My views on Cosmology and Physics
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Book by David Michalets
With Forces and Light
This is section 2 of 12 in the web-book.
Electromagnetism is about the combination of electric and magnetic fields and their forces.
Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force is carried by electromagnetic fields composed of electric fields and magnetic fields, and it is responsible for electromagnetic radiation such as light. It is one of the four fundamental interactions (commonly called forces) in nature, together with the strong interaction, the weak interaction, and gravitation. At high energy, the weak force and electromagnetic force are unified as a single electroweak force.
Lightning is an electrostatic discharge that travels between two charged regions.
Electromagnetic phenomena are defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as different manifestations of the same phenomenon. The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life.
The electromagnetic attraction between atomic nuclei and their orbital electrons holds atoms together. Electromagnetic forces are responsible for the chemical bonds between atoms which create molecules, and intermolecular forces.
The electromagnetic force governs all chemical processes, which arise from interactions between the electrons of neighboring atoms. Electromagnetism is very widely used in modern technology, and electromagnetic theory is the basis of electric power engineering and electronics including digital technology.
There are numerous mathematical descriptions of the electromagnetic field. Most prominently, Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.
The theoretical implications of electromagnetism, particularly the establishment of the speed of light based on properties of the "medium" of propagation (permeability and permittivity), led to the development of special relativity by Albert Einstein in 1905. [Reference:
Maxwell's equations are widely available, from many sources.
They are not important in this web-book, which is more about Newton than Maxwell.
The description implies Maxwell's definition of a medium suggested to Einstein that space-time could serve as a medium for light. That implication is consistent with Einstein's wrong belief that gravity or space-time can bend the path of light.
A spectrum is the entire range of wavelengths in electromagnetic radiation where light is the visible range. The ultraviolet and infrared ranges are not visible to the human eye but they are in the Sun's radiation. Because this topic is about the visible stars and galaxies, the word light is often used for the entire spectrum, including those frequency ranges not visible.
Electromagnetic radiation is the propagation of synchronized, perpendicular electric and magnetic fields. The propagation has a defined rate of oscillation measured as either a frequency or a wavelength.
The wavelength is usually measured in either nanometers (10-9 m) or Angstroms (10-10 m or 0.1 nm).
The velocity of this propagation has been measured in a vacuum using our standard definition for time and this measured value is called the constant c. This measurement also defined the standard unit of 1 meter. The velocity of propagation is reduced in a medium, defined by the medium's diffraction index.
Light transmits energy proportional to its frequency so the constant c appears in some physics equations involving energy.
Quantum physics defined a theoretical particle called a photon to refer to a single wavelength.
In this web-book, wavelength is used because a spectrum analysis uses specific numerical values. Using photon instead of wavelength only introduces possible confusion. Photon will not be used in this topic's original content. When photon is in a reference excerpt, wavelength can be substituted for photon for consistency.
2.3 Fraunhofer Lines
This description provides background for many terms and their use in a spectrum analysis.
In 1814, Fraunhofer independently rediscovered the [dark] lines and began to systematically study and measure the wavelengths where these features are observed. He mapped over 570 lines.
About 45 years later Kirchhoff and Bunsen noticed that several Fraunhofer lines coincide with characteristic emission lines identified in the spectra of heated elements. It was correctly deduced that dark lines in the solar spectrum are caused by absorption by chemical elements in the solar atmosphere. Some of the observed features were identified as telluric lines originating from absorption by oxygen molecules in the Earth's atmosphere.
Because of their well–defined wavelengths, Fraunhofer lines are often used to characterize the refractive index and dispersion properties of optical materials. [Reference:
The topic has this figure. which shows lines on a spectrum of thermal radiation..
Fraunhofer lines reveal light does not have a quantized nature. There is no photon.
Each element has its unique electron configuration. Each element absorbs its characteristic wavelength.
The atom determines the energy being absorbed, not the light source, or the light.
2.4 Atom's characteristic wavelengths
Hydrogen is the most common element in the universe; it is also the simplest having only one proton and one electron.
