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Terry Giblin
2010-Nov-28, 08:20 PM
Has anyone watch his program about Quasars?

Including interviews with Sir Fred Hoyle.

I am sorry, but pleased to say, no one can expect a Theoretical Cosmologist, Astrophysicist, Mathematician or Physicist to solve or think of a valid theory, to explain or predict every, 'line of sight' objects, observed in the known Universe.

Red Shift is proportional to Distance.

Or does anyone disagree?

Light in, Light out.

Shaula
2010-Nov-28, 08:48 PM
Red shift is proportional to distance only because speed of recession is (mostly). Two objects, same distance but different LOS speeds will have different red shifts.

Terry Giblin
2010-Nov-28, 09:43 PM
Red shift is proportional to distance only because speed of recession is (mostly). Two objects, same distance but different LOS speeds will have different red shifts.

'Recessional Velocity' is proportional to Distance.

forrest noble
2010-Nov-29, 01:43 AM
Has anyone watch his program about Quasars?

Including interviews with Sir Fred Hoyle.

I am sorry, but pleased to say, no one can expect a Theoretical Cosmologist, Astrophysicist, Mathematician or Physicist to solve or think of a valid theory, to explain or predict every, 'line of sight' objects, observed in the known Universe.

Red Shift is proportional to Distance.

Or does anyone disagree?

Light in, Light out.

I generally agree, but the details of what I think are exceptions must remain unnamed. The standard model explanation is simply yes. Since this is the Q & A section realize that "yes" is presently the only possible mainstream answer.

I think Sir Fred will be vindicated in part over time, a truly great man.


......to solve or think of a valid theory, to explain or predict every, 'line of sight' objects, observed in the known Universe.

Not any one man or vast group of men could ever do that regarding "every" observation. Even the sum of all their guesses might not be able do that.

The primary known reasons why redshifts do not exactly correlate to distances, although presently most variations are thought to be small:

gravitational effects, sometimes called Einstein redshifts; galactic relative motions unrelated to standard redshifts; absorption and re-emission of galactic light by intervening gases.

TonyE
2010-Nov-29, 08:34 AM
Red Shift is proportional to Distance.

Or does anyone disagree?

Yes. I disagree. Redshift is not proportional to distance.


'Recessional Velocity' is proportional to Distance.

I don't agree with this either.

Redshift is proportional to the amount the universe has expanded since the light was emitted.

z=(distance now - distance when emitted) / (distance when emitted).

So if z=2 then the universe has expanded by a factor of 2 while the light was on is way to us.

Amber Robot
2010-Nov-29, 04:44 PM
absorption and re-emission of galactic light by intervening gases.

Why would this cause redshift?

forrest noble
2010-Nov-29, 08:20 PM
Why would this cause redshift?

If an intervening galactic/ intergalactic cloud absorbs galactic radiation behind it (in our line of sight), it will re-radiate these wavelengths based upon its own relative distance. This is the process thought to cause BL Lacs which are quasar appearing objects with smeared emission and absorption lines. If the absorption and re-radiation is complete then we might only know the distance of the cloud thinking it is the distance to the quasar. This also could occur during gravitational lensing.

Amber Robot
2010-Nov-29, 08:43 PM
If an intervening galactic/ intergalactic cloud absorbs galactic radiation behind it (in our line of sight), it will re-radiate these wavelengths based upon its own relative distance.

But this shouldn't be confused with the redshift of the source emission. A quasar's redshift is usually determined by its intrinsic emission lines, not the redshift of the lines of any intervening intergalactic clouds.

forrest noble
2010-Nov-29, 10:50 PM
But this shouldn't be confused with the redshift of the source emission. A quasar's redshift is usually determined by its intrinsic emission lines, not the redshift of the lines of any intervening intergalactic clouds.

This is true but it is possible that only the re-emission lines remain as we may not be able to observe any of the original source emissions. If this were the case we may have only knowledge of the secondary emissions thinking they are the primary and miscalculate the source distance based upon the apparent redshift.

Shaula
2010-Nov-29, 10:54 PM
This is true but it is possible that only the re-emission lines remain as we may not be able to observe any of the original source emissions. If this were the case we may have only knowledge of the secondary emissions thinking they are the primary and miscalculate the source distance based upon the apparent redshift.
Why would the source emission lines be erased? They are not at the same frequency of the re-emission lines and would be left in the light unless absorbed by something else. If all the source light is absorbed then we wouldn't even know about the more distant object. Am I missing something about your argument here?

forrest noble
2010-Nov-29, 11:17 PM
Why would the source emission lines be erased? They are not at the same frequency of the re-emission lines and would be left in the light unless absorbed by something else. If all the source light is absorbed then we wouldn't even know about the more distant object. Am I missing something about your argument here?

