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TooMany
2013-Jan-12, 10:39 PM
Something new?

A structure in the early Universe at z ∼ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology (http://mnras.oxfordjournals.org/content/early/2013/01/07/mnras.sts497)

I couldn't find the paper on arvix.org so I've only seen the abstract, but there is a short article about it here (http://www.sciencedaily.com/releases/2013/01/130111092539.htm). The abstract suggests that the finding challenges the cosmological principal. (Or perhaps it challenges the age of the Universe?)

ASTRO BOY
2013-Jan-12, 10:57 PM
Something new?

A structure in the early Universe at z ∼ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology (http://mnras.oxfordjournals.org/content/early/2013/01/07/mnras.sts497)

I couldn't find the paper on arvix.org so I've only seen the abstract, but there is a short article about it here (http://www.sciencedaily.com/releases/2013/01/130111092539.htm). The abstract suggests that the finding challenges the cosmological principal. (Or perhaps it challenges the age of the Universe?)



Interesting article to say the least.
How do they define a "large scale structure"?
I would have said, a group of galaxies gravitationally bound.

If we cannot assume Isotropy and homegenity with regards to the Universe, what other cosmological principals does it put under the microscope?

Would this finding invalidate the established assumption re the topological shape of the Universe?

Could the finding itself be some sort of illusion produced by the AGN through lensing and warping of space/time?

The mind boggles!

TooMany
2013-Jan-13, 12:44 AM
I think it's about 8 Glyrs away, but 4 Glyrs long. It spans 20 degrees across the sky so I don't think that could be due to lensing. Maybe quasars aren't as far away as they seem? I suspect this is big news. Something has got to give in current theory.

antoniseb
2013-Jan-13, 01:05 PM
I think it's about 8 Glyrs away, but 4 Glyrs long. It spans 20 degrees across the sky so I don't think that could be due to lensing. Maybe quasars aren't as far away as they seem? I suspect this is big news. Something has got to give in current theory.
It isn't due to lensing, and your reasoning about that is sound. However, quasars are as far away as they seem. We've measured the redshifts of surrounding and neighboring galaxies for many of them.
At this point we are talking about 73 quasars out of hundreds of thousands, spread over a large fraction of the sky. This could be a statistical anomaly of superposition as seen from our POV. It could be a result of actual non-homogeneous distribution of matter. It could be something else yet unthought of.
Answering ASTRO BOY's doubt about what is meant by structure these are not gravitationally bound. It is too big for that. If it is what it appears to be, it is a long area of space with an overdensity of luminous matter, but that space is expanding faster than the matter in the middle can draw in the matter at the ends.

I recommend waiting for more papers to come out before going too far on this topic. If real, it is very important, and might modify some models about the first second.

TooMany
2013-Jan-13, 04:58 PM
It isn't due to lensing, and your reasoning about that is sound. However, quasars are as far away as they seem. We've measured the redshifts of surrounding and neighboring galaxies for many of them.
At this point we are talking about 73 quasars out of hundreds of thousands, spread over a large fraction of the sky. This could be a statistical anomaly of superposition as seen from our POV. It could be a result of actual non-homogeneous distribution of matter. It could be something else yet unthought of.
Answering ASTRO BOY's doubt about what is meant by structure these are not gravitationally bound. It is too big for that. If it is what it appears to be, it is a long area of space with an overdensity of luminous matter, but that space is expanding faster than the matter in the middle can draw in the matter at the ends.

I recommend waiting for more papers to come out before going too far on this topic. If real, it is very important, and might modify some models about the first second.

OK I'll take the distances as correct. Did you read the paper (http://mnras.oxfordjournals.org/content/early/2013/01/07/mnras.sts497.full)? It discusses the statistical methods used to classify it as a structure rather than coincidence.

There is a "3D" diagram that eliminates the possibility of a superposition. There is backup for the distances from MgII absorption of background quasars (I'm fuzzy on that measurement). One thing that I find interesting is that it is a filament-like structure which is often seen on smaller scales. Perhaps the structure formed more through EM interaction than gravitational.

Alignments on large scales seem to be common. I'm sure you've read the statistics on the direction of rotation of galaxies in our vicinity that shows some bias. Also mentioned is a correlation of polarization of quasars. Are alignments easily explained from gravity alone? There are number of references to other papers concerning the homogeneity of the Universe, including the large scale flows and the coincidence of a dipole in the SN data (which I had never heard of) with the CMB dipole.

Another paper referenced finds an inhomogeneity in CDM density also aligned with the CMB dipole Ultra-compact radio sources and the isotropy and homogeneity of the Universe (http://mnras.oxfordjournals.org/content/426/1/779.abstract?ijkey=9aca131fbd31a697fea5e43ebf206f8 9bf7694ee&keytype2=tf_ipsecsha).

These are all interesting observations that appear to contradict some prevailing ideas in concordance cosmology. Such fun when observation trumps theory, it humbles us a bit. I guess cosmologists will continue tweaking our ideas about the "first second" to make things come out right, as done with inflation.

antoniseb
2013-Jan-13, 05:40 PM
Yes I read the paper. I think it is an important observation.


... I guess cosmologists will continue tweaking our ideas about the "first second" to make things come out right, as done with inflation.

