Cosmology View

My views on Cosmology and Physics

`Book by David Michalets`

# 3 Light

This is section 3 of 18.

The web page series for Distant Spectral Shifts is based on my book Cosmology Crisis Cleared.

There are several interactions between light or electromagnetic radiation and atoms or matter.

3.1 Light and wavelengths

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 radiation can come from sources spanning beyond the visible range and for simplicity, 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 section, wavelength is used because a spectrum analysis uses specific numerical values. Using the word photon instead of wavelength only introduces possible confusion when the radiation is a continuum of energy having no discrete values.  A rainbow is a continuum, not dots.

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:

Observation:

There are many X-ray point sources in the universe including one at the core of most spiral galaxies. These sources were described in detail in the author's book Cosmology Transition.

As somewhat described in the excerpt above, all those X-ray sources have an electrical current whose path is bent by a magnetic field resulting in this broad spectrum of wavelengths spanning from X-ray to infrared.

Quasars are typically dimmed in the optical wavelengths by their surrounding clouds of gas and dust.

Note the source of synchrotron radiation is not an object in motion. The radiated energy originates from the point of interaction between an electric current and a magnetic field. This is not a mass in motion having kinetic energy.

It is impossible for the broad range of wavelengths in synchrotron radiation to be shifted by a Doppler Effect because the point of interaction is not a mass in motion.

As a simple comparison, a bolt of lightning is essentially a luminous electric current, often not in a linear path.

When this path changes its direction, between toward and away, in the line of sight to the observer, there is no Doppler effect on this light. The source is not a mass having kinetic energy which participates in the energy transfer from source to radiation by Doppler effect. Both lightning and synchrotron radiation are not generated by a body having mass and kinetic energy.

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.

Emissivity must be defined before continuing.

The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that may include both visible radiation (light) and infrared radiation, which is not visible to human eyes. The thermal radiation from very hot objects (see photograph) is easily visible to the eye. Quantitatively, emissivity is the ratio of the thermal radiation from a surface to the radiation from an ideal black surface at the same temperature as given by the Stefan–Boltzmann law. The ratio varies from 0 to 1. The surface of a perfect black body (with an emissivity of 1) emits thermal radiation at the rate of approximately 448 watts per square metre at room temperature (25 °C, 298.15 K); all real objects have emissivities less than 1.0, and emit radiation at correspondingly lower rates. [Reference:
https://en.wikipedia.org/wiki/Emissivity ]

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 for the wavelength.

Observation:

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 wavelength distribution, with the wavelength having the highest intensity related to the object's temperature.

The wavelength distribution 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 wavelengths 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 white Sun can appear yellow when overhead due to the wavelength distribution after the light passes through our atmosphere, with the yellow wavelength having the strongest intensity. The atmosphere can also cause a color change between sun rise and sun set, toward red, and it causes the sky to be blue.

Here is the thermal radiation spectrum from our Sun: [Reference:

https://en.wikipedia.org/wiki/Sun ]

Thermal radiation typically spans a continuum of energy from ultraviolet to infrared with wavelengths covering most temperatures.
Infrared is always present but shorter wavelengths arise only with a very high surface temperature. Our Sun's thermal radiation, seen as light, is in this wavelength range of UV to infrared.

Most emission lines from atoms range from visible to ultraviolet wavelengths. As a rule, any wavelengths 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, not thermal.

A fictitious black hole violates this rule because its impossible hot accretion disk is claimed to emit X-rays but that energy requires an impossible temperature.

Thermal radiation requires a surface, like found in a liquid or solid, or condensed matter, meaning not a gas.

The temperature of a gas is measured by the kinetic energy of its atoms or molecules. A gas cannot emit thermal radiation. When its atoms and molecules become ionized, then as each ion captures an electron, they emit their characteristic wavelength of electromagnetic radiation. This is the non-thermal mechanism for the color of a neon light.

3.4 Fraunhofer Lines

This description provides background for several 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:

https://en.wikipedia.org/wiki/Fraunhofer_lines ]

3.5 Atom's characteristic wavelengths

3.5.1 Calcium

M31 or Andromeda galaxy is an example of the calcium atom in a galaxy spectrum.

The M31 spectrum has the calcium ion's pair of calcium absorption lines at 3934 and 3969 Angstroms in its spectrum. They are from calcium ions in the line of sight to the galaxy. A red or blue shift of this pair of lines indicates the relative velocity of the ion. The neutral calcium atom has a different pair of wavelengths.
Nearly all matter in the universe is plasma, or it has an electrical charge. That includes electrons (-), protons (+), and ions (+) which are atoms having lost one or more electrons.

Hydrogen is the most common element in the universe; it is also the simplest having only one proton and one electron.
Other elements, beyond hydrogen and calcium, including carbon, nitrogen and oxygen are found in some galaxies. In cosmology, a metallic element is any other than hydrogen and helium. In chemistry, some elements are called metals because of their behaviors in chemical reactions. In this case of astronomical data and measurements, chemistry's use of the term must be ignored. In astronomy, all but 2 elements, H and He, of the 118, are metals.

When metals are observed in a galaxy, the specific elements can be inconsistent. One galaxy might have C, N, and O, while another might not have C. The specific mix is useful only for research. Atoms cannot indicate a galaxy's velocity.

3.6 Lyman-alpha line

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:

https://en.wikipedia.org/wiki/Lyman-alpha_line  ]

Observation:

This wavelength is important because a quasar usually has this emission line in its spectrum.
A shift of this emission line wavelength indicates the relative velocity of the atom, not the quasar or galaxy.

3.7 Neutral Hydrogen line

This line might be observed with many galaxies.

The hydrogen line, 21-centimeter line, or H I line is the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms.

This electromagnetic radiation is at the precise frequency of 1,420,405,751.7667±0.0009 Hz, which is equivalent to the vacuum wavelength of 21.1061140542 cm in free space. This wavelength falls within the microwave region of the electromagnetic spectrum, and it is observed frequently in radio astronomy because those radio waves can penetrate the large clouds of interstellar cosmic dust that are opaque to visible light. [Reference:

https://en.wikipedia.org/wiki/Hydrogen_line ]

Observation:
It is possible for neutral hydrogen atoms to be found anywhere. If the emission line is shifted, then the atom must be in motion. The neutral atom could be in motion for 2 reasons:
1) The force of gravity from another mass is pulling the neutral atom in that direction, or
2) The proton was in motion by the Coulomb's force between charges when it captured an electron becoming a neutral hydrogen atom.

When this line is observed in the spectrum of a distant galaxy it is always red shifted. That redshift suggests the neutral atom is moving toward the massive galaxy, away from the observer, here on or near Earth. Gravity explains that motion. The red shift of these atoms moving away Earth and toward another galaxy cannot be assumed to be the other galaxy's velocity.

3.8 NIST Reference

NIST has a web page to view the lines associated with each element if any values are needed. [Reference:

NIST element data with carbon already selected

https://www.physics.nist.gov/PhysRefData/Handbook/Tables/carbontable2.htm

select Element Name tab to select another element in NIST database..
]