Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The vicious circle of standard redshift explanations

  1. Jun 19, 2013 #1
    We should all know that photons only exist in quantum mechanics. In fact, the idea that energy comes bundled in discrete units is what actually caused QM in the first place.

    For some reason, however, I've spent my entire life under the assumption that cosmologists make true statements about the nature of light. But then I realized that GR consists of field equations that are only meant to model gravity fields. Other than gravity, these equations cannot be used to describe the nature of any other phenomena.

    Of course, it is possible for people with advanced degrees in cosmology to speak in rather informal ways about the nature of EM propagation within inter-galactic space. But this is a long way from the assertion that they are speaking in ways that are universally accepted by the scientific mainstream.

    Really, the only "mainstream" when it comes to the nature of EM propagation is the branch of QM known as quantum electrodynamics. Cosmologists are stuck in the 19th century if they think that Hubble's law can possibly be explained by a Doppler effect.

    In QM, a photon is simply an invariant unit of energy. There is absolutely no spacetime description involved in this concept, so relativistic arguments (either SR or GR) that depend on reference frames simply do not apply.

    In order to establish a mechanism for a Doppler effect on EM propagation, we have to eliminate the photon concept entirely, and go back to a classical, wave-based theory. But in this case, we revert back to the blackbody problem circa 1890's, and all of the issues of "ultraviolet catastrophe" that surrounded it.

    It is for all of these reasons that Einstein spent his later decades trying to come up with a unified field theory. If he had succeeded, we would have been given field equations that could be solved in order to yield cosmological solutions that include the EM field. But he didn't succeed, so we are left with immaterial metric systems that are supposed to expand over time.

    Cosmologists use flawed logic in the arguments concerning the reason for redshift. They say it cannot possibly be any quantum mechanical cause, and so it must be a relativistic one. But when it comes to offering any reasoning as to how a fundamentally quantum mechanical entity such as a photon can possibly suffer relativistic effects, they simply point to the empirical phenomenon of redshift itself.

    In other words:

    The phenomenon of redshift is caused by relativistic effects, and these effects are proven by the phenomenon of redshift itself.

    This is a vicious circle.
  2. jcsd
  3. Jun 19, 2013 #2


    User Avatar
    Science Advisor

    First of all, the wave solutions to the classical Maxwell equations are perfectly fine for studying the kind of phenomenon you are talking about; it is in the classical domain. Secondly, the curved space-time Maxwell equations are coupled to the Einstein field equations so the two are obviously not independent of each other in general.
  4. Jun 19, 2013 #3


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Doppler radar works. Police cars and aircraft use it.
    Quantum EM entities (e.g. photons) experience relativistic effects.
  5. Jun 19, 2013 #4
    This is also entirely incorrect.
    First off the photon is a proven particle it does not rely on QM to explain it. QM simply does a good job of it. By the way Einstein was involved in showing the quanta nature of EM.
    Hubbles law states " the greater the distance the greater the recessive velocity. It makes no claims such as what you described above.
    Doppler shift may be similar to cosmological redshift but is not the same thing. Although there have been attempts to prove otherwise.

    Did the nature of photons having both a particle and wave characteristics not mean anything to you?
    The reason why Einstein could not develop GUT has nothing to do with redshift, but rather due to lack of evidence for the graviton. Any GUT theory involves extremely high temperatures one could say at certain temperatures one force becomes indistinguishable from another this data is based upon its force carriers or bosons. Graviton being the theoretical boson of gravity. There are others better qualified than I to discuss the symmetry breaking.
    Blackbody temp is understood thanks to Hawkings and does
    involve QM.

    I highly recommend you revisit your studies as it appears your in serious error in many a concept
    from what you wrote above.

    Edit I see others posted while I was typing. Also I forgot to add gravitational redshift is also not quite the same as doppler shift. The prinary difference is the cause and degree of effect in each.
    Last edited: Jun 19, 2013
  6. Jun 19, 2013 #5
    Um, you are talking about the frequency differences between series of EM pulses, as applied in a classical setting. Changes in frequency of individual photons that move along linear paths in void space is another thing entirely. I really don't think you mean to say that police radar guns need to interpret atomic spectral patterns in order to issue speeding tickets!

    E=hv is the invariant definition of the photon in QM. Relativistic effects are not applicable to this strict defintion.
  7. Jun 19, 2013 #6


    User Avatar
    2017 Award

    Staff: Mentor

    Do you mean special or general relativity here? Special relativity is the framework of quantum electrodynamics. The doppler effect is a direct result of QED.

    You do not need QM to study the CMB, you can treat it as classical waves.
  8. Jun 19, 2013 #7


    User Avatar
    Science Advisor

    That is not the definition of a photon in the slightest. Regardless, you seem to be thinking that there is no relativistic description of QM, which is erroneous.
  9. Jun 19, 2013 #8
    A photon is a theoretical entity whose creation is identical with the creation of QM.

    photon discovery == QM

    Please show me a definition of cosmological redshift that is not described exactly in Doppler shift terminology.

