Alernatives: Cosmological redshift/BBE

OK DRD,

My question essentially is:

If you examine a redshifted spectrum, how do you determine what amount of redshift is due to:

Doppler effect
Earths motion.
Extra galactic body motion.
Gravitational effects.
Space expansion effects.

Where would you suggest I start reading?

Skwinty said:

OK DRD,

My question essentially is:

If you examine a redshifted spectrum, how do you determine what amount of redshift is due to:

Doppler effect
Earths motion.
Extra galactic body motion.
Gravitational effects.
Space expansion effects.

Where would you suggest I start reading?

Click to expand...

The short answer is you can't unravel them. The longer answer:

The Earth's motion compared to the rest of the universe is measurable by looking at the redshift/blueshift of the CMB - this should be uniform in every direction but there's a slight red and blueshift that can be measured and attributed to this - google term "CMB dipole"

The gravitational effects for a galaxy are small, so we basically ignore them.

Doppler effects and movements of the other galaxy - same thing right? Or am I misunderstanding you a bit? Anyway, these are 'peculiar motions' and basically can't be unravelled from the cosmological redshift (due to space expanding). They're not big though (for more distant things at least), and average out statistically - as many things move towards us as move away. It causes some funny effects in galaxy clusters. Google for "peculiar velocities", "fingers of god" and "Kaiser effect".

For distant objects the overwhelming majority of the redshift comes from the cosmological effect though.

Skwinty said:

OK DRD,

My question essentially is:

If you examine a redshifted spectrum, how do you determine what amount of redshift is due to:

Doppler effect
Earths motion.
Extra galactic body motion.
Gravitational effects.
Space expansion effects.

Where would you suggest I start reading?

Click to expand...

Perhaps with an introductory astronomy text?

Suppose someone hands you a spectrum, in the form of a squiggly line on a standard x-y plot (or graph or chart or whatever word you use).

Suppose the x-axis is labeled, in nm, Hz, Å, keV, or something else appropriate; suppose the y-axis is labeled 'relative intensity' or 'relative flux', or something like that.

Can you tell that it is "a redshifted spectrum"?

I guess it's possible that you might come across something like this, in some dusty archive, but even in the most extreme such case there would surely be wealth of other information about the spectrum, wouldn't there?

And with that extra information[ * ], you should find (or be able to reconstruct) things like:

* what object is this a spectrum of? Or, perhaps, what was the RA and Dec that the telescope/instrument was pointing to?

* when was it taken? And how long was the integration time?

* where was it taken (name of observatory/spacecraft/whatever)?

* what spectrograph (or other instrument) was used to take it?

* how was the x-axis calibrated?

Skwinty, can you confirm, please, that information of this kind would accompany the spectrum? Then I can walk you through how you might go about determining (actually 'estimating' would be a better word) the various components ...

[ * ] I'm assuming you have established, unambiguously, that it is a spectrum of something 'in the sky'

DeiRenDopa and/or sol invictus and/or anyone:

Do you think it is remotely possible that we have it all wrong regarding cosmological expansion and the big bang?
I am aware that cosmological expansion and the big bang are supported by a great deal of observational evidence and that GR provides a very strong theoretical framework for these theories.
Given that reality, this question may seem strange, but I have a nagging (but unsupported) feeling that there could possibly be another answer. However, I have absolutely no idea what any other answer might be.
I have been struggling to find a way to express my "nagging feeling." So, I’ll try this:
Could it not be that something other than cosmological expansion causes the red shift? And whatever that something else may be also accounts for the all the other supportive observations, like the CMB. By this I mean that something else would cause the red shift and the other phenomena that mimic expansion.
There are some examples in the history of science where a very wrong theory can find support from phenomena that turn out to be irrelevant or misunderstood.
For example, there were many supporting arguments making the earth the center of the universe. E. g.: if the earth turned, we would all be thrown off by the movement of the earth. Aristotelian physics made it so; it provided a “strong theoretical framework.” Another one: Stuff falls because its nature is to seek the center of the universe.
I don’t think very many physicists would take the position that our current understanding is the final word. There is yet more physics to be discovered.
You recall Plato's Allegory of the Cave. Similar to those cave dwellers (who saw only shadows), we see the universe through the EM spectrum, cosmic rays and extraterrestrial neutrinos. (I may be omitting something here). The universe may have more dimensions than four, there may exist types of radiation that are not detectible by us, and other forces or stuff that we cannot detect or describe or know about yet.
OK, now I know it’s easy to say, “Well, sure anything is possible.” That’s not exactly the response I am looking for. I’m aware of theories like “tired light” that have been examined and rejected as possible causes of the red shift. It seems that most research is done to confirm or develop nuances of cosmological expansion. Is anyone looking for alternative explanations for the red shift, other than “crackpots”?
So, there it is; I know all this is merely a layman’s naïve thoughts. If you can contribute any opinions or thoughts that may be interesting or helpful I would appreciate it.

edd said:

The short answer is you can't unravel them. The longer answer:......

........For distant objects the overwhelming majority of the redshift comes from the cosmological effect though.

Click to expand...

I understand cosmological redshift relates to the expansion of space.
Am I correct in this understanding?

How do you reconcile the seemingly contradictory statements that I have quoted from your post.

DRD:

Firstly, I have an introductory astronomy text by Ceceliia Payne Gaposchkin and Katherine Haramundanis.

The section on redshift really deals with the redshift -distance relationship and recession velocities.

Yes, the redshift spectrum X-Y plot will have all the necessary data attached such as the data you mentioned.

A quote from this text.

"It is thinkable that the redshifts are not velocity shifts, but have some other cause, such as the gravitational effect predicted by the General Theory of Relativity."

Perpetual Student said:

DeiRenDopa and/or sol invictus and/or anyone:

Do you think it is remotely possible that we have it all wrong regarding cosmological expansion and the big bang?

Click to expand...

