- 3177 - PARTICLES - are waves with mass? Imagine a particle. Chances are you picture a tiny ball, bobbing in space. Now, try to imagine that tiny ball as a particle with no mass. That gets us into particles being waves. What is the difference between particles and waves? It gets complicated. Let’s start with the word “mass”
- ----------------------- 3177 - PARTICLES - are waves with mass?
- Sometimes the word “mass” is used interchangeably with the word “weight.” That’s not entirely wrong. The mass of an object is measured by its resistance to a force. When you pick something up to test its weight, it is resisting the Earth’s gravity, so an everyday object’s weight on Earth is indeed one measurement of its mass.
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- But there’s more to mass than just a resistance to gravity, especially on the scale of the smallest pieces of matter. So physicists’ definition of mass gets more complicated.
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- Most fundamental matter particles, such as electrons, muons and quarks, get their mass from their resistance to a field that permeates the universe called the “Higgs field“. The more the Higgs field pulls on a particle, the more mass it has.
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- When it comes to composite particles like protons and neutrons, which are made up of quarks, most of their mass comes from the pull of the “strong force” that holds the quarks together.
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- Photons and gluons, two force-carrying particles, are fundamental and are unaffected by the Higgs field. Indeed, they seem to be without mass.
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- Massless particles are pure energy. These quanta of energy don’t have edges, and they don't have surfaces. A better way to think of “particles” is as ripples on a “quantum field“.
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- A quantum field has vibration modes like the harmonics on a guitar string. Pluck it with the right frequency and you get a particle.
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- The two particles physicists know to be massless, photons and gluons, are both force-carrying particles, also known as “gauge bosons“. Photons are associated with the electromagnetic force, and gluons are associated with the strong force.
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- The “graviton“, a gauge boson associated with gravity, is also expected be massless, but its existence hasn’t been confirmed yet.
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- These massless particles have some unique properties. They are completely stable, so unlike some particles, they do not lose their energy decaying into pairs of less massive particles.
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- Because all their energy is all “kinetic“, the energy of motion, they always travel at the speed of light. And thanks to special relativity, “things traveling at the speed of light don't actually age.”
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- Gravity affects anything with energy, even a particle that has no mass at all. That’s why the gravitational attraction of objects like galaxies and clumps of dark matter curves the path of light passing by them in space.
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- It could be that the photon and the gluon are not the only massless particles in the universe. Scientists could one day find the graviton. Or, the lightest of the three types of neutrinos has zero mass.
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- If everything in the universe reduces to particles, a question presents itself: What are particles?
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- The easy answer quickly shows itself to be unsatisfying. Namely, electrons, photons, quarks and other “fundamental” particles supposedly lack substructure or physical extent. “We basically think of a particle as a pointlike object. And yet particles have distinct traits, such as charge and mass. How can a dimensionless point bear weight?
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- With any other object, the object’s properties depend on its physical makeup its constituent particles. But those particles’ properties derive not from constituents of their own but from mathematical patterns. As points of contact between mathematics and reality, particles straddle both worlds.
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- The quest to understand nature’s fundamental building blocks began with the ancient Greek philosopher Democritus’s assertion that such things exist. Two millennia later, Isaac Newton and Christiaan Huygens debated whether light is made of particles or waves.
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- The discovery of quantum mechanics some 250 years after that proved both luminaries said light comes in individual packets of energy known as photons, which behave as both particles and waves.
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- “Wave-particle duality” turned out to be a symptom of a deep strangeness. Quantum mechanics revealed to its discoverers in the 1920s that photons and other quantum objects are best described not as particles or waves but by abstract “wave functions”.
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- Wave functions are evolving mathematical functions that indicate a particle’s probability of having various properties.
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- The wave function representing an electron is spatially spread out, so that the electron has possible locations rather than a definite one. Somehow when you stick a detector in the scene and measure the electron’s location, its wave function suddenly “collapses” to a point, and the particle clicks at that position in the detector.
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- A particle is thus a “collapsed wave function“. Why does observation cause a distended mathematical function to collapse and a concrete particle to appear? And what decides the measurement’s outcome? Nearly a century later, physicists have no idea.
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- The picture soon got even stranger. In the 1930s, physicists realized that the wave functions of many individual photons collectively behave like a single wave propagating through conjoined electric and magnetic fields exactly the classical picture of light discovered in the 19th century by James Clerk Maxwell.
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- They found that they could “quantize” classical field theory, restricting fields so that they could only oscillate in discrete amounts known as the “quanta” of the fields. In addition to photons, the quanta of light.
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- Paul Dirac and others discovered that the idea could be extrapolated to electrons and everything else. According to quantum field theory, particles are excitations of quantum fields that fill all of space.
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- “Quantum field theory” stripped particles of status, characterizing them as mere bits of energy that set into fields. As physicists discovered more of nature’s particles and their associated fields, a parallel perspective developed.
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- The properties of these particles and fields appeared to follow numerical patterns. By extending these patterns, physicists were able to predict the existence of more particles. Once you encode the patterns you observe into the mathematics, the mathematics is predictive; it tells you more things you might observe.
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- The patterns also suggested a more abstract and potentially deeper perspective on what particles actually are.
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- Particles are “representations” of “symmetry groups,” which are sets of transformations that can be done to objects.
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- Deep down, energy is simply the property that stays the same when the object shifts in time. Momentum is the property that stays the same as the object moves through space.
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- A third property is needed to specify how particles change under combinations of spatial rotations and boosts which, together, are rotations in space-time. This key property is “spin.”
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- Particle spin is a kind of “intrinsic angular momentum” that determines many aspects of particle behavior, including whether they act like matter (as electrons do) or as a force (like photons).
