Quasar Anomalies: Lack of Time Dilation in Variability

[Chronos]

I am very disturbed by the lack of time dilation in the variability of quasar v redshift studies.

http://www.arxiv.org/abs/astro-ph/0105073
Title: Time Dilation and Quasar Variability
Authors: M.R.S. Hawkins
The timescale of quasar variability is widely expected to show the effects of time dilation. In this paper we analyse the Fourier power spectra of a large sample of quasar light curves to look for such an effect. We find that the timescale of quasar variation does not increase with redshift as required by time dilation. Possible explanations of this result all conflict with widely held consensus in the scientific community.

I think this is a very serious challenge to modern theory.

 

[Garth]

All quiet on the Western Front!

It is indeed a disturbing paper, thank you Chronos, Fred Hoyle would have loved it!

The explanations for the lack of a time dilation effect in quasar light curves, all of which conflict with broad consensus in the astronomical community.

Firstly, time dilation might not in fact be a property of the Universe, which would effectively mean that the Universe was not expanding. Apart from the overwhelming support for the big bang theory, the direct measurements of time dilation quoted above strongly argue against this.

The second possibility is that quasars are not at cosmological distances. This is an argument which was hotly disputed in the 1970s, with an emerging consensus favouring cosmological distances. This has subsequently been strongly confirmed by studies of quasar host galaxies at high redshift.

The third possibility is that the observed variations are not intrinsic to the quasars but caused by some intervening process at lower redshift, such as gravitational microlensing. Although this idea has been strongly argued (Hawkins 1996), there is an opposing view that variations in quasars are dominated by instabilities in the central accretion disc. The reality of this mode of variability in active galactic nuclei is supported by detailed observations of Seyfert galaxies (Peterson et al. 1999) and gravitationally lensed quasars (Kundi´c et al. 1997), where the presence of intrinsic variations cannot be in doubt. The debate centres on whether this mechanism is responsible for the long timescale large amplitude variations which dominate the power spectra discussed in this paper.

Reactions?

Garth

 

[Chronos]

The the lensing explanation is a nice try:

http://www.arxiv.org/abs/astro-ph/0306434
Title: Can Microlensing Explain the Long-Term Optical Variability of Quasars?
Authors: Erik Zackrisson, Nils Bergvall, Thomas Marquart, Phillip Helbig
. . . Although controversial, the scenario of microlensing as the dominant mechanism for the long-term optical variability of quasars does provide a natural explanation for both the statistical symmetry, achromaticity and lack of cosmological time dilation in quasar light curves.

Unfortunately, it does not appear to hold water:

Structure Function Analysis of Long Term Quasar Variability
http://www.arxiv.org/abs/astro-ph/0411348
Authors: W. H. de Vries (1,2), R. H. Becker (1,2), R. L. White (3), C. Loomis
. . . We find the following: (1) the outbursts have an asymmetric light-curve profile, with a fast-rise, slow-decline shape; this argues against a scenario in which micro-lensing events along the line-of-sight to the quasars are dominating the long-term variations in quasars.

The authors understate the case in asserting this study 'argues against' microlensing. There is overwhelming evidence quasars are not local [i.e., within this galaxy], but, this is a serious blow to 'cosmology as usual', IMO. P.S, I'm not ready to buy any 'tired light' stock.

I searched long and hard trying to find a fatal flaw, or sensible explanation to the issue raised; and came up empty. What I find shocking is how little attention this has been given in the literature. I'm experiencing that same feeling I had as a child when mom, after intense grilling, admitted there was no Santa Claus.

 

[Nereid]

well worth studying further!

Some suggestions:

• Hawkins' analysis. It's highly unlikely that it contains gross errors (it wouldn't have passed peer-review), but maybe there are some subtle ones?
• An alternative analysis of the data. He employed one particular approach to determining a 'time dilation' footprint in the data - perhaps the same data, analysed a different way, might give a different result?
• Selection effects. This is the bane of astronomers' life, and some of these effects are subtle indeed. Perhaps a cold, hard look at the inputs - as compared with what we now know about quasars, and what we know we don't know - might turn up patterns that weaken the stated conclusion? For example:
• a) redshift-apparent magnitude. In the standard view, the higher the redshift, the greater the distance. Among other things this also means that two quasars with different redshifts but the same apparent magnitude will have quite different absolute magnitudes. In a (apparent) magnitude-limited selection (that was Hawkins' input catalogue, yes?), this introduces biases in the sample.
• b) colour. The input catalogue wasn't (AFAICS) characterised for quasar colour; there could be all kinds of selection effects relating to quasar colour (more later, if I have time).
• c) Variability. The quasars to be studied were not selected because of their (then known) variability. However, the extent to which the variability (or lack of it) played a part in them being detected as quasars in the first place should definitely be looked into.
• The nature of quasars. Unlike Cepheids or SNe, the details of quasars' variability is essentially unknown ('accretion disks' might be responsible for most of such variability, but just how do they give rise to the observed frequency spectrum?) Without some handle on this, the intrinsic causes and nature of quasar variability, I don't see how alternative explanations for an apparent absence of time dilation could be ruled out - intrinsically brighter quasars are variable in ways that are different from those not so bright? evolution effects? observed variability is due to the integration of several, quasi-independent causes?

I don't see much chance of a resolution via theory any time soon (there's just too much work to do, involving a lot of heavy-duty physics), so maybe an observational project could yield results (confirmation, or not) in the short term?

For example, studies of the observed variability of quasars, in several time regimes, in spectra, in different wavebands (gamma, X-ray, UV, NIR, FIR, ...), ... to tease out any systematic effects and put constraints on them.