Yes. But some seem impervious to this reality. Some do not. http://www.cosmology.info/2008conference/

I am aware that cosmological expansion and the big bang are supported by a great deal of observational evidence and that GR provides a very strong theoretical framework for these theories.

Click to expand...

Yes, but change some of the fundamental concepts underlying this evidence, and all of this evidence can act as strong evidence for a non big bang universe. All evidence is precarious depending on the axioms on which they are based.

Just watch this documentary, part two is probably the best starting point: http://www.youtube.com/watch?v=wchV5R9NhqY

Some extremely pertinent points are made by Lerner and others that no one yet has given adequate answers to.

I'm off on holiday now for a while and will remain lurking around for a week or two, but might pop back in for the odd comment when the odd blatent lie is posted.

Perpetual Student said:

DeiRenDopa and/or sol invictus and/or anyone:

Do you think it is remotely possible that we have it all wrong regarding cosmological expansion and the big bang?
I am aware that cosmological expansion and the big bang are supported by a great deal of observational evidence and that GR provides a very strong theoretical framework for these theories.
Given that reality, this question may seem strange, but I have a nagging (but unsupported) feeling that there could possibly be another answer. However, I have absolutely no idea what any other answer might be.
I have been struggling to find a way to express my "nagging feeling." So, I’ll try this:
Could it not be that something other than cosmological expansion causes the red shift? And whatever that something else may be also accounts for the all the other supportive observations, like the CMB. By this I mean that something else would cause the red shift and the other phenomena that mimic expansion.
There are some examples in the history of science where a very wrong theory can find support from phenomena that turn out to be irrelevant or misunderstood.
For example, there were many supporting arguments making the earth the center of the universe. E. g.: if the earth turned, we would all be thrown off by the movement of the earth. Aristotelian physics made it so; it provided a “strong theoretical framework.” Another one: Stuff falls because its nature is to seek the center of the universe.
I don’t think very many physicists would take the position that our current understanding is the final word. There is yet more physics to be discovered.
You recall Plato's Allegory of the Cave. Similar to those cave dwellers (who saw only shadows), we see the universe through the EM spectrum, cosmic rays and extraterrestrial neutrinos. (I may be omitting something here). The universe may have more dimensions than four, there may exist types of radiation that are not detectible by us, and other forces or stuff that we cannot detect or describe or know about yet.
OK, now I know it’s easy to say, “Well, sure anything is possible.” That’s not exactly the response I am looking for. I’m aware of theories like “tired light” that have been examined and rejected as possible causes of the red shift. It seems that most research is done to confirm or develop nuances of cosmological expansion. Is anyone looking for alternative explanations for the red shift, other than “crackpots”?
So, there it is; I know all this is merely a layman’s naïve thoughts. If you can contribute any opinions or thoughts that may be interesting or helpful I would appreciate it.

Click to expand...

Yes the cosmological expansion theory could be wrong.
That is the fact about all scientific theories. They are never right. they are always at the mercy of the advent of a new better theory that matches the existing data and makes more falsifiable, testable predictions. So far no one has come up with an alternative that fits the criteria for a better scientific theory.

There are many scientists looking for alternatives to cosmological expansion. In fact some of the papers on Zeuzz's list are from reputable scientists. Also look in arXiv or do a Google Scolar search for "alternative explanation for cosmological redshift".

Zeuzzz said:

Perpetual Student said:

DeiRenDopa and/or sol invictus and/or anyone:

Do you think it is remotely possible that we have it all wrong regarding cosmological expansion and the big bang?

Click to expand...

Yes. But some seem impervious to this reality. Some do not. http://www.cosmology.info/2008conference/

Click to expand...

I gotta hand it to you Z, you really are priceless!

Read what you wrote again ... your sentences can be read to mean that those who made presentations at that conference are "impervious to reality"!

I am aware that cosmological expansion and the big bang are supported by a great deal of observational evidence and that GR provides a very strong theoretical framework for these theories.

Click to expand...

Yes, but change some of the fundamental concepts underlying this evidence, and all of this evidence can act as strong evidence for a non big bang universe. All evidence is precarious depending on the axioms on which they are based.

Click to expand...

Which is, of course, true of all of science ...

But, as with all science, you go with what works best ... and in that regard there's no competition (none of the alternatives comes remotely close to the explanatory and predictive power of the current consensus cosmological models).

[...]

Some extremely pertinent points are made by Lerner and others that no one yet has given adequate answers to.

I'm off on holiday now for a while and will remain lurking around for a week or two, but might pop back in for the odd comment when the odd blatent lie is posted.

Click to expand...

I'll check that out later, but am expecting that it'll contain nothing new, that we didn't cover - at great length - in the PC woo or not thread.

Perpetual Student said:

DeiRenDopa and/or sol invictus and/or anyone:

Do you think it is remotely possible that we have it all wrong regarding cosmological expansion and the big bang?
I am aware that cosmological expansion and the big bang are supported by a great deal of observational evidence and that GR provides a very strong theoretical framework for these theories.
Given that reality, this question may seem strange, but I have a nagging (but unsupported) feeling that there could possibly be another answer. However, I have absolutely no idea what any other answer might be.
I have been struggling to find a way to express my "nagging feeling." So, I’ll try this:
Could it not be that something other than cosmological expansion causes the red shift? And whatever that something else may be also accounts for the all the other supportive observations, like the CMB. By this I mean that something else would cause the red shift and the other phenomena that mimic expansion.
There are some examples in the history of science where a very wrong theory can find support from phenomena that turn out to be irrelevant or misunderstood.
For example, there were many supporting arguments making the earth the center of the universe. E. g.: if the earth turned, we would all be thrown off by the movement of the earth. Aristotelian physics made it so; it provided a “strong theoretical framework.” Another one: Stuff falls because its nature is to seek the center of the universe.
I don’t think very many physicists would take the position that our current understanding is the final word. There is yet more physics to be discovered.
You recall Plato's Allegory of the Cave. Similar to those cave dwellers (who saw only shadows), we see the universe through the EM spectrum, cosmic rays and extraterrestrial neutrinos. (I may be omitting something here). The universe may have more dimensions than four, there may exist types of radiation that are not detectible by us, and other forces or stuff that we cannot detect or describe or know about yet.
OK, now I know it’s easy to say, “Well, sure anything is possible.” That’s not exactly the response I am looking for. I’m aware of theories like “tired light” that have been examined and rejected as possible causes of the red shift. It seems that most research is done to confirm or develop nuances of cosmological expansion. Is anyone looking for alternative explanations for the red shift, other than “crackpots”?
So, there it is; I know all this is merely a layman’s naïve thoughts. If you can contribute any opinions or thoughts that may be interesting or helpful I would appreciate it.