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- There are particles with three spin degrees of freedom. These particles rotate in the same way as familiar 3D objects. All “matter particles” have two spin degrees of freedom, nicknamed “spin-up” and “spin-down,” which rotate differently. If you rotate an electron by 360 degrees, its state will be inverted and comes back around pointing the opposite way.
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- Particles with the same energy, momentum and spin behave identically but they can differ in other ways. For instance, they can carry different amounts of electric charge. As “the whole particle zoo” was discovered where additional distinctions between particles were revealed, necessitating new labels dubbed “color” and “flavor.”
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- Physicists ascertained that “quarks“, the elementary constituents of atomic nuclei, exist in a probabilistic combination of three possible states, which they nicknamed “red,” “green” and “blue.”
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- These states have nothing to do with actual color or any other perceivable property. It’s the number of labels that matters: Quarks, with their three labels, are representations of a group of transformations called SU(3) consisting of the infinitely many ways of mathematically mixing the three labels.
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- While particles with color are representations of the symmetry group SU(3), particles with the internal properties of “flavor” and “electric charge” are representations of the symmetry groups SU(2) and U(1), respectively.
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- The Standard Model of particle physics which is the quantum field theory of all known elementary particles and their interactions, is often said to represent the symmetry group SU(3) × SU(2) × U(1), consisting of all combinations of the symmetry operations in the three subgroups.
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- The Standard Model is missing the force of gravity, which quantum field theory can’t handle. Albert Einstein’s general theory of relativity separately describes gravity as curves in the space-time fabric.
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- The Standard Model’s three-part SU(3) × SU(2) × U(1) structure raises more questions. Researchers placed even higher hopes in “string theory“: the idea that if you zoomed in enough on particles, you would see not points but one-dimensional vibrating strings. You would also see six extra spatial dimensions, which string theory says are curled up at every point in our familiar 4D space-time fabric.
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- The geometry of the small dimensions determines the properties of strings and thus the macroscopic world. “Internal” symmetries of particles, like the SU(3) operations that transform quarks’ color, obtain physical meaning.
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- These operations map, in the string picture, onto rotations in the small spatial dimensions, just as spin reflects rotations in the large dimensions. Geometry gives you symmetry gives you particles, and all of this goes together.
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- If any strings or extra dimensions exist, they’re too small to be detected experimentally. Over the past decade, two approaches in particular have attracted the brightest minds in contemporary fundamental physics. Both approaches refresh the picture of particles yet again.
- A Particle is a “Deformation of the Qubit Ocean’6“. The first of these research efforts goes by the slogan “it-from-qubit,” which expresses the hypothesis that everything in the universe, all particles, as well as the space-time fabric those particles arises out of quantum bits of information, or qubits.
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- Qubits are probabilistic combinations of two states, labeled 0 and 1. Qubits can be stored in physical systems just as bits can be stored in transistors, but you can think of them more abstractly, as information itself. When there are multiple qubits, their possible states can get tangled up, so that each one’s state depends on the states of all the others. Through these contingencies, a small number of entangled qubits can encode a huge amount of information.
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- In the “it-from-qubit” conception of the universe, if you want to understand what particles are, you first have to understand space-time. Entangled qubits might stitch together the space-time fabric.
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- Thought experiments suggest that space-time has “holographic” properties: It’s possible to encode all information about a region of space-time in degrees of freedom in one fewer dimension, often on the region’s surface.
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- What’s most surprising and fascinating to physicists about this holographic relationship is that space-time includes gravity. But the lower-dimensional system that encodes information about that space-time is a purely quantum system that lacks any sense of curvature, gravity or even geometry. It can be thought of as a system of entangled qubits.
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- Under the it-from-qubit hypothesis, the properties of space-time, its symmetries, essentially come from the way 0’s and 1’s are braided together. The long-standing quest for a quantum description of gravity becomes a matter of identifying the qubit entanglement pattern that encodes the particular kind of space-time fabric found in the actual universe.
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- Our universe is positively curved. But researchers have found, to their surprise, that anytime negatively curved space-time pops up like a hologram. Whenever a system of qubits holographically encodes a region of space-time, there are always qubit entanglement patterns that correspond to localized bits of energy floating in the higher-dimensional world.
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- Algebraic operations on the qubits, when translated in terms of space-time, behave just like rotations acting on the particles
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- When particles collide, amplitudes indicate how the particles might morph or scatter. Normally, to calculate amplitudes, physicists systematically account for all possible ways colliding ripples might reverberate through the quantum fields that pervade the universe before they produce stable particles that fly away from the crash site.
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- The scattering amplitudes involving gravitons, the putative carriers of gravity, turn out to be the square of amplitudes involving gluons, the particles that glue together quarks.
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- We associate gravity with the fabric of space-time itself, while gluons move around in space-time. Yet gravitons and gluons seemingly spring from the same symmetries.
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- “What is a particle?” We don’t know’ is the short answer. Here are some theories:
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1: At the moment that I detect it, it collapses the wave and becomes a particle. The particle is the collapsed wave function.
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2: What is a particle from a physicist’s point of view? It’s a quantum excitation of a field. We write particle physics in a math called quantum field theory. In that, there are a bunch of different fields; each field has different properties and excitations, and they are different depending on the properties, and those excitations we can think of as a particle.
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3: Particles are at a very minimum described by irreducible representations of the Poincaré group.
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4: Particles have so many layers.
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5: What we think of as elementary particles, instead they might be vibrating strings.
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6: Every particle is a quantized wave. The wave is a deformation of the qubit ocean.
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7: Particles are what we measure in detectors. It is the quantum fields that are real, and particles are excitations.
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- And you thought the discussion about ‘what is a particle” and ‘what is a wave’ would be simple! Think again.
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- May 30, 2021 PARTICLES - are waves with mass? 3169
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