Of course they will. Anyone who thinks that the nature of the universe is fully understood must wonder why we still are trying to observe and test ideas. Concordance Cosmology does a very good job as a basis for measurements. Deviations from expected observations gives us clues to help determine which models work better for increasingly remote times and places. You are interested in the hairy edge of what we can detect and see... we all are. With all things near the limit, there are competing models people have come up with to explain them, and there is room for doubt in the methods of collecting and analyzing the data. I'm not saying this team is wrong, and it will be exciting if they aren't. I am saying we should wait for some corroborating work before getting too excited about all of this, and using it to falsify anyone else's work.

The other things you bring up here, galaxy rotation axes, dipole in SN data, etc. are also at the edge. I saw a recent paper invalidating all the on-the-edge stuff about the directional and time variation in the fine structure constant. But for now, let's keep this thread about this one observation please.

TooMany
2013-Jan-13, 06:21 PM
The other things you bring up here, galaxy rotation axes, dipole in SN data, etc. are also at the edge. I saw a recent paper invalidating all the on-the-edge stuff about the directional and time variation in the fine structure constant. But for now, let's keep this thread about this one observation please.

I have no quarrel with how science works in trying to explain new observations, except that when scientist manipulate un-observable processes in arbitrary ways, I find the conclusions derived less than convincing. Can you site some information about the invalidation of all evidence of large scale structure? Maybe it will give me a different perspective on the issue. Thanks.

kzb
2013-Jan-16, 06:38 PM
The paper is available free of charge from the first link in TooMany's post#1. Top right of the page there are links to pdf and html versions. At least it is free in the UK....

Jeff Root
2013-Jan-17, 12:24 AM
It isn't clear to me why filaments of unlimited length
couldn't form. If there can be a billion-light-year-long
filament here and another one there, why can't the end
of the first coincide with the end of the second, making
a seamless two-billion-light-year-long filament?

-- Jeff, in Minneapolis

TooMany
2013-Jan-18, 05:16 PM
It isn't clear to me why filaments of unlimited length
couldn't form. If there can be a billion-light-year-long
filament here and another one there, why can't the end
of the first coincide with the end of the second, making
a seamless two-billion-light-year-long filament?

-- Jeff, in Minneapolis

Do you mean coincide by accident? If you read the paper, it makes some statistical arguments to claim that this is a single, continuous structure. The paper has a better illustration of the structure than the news article.

In LCDM there are some ideas about scale of variations and the uniformity of the universe. I don't know exactly how they arrive at this limiting structure size but it might have to do with how much time it takes a structure to be formed by gravity from a more or less uniform medium with very slight density variations, like we see in the CMB. The structure of the CMB is thought to be the basis for modern structure, so there are theoretical calculations you can do about what can form from that initial structure in the given time.

Antoniseb can probably shed some light on the structure size prediction.

No doubt much debate will follow about whether this counts as a structure or should be dismissed as accident. If it is conceded to be a structure, then some new explanation may be proposed. In the meantime, the authors are using the SDSS data to look for more large structures.

Jeff Root
2013-Jan-18, 09:46 PM
It isn't clear to me why filaments of unlimited length
couldn't form. If there can be a billion-light-year-long
filament here and another one there, why can't the end
of the first coincide with the end of the second, making
a seamless two-billion-light-year-long filament?
Do you mean coincide by accident?
Maybe, kinda-sorta. I deliberately tried to avoid using
terms like "accident" or "chance" because they are not
the point.

As a terribly crude analogy, imagine two separate
mountain chains that are roughly aligned end-to-end.
Like the Rockies in North America and the Andes in
South America. Is it all one mountain range, or two?
I don't know enough about the formation of the Rockies
and the Andes to say what the reality is in that case,
but we can suppose that they are in fact completely
separate. Yet looking at them overall, they look just
like one big chain of mountains from the Brooks Range
in Alaska to the Palmer Peninsula in Antarctica.



If you read the paper, ...
Haven't done so yet. :o



... it makes some statistical arguments to claim that
this is a single, continuous structure. The paper has a
better illustration of the structure than the news article.
Since it is just a grouping of quasars which are not
gravitationally bound together, I don't see that a
distinction can be made between single and non-single.
I don't see a difference between one group of quasars
in a line and two or three or five groups of quasars in
a line. That's my point. Unclear as it is.



In LCDM there are some ideas about scale of variations
and the uniformity of the universe. I don't know exactly
how they arrive at this limiting structure size ...
Well, that's my question.



No doubt much debate will follow about whether this
counts as a structure or should be dismissed as accident.
I guess that's what I'm doing, asking whether "structure"
and "accident" are the appropriate ideas.

-- Jeff, in Minneapolis

TooMany
2013-Jan-19, 05:08 PM
As a terribly crude analogy, imagine two separate
mountain chains that are roughly aligned end-to-end.
Like the Rockies in North America and the Andes in
South America. Is it all one mountain range, or two?
I don't know enough about the formation of the Rockies
and the Andes to say what the reality is in that case,
but we can suppose that they are in fact completely
separate. Yet looking at them overall, they look just
like one big chain of mountains from the Brooks Range
in Alaska to the Palmer Peninsula in Antarctica.


It's all related to the subduction of the pacific plates, so it's more than coincidence in that case.



Since it is just a grouping of quasars which are not
gravitationally bound together, I don't see that a
distinction can be made between single and non-single.
I don't see a difference between one group of quasars
in a line and two or three or five groups of quasars in
a line. That's my point. Unclear as it is.


