Could Red Shift Be Influenced by Gravitational Effects Over Long Distances?

[walkerfx]

Has anyone ever considered the possibility that the perceived Doppler effect of light from distant stars/galaxies is not caused by movement of the emitting bodies, but rather a side effect of light traveling extraordinarily long distances under the week gravitational force of the entire universe?

I have no basis to make such a theory, but intuitively I feel it is plausible. It has been proven that light is bent by gravity. Could it not also be possible that under certain circumstances it could also affect light resulting in a Doppler-like effect?

Whether the universe is expanding or not is not the nature of my inquiry, simply I wonder if the measurement method is 100% reliable, because even a slight deviation from absolute perfection in measurement could have huge consequences.

Any thoughts?

 

[russ_watters]

Yes, I'm not real up on the specifics, but there is an idea called "tired light" that is generally discounted. I'm not quite sure if it is based on gravitational redshift, but gravitational redshift is a very real effect. It is a well proven, but to be the cause of the redshift we see, the universe would need an enormous density.

 

[cristo]

Here is a page from Ned Wright's website which puts forward criticisms in tired light theories.

 

[walkerfx]

Thanks for the information. I did not know about the tired light theory.

Best regards

 

[shotgun]

I have the same feeling. Not very happy with the red shift = expanding universe assumption. OK, there may not be enough mass to account for the observed shift, but what about the waves themselves? I mean all of them. If our redshift measurements of the universe are based on these specific ubiquitous spectral lines, then it seems like we are floating on a sea of these waves. I wonder that, if in the billion years it has taken the light waves to reach us, that there could be interference effects with all the other sources of that light (including whatever existed a billion years ago where we are now). Such effects as could cause a shift in the observed wavelength. Even though this notation may seem silly, I still say the existing explanation is lacking . . . .

 

[FunkyDwarf]

Im not sure intereference between photons would create a redshift affect, in in analog scenario it would just create a new wave with properties of both, in the particle physics arena my beleif was that photons do not interact with each other under any of the primary forces (thought I am probably wrong)

 

[Chronos]

Other independent indicators are remakably consistent with the expansion hypothesis. Time dilation in supernova light curves, for example, is a compelling example. The expansion hypothesis is not refuted by theories that accept objects are at distances commensurate with their redshifts. To defeat the expansion hypothesis, you must provide irrefutable evidence of a 'rogue' object with properties [size, velocity, etc.] forbidden by physics as we know it. A nobel awaits the first successful applicant. Arp has been trying to do this for half a century without success.

 

[shotgun]

Hmmm, I didn't know there was more evidence piling up to support the theory. That does get the wheels turning.

It is an intriguing idea, I guess. Does the current theory imply that space expands at a rate that is a function of its extent (i.e. local space is not observed to expand because it has, almost by definition, a negligible extent)? Likewise does the space between us and the most distant object expand at the greatest rate?

If so, that's not too far off from the observed effects of gravitation. I am going out on a limb here (after all isn't that the best place to contemplate gravity?), but anyway, doesn't this sound a little like gravity: where space CONTRACTS at a rate that is a function of its extent?

 

[BoomBoom]

Has anyone ever considered the possibility that the perceived Doppler effect of light from distant stars/galaxies is not caused by movement of the emitting bodies, but rather a side effect of light traveling extraordinarily long distances under the week gravitational force of the entire universe?

Well, yeah, EVERYtime I try and consider the alternative...which is that the ENTIRE universe started out as a micro-dot.

...and the fact that this rule doesn't apply in our local universe.

But it would take an GIGANTIC amount of evidence to convince the cosmology community of this. As they would be forced to admit that everything they have believed in and formed conclusions by for the last 100 years was all false. :O :)

 

[marcus]

...
It is an intriguing idea, I guess. Does the current theory imply that space expands at a rate that is a function of its extent (i.e. local space is not observed to expand because it has, almost by definition, a negligible extent)? Likewise does the space between us and the most distant object expand at the greatest rate?
...

According to current cosmology (based on Gen Rel) our local space does NOT expand and that includes the entire Milkyway galaxy and even our local group of galaxies. These form a gravitational bound system and are not receding. Only much more distant things recede. Only much larger distances expand.

For large distances the current rate is one percent every 140 million years.
Or 1/140 of a percent every million years.

