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trinitree88
2012-Jul-09, 06:01 PM
I'm titling this paper KBCW2T, for the first letters of the authors last names. What they've done is check the galactic near infrared luminosity function for a very large sample ( 1436) ..of galaxies to see if the there is an underdensity (a void )...nearby, and if that could lead one to surmise that the type 1a supernovae samples might then make it seem like the expansion of the universe is accelerating. Yep, it does. The survey is not quite complete, but there is at least a hint that a retraction of dark energy might be in the offing. That'd mean a lot of people will read this paper...hence the acronym. Interesting. pete

SEE:http://arxiv.org/abs/1207.1588

Tensor
2012-Jul-10, 06:00 AM
The survey is not quite complete, but there is at least a hint that a retraction of dark energy might be in the offing.

Really, Pete?


More importantly, however, we require knowledge of the luminosity density at z > 0.1 to understand whether or not the local universe is under-dense.

We find that measurements of the NIR LF at z > 0.1, including our own, are still too uncertain to provide a robust comparison with lower redshift measurements.

While inconclusive, this result is noteworthy given the possible implications for locally measured cosmological observables.

What parts of those quotes from the paper hint at a retraction? Yeah, their interpretation of the data indicates it's possible, but the other studies they include indicate it isn't. Except for Feulner, 2003 in the J and K bands. So that makes 2 out of 9.

trinitree88
2012-Jul-10, 03:41 PM
Really, Pete?



What parts of those quotes from the paper hint at a retraction? Yeah, their interpretation of the data indicates it's possible, but the other studies they include indicate it isn't. Except for Feulner, 2003 in the J and K bands. So that makes 2 out of 9.

Tensor. First off, I make few posts about galaxy theory. There are numerous forum experts (Nereid et al ) who have done the ten thousand hours thing, and are far more knowledgeable. But, I found the paper interesting, and will courteously try to reply to your comments.

1. From the abstract to the paper: " Recent cosmological modeling efforts have shown that a local underdensity on scales of a few hundred Mpc (out to z~ 0.1), could produce the apparent acceleration of the expansion of the universe observed via type1a supernovae) .......sentence #1, title page, their comment not mine....
2. also from the abstract: "Several studies of galaxy counts in the near infrared (NIR) have found that the local universe appears underdense by ~ 25-50% compared with regions a few hundred Mpc distant......they endnote them, and caveat it with no claim of all studies, their words, not mine.
3. In the paper, page 2, paragraph2..." In particular, so called 'minimal void'scenarios (e.g. Alexander et.al.2009, Bolejko and Sussman 2011) have shown that very simple models that place the observer near the center of a void that is ~ 250 h-1 Mpc in radius (to z~ 0.1), and ~ 50% underdense compared to its surroundings are sufficient to explain the apparent acceleration observed via type1a supernovae....." (something I do know a bit about)
4. page 17 Section 6, summary. paragraph 3, last sentence: Our measurement of (phi*L*)for 0.1 < z < 0.3 could be considered a conservative underestimate of the true value (they got ~ 30%) because we avoid known galaxy clusters in this redshift range....(a data cut which they are entitled to make)

So when they finish their survey, I'm looking forward to see if they can wash away the accelerating universe...or not.. just like you, and everybody else is. I claimed nothing they didn't imply, they're just not @ sigma 5 yet. clear skies... pete

antoniseb
2012-Jul-10, 05:17 PM
I have pulled this out of the Fun Papers Thread to give it some discussion space.

And I merged the annoucement of the pulling with the actual pulled posts - Swift

Tensor
2012-Jul-10, 07:25 PM
Tensor. First off, I make few posts about galaxy theory. There are numerous forum experts (Nereid et al ) who have done the ten thousand hours thing, and are far more knowledgeable. But, I found the paper interesting, and will courteously try to reply to your comments.

1. From the abstract to the paper: " Recent cosmological modeling efforts have shown that a local underdensity on scales of a few hundred Mpc (out to z~ 0.1), could produce the apparent acceleration of the expansion of the universe observed via type1a supernovae) .......sentence #1, title page, their comment not mine....
2. also from the abstract: "Several studies of galaxy counts in the near infrared (NIR) have found that the local universe appears underdense by ~ 25-50% compared with regions a few hundred Mpc distant......they endnote them, and caveat it with no claim of all studies, their words, not mine.
3. In the paper, page 2, paragraph2..." In particular, so called 'minimal void'scenarios (e.g. Alexander et.al.2009, Bolejko and Sussman 2011) have shown that very simple models that place the observer near the center of a void that is ~ 250 h-1 Mpc in radius (to z~ 0.1), and ~ 50% underdense compared to its surroundings are sufficient to explain the apparent acceleration observed via type1a supernovae....." (something I do know a bit about)
4. page 17 Section 6, summary. paragraph 3, last sentence: Our measurement of (phi*L*)for 0.1 < z < 0.3 could be considered a conservative underestimate of the true value (they got ~ 30%) because we avoid known galaxy clusters in this redshift range....(a data cut which they are entitled to make)

So when they finish their survey, I'm looking forward to see if they can wash away the accelerating universe...or not.. just like you, and everybody else is. I claimed nothing they didn't imply, they're just not @ sigma 5 yet. clear skies... pete

No problem Pete, I just didn't see anything close (even in the above) that would allow them to say even a hint of a retraction was in the offing. That's why I asked. I just thought I missed something. I now see that we are just interpreting their data and conclusions differently, tis cool. I also look forward to the rest of the data and more, the investigating of the LF a z > .1 for the comparison.

Cougar
2012-Jul-12, 12:26 PM
Thus, if the local universe is under-dense, then the normalization of the NIR galaxy luminosity function (LF) at z>0.1 should be higher than that measured for z<0.1.

How does a local under-density cause the light from distant Type Ia supernovae to reach maximum brightnesses approximately 25 percent fainter than the peak brightnesses they would attain in a universe with a cosmological constant equal to zero?

StupendousMan
2012-Jul-12, 01:21 PM
The basic idea is that, if the local universe is under-dense, then it expands more rapidly than the surrounding volume. That causes distant objects to be carried away from us at an increasingly fast rate -- which _looks_ the same as an accelerating expansion rate due to lambda.

Don J
2012-Jul-13, 07:29 PM
The basic idea is that, if the local universe is under-dense, then it expands more rapidly than the surrounding volume. That causes distant objects to be carried away from us at an increasingly fast rate -- which _looks_ the same as an accelerating expansion rate due to lambda.
Does that mean that this study provide a physical mechanism proving that the accelaration of the expansion of the Universe is in reality only an illusion ?

Cougar
2012-Jul-13, 07:41 PM
Does that mean that this study provide a physical mechanism proving that the accelaration of the expansion of the Universe is in reality only an illusion ?

Apparently you missed that "if" in StupendousMan's response:


....if the local universe is under-dense, then it expands more rapidly than the surrounding volume. That causes distant objects to be carried away from us at an increasingly fast rate -- which _looks_ the same as an accelerating expansion rate due to lambda.