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---------------------------------- 2240 - Particle Physics - and quantum fields
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- Our Universe made out of particles found in the Periodic Table and in Fields. Every type of matter is composed of the known particles of the Standard Model of Particle Physics. Dark Matter is theorized to be a particle, while dark energy is theorized to be a field inherent to space itself.
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- All the particles that exist are even believed to be just excited quantum fields themselves. What gives them the properties that they have?
- If we model particle properties as excitations of various independent quantum fields (For example: the Higgs field for mass, the electromagnetic field for charge) then what field keeps these fields together?
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- What makes a particle have the properties that it does when traveling in these fields?
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- The particles and antiparticles of the Standard Model have now all been directly detected even the last one, the Higgs Boson. All of these particles can be created at energies produced by the Large Hadron Collider in CERN, Switzerland.
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- The masses of these particles lead to fundamental constants that are absolutely necessary to describe them fully. These particles can be described by the physics of the quantum field theories underlying the Standard Model, but whether they are truly fundamental is not known.
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- The particles that we know of have traits that appear to be inherent to them. All particles of the same type (electrons, muons, up quarks, Z-bosons, etc.) are, at some level, indistinguishable from one another. They all have a slew of properties that all other particles of the same type share, including:
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------------------------------ mass,
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------------------------------ electric charge,
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------------------------------ weak hypercharge
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------------------------------ spin (inherent angular momentum),
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------------------------------ color charge,
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------------------------------ baryon number,
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------------------------------ lepton number,
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------------------------------ lepton family number,
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- Some particles have a value of zero for many of these quantities; others have non-zero values for almost all of them. But somehow, every particle that exists contains all of these particular, intrinsic properties bound together in a single, stable, “quantum state” we call a particular particle.
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- The rest masses of the fundamental particles in the Universe determine when and under what conditions they can be created. The more massive a particle is, the less time it can spontaneously be created at the beginning of the early Universe. The properties of particles, fields, and spacetime are all required to describe the Universe.
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- There are also a variety of fields that exist in the Universe. There is the Higgs field which is a quantum field that permeates all of space. The Higgs is a relatively simple example of a field, even though the particle that arose from its behavior, the Higgs boson, was the last one ever to be discovered. The electromagnetic (QED) field and color-charge (QCD) field are also fundamental quantum fields.
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- The field exists everywhere in space, even when there are no particles present. The field is quantum in nature, which means it has a lowest-energy state that we call the zero-point energy, whose value may or may not be zero.
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- Across different locations in space and time, the value of the field fluctuates, just like all quantum fields do. The quantum Universe has rules governing its fundamental indeterminism.
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So if everything is fields, then what is a particle? Particles are “excitations” of quantum fields. Particles are quantum fields not in their lowest-energy state, but in some higher-energy state.
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- The quantum fields exist everywhere. But particles don’t exist everywhere at once. On the contrary, they are what we call “localized“, or confined to a particular region of space. The simplest way to visualize this is to impose some sort of boundary conditions: some region of space that can be different from purely empty space.
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- Particles are simply points, individual entities with a set of properties assigned to them. But we know that in the quantum Universe, we have to replace particles with wave functions, which are a “probabilistic” set of parameters that replace classical quantities like “position” or “momentum.”
- Instead of unique values, there are a set of possible values that a quantum field can take on. Some of the properties associated with a particle are continuous, like position, while others are discrete. The discrete ones are the those that can only take on specific values that are defined by the characteristic conditions.
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- For example: A guitar string, on its own, can vibrate in an infinite number of vibration modes, corresponding to an unconstrained set of conceivable sounds. But by constraining the thickness of the string, the tension it is under, and the effective length of the part that vibrates, only a specific set of notes can emerge. These ‘boundary conditions’ are inseparable from the set of possible outputs.
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- A simple way to visualize this is to imagine a guitar. On a guitar, you have six strings of different thicknesses, where we can view thickness as a fundamental property of the string. If all you had were these strings (and no guitar), and you asked the question of the number of different possible ways these strings could vibrate, you would wind up with an infinite number of allowable outcomes.
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- But, guitars don’t offer an infinite set of possibilities at all. We have boundary conditions on those strings. The effective length of each string is constrained by the start-and-end points, the number of possible excitations are constrained by the positions of the frets on the fretboard, the vibration modes are constrained by geometry and the music of overtones, and the possible sounds it can make are constrained by the tension of each string. These properties are uniquely determined by the size, string properties, and tuning of each individual guitar.