You ask does the space between us and the most distant object expand at the greatest rate? and the answer if you mean percentage rate is NO. It is always the same percentage increase in distance (at least with minor differences aveaged out).
But if you mean the milesperhour rate or km/second rate then the answer is YES because one percent of a large distance is a larger increase than one percent growth of a small distance.

... GIGANTIC amount of evidence to convince the cosmology community of this. As they would be forced to admit that everything they have believed in and formed conclusions by for the last 100 years was all false...

Where you always misjudge the community, and go wrong, BoomBoom is that you don't realize that people would LOVE to have a new, better theory of gravity to replace GenRel!
And people are always proposing revisions of GR, and if they are proposed by smart people they get eagerly examined. And a big research effort is always going on trying to find faults with GR. They would LOVE to find somewhere it gives a bad prediction, say out at the 5th or 6th decimal place.
We have been using GR for 100 years and we would love to find a flaw with it and get a better theory of gravity (and spacetime geometry) to replace it! Then that would totally change cosmology, which is based on classical GR.

The trouble is GR is an extremely accurate theory of gravity, which has passed tests over and over again with extraordinary high precision and flying colors.

In the context of cosmology Gen Rel predicts that distances change dynamically and to the extent that it shows a uniform patter then it has to be expanding or contracting. So if GR is the correct theory of gravity, then we have to be seeing either redshift caused by the stretching of distance, or we have to be seeing blueshift due to the shrinking of distance.

And it happens the universe is clearly not collapsing, at least for now.

So GR tells us to expect redshift caused by the percentage increase in largescale distances And that is what we SEE.

So if you don't like this, what you need is to find a new theory of gravity. And if it gets as rigorously tested and has superior precision to classic GR then you will be a HERO and everybody will love your theory.

Then we can see if your improved GR ALSO predicts that distances should be percentagewise increasing, or whether it has some other explanation for redshifts and some other history of the universe.

BUT FIRST IT HAS TO BE AS PRECISE AS GENERAL RELATIVITY, OR BETTER. The car has to run, or people will not be interested in buying it.

 

[BoomBoom]

...big research effort is always going on trying to find faults with GR. They would LOVE to find somewhere it gives a bad prediction...

The trouble is GR is an extremely accurate theory of gravity, which has passed tests over and over again with extraordinary high precision and flying colors.

It would seem this also only really applies locally though...

When they find a huge contradiction in GR (such as galaxy rotation and movement, or a perceived acelleration of expansion, etc.), then instead of revisiting the previous assumptions to find the apparent flaw, it seems as if they assume the previous assumption is still correct and invent new parameters to make the math fit the new observation. In the process, introducing a whole new assumption to pile on top of the old ones so that we get to where we are now: 90+% of our universe is made up of some mysterious undetectable "dark" matter and energy.

Black holes is another one where the math breaks down...perhaps there is some very fundamental way in which we misunderstand the very nature of how BHs and SMBHs effect their surroundings.

I don't know and don't claim to be any sort of expert in any way in these matters. I was just trying to convey to the OP that he is not alone... :)

 

[marcus]

You misrepresent how the scientific community operates. Maybe it looks to you as if they just blithely stuck in DE and DM and proceeded uncritically. Not so. A lot of effort has gone into imaging and mapping clouds of Dark Matter and it has been successful. So it is a good thing the model predicted Dark Matter. Another point for Gen Rel.

The initial arguments for DE and DM were treated with skepticism and much effort went into exploring ALTERNATIVE laws of gravity which would explain them away. A number of people are also still studying ways to explain the acceleration which don't require a cosmological constant or any form of DE.

You say instead of revisiting the previous assumptions but the previous assumptions, namely the basic theory of largescale geometry, GR, is precisely what has gotten revisited! Repeatedly, assiduously, by many people in a multiprong effort, over the past decade.

It would seem this also only really applies locally though...

When they find a huge contradiction in GR (such as galaxy rotation and movement, or a perceived acelleration of expansion, etc.), then instead of revisiting the previous assumptions to find the apparent flaw, it seems as if they assume the previous assumption is still correct and invent new parameters to make the math fit the new observation. In the process, introducing a whole new assumption to pile on top of the old ones so that we get to where we are now: 90+% of our universe is made up of some mysterious undetectable "dark" matter and energy.

Black holes is another one where the math breaks down...perhaps there is some very fundamental way in which we misunderstand the very nature of how BHs and SMBHs effect their surroundings.

