[2012.02.18] The dark side of the universe 宇宙的黑暗面

yannanchen

it has to have a very particular density—which in relativity is a measure not just of the mass contained in a certain volume, but also of the energy. 用相对论可以算出只有在宇宙的密度处于一个特定值时，宇宙才会是平坦的。相对论里的密度不仅是对单位体积内质量的测量，也包括了该体积内的能量。

原文里没有单位体积的意思

rhineyuan

马克~

悠悠万事97

回复 nayilus 的帖子

nayilus  嗯，因为robust是数学里一个很重要的概念，指一些参数有误差的情况下依然成立，似乎就是翻为灵活。  发表于 5 分钟前

Robust 数学上似乎译为“稳健”

nayilus

回复 悠悠万事97 的帖子

What the Supernova Cosmology Project and the High-z Supernova Search both found, and what others have later confirmed, is that distant exploding stars are dimmer, and so farther away, than their redshift implies they should be if the universe has been expanding at a steady clip throughout.超新星宇宙学计划和高红移超新星搜寻计划都发现了同一现象，后来也得到了其它研究项目确证，那就是遥远的超新星亮度比预期要暗。这说明以宇宙整体膨胀速度恒定为前提，从这些超新星的红移程度所算出的它们和地球的距离比真实距离要小。[感觉这里译文与原文有些误差]，建议：
超新星宇宙学计划和高红移超新星搜寻计划发现的同一现象是：如果宇宙的膨胀速度保持恒定，则遥远的超新星的亮度比其红移现象所显示的更为暗淡，也就是说更为遥远。[感觉在这里，宇宙的膨胀速度不是空间的函数，而是时间的函数，因此有后面的话：宇宙的膨胀速度一定在近期增加了]

这句简单分析一下

红移取决于光源离地球远去的速度，假设速度恒定，根据红移可以算出超新星的距离和远去的速度。但是这两项研究计划发现超新星的实际亮度，比根据红移算出的距离所应有的亮度暗。也就是说实际距离比假设膨胀速度恒定下根据红移计算出来的距离要远，这就说明膨胀在光离开光源之后加速了。

所以“如果宇宙的膨胀速度保持恒定”这句不能挂在全句前面，这是红移现象imply的距离的前提。

for instance by looking at how hot clouds of gas get as they are pulled towards the cluster’s dark-matter core by its gravity. 例如可以通过观察高温气体云受到星系团核心内的暗物质引力吸引的过程来进行推算。
例如可以通过观察气体云受到星系团核心内的暗物质引力吸引过程中达到多高的温度来推算。

这句糗大了，多谢指出

yannanchen

Any new theory, then, has its work cut out—which has not, of course, stopped theorists trying.所以任何新的理论能够适用的范围其实不多，当然，这并没有阻止理论物理学家进行尝试。
能够适用的范围其实不多？？？
have your work cut out (for you)
if you have your work cut out, you have something very difficult to do We're training a completely new team, so we've got our work cut out for us. (often in future tenses) Have you seen the state of the garden? She'll have her work cut out to get it looking nice in time for the summer.

yannanchen

With the photons no longer willing to play, there could be no more baryon-photon fluid. The baryons were stuck in position. Where the oscillations in the fluid had bunched the baryons tightly, they remained bunched; where they had been rarefied they remained sparse. The higher density regions became the seeds of galaxies—and the average separation of those galaxies thus reveals the wavelength of the oscillations in the primordial fluid. That characteristic scale has been stretched out to around 450m light years; measuring it at earlier times is another way to show how quickly the universe has been expanding. 因为光子的脱离，重子－光子流体也不复存在了。重子被困在各自当时的位置上。重子光子分离时流体内重子密集的地方之后会一直保持其高重子密度，而当时流体里重子稀疏的地方则会一直保持在低重子密度状态。那些高密度地区就是后来演变出星系的种子。因此，从星系之间的平均距离可以估算出原始流体内的振动波长。这一特征长度现在已经延展到大约4亿5000万光年了。测量在宇宙早期该长度多大可以得出宇宙膨胀的速度。
评论：Where the oscillations in the fluid had bunched the baryons tightly, they remained bunched; 这里谈的是上一段提到的baryon-acoustic oscillations (BAO).
我们知道空气中声波的传递是一种纵波， 因为传递的方向跟空气质点的振动方向平行。从声源开始， 声波以疏波和密波交替的形式传出。两个最靠近的密波（或疏波）之间的距离就是波长。
以重子组成的流体， 就像空气一样， 大爆炸时， 也是以疏波和密波交替的形式传递爆炸。疏波和密波因光子的逃逸，随后固定下来。
这句译成：重子光子分离时流体内重子密集的地方之后会一直保持其高重子密度。不完全尽意。
流体中的振动把重子挤到一堆的地方，重子随后保持了扎堆的状态。

yannanchen

The higher density regions became the seeds of galaxies—and the average separation of those galaxies thus reveals the wavelength of the oscillations in the primordial fluid. That characteristic scale has been stretched out to around 450m light years; measuring it at earlier times is another way to show how quickly the universe has been expanding.

这里， average separation = wavelength = characteristic scale
特征尺度

yannanchen

This could help answer the question whether expansion is down to dark energy alone, in which case physicists expect a correlation between results from all four techniques, or to modified gravity, if the last two do not square with the first two.这些结果可以帮助研究者理解宇宙的膨胀是否单纯由于暗能量引起，还是引力修正也有贡献。如果暗能量要付全责，那么物理学家应该在四个方法的结果中找到一致性，而如果引力修正也有贡献，那么后两个方法的结果将和前两个方法的结果相驳。

评论：原文等于= This could help answer the question whether expansion is down to dark energy alone, in which case physicists expect a correlation between results from all four techniques, or in which case physicists expect a correlation to modified gravity, if the last two do not square with （=correlate with） the first two。

原译：而如果引力修正也有贡献，那么后两个方法的结果将和前两个方法的结果相驳。？？？
如果后两个方法的结果和前两个方法的结果不一致， 那么物理学家就会期待跟引力修正相关。

nayilus

回复 yannanchen 的帖子

这里我的理解是流体中的密度是周期变化的，时高时低，某一特定时刻某些地方的重子密度高，某些地方低，但是光子一旦离开，流体就等于冻住了。那一瞬间高密度的地区就会一直保持高密度，反之亦然。考虑怎么修改更易于理解。

ecocnbell

as perplexing as any that faces physics 为何译为“最...”？