Click to expand...

(bold added)

To add to the responses your post has already generated ...

I don't know why you chose to focus on the Hubble relationship, rather than the CMB, the primordial abundance of light nuclides, LSS (large-scale structure), or GR - as in "Is anyone looking for alternative explanations for the CMB/the primordial abundance of light nuclides/LSS/GR, other than “crackpots”?" - can you clarify please?

After all, the BBT - which seems to be at the root of your nagging doubts - would be in trouble if any of these turned out to have an alternative explanation (usual caveats apply).

But to look at "alternative explanations for the red shift" itself.

How would you go about searching for such explanations? No, seriously ... how do you think anyone - scientist, crackpot, layman - would actually do that? This is worth exploring, at least in part because it will show you - and Skwinty (and maybe even Zeuzzz) - just what the doing of science involves, through a concrete example.

And by spending some time on this, I think you'll work out the answer to your own question, in a far better way than if I simply typed a few hundred words ...

DeiRenDopa said:

After all, the BBT - which seems to be at the root of your nagging doubts - would be in trouble if any of these turned out to have an alternative explanation (usual caveats apply)....

Click to expand...

Thanks, you just answered my question to TT.

DeiRenDopa said:

But to look at "alternative explanations for the red shift" itself.

How would you go about searching for such explanations? No, seriously ... how do you think anyone - scientist, crackpot, layman - would actually do that? This is worth exploring, at least in part because it will show you - and Skwinty (and maybe even Zeuzzz) - just what the doing of science involves, through a concrete example....

Click to expand...

Well,I googled alternative explanations for the red shift and got loads of hits. Unfortunately I am not qualified to vouch for the integrity of these alternatives, hence my questions to people with qualifications in this field.

DeiRenDopa said:

And by spending some time on this, I think you'll work out the answer to your own question, in a far better way than if I simply typed a few hundred words ...

Click to expand...

I agree, that is why I ask for links, papers or book recommendations. I certainly don't expect anyone to write a tome when answering any of my questions. A little guidance is what I am looking for.

PS, what is MPS. I gather that PS refers to Philosophy of Science. does the M refer to Marxist?

Perpetual Student said:

Do you think it is remotely possible that we have it all wrong regarding cosmological expansion and the big bang?

Click to expand...

It is remotely possible, yes. But the odds are so low I can't even estimate them.

Here's what would have to be wrong:

• GR (since there are no stable static cosmo solutions), Newtonian gravity (same reason), and in fact any theory in which gravity is attractive and there are no repulsive forces of comparable size acting over cosmological distances (same reason).
  
  
• that the redshift of distant objects is due to recession velocities (because if they are, the universe is expanding).
  
  
• that all of the myriad effects we see correlated with redshift - amounts of metals and other elements (you see those via absorption and emission lines in spectra), composition of stellar populations, shapes and configuration of large scale structures, etc. etc. - have some explanation other than that the universe was different when it was younger. Hard to imagine why, in a static universe, distance from earth would be correlated with so many changes in those things, isn't it?
  
  
• the simple explanation of the CMB that arises in BBT (in a static universe, it would have to be something like that there's a very hot, perfectly thermalized, perfectly spherical wall centered on the earth and about 13 billion lightyears in radius).
  
  
• the 2nd law of thermodynamics - if the universe is eternal, it should now be in equilibrium. Yet stars are still forming and igniting.
  
  
• as much of non-gravitational physics as is need to account for the redshift by some other means.

Point being, there's a vast array of many different kinds of evidence that all indicates that the universe is expanding and was very different in the past. For it all to have another interpretation is.... very difficult to imagine.

Skwinty said:

[...]

PS, what is MPS. I gather that PS refers to Philosophy of Science. does the M refer to Marxist?

Click to expand...

I wrote HPS (I think), which stands for History and Philosophy of Science.

AFAIK, it is nigh on impossible to do PS (or the PoS) without HS (the HoS), hence HPS ...

DeiRenDopa said:

I wrote HPS (I think), which stands for History and Philosophy of Science.

AFAIK, it is nigh on impossible to do PS (or the PoS) without HS (the HoS), hence HPS ...

Click to expand...

My bad once again, I am not thinking coherently as I have come down with flu. I guess the Feyerabend connection triggered that.

Skwinty said:

edd said:

The short answer is you can't unravel them. The longer answer:......

........For distant objects the overwhelming majority of the redshift comes from the cosmological effect though.

Click to expand...

I understand cosmological redshift relates to the expansion of space.
Am I correct in this understanding?

How do you reconcile the seemingly contradictory statements that I have quoted from your post.

Click to expand...

The trouble with short answers is that they can be quite misleading ...

Anyway, the path you and I are on, wrt your original question, will (I hope) lead you to understand what edd wrote (and if not, then I'm sure he'll jump in with his own corrections ...)

DRD:

Firstly, I have an introductory astronomy text by Ceceliia Payne Gaposchkin and Katherine Haramundanis.

The section on redshift really deals with the redshift -distance relationship and recession velocities.

Click to expand...

The purpose of the introductory book is to lay the foundations - or framework - for the answers, not for you to read a para or chapter which directly answers your questions.

