Expansion

[Catastrophe]

Looking through the above, Wiki probably gives the most concise answer:

"In Einstein's general theory of relativity, the gravitational redshift is the phenomenon that clocks deeper in a gravitational well tick slower when observed from outside the well. More specifically the term refers to the shift of wavelength of a photon to longer wavelength (the red side in an optical spectrum) when observed from a point at a higher gravitational potential. In the latter case the 'clock' is the frequency of the photon and a lower frequency is the same as a longer ("redder") wavelength.

The gravitational redshift is a simple consequence of Einstein's equivalence principle (that gravity and acceleration are equivalent) and was found by Einstein eight years before the full theory of relativity.

Observing the gravitational redshift in the solar system is one of the classical tests of general relativity. Gravitational redshifts are an important effect in satellite-based navigation systems such as GPS. If the effects of general relativity were not taken into account, such systems would not work at all."

 

[Catastrophe]

David

My head is beginning to hurt! Whilst looking at
Cosmological redshift Equivalence Principle

I came across the following:

Journal of Cosmology and Astroparticle Physics
Testing the equivalence principle on cosmological scales
Camille Bonvin and Pierre Fleury
Published 25 May 2018 • © 2018 IOP Publishing Ltd and Sissa

From Abstract:
The equivalence principle, that is one of the main pillars of general relativity, is very well tested in the Solar system; however, its validity is more uncertain on cosmological scales, or when dark matter is concerned.

Cat

 

[David-J-Franks]

Looking through the above, Wiki probably gives the most concise answer:

"In Einstein's general theory of relativity, the gravitational redshift is the phenomenon that clocks deeper in a gravitational well tick slower when observed from outside the well. More specifically the term refers to the shift of wavelength of a photon to longer wavelength (the red side in an optical spectrum) when observed from a point at a higher gravitational potential. In the latter case the 'clock' is the frequency of the photon and a lower frequency is the same as a longer ("redder") wavelength.

The gravitational redshift is a simple consequence of Einstein's equivalence principle (that gravity and acceleration are equivalent) and was found by Einstein eight years before the full theory of relativity.

Observing the gravitational redshift in the solar system is one of the classical tests of general relativity. Gravitational redshifts are an important effect in satellite-based navigation systems such as GPS. If the effects of general relativity were not taken into account, such systems would not work at all."

You've provided a good description of gravitational redshift. The whole point of my question to rod, is, that I think this is the wrong type of redshift used to measure the expansion of the universe and receding stars and galaxies etc. As I said, I think it is 'cosmological redshift' which is used, i.e. that caused by the fabric of space stretching. This is a separate phenomenon to gravitational redshift that you mentioned above.

I think it's 'cosmological redshift' which rod is saying can't be tested in a laboratory. Yet at the same time rod said - "the redshift used to explain the expanding universe depends upon the interpretation from the principle of equivalence" - which I take as gravitational redshift. That's why I'm asking rod to clarify things.

Personally I think it's none of the above, and that it's all down to the good old fashioned doppler shift

 

[Catastrophe]

Thank you for your patience over this redshift question. I think I will also be interested now when rod returns to clarify.

 

[rod]

Hi Cat, in my post above, rather than post 7, I should have used a quote from rod in post 5, as below:

"Hawkstein, the redshift used to explain the expanding universe depends upon the interpretation from the principle of equivalence. Do you have a specific particle experiment from labs studies that shows 3D space is expanding, and at what rate? Example, something by shooting particles around near c."

It looks clearer to me from this post, that rod is suggesting the expansion of the universe was measured using gravitational redshift. I'm under the impression that the type of redshift used to measure expansion is that caused by the expansion or stretching of space, not the type which is caused by gravity.

That's why I asked him to explain a bit more. So my question to rod still stands.

It's also why I asked him - "is the redshift due to the expansion of space or a doppler shift or a bit of both?"

