A Hole in Space

[Willamena]

I haven't seen this posted yet, so apologies if it's been done.

Astronomers have found an enormous void in space that measures nearly a billion light-years across.

It is empty of both normal matter - such as galaxies and stars - and the mysterious "dark matter" that cannot be seen directly with telescopes.
The "hole" is located in the direction of the Eridanus constellation and has been identified in data from a survey of the sky made at radio wavelengths.
BBC NEWS | Science/Nature | Great 'cosmic nothingness' found

Astronomy Picture of the Day representation:
APOD: 2007 August 27 - Huge Void Implicated in Distant Universe

 

[Halcyon]

I think they're making a few too many assumption with what they're saying, especially the stuff about this "void" not containing dark matter.
People haven't even confirmed the existence of dark matter, so claiming the lack of it in a particular region seems like a bit of a stretch.

 

[Panda]

I thought dark matter was a confirmed fact but it was found there is less than was initially thought? ie Not enough to slow the universe down and cause the "Big Crunch".

 

[silvermoon383]

Dark matter was confirmed. Caused quite a stir when it was too.

Wiki it.

 

[Halcyon]

Dark matter was confirmed. Caused quite a stir when it was too.

Wiki it.

I did, and i think you may be jumping the gun. The first sentence of that wiki article still maintains dark matter is hypothetical, and the rest of the article goes on to explain why.
There is a lot of evidence for "something" unusual out there which is causing unexpected and anomylous results, and dark matter is still only one hypothesis for what that "something" may be. The wiki article itself lists two viable alternative hypotheses.

Anyway, even if for the moment we accept that dark matter actually does exist, even then we need regular matter nearby to allow us to observe the changes wrought upon it by the dark matter. With no regular matter within this "void", i fail to see how it can be said that the "void" contains no dark matter, as we have nothing to observe.

 

[silvermoon383]

That's odd, cause Astronomy Magazine had a huge article about it when it was confirmed, and my local newspaper even had a front page article about it (doubly remarkable since the paper rarely carries a science article period).

Anyways, the way it was discovered was when a conjunction happened (one celestial object passed in front of another from our pov), in this case a galaxy passed in front of something else, allowing scientists to measure the mass of the closer galaxy by measuring the gravitational lensing effect. They discovered that this galaxy was bending light much more than the visible matter could account for, so the only thing that could "fill the gap" so to speak, was dark matter.

This greater lensing has been seen with other conjunctions, and now we know that most if not all galaxies are surrounded by a dark matter halo.

This isn't the actual article from my newspaper, but it is a good one: Astronomy - Hubble finds ring of dark matter - Provided by the ESA

 

[Halcyon]

That's odd, cause Astronomy Magazine had a huge article about it when it was confirmed, and my local newspaper even had a front page article about it (doubly remarkable since the paper rarely carries a science article period).

Anyways, the way it was discovered was when a conjunction happened (one celestial object passed in front of another from our pov), in this case a galaxy passed in front of something else, allowing scientists to measure the mass of the closer galaxy by measuring the gravitational lensing effect. They discovered that this galaxy was bending light much more than the visible matter could account for, so the only thing that could "fill the gap" so to speak, was dark matter.

This greater lensing has been seen with other conjunctions, and now we know that most if not all galaxies are surrounded by a dark matter halo.

This isn't the actual article from my newspaper, but it is a good one: Astronomy - Hubble finds ring of dark matter - Provided by the ESA

Uh huh, and it talks about it in the wiki article a bit. The thing is, although the dark matter hypothesis does make sense (it wouldn't be a seriously considered hypothesis if it didn't) even gravitational lensing doesn't confirm the existence of dark matter.

What it does do is add yet more evidence to the already substantial pile we have, that there is "something" having an effect of the gravitational attributes of large objects. What that something is is still unknown, it could well be dark matter but until we acquire a sample of this as yet unknown form of matter, or we invent a technology that can detect it directly, inference from observable effects is not enough to elevate dark matter beyond a hypothetical substance.
The effects, including the gravitational lensing, could be accounted for by an unknown force that for whatever reason is at the moment undetectable to us, it could be an aspect of the gravitational force that we are currently unaware of, or possibly even some unknown form of physics we simply haven't thought about yet.

Nonsymmetric gravitational theory - Wikipedia, the free encyclopedia
Tensor-vector-scalar gravity - Wikipedia, the free encyclopedia

Also, the wiki article mentions something about the dark matter ring you were talking about;

Dr. Myungkook James Jee and his colleagues announced on May 15, 2007 the discovery of a wispy ring of dark matter 2.6 million light-years wide that envelopes CL0024+17, a huge cluster of galaxies about 5 billion light-years away[9]. Their observation of the dark matter was by way of its gravitational lensing effect on light coming from behind the galaxy cluster as seen by the now broken Hubble Space Telescope's Advanced Camera for Surveys (ACS). Richard Massey, Cal Tech publisher of a dark matter map for a half million galaxies, notes that this announcement only comes from one instrument and that "the signal is very weak. Some people are not yet convinced it's more than an artifact." Confirming studies may need to wait until the James Webb Space Telescope is launched in 2013 unless the Hubble's ACS is repaired by a shuttle mission.

Emphasis mine.
If the observation is repeatable, then it's good evidence in favour of the dark matter hypothesis. However, it in no way confirms the existence of dark matter, for that we would need to go out there with a big jar and take a sample .

 

[Willamena]

It may be a semantical distinction. Evidence that supports the theory of gravity can be said to "confirm gravity."

 

[Halcyon]

It may be a semantical distinction. Evidence that supports the theory of gravity can be said to "confirm gravity."

I see what you mean, but no, in this case its a scientific distinction.

See, with the theory of gravity i think you may be confusing the observable effect with the cause of that effect. What we call the "force" of gravity is simply the product of an interaction, it has a cause which still remains unknown to us.
The cause of gravitational attraction may be the hypothetical graviton, but its just a guess, an idea, an imaginative answer to what the cause may be.

Dark matter is the same as the graviton, a hypothetical answer to the cause of anomalous mass vs gravitational discrepancies.
All the evidence we currently have, including the recent stuff, doesn't lend anymore credence to the hypothesis of Dark Matter being correct than it does for TeVeS - its just more evidence for "something".
Just like, no matter how many times you drop a brick off a building, all the evidence you collect for the existence of a gravitational attraction won't ever confirm the real-life existence of the graviton.

Am I making sense?

So what i am saying is, that for the article to declare the "void" lacks dark matter, is the scientific equivalent of a historian declaring the Mary Celeste was caused by an unknown group of pirates, and then going on to suggest that these pirates are also responsible for all other mysterious ship wrecks and maritime disappearances. It's taking a hypothesis as fact, making assumptions and jumping to conclusions.