 

[wolram]

http://arxiv.org/abs/astro-ph/0106220

Fourier Analysis of Gamma-Ray Burst Light Curves: Searching for Direct Signature of Cosmological Time Dilation
Authors: Heon-Young Chang (Korea Institute For Advanced Study)
Comments: 12 pages, 2 figures, 2 tables, accepted to ApJL

We study the power density spectrum (PDS) of light curves of the observed gamma-ray bursts (GRBs) to search for a direct signature for cosmological time dilation in the PDS statistics with the GRBs whose redshifts $z$'s are known. The anticorrelation of a timescale measure and a brightness measure is indirect evidence of its effect. On the other hand, we directly demonstrate that a time dilation effect can be seen in GRB light curves. We find that timescales tend to be shorter in bursts with small redshift, as expected from cosmological time-dilation effects, and we also find that there may be non-cosmological effects constituting to this correlation. We discuss its implication on interpretations of the PDS analysis results. We put forward another caution to this kind of analysis when we statistically exercise with GRBs whose $z$ is unknown.
An older paper.

 

[SpaceTiger]

It's highly unlikely that it contains gross errors (it wouldn't have passed peer-review)

I wouldn't give the peer review process that much credit. My roommate recently reviewed a paper that was absolutely loaded with errors and poor reasoning -- and it was nearly identical to several that had already been published. Unfortunately, many peer reviewers are just lazy.

That said, Hawkins doesn't appear to be a crackpot, so I wouldn't dismiss the paper outright. It will be interesting to see how this is resolved.

 

[Garth]

That said, Hawkins doesn't appear to be a crackpot, so I wouldn't dismiss the paper outright. It will be interesting to see how this is resolved.

Mike Hawkins is a doctorate member of staff of the Royal Observatory, Edinburgh and certainly not a 'crackpot'.

I agree with Chronos

What I find shocking is how little attention this has been given in the literature.

The most disturbing thing about this paper is the lack of interest. I would have thought that it would have stirred up a hornet's nest, either of refutations or a major effort of reconciliation with the standard model. After four years there has been more of less nothing published. The 'silent treatment' perhaps?

Those were very good points Nereid, especially the question of selection and colour dependent variability effects. From that OP paper of Hawkins:

The quasars in the field were found by a variety of techniques, including ultra-violet excess,variability, blue drop-out and objective prism. Altogether some 600 quasars have now been identified, with confirming redshifts in the range 0.1 < z < 3.5. There are sufficient numbers that the quasars can be binned in both redshift and luminosity to avoid the well-known degeneracy between these two parameters. All the quasars used in this study fluctuated significantly in brightness over the 24 year monitoring period, with an amplitude of mode 0.6 mag and a tail extending to 2 mag. In order to compare the spectrum of variations of subsamples of quasars from the survey, a Fourier power spectrum was calculated for each light curve. The quasars were then binned in red-shift and luminosity, in such a way that each bin contained approximately 100 objects, with a total of 407 quasars used for the analysis.

Quite a statistically significant sample?

We note the raw details of observed cosmological time dilation so far: Time dilation is seen in distant S/N decay profiles, in slow GRBs but not (apparently) in quasar variability. Could it be (if slow GRBs are distant hyper-novae) that in the first two the engine is basically 'normal' matter undergoing nuclear conflagration, whereas with a quasar the engine is degenerate mass, i.e. a black hole?

In http://en.wikipedia.org/wiki/Self_creation_cosmology non-degenerate matter and degenerate matter behave differently, because the scalar field is coupled to non-degenerate matter but decoupled from relativistic matter, therefore cosmological time dilation is to be expected in distant S/Ns but not BHs. I just thought I'll add that as a suggestion!

Garth

 

[Nereid]

Thinking about this some more, I see less reason to be concerned at the apparent absence of a time dilation signal in the data.

First and foremost, in the mainstream view of quasars, we have quasar evolution - http://arxiv.org/abs/astro-ph/0005368" , perhaps. If high-z quasars are different from low-z ones, then, a priori, expecting their (rest frame) variability to be unchanged is rather foolish, isn't it?

It may be possible to take some different views though Hawkins' data (as "a Fourier power spectrum was calculated for each [quasar's] light curve"), to look for an evolutionary effect, but the data as presented in the paper is too coarsely binned to do such a study.

Another way to test this may be to look at the power spectra of local AGNs (Seyfert nuclei, BL Lacs, ...).

Second, slicing and dicing the dataset in other ways would have been helpful - in terms of how the quasars were detected, for example, or weighted for 'completeness' (by comparison with data from SDSS, say), or X-ray or radio brightness.

Third, some 'field controls' would have increased confidence in the outputs (e.g. power spectra of variable stars on the plates) - I wonder why this wasn't done?

Fourth, why not make some artificial quasars? Modelling (monochromatic) variability, in a computer, should be a piece of cake - the outputs from the artificial quasars, as discrete 'plate magnitudes' (complete with errors and 'cloudy nights'), could then be fed into Hawkins' analysis pipeline. By tweaking the 'quasar properties' (evolutionary history - luminosity, variability, colour, ...), it should be fairly straight-forward to find out what sorts of things could mimic Hawkins' ~600 power spectra.

Finally, I think a different kind of analysis (approach) would be welcome.

 

[Chronos]

My impression was Hawkins bent over backwards trying to find a way to explain this unexpected result. His publication history suggests he is not afraid to go out on a limb, but they tend to be thick.

Nereid, my objection to relying upon quasar evolution is the extraordinary fine tuning it appears to require. The coarse binning actually strengthens the result, IMO. This smoothes out the oft seen outrageous probabilities suggested by over-binning [a typical crackpot tactic]. It is also evident there are two broad color classes of quasers. Assuming different mechanisms are involved, it appears improbable both would seemlessly cancel out the expected time dilation effect [please don't sentence me to TD ]

I don't entirely get the variable star thing. I suppose that would be a way of testing for selection effects, but given the large data set, I doubt any systematic effects of that nature are in play.