I did look up Principle of equivalence red shift as you suggested and discovered that what I referred to as redshift due to expansion of space is actually called 'cosmological redshift',

I'm still working on the second topic in your post

David-J-Franks, some good notes by you. The cosmological redshift from what I understand is the basis for determining distances to galaxies using H0 constant and the redshift is interpreted based upon the principle of equivalence too. Halton Arp in the past showed images of quasars with large redshifts that could be connected by gas to their host galaxies, those galaxies showed a much smaller redshift compared to the possible, nearby quasar. This challenged the cosmological interpretation of the redshift. Big Bang cosmology does not accept such challenges though. Photons are supposed to redshift as the photon travels through expanding space based upon the principle of equivalence. Based upon my readings, particle experiments (example, colliders and particle accelerators) has not documented this affect, presently. As I understand, photons are not observed doing their redshift as they travel across the solar system either, example, New Horizons communications or telescope spectra measurements of light from the Galilean moons at Jupiter. You mentioned the idea that expanding space is it *proven*. That is a difficult topic I think when it comes to proving something in science. Here is an example. From a source that sent me this info on the CMBR. "The basis of a very large redshift (z~1000+) for the CMBR is a comparison between its current temperature (2.7 K) and the presumed temperature at the "surface of last scattering", about 3,000 K - see for example https://www.universeadventure.org/big_bang/cmb-origins.htm and https://ned.ipac.caltech.edu/level5/Glossary/Essay_lss.html. It is based on a standard version of the big bang model."

My note back to my source, ["thanks. This is not the same as spectra obtained for high redshift galaxies then, but a model dependent interpretation of z. For example, ‘Characterizing the Environment Around The Most Distant Known Galaxy’, https://ui.adsabs.harvard.edu/abs/2019hst..prop15977O/abstract “The discovery of the very luminous galaxy GN-z11 at only 400 Myr after the Big Bang in the GOODS-North field with an HST grism spectroscopic redshift of z=11.1+/-0.1 presents a real puzzle for early Universe science. Its detection raises significant questions about our understanding of early galaxy formation…” I note a difference here. *spectroscopic redshift* vs. the model dependent assumption of original temperature some 3000K vs. near 3K today for the CMBR. Q:Is the science used to show z>=1000 for the CMBR as good as the spectroscopic redshift measurement for GN-z11? The CMBR interpretation may be supported by more circular reasoning I think.]

Is the CMBR redshift where z>=1000 proven? My answer is no. Is the *spectroscopic redshift* of GN-z11 a better supported measurement (because it is observable and measurable today) than the CMBR redshift (theoretical calculation)? My answer is yes.

 

[David-J-Franks]

David-J-Franks, some good notes by you. The cosmological redshift from what I understand is the basis for determining distances to galaxies using H0 constant and the redshift is interpreted based upon the principle of equivalence too. Halton Arp in the past showed images of quasars with large redshifts that could be connected by gas to their host galaxies, those galaxies showed a much smaller redshift compared to the possible, nearby quasar. This challenged the cosmological interpretation of the redshift. Big Bang cosmology does not accept such challenges though. Photons are supposed to redshift as the photon travels through expanding space based upon the principle of equivalence. Based upon my readings, particle experiments (example, colliders and particle accelerators) has not documented this affect, presently. As I understand, photons are not observed doing their redshift as they travel across the solar system either, example, New Horizons communications or telescope spectra measurements of light from the Galilean moons at Jupiter. You mentioned the idea that expanding space is it *proven*. That is a difficult topic I think when it comes to proving something in science. Here is an example. From a source that sent me this info on the CMBR. "The basis of a very large redshift (z~1000+) for the CMBR is a comparison between its current temperature (2.7 K) and the presumed temperature at the "surface of last scattering", about 3,000 K - see for example https://www.universeadventure.org/big_bang/cmb-origins.htm and https://ned.ipac.caltech.edu/level5/Glossary/Essay_lss.html. It is based on a standard version of the big bang model."

