What is Redshift: Definition and 384 Discussions

In physics, a redshift 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. The terms derive from the colours red and blue which form the extremes of the visible light spectrum.
In astronomy and cosmology, the three main causes of electromagnetic redshift are

The radiation travels between objects which are moving apart ("relativistic" redshift, an example of the relativistic Doppler effect)
The radiation travels towards an object in a weaker gravitational potential, i.e. towards an object in less strongly curved (flatter) spacetime (gravitational redshift)
The radiation travels through expanding space (cosmological redshift). The observation that all sufficiently distant light sources show redshift corresponding to their distance from Earth is known as Hubble's law.Relativistic, gravitational, and cosmological redshifts can be understood under the umbrella of frame transformation laws. Gravitational waves, which also travel at the speed of light, are subject to the same redshift phenomena.
Examples of strong redshifting are a gamma ray perceived as an X-ray, or initially visible light perceived as radio waves. Subtler redshifts are seen in the spectroscopic observations of astronomical objects, and are used in terrestrial technologies such as Doppler radar and radar guns.
Other physical processes exist that can lead to a shift in the frequency of electromagnetic radiation, including scattering and optical effects; however, the resulting changes are distinguishable from (astronomical) redshift and are not generally referred to as such (see section on physical optics and radiative transfer).
The value of a redshift is often denoted by the letter z, corresponding to the fractional change in wavelength (positive for redshifts, negative for blueshifts), and by the wavelength ratio 1 + z (which is >1 for redshifts, <1 for blueshifts).

View More On Wikipedia.org
Recent contents Top users
  1. C

    Redshift > 1.46 means Recessional Velocity over C?

    I read this recently, but did not understand how one calculates this, since I'm used to: Distance = Recessional Velociy / Hubble's Constant = Beta x C / Hubble's Constant ALSO SEE ATTACHMENT I thought that as Z approaches infinity, Recessional Velociy approaches C...
  2. C

    Exploring the Highest Redshift Objects in the Universe

    Hi, what is the highest redshift observed for any 'object' in the Universe? Also, is the Abell-lensed 'object' still viewed as a possible candidate (at Z=10) or have people further studied this lensed 'object' and determined its high redshift as an error? Thanks you.
  3. L

    Do quasar redshift anomalies challenge mainstream theories?

    Hi! I just read an article about galactic redshift anomalies discovered by Halton Arp. Do these pose a problem for Big Bang Theory? Thanks in advance!
  4. S

    How Does Hubble's Law Calculate Redshift for Distant Galaxies?

    How would one use hubble's law to find the redshift of a galaxy 10^10 light years away? (in other words 3*10^9 pc) All I know however is the version of hubble's where v=H_o d, with H_o=71 \frac{m}{s*pc}, which tells me that v= 2.2*10^11 m/s. But this violates the second principle of...
  5. M

    Is the Redshift of Light at a Black Hole's Surface Infinite?

    The gravitational redshift to light at emission is known as the Einstein shift. There is a problem with it in General Relativity. It becomes infinite at the surface of a black hole. Light emitted there will be infinitely redshifted. GR predicts this energyless light. In this way as...
  6. V

    Gravitational redshift +blackbody spectrum

    Hi, How can I prove that gravitational redshift preserves the characteristic shape of a blackbody spectrum?
  7. SpaceTiger

    Non-Cosmological Interpretation of Redshift

    In order to quell complaints from those members of the board who feel they are being discriminated against in my recent threads, I would like to directly address the issue of a non-cosmological interpretation of redshift. If you're a layman trying to learn about astronomy, I advise you to...
  8. L

    Redshift & Blueshift: Is There a Consensus?

    Since we have been taken readings of redshift, blueshift for sometime now, is there a consensus on a percentage of each?
  9. M

    Quantum Redshift: Exploring the Photoelectric Effect

    I think the cosmological redshift, called the "Hubble" redshift which Edwin Hubble discovered and photographed, is caused by quantum decay in light and other electric field) waves, i.e. photoelectric radiation. When emitted, light from a particular elements electronic transitions are at the...
  10. D

    How to calculate age of universe with a certain redshift?

    Hi i am confused as to how to calculate the age of the universe with redshift say for example The age of the universe now is 13 billion years old (and a critical universe). How do i find the age of the universe if it was a redshift at say 10?? Do i have to find the scale factor first? I...
  11. M

    Cosmological vs Doppler redshift

    generic redshift is characterised (defined) by z = (L-L0)/L0 where L is the wavelength at time of absorption (detection), and L0 was the wavelength at time of emission. for Doppler redshift z = v/c for small (non-relativistic) values of v. assuming the universe is expanding, I've read...
  12. H

    A redshift derivation question

    Hello I have been reading a textbook on cosmology and have come up against a self test question I just can't crack! Any help would be greatly appreciated: "The Cosmological redshift of a quasar is normally deduced from its emission lines. Let this redshift be ze. Suppose the quasar has...
  13. turbo

    Can Non-Cosmological Redshifts Explain Anomalies in Galaxy Interactions?

    Interestingly, the SDSS interactive learning site http://cas.sdss.org/dr3/en/ lists NGC 7603 and PGC 07041 as an interacting pair of galaxies, although their redshifts are very different. Go to the page below and find the image of NGC 7603 and PGC 07041. Click on the image to use the...
  14. J

    Debrolie Redshift missing energy?

    I'm a college freshman at the moment, so perhaps I'm just missing something simple. But none of my professors can give me an actual answer. If photons of light from distant galaxies undergo redshift because of the expanding universe. Also since particles have a wavelength according to...
  15. turbo

    Quantized space-time and redshift.