    Ahh... the so-called "wave-particle" duality. Let's look at what wikipedia has to say about this:

    This means that things which are particles show characteristics that can be alternatively described as particle-like and wave-like. First of all, if something is a particle, then it is completely redundant to say that it exhibits particle-like properties. If you really want to get into the precise nature of the "wave-like" properties, you are going to have to dive into the insanity that is otherwise known as interpreting the physical significance of the wavefunction. I wouldn't recommend getting involved in such a pursuit.

    Einstein didn't have anything to do with modern GUT's...

    unified field theory != modern GUT

    I highly recommend you read Thomas Kuhn's Black-Body Theory and the Quantum Discontinuity, 1894-1912 for an in depth discussion of the history of QM.
    Last edited by a moderator: May 6, 2017
  10. Jun 19, 2013 #9
    Sorry but the photon is an elementary particle with known properties. Not theoretical. Yes the term quantum relates to photon.

    not sure how Kuhn's book on blackbody help considering the dates you published. However as I enjoy historical articles I'll try to dig it up. If you look at my signature you'll see my interest in the history of sciences from the first link. If I can find that book I may include it.
    Would be interesting on the blackbody aspects. Might even include some older terms
    white or grey body lol.
    For that matter I own a physics textbook written in the 1920's
    here is a passage of said book.

    How is light transmitted?

    "One method is commonly called emission or Corpuscular theory which was strongly upheld by Isaac Newton he believed luminous bodies sent out small particles which produce the sensation of light when they strike the eye. This theory was commonly accepted for over a century and was finally overturned because of experimental evidence and results that could not be explained. We must necessarily turn to the second method which has been called the wave theory"

    coincidentally this book does not include any of Einsteins work or QM. Also the atom had no neutron.
    So to say that photon and QM developed at the same time isn't accurate. Considering that there was evidence for the wave
    particle duality prior to QM

    edit I just clued in that I completely forgot about Plancks blackbody radiation law. My apologies on that score
    Last edited: Jun 19, 2013
  11. Jun 19, 2013 #10
    I mainly mean SR, because it is less controversial, easier to understand, easier to talk about, etc.

    Haha, that is a very interesting statement that seems to fly in the face of everything I know about modern physics.

    Wikipedia makes the following statements about QED:

    1) In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved.

    2) In technical terms, QED can be described as a perturbation theory of the electromagnetic quantum vacuum.

    I find it highly inadvisable to naively accept any and all "in essence" type statements about topics that are as technical as QED. Nevertheless, the idea that SR is the "framework" of QED is a far cry from statement #1. Which leaves statement #2. This one is much closer to my understanding, and I have no earthly idea with what SR has to do with perturbation expansions, aka Feynman diagrams.

    QED is purely a theory of interactions between quantum objects. Doppler effects have nothing to do with interactions. The primary mechanism to change the wavelength of a photon in QED is Compton scattering. But this is a "tired light" mechanism that is abhorred by modern cosmologists.

    Right... so we therefore need a theoretically acceptable wave-like model of EM signal propagation. But the currently accepted theory is based on the statistical interpretation of the wavefunction. Welcome to my world.
  12. Jun 19, 2013 #11


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I'm trying to understand. What I suspect is that you are totally mistaken and off on your own eccentric theory. But I have to study what you are saying. Here's related stuff from another thread 17 June:
    It sounds like you are saying a photon is a definite amount of energy. But it isn't! The amount of energy it represents depends on the reference frame. And also like you especially mistrust cosmologists, for some reason.

    So cosmologists as a group are flawed reasoners and going against Quantum Mechanics. Also sounds like God gets into it.

    With all respect the idea that QM contradicts redshift sounds quite wrong, even a bit crackpot. Doppler effect is perfectly in accord with QM. And Bunn and Hogg have shown that the cosmological redshift can be considered/analyzed as a series of many successive Doppler redshifts along the photon's path.

    I think this has been pointed out several times already. When one says relativistic QFT one means special. Quantum theory of matter is in good accord with SR. Likewise QED is in accord with SR. The remaining challenge in that department is to get the quantum theory of matter to work with general relativity. But redshift and Doppler is not the issue, there. Doppler is SR and OK with QM, plus redshift can be analyzed as Doppler.
    Last edited: Jun 19, 2013
  13. Jun 19, 2013 #12
    Quibble with semantics much? :uhh:

    Okay, I'll call your bluff. I would just love to know how the highly abstract/mathematical notion of "relativistic", as applied to the Dirac equation has any relation to the everyday notion of relativity, in terms of causal/deterministic descriptions of physical processes that occur in classical spacetime.
  14. Jun 19, 2013 #13
    There is a book I have a link to although its incredibly lengthy 889 pages. Its called fields. It may offer some insight on QFT in terms of QM and SR. Im still studying it myself I recall the beginning section describing that as well as feyman diagrams in similar regards. May or may not interest you.