My note back to my source, ["thanks. This is not the same as spectra obtained for high redshift galaxies then, but a model dependent interpretation of z. For example, ‘Characterizing the Environment Around The Most Distant Known Galaxy’, https://ui.adsabs.harvard.edu/abs/2019hst..prop15977O/abstract “The discovery of the very luminous galaxy GN-z11 at only 400 Myr after the Big Bang in the GOODS-North field with an HST grism spectroscopic redshift of z=11.1+/-0.1 presents a real puzzle for early Universe science. Its detection raises significant questions about our understanding of early galaxy formation…” I note a difference here. *spectroscopic redshift* vs. the model dependent assumption of original temperature some 3000K vs. near 3K today for the CMBR. Q:Is the science used to show z>=1000 for the CMBR as good as the spectroscopic redshift measurement for GN-z11? The CMBR interpretation may be supported by more circular reasoning I think.]

Is the CMBR redshift where z>=1000 proven? My answer is no. Is the *spectroscopic redshift* of GN-z11 a better supported measurement (because it is observable and measurable today) than the CMBR redshift (theoretical calculation)? My answer is yes.

Some great links rod, thanks for that. It's especially easier to understand coloured diagrams with moving squiggly lines on them than it is reading Wikipedia. However all the redshifts seem to be explained by saying that space is expanding. There's no mention anywhere of the equivalence principle, so I've come back to haunt you.

As far as I understand there are 3 causes of redshift

1 - Gravitational redshift including the equivalence principle.

2 - Dopler shift.

3 - Cosmological redshift, i.e. that due to expanding space.

The cosmological redshift from what I understand is the basis for determining distances to galaxies using H0 constant and the redshift is interpreted based upon the principle of equivalence too.

You seem to have put 2 methods in one sentence, in other words, what has the cosmological redshift got to do with the equivalence principle.
You go on below to say a similar thing -

Photons are supposed to redshift as the photon travels through expanding space based upon the principle of equivalence.

Again what has the photon travelling through expanding space got to do with the principle of equivalence.

Gravitational redshift requires a strong gravitation field or big acceleration. There is almost no gravity between us and distant galaxies and very little acceleration, so I can't understand what use the equivalence principle is for measuring galactic distances.

If you don't like cosmological redshift, as I don't, that just leaves the doppler shift as the only redshift method.

Have I got my redshifts in a twist rod?

 

[Catastrophe]

David
The following is from Swinburne:
"For example, in a distant binary system it is theoretically possible to measure both a Doppler shift and a cosmological redshift. The Doppler shift would be determined by the motions of the individual stars in the binary – whether they were approaching or receding at the time the photons were emitted. The cosmological redshift would be determined by how far away the system was when the photons were emitted. The larger the distance to the system, the longer the emitted photons have travelled through expanding space and the higher the measured cosmological redshift."

This seems to agree with your conclusions re: 2 and 3.
It seems to me to come down to whether you think the 'possible' expansion of intervening space has any validity. If not, then you are right (in my humble opinion) to settle only on 2.
I am not sure whether 'expansion' has any validity in this case or not. As you know, I have reservations on this. However, something is going on in the intervening space. It seems to me to be suspiciously like 'the ether'. Ouch! Back to the Michelson-Morley Experiment. Then look again on my comment on dark matter and cosmological scale.
I feel that I am siding with your conclusion but for different reasons. Doppler, yes, but I still think something else in there needs consideration. Keep up the good work!

Rod, I would welcome your comment on the Swinburne quote.

Cat

 

[Catastrophe]

I am coming back to this (from abstract above):

"The equivalence principle, that is one of the main pillars of general relativity, is very well tested in the Solar system; however, its validity is more uncertain on cosmological scales, or when dark matter is concerned."

 

[dfjchem721]

Sorry to bring this up in case I missed it earlier, but have any of you folks looked up Hubble's Law? Clearly the majority view of learned scientists in the field of cosmology have no problem with the expansion of the universe, nor the red-shift, or how it occurs. The expansion is known as the "Hubble Flow". It should be pointed out that while civil courts have overturned many laws, science has never done so.