That is the point. We wouldn't even know about the more distant object which could have a much greater redshift. There might be some kind of a clue in the absorption emission lines that we observe that might suggest the possibility that the object that we are observing is not the primary source of the EM radiation.

Amber Robot
2010-Nov-29, 11:25 PM
Have you actually seen what quasar spectra look like? You seem to be describing something that shows up as emission lines only but that is not what quasar spectra look like. Intervening intergalactic gas clouds show up only in absorption. You do not see the resultant re-emission.

forrest noble
2010-Nov-29, 11:59 PM
Have you actually seen what quasar spectra look like? You seem to be describing something that shows up as emission lines only but that is not what quasar spectra look like. Intervening intergalactic gas clouds show up only in absorption. You do not see the resultant re-emission.

I agree it would be pretty unlikely that such an observation could fool us into thinking that it was a original-galaxy emission. But if erased we could only make an estimate of a parent galaxy's distance based upon the intensity and clarity of the re-emission. Besides absorption, intervening gases produce their own emissions which may be similar or differ from the radiation that they are absorbing but much fainter.

Amber Robot
2010-Nov-30, 01:58 AM
I guess I'm not really understanding what you're picturing here. What is the spectral character you are imagining the source to have such that it can be completely absorbed by gas at a different redshift and left with only the re-emitted light at the redshift of the absorber?

WayneFrancis
2010-Nov-30, 04:01 AM
I'm not sure who is pitching what here but here is what we should expect from the following thought experiment.

Distant object is emitting a given spectrum which will inform us of the elements involved in that object.
As the photons travel through space and over time their frequency will be red shifted
If the photons are absorbed by an intermediate object then the absorption will be based on the frequency they where shifted to at that point.
Any photons that are not of the correct energy levels will pass through the medium unaltered besides having their paths possibly altered due to gravitational effects of the intermediate object's gravity well.

Any re-emission of photons from the original source will
A) be in a random direction
B) have frequencies dictated by the atom that the photon was absorbed by and the possible paths the excited electrons can take while traversing to their ground state.

Any photon continuing on from the intermediate medium will have photons continue to be red shifted by cosmological expansion as they travel through space-time.

resulting image will be a mix of spectra from the original object and the intermediate object and will be red shifted by 2 different amounts according to the last emission of the photon.

That said if a photon starts with frequency f1 and is red shifted by f2 before being absorbed it is possible that it will be re-emitted as f2 and arrive at a distance object at a frequency of f3 which is the same over all red shift as if the photon didn't get absorbed during the trip.

forrest noble
2010-Nov-30, 06:46 AM
I think there are several possibilities which might throw us off similar to Wayne Francis's example. A few BL Lacs, as I recall, have mixed redshift elements that seem likely related to re-emitted light. One that could be solely re-emitted radiation/ absorption/ emission lines and therefore misinterpreted concerning its distance, is speculative.

Shaula
2010-Nov-30, 06:54 AM
I think there are several possibilities which might throw us off similar to Wayne Francis's example. A few BL Lacs, as I recall, have mixed redshift elements that seem likely related to re-emitted light. One that could be solely re-emitted radiation/ absorption/ emission lines and therefore misinterpreted concerning its distance, is speculative.
The examples you give might (just might) work for one line, but relies on the redshift being just right to cause two otherwise unrelated lines to line up. But no one relies on one line to determine distance. We look for a spectrum. It is so unlikely as to be verging on the impossible for all the lines in an object spectrum to be given an offset that causes them to exactly line up with the lines of another object. For all practical intents and purposes redshift is related to recessional velocity and therefore distance.

Nereid
2010-Nov-30, 09:01 AM
The examples you give might (just might) work for one line, but relies on the redshift being just right to cause two otherwise unrelated lines to line up. But no one relies on one line to determine distance. We look for a spectrum. It is so unlikely as to be verging on the impossible for all the lines in an object spectrum to be given an offset that causes them to exactly line up with the lines of another object. For all practical intents and purposes redshift is related to recessional velocity and therefore distance.
Actually, you do come across papers in which some objects' redshifts are estimated based on only one, or two, line(s). In these cases, AFAIK, there is a lengthy discussion of just how reliable that estimate is (and it's always given with strong caveats), with considerable other observational data being brought in, such as the continuum SED, nearby objects with more reliable redshifts, absence of other emission (or absorption) lines (testing for redshift systems), line widths, etc.

Strange
2010-Nov-30, 11:06 AM
One that could be solely re-emitted radiation/ absorption/ emission lines and therefore misinterpreted concerning its distance, is speculative.