The quasars are assumed to be associated with galactic clusters and super-clusters, so there is a large concentration of matter surrounding these. You have to ask how did matter became so dense over this large area beginning from the ultra-smooth CMB.

I assume that they expect certain statistical properties in the distribution of matter, but this sticks out as very low probability for that distribution. Suppose you flip a coin twenty times and count the percentage of heads and you do this 1000 times, but one time it's 100% heads. The chances of all heads is 1 in 220 which is about 1 in a million. But you only did the experiment 1/1000th of the number of times required (on average) to get all heads. It could be an accident, but it's very unlikely to be an accident.

It's pretty fuzzy, but this kind of analysis is applied frequently in astronomy.



Well, that's my question.

I guess that's what I'm doing, asking whether "structure"
and "accident" are the appropriate ideas.


What other ideas do you have in mind? (BTW, how cold is it in Minneapolis?)

Jeff Root
2013-Jan-19, 08:07 PM
I'll try again.

You have a roughly uniform distribution of matter, and a
process which pulls that matter together by its mutual
attraction into clumps and strings. Only bits of matter
which are close to each other affect each other. So the
longest string you could get in the time available is five
yarlumphs. But there's no reason a three-yarlumph string
can't be close to another three-yarlumph string, which is
close to another three-yarlumph string, which is close to
yet another three-yarlumph string, and you've got what
looks like a 12-yarlumph-long string.

The matter at one end of a three-yarlumph-long string
doesn't affect the matter at the far end of an adjacent
three-yarlumph-long string, but it does affect the matter
at the near end of that adjacent string.

Is the whole mess a "single" string? Is it an "accident"?
I don't think there is a real difference. I think it is the
philisophical viewpoint of the person describing it which
determines whether it is a single string or an accident.

While the observed group of quasars undoubtedly
represents a very large quantity of matter, it is a very
small number of quasars. Even over the extremely large
extent of the grouping, that does not suggest much of
a concentration. A little bit of concentration here, a
little bit further on, some more beyond that, and you've
got an enormously long string that is neither a single
structure nor a particularly unlikely accident.

It was warm here yesterday. Water in a puddle in the
yard. I don't trust my new toy. It shows temperatures
now in the twenties and thirties (not very consistent!),
and that's what it feels like, but the last forcast I heard
said it would be cold today. Maybe later on.

-- Jeff, in Minneapolis

TooMany
2013-Jan-19, 08:21 PM
I'll try again.

You have a roughly uniform distribution of matter, and a
process which pulls that matter together by its mutual
attraction into clumps and strings. Only bits of matter
which are close to each other affect each other. So the
longest string you could get in the time available is five
yarlumphs. But there's no reason a three-yarlumph string
can't be close to another three-yarlumph string, which is
close to another three-yarlumph string, which is close to
yet another three-yarlumph string, and you've got what
looks like a 12-yarlumph-long string.

The matter at one end of a three-yarlumph-long string
doesn't affect the matter at the far end of an adjacent
three-yarlumph-long string, but it does affect the matter
at the near end of that adjacent string.

Is the whole mess a "single" string? Is it an "accident"?
I don't think there is a real difference. I think it is the
philisophical viewpoint of the person describing it which
determines whether it is a single string or an accident.

While the observed group of quasars undoubtedly
represents a very large quantity of matter, it is a very
small number of quasars. Even over the extremely large
extent of the grouping, that does not suggest much of
a concentration. A little bit of concentration here, a
little bit further on, some more beyond that, and you've
got an enormously long string that is neither a single
structure nor a particularly unlikely accident.

-- Jeff, in Minneapolis

I'm no expert on the subject Jeff, but astronomers do have ideas about large scale structure and limitations on what they expect. You seem to be suggesting that this structure is imagined and that actually what is seen is just coincidence. On the other hand you probably don't think that a spiral galaxy is just some stars and dust that happen to line up in that way, but not a structure? There is a spectrum here of what is structure and what may not be.

Read the paper and some of the literature sited about large scale structure if you want the straight dope.

noncryptic
2013-Jan-27, 05:36 PM
The abstract suggests that the finding challenges the cosmological principal.


I'd suggest it challenges the cosmological principal only if it is assumed that the universe is/must be homogenous at the scale of the observable universe - but the scale of the observable universe and hence that assumption is arbitrary, and we know essentially for a fact that the universe is much larger than the observable universe.
There's plenty room for the universe to be homogenous "at a large enough scale".

It might mean however that we will never know at what scale the universe is homogenous, so we might never be able to confirm the cosmological principal.

TooMany
2013-Jan-28, 12:38 AM
The study of the CMD in the context of mainstream cosmology sets limits on the expected size of structure. If we find larger structures, then something may be wrong within that theory. The homogeneity is not arbitrary, it needs to be consistent with the observed state of the early universe and known physics.

Jeff Root
2013-Jan-28, 03:10 AM
I completely ignored my own pet ATM hypothesis in my
above posts. Just in case some future historian is checking
on when I said what about it, I'll add that my hypothesis
appears to predict considerably earlier, larger, and stronger
clumping than mainstream theory does, so anything like the
quasar grouping reported here tickles me. :D

-- Jeff, in Minneapolis

noncryptic
2013-Jan-29, 01:41 PM
The study of the CMD in the context of mainstream cosmology sets limits on the expected size of structure. If we find larger structures, then something may be wrong within that theory. The homogeneity is not arbitrary, it needs to be consistent with the observed state of the early universe and known physics.

