Posts Tagged ‘subatomic particles’
“Reality is that which, when you stop believing in it, doesn’t go away”*…
Particles are nature’s smallest constituents, but that doesn’t mean they’re fundamental. So of what, physicist Felix Flicker asks, does the Universe consist?…
What is the world made of? For centuries, people have believed that matter is constructed from tiny, indivisible parts. Some of the earliest known references come from the Greek philosopher Democritus, who taught that the Universe was composed of atoms the size of dust motes floating in sunlight. Theravada Buddhism developed the concept of kalapas, indivisible bundles of properties fleeting into and out of existence. Alchemy’s description of fundamental ‘corpuscles’, expounded by Isaac Newton and others, derived from translations of Aristotle by mediaeval Islamic scholars. And Hideki Yukawa, winner of the 1949 Nobel Prize in Physics for his work developing the modern theory of elementary particles, took inspiration from a passage in the Zhuangzi, a Daoist text written during China’s warring states period, in which fast-moving entities puncture holes within formless chaos. Yukawa saw a parallel to particle collisions.
The concept of a particle, as we now refer to these indivisible parts, has therefore been repeatedly re-introduced in contradictory ways. The modern view continues this tradition. In late-19th-century physics, particles were tiny indivisible objects with well-defined positions and momenta. The advent of quantum mechanics led these clear waters to become muddied. But the basic idea persists: we are taught from a young age that matter is made of atoms, built from particles such as electrons, and electrons are not built from anything else. For this reason, these particles are sometimes said to be fundamental. But are they? Is the Universe really made from the smallest constituents, as a beach is made from sand?
The answer to this question, I will contest, is perhaps a surprising one: yes, the Universe is built from fundamental units – but fundamental need not mean smallest. This view is generally adopted by those physicists, such as myself, who work in the largest discipline within the subject: quantum matter. This is the study of quantum behaviours that manifest on everyday scales: the attraction of iron to a magnet, the flow of electricity along a wire, or the passage of sound through a crystal. In these settings, too, we find particles. But these particles are not elementary, like the electron: they are emergent.
The distinction can be pictured as follows. Imagine a lightbulb, its rays of light travelling to your eyes. We can ask what those rays are made of. Quantum mechanics has an answer: a ray of light is a stream of individual particles called photons. In turn, we can ask what the photons are made of. The answer this time is that they are not made of anything else: they are elementary. Now imagine that this lightbulb is of a vintage sort, and gives off a gentle hum. It emits waves of sound that travel to your ears. We can again ask what those waves are made of. And, once again, quantum mechanics has an answer: a wave of sound can be described by individual particles called phonons. Now, if you are familiar with the Standard Model of particle physics, you will know that it contains photons but not phonons. The reason is that phonons are not elementary. If you ask what a phonon is made of, there is an answer: it is a pattern of vibrations of the atoms in the air. In the study of quantum matter, however, we say it is an emergent particle.
So what are emergent particles? Are they as real as elementary particles? And, perhaps most importantly, can they tell us anything new about the nature of reality?…
[Flicker answers the first two of those questions, then turns to the third…]
… So, are elementary particles emergent? Even if we can ever answer this, we will be faced with the same question, whatever we find. In the end, whether you like the idea comes down to personal taste and, perhaps, a degree of cultural upbringing. The more widely publicised attempts at a ‘theory of everything’ always struck me as suspiciously similar to themes in the Old Testament: the Universe was once describable by a single mathematical formula, but that one, true quantum field spontaneously broke in a cataclysmic event that resulted in the messy collection of particles we find before us. I find that the quantum matter perspective, on the other hand, resonates with me in a similar manner to the Daoist texts such as the Zhuangzi. From this new perspective, it is our current world that is beautiful. It grew from a swamp of possible theories, each ugly in its arbitrariness: it doesn’t matter which way we followed, as they all lead here…
A physicist argues that our universe is more than the sum of its particles: “Reality Emerges,” from @aeon.co.
Resonant: “There Is No ‘Hard Problem Of Consciousness’,” from Carlo Rovelli
Also apposite (and fascinating): “Physicists just found a tiny flaw in time itself,” from ScienceDaily.
* Philip K. Dick
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As we muse on materialization, we might send insightful birthday greetings to Jack Steinberger; he was born on this date in 1921. An experimental physicist, he worked on sub-atomic particles– the “elementary” constituents of matter discussed above– at Columbia, UC Berkeley, and CERN. He shared the 1988 Nobel Prize in Physics (with Leon M. Lederman and Melvin Schwartz) for the discovery of the muon neutrino.
“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.
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