Hubble's law - Wikipedia

en.wikipedia.org

My limited commentary on the whole issue is the current (and probably unending) debate on the value of the Hubble Constant (HC). This constant is a unit that describes how fast the universe is expanding at different distances from a particular point in space. Most who study this largely base the value on the CBR. I have always had a problem with how much information can be obtained from all that ancient radiation. A quick look at that story compels many to have the same qualms:

Cosmic background radiation - Wikipedia

en.wikipedia.org

I read recently somewhere that empirical data of redshifted red giant stars in distant galaxies provided a different value for the HC, and there can be only one value if you are playing it "by the law". This pits some hard data against the presumptions made with the CBR data, but I am in no position to grade these observations. I am however a big fan of empirical data, and while the CBR may also be called that, its interpretation is vastly more complex than "average".

Everybody has their own idea of this whole thing no doubt, but most seem to have a firm grip on the overall picture. I could be wrong on that one.......

 

[Catastrophe]

dfj

"I read recently somewhere that empirical data of redshifted red giant stars in distant galaxies provided a different value for the HC, and there can be only one value if you are playing it "by the law.""

I, too, am concerned with the (almost) many values to be found for the HC. To me, this just underlines the abstract I quoted above.

I am beginning to see a picture where the BB may be based on unjustifiable assumptions, and the same is beginning to apply to expansion when empirical data seems to fit within the Solar System but begins to turn upside on a cosmological level.

Cat

 

[Catastrophe]

So, about the Hubble 'Constant':

Date published Hubble constant (km/s)/Mpc
2017-10-16 70.0+12.0 −8.0
2016-11-22 71.9+2.4 −3.0
2016-08-04 76.2+3.4 −2.7
2016-07-13 67.6+0.7 −0.6
25 more rows

The 25 more rows takes you to Hubble's Law which concludes:
"Hubble inferred the recession velocity of the objects from their redshifts, many of which were earlier measured and related to velocity by Vesto Slipher in 1917. Though the Hubble constant {\displaystyle H_{0}}H_{0} is roughly constant in the velocity-distance space at any given moment in time, the Hubble parameter {\displaystyle H}H, which the Hubble constant is the current value of, varies with time, so the term 'constant' is sometimes thought of as somewhat of a misnomer."

Sorry about the table formatting; it got scrambled in the paste. I think it is understandable. The first value should be 70.0 and so on with subsequent values.

 

[dfjchem721]

Had to find a reference to that red giant data. Actually they used the HST to observe the "helium flash" from distant red giants and used their light intensities to develop a measuring stick to more and more distant flashes in more distant galaxies and came up with redshift values for various galaxies containing these red giants. From this data the HC has a slightly different value than they have found using Cepheid variables.

Certainly worth a read:

New measure of Hubble constant adds to mystery about universe’s expansion rate

Prof. Wendy Freedman leads study of red giant stars for new measurement of disputed constant

news.uchicago.edu

 

[Catastrophe]

dfj

Thank you for that interesting reference.
The following is extracted therefrom:
"Twenty years ago, the Hubble Space Telescope Key Project team, which Freedman led, announced it had measured the value using distant stars called Cepheids, which pulse at regular intervals. Their program concluded that the value of the Hubble constant for our universe was 72. As astronomers have refined their analyses and gathered new data, this number has remained fairly stable, at about 73.

But more recently, scientists took a very different approach: building a model based on the rippling structure of light left over from the earliest moments of the Big Bang, which is called the Cosmic Microwave Background. If they ran a model forward in time, extrapolating from the first few moments of the universe, they reached a value of 67. That disagreement is significant—nearly 10 percent—and it has continued to solidify over time.

Both camps have looked for anything that might be causing the mismatch. “Naturally, questions arise as to whether the discrepancy is coming from some aspect that astronomers don’t yet understand about the stars we’re measuring, or whether our cosmological model of the universe is still incomplete,” Freedman said. “Or maybe both need to be improved upon.”

I do understand extrapolation but I have an increasing worry that it is not entirely valid outside the Solar System (see Abstract above). This applies (in my opinion) both to the Big Bang and to Expansion. I believe that extrapolation is breaking down at limiting values.

Cat

 

[dfjchem721]

I also understand extrapolation, and buy into the HST data on distant stars and the galaxies they reside in. That data for the HC seems much more reliable than the extrapolation from the CBR, a "hard-to-interpret" data set if there ever was one. We can be sure of one thing. This debate won't be ending anytime soon.


