involved in this research.
Physicists have good reason to trust the calculation, which builds on fundamental physical ideas. The math implies a universe with only one state; our universe is clearly not like that. Now a team of theorists has floated a possible answer. The paradoxical result occurred when physicists sought an objective description of the state of an entire universe. But a description like that might not be possible, even in principle. It implicitly assumes a universe that exists without an observer to observe it. And perhaps without observers, the complexity of the universe loses its meaning…
[von Hippel unpacks the scientific thinking that led to this conundrum. He concludes with an account of recent work by Ying Zhao that hints at a resolution…]
… Quantum mechanics requires a distinction between an observer — such as the scientist carrying out an experiment — and the system they observe. The system tends to be something small and quantum, like an atom. The observer is big and far away, and thus well described by classical physics… Perhaps an observer could do the same to these closed, impossibly simple-seeming universes?
In 2024, Zhao moved to the Massachusetts Institute of Technology, where she began to work on the problem of how to put an observer into a closed universe. She and two colleagues —Daniel Harlow and Mykhaylo Usatyuk — thought of the observer as introducing a new kind of boundary: not the edge of the universe, but the boundary of the observer themself. When you consider a classical observer inside a closed universe, all the complexity of the world returns, Zhao and her collaborators showed.
The MIT team’s paper came out at the beginning of 2025, around the same time that another group came forward with a similar idea. Others chimed in to point out connections to earlier work.
At this stage, everyone involved emphasizes that they don’t know the full solution. The paradox itself may be a misunderstanding, one that evaporates with a new argument. But so far, adding an observer to the closed universe and trying to account for their presence may be the safest path.
“Am I really confident to say that it’s right, it’s the thing that solves the problem? I cannot say that. We try our best,” Zhao said…
“Cosmic Paradox Reveals the Awful Consequence of an Observer-Free Universe,” from @quantamagazine.org.
Apposite: “Biology Might Not Be Quantum, but Its Math Is Quantumlike“
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As we keep an eye out, we might send cosmological birthday greetings to Enrico Fermi; he was born on this date in 1901. A physicist and Nobel Laureate (1938) for his discovery of nuclear reactions brought about by slow neutrons, he is best remembered for (literally) presiding over the birth of the Atomic Age. Fermi was perhaps especially remarkable as the last “double-threat” in his field: a genius at creating both important theories and elegant experiments. As observed before (and illustrated above :), the division of labor between theorists and experimentalists has since been pretty complete.
The novelist and historian of science C. P. Snow wrote that “if Fermi had been born a few years earlier, one could well imagine him discovering Rutherford’s atomic nucleus, and then developing Bohr’s theory of the hydrogen atom. If this sounds like hyperbole, anything about Fermi is likely to sound like hyperbole.”
“Great inventions are never, and great discoveries are seldom, the work of any one mind. Every great invention is really an aggregation of minor inventions, or the final step of a progression. . It is not usually a creation, but a growth, as truly so as is the growth of the trees in the forest.”*…
Our old friend (and here and here) Brian Potter thinks deeply about scientific and technological advance. Here, he ponders the pace of progress…
In her book on the history of the laser, historian Joan Bromberg notes that the technological and scientific predecessors of the maser (which itself preceded the laser – two critical technologies whose developmental histories I sketched in this piece two months ago) were in place for decades before physicist Charles Townes had the insight to combine them…
… This sort of decades-long wait between when a technology first becomes possible, and when it actually appears, seems common, or at least seems like it might be common. I’ve previously written about why it took so long for wind power to be widely deployed after it became technologically possible, and people often idly speculate whether inventors in the Roman Empire could have built a steam engine, or why we waited so long to put wheels on luggage.
Knowing how long this gap between when an invention becomes possible, and when it actually appears, is useful, because it tells us something about the nature of technology and technological progress. What factors govern whether some new technology appears? How much does mere technical possibility matter, and how much do things like cross-pollination of knowledge, economic feasibility, and political factors contribute? Knowing more about how long it takes for an invention to appear once it becomes technically possible can help us answer these sorts of questions.
I wanted a better sense of how long it takes for some technology to appear once its necessary predecessors are in place. So I used AI to try and find out…
[Potter explains his method, then unpacks his results…]
We can clearly see a few trends on this graph. One is that for most inventions, the gap between when it could have been invented and when it was actually invented is not particularly large. Of the 166 inventions Claude estimated a date for, 107 of them (64%) had an “earliest plausible” date 50 years or less from the actual date, and 150 of them (90%) had an “earliest straightforward” date 50 years or less from the actual date. For more than half the inventions, the average earliest straightforward date of invention was 10 years or less from the actual date.
Conversely, there were a relatively small number of inventions where the gap between “could have been invented” and “was invented” was very large. 30 inventions (18%) had an average gap of more than 100 years between “earliest plausible” and actually invented, and eight inventions had a gap of more than 1000 years. You can see this clearly on a histogram, which shows a large bump of small time gaps, and a long tail of fewer, larger gaps.
The inventions with the longest period between “could have been invented” and “was invented” are below.