I like the computer modelling suggestion, Nereid. Sounds like good thesis material. This is surely something that demands further study.

I am also concerned about how this same logic could be applied to the apparent time dilation of supernova and GRB light curves. This inconsistency is what I find most troubling.

Nonetheless, Nereid, your observations are soundly based and logically consistent. And that is exactly what I expected to find from the cosmology community. But, their silence is deafening.

 

[Garth]

Nonetheless, Nereid, your observations are soundly based and logically consistent. And that is exactly what I expected to find from the cosmology community. But, their silence is deafening.

Absolutely, Nereid your ideas appear to be worthy of a good hearing, if nobody else has done so, why not write a paper?

Garth

 

[Nereid]

My impression was Hawkins bent over backwards trying to find a way to explain this unexpected result. His publication history suggests he is not afraid to go out on a limb, but they tend to be thick.

All the more curious then that he seems not to have done several of the (to me) more obvious 'sanity checks' (or, if you prefer, quality controls).

Nereid, my objection to relying upon quasar evolution is the extraordinary fine tuning it appears to require.

I think the operative word is "appears" - without doing some simulation, I don't see how anyone could say just how 'extraordinary' any 'fine tuning' would need to be (more later, not necessarily in this post).

The coarse binning actually strengthens the result, IMO. This smoothes out the oft seen outrageous probabilities suggested by over-binning [a typical crackpot tactic]. It is also evident there are two broad color classes of quasers. Assuming different mechanisms are involved, it appears improbable both would seemlessly cancel out the expected time dilation effect [please don't sentence me to TD ]

Not at all - we tend to get tunnel vision, when it comes to 'colour'. 'Red' and 'blue' actually differ very little, when the full range of EM that quasars are well known to emit over, in significant quantities, is considered.

I don't entirely get the variable star thing. I suppose that would be a way of testing for selection effects, but given the large data set, I doubt any systematic effects of that nature are in play.

You could think about it as just a 'being careful' step, or you could say that without this, the conclusions rest on weak foundations.

Imagine there are ~600 variables in the same field(s) where the quasars are to be found. Imagine their colour and (apparent) magnitude distributions are similar to those of the quasars. Imagine Hawkins produced 600 Fourier power spectra, of these variables. Imagine that a computer program blindly, and randomly, applied 'time dilation' to subsets of those spectra, in a distribution which matched the z's of the quasars.

Now feed those two sets of 600 power spectra into Hawkins' "bin and analyse" pipeline ... what would the results be?

At the very least, we would have (hopefully) internal consistency checks on the approach (and tools) which Hawkins used.

I like the computer modelling suggestion, Nereid. Sounds like good thesis material. This is surely something that demands further study.

How about we lay the groundwork, here in PF? (more later).

I am also concerned about how this same logic could be applied to the apparent time dilation of supernova and GRB light curves. This inconsistency is what I find most troubling.

Different bathtub of fish ... quasars are a zoo, of animals which range from shrews to elephants; SNe and GRBs are private collection of different species of mice.

 

[Nereid]

Just quickly - another systematic effect might be evident in the fainter (apparent mag) quasars.

The errors in estimating magnitude would have been - presumably - greater for fainter images; to what extent was this incorporated in the analysis? The paper seems to say estimates of magnitude were all given the same (per plate?) errors.

Also, for quasars near the (faint) limit, how many 'disappeared' over the history of the data collection (i.e. dimmed below detectability)? If the mode was 0.6 mag, "with a tail extending to 2 mag", this is not a trivial consideration.

 

[ratfink]

Dare one ask why anyone hasn't repeated the observations - to at least prove them wrong?

 

[Nereid]

Dare one ask why anyone hasn't repeated the observations - to at least prove them wrong?

Welcome to Physics Forums, ratfink!

From the Hawkins paper:

a large sample of quasars which have been homogeneously monitored every year for 24 years

IOW, it isn't easy to 'repeat' them.

It is certainly worth checking various observatory (plate) records, to see what sort of comparable consistent, (historical) datasets there might be.

Any suggestions?

 

[ratfink]

Thanks,
It is just that I read this quote

I wouldn't give the peer review process that much credit. My roommate recently reviewed a paper that was absolutely loaded with errors and poor reasoning -- and it was nearly identical to several that had already been published. Unfortunately, many peer reviewers are just lazy.

That said, Hawkins doesn't appear to be a crackpot, so I wouldn't dismiss the paper outright. It will be interesting to see how this is resolved.

So do the plates lie? If not, are they part of the public domain? If so, they could be checked to see if 'non time dilation' is what the results show and that it is not a 'mistake'. Would other scientists looking at the same data set come to the same conclusions - or different ones? and if so why haven't they done it?

 

[SpaceTiger]

So do the plates lie? If not, are they part of the public domain? If so, they could be checked to see if 'non time dilation' is what the results show and that it is not a 'mistake'. Would other scientists looking at the same data set come to the same conclusions - or different ones? and if so why haven't they done it?

Different researchers have reached this same conclusion -- that there is no apparent time dilation in the quasar light curves. I don't think many people argue the results, it's mostly a question of interpretation. In my opinion, the most likely explanation is some kind of evolution (see Nereid's posts). I don't think it would take a great deal of fine-tuning to reproduce these results because the error bars are still large (the high- and low-redshift subsamples appear to only be a few sigma apart). If we reduce the size of the error bars by another factor of a few and still see no significant difference in the subsamples, then I think that would be cause for concern.

Keep in mind that the author, in the introduction to his paper, makes note of previous studies that had already confirmed the existence of cosmological time dilation in other sources (GRBs, SNe), so I suspect we're not seeing much interest in this topic because the mainstream has already dismissed this effect as evolution (or selection effects). Although this kind of evolution is interesting in of itself, it's considerably less boat-rocking than a challenge to mainstream cosmology.

