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Cosmological vs Doppler redshift

  1. Mar 21, 2005 #1
    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 that the cosmological redshift is (for bodies co-moving with the expansion) directly and strictly related to this expansion of space z = (R0-R)/R where R0 is the scale size at time of absorption (detection), and R was the scale size at time of emission. However the important point here is that the equivalent "recession velocity" does not come into the equation - it is only the expansion of space during the time the photon travels from emitter to absorber which causes the redshift, and NOT the relative velocities of emitter and absorber (both emitter and absorber assumed to be co-moving with space).

    imagine a "model" universe which is expanding uniformly under a "freely coasting" scenario, ie neither accelerating nor decelerating. let us say the age of this universe (from Big Bang to now) is (for the sake of argument) 10 billion years. Now let us study a stellar object in this universe which is 1 billion light years away from us, ie the light from that object was emitted 1 billion years in the past, ie when the universe was only 9 billion years old and hence only 90% of the size it is now (it is freely coasting, so size is proportional to time). we measure the cosmological redshift of this object - what should we find? well R/R0 = 0.9 hence z = 1/0.9 - 1 = 0.111. This is for an object which is 1 billion light years distant.

    Let us study another object, which is now 2 billion light years distant. In this case R/R0 = 0.8 hence z = 0.25.

    Similarly, an object 3 billion light years distant will have R/R0 = 0.7 hence z = 0.429

    If we now plot z vs distance, we do not get a linear relationship :


    i know i must be doing something stupid, but what?

    where am I going wrong?
    Last edited: Mar 21, 2005
  2. jcsd
  3. Mar 23, 2005 #2
    I am not at all sure of the issues involved within the particulars of your proposition to answer, my appologies.
    However the subject is one which I find interesting. You see, the dynamics involved with the red shifts are those not just of the expansion of space, but of the effects of that expansion with the density of gravity.
    Were you to measure the red shift of light emitted by a body in your universe created say 9 1/2 billion years prior, the universe would have been a very small place indeed when that light was cast out. All the energy within that universe would be in a very small place as well. The gravity density therefore would be quite high. The time would be therefore quite slow.
    Now, energy emitted in a slow time frame would be red shifted when viewed from a faster time frame... even without spacial expansion to confuse the issue.
    Where does one draw the lines at???? I am uncertain as to how to view this issue, and remain puzzled at its implications in red shift theories.
    Failing to understand even as much as you now ask, I fear I shall only remain puzzled.
  4. Mar 23, 2005 #3


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    the relation between z and present distance to the object is not supposed to be linear (except approx at small distances)

    the relationship depends on the model. my advice is to learn how it goes in the standard model that most working cosmologists use (which is easy to learn because there are online calculators to compute it for you) and get accustomed to that before you try more exotic models

    suggest you experiment with Ned Wright's calculator at his website
    he teaches cosmology at UCLA and he has a popular website with an FAQ
    and everything is mainstream consensus

    or try Siobhan Morgan's calculator, she is another astronomy professor with a website of stuff for her students to use, the two calculators give the same answers about z and distance.

    you can google Ned Wright, the calculator is easy to find

    Last edited: Mar 23, 2005
  5. Apr 13, 2005 #4
  6. Apr 13, 2005 #5


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    Tired light rears its ugly head again. Is there no slaying the beast? I need to know where the missing energy went and what new laws of thermodynamics explain this anomaly.
  7. Apr 14, 2005 #6


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    Then you might like to read the eprintThe derivation of the coupling constant in the new Self Creation Cosmology pages 20 - 24.

    GR does not conserve energy - it conserves energy-momentum, which is different. Do not be surprised that the energy of the CMB is not conserved.

    The problem is the same question as where does the energy of a gravitationally red shifted photon go? Most textbooks talk about it climbing out of a potential well but the concept of potential energy is foreign to GR. There are no forces acting on such a photon, gravitation is understood simply to be an effect of curvature, no work is being done on or by the photon so why does its energy decrease? Again it is a time dilation effect that results in energy non-conservation.

    Energy is a frame dependent concept. To conserve energy you need to specify a particular, preferred even, frame of reference. The approach of SCC is to identify such a frame as that selected by Mach's Principle, i.e. the Centre of Mass/Momentum of the system. And to be consistent you have to both include a Machian - 'Brans Dicke type' scalar field and modify the equivalence principle, which is what SCC does.