But if we are solely seeing re-emitted radiation then we will (correctly) measure the distance to the object emitting that light. We will not see (by definition) any more distant source for that light and so we will not "misinterpret" its distance.

forrest noble
2010-Dec-02, 01:32 AM
Strange,

This would be true for wholly re-emitted light. But sometimes the redshift has been blurred and as Nereid said maybe only one or two lines of absorption from a closer "cloud" may remain even though the primary light may have come from a more distant source. Of course this is only speculation and if valid such a misinterpretation would only be an exception to the normal distance-redshift correlation.

Amber Robot
2010-Dec-02, 02:46 AM
Strange,

This would be totally for wholly re-emitted light. But sometimes the redshift has been blurred and as Nereid said maybe only one or two lines of absorption from a closer "cloud" may remain even though the primary light may have come from a more distant source. Of course this is only speculation and if valid such a misinterpretation would only be an exception to the normal distance-redshift correlation.

You would need to know the distance to the "source" in your scenario for there to be an exception to the distance-redshift correlation. If you are picturing a source emitting light and then it getting absorbed completely by the IGM and re-emitted with enough intensity along the line of sight to still be observed, but now somehow the light looked like the source but only emitted at a different redshift (and I find it very difficult to figure out how this scenario would actually exist) the observer would only see a source at the emitted redshift with no information of the original source. Without having a distance how would you put this on a distance-redshift correlation plot?

Cougar
2010-Dec-02, 01:17 PM
I think Sir Fred will be vindicated in part over time, a truly great man.

Hoyle had a few good hits and a lot of misses. What specific misses do you think will be vindicated?




[Regarding Hoyle's BBC programs] Lord Simon turned to Sydney Goldstein, then professor of applied mathematics at Manchester, for an expert opinion. Goldstein, who had been a fellow of St. John's College, responded by saying it all depended what programming the corporation wanted. "If they want entertainment, the lectures are fine. If they want science they are not fine. The best astronomers would not agree with many of his conclusions. Hoyle has not the humility of a good scientist. - Simon Mitton

Strange
2010-Dec-02, 01:21 PM
Strange,

This would be totally for wholly re-emitted light. But sometimes the redshift has been blurred and as Nereid said maybe only one or two lines of absorption from a closer "cloud" may remain even though the primary light may have come from a more distant source. Of course this is only speculation and if valid such a misinterpretation would only be an exception to the normal distance-redshift correlation.

If you can't see why your scenario makes no sense at all then I give up ....

Nereid
2010-Dec-02, 05:20 PM
Strange,

This would be totally for wholly re-emitted light. But sometimes the redshift has been blurred and as Nereid said maybe only one or two lines of absorption from a closer "cloud" may remain even though the primary light may have come from a more distant source. Of course this is only speculation and if valid such a misinterpretation would only be an exception to the normal distance-redshift correlation.
I should have been clearer; I've never seen a redshift confidently estimated based on only one absorption line; rather what I was referring to was emission line(s).

Even in analyses of Lyman systems (i.e. Lyman-alpha "forests", of absorption lines) more than one line needs to be clearly detected before an individual system is confidently deduced (AFAIK); of course, one can do good studies based on a large sample of forests, from many different objects, and in such research a single absorption line in the spectrum of an object may be informative.

But perhaps the most important thing you seem to be overlooking - well, besides the general concept itself - is that a good spectrum doesn't just contain a "line", as in the observed wavelength of a feature ... lines have widths, and one can usually estimate the intrinsic "equivalent width", which can tell you quite a bit about the physics of the region doing the emitting (or absorbing); too, there's nearly always a continuum (and the absence of such is usually even more informative); and so on.

forrest noble
2010-Dec-03, 08:43 PM
Cougar,


Hoyle had a few good hits and a lot of misses. What specific misses do you think will be vindicated?

Not all of his "misses" of course but a number of his "primary assertions" that are akin to my own related theories which must go unnamed excepting in an ATM proposal which I will assert when I think I have the time to defend it. If you would like my answer sooner PM me. I should be able to respond quickly to such a request.

forrest noble
2010-Dec-03, 08:56 PM
I should have been clearer; I've never seen a redshift confidently estimated based on only one absorption line; rather what I was referring to was emission line(s).

Even in analyses of Lyman systems (i.e. Lyman-alpha "forests", of absorption lines) more than one line needs to be clearly detected before an individual system is confidently deduced (AFAIK); of course, one can do good studies based on a large sample of forests, from many different objects, and in such research a single absorption line in the spectrum of an object may be informative.