So the finding does not challenge the cosmological principal (which was my point), but rather challenges CDM theory?

antoniseb
2013-Jan-29, 05:26 PM
... but rather challenges CDM theory?
(My Bold), It challenges some of the assumptions in the concordance model. Using the word "theory" suggests a different kind of challenge.

Jerry
2013-Feb-02, 11:10 PM
(My Bold), It challenges some of the assumptions in the concordance model. Using the word "theory" suggests a different kind of challenge.

It is a challenging observation to explain within the context of currently accepted theory. I would argue that it does not challenge the Cosmological Principle, these observations and the Cosmological Principle force the physical contructs of the universe beyond current theoretical limits: The universe no longer fits in the tidy little corner current theoretical contraints put it in.

An interesting question that pops out of this, is why didn't this extant structure show up in either the WMAP or COBE surveys; and what does it look like in the Planck survey?

Cougar
2013-Feb-03, 04:02 PM
It's pretty fuzzy, but this kind of analysis is applied frequently in astronomy.

I remain skeptical about this type of statistical analysis. I recall one of the longest-ever discussions on Bad Astronomy about Halton Arp's statistical analysis claiming an association between several low-redshift peculiar galaxies and high-redshift quasars - in a rough pairing sense. Problem is, the redshifts implied the quasars were in the deep background, thus not associated. Arp didn't give up there, though. He came up with the crazy idea that the quasar had been "ejected" from the AGN and so the matter making up the quasar was "new", and that's why it had the higher redshift. Or something like that. This explanation didn't fly.

The CMB depicts the smooth distribution of baryonic matter at 380,000 years after the beginning of the expansion. It does not, however, show the distribution of dark matter at that time. Dark matter would have already begun gravitational clumping well before this time, since it is non-interacting with the electromagnetic and strong interactions. So when the universe came out of thermal equilibrium at 380,000 years, the baryonic matter promptly began falling into the dark matter gravitational wells, forming structure earlier than would otherwise be expected.

ASTRO BOY
2013-Feb-03, 08:37 PM
It isn't due to lensing, and your reasoning about that is sound. However, quasars are as far away as they seem. We've measured the redshifts of surrounding and neighboring galaxies for many of them.
At this point we are talking about 73 quasars out of hundreds of thousands, spread over a large fraction of the sky. This could be a statistical anomaly of superposition as seen from our POV. It could be a result of actual non-homogeneous distribution of matter. It could be something else yet unthought of.
Answering ASTRO BOY's doubt about what is meant by structure these are not gravitationally bound. It is too big for that. If it is what it appears to be, it is a long area of space with an overdensity of luminous matter, but that space is expanding faster than the matter in the middle can draw in the matter at the ends.

I recommend waiting for more papers to come out before going too far on this topic. If real, it is very important, and might modify some models about the first second.




I think that just about sums it up.
We have one observation and I'm sure more research and observations are being made as we speak.

It actually reminds me of a report a few years ago, re the observation of a huge "hole in space" more then a billion L/years across.
Does anyone have any follow up on that observation?

here is that article....
http://www.space.com/4271-huge-hole-universe.html

and here.....

http://www.newscientist.com/article/dn12546-biggest-void-in-space-is-1-billion-light-years-across.html

TooMany
2013-Feb-03, 10:09 PM
I think that just about sums it up.
We have one observation and I'm sure more research and observations are being made as we speak.

It actually reminds me of a report a few years ago, re the observation of a huge "hole in space" more then a billion L/years across.
Does anyone have any follow up on that observation?

here is that article....
http://www.space.com/4271-huge-hole-universe.html

and here.....

http://www.newscientist.com/article/dn12546-biggest-void-in-space-is-1-billion-light-years-across.html

I think there is on ongoing controversy about whether it is really there. The radio source study that made claims of confirming it has been found wanting by others. Still there is something in WMAP view of the CMB. Many are betting that this "anomaly" will disappear. Maybe the Planck results will settle the issue. I think the Planck data is supposed to be released very soon.

TooMany
2013-Jun-10, 07:23 PM
From Fun Papers today we have a sort of refutation of this large scale structure:


*Structure or Noise?* http://arxiv.org/abs/1306.1700 You remember those giant Large Quasar Groups that were announces last fall? Do they violate homogeneity, or extend the minimum size that homogeneity requires? This paper points out that a few such seeming object could simply be noise in an otherwise real signal.

This author claims that the detection is perfectly consistent with predictions of LCDM. It criticises the statistical method used as allowing too much distance between quasars assumed to be related.


Since the linkage length used to identify the Huge-LQG is so large, there is no reason I know of to believe that it forms a gravitationally bound structure. Certainly no real structures of such size are expected in the standard cosmology. On the other hand, when using this linkage length the clustering algorithm often finds such extended structures even in pure Poisson noise. It therefore appears that the Huge-LQG fails to satisfy either criterion, and so its interpretation as a ‘structure’ is highly questionable. This conclusion is even more applicable to the other slightly smaller quasar groups whose existence has also been claimed (e.g. Clowes & Campusano 1991; Clowes et al. 2012).

How often is such a large structure found in pure noise? The paper says in 8.5% of 10,000 simulated cases. I guess another way of putting it is that there is a mere 91.5% chance that the structure is real.

It seems especially odd to suggest that the same refutation applies to all similar structures whose existence is claimed, when the existence of several such structures in random noise should be far rarer that the existence of one. Why did the author not examine the question: "How often are the total number of such structures detected found in a random distribution?"