I don't know and don't claim to be any sort of expert in any way in these matters. I was just trying to convey to the OP that he is not alone... :)

Look BoomBoom, you apparently don't follow the literature. So you don't know how the community operates or what it has been doing. Before you criticize something find out something about it.

What you can, I think, criticize responsibly is popular science journalism because the journalists have not kept you informed about all the work being done on alternatives to GR and alternative explanations of the data.

 

[shotgun]

Thanks Marcus, that was an interesting read. So GR predicts that large distances change with time, ok. That makes me wonder, does GR also predict that if one were observing a variable star at large distances, that the star's observed period (or even luminosity) would be different than the actual period due to the dilation across such large distances?

 

[marcus]

Thanks Marcus, that was an interesting read. So GR predicts that large distances change with time, ok. That makes me wonder, does GR also predict that if one were observing a variable star at large distances, that the star's observed period (or even luminosity) would be different than the actual period due to the dilation across such large distances?

Thanks for the kind word Shotgun. All signals get stretched out by the same factor, the factor by which distances got expanded while the light was in transit. Several people here are hands-on astronomers. I hope they respond to quantitative questions like this.

The lightcurves of supernovae ARE affected by the expansion of distance to them. the schedule of the flash gets stretched out just like light gets redshifted. So that effect is taken into account.

You are talking about ordinary variable stars, not supernovae. The lightcurve from a Cepheid variable should also be stretched out by the same factor (z+1) that the lightwaves are stretched out. So that is probably also taken into account. Should be, unless z is negligibly small.

 

[hejin]

What does `stretch-out` mean scientificly?

Thanks for the kind word Shotgun. All signals get stretched out by the same factor, the factor by which distances got expanded while the light was in transit. Several people here are hands-on astronomers. I hope they respond to quantitative questions like this.

The lightcurves of supernovae ARE affected by the expansion of distance to them. the schedule of the flash gets stretched out just like light gets redshifted. So that effect is taken into account.

You are talking about ordinary variable stars, not supernovae. The lightcurve from a Cepheid variable should also be stretched out by the same factor (z+1) that the lightwaves are stretched out. So that is probably also taken into account. Should be, unless z is negligibly small.

What does it mean that lightcurves are stretched out? Please explain it scientificly!

 

[marcus]

What does it mean that lightcurves are stretched out? Please explain it scientificly!

Lightcurve is a scientific term for the recorded brightness as it changes over several hours or days.

Certain types of supernovae have a characteristic shape to the lightcurve. Just as an example, say it rises for 1 day and reaches a peak and then takes 3 days to die down.

if something is observed at redshift z=1, that means that everything is stretched out by a factor of z+1=2

So the wavelengths of the light are stretched by a factor of 2.

And the lightcurve is stretched by the same factor, namely 2.

Instead of taking 4 days to go through its flash it takes 8 days.

this is not a Doppler effect. it is not what is usually called "time dilation" either.
it is the effect of the whole message getting stretched out as it traveled thru space where distances were getting stretched out. Space got stretched by a factor of 2 while the signal was on its way, so it got stretched too.

You asked "please explain it scientifically" but I think I already explained. Lightcurve is a technical scientific term already. Hope that helps.

 

[hejin]

Lightcurve is a scientific term for the recorded brightness as it changes over several hours or days.

Certain types of supernovae have a characteristic shape to the lightcurve. Just as an example, say it rises for 1 day and reaches a peak and then takes 3 days to die down.

if something is observed at redshift z=1, that means that everything is stretched out by a factor of z+1=2

So the wavelengths of the light are stretched by a factor of 2.

And the lightcurve is stretched by the same factor, namely 2.

Instead of taking 4 days to go through its flash it takes 8 days.

this is not a Doppler effect. it is not what is usually called "time dilation" either.
it is the effect of the whole message getting stretched out as it traveled thru space where distances were getting stretched out. Space got stretched by a factor of 2 while the signal was on its way, so it got stretched too.

You asked "please explain it scientifically" but I think I already explained. Lightcurve is a technical scientific term already. Hope that helps.

According to General Relativity, every where and each time the physics is the same. Therefore the event at factor 2 is the same event that would happen in Milky Way.
The two-todays or two-hours spanned short-period events can be affected by large-scale cosmological expansion? It is hard to understand. Would you give me the right references?

