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The alternative phenomena of redshift




One of the biggest pieces of evidence for the big bang theory is a phenomenon called 'Redshift'. It is a key concept for astronomers to understand the expanding universe and is an example of the doppler effect/shift. As the term mentions it itself, this idea can be understood as: The wavelength of light being stretched (or shifted) towards the red part of the spectrum of light. In physics, redshift is is an increase in the wavelength and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in frequency and energy, is known as a negative redshift, or blueshift.

In 1929, Mr. Edwin Hubble, an American astronomer announced that far-off galaxies were moving away from the Milky Way galaxy and that their redshifts increase in proportion to the increase in the distance. If we'd observe a certain galaxy and notice one spectral line at a longer

wavelength than it'd be on earth, we'd know that the galaxy was redshifted.




Doppler Effect



Named after the Austrian physicist, Christian Doppler, Doppler shift is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. When the main source of the waves is shifting towards the spectator, each progressive wave crest is transmitted from a position nearer to the eyewitness than the crest of the past wave. Accordingly, each wave sets aside marginally less effort to arrive at the eyewitness than the past wave. Thus, the time between the appearances of progressive wave crests at the spectator is diminished, causing an expansion in the frequency. Light from inaccessible stars and galaxies can be shifted similarly. ... Since red is at the low-frequency end of the noticeable spectrum, we say that light from a retreating star is shifted toward red, or redshifted.


The redshift of a distant galaxy or quasar is easily measured by comparing its spectrum with a reference laboratory spectrum. Atomic emission and absorption lines occur at well-known wavelengths. By measuring the location of these lines in astronomical spectra, astronomers can determine the redshift of the receding sources.


However, to be accurate, the redshifts observed in distant objects are not exactly due to the Doppler phenomenon but are rather a result of the expansion of the Universe.


Doppler shifts arise from the relative motion of source and observer through space, whereas astronomical redshifts are 'expansion redshifts' due to the expansion of space itself.

Two objects can actually be stationary in space and still experience a redshift if the intervening space itself is expanding.



History


During the advancement of wave mechanics and the investigation of the phenomenon related to the doppler shift in the 19th century, the hypothesis was tried and affirmed by Cristophorus Buys Ballot, a dutch scientist in 1845. Doppler effectively anticipated that the phenomenon ought to apply to all waves and specifically recommended that the different shades of stars could be credited to their movement concerning the earth. Before this was checked, it was tracked down that stellar shadings were because of a star's temperature, not by its movement.

Hippolyte Fizeau, a french physicist announced the main Doppler redshift in the year 1848. He highlighted the change in spectral lines found in stars being because of the doppler effect which is once in a while considered as the "Doppler-Fizeau effect"

William Huggins, a British Astronomer was quick to decide the velocity of a star moving away from the earth by this strategy in 1868. The optical redshift was then affirmed when the phenomenon was seen in Fraunhofer lines utilizing a solar rotation about 0.1 Å in the red in 1871.

Vogel and Scheiner discovered the annual Doppler effect in 1887 which is considered as the yearly change in the doppler shift of stars situated close to the ecliptic because of the orbital velocity of the earth.

Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors in 1901.

One of the earliest pervasiveness of this wonder was by Walter S. Adams, an American Astronomer in 1908 where he mentions "Two methods of investigating that nature of the nebular red-shift". The word does not seem unhyphenated until around 1934 by Willem de Sitter, perhaps showing that up to that point its German equivalent, Rotverschiebung, was all the more regularly used.

Vesto Slipher revealed that most spiral galaxies, at that point most idea spiral nebula had extensive redshifts. Starting with perceptions in 1912. Slipher originally wrote about his estimation in the debut volume of the Lowell Observatory Bulletin. After three years, he composed an audit in the diary Popular Astronomy. In it, he expresses that "the early revelation that the incomparable Andromeda spiral had the very uncommon velocity of – 300 km(/s) showed the methods then accessible, equipped for researching the spectra of the spirals as well as their velocities also. He announced the velocities for 15 spiral nebulae spread across the whole celestial circle, everything except three having noticeable "positive" (that is recessional) velocities.

