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My question is, we can only lay our hands on the modified frequency, not the original frequency. So how to calculate the doppler shift from that?

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My question is, we can only lay our hands on the modified frequency, not the original frequency. So how to calculate the doppler shift from that?

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But how do we know before hand that all the bodies radiate in the same wavelength?

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Are you referring to spectral lines being in the same wavelength?

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No.. Spectral lines of same elements will. obviously be in the same wavelength!

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Like I am saying if blue shifted, the infrared will become red, red becomes orange..........

....... Violet becomrs ultraviolet.. So?

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How wud we know which spectral line has shifted how much, if there are lines presnt all over...

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Once we know what elements are being displayed, we can then figure out how much they have shifted from their base positions.

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Drakkith

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The emission or absorption lines of an element are like fingerprints. The following image is of the emission lines of hydrogen that fall within the visible range. Redshift and blueshift results in a shift of all four lines in the same ratio. For example, let's say a source of hydrogen is moving towards us fast enough so that the wavelengths of the emission lines will be half what they normally are. The red emission line at 656.2 nm would be blueshifted to 328.1 nm, while the blue-green line at 486.1 nm would be shifted to 243.05 nm. Make sense?How wud we know which spectral line has shifted how much, if there are lines presnt all over...

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this is an older article that will help you understand the cosmic distance ladder determination. Its covered in some detail at the end of the article.

1) What is outside the universe?

2) What is causing the expansion of the universe?

3) Is expansion, faster than light in parts of the Universe, and How does this not violate the faster than light speed limit?

4) What do we mean when an object leaves our universe?

5) What do we mean when we say homogeneous and isotropic?

6) Why is the CMB so vital in cosmology?

7) Why is the LambdaCDM so vital to cosmologists?

8) Why are all the galaxies accelerating from us?

9) Is Redshift the same as Doppler shift?

9) How do we measure the distance to galaxies?

10) What is a Cepheid or standard candle

These are some of the common questions I will attempt to address in the following article

First we must define some terms and symbols used.

Planck constant: [itex]h\ =\ 6.62606876(52)\ \times\ 10^{-34}\ J\ s[/itex]

Gravitational constant: [itex]G\ =\ 6.673(10)\ \times\ 10^{-11}\ m^{3} kg^{-1} s^{-2}[/itex]

Speed of light in a vacuum:[itex]c\ =\ 2.99792458\ \times\ 10^{8}\ m\ s^{-1}[/itex]

The parsec (symbol: pc) is a unit of length used in astronomy, equal to about 30.9 trillion kilometers (19.2 trillion miles). In astronomical terms, it is equal to 3.26 light-years, and in scientific terms it is equal to 3.09×10

Mpc=1 million Parsecs

In the hot big bang model we do not think of the universe as starting from a singularity (infinitely, hot, dense point) instead measurements agree space-time as simply expanding. That expansion is

Common misconceptions arise when one tries to visualize a finite universe such questions include.

"So how do we see farther than 13.772 billion light years?" The answer lies in expansion; as light is travelling towards us, space-time has expanded.

“If the universe is finite what exists outside the Universe?" If you think about this question with the above definition of the universe you will realize that the question is meaningless. One accurate answer in regards to cosmology is nonexistent.

"What makes up the barrier between our universe and outside our universe?" The short answer is there is no barrier.

In order to measure an objects motion and distance in cosmology it is important to properly understand redshift, Doppler shift and gravitational redshift. Incorrect usage of any of these can lead to errors in our measurements.

[tex]\frac{\Delta_f}{f} = \frac{\lambda}{\lambda_o} = \frac{v}{c}=\frac{E_o}{E}=\frac{hc}{\lambda_o} \frac{\lambda}{hc}[/tex]

A key note is expansion is the same throughout the cosmos. However gravity in galaxy clusters is strong enough to prevent expansion. In other words galaxy clusters are gravitationally bound. In regards to expansion it is important to realize that galaxies are not moving from us due to inertia, rather the space between two coordinates are expanding. One way to visualize this is to use a grid where each vertical and horizontal joint is a coordinate. The space between the coordinates increase rather than the coordinates changing. This is important in that no FORCE is acting upon the galaxies to cause expansion. As expansion is homogeneous and isotropic then there is no difference in expansion at one location or another. In the [itex]\Lambda[/itex]CDM model expansion is attributed to the cosmological constant described later on. The rate a galaxy is moving from us is referred to as recession velocity. This recession velocity then produces a Doppler (red) shift proportional to distance (please note that this recession velocity must be converted to a relative velocity along the light path before it can be used in the Doppler formula). The further away an object is the greater the amount of redshift. This is given in accordance with Hubble’s Law. In order to quantify the velocity of this galactic movement, Hubble proposed Hubble's Law of Cosmic Expansion, aka Hubble's law, an equation that states:

Velocity = H

Velocity represents the galaxy's recessive velocity; H

Any measurement of redshift above the Hubble distance defined as H

z = (Observed wavelength - Rest wavelength)/(Rest wavelength) or more accurately

1+z= λ

[tex]1+Z=\frac{\lambda}{\lambda_o}[/tex] or [tex]1+Z=\frac{\lambda-\lambda_o}{\lambda_o}[/tex]

λ

Note that positive values of z correspond to increased wavelengths (redshifts).