 

[marcus]

http://arxiv.org/abs/astro-ph/0608639

Here's a reference on the lightcurves of type 1A supernovae

very roughly speaking they take 10 days to rise to peak brightness
then they stay near peak for around 10 days
and then they take about 20 days to get back down to near what they were

the curve is actually smoother, and kind of pretty
you can find a smoothed out version graphed in the paper towards the end

if it is at z=1
whatever it takes 40 days to do, in its restframe, that signal will get stretched out by a factor of 2
so it will take us 80 days to watch the whole show

whatever takes the star 10 days, like ten days to rise to max brightness, that will take 20 days for us to watch.

because the signal gets stretched while in transit, just like the wavelengths of the light itself

But Jin He you are the author of these papers:
6. arXiv:astro-ph/0605213 [ps, pdf, other]
Title: The Faulty Assumptions of the Expanding-Universe Model vs. the Simple and Consistent Principles of a Flat-Universe Model -- with Moving Pisa Tower Experiment which Tests General Relativity
Authors: Jin He

7. arXiv:astro-ph/0604084 [ps, pdf, other]
Title: Einstein Field Equation: the Root of All Evil? Prediction on Gravity Probe B, Quantum Gravity and Solar Application
Authors: Jin He
Comments: Gravity Probe B prediction is corrected

8. arXiv:astro-ph/0512614 [ps, pdf, other]
Title: The Possibility of Curved Spacetime, Black Holes, and Big Bang is Less than One Billionth
Authors: Jin He

I doubt that I can explain anything satisfactorily to you,
maybe someone else can explain things to you better

 

[ahhaha]

According to current cosmology (based on Gen Rel) our local space does NOT expand and that includes the entire Milkyway galaxy and even our local group of galaxies. These form a gravitational bound system and are not receding. Only much more distant things recede. Only much larger distances expand.]

Where between us and farther out does space start or stop expanding?

 

[marcus]

===============

Where between us and farther out does space start or stop expanding?

I am guessing on the order of 10-100 megaparsecs---dont think it can be pinned down. Wallace, if he sees this, may choose to correct or make this estimate more precise

BTW I was speaking very loosely about space expanding and not expanding. I used those phrases because that is how everybody talks.

But if you want to be really precise you might want to read an article about this that Wallace and some other astronomers wrote.

I'll get the URL
http://arxiv.org/abs/0707.0380

space is not a material.
distances between things can increase in an approximately systematic way, but only approximately
there is no sharp cutoff where distances below a certain length do not and all distances above that length do

the nearby galaxies form a gravitationally bound system with us, distances in a gravitationally bound system, a cluster, are not part of the largescale systematic increase of distances.

how large a patch of space around you is occupied by a gravitationally bound system of galaxies depends on who you are and where you live. some clusters are larger than others, some clusters belong to superclusters
the whole thing is irregular

all you know is that if you go out far enough things vaguely and gradually begin to look like a systematic expansion
how far you have to go depends on where you start and what the local neighborhood is like.

http://arxiv.org/abs/0707.0380
Expanding Space: the Root of all Evil?
Matthew J. Francis, Luke A. Barnes, J. Berian James, Geraint F. Lewis
8 pages, accepted for publication in PASA
(Submitted on 3 Jul 2007)

"While it remains the staple of virtually all cosmological teaching, the concept of expanding space in explaining the increasing separation of galaxies has recently come under fire as a dangerous idea whose application leads to the development of confusion and the establishment of misconceptions. In this paper, we develop a notion of expanding space that is completely valid as a framework for the description of the evolution of the universe and whose application allows an intuitive understanding of the influence of universal expansion. We also demonstrate how arguments against the concept in general have failed thus far, as they imbue expanding space with physical properties not consistent with the expectations of general relativity."

 

[ahhaha]

I was speaking very loosely about space expanding and not expanding. I used those phrases because that is how everybody talks.]

Doesn't it make some kind of sense to try to make sense out of what others are trying to make sensible?

[But if you want to be really precise you might want to read an article about this that Wallace and some other astronomers wrote.]

No. I think you and I can figure it out. Who needs more clowns?