The paper also suggests that the Sloan Great Wall is a similar statistical oddity and not in tension with LCDM.

The paper concludes:


We should regard this as a reminder not to trust inferences based on rare structures found using such algorithms in the absence of a proper quantification of their action on simulated distributions.

This leaves me feeling a little queasy. I eagerly await a rebuttal from the original authors.

Jens
2013-Jun-11, 02:07 AM
Also, just a little nitpick, and a little bit late at that, but I just wanted to point out, because it comes up so many times in this thread, that it should be cosmological principle, not principal.

TooMany
2013-Jun-11, 03:25 PM
Also, just a little nitpick, and a little bit late at that, but I just wanted to point out, because it comes up so many times in this thread, that it should be cosmological principle, not principal.

I suppose the latter would refer to the biggest cheese.:)

Jens
2013-Jun-11, 10:37 PM
I suppose the latter would refer to the biggest cheese.:)

If you're willing to stretch the meaning of the terms a tad, it could be the headline of a story about Brian May. :)

TooMany
2013-Jun-11, 10:48 PM
Ha, ha. I had to look that up. He is a man of diverse talents. A large-scale structure of sorts.

TooMany
2013-Jun-19, 09:19 PM
We have yet another paper entering into the debate about these large scale structures reported in quasar distributions: Testing statistical significance of large quasar groups with sheets model of large scale structure (http://arxiv.org/pdf/1306.3970v1.pdf).

This paper is also critical of the original paper by Clowes (http://mnras.oxfordjournals.org/content/early/2013/01/07/mnras.sts497). The conclusion is:


We found that the probability to find a LQG similar to U1.27 in a random catalogue is 1.4% (2.45σ) or even 2.8% (2.2σ) if we take into account the large-scale structure of the Universe modelled by plane sheets. Both these quantities are significantly higher than the probability estimated by Clowes et al. (2013).

We also point out that MST-like algorithms tend to find large clusters with high significance by travelling through the multiconnected large scale structure. The sizes of such clusters do not correspond directly to the size of scale of homogeneity of the Universe.

They state that the probability of one such cluster in a random catalogue is as much as 2.8%, in other words the probability that it is a real large scale structure is a mere 97.2%.

The second part of their conclusion is not quantitative. I think that if you are going to argue that such clusters do not disagree with the expected homogeneity then you need to more carefully define what this expected homogeneity actually is. As I understand it, theory derives the expected homogeneity from the high homogeneity of the CMB itself which is the baby picture of the Universe from which all structure has subsequently emerged.

So what is this homogeneity supposed to be and how can we actually decide whether observations of structure are indeed consistent with the CMB?

Once again, I don't see where they attempt to deal quantitatively with the probability of more than one large structure as is reported in the original paper.

It's fun watching the scramble to explain away observations that don't appear to jive with theory.

antoniseb
2013-Jun-19, 10:36 PM
... It's fun watching the scramble to explain away observations that don't appear to jive with theory.
You and I have some differences in our approach, but I also enjoy seeing how things resolve when new observations are made. It is worth noting that when you look at the edge of what's known, it usually takes a few years for a favorite explanation to resolve, and even then they can be overturned. This process is what is most interesting to me about the leading edge of science.

TooMany
2013-Jun-20, 12:49 AM
I guess because people feel that the overall theory is so well established that the natural reaction to an apparent contradiction is "there must be something wrong with the analysis". So, much effort naturally goes into resolving evidence that apparently contradicts theory. I see this a lot in the following areas - problems with cold dark matter (cusps, stripped dwarf galaxies, missing dwarfs), nucleosynthesis (the lithium problem has a new solution every few months), CMB anomalies and large scale structure. I've seen a number of papers claiming to demonstrate how the dark matter cusps get erased only to find later that detailed simulations do not support the claimed mechanisms.

What bothers me is an apparent attempt to dismiss problems, as in this large scale structure case. The rebuttal papers may demonstrate that the proof is not 100% convincing, just 95-98% convincing. Particularly in the case of the first rebuttal, the sense of the conclusion is that the problem has been dismissed by showing it's not at the sigma 5 level, the original author is admonished, so we can all relax and move on. One the other hand, if some dark matter detector finds 3 events over a long period of time that may be represent evidence of non-baryonic dark matter, that evidence is not dismissed but is considered as promising.

I see a tendency to dismiss that which disagrees with theory and to enhance that which confirms theory. This is not really surprising. If theory is indeed wrong it will clearly take truly overwhelming evidence to kill it.

Jean Tate
2013-Jun-20, 01:17 AM
I guess because people feel that the overall theory is so well established that the natural reaction to an apparent contradiction is "there must be something wrong with the analysis".

I'm sure there are such people. How many of them are astronomers/astrophysicists/cosmologists active in this field, well, who knows?


So, much effort naturally goes into resolving evidence that apparently contradicts theory.

I think I read, in one of your posts somewhere in this forum, that you yourself are not actively engaged in on-going research in this field (if not, please correct my misunderstanding). If that is so, then what you wrote - the part I just quoted - reads like your own projection, based perhaps on ignorance (i.e. you do not know, from first-hand experience, what's actually going on).


I see this a lot in the following areas - problems with cold dark matter (cusps, stripped dwarf galaxies, missing dwarfs), nucleosynthesis (the lithium problem has a new solution every few months), CMB anomalies and large scale structure. I've seen a number of papers claiming to demonstrate how the dark matter cusps get erased only to find later that detailed simulations do not support the claimed mechanisms.