Strictly speaking, when z < 0, this quantity is called a blueshift, rather than

a redshift. However, the vast majority of galaxies have z > 0. One notable blueshift example is the Andromeda Galaxy, which is gravitationally bound and approaching the Milky Way.

WMAP nine-year results give the redshift of photon decoupling as z=1091.64 ± 0.47 So if the matter that originally emitted the oldest CMBR photons has a present distance of 46 billion light years, then at the time of decoupling when the photons were originally emitted, the distance would have been only about 42 million light-years away.

this is described in the form.

H

Another term often used for the cosmological constant is vacuum energy described originally by the false vacuum inflationary Model by A.Guth. The cosmological constant uses the symbol Λ, the Greek letter Lambda.

The dark energy density parameter is given in the form:

[itex]\Omega_\Lambda[/itex] which is approximately 0.685

(Observed wavelength - Rest wavelength)/(Rest wavelength) = (v/c)

[tex] f=\frac{c+v_r}{c+v_s}f_o[/tex]

c=velocity of waves in a medium

[tex]v_r[/tex] is the velocity measured by the source using the source’s own proper-time clock(positive if moving toward the source

[tex]v_s[/tex] is the velocity measured by the receiver using the source’s own proper-time clock(positive if moving away from the receiver)

The above are for velocities where the source is directly away or towards the observer and for low velocities less than relativistic velocities. A relativistic Doppler formula is required when velocity is comparable to the speed of light. There are different variations of the above formula for transverse Doppler shift or other angles. Doppler shift is used to describe redshift due to inertial velocity one example is a car moving away from you the light will be redshifted, as it approaches you the light and sound will be blueshifted. In general relativity and cosmology, there is a fundamental complication in this simple picture - relative velocity cannot be defined uniquely over large distances. However, it does become unique when compared along the path of light. With relative velocity compared along the path of the light, the special relativity Doppler formula describes redshift for all situations in general relativity and cosmology. It is important to realize that gravity and expansion of the universe affect light paths, and how emitter velocity information is carried along a light path; thus gravity and expansion contribute to Doppler redshift

[tex]

\frac{\lambda}{\lambda_o}=\frac{1}{\sqrt{(1 - \frac{2GM}{r c^2})}}

[/tex]

G=gravitational constant

c=speed of light

M=mass of gravitational body

r= the radial coordinate (measured as the circumference, divided by 2pi, of a sphere centered around the massive body)

The rate of expansion is expressed in the [itex]\Lambda[/itex]CDM model in terms of

d(t)=a(t)d

where d(t) is the proper distance at epoch (t)

d

a(t) is the comoving angular scale factor. Which is the distance coordinate for calculating proper distance between objects at the same epoch (time)

r(t) is the comoving radial scale factor. Which is distance coordinates for calculating proper distances between objects at two different epochs (time)

[tex]Proper distance =\frac{\stackrel{.}{a}(t)}{a}[/tex]

The dot above a indicates change in.

the notation R(t) indicates that the scale factor is a function of time and its value changes with time. R(t)<1 is the past, R(t)=1 is the present and R(t)>1 is the future.

[tex]H(t)=\frac{\stackrel{.}{a}(t)}{a(t)}[/tex]

Expansion velocity

[tex] v=\frac{\stackrel{.}{a}(t)}{a}[/tex]

This shows that Hubble's constant is time dependant.

Luminosity is often measured in flux where flux is

[tex]f=\frac{L}{4\pi r^2}[/tex]

However cosmologists typically use a scale called magnitudes. The magnitude scale has been developed so that a 5 magnitude change corresponds to a differents of 100 flux.

Rather than cover a large range of those distance scales or rungs on the ladder I will cover a few of the essential steps to cosmological distance scales. The first rung on the ladder is naturally.

With the standardized AU unit we can take two AU to form the short leg. With the Sun at a right angle to us the distance to the object to be measured is the long leg of the triangle.

My thanks to the following Contributors, for their feedback and support.

PAllen

Naty1

Jonathon Scott

marcus

Article by Mordred, PAllen

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Thanks a lot.. That surely was helpful!

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http://www.einsteins-theory-of-relativity-4engineers.com/LightCone7/LightCone.html

http://cosmocalc.wikidot.com/start

the second link is an easy access to the manuals for its usage but more examples can be found in the pinned thread for this calc

https://www.physicsforums.com/showthread.php?t=634757

keep in mind the thread covers previous versions of the calculator so you may want to jump to near the end of the thread

though not sure if this is the latest version lol

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