Accordingly, Edwin Hubble found an inexact connection between the redshifts of such "nebulae" and the distances to them with the definition of his eponymous Hubble's law. These perceptions verified Alexander Friedmann's 1922 work, in which he inferred the Friedmann–Lemaître equations. They are today viewed as solid proof for an extending universe and the Big bang.



Ways to calculate the redshift


Spectroscopy

Spectroscopy is the study of the interaction between matter and electromagnetic radiation as a function of the wavelength or frequency of the radiation. The spectrum of light that comes from a source can be measured.

To decide the redshift, one looks for highlights in the spectrum, for example, absorption lines, emission lines, or different varieties in light intensity. Whenever discovered, these highlights can measure up to known highlights in the spectrum of different chemical compounds found in experiments where that compound is situated on Earth.

A typical atomic element in space is hydrogen. The spectrum of initially featureless light radiated through hydrogen will show a signature spectrum explicit to hydrogen that has highlighted at standard spans. On the off chance that a similar example of stretches is found in a noticed spectrum from a far-off source however happening at shifted wavelengths, it very well may be recognized as hydrogen as well.

To calculate the redshift the wavelength would be measured by an observer located adjacent to and comoving with the source. This measurement cannot be done directly, because that would require traveling to the distant star of interest, the method using spectral lines described here is used instead. Redshifts cannot be calculated by looking at unidentified features whose rest-frame frequency is unknown, or with a spectrum that is featureless or white noise (random fluctuations in the spectrum).


The redshift equation

Positive z values mean the galaxy has a redshift; negative z values mean the galaxy has a blueshift.


For instance, the Doppler effect blueshifts (z < 0) are related to objects moving towards the observer with the light shifting to more noteworthy energies. On the other hand, Doppler effect redshifts (z > 0) are related to objects subsiding from the observer with the light shifting to bring lower energies. Similarly, gravitational blueshifts are related to light emitted from a source dwelling inside a more fragile gravitational field as seen from inside a more grounded gravitational field, while gravitational redshifting suggests the contrary conditions. In general relativity, one can infer a few significant uncommon case formulae for redshift in certain exceptional spacetime geometries, as summed up in the accompanying table. In all cases, the magnitude of the shift (the worth of z) is free of the wavelength


Gravitational Redshift


In the theory of general relativity, there is time dilation within a gravitational well. This is known as the gravitational redshift or Einstein Shift. The theoretical derivation of this effect follows from the Schwarzschild solution of the Einstein equations which yields the following formula for redshift associated with a photon traveling in the gravitational field of an uncharged, nonrotating, spherically symmetric mass:


G is the gravitational constant,

M is the mass of the object creating the gravitational field,

r is the radial coordinate of the source (which is analogous to the classical distance from the center of the object, but is actually a Schwarzchild coordinate), and

c is the speed of light.

This gravitational redshift result can be derived from the assumptions of special relativity and the equivalence principle; the full theory of general relativity is not required.

The Mossbauer effect is a small but significant phenomenon that occurs when an object approaches a black hole. It can also be caused by cosmic microwave background radiation.


The effect is very small but measurable on Earth using the Mössbauer effect and was first observed in the Pound–Rebka experiment. However, it is significant near a black hole, and as an object approaches the event horizon the redshift becomes infinite. It is also the dominant cause of large angular-scale temperature fluctuations in the cosmic microwave background radiation (see Sachs–Wolfe effect).




Sources:

https://en.wikipedia.org/wiki/Redshift

https://www.britannica.com/science/redshift

https://earthsky.org/astronomy-essentials/what-is-a-redshift/

https://astronomy.swin.edu.au/cosmos/c/cosmological+redshift

https://physics.uiowa.edu/itu/labs/astronomical-redshift

https://lco.global/spacebook/light/redshift/

https://www.esa.int/Science_Exploration/Space_Science/What_is_red_shift

https://www.space.com/25732-redshift-blueshift.html

https://www.khanacademy.org/science/cosmology-and-astronomy/universe-scale-topic/big-bang-expansion-topic/v/red-shift

https://www.youtube.com/watch?v=-mQ41yA6LaA


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