In physics, the Lyman-alpha line is a spectral line of hydrogen, or more generally of one-electron ions, in the Lyman series, emitted when the electron falls from the n = 2 orbital to the n = 1 orbital, where n is the principal quantum number. In hydrogen, its wavelength of 1215.67 angstroms corresponding to frequency of 1015 hertz, places the Lyman-alpha line in the ultraviolet part of the electromagnetic spectrum, which is absorbed by air. Lyman-alpha astronomy must therefore ordinarily be carried out by satellite-borne instruments, except for extremely distant sources whose red shifts allow the hydrogen line to penetrate the atmosphere. [Reference:
This Lyman-alpha wavelength is important because a galaxy or quasar can have this emission line in its spectrum. A shift of this emission line wavelength indicates the relative velocity of the proton at the instant of the electron capture, creating a hydrogen atom.
2.5 Doppler Effect
Doppler effect, the apparent difference between the frequency at which sound or light waves leave a source and that at which they reach an observer, caused by relative motion of the observer and the wave source. This phenomenon is used in astronomical measurements.[Reference:
The Doppler Effect is observed by the entire spectrum of the light source being shifted in proportion to the source's velocity in that direction.
The Doppler Effect occurs only at the moment of radiation emission or at the moment of radiation absorption when the motion of the object at that instant affects the spectrum.
2.6 Synchrotron Radiation
Synchrotron radiation, electromagnetic energy emitted by charged particles (e.g., electrons and ions) that are moving at speeds close to that of light when their paths are altered, as by a magnetic field. It is so called because particles moving at such speeds in a variety of particle accelerator that is known as a synchrotron produce electromagnetic radiation of this sort.
Many kinds of astronomical objects have been found to emit synchrotron radiation as well. High-energy electrons spiraling through the lines of force of the magnetic field around the planet Jupiter, for example, give off synchrotron radiation at radio wavelengths. Synchrotron radiation at such wavelengths and at those of visible and ultraviolet light is generated by electrons moving in the magnetic field associated with the supernova remnant known as the Crab Nebula. Radio emissions of the synchrotron variety also have been detected from other supernova remnants in the Milky Way Galaxy and from extragalactic objects called quasars. [Reference:
Hannes Alfven was awarded the 1970 Nobel Prize in Physics for his extensive work on plasma physics.
Despite 50 years, cosmologists often miss electromagnetic effects, like a source of synchrotron radiation.
2.7 Thermal Radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation.
If a radiation object meets the physical characteristics of a black body in thermodynamic equilibrium, the radiation is called blackbody radiation. Planck's law describes the spectrum of blackbody radiation, which depends solely on the object's temperature. Wien's displacement law determines the most likely frequency of the emitted radiation, and the Stefan–Boltzmann law gives the radiant intensity. [Reference:
Thermal radiation is also one of the fundamental mechanisms of heat transfer. Conduction between adjacent solid objects is another.
Its spectrum is characterized by a frequency distribution, with the frequency having the highest intensity related to the object's temperature.
The frequency distribution emitted by a solid affects whether it is visible.
A cool temperature won't be. When warmer the increasing infrared intensity can be felt as heat or warmth but not seen.
A rising temperature will become visible as red. When even hotter the mix of color frequencies can result in "white hot." Our Sun is hot enough to generate the ultraviolet frequency which is not visible but can affect the eyes and skin.
Our Sun appears yellow, because that wavelength has the highest intensity in its spectrum and our eye distinguishes that wavelength from the others.
Important note about frequencies:
Thermal radiation typically spans from infrared to ultraviolet frequencies. Our Sun's thermal radiation, seen as light, is in this frequency range. Our Sun appears yellow because that frquency has the highest intensity.
A colder star, like a red giant, will have the peak intensityin the energy distribution in red
Most emission lines from atoms range from visible to ultraviolet frequencies. As a general rule, any frequencies measured outside of this range, like radio at the low end, and X-ray or gamma ray at the high end, were emitted by a source of synchrotron radiation.
A black hole violates this general rule because the hot accretion disk is claimed to emit X-rays but that requires an impossible temperature.
2.8 Summary of section
Light is contently a wave A spectrum is a continuum of wavelengths.
With stars and their thermal radiation, the range is usually from UV or longer at the shortest wavelength, but always infrared as the longest wavelength.
With galaxies and their synchrotron radiation, the range is from UV as the shortest wavelength, but always infrared as the longest wavelength. Depending on the AGN mechanism, Z-pinch or plasmoid, many have the X-ray wavelengths having a high intensity.
With quasars and their synchrotron radiation from a plasmoid, their range is from UV as the shortest wavelength, but always infrared is present, but often rado is the longest wavelength. Most quasars are discovered in radio.
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last change 01/25/2022