To what extent do you think this is a common phenomenon, in all of science? Is it, for example, something you have observed in the field of science in which you are currently active (i.e. have recently published papers in)?


What bothers me is an apparent attempt to dismiss problems, as in this large scale structure case. The rebuttal papers may demonstrate that the proof is not 100% convincing, just 95-98% convincing. Particularly in the case of the first rebuttal, the sense of the conclusion is that the problem has been dismissed by showing it's not at the sigma 5 level, the original author is admonished, so we can all relax and move on. One the other hand, if some dark matter detector finds 3 events over a long period of time that may be represent evidence of non-baryonic dark matter, that evidence is not dismissed but is considered as promising.

Why are you bothered? Is it something you have seen that is peculiar to this part of astronomy/astrophysics/cosmology? If it's simply a pretty common pattern, in any branch of contemporary science, wouldn't you agree that's no more cause for being bothered than, say, similar patterns in the evolutionary biology of slime molds?


I see a tendency to dismiss that which disagrees with theory and to enhance that which confirms theory. This is not really surprising. If theory is indeed wrong it will clearly take truly overwhelming evidence to kill it.

Huh?!? Isn't this sort of thing more appropriate for the ATM or CT section of this forum? Do you consider the two, independent, sets of Ia SNe observations - that the existence of 'dark energy' was then based on - to have been 'overwhelming evidence', sufficient to 'kill' the until-then favored cosmological models?

Jens
2013-Jun-20, 02:25 AM
I guess because people feel that the overall theory is so well established that the natural reaction to an apparent contradiction is "there must be something wrong with the analysis".

I don't think it's so simple. Let me just address two issues that you brought up: cold dark matter and the large scale structure. With cold dark matter, we have a clear observation (the flat rotation curves of galaxies) that does not make sense under Newtonian or Einsteinian gravity. So dark matter is posited as a way of explaining that anomalous observation. Since nobody has come up with any better explanation, we are working with the best we have.

Same with large-scale structure. The Hubble observation shows us that objects that are further away are moving away faster. The obvious conclusion is that the universe is expanding. If so, you get to the big bang and there shouldn't be large-scale structure over a large area. If it does turn out that there is, then fine, but then you have a problem of explaining other things like the Hubble redshift. So for the time being, it makes sense to assume that the large-scale structure is consistent with the big bang. If it turns out to be incompatible, then you have to go back and start explaining why then the universe appears to be expanding, which is a strong observation.

TooMany
2013-Jun-20, 09:22 PM
I'm sure there are such people. How many of them are astronomers/astrophysicists/cosmologists active in this field, well, who knows?



I think I read, in one of your posts somewhere in this forum, that you yourself are not actively engaged in on-going research in this field (if not, please correct my misunderstanding). If that is so, then what you wrote - the part I just quoted - reads like your own projection, based perhaps on ignorance (i.e. you do not know, from first-hand experience, what's actually going on).



To what extent do you think this is a common phenomenon, in all of science? Is it, for example, something you have observed in the field of science in which you are currently active (i.e. have recently published papers in)?



Why are you bothered? Is it something you have seen that is peculiar to this part of astronomy/astrophysics/cosmology? If it's simply a pretty common pattern, in any branch of contemporary science, wouldn't you agree that's no more cause for being bothered than, say, similar patterns in the evolutionary biology of slime molds?



Huh?!? Isn't this sort of thing more appropriate for the ATM or CT section of this forum? Do you consider the two, independent, sets of Ia SNe observations - that the existence of 'dark energy' was then based on - to have been 'overwhelming evidence', sufficient to 'kill' the until-then favored cosmological models?

I'm just an observer here. I'm not an astronomer, just someone interested in astronomy. I read papers (to the depth that I am capable of understanding them) and I am aware of some of the current issues.

I cannot speak about what goes on in biology or other sciences because I don't have any relevant training nor great interest in the details. Those other sciences have a somewhat different nature. They are laboratory sciences where conditions can be manipulated. Astronomy is a more difficult science because it has only observations and from a single viewpoint.

Mainstream cosmology incorporates speculative aspects such as non-baryonic dark matter, inflation, and a beginning at unbounded density. What I brought up in this thread is just one of many issues that mainstream theory is currently grappling with. I've made some observations above about the approach by some to observations that create "tension" with theory. These are my perceptions and if you don't like them that's fine. Since I'm not entirely on-board with current theory, I don't like to see contrary evidence dismissed.

Do you have any comment on large scale structures or any of the three papers discussed?

Jean Tate
2013-Jun-23, 01:47 PM
I'm just an observer here. I'm not an astronomer, just someone interested in astronomy. I read papers (to the depth that I am capable of understanding them) and I am aware of some of the current issues.

Thanks for clarifying this.


I cannot speak about what goes on in biology or other sciences because I don't have any relevant training nor great interest in the details. Those other sciences have a somewhat different nature. They are laboratory sciences where conditions can be manipulated. Astronomy is a more difficult science because it has only observations and from a single viewpoint.

Here I think you are at least largely wrong. And the example I gave - the evolutionary biology of slime molds - may serve to illustrate why I think this way.

Many fields of science are similar to astronomy in the sense that 're-creation in the lab' is equally impossible. The evolutionary history of primates, if not slime molds, is one example. And of course astrophysics does involve lab work, 'where conditions can be manipulated' (basically most of physics).