BTW, according to theory, the HC actually is a constant in a given time frame, and is not a misnomer (as was quoted from somewhere). I believe "It varies with time" relates to the presumably observed increase in the rate of expansion, so where ever you are in that expansion, you will measure a different HC. But from a fixed view and time frame, it should be measured at a constant value. That we cannot yet find an invariant value reflects more on the scientific approaches to finding the value than anything else.

 

[Catastrophe]

dfj

I appreciate what you are posting.

The following is extracted from Wiki Hubble's Law which is also the source of the 'misnomer' comment.

Quote
The discovery of the linear relationship between redshift and distance, coupled with a supposed linear relation between recessional velocity and redshift, yields a straightforward mathematical expression for Hubble's law as follows:
{\displaystyle v=H_{0}\,D}
Where etc.

Hubble's law is considered the first observational basis for the expansion of the universe and today serves as one of the pieces of evidence most often cited in support of the Big Bang model.
Unquote

I totally agree with your expected reply re context and possibly selective quoting, but I admit these are selective and just intended to make a point to the less initiated that Hubbles Law and the Big Bang are not 'cast in stone'.

By the way, just for the record, I am a scientisr (B.Sc. Chemical Engineering) and agree with your comments. This debate won't be ending anytime soon.

Thank you for your input which is vary much appreciated.

Cat

 

[Catastrophe]

Quote
That we cannot yet find an invariant value reflects more on the scientific approaches to finding the value than anything else.
Unquote
I would include assumptions and extrapolations here.

But, also:
Quote
Hubble's law is considered the first observational basis for the expansion of the Universe and today serves as one of the pieces of evidence most often cited in support of the Big Bang model.
Unquote

Couple that with my above comments on extrapolation and you have my viewpoint in a nutshell. Big Bang / Expansion of the Universe. CARE.

Cat

 

[dfjchem721]

Thanks for the comments, Cat. I am also a scientist, and study protein structure and function. Many biochemists think DNA is where its at. But it is the proteins that are the true marvels of life.

And right up there with the origin of life, the BB will remain one of the great mysteries of all time.

 

[rod]

Some great links rod, thanks for that. It's especially easier to understand coloured diagrams with moving squiggly lines on them than it is reading Wikipedia. However all the redshifts seem to be explained by saying that space is expanding. There's no mention anywhere of the equivalence principle, so I've come back to haunt you.

As far as I understand there are 3 causes of redshift

1 - Gravitational redshift including the equivalence principle.

2 - Dopler shift.

3 - Cosmological redshift, i.e. that due to expanding space.

You seem to have put 2 methods in one sentence, in other words, what has the cosmological redshift got to do with the equivalence principle.
You go on below to say a similar thing -
Again what has the photon travelling through expanding space got to do with the principle of equivalence.

Gravitational redshift requires a strong gravitation field or big acceleration. There is almost no gravity between us and distant galaxies and very little acceleration, so I can't understand what use the equivalence principle is for measuring galactic distances.

If you don't like cosmological redshift, as I don't, that just leaves the doppler shift as the only redshift method.

Have I got my redshifts in a twist rod?

David-J-Franks, my comments about the cosmological redshift interpretation is based upon different readings I did that suggest there are problem(s) with the explanation - perhaps. The doppler shift interpretation has a problem. George Abell in his astronomy book from the early 1970s made it clear that when an object z >= 1.0, that object is traveling at or faster than the speed of light or could be. You can see this in the formula used by wikipedia, https://en.wikipedia.org/wiki/Redshift, however there are work arounds in math too to avoid overthrowing Special Relativity.

The thrust of what I said about the spectroscopic redshift vs. cosmological redshift for the CMBR stands. Is the CMBR redshift where z>=1000 proven? My answer is no. Is the *spectroscopic redshift* of GN-z11 is a better supported measurement (because it is observable and measurable today) than the CMBR redshift (theoretical calculation)? My answer is yes. This means the cornerstone of the Big Bang model explanation for the CMBR redshift is not proven in science but an extrapolation and model interpretation (and it uses the principle of equivalence for the redshifting photons as space expands), that includes a universe with radius some 46 billion light years. GN-z11 redshift is on firm observational ground compared to the z 1000+ extrapolation for the CMBR. Where is that pointed out in cosmology?