I'm not familiar with that particular book, but with Ceceliia Payne Gaposchkin as an author I doubt you could go wrong ...

Yes, the redshift spectrum X-Y plot will have all the necessary data attached such as the data you mentioned.

[...]

Click to expand...

Good.

One result of many hundreds (thousands?) of years of work by thousands of scientists - not all of them astronomers - is a simple model of the Earth and the Sun that has exceptionally good explanatory and predictive power: the Earth is a rigid sphere which rotates on its axis and revolves around the Sun.

Of course that's an oversimplification, but for our purposes it gets us to the starting gate: whatever redshift you estimate your spectrum has (we'll get onto how to say this a little more precisely later), you can convert it to a 'barycentric' redshift by virtue of the work of thousands of diligent astronomers, engineers, physicists, etc.

IOW, you know when you took your spectrum, where you pointed your gadget, and where your observatory (telescope, instrument on a spacecraft, ...) was when you made your observation, and you can use this information to do a straight-forward transform into a frame of reference whose origin is the solar system barycentre.

And here might be an appropriate point to introduce "errors".

Whatever your spectrum is, it is not perfect, in almost any sense (and especially a Platonic one). There are (quantum) theoretic limits, but they are not directly relevant here. With some exceptions, the uncertainty, imprecision, inaccuracy, etc of knowing the *exact* time you took the spectrum and the *exact* location can also be left out, as can the estimated location of the solar system barycentre - the uncertainty in your derived 'wrt the barycentre' redshift arising from these sources of 'error' will be trivial (there are some exceptions, which I'm happy to go into if you're interested).

For the cosmological redshifts we will eventually get onto, the major sources of uncertainty in the estimated redshift in the spectrum have to do with things like the (spectral) resolution of the spectrograph, its precision and accuracy, and the faintness of the source (star, galaxy, quasar) ... oh, and the 'perfect' spectrum of the object itself!

But as you have the flu, it might be sensible to stop here and ask if you're OK with transforming what comes out of an instrument into a barycentric redshift ... leaving for later the (extremely important) details of how the squiggles in the graph get turned into something magic called a redshift in the first place.

Yes? No? Not sure??

Skwinty said:

I understand cosmological redshift relates to the expansion of space.
Am I correct in this understanding?

How do you reconcile the seemingly contradictory statements that I have quoted from your post.

DRD:

Firstly, I have an introductory astronomy text by Ceceliia Payne Gaposchkin and Katherine Haramundanis.

The section on redshift really deals with the redshift -distance relationship and recession velocities.

Yes, the redshift spectrum X-Y plot will have all the necessary data attached such as the data you mentioned.

A quote from this text.

"It is thinkable that the redshifts are not velocity shifts, but have some other cause, such as the gravitational effect predicted by the General Theory of Relativity."

Click to expand...

Yes but that asks other questions:

1. If the gravitational/mass of an object is know or approximated and the amount of shift is higher related to distance, then what does that say?
a. That gravity becomes stronger with distance ?
b. That there is some source of gravity beyond the observable horizon, that is different from the observable universe?

Zeuzzz said:

Yes. But some seem impervious to this reality. Some do not. http://www.cosmology.info/2008conference/

Click to expand...

Uh huh, sure Zuezzz, there are going to be papers all right but you have yet to produce any specifics that have not been addressed, so why not tell us what wonderful things they present at the conferenec? It should be better than you quoting material by Perrat that was way out of date as evidence.
'Each member of the first set of panels will focus on specific observational challenges to or problems with the consensus cosmology. Examples are the lack of Gaussianity or isotropy in the microwave radiation, the excessive apparent ages of high-z galaxies, the early formation of large-scale structure, discordant results for light element abundances, the surface-brightness / redshift relation, etc. Each member of the second set of panels will focus on a particular alternative cosmology, or on alternative explanations for the key phenomena of the universe, such as the origin of redshift, the microwave radiation, large-scale structure, gravitational forces, light element abundances, quasars, dark matter, and dark energy.'

The boldeed ones seem to be outrights lies!


So what are these wonderful anamaloies, really do tell.

Yes, but change some of the fundamental concepts underlying this evidence, and all of this evidence can act as strong evidence for a non big bang universe. All evidence is precarious depending on the axioms on which they are based.

Just watch this documentary, part two is probably the best starting point: http://www.youtube.com/watch?v=wchV5R9NhqY

Some extremely pertinent points are made by Lerner and others that no one yet has given adequate answers to.

I'm off on holiday now for a while and will remain lurking around for a week or two, but might pop back in for the odd comment when the odd blatent lie is posted.

Click to expand...

Sure Zeuzz, these are such strong and perinent points that you can't post them.

the lie is that you say these things exist but you can't say what they are, what they mean or what data they represent.

Each of your points has been specifically addressed before, what new material are you bringing to the table?

DeiRenDopa said:

But as you have the flu, it might be sensible to stop here and ask if you're OK with transforming what comes out of an instrument into a barycentric redshift ... leaving for later the (extremely important) details of how the squiggles in the graph get turned into something magic called a redshift in the first place.

Click to expand...

No need to stop. If I blunder through incoherent thinking, I am sure it will be pointed out.
When you refer to barycentric, I presume you are referring to a triangulation process which would be mapped out when you make observations when the earth is in opposite positions in its orbit and thus showing a central point in the universe about which the earth and solar system is moving. If so, no problem.

I also understand that the spectra in question are compared to spectra obtained in a laboratory so that one would know the element or elements that the spectra are showing, otherwise the spectra would be meaningless. These spectra could be either emission or absorption spectra.

Am I on the right track here?

DeiRenDopa said:

The trouble with short answers is that they can be quite misleading ...

Click to expand...

I meant no disrespect to Edd, it just sounded a bit like saying "This equation is unsolvable, however the answer is 42"

Dancing David said:

1. If the gravitational/mass of an object is know or approximated and the amount of shift is higher related to distance, then what does that say?

