Posts Tagged ‘particle physics’
“Protons give an atom its identity, electrons its personality”*…
If the electron’s charge wasn’t perfectly round, it could reveal the existence of hidden particles– and launch a “new physics.” But, as Zack Savitsky reports, a new measurement approaches perfection…
Imagine an electron as a spherical cloud of negative charge. If that ball were ever so slightly less round, it could help explain fundamental gaps in our understanding of physics, including why the universe contains something rather than nothing.
Given the stakes, a small community of physicists has been doggedly hunting for any asymmetry in the shape of the electron for the past few decades. The experiments are now so sensitive that if an electron were the size of Earth, they could detect a bump on the North Pole the height of a single sugar molecule.
The latest results are in: The electron is rounder than that.
The updated measurement disappoints anyone hoping for signs of new physics. But it still helps theorists to constrain their models for what unknown particles and forces may be missing from the current picture…
More at “The Electron Is So Round That It’s Ruling Out Potential New Particles,” from @savagitsky in @QuantaMagazine.
* Bill Bryson
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As we ponder perfection, we might spare a thought for Jean Baptiste Perrin; he died on this date in 1942. A physicist, he studied the Brownian motion of minute particles suspended in liquids (sedimentation equilibrium), and verified Albert Einstein’s explanation of the phenomenon– thereby confirming the atomic nature of matter… for which he was awarded the Nobel Prize for Physics in 1926.
“I have not yet lost a feeling of wonder, and of delight, that the delicate motion should reside in all the things around us”*…
The proton, the positively charged particle at the heart of the atom, is an object of unspeakable complexity, one that changes its appearance depending on how it is probed…
“This is the most complicated thing that you could possibly imagine,” said Mike Williams, a physicist at the Massachusetts Institute of Technology. “In fact, you can’t even imagine how complicated it is.”
The proton is a quantum mechanical object that exists as a haze of probabilities until an experiment forces it to take a concrete form. And its forms differ drastically depending on how researchers set up their experiment. Connecting the particle’s many faces has been the work of generations. “We’re kind of just starting to understand this system in a complete way,” said Richard Milner, a nuclear physicist at MIT.
As the pursuit continues, the proton’s secrets keep tumbling out. Most recently, a monumental data analysis published in August found that the proton contains traces of particles called charm quarks that are heavier than the proton itself.
The proton “has been humbling to humans,” Williams said. “Every time you think you kind of have a handle on it, it throws you some curveballs.”
Recently, Milner, together with Rolf Ent at Jefferson Lab, MIT filmmakers Chris Boebel and Joe McMaster, and animator James LaPlante, set out to transform a set of arcane plots that compile the results of hundreds of experiments into a series of animations of the shape-shifting proton…
Charlie Wood (and Merrill Sherman) have incorporated that work into an attempt to unveil the particle’s secrets: “Inside the Proton, the ‘Most Complicated Thing You Could Possibly Imagine’,” from @walkingthedot in @QuantaMagazine.
* Edmund Burke
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As we ponder presumptive paradoxes, we might send insightful birthday greetings to David Schramm; he was born on this date in 1945. A theoretical astrophysicist, he established the field of particle astrophysics, a branch of particle physics that studies elementary particles of astronomical origin and their relation to astrophysics and cosmology. He was particularly well known for the study of Big Bang nucleosynthesis and its use as a probe of dark matter and of neutrinos. And he made important contributions to the study of cosmic rays, supernova explosions, heavy-element nucleosynthesis, and nuclear astrophysics generally.
“A nothing will serve just as well as a something about which nothing could be said”*…
Metaphysical debates in quantum physics don’t get at “truth,” physicist and mathematician Timothy Andersen argues; they’re nothing but a form of ritual activity and culture. After a thoughtful intellectual history of both quantum mechanics and Wittgenstein’s thought, he concludes…
If Wittgenstein were alive today, he might have couched his arguments in the vocabulary of cultural anthropology. For this shared grammar and these language games, in his view, form part of much larger ritualistic mechanisms that connect human activity with human knowledge, as deeply as DNA connects to human biology. It is also a perfect example of how evolution works by using pre-existing mechanisms to generate new behaviors.