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- The Standard Model Lagrangian is a single equation encapsulating the particles and interactions of the Standard Model. It has five independent parts:
------------------------------ the gluons
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------------------------------ the weak bosons
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------------------------------- how matter interacts with the weak force and the Higgs field
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------------------------------ the ghost particles that subtract the Higgs-field redundancies
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------------------------------ and the ghosts, which affect the weak interaction redundancies
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------------------------------ Neutrino masses are not included.
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- Also, this is only what we know so far; it may not be the full Lagrangian describing 3 of the 4 fundamental forces.
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- In the case of our Standard Model particles, there are also a finite set of possibilities. They arise from a specific type of quantum field theory: a gauge theory. Gauge theories are invariant under a slew of transformations (like speed boosts, position translations, etc.) that our physical laws should also be invariant under.
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- The Standard Model in particular comes from a quantum field theory made up of three groups ( in the mathematics of Lie groups) all tied together:
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- The Standard Model isn’t just a set of laws of physics, but provides boundary conditions that describe the spectrum of particles that can exist. Because the Standard Model isn’t just made of a single quantum field in isolation, but all of the fundamental ones (except gravity) working together, the spectrum of particles we wind up with has a fixed set of properties.
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- Each particle corresponds to the fundamental quantum fields of the Universe all excited in a particular way, with explicit couplings to the full suite of fields. This determines their particle properties, like:
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---------------------------------------- mass,
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---------------------------------------- electric charge,
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---------------------------------------- color charge,
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---------------------------------------- weak hypercharge,
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---------------------------------------- lepton number,
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---------------------------------------- baryon number
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---------------------------------------- lepton family number,
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---------------------------------------- and spin.
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- If the Standard Model were all there were, no other combinations would be allowed. The Standard Model gives us the fermion fields, which correspond to the matter particles (quarks and leptons), as well as boson fields, which correspond to the force-carrying particles (gluons, weak bosons, and photon), as well as the Higgs.
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- The Standard Model was built with a set of symmetries in mind, and the particular ways these symmetries break determine the spectrum of allowed particles. They still require us to put in the fundamental constants that determine the specific values of particle properties, but the generic properties of a theory with:
---------------------------------------- 6 quarks and antiquarks with three colors each,
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---------------------------------------- 3 charged leptons and antileptons,
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---------------------------------------- 3 neutrinos and antineutrinos,
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---------------------------------------- 8 massless gluons,
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---------------------------------------- 3 weak bosons,
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---------------------------------------- 1 massless photon,
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---------------------------------------- and 1 Higgs boson,
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---------------------------------------- are determined by the Standard Model itself.
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- The Standard Model of particle physics accounts for three of the four forces (excepting gravity), the full suite of discovered particles, and all of their interactions. Whether there are additional particles or interactions that are discoverable with colliders we can build on Earth is a debatable subject, but one we’ll only know the answer to if we explore past the known energy frontier.
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- To get quantum particles with the properties we do three things come together:
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- We have the laws of quantum field theory, which describe the fields permeating all of space that can be excited to different characteristic states.
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- We have the mathematical structure of the Standard Model, which dictates the allowable combinations of field configurations (i.e., particles) that can exist.
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- We have the fundamental constants, which provide the values of specific properties to each allowable combination: the properties of each particle.
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- The Standard Model may describe reality extremely well, but it doesn’t include everything. It doesn’t account for dark matter. Or dark energy. Or the origin of the matter-antimatter asymmetry. Or the reasons behind the values of our fundamental constants. The values are what they are but we don’t know why they are what they are. But, if they were the least bit different we would not be here to question it.
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- The Standard Model only provides the allowable configurations we know of. If neutrinos and dark matter are any indication, there ought to be more. One of the prime goals of 21st century science is to find out what else is there. Welcome to the cutting-edge frontier of modern physics.
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- (More reviews on this subject are available if requested)
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- 2018 - A lesson in Particle Physics. Think about it! A simple thing as the direction of spin is the difference enabling every different thing in the Universe to exist.
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- 1921 - Particle physics in the year 2016. The Large Hadron Collider is producing one Higgs Boson per second.
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- 1883 - Fundamental particles and the fifth force carrier. This Review lists 8 more Reviews about Particle Physics. Could there be such a thing as a dark photon? The force carrier for Dark Matter?
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- 1868 - What do neutron lifetimes have to do with it. This Review lists 16 more Reviews about Particle Physics.
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- 1848 - Includes a bibliography of seven of the pioneers in particle physics.
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- 1217 - How to find the Higgs Boson. Lecture at Sonoma State University.
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- 973 - Physics in a nutshell. It is about the particles that are inside the atoms that makeup the elements that make up our world.
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- 811 - The Large Hadron Collider. Why are they using Hadrons?
- January 20, 2019
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-------------------------- Monday, January 21, 2019 --------------------------
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