  8. Apr 14, 2005 #7
    Both energy- and momentum conservation are concepts from classical Newtonian physics that can not be generalized to radiative i.e. quantum mechanical processes (Noether's Theorem or other similar theoretical arguments that purport to derive a general law of energy conservation use Lagrangian functions which in turn depend on the potential energy; the latter however is a concept of classical Newtonian physics and hence the theorem is also limited to it; for more see me webpage regarding Energy and Momentum conservation).
    There us therefore strictly speaking no energy conservation law for light. The latter could anyhow only be defined through its interaction with matter which depends not only on its frequency (i.e. the 'energy') but also on other parameters like the coherence length of the wavetrain of light or disturbances of the photoelectric process by other electric fields for instance (a wavetrain that consists only of a few coherent cycles won't be able to photoionize an atom i.e. for all practical purposes it will be lost; see also my page regarding the Photoeffect).
  9. Apr 17, 2005 #8


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    There's always 'death by a thousand observations' :smile:

    What specific, concrete, testable (in principle) predictions do these alternative views have for those with idle time on the Kecks, INTEGRAL, Spitzer, VLA, ... to get our teeth into?

    {Garth's OK; we need only wait another year or so, and GPB will reveal all}.
  10. Jan 9, 2012 #9


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    In http://home.claranet.nl/benschop/ether.htm I explain that Hubble's redshift readily follows from energy loss of a photon, proportional to travelled distance. This loss is absorbed by the medium it travels through, which is a dissipative ether medium (discarded by Michelson/Morely in the 1880's, because they ignored the possibility that ether could adhere to the rotating Earth, so naturally no propagation speed difference occurs in X and Y direction along the Earth surface).

    Eddington, who in the 1919 Sun eclipse measured light to bend around the Sun, explained this by a 'simulation' as he called it: an assumed ether would have a greater density near the Sun and cause by Snellius' refraction law this bending effect. This is precisely what I propose, but now as the REAL model of what happens. Also Mercury's precession (moving of its long axis of elliptic orbit) is then explained, as well as the microwave background noise in the Universe, namely all photon losses 'warming up' the (ether-) environment to some 3 degrees Kelvin.

    Notice also that Hubble himself (in a footnote of his 1931 paper with Humason) was in favor of the 'tired light' explanation, but since by Einstein (1916) the ether was discarded, he felt it safer to go with the establishment - because as he said "some new physics" would be required (here: existence of a dissipative ether medium), which he apparently did not feel to enter into.

    No expanding Universe is necessary for the redshift, which moreover is quantized, possibly due to the photon energy to be quantized at its generation (a photon is generated when an electron falls back one or more orbits in an atom). Ether-drag could be shown in the laboratory, with a Sagnac (1915) type of experiment: two glass fiber coils (clockwise and counter clockwise) around a fast rotating heavy core. Such equipment (without the rotating core) is used in modern airplanes as a 'fiber gyroscope'.
    ---- Best regards, Nico Benschop.
  11. Jan 9, 2012 #10
  12. Jan 10, 2012 #11


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    It is not a matter of scattering, as the wikipedia article say, but ether is a continuous medium -- which is necessary for light propagation. After all, light (photons) is agreed to be a wave phenomenon. How light propagation can happen without a medium (that 'waves') has always been a mistery to me. The propagation speed in that ether medium is for all practical purposes the lightspeed c in "vacuum", but likely changes by density modulation near a heavy body such as the Sun or Earth. There is then no law against breaking the lightspeed barrier by a projectile of enough energy (re: the CERN neutrino).

    For instance, if ether density near a heavy body is to drop off by 1/r , and if 'gravity' is assumed to be its gradient -1/(r^2) , then you have Newton's gravity law!.

    Last edited: Jan 10, 2012
  13. Jan 10, 2012 #12


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  14. Jan 10, 2012 #13


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    So why can't we accelerate other particles to beyond light speed here on Earth? We give them MUCH more energy than the neutrino's at CERN have.
  15. Jan 10, 2012 #14


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    That may have to do with certain neutrino properties, like having no charge (can't be accelerated by EM field). At CERN they are produced by collision of other particles that can be accelerated, such as protons.

    It would be interesting to find out if a cone-formed shockwave occurs at breaking the lightspeed barrier, similar to the shockwave resulting from breaking the sound barrier.
  16. Jan 10, 2012 #15


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    The neutrino's are a product of the decay of certain particles. The decays have nothing to do with the kinetic energy of the particle other than to cause time dilation relative to us.

    I don't think the neutrinos are acceleratred upon decay. I think they simply have the velocity from the decay.
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