Click to expand...

I am not sure, but seems like the object is further away.

Dancing David said:

a. That gravity becomes stronger with distance ?

Click to expand...

My understanding is that gravity is ruled by the inverse square law and that implies that gravity gets weaker with distance.

Dancing David said:

b. That there is some source of gravity beyond the observable horizon, that is different from the observable universe?

Click to expand...

Wouldn't dark matter or dark energy have an influence on gravity, or create its own gravity. Also the dark matter or dark energy may have been in that specific location a long time ago and is no longer in that location when the redshifted photons arrive at our instruments?

Skwinty said:

[...]

DeiRenDopa said:

But to look at "alternative explanations for the red shift" itself.

How would you go about searching for such explanations? No, seriously ... how do you think anyone - scientist, crackpot, layman - would actually do that? This is worth exploring, at least in part because it will show you - and Skwinty (and maybe even Zeuzzz) - just what the doing of science involves, through a concrete example....

Click to expand...

Well,I googled alternative explanations for the red shift and got loads of hits. Unfortunately I am not qualified to vouch for the integrity of these alternatives, hence my questions to people with qualifications in this field.

[...]

Click to expand...

Not waiting for PS to post may be a little rude, but ...

Googling is like doing a literature search, isn't it, only more 21st century.

I think it's fair to say that there are unlikely to be any such <alternative explanations for the red shift> that Z and MM between them haven't already found and put on the table.

Anyway, with a slight change of focus - for your search of the literature - you could start with being a super-diligent MM ... find all the published results - of experiments done in the lab, under controlled conditions - that report not only "redshift" (because the experimenters might have used different terms), but anything that is a redshift.

If you do this, you'll find things like Doppler effect, Wolf effect, Compton effect, Raman effect, gravitational redshift, ...

What now?

(there are other 'google-based' paths to explore too - can you think of one?)

Skwinty said:

No need to stop. If I blunder through incoherent thinking, I am sure it will be pointed out.
When you refer to barycentric, I presume you are referring to a triangulation process which would be mapped out when you make observations when the earth is in opposite positions in its orbit and thus showing a central point in the universe about which the earth and solar system is moving. If so, no problem.

Click to expand...

Not exactly ...

Think of the solar system barycentre as the point where the gravitational pulls of all the bodies in the solar system balance; the solar system's 'centre of mass' if you like.

Conceptually, if you had taken your spectrum from this point, then it would show the same redshift no matter when you took it (barring any changes in the relative motion - etc - between the solar system as a whole and the object whose spectrum you are taking). Of course, you can't go the barycentre and do this with the various spectroscopes used to produce astronomical spectra (do you know why?), at least not within our current technological capability.

The key point here is that the effects of the motion of the instrument wrt the solar system barycentre are factored out of the spectrum, whether due to the Earth's rotation, its motion around the Sun, the motion of the spacecraft wrt the Earth, ...

I also understand that the spectra in question are compared to spectra obtained in a laboratory so that one would know the element or elements that the spectra are showing, otherwise the spectra would be meaningless. These spectra could be either emission or absorption spectra.

Am I on the right track here?

Click to expand...

Yes, and that's what I'm going to get onto next ...

DeiRenDopa said:

If you do this, you'll find things like Doppler effect, Wolf effect, Compton effect, Raman effect, gravitational redshift,

Click to expand...

Yes, I have come across the above mentioned effects, but I couldn't assert that they are valid arguments to overthrow GR and cosmological redshift.

DeiRenDopa said:

(there are other 'google-based' paths to explore too - can you think of one?)

Click to expand...

arXiv is one that springs to mind, but as I am a noob in this regard, there are probably lots more. I certainly won't look at Our Undiscovered Universe again.

DeiRenDopa said:

Not exactly ...

Think of the solar system barycentre as the point where the gravitational pulls of all the bodies in the solar system balance; the solar system's 'centre of mass' if you like....

Click to expand...

OK, understood.

DeiRenDopa said:

Of course, you can't go the barycentre and do this with the various spectroscopes used to produce astronomical spectra (do you know why?), at least not within our current technological capability....

Click to expand...

Well, I doubt whether our spacecraft would be able to maintain that position for a long enough period of time.

DeiRenDopa said:

The key point here is that the effects of the motion of the instrument wrt the solar system barycentre are factored out of the spectrum, whether due to the Earth's rotation, its motion around the Sun, the motion of the spacecraft wrt the Earth, ......

Click to expand...

OK, understood. The gravition effects of the solar system could now be factored out of the equation.

Thanks for all the responses. I think the problem here is that it is extremely difficult for a layman (at least, this one) to understand and appreciate just how overwhelming the observational and theoretical evidence is for the BB.

s.i.
Here's what would have to be wrong:

GR (since there are no stable static cosmo solutions), Newtonian gravity (same reason), and in fact any theory in which gravity is attractive and there are no repulsive forces of comparable size acting over cosmological distances (same reason).


that the redshift of distant objects is due to recession velocities (because if they are, the universe is expanding).


that all of the myriad effects we see correlated with redshift - amounts of metals and other elements (you see those via absorption and emission lines in spectra), composition of stellar populations, shapes and configuration of large scale structures, etc. etc. - have some explanation other than that the universe was different when it was younger. Hard to imagine why, in a static universe, distance from earth would be correlated with so many changes in those things, isn't it?


the simple explanation of the CMB that arises in BBT (in a static universe, it would have to be something like that there's a very hot, perfectly thermalized, perfectly spherical wall centered on the earth and about 13 billion lightyears in radius).


the 2nd law of thermodynamics - if the universe is eternal, it should now be in equilibrium. Yet stars are still forming and igniting.


as much of non-gravitational physics as is need to account for the redshift by some other means.

Point being, there's a vast array of many different kinds of evidence that all indicates that the universe is expanding and was very different in the past. For it all to have another interpretation is.... very difficult to imagine.