If space is to be considered a continuum, it must be the case that somewhere between here and there space must be "expanding". Further, it must be the case that everywhere along that path space must be undergoing some degree of transformation, else, space is not a continuum and that is unthinkable. Maybe it doesn't make sense to think in terms of space as a three dimensional continuum when we are actually dealing with a four dimensional(at least) continuum. Hard to do. One way of doing it is to think in terms of lapse and shift. Is that the way to handle the informal notion, "expanding space"? Probably doesn't work any better than talking about expansion taking place in a direction perpendicular to a point comoving with the cosmological fluid, because it requires a lapse in time that is perpendicular to a shift in three space, and we run into the discontinuity problem again.

In fact, we can't really claim that redshift is the result of cosmological expansion, because we have no evidence to support the claim. We haven't gone far enough out in space to directly confirm it, but we have other indirect evidence. Surprisingly, what is more convincing , and what we do have is that cosmological expansion fell out of Einstein's field equations as a natural occurrence, that Einstein's felt compelled to get rid of by inventing something artificial that would compensate to keep things balanced or unexpanding. Voila, the first cosmological constant. Later when Hubble confirmed Lemaitre's identification of the expansion as the simplest assumption through the discovery of the redshift, it was taken as a complete confirmation. Einstein had derived this consequence by pure theory and it predicted the existence of cosmological expansion which is perfectly identified or correlated to redshift. We are always impressed when theory predicts unsuspected fact. Impressed and possibly fooled. They might have been incidentally identified.

Because of this possibility of incidentiality many authors ever since have tried alternative explanations some of which have been mentioned here. To this day there are still valid challenges being made, but the simplest explanation, and we are certainly justified in applying Occam's Razor, is that redshift is caused by cosmological expansion. Next job is to get under control what cosmological expansion is, and forget the terms like "expanding space" that you hear in science popularizations.

It is not possible to quite grasp on a local basis the redshift exhibited cosmological expansion, just as it is impossible to conceive electromagnetic radiation. What is EM? Rolling tubes which are expanding and have a sense of circulation. How is it possible to imagine in some three dimensional representation such a collection of somewhat contradictory motions? It isn't. Same thing with the cosmological expansion. And that means we must get rid of toy concepts like pennies glued to the surface of a balloon being pumped up. They're all 3 space conceptualizations. In these situations you just have to leave your common experience at home and go with the math. Surprisingly, the math itself develops its own kind of intuition about what will work and what won't. You get that experience by doing a lot of it just as you get good at anything by practice.

Back to the question at hand. You said that locally where we have Minkowski space and inertial frames itcan't make any sense to talk in terms of expanding space. Quite right, but that's only an approximation. Similarly, at cosmological distances where we can no longer cling to Minkowski and not much to Lorentz, we can't make much sense out of flat space. However, it can't be adequately decided where exactly flat space turns into curved space, if I may use those popularizations. What happened to the idea of continua? Like in quantum mechanics we are limited in our use of ideas that can't be simply extended. It is true that nowhere along the path between here and there and it is true that everywhere between here and there does space continually expand! This seeming contradiction merely shows we keep falling back on 3 space conceptualizations.

Also, no one can say that "tired light" is a false theory. What is false about it is the form of tiredness so far submitted. There may be a drag or coupling between photons and the metric that springs from Einstein's field equations when they're slightly modified. There's nothing wrong with extending GR's field equations in a way that doesn't disturb existing evidence. For example, we might extend the equations to explain something that GR fails to explain, galactic rotation curves, and in doing so we find there's a slight residual effect that accumulates over distances where the photon donates some of its energy to the metric. It can be shown that this isn't the case, but this gives you an idea how redshift explanations and the nature of the cosmological expansion are still open questions.

 

[hejin]

http://arxiv.org/abs/astro-ph/0608639

Here's a reference on the lightcurves of type 1A supernovae

very roughly speaking they take 10 days to rise to peak brightness
then they stay near peak for around 10 days
and then they take about 20 days to get back down to near what they were

the curve is actually smoother, and kind of pretty
you can find a smoothed out version graphed in the paper towards the end

if it is at z=1
whatever it takes 40 days to do, in its restframe, that signal will get stretched out by a factor of 2
so it will take us 80 days to watch the whole show

whatever takes the star 10 days, like ten days to rise to max brightness, that will take 20 days for us to watch.

because the signal gets stretched while in transit, just like the wavelengths of the light itself