There’re a few interesting trends observable here. Many of the longest-delayed inventions — the hypodermic needle, general anaesthetic, stethoscope — are medical inventions. (You could argue the surgical mask could be in this category as well). For the hypodermic needle, this probably needed to wait until the existence of some substance that needed to be injected (such as morphine, first synthesized in 1804), but for other medical inventions this possibly also reflects folks’ reluctance to do inventive-tinkering in a medical context. For general anaesthetic, for instance, the trial and error of getting the dose right was incredibly dangerous, and the inventor Hanaoka Seishu “crippled his mother and blinded his wife perfecting the dose.”
Several of the longest-awaited inventions are ones where the version in the list is an early, impractical version of the one that actually solved a problem. So the “dandy horse” — a two-wheeled, wooden vehicle that was a predecessor of the bicycle — could have been built in antiquity, but the dandy horse wasn’t particularly practical as a means of transportation, and actually useful bicycles had to wait for the improved manufacturing technology of the later 19th century. Likewise, the version of the ballpoint pen that Claude thinks could have been invented much earlier is John Loud’s 1888 version, but Loud’s pen worked poorly and wasn’t successful. Actually useful ballpoint pens are surprisingly difficult to manufacture (China famously couldn’t manufacture them until very recently), and credit for the “useful ballpoint pen” is usually given to Lazlo Biro in 1938. (Claude correctly notes that “useful” versions of both these inventions would need to wait until much later.) Judson’s early zipper and de Martinsville’s early sound-recording device are also examples of early, not-particularly-useful inventions.
Other inventions on this list seem like they might be a case of the surrounding social or technological conditions needing to be right for the invention to appear. So Otis’ elevator safety brake needed to wait until elevators were in higher demand, which probably didn’t occur until steam engines or some other similar power source came along (though maybe you could have water-driven elevators much earlier). Barbed wire perhaps needed to wait until enclosing very large areas of land for grazing became something people needed to do.
And some inventions seem like they might have been genuinely useful had someone thought of them earlier, and simply nobody did. Blanchard’s pattern-tracing lathe, Neilson’s hot blast, and the safety pin all seem like they fall into this category, though perhaps there were good reasons these didn’t appear earlier.
Going back to the scatterplot, the other obvious trend on this chart is that the gap between when an invention becomes possible and when it appears has narrowed over time. If we graph the average and median gaps for inventions by 20-year time periods, we can see that they have fallen over time.
For the 60 post-1900 inventions, every one has a “straightforward” invention date of 50 years or less than the actual date, and 75% of them have a straightforward date of 10 years or less before the actual date. Of the 30 inventions with a gap of more than 100 years between when they could have been invented and when they actually appeared, 29 of them were invented before 1900. So the process for creating new inventions seems to be getting more and more efficient — opportunities are getting noticed and exploited sooner and sooner, up through 1970 at least (which is when the list of major inventions extends to).
We can also look at how wait times vary by type of technology. The chart below shows average wait times by different categories, for both inventions overall and for just post-1900 inventions. We can see that medical inventions have the longest wait, while electronic inventions have the shortest wait…
… We can also look at what types of factors tend to be bottlenecks. For some inventions, the bottleneck is primarily scientific: the limiting factor for the transistor is the band theory of quantum mechanics, and the limiting factor for the radio was Hertz’s demonstration of electromagnetic waves. But for other inventions, it’s primarily technological: the turbojet had to wait not for some new physical theory, but until compressor technology and high-temperature steels appeared; likewise the airplane had to wait not for some novel theory of aerodynamics but until a light enough engine appeared. The chart below shows how often “science” or “technology” was the limiting factor for a given invention, for both inventions overall and post-1900 inventions.
In both cases, technology is the bottleneck far more often than science (though of course if you removed enough technological bottlenecks eventually you’d hit a scientific one, and vice versa).
There is of course only so much you can learn from this sort of exercise: at the end of the day, this is based on an AI’s best guess, not a thorough analysis of the various controlling factors by experts. But while I wouldn’t swear to its accuracy, I think the answers are probably mostly pretty good, and enough for us to draw some general (if tentative) conclusions about the nature of technological progress.
My main takeaway is that we mostly don’t wait all that long for new inventions. Since 1800 most inventions have appeared within a few decades of when it was possible to build them, and since 1900 these gaps been even narrower. It also seems likely that medical inventions are more likely to have long wait times than other types of inventions, and that the limiting factor for how early some new technology could appear is most likely to be technological, rather than scientific.
On the (maybe suprisingly) quick– and quickening– pace of progress: “How Long Do We Wait for New Inventions?” from @constructionphysics.skystack.xyz
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As we analyze advance, we might send inventive birthday greetings to William Webster (W. W.) Hansen; he was born on this date in 1909. A physicist and one of the founders of the technology of microwave electronics, he had a central hand in the development of klystron technology (essential to high frequency amplification, thus central to microwave technology, radar, and UHF television transmission), and linear accelerators (he led the development of SLAC), and along with the Varian brothers and Edward Ginzton, co-founded Varian Associates (in 1948)–one of the first high-tech companies in Silicon Valley.
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