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ToSeek
2006-Jan-11, 05:19 PM
Gamma-ray burst study may rule out cosmological constant (http://www.newscientistspace.com/article.ns?id=dn8566&feedId=online-news_rss20)


Dark energy the mysterious force that drives the acceleration of the universe changes over time, controversial new calculations suggest. If true, the work rules out Einstein's notion of a "cosmological constant" and suggests dark energy, which now repels space, once drew it together.
...
Now, astronomer Bradley Schaefer of Louisiana State University in Baton Rouge, US, has used observations of 52 GRBs to suggest that dark energy has changed over time.

In the largest GRB study of its kind, Schaefer found that 12 of the most distant GRBs lying nearly 13 billion light years away were all brighter than expected, suggesting the universe was expanding at a slower rate than it is today.

(I met Brad when he was an astronomer at Goddard - he's a real go-getter.)

peteshimmon
2006-Jan-11, 06:33 PM
Mmmm...does the width of the very short GRBs
show progressive widening at increasing
red shift? For those that have had a red shift
measured in the apparent host galaxy that is.

Kullat Nunu
2006-Jan-11, 08:16 PM
The Bad Astronomer (http://www.badastronomy.com/bablog/2006/01/11/aas-post-6-the-cosmological-not-so-constant/) has a long and interesting blog entry about this.

If the acceleration itself is accelerating, does that mean that the universe is becoming empty even faster?

Blob
2006-Jan-11, 09:11 PM
Hum,
New evidence is highly speculative.
Though if it were true, we would have to find some mechanism that dims the 1a supernova data, dims the intrinsic size and brightness of those galaxies, and also affects the gravitational lensing distances at large distances.
(The 1a and intrinsic brightness data from early galaxies show that dark energy kicked in about 6 billion years ago.)

So if that were wrong, then it should be said that the new GBR data although plotted below Lambda, still would mean that the universe could expand forever, though, it would rule out a Big Rip.

Spherical
2006-Jan-11, 09:26 PM
Does any of this jibe with what the Quantum Loop Gravity guy are saying?

http://www.edge.org/3rd_culture/smolin03/smolin03_p4.html

peteshimmon
2006-Jan-14, 12:30 AM
Well it was a rhetorical question. I am
reminded of a short paper on Quasars some
30 years ago. It investigated whether variations
in brightness of a few quasars were intrinsically
slower at increasing redshifts. There were
gaps in the data but interpolation solved that.
Then the magical deconvolution or something
indicated the hypothesis was correct. And the
investigators got their brownie points!

Ken G
2006-Jan-14, 05:01 AM
What I didn't understand is, why did he have a curve for just one value of the cosmological constant? So is he trying to rule out any cosmological constant value, or just the popular one?
And is it really true that he can constrain not only the acceleration, but the acceleration of the acceleration, with 52 GRBs, which are notoriously varied in their properties? You can count me very skeptical.

Bob
2006-Jan-14, 07:52 PM
There was an article about this announcement in the science section of the NY Times on Tuesday the 10th. The announcement was received as very close to dead on arrival by other astronomers in this area of research. As well as skepticism about predictable intrinsic brightness of GRBs there were accusations of mathematical errors as well. Peer review can be brutal.

iron4
2006-Jan-15, 02:49 AM
It's really curious, I remember an article barely a month and a half ago about another study showing that the Cosmological constant was the main candidate, as the study showed that the density of Dark energy has been constant over time

I'm talking about this article (http://www.sciam.com/article.cfm?chanID=sa003&articleID=00023144-9B65-1383-9A5083414B7FFE87)

The Bad Astronomer
2006-Jan-15, 03:10 AM
"Dead on arrival" is too harsh. I know some astronomers who have been loudly declaring this result to be wrong. I disagree with them, strongly.

It might be right. It might not. But right now, we don't know. To declare it wrong at this point is prejudicial at best. The best thing to do here is collect more data, and that's something Swift will do (and INTEGRAL, and HETE-2).

Bob
2006-Jan-15, 05:43 PM
Scientists quoted the article:
"I flat out don't believe this result."
"At large distances the parameter (w-prime, used by Dr Schaeffer) becomes mathematically meaningless."
If Dr Schaeffer's result is eventually verified such quotes will make it all the sweeter for him.
Here is a link to the Times article:

http://www.nytimes.com/2006/01/12/science/12cosmos.html

Fortunate
2006-Jan-15, 09:36 PM
I like the fact that people try things like this. No harm done if nothing comes of it. Using gamma ray bursts as cosmic measuring sticks? - interesting idea. Even if the method can't ever be refined to measure the rate of acceleration, it might help us learn more about variations in gamma ray bursts.

Ken G
2006-Jan-18, 07:10 PM
But note there is something inherently unscientific about over-interpreting data. It's more like pseudoscience, and here is how it works. Imagine a fairly obscure researcher, who analyzes some data in a way that doesn't really stand up. This means he still gets a result, but it is essentially a random result. Does this mean it has to be wrong? Of course not! It could actually be right. Here's the pseudoscience-- if it turns out to be wrong, everyone forgets about it, but that's no skin off the back of the obscure scientist who was not going to be remembered by history anyway. However, if by chance the result is correct, that astronomer can lay claim to a huge discovery, despite the random analysis process. The only defense against this is to analyze the analysis, and if it doesn't hold water, then it doesn't matter if it's right or not. So the question isn't whether the research is right, it's whether it's good. I can't speak to that, not knowing the details, but it sounds pretty hokey to me.

Thanatos
2006-Jan-19, 08:07 AM
It more likely suggests, IMO, we have much to learn about GRB's:

http://arxiv.org/abs/astro-ph/0601252
Missing GRB host galaxies in deep mid-infrared observations: implications on the use of GRBs as star formation tracers

jfribrg
2006-Jan-19, 09:14 PM
How do these GRB's compare with MOND-based predictions?