 

[ratfink]

Thanks,
But I thought that in science to 'prove' something then one had to look at the same sort of thing from all sorts of angles and show that it is consistent. If one has time dilation in SIa's but not in quasars then isn't 'confirm' the wrong word to use for time dilation?

 

[SpaceTiger]

Thanks,
But I thought that in science to 'prove' something then one had to look at the same sort of thing from all sorts of angles and show that it is consistent. If one has time dilation in SIa's but not in quasars then isn't 'confirm' the wrong word to use for time dilation?

I'm not sure what you mean. Cosmological time dilation has been confirmed to exist in SNe and (possibly) GRBs, but not in quasars. Nothing has been proven 100%, but the effect has been observed in those objects to whatever significance the observations can be trusted. It's possible there is some exotic explanation for the effect (like Garth's theory), but I'm just talking about observations, not theory.

 

[ratfink]

Thanks,

I'm not sure what you mean. Cosmological time dilation has been confirmed to exist in SNe and (possibly) GRBs, but not in quasars. Nothing has been proven 100%, but the effect has been observed in those objects to whatever significance the observations can be trusted. It's possible there is some exotic explanation for the effect (like Garth's theory), but I'm just talking about observations, not theory.

I was just wondering why supernova Ia results are said to be 'proof' and consequently quasar results must be 'flawed' as far as time dilation is concerned. Why not the other way around? i.e. Quasar 'non time dilation' show the Universe is not expanding and supernovae Ia results are an 'exotic effect?'
BTW http://xxx.lanl.gov/abs/astro-ph/0511628"

 

[selfAdjoint]

Thanks,
But I thought that in science to 'prove' something then one had to look at the same sort of thing from all sorts of angles and show that it is consistent. If one has time dilation in SIa's but not in quasars then isn't 'confirm' the wrong word to use for time dilation?

Go back and read Nereid's post on this; if it's too compressed for you I'm sure she'd be glad to expand it. Then pay attention to Space Tiger's remarks about error bars. From just these two posts we find: (1)There is a plausible explanation for the plates, and (2)Astronomical data is inherently noisy. And so the case is still open. Time dilation is supported by a huge amount of independent evidence, and this contradictory evidence is perhaps not all it seems to be.

In science you never "prove" anything, you just have more or less support. I repeat, dilation has an enormous amount of supporting evidence.

 

[ratfink]

Go back and read Nereid's post on this; if it's too compressed for you I'm sure she'd be glad to expand it. Then pay attention to Space Tiger's remarks about error bars. From just these two posts we find: (1)There is a plausible explanation for the plates, and (2)Astronomical data is inherently noisy. And so the case is still open. Time dilation is supported by a huge amount of independent evidence, and this contradictory evidence is perhaps not all it seems to be.

In science you never "prove" anything, you just have more or less support. I repeat, dilation has an enormous amount of supporting evidence.

All I am asking is why is 'time dilation' in supernovae taken as fact and 'non time dilation' in quasars put down to an 'exotic effect?'

Time dilation is supported by a huge amount of independent evidence

isn't it all SnIa's? (Gamma Ray bursts seem have a long way to go to support anything)

 

[SpaceTiger]

All I am asking is why is 'time dilation' in supernovae taken as fact and 'non time dilation' in quasars put down to an 'exotic effect?'

The facts are:

- Supernovae exhibit time dilation
- GRBs exhibit time dilation (somewhat more tentatively)
- Quasars do not (to the current precision)

That's it. I don't know why you're trying to read into this so much. From the theoretical standpoint, I find it very hard to believe that the explanation for the apparent lack of time dilation in quasars is due to new physics and I've already explained why I think it's an evolutionary effect.

 

[ratfink]

The facts are:

- Supernovae exhibit time dilation
- GRBs exhibit time dilation (somewhat more tentatively)
- Quasars do not (to the current precision)

That's it. I don't know why you're trying to read into this so much. From the theoretical standpoint, I find it very hard to believe that the explanation for the apparent lack of time dilation in quasars is due to new physics and I've already explained why I think it's an evolutionary effect.

Sorry to be pedantic here but this is incorrect.
The FACTS are that:
Light curves from supernovae are stretched.
Light curves from quasars are not stretched.
Now some people say that the stretching of supernovae Ia light curves is explained by 'time dilation' and that the non stretching of quasar light curves is an 'exotic effect!"
Others wonder why they cherry pick.

 

[SpaceTiger]

Sorry to be pedantic here but this is incorrect.
The FACTS are that:
Light curves from supernovae are stretched.
Light curves from quasars are not stretched.

What do you mean they're "stretched"? Relative to what? How is this different from saying they're "dilated"? If you wish to be very precise, we should say:

- Assuming no evolution or observational biases, the power spectra of light curves from supernovae are consistent with cosmological time dilation.
- Ditto for GRBs.
- Not so for quasars.

I'm not saying that the quasar "fact" above is unreliable as compared to the others. In fact, it's probably more reliable than the GRB measurements.

Now some people say that the stretching of supernovae Ia light curves is explained by 'time dilation' and that the non stretching of quasar light curves is an 'exotic effect!"

Most likely, it's due to ordinary evolution of quasars in the universe, an effect that is in no way exotic. I was simply trying to allow for unconventional ("exotic") ideas, like Garth's theory.

Others wonder why they cherry pick.

Cherry pick what? The observations are all being considered. Please specify which part of the interpretation you didn't understand.

 

[Nereid]

Plates (and facts)

In his paper, Hawkins references an earlier one by him (Hawkins, M. R. S., 1996. MNRAS, 278, 787), which contains more details of raw data, the data reduction techniques etc. I will dig that up (if no one beats me to it), and check, but in the meantime, I'm guessing it simply says (in more detail) what's already in the Hawkins paper: plates were taken, and measured by an automated system (that's been thoroughly shaken down), producing ~24x600 pairs of estimates (magnitude, mid-time of exposure), together with estimates of both measurement error (per pair) and systematic error (possibly per plate, or region of each plate). There will be ~18x400 similar pairs (for the red plates).

