Re: ....I have always refused to accept the speed of light as the upper limit of speed.

I actually feel that special relativity looks a lot less absurd if you first formulate general relativity -- then everything drops out really quite neatly. Obviously other people think differently again :) The absurdity to my mind is quite a superficial one, but it's certainly there (at least for many people) when you first hit special relativity.

Re: 1.2 billion light years was the upper limit for the size of a structure

Ultimately whether we like it or not, the point of physics is to make predictions and the predictions that come out of special relativity, both on a quantum and a classical level, match reality to whatever accuracy we can push it. That then implies that any theory we come up with to replace special relativity has to mimic it in these regimes so closely as to be indistinguishable.

World class summation IMHO :). Have an upvote!

Re: crowded

The universe isn't 13.7 billion light years across, it's 13.7 billion years old. Even ignoring issues of how long it would take a photon to propagate from the Big Bang to now (it's not quite the same thing), a structure can be tangential and be extremely large. If you look at it one way, you can split the universe into slices of constant redshift (which isn't quite the same as constant cosmic time, but in the Big Bang theory is closely related). Each slice of constant redshift is at a certain proper distance from Earth, but then structure can be distributed *across* that slice quite happily. I remember about six years back the Sloane found the Sloane Great Wall and there were half-nervous half-excited twitches because the damn thing never seemed to end -- and if it never ended then the assumptions that build up the cosmological model fail. The Sloane Wall does end, of course, but it probably helped shift the homogeneity scale up from roughly 150Mpc to 300Mpc. (That scale is, by the by, horribly loose and badly-defined, but I've gone off on one about unsubstantiated assumptions in cosmology before so I'll skip it here.)

Re: crowded

Where did 30% come from? Not that it's wrong: if you apply Benford's Law to it this could be as much as 30.1% or as little as 4.6% of the universe. it just depends on how many Quasar groups of that size they find.

I should also note that the article says the limit was derived from a computer model. We all know computer models are bastions of accuracy don't we?

Re: crowded

"There's something out there that's nearly 30% the width of the universe?"

To have a width you need an edge. What there is at the edge of the universe, and what's outside it?

"to have width you need an edge..."

Not true.

Drop a dimension and imagine the universe is the surface of a balloon. It can expand (meaning the surface becomes larger) and can be said to have a 'width' - i.e. the circumference of the balloon. It does not follow that the surface of the ballon must have an 'edge'. Not saying this is an accurate representation, just demonstrating the false initail assumption, and hence the moot question that followed it.

Re: "to have width you need an edge..."

"Drop a dimension and imagine the universe is the surface of a balloon"

Alright, you've got me on that one. But, wilfully taking your analogy as factual, now the question from Dullard Towers metamorphasises (or som't like that) into an equally profound couple of questions: What's inside the balloon? And is the stuff outside the balloon the same or different to the stuff on the inside?

Re: "to have width you need an edge..."

...and what happens when the knot at the end comes undone and the universe flies around the room making a 'pbltltttbhbbbttttt!' sound?

Re: crowded

My mistake. Okay, so it's 93 billion light years wide, so about 5%. Still way too big.

Re: Quasar and a black hole

Well, the assumption is that a Quasar is powered by a black hole. So there.

Re: London buses

Nah, it's too big for buses. Too big for Nelson's Columns and Waless too.

Travelling at the speed of tectonic drift would be an improvement......

Re: Is it possible...

Not in anything like the standard model -- gravitational instability tends to make inhomogeneities *grow* over time, not diminish. So the universe gets larger and the matter gets more and more concentrated. That's basically why if you compare a shot of the microwave background with a shot of the large-scale distribution of galaxies you see such different things. The microwave background is smooth to one part in a hundred and, if you take off a dipole that is so clean it's almost certainly a straight Doppler, it's smooth to one part in 100,000! In the standard model that microwave background is effectively a photograph of the universe when it was about 300,000 years old -- so it was really, really smooth. The assumption is then that the little fluctuations are a picture of the seeds that would later grow into today's galaxy clusters. If you then look at, say, the Sloan Digital Sky Survey's results there are massive voids with dense clumps living on the edges. It's nothing like as smooth except when you look across truly massive scales (and the scales needed - as this result seems to show - are actually beyond what the SDSS has yet seen, will likely be beyond anything until Euclid and perhaps SKA come online in a decade or so). Even though the universe now - in the standard model - is massively larger than it was when the microwave background formed, the clumpiness of the matter is much greater.