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and:

D.
I don't know why you chose to focus on the Hubble relationship, rather than the CMB, the primordial abundance of light nuclides, LSS (large-scale structure), or GR - as in "Is anyone looking for alternative explanations for the CMB/the primordial abundance of light nuclides/LSS/GR, other than “crackpots”?" - can you clarify please?

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There not much to clarify, other than the Hubble relationship was the initial impetus for the BB before the other discoveries were made. But the same point is being made here; the evidence is overwhelming!

Skwinty said:

[...]

DeiRenDopa said:

Of course, you can't go the barycentre and do this with the various spectroscopes used to produce astronomical spectra (do you know why?), at least not within our current technological capability....

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Well, I doubt whether our spacecraft would be able to maintain that position for a long enough period of time.

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OK, that would be one reason ...

... however, there's a rather more important one ...

HINT: suppose the solar system consisted of only the Earth-Moon and the Sun. Where would the centre of mass of such a solar system be?

The key point here is that the effects of the motion of the instrument wrt the solar system barycentre are factored out of the spectrum, whether due to the Earth's rotation, its motion around the Sun, the motion of the spacecraft wrt the Earth, ......

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OK, understood. The gravition effects of the solar system could now be factored out of the equation.

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Not really, ...

Way back you asked:

Skwinty said:

If you examine a redshifted spectrum, how do you determine what amount of redshift is due to:

Doppler effect
Earths motion.
[...]
Gravitational effects.
[...]

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What I've shown you is that you can factor out the component(s) in the redshifted spectrum that are due to the Doppler effect due to the motion of your observatory/instrument (as the Earth to which it is attached rotates) AND the motion of the Earth as a whole as it revolves around the Sun (or, more precisely, its motion wrt the solar system barycentre).

Along the way I've also made any gravitational redshift (due to the Earth, Sun, etc) go away (can you see how I did that?).

Skwinty said:

DeiRenDopa said:

If you do this, you'll find things like Doppler effect, Wolf effect, Compton effect, Raman effect, gravitational redshift,

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Yes, I have come across the above mentioned effects, but I couldn't assert that they are valid arguments to overthrow GR and cosmological redshift.

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OK, but ...

... you left out the key part, namely "What now?"!

It seems you jumped too many steps ahead ... with a list of such effects (nearly all of them have names which include the word "effect"), plus a detailed description of what they are (based firmly on pure empiricism, i.e. what was found in labs when experiments were done), what do you do next (logically)?

(there are other 'google-based' paths to explore too - can you think of one?)

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arXiv is one that springs to mind, but as I am a noob in this regard, there are probably lots more. I certainly won't look at Our Undiscovered Universe again.

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Oops, my bad.

What I meant was, what sort of other things would you use to do a literature search on, other than what has been found in (controlled) experiments in labs? As applied, directly or indirectly, to "redshifts"?

HINT: not everything in physics is, or was, discovered in the lab, essentially by luck or coincidence; many things were found as a result of ...

Skwinty said:

DeiRenDopa said:

The trouble with short answers is that they can be quite misleading ...

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I meant no disrespect to Edd, it just sounded a bit like saying "This equation is unsolvable, however the answer is 42"

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Here's your statement: "How do you reconcile the seemingly contradictory statements that I have quoted from your post."

edd is quite right ... if all you have is something which you have been told is "a redshifted spectrum", then there is no way to work out what the cause (or causes) of the redshift is.

And that's what I'm in the process of explaining to you ... you never have just a number (the redshift of the spectrum is ...), you always have other information.

And it's that other info that leads to the conclusion that the redshift in the spectrum is due to x parts motion of the observatory/instrument wrt the solar system barycentre, y parts gravitational redshift at the source, z parts 'peculiar velocity', w parts expansion, ...

OK, now that I understand the barycentre, The centre of mass of the solar system would lie either very close to the sun, or within the sun.
On top of this, the barycentre is not a fixed position but rather changes as the planets revolve around the sun. So, our spacecraft would have difficulty maintaining this position as well as resisting the heat generated by the sun.

I can understand how the motion of the earth's contribution to the doppler effect can be determined. The earth's velocity in its orbit around the sun is about 28km/s so this contribution to the doppler effect is small.
If we aimed our spectrograph at a specific star, say Arcturus, then the redshift would be measured when the earth moves away from Arcturus and the blue shift when earth moves toward Arcturus. Any difference between the red and blue component could be construed as the motion of Arcturus itself.

WRT to laboratory spectroscopy, once the at rest spectra of the elements have been determined, the next step would be to compare these known rest spectra with the spectra of moving galactic objects. This would enable a determination to be made of the motion of the extragalactic body. ie if it is redshifted the extragalactic body is moving away and if blue shifted , moving towards us. By subtracting the results obtained in the previous paragraph would leave the redshift of the extragalactic body.

WRT to the gravitational aspect, I am not quite sure as to how this is removed from the equation. Initially, I thought, as we had a reference to the barycentre, we could measure the gravitational effect on redshift much the same way as Eddington did when he measured the bending of light due to the sun during a solar eclipse. Perhaps I need some clarification here.

As to the What Now, I think observation and more observation and comparisons to what we see in the lab and what we observe in the sky.

Skwinty said:

I am not sure, but seems like the object is further away.



My understanding is that gravity is ruled by the inverse square law and that implies that gravity gets weaker with distance.

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So then it might be hard to explain why the redshift increases with distance, if the effect is gravitational.

Wouldn't dark matter or dark energy have an influence on gravity, or create its own gravity.

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Yes, that is why dark matter is hypothesized.

Also the dark matter or dark energy may have been in that specific location a long time ago and is no longer in that location when the redshifted photons arrive at our instruments?

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That may be but it would still require that the amount of dark matter increase with distance.

Dancing David said:

So then it might be hard to explain why the redshift increases with distance, if the effect is gravitational.