Mainstream cosmology incorporates speculative aspects such as non-baryonic dark matter, inflation, and a beginning at unbounded density.

I get that you don't like CDM, inflation, etc. And that your dislike of these leads you to use lots of charged words in a blatantly biased way (see, I just used some myself!). Smoother dialog might happen - and your understanding of astronomy grow faster - if you try extra-hard to avoid projecting your own ideas onto others, and at least be careful with words like 'speculative' (all that 21-cm electromagnetic radiation observed coming from the sky; a 'speculative aspect' of mainstream astrophysics is that arises from a particular atomic transition of hydrogen).


What I brought up in this thread is just one of many issues that mainstream theory is currently grappling with.

"Mainstream theory" "grapples" with issues?


I've made some observations above about the approach by some to observations that create "tension" with theory. These are my perceptions and if you don't like them that's fine.

Glad you clarified that too.


Since I'm not entirely on-board with current theory, I don't like to see contrary evidence dismissed.

Which is kinda where we got started; if you yourself are not actively involved in doing research in this field (or were, until recently), how can you possibly know that "contrary evidence" is being "dismissed"? More fundamentally, how can you, yourself, evaluate the quality of this "contrary evidence"?

Cougar
2013-Jun-23, 02:19 PM
It's fun watching the scramble to explain away observations that don't appear to jive with theory.

It's just called "checking the results," not "explaining away." In the case of the OP, apparently the results were checked and found not to be exactly accurate.

A fairly recent example of a finding that did not jive with existing theory is the accelerating expansion. Obviously a lot of effort has been expended to find another explanation for this finding, based on the belief that "this can't be right" (a lot of that effort coming from the original investigators themselves). After a lot of "checking," the result is still holding up.

TooMany
2013-Jun-23, 09:23 PM
I get that you don't like CDM, inflation, etc. And that your dislike of these leads you to use lots of charged words in a blatantly biased way (see, I just used some myself!).

Are you saying the calling CDM and inflation speculative is emotionally charged? I don't think so, it's simply a fact until we have verification of the actual existence of these proposals.



Smoother dialog might happen - and your understanding of astronomy grow faster - if you try extra-hard to avoid projecting your own ideas onto others, and at least be careful with words like 'speculative' (all that 21-cm electromagnetic radiation observed coming from the sky; a 'speculative aspect' of mainstream astrophysics is that arises from a particular atomic transition of hydrogen).

Are you implying that I've suggested that spectral lines are speculative? Are you trying to conflate our knowledge about non-baryonic dark matter and inflation with our understanding of spectral lines?



"Mainstream theory" "grapples" with issues?

What exactly is the problem with that figure of speech? When unexpected things occur we "struggle" to explain them (almost literally).



Which is kinda where we got started; if you yourself are not actively involved in doing research in this field (or were, until recently), how can you possibly know that "contrary evidence" is being "dismissed"? More fundamentally, how can you, yourself, evaluate the quality of this "contrary evidence"?

How? I can read. Did you read these papers? There is a disconnect between the claimed findings (only 95% significance rather than higher) and the expressed verbal conclusion which is that the large scale structures are not significant, they are expected in the LCDM model.

Jean Tate
2013-Jun-23, 11:01 PM
(snip)
This leaves me feeling a little queasy.

Why?


I eagerly await a rebuttal from the original authors.

Why? Would "a rebuttal" from authors other than originals be just as eagerly awaited?

As I understand it, while there are certainly instances where observations which apparently seemed unexpected at first were 'resolved' within months if not weeks, it is more usual that these discussions cover many 'positions' (not just an A/B, 'pro/con', 'yes/no'), and last years. And that the eventual resolution involves at least one subtle aspect that was not appreciated by anyone, at the beginning.

Jean Tate
2013-Jun-23, 11:11 PM
... but rather challenges CDM theory?(My Bold), It challenges some of the assumptions in the concordance model. Using the word "theory" suggests a different kind of challenge.

I think it's about 8 Glyrs away, but 4 Glyrs long. It spans 20 degrees across the sky so I don't think that could be due to lensing. Maybe quasars aren't as far away as they seem? I suspect this is big news. Something has got to give in current theory.(my bold)

Such fun when observation trumps theory, it humbles us a bit. I guess cosmologists will continue tweaking our ideas about the "first second" to make things come out right, as done with inflation.(my bold)

As I understand it, theory derives the expected homogeneity from the high homogeneity of the CMB itself [...] It's fun watching the scramble to explain away observations that don't appear to jive with theory.(my bold)

And so on.

As noncryptic, so TooMany.

Jean Tate
2013-Jun-23, 11:46 PM
Are you saying the calling CDM and inflation speculative is emotionally charged?

If you don't also call the identification of the observed 21-cm line as a hydrogen transition speculative, yes.


I don't think so, it's simply a fact until we have verification of the actual existence of these proposals.

Yet I do not recall you saying that the association identification of two green emission ('nebular') lines with as 'forbidden' transitions in an oxygen ion speculative (I may be wrong; please correct me if I am). I speculate that your selection of verified facts is, um, blatantly biased.


Are you implying that I've suggested that spectral lines are speculative?

No.


Are you trying to conflate our knowledge about non-baryonic dark matter and inflation with our understanding of spectral lines?

