Physics Concepts And Connections Chapter 17

Front 1

Quantum Field Theory

Back 1

Everything is made of quantized fields that obey special relativity and quantum theory. All the particles of nature are field quanta. A field's intensity represents the probability of finding the particles that are the quanta of that field.

Front 2

Field View of Reality

Back 2

The view that the universe is made of fields, subject to the rules of relativity and quantum physics.

Front 3

Field

Back 3

A physical entity that is spread throughout a region of space.

Front 4

Quantized Field

Back 4

A continuous, space-filling field that is subject that is subject to the laws of quantum physics. A quantized field's range of possible energies is "digitized," with only certain specific energy values allowed. Examples: quantized electromagnetic field, quantized matter field.

Front 5

Quantum

Back 5

The smallest allowed energy increment, hf, is called a quantum of energy.

Front 6

Quantum Electrodynamics

Back 6

The quantum field theory of electrons and protons (i.e., of the electron matter field and the EM field.) According to this theory, when we say that a particle is electrically charged, we mean that it has the ability to emit and absorb photons. Particles exert electric forces on each other in tiny quantized increments, by photon exchanges in which one particle emits a photon that is then absorbed by the other particle.

Front 7

Electron Fields

Back 7

The quantized matter field for electrons and positrons.

Front 8

Photon Exchange

Back 8

According to quantum field theory, charged particles exert the electromagnetic force on each other means of exchanging photons.

Front 9

Electrically Charged

Back 9

A particle that has the ability to emit and absorb photons.

Front 10

Positron

Back 10

The electron's antiparticle. Identical to the electron except that it carries a positive charge.

Front 11

Muon, tau

Back 11

These two particles are identical to the electron except for the facts that they are heavier and are unstable (they have short lifetimes). Like the electron, they are point particles (so far as we know).

Front 12

Antiparticles

Back 12

Theory of special relativity requires that for every existing type of particle, there is an antiparticle carrying the opposite charge. Quantum uncertainties allow the creation and annihilation of particle-antiparticle pairs such as electron-position pairs.

Front 13

Antiproton

Back 13

Antiparticle of the proton.

Front 14

Antineutron

Back 14

Antiparticle of the neutron.

Front 15

Antimatter

Back 15

Made of antiprotons, antineutrons, and positrons. Today's universe consists overwhelmingly of matter, not antimatter.

Front 16

Particle Accelerators

Back 16

A device to accelerate microscopic particles to high energies.

Front 17

Large Hadron Collider (LHC)

Back 17

Currently the world's largest particle accelerator. It accelerates two narrow beams of protons in different directions around a circular ring 27 km long lying 100 m underground near Geneva, Switzerland. The beams collide to create many kinds of particles and phenomena. Each collision has an energy of 14 trillion electron-volts.

Front 18

Vacuum

Back 18

A region that contains no matter (no material particles). According to quantum field theory, fields exist even in vacuum. Since these fields are quantized, there is some probability that field quanta-photons, or particle-antiparticle pairs-will pop into and out of existence, even in vacuum. Furthermore, quantum uncertainties allow the energy present at any point in vacuum to undergo random energy fluctuations around its long-term average value.

Front 19

Lamb Shift

Back 19

A small change in the energy levels of the hydrogen atom that is caused by vacuum energy fluctuating in the space surrounding the atom.

Front 20

Neutrino

Back 20

A uncharged particle that experiences only the weak and gravitational forces and hence penetrates easily through matter. At least two of the three types of neutrons are now known to have a tiny, but nonzero, mass.

Front 21

Electroweak Force Field

Back 21

The combined EM and weak forces. The quanta (or exchange particles) of the electro weak force field are protons, W+, W-, and Z particles. The quanta of the electroweak matter field are electrons and electron-neutrinos. In addition, there are two more electroweak matter fields corresponding to a second and third generation of particles: the muon and its neutrino and the tau and its neutrino. Only the first generation is stable and contributes to ordinary matter. The other two generations are unstable and transmute quickly into other particles.

Front 22

Exchange Particles

Back 22

In quantum field theory, forces between two particles A and B are exerted by means of other particles, called exchange particles, that pass back and forth between A and B. For example, The electromagnetic force is exerted by exchanging photons.

Front 23

Point Particles

Back 23

A particle whose force field is centered on a single point and that itself takes up no volume. All of the fundamental particles described by quantum field theory appear to be point particles.

Front 24

Quarks

Back 24

Fundamental particle, thought to be a point particle. Protons and neutrons are each made of three quarks of two different types, known as "up" and "down."

Front 25

Strong Force Field

Back 25

One of natures fundamental forces. It holds the nucleus together, acts between nuclear particles (protons and neutrons), and is strongly attractive at separations of around 10-15 and negligible at larger distances. The quanta (or exchange particle) of the strong force are gluons. The quanta of the strong matter field are the up quark (u) and the down quark (d). In addition, there are two more strong matter fields corresponding to a second and third generation of particles: the c-quark, and the s-quark, and the t-quark and b-quark. Only the first generation is stable and contributes to ordinary matter: Protons are made of u-u-d, and neutrons are made of u-d-d. The other two generations are unstable and transmute quickly into other particles. Quarks are not found in isolation because any attempt to isolate them creates more quarks.

Front 26

Gluons

Back 26

The exchange particle of the strong force. Gluons have zero mass and travel at light speed.

Front 27

Grand Unified Theory

Back 27

A quantum field theory that would unify the standard model's electroweak and strong forces into a single force, much as the EM force and the weak force were unified into a single electroweak force. Although the parallels between the theories of the electroweak and strong forces suggest that such a theory should exist, there is as yet no agreed-on grand unified theory.

Front 28

Standard Model

Back 28

The theory of the electroweak and strong forces.

Front 29

Higgs Field

Back 29

The standard model requires this field because without it all the particles of the standard model would need to have zero mass. However, there is as yet no direct evidence for this field. Its quanta, called Higgs particles, are currently sought in high-energy accelerators. The Higgs field predicted to pervade the universe, interacting even with isolated particles. This interaction acts on accelerated particles in such a way as to resist their acceleration. Thus the Higgs field could be the reason that some of the fundamental particles have mass.

Front 30

Graviton

Back 30

The quantum of the gravitational field, predicted but not yet observed. It is predicted to move at lightspeed and have zero mass.

Front 31

Planck Scale

Back 31

The range or scale at which physicists expect typical quantum-gravitational events to occur. Specifically, such events are expected to occur within regions about as big as the Planck length, with a duration of about the Planck time, and an energy about equal to the Planck energy. The Planck mass is the mass of this much energy.

Front 32

String Hypothesis

Back 32

A promising hypothesis that unifies general relativity with quantum theory but that has as yet no direct experimental verification. Its key idea is that a fundamental particle such as an electron is not concentrated as one infinitely small point but is instead a tiny loop called a string. This spreading out of the point-particle model smoothes its effects on the space around it enough so that strings can fit into general relativity. Strings are comparable in size to the plank distance. One odd thing about strings is that they exist in 10 special dimensions, 7 of which are "rolled up" so that we do not observe them in the macroscopic world. Although all strings are identical, they can vibrate in a variety of ways, and each different mode of vibration is a different elementary particle.