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I can understand that if you were referring to the gravitational field between earth and the extragalactic object.
I was thinking along the lines of gravitational fields the light encountered as it leaves the extragalactic object and any other gravitational fields it encounters enroute.
For example: Light leaves the extragalactic object and it must travel 300,000 light years to get to earth. The gravitational field relating to the mass of earth and the mass of the extragalactic body is very, very small.
However, 10,000 light years after leaving the extragalactic object, the light encounters the gravitational field of a supermassive black hole. This induces a massive redshift to the light and this is detected on earth 290,000 light years later. We may then erroneously ascribe this redshift to recessional velocity rather than gravity.

Skwinty said:

However, 10,000 light years after leaving the extragalactic object, the light encounters the gravitational field of a supermassive black hole. This induces a massive redshift to the light and this is detected on earth 290,000 light years later. We may then erroneously ascribe this redshift to recessional velocity rather than gravity.

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Any redshift climbing away from a gravitational field is countered by the blueshift as the light initially falls in to it.

The only exception to this is if the gravitational field changes over time (see for example the Integrated Sachs-Wolfe Effect).

Skwinty said:

OK, now that I understand the barycentre, The centre of mass of the solar system would lie either very close to the sun, or within the sun.
On top of this, the barycentre is not a fixed position but rather changes as the planets revolve around the sun. So, our spacecraft would have difficulty maintaining this position as well as resisting the heat generated by the sun.

I can understand how the motion of the earth's contribution to the doppler effect can be determined. The earth's velocity in its orbit around the sun is about 28km/s so this contribution to the doppler effect is small.
If we aimed our spectrograph at a specific star, say Arcturus, then the redshift would be measured when the earth moves away from Arcturus and the blue shift when earth moves toward Arcturus. Any difference between the red and blue component could be construed as the motion of Arcturus itself.

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Good enough (don't forget that unless the observatory is at one of the Earth's poles there is also the motion of the observatory around the Earth's rotational axis, and that for instruments aboard spacecraft there is the motion of the spacecraft wrt the solar system barycentre).

WRT to laboratory spectroscopy, once the at rest spectra of the elements have been determined, the next step would be to compare these known rest spectra with the spectra of moving galactic objects. This would enable a determination to be made of the motion of the extragalactic body. ie if it is redshifted the extragalactic body is moving away and if blue shifted , moving towards us. By subtracting the results obtained in the previous paragraph would leave the redshift of the extragalactic body.

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Fair enough, at a very high level.

However, there are some points that are very important to your, and PS', question about alternative explanations of the redshift; I'll go over some of these in a later post.

WRT to the gravitational aspect, I am not quite sure as to how this is removed from the equation. Initially, I thought, as we had a reference to the barycentre, we could measure the gravitational effect on redshift much the same way as Eddington did when he measured the bending of light due to the sun during a solar eclipse. Perhaps I need some clarification here.

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The first thing to note about the gravitational redshift is that it is predicted by GR.

The second thing is that Pound and Rebka (and others) measured it, in labs here on Earth, in controlled conditions, in a series of experiments (starting in 1959?). The experiment has been repeated many times and in many different ways; the results are consistent with the GR predictions.

With some simplification, the gravitational redshift of a compact, spherical object* of mass M and radius r, observed at a great distance (zero relative velocity) is z = GM/rc^2 (G is the gravitational constant; c is the usual suspect).

If the roles of source and observer are reversed, then there's a gravitational blueshift.

Would you care to take a crack at estimating the gravitational blueshift that observers on the surface of the Earth must factor out of any spectrum of a distant source?

As to the What Now, I think observation and more observation and comparisons to what we see in the lab and what we observe in the sky.

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For readers who have not been keeping up: we've done a thorough literature search and have made a list of all the things that scientists have found, in the lab, that can result in redshifts (Doppler effect, Compton effect, ...).

Our quest is to outline how a diligent scientist might go about investigating the possibility of alternative explanations for the redshifts conventionally ascribed to 'cosmological expansion'.

Certainly nothing wrong with "observation and more observation and comparisons to what we see in the lab and what we observe in the sky"!

But perhaps that's a little too terse?

For example, wouldn't it be a very good idea to understand - in considerable detail - the actual, physical mechanisms at work in each of the (empirically founded) causes of redshift? IOW, to see if you can account for them - quantitatively - within the framework of the physics found in standard textbooks? And if you can't, then maybe some more research would be needed, to nail down just what's going on, to as many decimal places (significant figures) as the errors and uncertainties in your lab results allow?

* more precisely, this is the redshift from a source on the surface of such an object; we also assume that the object is not rotating (etc)

Perpetual Student said:

DeiRenDopa and/or sol invictus and/or anyone:

Do you think it is remotely possible that we have it all wrong regarding cosmological expansion and the big bang?
I am aware that cosmological expansion and the big bang are supported by a great deal of observational evidence and that GR provides a very strong theoretical framework for these theories.
Given that reality, this question may seem strange, but I have a nagging (but unsupported) feeling that there could possibly be another answer. However, I have absolutely no idea what any other answer might be.
I have been struggling to find a way to express my "nagging feeling." So, I’ll try this:
Could it not be that something other than cosmological expansion causes the red shift? And whatever that something else may be also accounts for the all the other supportive observations, like the CMB. By this I mean that something else would cause the red shift and the other phenomena that mimic expansion.
There are some examples in the history of science where a very wrong theory can find support from phenomena that turn out to be irrelevant or misunderstood.
For example, there were many supporting arguments making the earth the center of the universe. E. g.: if the earth turned, we would all be thrown off by the movement of the earth. Aristotelian physics made it so; it provided a “strong theoretical framework.” Another one: Stuff falls because its nature is to seek the center of the universe.
I don’t think very many physicists would take the position that our current understanding is the final word. There is yet more physics to be discovered.
You recall Plato's Allegory of the Cave. Similar to those cave dwellers (who saw only shadows), we see the universe through the EM spectrum, cosmic rays and extraterrestrial neutrinos. (I may be omitting something here). The universe may have more dimensions than four, there may exist types of radiation that are not detectible by us, and other forces or stuff that we cannot detect or describe or know about yet.
OK, now I know it’s easy to say, “Well, sure anything is possible.” That’s not exactly the response I am looking for. I’m aware of theories like “tired light” that have been examined and rejected as possible causes of the red shift. It seems that most research is done to confirm or develop nuances of cosmological expansion. Is anyone looking for alternative explanations for the red shift, other than “crackpots”?
So, there it is; I know all this is merely a layman’s naïve thoughts. If you can contribute any opinions or thoughts that may be interesting or helpful I would appreciate it.

