Comments on: Evolving dark energy? http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/ Random samplings from a universe of ideas. Thu, 08 Jan 2009 11:23:33 +0000 http://wordpress.org/?v=2.3.1 By: Cosmology at Professor Cormac O’Raifeartaigh’s blog « Gauge theory mechanisms http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9942 Cosmology at Professor Cormac O’Raifeartaigh’s blog « Gauge theory mechanisms Sat, 16 Aug 2008 14:27:52 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9942 [...] However, in 1998 the cosmological constant (albeit with a much smaller magnitude than Einstein had stipulated) had to be taken back into the field equation to account for the observed lack of gravitational curvature on the largest distances. The exact value is still hazy, but the approximate order of magnitude is well established: it’s certain from the evidence that there is cosmological acceleration on the order of 10^{-10} m/s^2 or so at large redshifts. There is some uncertainty from gamma ray burster evidence over whether the cosmological acceleration actually implies a cosmological constant or an evolving parameter: http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/ [...] […] However, in 1998 the cosmological constant (albeit with a much smaller magnitude than Einstein had stipulated) had to be taken back into the field equation to account for the observed lack of gravitational curvature on the largest distances. The exact value is still hazy, but the approximate order of magnitude is well established: it’s certain from the evidence that there is cosmological acceleration on the order of 10^{-10} m/s^2 or so at large redshifts. There is some uncertainty from gamma ray burster evidence over whether the cosmological acceleration actually implies a cosmological constant or an evolving parameter: http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/ […]

]]> By: light dimmer http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9941 light dimmer Wed, 04 Apr 2007 13:17:21 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9941 <strong>light dimmer</strong> leave alone spending time on their computers spamming people for light dimmer

leave alone spending time on their computers spamming people for

]]> By: Elliot http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9940 Elliot Thu, 02 Feb 2006 17:29:34 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9940 cox, your questions contain some myths that need to be addressed before they can be answered. 1) the speed of light is constant (the same) for all colors, the frequency and wavelength change but not the speed. 2) there is no physical parameter called "speed of sight". It is just the speed of light + the processing of the light by the eye and nervous system. Not a meaningful parameter to consider. 3) Temperature does not have an affect on the speed of light. So there is a high degree of confidence that distances to stars are not exaggerated by this. 4) Mars is red because the material it is composed of. Therefore it would look the same from Earth and Mars. Hope that helps. cox,

your questions contain some myths that need to be addressed before they can be answered.

1) the speed of light is constant (the same) for all colors, the frequency and wavelength change but not the speed.

2) there is no physical parameter called “speed of sight”. It is just the speed of light + the processing of the light by the eye and nervous system. Not a meaningful parameter to consider.

3) Temperature does not have an affect on the speed of light. So there is a high degree of confidence that distances to stars are not exaggerated by this.

4) Mars is red because the material it is composed of. Therefore it would look the same from Earth and Mars.

Hope that helps.

]]> By: cox http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9939 cox Thu, 02 Feb 2006 17:19:15 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9939 if different colors reflect different light speeds then why does mars appear red when viewed from earth and also appears red when viewed from mars? what is actually the speed of light or for that matter the speed of sight when considered that light breaks up into the spectrum when passed through a prism? is the speed of sight a significant variable previously ignored? is temperature a variable to the speed of light? are our measurements of star distances highly exaggerated because of the unknown extreme cold in outer space? if different colors reflect different light speeds then why does mars appear red when viewed from earth and also appears red when viewed from mars? what is actually the speed of light or for that matter the speed of sight when considered that light breaks up into the spectrum when passed through a prism? is the speed of sight a significant variable previously ignored? is temperature a variable to the speed of light? are our measurements of star distances highly exaggerated because of the unknown extreme cold in outer space?

]]> By: The future of the universe | Cosmic Variance http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9938 The future of the universe | Cosmic Variance Thu, 26 Jan 2006 16:13:30 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9938 [...] This month’s provocative results on the acceleration of the universe raise an interesting issue: what can we say about our universe’s ultimate fate? It the old days (like, when I was in grad school) we were told a story that was simple, compelling, and wrong. It went like this: matter acts to slow down the expansion of the universe, and also to give it spatial curvature. If there is enough matter, space will be positively curved (like a sphere) and will eventually collapse into a Big Crunch. If there is little matter, space will be negatively curved (like a saddle) and expand forever. And if the matter content is just right, space will be flat and will just barely expand forever, slowing down all the while. [...] […] This month’s provocative results on the acceleration of the universe raise an interesting issue: what can we say about our universe’s ultimate fate? It the old days (like, when I was in grad school) we were told a story that was simple, compelling, and wrong. It went like this: matter acts to slow down the expansion of the universe, and also to give it spatial curvature. If there is enough matter, space will be positively curved (like a sphere) and will eventually collapse into a Big Crunch. If there is little matter, space will be negatively curved (like a saddle) and expand forever. And if the matter content is just right, space will be flat and will just barely expand forever, slowing down all the while. […]

]]> By: Paul Valletta http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9937 Paul Valletta Thu, 26 Jan 2006 00:52:07 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9937 A new take on Matter's: http://arxiv.org/abs/astro-ph/0601517 The authors delve into things, and cite Sean's paper. A new take on Matter’s: http://arxiv.org/abs/astro-ph/0601517

The authors delve into things, and cite Sean’s paper.