Of course, change the cosmological model and this argument changes, but you have to go some to find a model that fits anything like as well as the standard (so-called Lambda CDM, based on a Robertson-Walker) model, for all its flaws.

Re: Is it possible...

But the ( current ) standard model of the universe has the elephant-in-the-room assumption that everything we currently see flying apart was ejected from some implausibly dense signularity, without accounting for how that singularity existed.

It is perfectly possible that the universe if far larger and far older than we can currently determine, and the singularity that exploded as "The Big Bang" was formed from the gravitational collapse of simply a section of cosmos that eventually reached an explosive instability.

Re: Is it possible...

Sure. Now formulate a theory that encapsulates all this, can explain the data that the big bang theory fits eerily (and distressingly) well...

What you're basically talking about are cyclic scenarios, which have been around a very long time -- and those are certainly still studied. A famous example from about ten years back is the so-called ekpyrotic scenario, where there may be a singularity in 4D gravity but that's OK because the fundamental theory is 5D. We live on a 4D brane and close by is a second 4D brane. These clap together like cymbals, and, like cymbals, massive waves go shuddering through the branes. These waves, viewed from the brane we live on, looks like a Big Bang. Ekpyrosis is little more than a toy model, but it is an attempt to build a cosmology based on ideas from string theory ("M theory", if you like that expression), avoid this initial singularity, and predicts a universe almost, but not entirely, identical to the standard one. (The difference, if you're interested, is that the standard approach involves an inflationary phase that produces relic gravitational waves that we should be able to observe at some point. Ekpyrosis produces no waves whatsoever. Unfortunately that means that while we can rule out ekpyrosis we can't rule out the standard approach, since the amplitude of those waves can be unobservable low.)

Ekpyrosis isn't the only attempt at a cyclic scenario, of course, though it's the one I know best. Most cyclic universes are plagued by the issue of entropy; if the universe is cyclic, then the entropy should be amazingly enormous. Since it isn't -- it's big, but not *that* big; near the start of the expansion it seems the universe was in a very low entropy state -- then we have to be very close to the start of the cycles, or else you have to find a way of reducing the entropy, which might involve dumping it into the rest of the universe. That then raises naturalness issues: why are we in this part? The only easy answers reduce to anthropic arguments ("Because if it were different we couldn't be here to ask the question") which are neat and tell us precisely nothing.

One neat theory, by the by, was proposed by Penrose a few years back. Basically he noted that the infinite future in the standard big bang approach will contain a universe filled only with photons. For various technical reasons this then means that the concept of "length" becomes rather ambiguous, and one can link that state very easily with the infinite *past*, which was also filled with photons and nothing else. Quite how Penrose deals with entropy I'm not sure since I'm not aware he's ever published any mathematical details of this rather neat concept, and I'm also not sure how he sets about generating particles in the early universe, but I really quite like the concept.

Anyway, I kind of rambled off there. The point was that yes, you're quite right, it's perfectly possible that the universe is far larger and older than we might think (though it's normal thinking to assume it's at least effectively infinite). Since our theory breaks down near to the predicted singularity we've got no hope, with the standard model, of answering the question, which is why we move to approaches inspired by M theory or loop quantum gravity (or Penrose's mathematical trick). The devil unfortunately is in the details: firstly finding a consistent model based on your idea, and then finding a way of generating observational differences to the standard model. But it's a very active area of research.

(Also, and everyone should feel free to ignore this because it's grossly off-topic, there are other elephants in the room, too. My favourite bugbear is that of the "average" which is assumed throughout cosmology and, somewhat surprisingly, is never actually defined. It turns out this is because you *can't* define an average in general relativity. There are others. One nice one is MOND, which effectively replaces Newton's law of gravity for very low accelerations. MOND is clearly bullshit -- by which I mean "unmotivated phenomenology" -- and would have been forgotten by now except for the embarrassing fact that it explains the rotation curves of pretty much every galaxy we've ever observed, without need for dark matter. While it does run into problems with something like the Bullet Cluster, those problems aren't necessarily insurmountable, not least because by it's very nature MOND is non-relativistic and does not predict lensing signals. MOND dies when you try and apply it to cluster scales, but its success on galactic scales says to me, very strongly, that something extremely interesting is going on. Unfortunately there's little benefit devoting oneself to this because it would kill one's career. What a lovely world we attempt to do research in...)