 

[Catastrophe]

I think it a pity that Hoyle came up with the BB epithet.

My guess (and just a guess) is that there is a gentle curve through like an eggtimer to a similar shape 'on the other side'. I don't care much about speculations such as life running backwards 'on the other side'.

BTW, how are the uncertainties in the expansion extrapolated backwards to a BB?

I do worry a little about 'gospel' theories being overturned so completely. I am all for the scientific method but, having accepted the Theia impact of Moon formation we now have a new explosion hypothesis. I am all in favour of scientific progress but I am a little surprised that no one saw this one coming. Or am I missing something?

 

[dfjchem721]

I should have added that the "hard-to-interpret" data for the cosmic background radiation (CBR), upon which so much of modern BB cosmology relies, perhaps belongs in a special position. It isn't just in the "hard-to-interpret" line of data, it is the all-time, grand-champion, hall-off-fame top of the category.

Having noted that, much can be interpreted from the CBR based on an enormous amount of data from colliders, which of course dove-tails in many regards to the CBR and where it all came from. Without expanding any further, it should be admitted by all that collider data does provide empirical evidence for the Standard Model of elemental particles. Because almost all of this data is derived from various labs, the LHC being the exception, one has to be a firm believer in what they have found. The science behind it is rock solid.

 

[rod]

I think it a pity that Hoyle came up with the BB epithet.

My guess (and just a guess) is that there is a gentle curve through like an eggtimer to a similar shape 'on the other side'. I don't care much about speculations such as life running backwards 'on the other side'.

BTW, how are the uncertainties in the expansion extrapolated backwards to a BB?

I do worry a little about 'gospel' theories being overturned so completely. I am all for the scientific method but, having accepted the Theia impact of Moon formation

Cat. My source told me "The "surface of last scattering" is a sound physical concept in that in a hot plasma the radiation is constantly interacting with the plasma, where everything is electrically charged - Thompson scattering. However, once the assumed fireball has cooled sufficiently, electrons begin to bind to atomic nuclei and thus form neutral atoms, allowing photons to pass freely - a stage known as decoupling, which corresponds to a temperature of about 3,000 K. Within the standard BB paradigm, the light first radiated from this process is now seen as the Cosmic Microwave Background. Thus the z~1000+ redshift figure is partly based on well-established physics, and partly on the BB paradigm."

However, z1000+ is not a spectroscopic measurement but an extrapolation. I use NOO to describe Theia. Non-Observable Object. A giant impact creating the Moon is an UOE, an unobserved event or perhaps, an unobservable event.

 

[Catastrophe]

Rod

Thank you for that. You are always a source of interesting and reliable information.

Cat

 

[David-J-Franks]

David
The following is from Swinburne:
"For example, in a distant binary system it is theoretically possible to measure both a Doppler shift and a cosmological redshift. The Doppler shift would be determined by the motions of the individual stars in the binary – whether they were approaching or receding at the time the photons were emitted. The cosmological redshift would be determined by how far away the system was when the photons were emitted. The larger the distance to the system, the longer the emitted photons have travelled through expanding space and the higher the measured cosmological redshift."

This seems to agree with your conclusions re: 2 and 3.
It seems to me to come down to whether you think the 'possible' expansion of intervening space has any validity. If not, then you are right (in my humble opinion) to settle only on 2.
I am not sure whether 'expansion' has any validity in this case or not. As you know, I have reservations on this. However, something is going on in the intervening space. It seems to me to be suspiciously like 'the ether'. Ouch! Back to the Michelson-Morley Experiment. Then look again on my comment on dark matter and cosmological scale.
I feel that I am siding with your conclusion but for different reasons. Doppler, yes, but I still think something else in there needs consideration. Keep up the good work!

Rod, I would welcome your comment on the Swinburne quote.