But Jin He you are the author of these papers:
6. arXiv:astro-ph/0605213 [ps, pdf, other]
Title: The Faulty Assumptions of the Expanding-Universe Model vs. the Simple and Consistent Principles of a Flat-Universe Model -- with Moving Pisa Tower Experiment which Tests General Relativity
Authors: Jin He

7. arXiv:astro-ph/0604084 [ps, pdf, other]
Title: Einstein Field Equation: the Root of All Evil? Prediction on Gravity Probe B, Quantum Gravity and Solar Application
Authors: Jin He
Comments: Gravity Probe B prediction is corrected

8. arXiv:astro-ph/0512614 [ps, pdf, other]
Title: The Possibility of Curved Spacetime, Black Holes, and Big Bang is Less than One Billionth
Authors: Jin He

I doubt that I can explain anything satisfactorily to you,
maybe someone else can explain things to you better

Let us focus on the problem of `stretch-out`!
According to your report, the stretch-out depends only on redshift. If it were due to cosmological expansion, the factor of the stretch-out would depend on the temporal interval between two supernovae events at the SAME LOCATION. We would expect there were no stretch-out factor if the interval approached zero.

According to your report, the stretch-out depends only on redshift. It is the absolute stretch-out which depends only on redshift. If so, the stretch-out MUST result from the time slowing-down of the universe.

The first post of the current thread proposed gravitational redshift. Gravitational redshift is exactly the time slowing-down of the universe!

Therefore, to maintain a stretch-out which depends only on redshift and results from cosmological expansion, relativists have to identify other dark stuff other than DM, DE, so that the cosmological expansion maintains an exact stretch-out which depends only on redshift!

 

[marcus]

Back to the question at hand. You said that locally where we have Minkowski space and inertial frames it can't make any sense to talk in terms of expanding space. Quite right, but that's only an approximation.

I don't think I mentioned Minkowski space, or any flatspace approximation. In reality the expansion of distances is highly irregular----in some regions distances are on the whole contracting, or on average not changing, in some sense. Perhaps I did mention Minkowski space and have forgotten. You could find the quote. Feel free to refresh my memory.

Also, no one can say that "tired light" is a false theory. What is false about it is the form of tiredness so far submitted. There may be a drag or coupling between photons and the metric that springs from Einstein's field equations when they're slightly modified. There's nothing wrong with extending GR's field equations in a way that doesn't disturb existing evidence. For example, we might extend the equations to explain something that GR fails to explain, galactic rotation curves, and in doing so we find there's a slight residual effect that accumulates over distances where the photon donates some of its energy to the metric. It can be shown that this isn't the case, but this gives you an idea how redshift explanations and the nature of the cosmological expansion are still open questions.

To be a physics or astronomy theory something has to be formulated mathematically so it can be checked for consistency and compared with observation. I don't know of any tired light theory that has not been falsified and justly discarded. that was all a long time ago, wasn't it?

I know of a number of modications of GR that are being studied. I mean modifications that seem to me, at least, to be seriously interesting. Mostly they come under the heading of quantized GR. Different approaches to quantizing leading to different models.

None of these modifications would avoid largescale expansion of distances.
None of them would explain away the cosmological redshift by proposing some alternative mechanism such as what you suggest.

The one example you give is flawed:
For example, we might extend the equations to explain something that GR fails to explain, galactic rotation curves,...

GR does a beautiful job of explaining galactic rotation curves. It was a recent triumph of the theory.
Based on the rotation curves, GR predicted DM. Then it was found that DM was also needed to stabilize clusters. Then it was found that DM was also useful in explaining largescale structure formation in the early universe. So GR predicted DM on the basis of several different kinds of data. Then Dark Matter was IMAGED and maps of it are being made. This was a remarkable triumph. The theory predicted something, which seemed dubious and unintuitive, and the theory was vindicated by observation.

It was show to NOT require modification, one more time. Eventually we will find some way to trip the theory up and it will have to be modified (that's how science progresses) but the galactic rotation curves thing you mentioned is not it.

 

[DVDjHex]

What does it mean that lightcurves are stretched out? Please explain it scientificly!

See time dilation.

[Edited to add:] Or better yet: spacetime dilation.

 

[DVDjHex]

...In the context of cosmology Gen Rel predicts that distances change dynamically and to the extent that it shows a uniform patter then it has to be expanding or contracting...

GR shows that the universe could either expand, collapse, or remain stationary.

Yes, according to GR the universe could remain static (non-expanding). See Tolman 1929.