No ... I'm simply asking about a single emission line (well, now three), in light of your "... laboratory sciences where conditions can be manipulated" comment. By the way, in researching your previous posts, and responses to them, I see that I am not the first to ask you about this apparent blatant bias inconsistency; perhaps you have addressed this before?


How? I can read. Did you read these papers?

Yes.


There is a disconnect between the claimed reported findings (only 95% significance rather than higher)
ftfy

and the expressed verbal conclusion which is that the large scale structures are not significant, they are expected in the LCDM model.(my bold)

I'm happy to see that you have moved from (the) "theory" to "the model"; I look forward to you internalizing finer distinctions, as your understanding of astronomy, and astrophysics, becomes deeper.

TooMany
2013-Jun-23, 11:59 PM
Why?

Because the lack of examination of statistical likelihood of all of the large scale structures identified using his own statistical method. What bothers me is the dismissive attitude. If it's not 99.99999% proven, it can be dismissed. And why dismiss it at 92-98% significance? Because it is contrary to theory?



Why? Would "a rebuttal" from authors other than originals be just as eagerly awaited?

Did you read the papers? Author A claims a significant large scale structure. Author B says the structure is "only" significant at the 92% level. Author B suggests that if one such structure has a probability of 8% in his random experiment, then multiple such structures are also probable with no mathematical justification. Author B writes into his title his conclusion "Seeing patterns in noise: Gigaparsec-scale ‘structures’ that do not violate homogeneity". But, to put it another way, author B has actually shown (according to his own estimate) that there is only an 8% chance that the structure does not violate [CDM] homogeneity.

Author C comes along and offers a bit more modest rebuttal of author A saying that the large scale structure has a 2.4% chance of being a random result (if you consider the possibility of the claimed structure being formed by traveling through a "multi-connected large scale structure". Author C mainly complains that the claimed significance is too high and should be only 97.6%, but leaves the impression (without numbers) that the whole thing could be a misinterpretation anyway with this non-quantitative last paragraph:


We also point out that MST-like algorithms tend to find
large clusters with high significance by travelling through
the multiconnected large scale structure. The sizes of such
clusters do not correspond directly to the size of scale of
homogeneity of the Universe.


So, in this interesting disagreement, author A has served up a challenge and author's B and C have returned some criticism. So what I'm very curious to see is how author A might respond to the criticism. One would hope that when scientist disagree whoever may have made a mistake would own up to it. I see a clear bias by B for dismissing the issue because this particular structure only has a 92% chance of actually showing a violation of homogeneity (according to his own estimate).

It's sort of like a soap and I'm waiting for the next episode. I hope that answers your question about my eagerness to hear from author A. However, anyone else's analysis would be very interesting as well. I'll bet some more are in the works.

Jean Tate
2013-Jun-24, 07:11 PM
Because the lack of examination of statistical likelihood of all of the large scale structures identified using his own statistical method.

How comfortable do you yourself feel, about accepting the results of others' work involving "statistical likelihood"? Particularly when it involves cosmology? In my own experience, this is one of the hardest things to get my head around (the calculations may not be so hard - though they often are - but trying to convince myself I fully understand the rationales and interpretations?)


What bothers me is the dismissive attitude.

"Attitude" is, surely, in the eye of the beholder, isn't it?


If it's not 99.99999% proven, it can be dismissed. And why dismiss it at 92-98% significance?

This is one place where it gets tricky. At the LHC, 5σ is, I think, the threshold; in various astronomical surveys, thresholds can be as low as 2σ (and as high as 10σ). There's only one universe, how do you go about determining a threshold, robustly?


Because it is contrary to theory?

No.


Did you read the papers? Author A claims a significant large scale structure. Author B says the structure is "only" significant at the 92% level. Author B suggests that if one such structure has a probability of 8% in his random experiment, then multiple such structures are also probable with no mathematical justification. Author B writes into his title his conclusion "Seeing patterns in noise: Gigaparsec-scale ‘structures’ that do not violate homogeneity". But, to put it another way, author B has actually shown (according to his own estimate) that there is only an 8% chance that the structure does not violate [CDM] homogeneity.

Author C comes along and offers a bit more modest rebuttal of author A saying that the large scale structure has a 2.4% chance of being a random result (if you consider the possibility of the claimed structure being formed by traveling through a "multi-connected large scale structure". Author C mainly complains that the claimed significance is too high and should be only 97.6%, but leaves the impression (without numbers) that the whole thing could be a misinterpretation anyway with this non-quantitative last paragraph:



So, in this interesting disagreement, author A has served up a challenge and author's B and C have returned some criticism. So what I'm very curious to see is how author A might respond to the criticism. One would hope that when scientist disagree whoever may have made a mistake would own up to it.

Perhaps there's no mistake, by anyone? Perhaps they're all 'right', and all 'wrong'? Perhaps a long and hard look at the methods and assumptions of all authors will show some overlooked - apparently minor - aspect that turns out to be anything but?


I see a clear bias by B for dismissing the issue because this particular structure only has a 92% chance of actually showing a violation of homogeneity (according to his own estimate).

Which gets back to the question of threshold, doesn't it?


It's sort of like a soap and I'm waiting for the next episode. I hope that answers your question about my eagerness to hear from author A. However, anyone else's analysis would be very interesting as well. I'll bet some more are in the works.

I find the universe (Nature, if you prefer) vastly more interesting than any soap. Sadly, I am unlikely to live long enough to see many of my favorite deep questions - in astronomy and cosmology - answered ...