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(bold added)

Hey PS, Skwinty is boldly trying to be a scientist here, working out how to go about looking for "alternative explanations for the red shift".

What about you? It was your question, after all, that got the ball rolling!

Are you following along? Do you see any shortcomings in the (high-level) outline of how the question may be answered? Have we lost you, wrt understanding any of the details so far?

Skwinty said:

I can understand that if you were referring to the gravitational field between earth and the extragalactic object.
I was thinking along the lines of gravitational fields the light encountered as it leaves the extragalactic object and any other gravitational fields it encounters enroute.
For example: Light leaves the extragalactic object and it must travel 300,000 light years to get to earth. The gravitational field relating to the mass of earth and the mass of the extragalactic body is very, very small.
However, 10,000 light years after leaving the extragalactic object, the light encounters the gravitational field of a supermassive black hole. This induces a massive redshift to the light and this is detected on earth 290,000 light years later. We may then erroneously ascribe this redshift to recessional velocity rather than gravity.

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It does make some cool arcs , crosses and other effects, but I don't know how that would create a redshift that is the same in all directions and increases with distance. I would think that it would also take a whole whole lot of them to create the effect.

http://apod.nasa.gov/apod/ap011007.html
http://antwrp.gsfc.nasa.gov/apod/ap080728.html
http://antwrp.gsfc.nasa.gov/apod/ap080330.html

DeiRenDopa;4498764Hey PS said:

alternative explanations for the red shift[/I]".

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I am trying to improve my understanding of the topics under discussion within the realm of fact.
I don't for one minute believe that I have the capacity to be a scientist, although I am extremely interested in the current state of cosmology.
I suppose my main objective is to try and separate fact from fiction and this makes my love of amateur astronomy all the more fascinating.

It is very satisfying to observe the universe with a telescope and have a modicum of understanding of what you see.

DeiRenDopa said:

Would you care to take a crack at estimating the gravitational blueshift that observers on the surface of the Earth must factor out of any spectrum of a distant source?

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I will have to think about the content of this post, but I will say that the blue shift is the inverse of the redshift.

Ie the redshift wavelength increases (frequency decreases) in comparison to the rest spectra whilst the blue shift wavelength decreases (frequency increases) in comparison with the rest spectra.

Originally Posted by DeiRenDopa
Would you care to take a crack at estimating the gravitational blueshift that observers on the surface of the Earth must factor out of any spectrum of a distant source?

Using doppler formula and assuming that the emitter is stationary, earth velocity 30km/sec towards the emitter and incoming photon frequency of 100hz, z=.0001.

Skwinty said:

I am trying to improve my understanding of the topics under discussion within the realm of fact.
I don't for one minute believe that I have the capacity to be a scientist, although I am extremely interested in the current state of cosmology.
I suppose my main objective is to try and separate fact from fiction and this makes my love of amateur astronomy all the more fascinating.

It is very satisfying to observe the universe with a telescope and have a modicum of understanding of what you see.

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Fair enough.

Perhaps it's more accurate to say that you are trying to work though some of the ways in which you can more satisfyingly distinguish between fact and fiction in what you read? And part of that process involves critical thinking and working out methodical and logical ways to test ideas you read?

DeiRenDopa said:

Fair enough.

Perhaps it's more accurate to say that you are trying to work though some of the ways in which you can more satisfyingly distinguish between fact and fiction in what you read? And part of that process involves critical thinking and working out methodical and logical ways to test ideas you read?

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You stated my feelings better than I did.

PS seems to have left us, and Skwinty's flu may still be messing with his head, so here's some thoughts on the steps one could take - in principle - to check out "alternative explanations for the red shift".

Recall that we have done a thorough literature search and collected everything, and I mean everything, in the relevant published papers that even remotely looks like "we, the scientist authors of this paper, found some redshift in this experiment", and that includes results where "redshift" (the term) was not used.

We then did a whole bunch of other experiments, and developed theories and models etc, so now we understand what's going on, physically, with all these effects, and so can confidently examine the extent to which any - or any combo - of them could apply to astronomical objects (and so to their observed redshifts).

We have also done an extensive literature search for possible causes of redshift that arise from various theories or models reported in published papers. This is the counterpart to our first literature search, which focused on what came out of experiments in labs. Again, we draw up a list of possible causes - based on theories this time - and leave out only those which have been shown, in later papers, to be wrong due to internal inconsistency or failure to match relevant experimental tests. Note that there may be some possible causes of redshift, derived from some theory or other, that cannot be directly tested in controlled experiments in the lab; pace MM, we include those in our list.

We have at least one more thing to check out, as a possible source of possible causes of redshift, before we move on to see how well - or not - any of those on our lists (or any combo of them) can explain the observed redshifts in astronomy; that we will do in a later post.

NOTE: in parallel we're doing a tutorial on how astronomers distinguish among the causes of redshift, as seen in astronomical objects; we're using Skwinty's checklist (at least to start with). So far we've addressed "Earth motion" and "Gravitational effects" (within the solar system), and necessarily looked at "Doppler effect".

You're impatient, and just want the conclusion? OK, here it is: there are no "alternative explanations for the red shift" which are both based on sound science and which meet reasonable criteria for "explain".