Three such static solutions to the field equations exist: Einstein, de Sitter, Minkowski.



DVDjHex

 

[marcus]

Yes, according to GR the universe could remain static (non-expanding). See Tolman 1929.
Three such static solutions to the field equations exist: Einstein, de Sitter, Minkowski.

I knew of static solutions to the field equations, but I did not think any were stable. My impression was that a small perturbation would cause any static solution to change into either expanding or contracting. Like trying to balance a knife upright on its point.

If you know of a stable static solution, please give me a reference to something online about it. An arxiv preprint number would do fine. Thanks.

 

[AWA]

The redshift that supports the expanding universe hypothesis and thus all modern cosmology is not a doppler redshift which does not apply to astronomical distances but the so called "cosmological redshift" , IMHO this type of redshift is defined somewhat tautologically meaning that previous to the Hubble 1929 publications about distance-redshift relation there was a whole group of scientists pushing forward an "expanding universe" theory from Einstein's GR equations and Lemaitre interpretation,etc.. , so the redshift-distance relation by Hubble was inmediately taken as the "ad hoc" piece of the puzzle (Hubble himself never supported this derivations directly-nor opposed it manifestly-,in fact he was very cautious about conclusions from his empirical data as shown in his correspondence with de Sitter.i.e.).
So this type of redshift termed cosmological to differentiate it from the two other types(namely doppler and gravitational) is defined as the redshift caused by space expansion as derived from GR equations but is also the main justification for expansion itself. It feels to me there's some circular reasoning here but might as well be just that, a feeling. could anybody redirect me to the solid path of the standard model?

 

[Ich]

So this type of redshift termed cosmological to differentiate it from the two other types(namely doppler and gravitational) is defined as the redshift caused by space expansion as derived from GR equations but is also the main justification for expansion itself.

The observed redshift does not have three distinct "causes".
If you use static coordinates, the redshift is caused either by velocity or gravitation, the first factor increasing linearly with distance, the second parabolic (plus higher order corrections). However, static coordinates in a dynamic universe become somewhat artificial and contrived when it comes to long periods of time, where the matter fields change significantly.
That's why cosmologists use cosmological coordinates. Exactly the same redshift is then characterized by the "scale factor": this is not a new "mechanism" for redshift, it's a different description.
So the evidence for expansion lies in the redshift itself, and it is perfectly valid to regard the Hubble data (i.e. data of "near" galaxies) as a doppler shift. Cosmolgical redshift = doppler shift at small distances.

 

[marcus]

The redshift that supports the expanding universe hypothesis and thus all modern cosmology is not a doppler redshift which does not apply to astronomical distances but the so called "cosmological redshift" ...

AWA thanks for making this point. It is an important one to make. The cosmological redshift can be analysed somewhat artificially in terms of a progression of a large number of little doppler shifts. Or it can be treated approximately as a single doppler shift in the case of what Ich called "near" galaxies. These would be, like, redshift z = 0.1.

But for newcomers it works best not to waste time building a complicated bridge between the concepts---but rather to treat cosmo redshift as its own thing. As you do.

One of several strong clinchers here, is that most galaxies we observe have redshift z > 1.4. Often the redshift is much more than 1.4! An indisputable observational fact. If you convert that to the type of distance measure that goes into the Hubble law v = Hd
then you find that the rate the distance is increasing is greater than c.

With most galaxies that we observe receding faster than c, it is easy to see that interpreting redshift as a doppler shift is not going to be easy. It is going to take some sweat and calculus.

 

[AWA]

thanks for the clarifications

 

[PoeticMine]

I too have wondered about the theories and conclusions derived from "only" the Red Shift observation. What lead me to even ponder this was that they say, the further away a galaxy is, the faster it appeared to be moving away. I was bothered by how the Universe could be expanding away from us, in all directions equally and with distance this expansion uniformly increases in speed.

Had it been considered that the Red Shift was more of an optical effect caused by the Gravitation Lensing of a Galaxy's Halo and a "Galactic Black Hole" at the center of the distant galaxy?
To say, if you think of a galaxy as a clear glass sphere. Up close, we can see the stars are casting their light independently. As the sphere moves further away from us, the collective light would become more intensely focused toward the center of the sphere, magnifying all the light within and in our observed direction. This focused light is now caught between it's "Galactic Black Hole," pulling the light back (Red Shift) and our observations.