Independently, from other work, there will be >600 estimates of redshift, at least one for each quasar.

Hawkins would have fed the magnitude/epoch pairs into a (standard?) Fourier transform software package (possibly one tailored for astronomical observations), and produced ~1,000 Fourier power spectra (~600 blue and ~400 red).

Other than checking that all this work was done properly (which no one really doubts), there's not much point duplicating it.¹

Fast forward to this "fact":

Light curves from quasars are not stretched.

First, without a 'sanity check' (or 'quality control') of the kind I outlined above, even the analysis which Hawkins did (let alone the conclusions) has a weak foundation. Ergo, any conclusion ('fact') is, strictly speaking 'provisional'.

Second, as SpaceTiger has said (and as I've pointed to), even accepting the approach Hawkins took (without checking by deploying a different approach), the Hawkins results need only to have modest increases in their error bars and the 'fact' itself becomes marginal.

But the worst part of this 'fact' is, as several people have already pointed out, it is based on the assumption that apples are oranges (a.k.a. 'quasars' are a homogeneous class of astronomical object which undergo no evolution).

Compare this with Type 1a SNe - they are not only all apples, nor even all granny smith apples, but they all come from the same state in the great country of Australia (though maybe one or two come from New Zealand).

There may be ways to disentangle evolution from the Hawkins data (the Fourier power spectra), by assuming certain things about that evolution (e.g. that it is pure luminosity evolution). However, you can't do that from the data presented in the published paper - you need the actual spectra (or, better, the ~24x600 + ~18x400 magnitude-epoch data pairs).

Now, if ratfink (or any other PF member) is interested in examining 'facts' in terms of non-mainstream theories (or, worse, crackpot ideas), then we enter territory that few 'alternativists' willingly enter - re-interpretation of huge parts of standard astrophysics (I note, for the record, that Garth has shown a good appreciation of at least some of the issues involved in going down this path).

If you wish, ratfink (or any other PF member wishes), we can embark on a trip to disentangle 'facts' from 'theory', using the above quote from ratfink as our guide.

In the meantime, I intend to outline some ideas on the nature of quasars, how such might affect variability throughout their evolution, and how we could go about building some quasar simulations to test various ideas about what we might observe (in observations like those Hawkins reports).

¹As I indicated earlier, there are some checks that I think would be worthwhile, at this level (crudely, how were the faintest observations handled), but they'd likely result in, at worst, dropping a few marginal quasars, and maybe making the error bars a bit bigger on as much as a significant minority of the rest.[/size]

 

[Garth]

Here, on PF we are having a good attempt to understand and criticize the conclusions of this surprising and disturbing paper.

One outstanding question is: "Has anybody else done so and published the results? If not why not?"

My search on NASA ADS turned up nothing, does anybody else know of a paper that either:
a) refutes that paper's conclusion - that quasar variablity does not exhibit cosmological time dilation or
b) makes a good case for accommodating it within the mainstream model - such as quasar evolution as suggested by Nereid and SpaceTiger.

It seems so unsatisfactory that it is left 'hanging in the air' - but then perhaps the solution to the enigma has already been discovered and will be published tomorrow!

Garth

 

[SpaceTiger]

It seems so unsatisfactory that it is left 'hanging in the air' - but then perhaps the solution to the enigma has already been discovered and will be published tomorrow!

Unfortunately, if it is quasar evolution, then it would be hard to publish a meaningful paper to support the case. The quasar accretion and growth processes are very poorly understood and we're a long way off from predicting the evolution of their variability timescales.

 

[ratfink]

But the worst part of this 'fact' is, as several people have already pointed out, it is based on the assumption that apples are oranges (a.k.a. 'quasars' are a homogeneous class of astronomical object which undergo no evolution).

Compare this with Type 1a SNe - they are not only all apples, nor even all granny smith apples, but they all come from the same state in the great country of Australia (though maybe one or two come from New Zealand).

As I said earlier, http://xxx.lanl.gov/abs/astro-ph/0511628"

 

[SpaceTiger]

As I said earlier, http://xxx.lanl.gov/abs/astro-ph/0511628"

Discussed here:

https://www.physicsforums.com/showthread.php?t=101048"

 

[ratfink]

Thanks,
I see that the paper was 'discounted' by this board because members didn't like the statistics used. Has this work been repeated by anyone? This is how science works, rather than discounting something on speculation, one repeats it and see if the results come out the same. Until then, the paper stands.
If as he says

This raises doubts against the `standard candle'-hypothesis of the supernovae Ia and their use to constrain the cosmological models

Then we can discount supernova results as 'proof' of time dilation and hawkins quasar paper on non time dilation takes on a new importance

 

[Nereid]

Thanks,
I see that the paper was 'discounted' by this board because members didn't like the statistics used.

I don't think you read the other thread very clearly (or perhaps you merely summarised badly); it's more that the approach he took was a poor one.

Has this work been repeated by anyone?

Each of the individual studies Vishwakarma cites is its own 'repetition', so there are ~5 such.

This is how science works, rather than discounting something on speculation, one repeats it and see if the results come out the same. Until then, the paper stands.

I don't know in which universe they practice science like this, perhaps a naive Popperian one? For avoidance of doubt, the naive Popperian 'falsificationism' died at the hands of empirical studies of just how science is actually done (not how some philosopher imagined that it might be done) - even Popper moved on from this view.

Rather than continue to discuss the Vishwakarma paper further here, why don't we continue in the thread devoted to it?

If as he says

This raises doubts against the `standard candle'-hypothesis of the supernovae Ia and their use to constrain the cosmological models

Then we can discount supernova results as 'proof' of time dilation and hawkins quasar paper on non time dilation takes on a new importance

At the level of handwaving, your logic is impeccible; at the level of the quantitative data, it's nonsense.