Cat

I have found a riveting explanation to back up our beliefs (confirmation bias at its best ), in favour of redshifts being Dopler shifts, even at the greatest of distances, and hopefully dispensing with expanding space nonsense used for cosmological redshift (and gravitational/equivalence principle as well).

It comes from a link in a link given to us by dfjchem721

Hubble's law - Wikipedia

en.wikipedia.org

Then go to section
Combining redshifts with distance measurements
Near the bottom of this is ref 29, this eventually takes you to -

https://arxiv.org/pdf/0808.1081.pdf

It's just about understandable to someone without a maths degree until the maths hits the fan.

 

[dfjchem721]

I printed out that article you posted. It is a real read all right. It will take me some time to get through it, but until then, there are some comments to be made from my very limited perspective. Think in terms of "space", and forget matter for a moment.

If space is infinite, then the universe is likely expanding into an infinite void. In this case I would have to say that Doppler is the most likely cause of redshift. Again, in my limited knowledge of this subject (and an oppressive tendency to think only with Newtonian physics), it would seem that both Doppler and space expansion represent similar phenomena. Does it really matter from the perspective of the observer how the redshift is generated - whether it is Doppler or expansion? Both would seem to have the same effect, and both could even be playing a role. So objects are moving away from the observer in both cases, only by a different mechanism. I don't see how either approach would effect the redshift, or how that redshift could define either mechanism (maybe something in that article I just printed out).

From a very simplistic view, the BB suggests that no matter where you are in the universe, everything appears to be moving away from everything else, and there is no center of the universe. This strongly suggests expansion of space. If, however, matter is expanding into an infinite void, it seems likely it would therefore have a point of origin, and an outer edge. I believe most high brows in Cosmology would suggest that this is simply not likely. It would require that our local space be the center of the universe. Otherwise, redshifts would not be the same for the most distant galaxies in all directions. Certainly our instruments are sensitive enough to pick up even a slight variance in such redshifts and none are seen, at least to my knowledge.

This is such a contentious issue that it is not possible for anyone to provide a "correct" answer. I would suggest if your considerations of the origin of the universe has a significant following of learned professionals, who can say that you are wrong? No one!

 

[dfjchem721]

Read the intro to that paper by Bunn and Hogg* and their treatment of Doppler redshift. Got a sense of deja vu as it seems likely had already read this. The opening comment in the abstract "the most natural interpretation of the redshift is a Doppler shift....." automatically raised red flags regarding an inherent bias.

There could not be a "natural interpretation" regarding the BB (which started it all), much less any expansion! Natural to who? The Standard Model** of elementary particles, widely confirmed by a vast amount of bench data from colliders, etc. has no "natural interpretation" either. How could it? Many of these are/were observations dreamed up theoretically and then applied to observable data collected afterwards, most famously the Higgs Boson. It certainly required some very clever people who are not exactly out in left field. Collider data puts together all of the components of atomic structure that we are so fond of. Natural interpretation was nowhere in sight.

Getting back to the very nature of "space", it is classically defined as the voids between heavenly bodies. Of course this space is often filled with photons and dust, etc, but is largely clear to optical observations. "Outer space" is defined as being above our planet higher then 62 miles (the Kármán line***), next comes interplanetary space, ending at the edge of our solar system. You then enter interstellar space, then intergalactic space, and possibly encounter massive voids between galaxy superclusters if you can travel far enough.

The point is that the space we are referring to, whether it was already present (infinite space), or created by its expansion, remains within the definition above. It is the largely void regions between heavenly bodies.

So for the (strictly) Doppler principle to hold, one seemingly must rely on an infinite space in which to expand, and different from space occupied by baryonic matter (etc.). It is also beyond the known universe and this is what we are expanding into.

Some might not find that more or less fanciful than the creation of space by the BB. Certainly neither seem to offer any "natural interpretation " of the issue at hand. It certainly could not be natural like life sciences or geology. Indeed, I cannot imagine a better description of the term "unnatural" then the very topic of this discussion!


*

https://arxiv.org/pdf/0808.1081.pdf

** https://en.wikipedia.org/wiki/Standard_model


** https://en.wikipedia.org/wiki/Outer_space#Interplanetary_space