]]> By: Sean http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9936 Sean Wed, 25 Jan 2006 20:51:41 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9936 Shantanu, newer data are certainly better: see <a href="http://arxiv.org/abs/astro-ph/0309368" rel="nofollow">astro-ph/0309368</a> or <a href="http://arxiv.org/abs/astro-ph/0402512" rel="nofollow">astro-ph/0402512</a>. And they certainly don't rule out all cosmologies; they're perfectly consistent with ordinary LambdaCDM. But supernovae by themselves are not extremely statistically significant indicators of the existence of dark energy; I don't know how many sigma, but it's just a few. But that's because you can come close to fitting them if you assume the universe is nearly empty of matter and highly spatially curved. And we know those things just aren't true: we've measured the matter density from dynamics, and the CMB tells us that there is not appreciable spatial curvature. In a flat universe, the supernovae require dark energy at more than ten sigma. Shantanu, newer data are certainly better: see astro-ph/0309368 or astro-ph/0402512. And they certainly don’t rule out all cosmologies; they’re perfectly consistent with ordinary LambdaCDM.

But supernovae by themselves are not extremely statistically significant indicators of the existence of dark energy; I don’t know how many sigma, but it’s just a few. But that’s because you can come close to fitting them if you assume the universe is nearly empty of matter and highly spatially curved. And we know those things just aren’t true: we’ve measured the matter density from dynamics, and the CMB tells us that there is not appreciable spatial curvature. In a flat universe, the supernovae require dark energy at more than ten sigma.

]]> By: Shantanu http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9935 Shantanu Wed, 25 Jan 2006 19:58:16 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9935 Sean, how strong is the statistical evidence for dark energy from ONLY type 1a SN(with latest data)? In astro-ph/0207347 (which probably includes data up to 2001 or so) they claim the evidence is only 2 sigma. Recently astro-ph/0511628 claims that the latest SN data rule out all cosmologies. so question is how strong is the statistical evidence dor dark energy from the latest SN data ONLY? Sean, how strong is the statistical evidence for dark energy from ONLY type 1a SN(with latest
data)? In astro-ph/0207347 (which probably includes data up to 2001 or so) they claim the evidence is only 2 sigma.
Recently astro-ph/0511628 claims that the latest SN data rule out all cosmologies.
so question is how strong is the statistical evidence dor dark energy from the latest SN data ONLY?

]]> By: Cycle Quark » Can Gamma Ray Bursts Be Used to Measure Dark Energy http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9934 Cycle Quark » Can Gamma Ray Bursts Be Used to Measure Dark Energy Thu, 19 Jan 2006 04:32:35 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9934 [...] I found that one of the best explanations can be found at Cosmic Variance. It even has a comment from Schaefer. This result is based on 52 gamma ray bursts. This actually compares favorably with the original dark energy paper using supernovae that had 42 supernova. Interestingly, Schaefer has found more than one way to measure the luminosity for each gamma ray burst, so that he gets 172 independent measures of the luminosity. In his paper he lists other attempts to do this type of measurement and the other groups have always restricted themselves to one luminosity indicator per gamma ray burst. [...] […] I found that one of the best explanations can be found at Cosmic Variance. It even has a comment from Schaefer. This result is based on 52 gamma ray bursts. This actually compares favorably with the original dark energy paper using supernovae that had 42 supernova. Interestingly, Schaefer has found more than one way to measure the luminosity for each gamma ray burst, so that he gets 172 independent measures of the luminosity. In his paper he lists other attempts to do this type of measurement and the other groups have always restricted themselves to one luminosity indicator per gamma ray burst. […]

]]> By: Cycle Quark » Can Gamma Ray Bursts Be Used to Measure Dark Energy http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9933 Cycle Quark » Can Gamma Ray Bursts Be Used to Measure Dark Energy Thu, 19 Jan 2006 04:31:48 +0000 http://blogs.discovermagazine.com/cosmicvariance/2006/01/11/evolving-dark-energy/#comment-9933 [...] I found that one of the best explanations can be found at Cosmic Variance. It even has a comment from Schaefer. This result is based on 52 gamma ray bursts.  This  actually  compares  favorably with the original  dark energy paper using supernovae that had 42 supernova. Interestingly, Schaefer has found more than one way to measure the luminosity for each gamma ray burst, so that he gets 172 independent measures of the luminosity. In his paper he lists other attempts to do this type of measurement and the other groups have always restricted themselves to one luminosity indicator per gamma ray burst. [...] […] I found that one of the best explanations can be found at Cosmic Variance. It even has a comment from Schaefer. This result is based on 52 gamma ray bursts.  This  actually  compares  favorably with the original  dark energy paper using supernovae that had 42 supernova. Interestingly, Schaefer has found more than one way to measure the luminosity for each gamma ray burst, so that he gets 172 independent measures of the luminosity. In his paper he lists other attempts to do this type of measurement and the other groups have always restricted themselves to one luminosity indicator per gamma ray burst. […]

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