For starters, your apparently black and white view of 'results' is ridiculous (for example, 'proof' - even in inverted commas - is a far, far more nuanced thing).

For seconds, the 1a SNe data may be clear on time dilation (they are) and not clear on the second decimal place for some parameters in one or more specific cosmological models (they are ... not clear).

Perhaps the biggest mistake you seem to be making is equating astronomical observations with lab experiments - astronomers don't have the luxury of setting up controlled experiments, where just a single variable at a time is tested.

 

[ratfink]

Hi Nereid,
There is no need to continue to discuss the Vishwakarma paper in detail any further - if there was something wrong with it someone would have redone the work and disproved it by now. We only need mention it as to its relevence regarding the Hawking paper and this thread.
You see earlier you said:

Originally posted by Nereid
But the worst part of this 'fact' is, as several people have already pointed out, it is based on the assumption that apples are oranges (a.k.a. 'quasars' are a homogeneous class of astronomical object which undergo no evolution).

Compare this with Type 1a SNe - they are not only all apples, nor even all granny smith apples, but they all come from the same state in the great country of Australia (though maybe one or two come from New Zealand).

Well the Vishwakarma paper shows that there is something rotten in the orchard!

So where have we gotten to with this thread?

Supernovae Ia show a stretching of the light curves which some people say shows time dilation.
This asumes that all Supernovae Ia are from the same state in australia - but the Vishwakarma paper shows this not to be so.
This paper is ignored because it is said that the Vishwakarma's approach was 'a poor one'.
Hawking and his quasars show no stretching of the light curves and hence no time dilation.
This result must be wrong because it goes against time dilation and therefore, it must be the quasars that are wrong.
I don't know about the condition of the apples in Australia but the cherry trees are blooming!

 

[Nereid]

Hi Nereid,
There is no need to continue to discuss the Vishwakarma paper in detail any further - if there was something wrong with it someone would have redone the work and disproved it by now.

Perhaps you do have a different set of expectations about how science is done.

One last time: "proof" is not possible in science (so no one can 'disprove the Vishwakarma paper').¹

And as for 'something wrong with it someone would have redone the work'; again, that's not how it works - there are lots of things that are not sufficiently interesting or important that they need 'redoing'; there are 're-doings' which make some earlier work simply irrelevant (you don't see much reference to the early surveys on quasars any more, for example, now that we have 2dF and SDSS); and many others.

We only need mention it as to its relevence regarding the Hawking paper and this thread.

Indeed ... little to none.

You see earlier you said:

But the worst part of this 'fact' is, as several people have already pointed out, it is based on the assumption that apples are oranges (a.k.a. 'quasars' are a homogeneous class of astronomical object which undergo no evolution).

Compare this with Type 1a SNe - they are not only all apples, nor even all granny smith apples, but they all come from the same state in the great country of Australia (though maybe one or two come from New Zealand).

Well the Vishwakarma paper shows that there is something rotten in the orchard!

So where have we gotten to with this thread?

Supernovae Ia show a stretching of the light curves which some people say shows time dilation.
This asumes that all Supernovae Ia are from the same state in australia - but the Vishwakarma paper shows this not to be so.

As I said earlier, you don't seem to have read the other thread very well - the Vishwakarma paper did not show this (at best all it showed was that different authors have different methods for reducing the SNe 1a light curve data, and that he - Vishwakarma - didn't take this into account properly in his meta-analysis).

Let's do it like this - make your case for whatever conclusions you think are warranted, in the other thread - and when you've made it, come back here and pick up the discussion.

This paper is ignored because it is said that the Vishwakarma's approach was 'a poor one'.
Hawking and his quasars show no stretching of the light curves and hence no time dilation.
This result must be wrong because it goes against time dilation and therefore, it must be the quasars that are wrong.

I believe this is called a strawman.

One last time - no more 'black or white'; no more distorting the research; no more blanket declarations based on ignorance of mainstream astronomy (and physics).

¹You might like to start getting used to using 'consistency', as in 'internally consistent', or 'consistent with observational data'; best if you could begin to 'talk' quantitatively (see SpaceTiger's 'several sigma', for example).[/size]

 

[SpaceTiger]

Hi Nereid,
There is no need to continue to discuss the Vishwakarma paper in detail any further - if there was something wrong with it someone would have redone the work and disproved it by now.

Even if the paper had made it to publication, this would be an absurd statement. Papers with contradictory results are published all of the time and people don't always bother to put up a rebuttle, especially when the author has a weak standing in the community. A published paper is not a "proof" and I can assure you that nobody in my department was talking about this one when it was put up.

 

[Nereid]

modelling quasar evolution - some fun!

This is not intended to be the kind of thing a graduate student might do as a project, or even as a summer project for an undergrad, rather just some fun that PFers might enjoy.

The http://www.mssl.ucl.ac.uk/www_astro/agn/agn_quasartour.html" (in the mainstream) has several components:

• black hole (which does not, of course, emit any photons)
• accretion disk, which may be a few light-days across
• jet, which may be hundreds of thousands of ly long
• broad line region, up to 1 ly in size
• molecular torus, up to ~100 ly across; unlikely to be uniform across quasars
• narrow line region, which may not contribute much to the observed variability
• host galaxy

At this time, the evolutionary history of each of these components is essentially unconstrained by observation (except for the host galaxy, whose evolution likely doesn't follow differ wildly from that of 'normal' galaxies).

For the sake of our toy model (and fun!), let's ignore the narrow line region and the molecular torus, and look only at the accretion disk, jet, and broad line region.

Leaving aside how we generate 'quasar light curves' for the moment, how could we develop an outline of a model for each of our three regions?

