Biggest Supercluster So Far

In article , "Robert L.
Oldershaw" writes:

I'm off soon for two weeks, so very quickly (and this explains my
absence from here in the next two weeks), off the top of my head, but I
think a good summary: I would say that we are confident that there is
homogeneity at scales of more than a few hundred Mpc at somewhere
between 3 and 4 sigma---maybe more, but not significantly less.

1. Can you give us a scientific definition for what you are referring
to as "homogeneity"?

Statistical similarity. Basically all papers looking at this use the
same definition.

2. Can you be a bit more specific than "a few hundred Mpc", or is the
location of the hypothetical turnover somewhat adjustable?

It depends on the data. I don't have them all in my heard.

3. Can you be a bit more specific than "somewhere between 3 and 4
sigma--maybe more", or is this sigma value a variable?

No. However, you asked about my impression. My impression is 3 or 4
sigma.

For what it's worth, at the Moriond meeting I was at last week (all
talks are on the web---easy to find), there was a talk on this topic,
with confirmation of "homogeneity above a few Mpc".

On Saturday, March 26, 2016 at 4:07:00 PM UTC-4, Phillip Helbig (undress to reply) wrote:


For what it's worth, at the Moriond meeting I was at last week (all
talks are on the web---easy to find), there was a talk on this topic,
with confirmation of "homogeneity above a few Mpc".

Or, by your definition, ""statistical similarity" above a few Mpc".

As I noted in my response to SW in another thread posted today (after
5 tries over 3 days, I might mention), I think one could argue that
"homogeneity" should never be used to describe a distribution that is
merely "statistically similar". My reasoning for that assertion is
that the former is misleading in the case of a distribution that is
not at all "homogeneous" (in any exact sense) since it has
considerable hierarchical structure, e.g., the vast cosmic web.

[Mod. note: if this discussion is all about your misunderstanding of
what everyone else uses the word 'homogeneity' to mean, then perhaps
it should be terminated here -- mjh]

RLO http:/www3.amherst.edu/~rloldershaw

On Sunday, March 27, 2016 at 3:16:51 AM UTC-4, Robert L. Oldershaw wrote:


[Mod. note: if this discussion is all about your misunderstanding of
what everyone else uses the word 'homogeneity' to mean, then perhaps
it should be terminated here -- mjh]


Well, of course you are the gatekeeper for these discussions, but I
would remind you of this piece of history.

Not that long ago "everyone" used the word "simultaneity" and
"understood" what it meant. No doubt the majority of physicists argued
that it was foolish to question the common sense and almost
universally agreed upon concept of simultaneity.

But everyone who accepted this "obvious" assumption was wrong. The
concept of simultaneity turned out to be much more complicated and
questioning the concept was important to a major advance in physics.

The take home lesson, as always, is that we must be careful about
assumptions, definitions, concepts, etc. that we treat as absolute and
unalterable fact.

The distinction between cosmological "homogeneity" and "statistical
homogeneity" on the largest currently observable scales may well turn
out to be a meaningful and important distinction. Not just a semantic
facetious argument.

[Mod. note: if you explained your new, insightful view of what
'cosmological homogeneity' might mean, you might have more to go on
with this analogy. But I would suggest you start by demonstrating an
understanding of what everyone else means... -- mjh]