Until this observation, those single points of light we now know to be galaxies, were merely thought to be regular stars.

Just a thought.

 

[Chronos]

Perhaps light passing the galactic core gets blueshifted on the way in, then redshifted on the way out. Your explanation does not work for me.

 

[PoeticMine]

Perhaps light passing the galactic core gets blueshifted on the way in, then redshifted on the way out. Your explanation does not work for me.

From the point of view of the observer, any starlight beyond and behind the galaxy being observed, would be push away curving around that galaxy and can sometimes have a mirror image on both sides of that galaxy.
I thought, if Gravitational Lensing is causing such a huge optical effect on starlight outside that galaxy, would not it be worth considering that it also could have a possible inverse effect on starlight within the galaxy?

I was suggesting that only the starlight "within" a distance galaxy, is possibly observed to be more intensely focused with distance, by the convex shaped halo of the galaxy as with gravitational lensing and then also red shifted along the line of sight of the observer due to the gravitation force of galaxy's galactic core.
Line of sight being; the gravitational force of the galactic core, starlight within the galaxy focused by the convex sphere of the halo and red shifted by the galactic core.

I apologize if my first comment was not clear and Thank You for the term "galactic core."

 

[inflector]

I know this particular quote is a bit old but I am trying to make sure that I understand the issues properly.

The one example you give is flawed:
For example, we might extend the equations to explain something that GR fails to explain, galactic rotation curves,...

GR does a beautiful job of explaining galactic rotation curves. It was a recent triumph of the theory.
Based on the rotation curves, GR predicted DM.

Isn't it also valid to say that in order for GR to be valid without modification there needs to be something that supplies the mass required to fit the observed data, and that Dark Matter is currently the most widely accepted explanation for this missing mass, for various reasons that have been expounded upon here quite rigorously and with continuing frequency.

Then it was found that DM was also needed to stabilize clusters.

Another way of saying this is that clusters were not stable in a way that matched observations using the equations of GR alone without supplying additional mass.

Then it was found that DM was also useful in explaining largescale structure formation in the early universe.

Could one not likewise say that GR without Dark Matter does not explain the largescale structure formation in the early universe?

So GR predicted DM on the basis of several different kinds of data. Then Dark Matter was IMAGED and maps of it are being made. This was a remarkable triumph. The theory predicted something, which seemed dubious and unintuitive, and the theory was vindicated by observation.

It was show to NOT require modification, one more time. Eventually we will find some way to trip the theory up and it will have to be modified (that's how science progresses) but the galactic rotation curves thing you mentioned is not it.

Could it not still be the case that Dark Matter is a placeholder for a consistent set of unseen (electromagnetically anyway) gravitational effects, and that GR is incomplete in so far as it does not account for these effects? Much like Newtonian Gravity was incomplete before GR?

I'm trying to determine if the statement that ahhaha made:

Also, no one can say that "tired light" is a false theory. What is false about it is the form of tiredness so far submitted. There may be a drag or coupling between photons and the metric that springs from Einstein's field equations when they're slightly modified. There's nothing wrong with extending GR's field equations in a way that doesn't disturb existing evidence. For example, we might extend the equations to explain something that GR fails to explain, galactic rotation curves, and in doing so we find there's a slight residual effect that accumulates over distances where the photon donates some of its energy to the metric. It can be shown that this isn't the case, but this gives you an idea how redshift explanations and the nature of the cosmological expansion are still open questions.

is possibly true or not. I realize that the vast majority would say this idea is extremely unlikely, but is it POSSIBLE? Have we ruled out the possibility of a modification to gravity that fits the data AND that could result in a photon donating some portion of its energy to the metric? I'm sure most would consider this extremely unlikely, but I like to keep the impossible and unlikely in separate compartments.

Finally, on the subject of redshifts, has anyone looked at the idea of whether or not the acceleration of the expansion itself is being caused by the energy that is given up during the process of redshifting itself? i.e. that dark energy is nothing more than energy lost to the metric of spacetime during photon travel? If this idea has been refuted, can anyone point me to the relevant papers?

I tried a few google searches and didn't come up with anything useful. As ahhaha pointed out, most of the "tired light" theories are pretty naive and easily refuted so the literature seems to consider them as a sort of "stupid" idea that is easily brushed off, from my reading.