As this is fun, perhaps the easiest thing to do might be to assume three independent sources of light, which have independent (absolute) luminosities and variabilities? Perhaps we could simply assume that each region has an intrinsic power spectrum of {insert equation or descriptor here}, and that each component contributes a, j, and b to the total luminosity (a+j+b = 1)? To cut down on independent variables, we could set one of these as fixed.

OK so far?

'Evolution' then becomes a change in the input variables by z.

As to the outputs, it seems to me that we have (at least) two alternatives - we could produce an entire light curve, covering 24 years, in time steps as fine as the average exposure time of each plate, or simply ~24 outputs, corresponding to the times of the (annual) observations.

Thoughts?

 

[ratfink]

Before embarking on this project, it might be best to consider if a ‘quasar evolution model’ stands a chance of being consistent with observational data.

If we assume that the Hawkins paper is correct in its results and that there is no time dilation (within the 2 sigma confidence limits) then we must ask ourselves what this means and talk quantitatively about the consequences.

On the scales of these redshifts, time dilation should be exhibited – but it is not. So, if the ‘non time dilation’ is due to evolution then the evolution process must ‘squash’ the light curves in a reverse manner to expansion, which stretches them – and at the same rate.

That is, younger and more distant quasars must ‘wink’ at a much faster rate than older and nearer quasars so that when effects of time dilation are taken into account, they both ‘wink’ at the same rate here on Earth. Ignoring acceleration of the universe, this evolution model must be linear with distance and hence time, and also imply that all the quasars were formed at the same time – otherwise one would have to include ‘point of creation dependency’ in ones equations. OK so far?
Personally, I feel that this is pushing the limits of credulity too far.
If one must look for an explanation of the light curves that is internally consistent with the expansion model, then might it be better to talk about quasars having a consistent light curve but are lensed by a nearby galaxy? Then one could hand wave about the nearby galaxy producing the variation in light curves and, since it is close, there would be no time dilation effects.

Though personally, I prefer the non expansion explanation.

 

[Garth]

First - there have been other papers by Hawkins on the same no-time-dilation effect in quasar variability such as Nature 366, 242 - 245 (18 November 1993); (definitely not a journal for crackpots!) http://www.nature.com/nature/journal/v366/n6452/abs/366242a0.html;jsessionid=B68F2073D4B04C195A14FDABD18C7A55.

Second - Hawkins has published other papers on his favourite explanation for the phenomenom - http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1996MNRAS.278..787H&amp;data_type=PDF_HIGH&amp;type=PRINTER&amp;filetype=.pdf[/URL] he argued that this effect, along with a number of other properties of the light curves, are best explained by gravitational microlensing of the quasar continuum region. A population of Jupiter sized primordial BHs with a total density contribution of $\Omega_{BHs} = 0.1$, (i.e. not baryonic matter) is responsible.

Not such an outlandish suggestion after all!

[quote=ratfink]Though personally, I prefer the non expansion explanation.[/quote] In which case you have to explain why distant SN and (apparently) long GRBs [b]do[/b] exhibit time dilation.

Garth

 

[Nereid]

Thanks Garth - the Dark matter from quasar microlensing is the 1996 Hawkins paper* I referred to earlier; it contains more details on the observing program, the data reduction techniques, some (different) analyses of (observed) variability, some wider thoughts on possible causes of the (apparent) lack of time dilation, and so on.

Towards the end of the paper we read the following:

None of these arguments [concerning physical processes which might, or could not, generate the observed characteristics of variability in quasars] precludes the possibility of a theory of intrinsic variation, which is consistent with the observations, although current AGN models [...] do not seem to produce variation of the observed character.

[*Edit: seeing the comments about Nature, I decided to edit this post to add that this 1996 paper was published in MNRAS!]

 

[SpaceTiger]

Nature 366, 242 - 245 (18 November 1993); (definitely not a journal for crackpots!)

The journal has developed into a sort of a running joke around here. People often publish in Nature if they have a really exciting result. Unfortunately, the most exciting results are also the most outlandish and are usually wrong, so a large fraction of Nature papers end up being totally bogus.

It's not a crackpot journal, to be sure, but those papers are viewed with a lot of skepticism in the community.

 

[Garth]

I think they tend to go on the reputation of both the institution and author from whom the paper is submitted.

Garth

 

[Nereid]

Before embarking on this project, it might be best to consider if a ‘quasar evolution model’ stands a chance of being consistent with observational data.

OK

If we assume that the Hawkins paper is correct in its results and that there is no time dilation (within the 2 sigma confidence limits) then we must ask ourselves what this means and talk quantitatively about the consequences.

That's what the project sets out to do (besides having fun).

On the scales of these redshifts, time dilation should be exhibited – but it is not. So, if the ‘non time dilation’ is due to evolution then the evolution process must ‘squash’ the light curves in a reverse manner to expansion, which stretches them – and at the same rate.

No. It only needs to 'squash' them to the extent that produces results which are consistent with the observational data. The difference between 'the same rate' and what I just wrote may seem small, almost trivial, but it is a trap that thinking about things like this in a qualititative way ("the same rate") can too easily lead you to fall into.

That is, younger and more distant quasars must ‘wink’ at a much faster rate than older and nearer quasars so that when effects of time dilation are taken into account, they both ‘wink’ at the same rate here on Earth.

And this oversimplification is another trap - if the light which we observe, here on Earth, from a quasar comes from several different regions (accretion disk, jet, etc), each of which is driven by different -though somewhat coupled - physical processes, then a priori I would say it's impossible to estimate anything about the integrated 'winking', using the kind of reasoning you're using here.

Compare this with 1a SNe - a single 'region', and one set of physical processes, suffice to produce all the light we see (until well past the peak).

Ignoring acceleration of the universe, this evolution model must be linear with distance and hence time, and also imply that all the quasars were formed at the same time – otherwise one would have to include ‘point of creation dependency’ in ones equations. OK so far?