The conclusion from all of this is that interpretation and representation in language and mathematics are little different than the supernatural explanations of ancient religions. Trying to resolve the debate between Bohr and Einstein is like trying to answer the Zen kōan about whether the tree falling in the forest makes a sound if no one can hear it. One cannot say definitely yes or no, because all human language must connect to human activity. And all human language and activity are ritual, signifying meaning by their interconnectedness. To ask what the wavefunction means without specifying an activity – and experiment – to extract that meaning is, therefore, as sensible as asking about the sound of the falling tree. It is nonsense.
As a scientist and mathematician, Wittgenstein has challenged my own tendency to seek out interpretations of phenomena that have no scientific value – and to see such explanations as nothing more than narratives. He taught that all that philosophy can do is remind us of what is evidently true. It’s evidently true that the wavefunction has a multiverse interpretation, but one must assume the multiverse first, since it cannot be measured. So the interpretation is a tautology, not a discovery.
I have humbled myself to the fact that we can’t justify clinging to one interpretation of reality over another. In place of my early enthusiastic Platonism, I have come to think of the world not as one filled with sharply defined truths, but rather as a place containing myriad possibilities – each of which, like the possibilities within the wavefunction itself, can be simultaneously true. Likewise, mathematics and its surrounding language don’t represent reality so much as serve as a trusty tool for helping people to navigate the world. They are of human origin and for human purposes.
To shut up and calculate, then, recognizes that there are limits to our pathways for understanding. Our only option as scientists is to look, predict and test. This might not be as glamorous an offering as the interpretations we can construct in our minds, but it is the royal road to real knowledge…
A provocative proposition: “Quantum Wittgenstein,” from @timcopia in @aeonmag.
* Ludwig Wittgenstein, Philosophical Investigations
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As we muse on meaning, we might recall that it was on this date in 1954 that the official ground-breaking for CERN (Conseil européen pour la recherche nucléaire) was held. Located in Switzerland, it is the largest particle physics laboratory in the world… that’s to say, a prime spot to do the observation and calculation that Andersen suggests. Indeed, it’s been the site of many breakthrough discoveries over the years, maybe most notably the 2012 observation of the Higgs Boson.
Because researchers need remote access to these facilities, the lab has historically been a major wide area network hub. Indeed, it was at CERN that Tim Berners-Lee developed the first “browser”– and effectively fomented the emergence of the web.
“For the moment we might very well can them DUNNOS (for Dark Unknown Nonreflective Nondetectable Objects Somewhere)”*…
When does one give up on a hypothesis?…
In 1969, the American astronomer Vera Rubin puzzled over her observations of the sprawling Andromeda Galaxy, the Milky Way’s biggest neighbour. As she mapped out the rotating spiral arms of stars through spectra carefully measured at the Kitt Peak National Observatory and the Lowell Observatory, both in Arizona, she noticed something strange: the stars in the galaxy’s outskirts seemed to be orbiting far too fast. So fast that she’d expect them to escape Andromeda and fling out into the heavens beyond. Yet the whirling stars stayed in place.
Rubin’s research, which she expanded to dozens of other spiral galaxies, led to a dramatic dilemma: either there was much more matter out there, dark and hidden from sight but holding the galaxies together with its gravitational pull, or gravity somehow works very differently on the vast scale of a galaxy than scientists previously thought.
Her influential discovery never earned Rubin a Nobel Prize, but scientists began looking for signs of dark matter everywhere, around stars and gas clouds and among the largest structures in the galaxies in the Universe…
But… over the past half century, no one has ever directly detected a single particle of dark matter. Over and over again, dark matter has resisted being pinned down, like a fleeting shadow in the woods. Every time physicists have searched for dark matter particles with powerful and sensitive experiments in abandoned mines and in Antarctica, and whenever they’ve tried to produce them in particle accelerators, they’ve come back empty-handed. For a while, physicists hoped to find a theoretical type of matter called weakly interacting massive particles (WIMPs), but searches for them have repeatedly turned up nothing.