    I have been reading about Loop Quantum Gravity and about Spin Foam, and I am stuck on a (probably stupid) idea. It seems that one of the underpinnings of these concepts is that space-time is quantized in discrete units at the Planck scale. If space-time is quantized and the universe is...
  16. K

    Redshift depends on dark energy

    cosmological constant = lambda rho = mass density of dark energy lambda = constant x rho rho = lambda / constant rho x volume of universe = lamda / constant x volume of universe = total mass of dark energy in universe volume of universe = lambda / constant x total mass of dark...
  17. Link

    Light and Redshift in material?

    I have been reading in astrophysics that when light escapes a massive object its being slowed down by its gravity, but since it can't be slowed down its being redshifted. now in our high school physics books it says that light takes a diffrent path when its being slowed down when entering aother...
  18. T

    If light experiences gravitational redshift as said by GR

    If light experiences gravitational redshift as said by GR, then, where did the difference between the initial and final energy, E = \frac {hc}{\lambda} go? From Hubble expansion, there is also redshift. Where did the energy difference go?
  19. A

    Cosmology: Expansion & Redshift Explained

    In my last Cosmology class, the professor explained how the expansion of the universe increase the wavelength of the light. But his explanation was a non-local one, I mean, you need to compare the time beween two wavecrests to determine that the light was redshifted. The explanation was that the...
  20. turbo

    Is the Redshift of Distant Objects Due to Expansion or Gravitational Effects?

    All other issues aside, a mathemetician who is asked to explain cosmological redshift (more distant objects regularly appear redshifted) could easily come up with a couple of reasons: 1) the universe is expanding rapidly in all directions, and the light from distant galaxies is redshifted due...
  21. K

    Is the Doppler effect responsible for redshifted photons and time dilation?

    If photons get redshifted on their way to the Earth by transferring energy to the dark energy of the cosmos their momenta would not be changed and cause blurring of objects because dark energy may not have momentum itself and so classical behaviour that would cause blurring would not...
  22. C

    Relativity vs Doppler redshift

    As I understand it, light will be redshifted when it travels from a large ( gravitationally speaking ) object to us. It will also be redshifted if the object is moving away from us. How do we know how much of the redshift is due to either effect ? :confused:
  23. B

    Silly question about redshift, relativity

    when we use redshift to determine direction, velocity of distant radiation sources do we not take into account the redshift due to gravitational forces? that is, if gravitational fields can lengthen wavelengths of light (as well as bend them) wouldn't more distant objects like far off...
  24. T

    Redshift Mechanisms and Supernova Lightcurves

    I came across Ned Wright's webpage http://www.astro.ucla.edu/~wright/tiredlit.htm which states that alternative explanations for the redshift of galaxies would not be consistent with the z-dependence of supernova lightcurves. However, this assertion is not further substantiated and as far as...
  25. I

    Is Redshift Really Proof of Universe Expansion?

    quote: ---------------------------------------------------------------------- Originally posted by shrumeo ... there has to be other data besides redshifting to confirm the expansion of the universe. I'd hate to know that so much theory is built on one type of data point...
  26. O

    Gravitational Redshift: Exploring a Theory with Physics

    Having only just learned of the existence of this board I feel that I should make use of it as i spend most of my free time working on seemingly useless theories, might as well see what others think. I have read a little on gravitational redshift but have never really understood the theory...
  27. S

    Redshift & Expansion: What Else Is There?

    Redshift = expansion?? I'm not a physicist so I'll probably be laughed at for asking this. I understand the concepts of redshift and the Doppler effect being used to substantiate the hypothesis that the universe is expanding, indeed accelerating, since the farther an object is the higher its...
  28. wolram

    Spectroscopic Observation of Anomalous Redshift in NGC 7603

    http://arxiv.org/abs/astro-ph/0203466 We present new spectroscopic observations of an old case of anomalous redshift--NGC 7603 and its companion. The redshifts of the two galaxies which are apparently connected by a luminous filament are z=0.029 and z=0.057 respectively. We show that in the...
  29. Greg Bernhardt

    Unraveling the Energy Redshift Paradox in General Relativity | Physics Post

    Within the framework of General Relativity in one of its most simple forms, the Schwarzschild solution, a very interesting paradox can be proposed involving the conservation of work / energy. It’s a puzzle for the Relativity buff. In this short discussion I outline this energy redshift paradox...
  30. R

    Time for Change: Exploring Relativistic Redshift Effects

    About Time! This paper has such a obvious ring of truth about it, one can only hope that the misconceptions are finally laid to rest, and we can move forward, for there is Relativistic change in the air. http://uk.arxiv.org/abs/astro-ph/0310808 Here is an interesting paragraph:In special...
  31. marcus

    The cosmological redshift is not the result of a Lorentz transformation

    We have a theoretical issue here. There is a misconception floating around PF about the relation of the cosmological redshift to present and past recession velocity. If a redshift is Doppler in origin then in the context of Special Relativity one has Einstein's correction of the Doppler...
  32. marcus

    Cosmological redshift: how much energy has gone missing?

    In the cosmol. redshift thread (Q) asked [[I would like to hear some interpretations of this phenomenon, especially in regards to what happens to the energy of photons in cosmological redshift – where do YOU think it goes? Is it lost or is it conserved?]] It is clear that a whole lot of...
  33. Q

    Cosmological Redshift: Exploring Photon Energy Loss or Conservation

    I would like to hear some interpretations of this phenomenon, especially in regards to what happens to the energy of photons in cosmological redshift – where do YOU think it goes? Is it lost or is it conserved?
  34. V

    Redshift Basics: What is the Redshift Phenomenon?

    Can anyone explain to me the red shift
Back
Top