As we've seen, none of this sentence applies - the logic broke down before it even got started.

Personally, I feel that this is pushing the limits of credulity too far.

And personally, I feel that skipping over important details early in the chain of reasoning all too often leads to incredulous results (or, if you prefer, conclusions that should be re-thought).

If one must look for an explanation of the light curves that is internally consistent with the expansion model, then might it be better to talk about quasars having a consistent light curve but are lensed by a nearby galaxy? Then one could hand wave about the nearby galaxy producing the variation in light curves and, since it is close, there would be no time dilation effects.

Interesting idea ... and that (and variations) is what Hawkins in fact did, in a series of papers.

 

[selfAdjoint]

Nereid, would this post by Space Tiger on the Eddington luminosity of the accretion disc be relevant to your project?

https://www.physicsforums.com/showpost.php?p=937955&postcount=42

 

[ratfink]

So, Nereird.
what constraints do you feel that a quasar evolutionary theory might have on the Hubble law?

 

[turbo]

First and foremost, in the mainstream view of quasars, we have quasar evolution - http://arxiv.org/abs/astro-ph/0005368" , perhaps. If high-z quasars are different from low-z ones, then, a priori, expecting their (rest frame) variability to be unchanged is rather foolish, isn't it?

I have linked this lecture video on another forum, but feel that it is relevant here, and I do not know if you have watched it or not. The presenter is Michael Strauss of the SDSS team and he demonstrates that high-redshift quasars are just like low-redshift quasars in all measurable respects. Interestingly, there is no evolution in either absolute or relative MgII and FEII abundances all the way out to z~6.5, although those metals are believed to be generated by different supernovae classes.

http://www.stsci.edu/institute/center/information/streaming/archive/STScIScienceColloquiaFall2005/MichaelStrauss110205

 

[pallidin]

Sorry to jump into this thread with my having little authorative knowledge, but I have a few questions I would like to ask in order for me to more properly understand the "jist" of the comments:

1) Are Quasars currently the most distant observable cosmological "objects"?

2) Is it speculated that Quasars more or less spherically encompass the most outer "edges" of our universe? Not close to each other of course.

3) Has a Quasar even been observed that is "closer" than the "outer-edges" of our universe? That is, has a Quasar been observed that a galaxy is found to be "farther"?

4) Do Quasars exist NOW? That is, since it takes such a long time for light to reach us, and of the fact that some very distant stars that we see in the night sky no longer actually exist, do(or can) Quasars "die"?

Thank you.

 

[Chronos]

Sorry to jump into this thread with my having little authorative knowledge, but I have a few questions I would like to ask in order for me to more properly understand the "jist" of the comments:

1) Are Quasars currently the most distant observable cosmological "objects"?

2) Is it speculated that Quasars more or less spherically encompass the most outer "edges" of our universe? Not close to each other of course.

3) Has a Quasar even been observed that is "closer" than the "outer-edges" of our universe? That is, has a Quasar been observed that a galaxy is found to be "farther"?

4) Do Quasars exist NOW? That is, since it takes such a long time for light to reach us, and of the fact that some very distant stars that we see in the night sky no longer actually exist, do(or can) Quasars "die"?

Thank you.

1. No, GRB's.

2. No, excepting crackpots.

3. No, excepting crackpots.

4. Unknown. The nearest known quasar is around z = 1.

 

[Nereid]

Nereid, would this post by Space Tiger on the Eddington luminosity of the accretion disc be relevant to your project?

https://www.physicsforums.com/showpost.php?p=937955&postcount=42

Thanks selfAdjoint.

It could help, in the sense that it sets a constraint on one of the actors in the quasar drama (the accretion disk).

OTOH, those constraints may be weak at best, in terms of the variability we will be playing with. Too, there's the question of the role of magnetic fields (ST's envelope had room for only radiation pressure and gravity; a more complete analysis would have to include MHD).

 

[Nereid]

So, Nereird.
what constraints do you feel that a quasar evolutionary theory might have on the Hubble law?

Do you mean the redshift-distance relationship?

 

[Nereid]

quasar evolution, as seen in Hawkins' data?

In the 'time dilation' paper, Fig.1. has two sets of two graphs.

At the handwaving, qualitative level, there is a good story to make re quasar evolution and variability; it goes something like this:

• in the top row, we clearly see that high-z QSOs have more power (= greater variability) than low-z ones, consistent with the idea that the component with the greater/greatest variability declines - in terms of its contribution to the observed optical magnitude - as the QSO evolves
• in the bottom row, we clearly see that the low luminosity QSOs have more power than the high luminosity ones, consistent with the idea that the component with the greater/greatest variability contributes less in high luminosity QSOs
• Perhaps the jet has the greatest variability - it is a smaller component of the total observed light in high luminosity QSOs, and it declines - wrt its relative contribution - as the QSO evolves.

Of course, this idea is nothing more than some words. However, it does give some pointers as to where to look to test it (for example, there are several nearby AGN, with visible jets; some jets can be 'seen' - in the radio if not the optical - almost down to the accretion disk).

 

[Nereid]

4) Do Quasars exist NOW? That is, since it takes such a long time for light to reach us, and of the fact that some very distant stars that we see in the night sky no longer actually exist, do(or can) Quasars "die"?

In http://www.mssl.ucl.ac.uk/www_astro/agn/agn_quasartour.html" , nuclei of Seyfert galaxies, BL Lac objects (blazars), and quasars are all the same kind of thing - SMBH (supermassive black holes) fed by matter via an accretion disk, with polar jets (whose mechanisms for creation and maintenance are not well understood yet), gas clouds in all kinds of trouble ('broad line region) or not ('narrow line region), and a dusty 'molecular torus'.

Perhaps our very own http://www.einstein-online.info/en/spotlights/milkyway_bh/index.html" was once a brilliant quasar?