But perhaps the most important thing you seem to be overlooking - well, besides the general concept itself - is that a good spectrum doesn't just contain a "line", as in the observed wavelength of a feature ... lines have widths, and one can usually estimate the intrinsic "equivalent width", which can tell you quite a bit about the physics of the region doing the emitting (or absorbing); too, there's nearly always a continuum (and the absence of such is usually even more informative); and so on.

Since the consensus of opinion in this thread seems to be that the possibility concerning mis-identification of the proper redshift of a galaxy/ quasar is "generally non-existent" concerning intervening emission or absorption lines, then I will withdraw such a suggestion since this is the Q & A section whereby the mainstream positions are often best represented by a consensus of present thought.

Terry Giblin
2010-Dec-04, 03:23 PM
I did not wish to cause an argument or disagreement.

The only reason I posted this thread was to answer a question, which had been puzzelling me for the past 25 years, which I hope everyone agrees was answered in the 'documentry'.

When I told my Maths Prof. that I wanted to study Quasars, he said I couldn't, until I proved or disproved what Dr. H. Arp had said or indicated.

From listening and watching the video, Universe - The Cosmology Quest (http://www.youtube.com/watch?v=1yTfRy0LTD0), I now understand what my Math's Prof. meant.

There is no point in studying Quasars, until you can prove or disprove that they are at distances implied by their 'red shift'.

Due to several 'line of sight', observations or discoveries, made by Dr. H. Arp, he argued that the Quasars were not at their implied distances and therefore not so bright or powerful as first suggested.

But in the documentry, I think it is now clear that even Dr. H. Arp accepts or admits thats is not the case.

You can not write a mathematical physical model of two colliding galaxies, which can produce the same effects, as shown in the 'line of sight' discoveries and observation made by Dr. H. Arp.

No 'computer model' of two colliding galaxies with ever form, nearby 'gas clouds' or 'Quasars', with varrying red shifts.

Quasars are at the distances implied by there red shift.

But every now and then, a new 'line of sight' observation or discovery is made and the whole argument is started over again.

Light in, Light out.

Strange
2010-Dec-04, 03:30 PM
There is no point in studying Quasars, until you can prove or disprove that they are at distances implied by their 'red shift'.

Wouldn't that be part of the very purpose of studying quasars? (i.e. to confirm their distance) How can you prove/disprove something about quasars without studying them?

Terry Giblin
2010-Dec-04, 04:46 PM
Wouldn't that be part of the very purpose of studying quasars? (i.e. to confirm their distance) How can you prove/disprove something about quasars without studying them?

Dr. H. Arp, argument was that certain Quasars appeared to be connected to other galaxies, which had different red shifts.

So before I could even start to study the maths or physics of Quasars, I first had to prove or disprove Dr H. Arp arguments or observations.

The question is how?

As it turned out the answer is simple.

Take any mathematical or 'computer' model, of two galaxies colliding with each other. You can never get them to produce other objects with different red shifts, as implied by the 'light of sight' observations discovered by Dr. H. Arp, without cheating or changing the laws of physics as we know them.

Once I proved this and convinced myself and my Prof. that Quasars are at distances implied by their red shift, I could begin working on trying to solve and work out, how a Quasar were formed and what their properties would be.

Nereid
2010-Dec-04, 05:19 PM
I guess you worked this out before many lensed quasars were discovered, right?

AFAIK, lensed quasars are the most compelling (well certainly the most straight-forward) evidence, because Arp has never claimed that quasars are more than a single class of object (and as 'quasars' now includes BL Lacs, both radio loud and quiet, at least the brightest Seyfert 1 galaxies, etc it's an even easier case to make).

Terry Giblin
2010-Dec-04, 06:58 PM
I guess you worked this out before many lensed quasars were discovered, right?

No, I simply used the methods available to me at the time, lots of maths and computing.

I learnt or studied about gravitational lensing later on, but without looking it up, I don't know when they were first discovered.

forrest noble
2010-Dec-04, 11:25 PM
Terry Giblin,

Quasars are at the distances implied by there red shift.
But every now and then, a new 'line of sight' observation or discovery is made and the whole argument is started over again.


There certainly could be no proof that all quasars are at the distances indicated by their redshifts. There is evidence that a number of quasars are truly distant galaxies since their surrounding starlight has been observed which also seem to indicate a similar distance. There are however "naked quasars" by which no determinations can be made. The only mainstream argument that I've seen concerning that all quasars are at their observed redshift distances involves O'camm's Razor (a concept of logic) which generally states that all else being equal, the simpler answer is probably the better answer. Meaning in this case that if there is evidence that some/ many quasars are at their redshift distances then probably all of them are.

I do, however, think your professor was overly zealous if he used the word "proof" rather than the word "evidence" against Arp's proposal(s) which does not necessarily have to include all quasars or even most.