    forgot to mention it also covers classical fields QCD QED perturbation theory as well as string theory. Also goes into GUT etc. A quite handy compilation of anything involving feilds

    here is one related passage

    Cosmology is discussed with just the dilaton instead of full general relativity (subsectionIVA7).With only some minor fudges, this is sufficient to fit the post-inflation universe to observations. (3)We derive the Feynman rules in terms of background fields rather than sources (subsectionVC1);this avoids the need for amputation of external lines for S matrices or effective actions, and is more useful for background-
    field gauges
    Last edited: Jun 19, 2013
  15. Jun 19, 2013 #14


    User Avatar
    Science Advisor

    Calling out wrong physics is not semantics.

    Open up any book on QFT. Before you make blanket authoritative remarks make sure you learn the physics first please.
  16. Jun 19, 2013 #15


    User Avatar
    Gold Member
    2017 Award

    I don't think so. That's no definition, it's a formula. E.g. do you see any mass, charge and spin present in that formula? Einsteins photoelectric photon is from 1905; photon discovery ≠ QM, you've skipped the rest of quantum mechanics and quantum field theory. Cherrypicking is not helpful if a person wants to get a better understanding.

    I'm not sure at all what you are getting at here, but if you think we can't see any relativistic effects, you are wrong:

  17. Jun 19, 2013 #16
  18. Jun 19, 2013 #17
    Yes, those cosmologists in the 1800s were really immature when they tried to apply the Doppler Shift to a theory postulated by Lemaître in 1927, and confirmed by Edwin Hubble a few years later.
  19. Jun 20, 2013 #18


    User Avatar
    2017 Award

    Staff: Mentor

    I suggest to take an actual book about QFT, not Wikipedia. Anyway, this is the relevant part:
    I can remove the "in essence" if you like ;).

    Newtonian mechanics uses Newtonian spacetime as framework.
    QFT uses special relativity as framework.

    Don't do it naively, read a book and do it in an educated way!
    QED is not perturbation theory. Perturbation theory is a possible method to calculate QED processes.
    You can do Lorentz transformations on your interactions. QED makes sure that the resulting physics stays the same, but you get different photon energies in different frames.

    You do not need any statistical interpretation of a wavefunction.
  20. Jun 20, 2013 #19
    Special relativity is a theory about of and reference frames, mass and energy. You can put deterministic interactions into it, but that's not special relativity itself; SR is just the stage!
    Similarly, one can put non-deterministic interactions into the SR setup, which is essentially just a geometric model of spacetime - Minkowski space - along with laws describing how to move from one reference frame to another - Lorentz transformations (or the Poincare group).
    In this sense, QED fits perfectly into SR just as electromagnetism did. I'm sure you'd agree EM takes place in SR, but that EM isn't itself SR. QED is a quantised version of EM and takes place in SR the same way classical EM does.
  21. Jun 20, 2013 #20
    From the glengarry...quite a post..too wdie ranging to cover it all, but let's try this piece:

    simple example why this is wrong: a photon emitted from a star loses energy, is redshifted, as it moves to a less negative potential further from the star....it gives up kinetic energy [but not speed] and gains potential energy. [This is a static spacetime example]

    This issue of dynamic spacetime [expanding cosmological distances] is [I think] more subtle....theBunn and Hogg paper Mordred linked explains...it IS worth reading....

    You can also think about how you would true up your statement with this fact: the CMBR has cooled from about 3,000 to about 3 degrees Kelvin.... so you KNOW the energy of CMBR photons has dropped dramatically....otherwise, earth could not have formed....nor galaxies....

    Here are some descriptions from an earlier discussion [I'll see if I have the link in my notes] that if you read them carefully, will show how your statement is not accurate in cosmological settings. It took me a few years of reading expert explanations here before I tumbled to some of the subtleties..[likely some still elude me]!!

    Jonathan Scott:

    PAllen: gravity or no, at any point along the light path, there are observers who will measure every possible frequency (different states of relative motion between observers). So trying to factor out change due to gravity versus relative motion means identifying which of these frames at different places and times are ‘statically related’, thus differences in frequency are then considered due to gravity.

    However, in general, there is no unique or preferred way to make such a global assignment; thus no unambiguous way to separate out gravity from relative motion. In effect, such an assignment amounts to a choice of coordinates. For any such choice, you can say “yes, there is mass/energy producing curvature”, but different choices lead to different divisions of gravitational versus Doppler shift.

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: The vicious circle of standard redshift explanations
  1. The standard (Replies: 2)

  2. Cosmological redshift (Replies: 8)