博客李淼

一段时间以来，暗能量被许多人认为可能是phantom，就是说，能量密度会随时间变得越来越大。最早从超新星数据看出这个的是Huterer和Cooray,（文章），接着张新民等人也号称看到了，并且引进了一种所谓quintom（精灵）模型（文章），我直到不久之前还将信将疑，因为phantom在理论上很难实现，需要一种不稳定标量场，当然，我的全息暗能量模型也能容纳phantom。

现在，有人声称射线爆的数据也支持一个随着时间变化而增大的暗能量了，可信度大约是97%。这是第三次有人说虎来了，我不由得相信起来。张新民私下跟我开玩笑，现在的自然科学二等奖实在没有得头，要得就得一等奖，如果暗能量果真是phantom，他倒真的有希望。我更希望我的全息暗能量是对的，哪怕是phantom

在宇宙学中，这是一个需要奇迹也产生奇迹的时代。Michael Turner在Brad Schaefer的记者招待会后说：”It’s an exciting time to be an astronomer. The mysteries run — literally — from our own back yard to the edge of the Universe.”

也许，可怕的幻影（phantom）真的来了：

（13日：刚收到张鑫的一个email：
最早从超新星数据中看出w从>-1变化到<-1的应该是Ujjaini Alam, Varun Sahni, A. A. Starobinsky的文章
astro-ph/0403687。从他们的文章的图中可以清楚看到这一点，暗能量的能量密度的演化行为是先变小再变大。
Dragan Huterer和Asantha Cooray的文章稍微晚了一点点(astro-ph/0404062)。我那天做报告时可能将他们的次序列颠倒了，呵呵。）

刚刚看到Brad Schaefer在Carroll的blog上的发言，转载如下，希望能够帮助对此感兴趣的人（这是blog帮助研究的一个好例子）

Brad Schaefer on Jan 12th, 2006 at 12:56 pm
Sean has pointed me to this blog and requested me to send along any comments that I might have. His summary at the top is reasonable.
I’d break my results into two parts. The first part is that I’m putting forward a demonstration of a new method to measure Dark Energy by means of using GRBs as standard candles out to high red shift. My work is all rather standard with most everything I’ve done just following what has been in the literature.
For this, what is new is that I am using

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Brad Schaefer on Jan 12th, 2006 at 1:29 pm
****Oops, this message is broken up by my accidently hitting a return after a tab. The network link here at the AAS meeting is slow and balky. The message will now be continued****

The GRB Hubble Diagram has been in print since 2003, with myself and Josh Bloom independently presenting early version in public talks as far back as 2001. Over the past year, several groups have used the GRB Hubble Diagram to starting putting constraints on cosmology. This prior work has always used only one GRB luminosity indicator (various different indicators for the various papers) and for no more than 17 GRBs (neglecting GRBs with only limits).

What I am doing new is I am using much more data and I’m directly addressing the question of the change of the Dark Energy. In all, I am using 52 GRBs and each GRB has 3-4 luminosity indicators on average. So I’ve got a lot more data. And this allows for a demonstration of the GRB Hubble Diagram as a new method.

The advantages of this new method is that it goes to high redshift, that is, it looks at the expansion history of the Universe from 1.7-6.3 in redshift. It is impervious to extinction. Also, I argue that there should be no evolution effects as the GRB luminosity indicators are based on energetics and light travel time (which should not evolve). Another advantage is that we have the data now, with the size of the data base to be doubled within two years by HETE and Swift.

One disadvantage of the GRB Hubble Diagram is that the GRBs are lower in quality than supernovae. Currently my median one sigma error bar is 2.6-times worse in comparing a single GRB and a single supernova. But just as with supernovae, I expect that the accuracy of GRB luminosities can be rapidly improved. [After all, in 1996, I was organizing debates between the gradaute students as to whether Type Ia SNe were standard candles or not.] Another substantial problem that is hard to quantify is that our knowledge of the physical processes in GRBs is not perfect (and certtainly much worse than what we know for SNe). It is rational and prudent for everyone to worry that there are hidden problems (although I now know of none). A simple historical example is how Cepheids were found to have two types with different calibrations.

So the first part of my talk was simply presenting a new method for getting the expansion histoy of the Universe from redshifts up to 6.3. For this, it is pretty confident that the method will work. Inevitably there will be improvements, new data, corrections, and all the usual changes (just as for the supernova).

The second part of my talk was to point out the first results, which I could not avoid giving. It so happens that the first results point against the Cosmological Constant. I agree with Sean that this second part should not be pushed, for various reasons. Foremost is that the result is only 2.5-sigma.

Both parts of my results are being cast onto a background where various large groups are now competing for the a new dedicated satellite.

这篇文章发表于 2006年1月12日, 星期四 7:14:02，属于分类 宇宙学。 你可以查看 HTML打印版 或通过 新闻聚合(RSS) 来追踪这篇文章的最新评论。 在文章后 发表评论。