With the WIMP candidacy all but dead, dark matter is apparently the most ubiquitous thing physicists have never found. And as long as it’s not found, it’s still possible that there is no dark matter at all. An alternative remains: instead of huge amounts of hidden matter, some mysterious aspect of gravity could be warping the cosmos instead…
Dark matter is the most ubiquitous thing physicists have never found; Ramin Skibba (@raminskibba) wonders if it isn’t time to consider alternative explanations: “Does dark matter exist?” in @aeonmag.
* Bill Bryson on dark matter, in A Short History of Nearly Everything (2003)
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As we interrogate the invisible, we might send observant birthday greetings to Val Logsdon Fitch; he was born on this date in 1923. A particle physicist, he shared the 1964 Nobel Prize in Physics with his collaborator James Cronin for their experiments proving that some subatomic reactions do not adhere to fundamental symmetry principles (and are therefore indifferent to the direction of time).
By examining the decay of K-mesons, they proved that a reaction run in reverse does not retrace the path of the original reaction, which showed that the reactions of subatomic particles are not indifferent to time. Thus the phenomenon of CP violation was discovered… and thus was demolished the faith that physicists had previously had that natural laws were universally governed by symmetry.
“Men knew better than they realized, when they placed the abode of the gods beyond the reach of gravity”*…
In search of a theory of everything…
Twenty-five particles and four forces. That description — the Standard Model of particle physics — constitutes physicists’ best current explanation for everything. It’s neat and it’s simple, but no one is entirely happy with it. What irritates physicists most is that one of the forces — gravity — sticks out like a sore thumb on a four-fingered hand. Gravity is different.
Unlike the electromagnetic force and the strong and weak nuclear forces, gravity is not a quantum theory. This isn’t only aesthetically unpleasing, it’s also a mathematical headache. We know that particles have both quantum properties and gravitational fields, so the gravitational field should have quantum properties like the particles that cause it. But a theory of quantum gravity has been hard to come by.
In the 1960s, Richard Feynman and Bryce DeWitt set out to quantize gravity using the same techniques that had successfully transformed electromagnetism into the quantum theory called quantum electrodynamics. Unfortunately, when applied to gravity, the known techniques resulted in a theory that, when extrapolated to high energies, was plagued by an infinite number of infinities. This quantization of gravity was thought incurably sick, an approximation useful only when gravity is weak.
Since then, physicists have made several other attempts at quantizing gravity in the hope of finding a theory that would also work when gravity is strong. String theory, loop quantum gravity, causal dynamical triangulation and a few others have been aimed toward that goal. So far, none of these theories has experimental evidence speaking for it. Each has mathematical pros and cons, and no convergence seems in sight. But while these approaches were competing for attention, an old rival has caught up.
The theory called asymptotically (as-em-TOT-ick-lee) safe gravity was proposed in 1978 by Steven Weinberg. Weinberg, who would only a year later share the Nobel Prize with Sheldon Lee Glashow and Abdus Salam for unifying the electromagnetic and weak nuclear force, realized that the troubles with the naive quantization of gravity are not a death knell for the theory. Even though it looks like the theory breaks down when extrapolated to high energies, this breakdown might never come to pass. But to be able to tell just what happens, researchers had to wait for new mathematical methods that have only recently become available…
For decades, physicists have struggled to create a quantum theory of gravity. Now an approach that dates to the 1970s is attracting newfound attention: “Why an Old Theory of Everything Is Gaining New Life,” from @QuantaMagazine.
* Arthur C. Clarke, 2010: Odyssey Two
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As we unify, we might pause to remember Sir Arthur Stanley Eddington, OM, FRS; he died in this date in 1944. An astrophysicist, mathematician, and philosopher of science known for his work on the motion, distribution, evolution and structure of stars, Eddington is probably best remembered for his relationship to Einstein: he was, via a series of widely-published articles, the primary “explainer” of Einstein’s Theory of General Relativity to the English-speaking world; and he was, in 1919, the leader of the experimental team that used observations of a solar eclipse to confirm the theory.
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