The cosmological redshift is primarily caused by the metric expansion of space, which stretches photons as they travel through the universe. This phenomenon results in a shift of light towards longer wavelengths, typically observed as redshift in distant galaxies. Compton scattering with free electrons in stellar atmospheres does not contribute to cosmological redshift, as it cannot shift emission lines to different wavelengths. Instead, the redshift is accurately measured through specific emission lines unique to each atom, which remain consistent despite the expansion of space.
PREREQUISITESAstronomers, astrophysicists, and students of cosmology seeking to deepen their understanding of redshift phenomena and the underlying principles of light behavior in an expanding universe.
The metric expansion of space "stretches" photons in flight. That's not very rigorous, but I don't know how to state it rigorously at B level.itoero said:
No. The corona isn't uniform across the sky, nor is the Sun's position in the sky constant. So you'd expect to see a strong angular dependence and seasonal variation to any effects related to the Sun. We don't.itoero said:
And you should understand that's just an explanation.Ibix said:
Blueshift and redshift is due to inelastic scattering of photons.CWatters said:
It can't be compton scattering. Compton scattering dims bluer light while emitting light at a spread of lower wavelengths.itoero said:
By just losing it. Your very understandable confusion arises because you think you can extrapolate a local effect (energy is conserved) to cosmological distances, where in fact it doesn't work. That is, energy is NOT conserved on cosmological scales. **itoero said:
Redshift typically varies with distance from the star, why/how would scattering at the source effect that?itoero said:
Also, you can interpret it as just a version of the Doppler effect: the photon is redshifted because the source is moving away from us.phinds said:
phinds said:
But it can create red light and inverse compton scattering blue light.kimbyd said:
Not sure what your thought process is that leads you to this erroneous conclusion, but you would be well served to consider that thousands of physicists have looked at this and are all in agreement with Caroll. Do you really think you've figured it out where they have not?itoero said:
I do recommend reading Carroll's blog post, which describes what I'll say here in different words. It's not that there isn't any conservation law at all. General Relativity follows a different conservation law (technical name: conservation of stress-energy). This conservation law forces energy to change in a predictable, consistent way under certain conditions.itoero said:
But you can't create emission lines that way. Compton scattering takes incoming blue light and emits a spread of wavelengths in a variety of directions. The overall effect when looking at a source through intervening gas is that incoming blue light has been reduced, while a much fainter and redder glow is produced (it's fainter because most of it gets deflected in a different direction). There's no noticeable effect on emission lines.itoero said:
The cosmological redshift is due to increasing distances between emission and absorption of the photon. In flat Minkowski spacetime we talkt about Doppler redshift in this case (increasing distances). In FRW spacetime we have no global inertial system like in Minkowski spacetime but it is legitimate to consider an accumulation of infinitesimal redshifts as @kimbyd pointed out in #8.hitoero said:
itoero said:
Galaxies with reasonably-high redshifts are often blue to the eye. Galaxies with lots of active star formation were more common a few billion years ago. When a galaxy, or a part of a galaxy, is actively forming stars, most of the light we see comes from the most massive stars. Even though the massive stars are relatively few in number, they are so much brighter than the smaller stars around them that they make up most of the light. But those bright stars don't last very long, sometimes only tens of millions of years. The longer-lived stars are dimmer and redder, so over time galaxies get dimmer and redder.timmdeeg said:
In this case the corresponding emission lines should be in the ultraviolet range, not sure which electronic transitions are involved here. Whereas the visible emission spectrum of such galaxies is depending on ##z## shifted to infrared wavelenghts and hence is invisible to us, correct?kimbyd said:
The primary Hydrogen Lyman-##\alpha## line is in the UV range, so, yes!timmdeeg said:
Yes indeed, its easy to see them. Thanks for your explanations.kimbyd said:
Arp's ideas might have been considered an alternative maybe 50 years ago. As evidence kept mounting in favour of BB cosmology, he stuck to his guns, accusing mainstream cosmologists of dogmatic rigidity - which is what the majority of Seeing Red is about. The irony must have been lost on him.Torog said:
It means that if you integrate Doppler shift between a string of infinitesimal points along the path of light traveling through expanding space, you get cosmological redshift.itoero said:
You've got this backwards. One needs to propose a mechanism to account for the observables (precise mathematical formulation of the physical process, not 'maybe it's X') to at least a degree comparable to the cosmological redshift. Nobody says expansion is the only possible cause of redshift - in fact, other causes are known, such as gravitational redshift. But it's the only cause that could be shown to account for the observables in a satisfactory manner. And by now there's a lot of observables.itoero said:
Bandersnatch said:
Well of course there is -- redshift is just light's equivalent of doppler shift. This has been mundane science (obvious, well accepted) for 150 years!itoero said:
No. Not even a little bit possible. Let me be clear: Redshift due to motion happens. It has been confirmed in observations in our own solar system, where cosmological effects don't exist. So any alternate explanation to cosmological redshift would have to be in addition to the effect of motion.
"Seeing Red" might be from 20 years ago, but his idea on intrinsic redshift originated more than 50 years ago. That's the point: it hasn't gotten better since then, but mainstream cosmology has.Torog said:
russ_watters said:
The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It describes how properties of a wave change, it doesn't explain how they change.Bandersnatch said:
Yes redshift due to motion happens.. But it's unknown how/why motion causes redshift. The 'fact' that we don't observe Cosmo shift in our solar system is rather normal since we circle(ellipse) around the sun, which means the Earth remains+/- in the same gravitational field and the Corona of the sun remains +/- on the same distance so no reason to observe Cosmo shift.russ_watters said:
This just isn't true. Predicting Doppler/red shift is a simple matter of geometry and it works as predicted because it is clearly understood how/why it is happening. There is no mystery here and you are going to need to put more effort into understanding the how/why instead of ignoring it if this thread is to continue.itoero said:
To add a little bit to what russ_watters said above, this is really not true. The Doppler Effect is really easy to understand as a consequence of the fact that relative to the observer, the source was at a different location when it emitted one part of the wave versus another.itoero said:
