开始翻译 Einstein@Home 主题站

Youth

Have we had any positive detections of gravitational waves other than the detection of their effects?

有没有直接探测到过引力波而不是探测其效应？

Submitted by Phillip from Canada

由来自加拿大的Phillip提交

Not yet. We just passed the thirtieth anniversary of the discovery of the first indirect evidence, two neutron stars orbiting each other whose orbit has been shrinking at precisely the rate it should due to recoil from gravitational waves. And nowadays we know of a lot more systems like that one. But we haven't directly detected the waves.

还没有。第一次对引力波的间接的证明是在观察互相绕对方旋转的双中子星时找到的，双星轨道的收缩速度精确地符合由引力波导出的收缩速度。从那时到现在已经13年了，我们还找到了大量其它类似的系统，但我们仍然没有直接探测到引力波。

The next question is probably "When do we expect to detect something?" That depends who you ask, and the answers vary so widely that the bookies at Ladbrokes cut off betting on it. There is a small chance we'll see something in the next five years, and a very good chance after that when some upgrades are made to LIGO and the LISA spacecraft (think "LIGO in space") are launched. By that time a lack of detection would be more revolutionary than a detection!

下一个问题可能就是“那我们什么时候才能探测到些什么？”。这要看你在问谁，答案如此多样，以至于立博公司的那些经纪人也会拒绝下注。在接下来的五年我们能看到些什么的几率不大，但在那之后，当LIGO升级、LISA飞船（可以认为就是太空中的LIGO）发射后，我们的机会将大很多。如果到那时还什么都探测不到，那就比只探测到哪怕一个信号都更具有革命性！

Why the big uncertainty? Basically, the kinds of things that make gravitational waves (at frequencies LIGO can see) are things we don't know much about with other observations. Radio astronomers can tell us all sorts of things about a couple thousand neutron stars in our galaxy, and x-ray and other astronomers can tell us about a few more.

为什么会有这么大的不确定性？基本上我们对于产生引力波（在LIGO可以看见的频率范围）的事物的了解并不像其它观测手段那样多。射电天文学家可以告诉我们银河系中几千个中子星的各类属性，X射线或其它天文学家也能告诉我们其它更多的。

But only a handful of neutron stars are paired up with other neutron stars that are close enough to show the indirect evidence of gravitational waves. Based on our knowledge of the life cycles of stars, we expect that there are a lot more pairs that are not seen with radio or anything else. You can try to leverage that handful that are seen to estimate the population that is invisible to radio but not to LIGO, but there are huge uncertainties. It's like trying to estimate the demographics of the United States from a sample of ten Americans, and they were chosen from a bodybuilders' convention so you know it's not a representative sample.

但是只有少量的中子星是和其它中子星靠得足够近并显示出引力波存在的证据。根据我们对恒星生命周期的了解，应该还有非常多的不能通过射电或其它方法看到的双星。你可以试图去估计有多少中子星是用射电方法看不到而LIGO可以看到的，但这有非常大的不确定性。这就好比你想通过十个体形相当的美国人来估算美国的人口，这样的样例显然是不具有代表性的。

If you try to guess how many isolated neutron stars are emitting gravitational waves (the ones Einstein@Home is searching for), it's even harder because less is known. The same goes for black holes, supernova explosions, and so on. But if you turn that around, it means when we do detect gravitational waves we'll be learning information that can't be learned any other way, which makes it much more interesting.

如果你试图猜测有多少中子星正在放射出引力波（也就是我们在Einstein@Home项目中所寻找的），这将会相当困难，因为我们对它们几乎没有什么了解。类似的还有黑洞、超新星等等。但如果你反过来想想，这也意味着如果我们探测到引力波，我们将能开始了解这些目前还不能通过其它途径去研究的事物，这是多么地有趣啊：）

碧城仙

官方网站又在做坏事了，他们各个分站的主页及总的主页都改成 html 后缀名了，以前都是 htm 的后缀名的，麻烦了....

全改起来太麻烦，我们暂时先不改了，再看看官方网站的改版动向再说吧...

现在先把所有该传的页面都传上去。还有几个小地方有几句话需要翻译翻译。

刚上传的看这里吧：http://boinc.equn.com/einstein/ask/index.htm

Youth

刚发现这里漏翻了第一句：

http://boinc.equn.com/einstein/ask/archive/light-qa3.html

First, why do we get light propagating at all?

首先，我们来看看光为什么可以传播？


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另外，archive的分类名：
LIGO、引力波源、广义相对论、光速、其它

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Ask a Physicist is an opportunity for you to ask questions about gravitational waves and related science. Relevant questions and their answers will be posted online.

“专家问答”部分供大家提出关于引力波及相关科学的问题。相关的问题及解答将发布在网站上。

引用 Youth 在 2006-2-13 11:03 PM 时的帖子:
Why does combining the principle of relativity with the invariance of the speed of light lead one to conclude that no medium is required for light to propagate?

为什么由相对论原理以及光速的不变性 ...

[ Last edited by Youth on 2006-2-14 at 19:05 ]

Youth

专家问答部分又有更新咯！

原来中文版的最新问题可以归档到LIGO那一组，也就是这篇：
有没有直接探测到过引力波而不是探测其效应？

除了更新后的最新问题，引力波源部分还增加了：
http://www.einsteinathome.org/ask/archive/sources-qa3.html

Youth

另外，新闻报道＆相关链接＆联系我们也都有部分更新。

顺便先认领一下现在的最新问题：）

Youth

Does the graviton exist? If so, why has it never been detected? How does this fit with Einstein's belief that gravity is actually the curving of space/time?

Submitted by Nick from the USA

引力子是否存在？如果存在的话，为什么还从来没有探测到过？引力子如何与爱因斯坦的引力理论（引力实际上是时空结构的扭曲）相结合？

由来自美国的Nick提交

First, what's a graviton?

首先，什么是引力子？

On the microscopic level, the other fundamental forces in the universe work by exchanging "carrier" particles. The photon is the carrier of electromagnetism. Microscopically speaking, static cling in your laundry is your socks tossing photons back and forth. The zap in a freshly dried sock contains an enormous number of photons, but there are more delicate experiments where single photons are evident. The weak nuclear force has carriers called W and Z bosons, which didn't get detected until more recently because they're massive and thus hard to make in accelerators. The strong nuclear force is carried by gluons, which haven't been directly detected on their own and probably never will be because of the way they combine. But the matter particles are arranged in groups exactly like you'd expect from the combination rules for gluons, which is regarded as solid indirect evidence that gluons exist.

微观上来看，宇宙中其它的基本力都是通过交换“载体”粒子来作用的。光子是电磁波的载体。从微观上讲，随着在你衣物上的静电其实就是你的衣物在来回地投掷光子。刚晾干的袜子上就包含了大量的光子，但如果要检测单个的光子，就需要更精细的实验了。弱核力的载体是W和Z玻色子，因为它们有质量以至于难以在加速器中产生出来，人们最近才探测到。强核力的载体是胶子，目前还没有直接探测到，而且由于它们组合的方式，也许永远也不能探测到。但如果粒子组合在一起的方式和你所期待的胶子组合的方法相同，这也就是对胶子存在的有力的间接证明。

Since the other forces work by exchanging carrier particles, we assume that gravity does too and call the carrier the graviton. From the macroscopic properties of gravity you can work out what the graviton should be like. For example, it should be massless since the range of gravity is infinite. It doesn't do combinatorics like the gluon, so it should be out in the open and detectable in principle.

既然其它的力都是通过交换载体粒子来作用，我们假设引力也是如此并且称其载体为引力子。从引力的宏观属性，你可以推算出引力子的大致情况。比如，由于引力的作用范围是无限的，那引力子应该是无质量的。它不会像胶子那样组合，因此理论上它也是可以探测到的。

But in practice, it'll be a long time before anyone detects a graviton. You need lots of them to make any visible effect because gravity is the weakest of the fundamental forces. Since gravity holds you down all your life that might sound strange, but it's true on a microscopic level. Any two electrons are pushed apart by electricity far more strongly than they're pulled together by gravity. So you only detect things involving huge numbers of gravitons, where the collective effects swamp the microscopic effects which indicate the existence of individual particles.

不过实际上，人们要探测到引力子将需要很长的时间。因为引力是基本力中最弱的一种力，需要大量的引力子才能产生任何可观察的效应。如果说引力在你的生活中都是拉后腿的可能有些奇怪，但微观上看确实如此。任何两个电子由于电荷作用被互相推开的程度要远远大于它们被引力拉到一块的程度。因此如果要探测引力子，其数量必须非常之大，这样累积的效应才会盖过微观的效应，而这也将证明微观粒子的存在。

So how does this fit with Einstein's idea of gravity being geometry? There is some suggestion that the graviton itself is a collective effect that shows up when you tweak the underlying structure of spacetime in a certain way. But the whole question of how quantum mechanics (which includes the business with the carrier particles) fits with general relativity is still wide open.

至于引力子和爱因斯坦理论中的关系，有人认为引力子本身也是当你以特定方式调节宇宙的时空结构时所展现出来的一种累积效应。不过如何将量子力学（这就包括了与载体粒子相关的理论）与广义相对论结合起来仍然是一个悬而末决的问题。

Youth

http://www.einsteinathome.org/ask/archive/sources-qa3.html

Is there an estimate of the speed of propagation of gravitational waves?
Submitted by Jaime from Canada

是否有估算过引力波的传播速度？
由来自加拿大的Jaime提交

Einstein's answer is that gravitational waves should propagate at the same speed as light. Light in vacuum, that is; not the slower speed light has going through matter. Or you could say that light propagates at the speed of gravitational waves: Gravity determines the structure of spacetime, which in turn determines how things can move. Including light.

爱因斯坦认为引力波应该是以光速来进行传播的。注意：是真空中的光速，而不是在介质中被减慢的光速。或者你也可以说是光是以引力波的速度来传播的：因为引力决定了时空结构，而后者又决定了物质的移动方式，当然，这也包括光的传播。

But that's not the whole story. Light slows down in matter because of quantum mechanical interactions with the atoms. We usually think of a piece of glass as a continuous medium, but on a length scale a millionth the thickness of a human hair it's not. There are atoms, separated by about that scale, and the light interacts with the atoms. Changing the type of atoms, or even the arrangement of a given type of atoms, can drastically affect the behavior of light. And how big the effect is depends on the wavelength of the light. At some wavelengths light travels almost as fast as in vacuum, at others it can't get through at all.

但这还并不是全部。光在介质中传播时会因为与原子的量子交互作用而减慢。我们通常会认为玻璃是一种连续的介质，但如果从比一根头发的精细度还要小一百万倍的尺度上看就不是这样了。在这个尺度上分布着大量的原子，光会与这些原子产生交互。改变原子的类型，甚至是改变同一种原子的排列方式，都能极大地影响光的行为。影响的程度依赖于光的波长。某些波长的光几乎可以像在真空中一样快速的穿过，而其它一些刚可能完全无法通过。

Something similar might happen with gravitational waves. Einstein treated spacetime as a continuous arena for things to happen in, but at scales less than a trillionth of a trillionth of the spacing between atoms the effects of quantum mechanics should show up. Einstein never worked out how to combine quantum mechanics with gravity. Even today we don't know how to do that, but we have some idea that spacetime at very small scales might have an "atomic" structure like matter. Then gravitational waves would slow down at some wavelengths, just like light in matter. (And light of the right wavelengths would slow down in vacuum too.)

类似的情况也可能发生在引力波身上。爱因斯坦将时空结构看成一块连续的区域，但是在比原子间间隔的百万分之一再百万分之一的尺度上，量子力学的效应将更为显著。爱因斯坦并没有找到将量子力学与引力结合起来的理论。即便是今天我们也没法做到，但我们推测时空结构在非常小的尺度上也有类似物质中原子的结构。那样某些波长的引力波就会像介质中的光一样走得慢一些。（另外，特定波长的光在真空中也会慢下来。）

Because this length scale is very small, it would be very hard to observe this effect. Most predictions say that LIGO and LISA (like LIGO, but in space) won't even come close, since the effect should be very small at the wavelengths they are sensitive to. But they'll be looking anyway, and people are already looking for the effect in light from astronomical objects. The odds are pretty long, but if anyone finds such an effect it will be the first observation of something related to quantum gravity. Einstein spent half a lifetime looking for such a thing, so you'll hear it in the news if somebody does find gravitational waves at anything but light speed.

因为这个尺度非常之小，要对这种效应进行观察将非常困难。大部分的人都预言LIGO和LISA（也就是太空中的LIGO）将永远都无法得到什么结果，因为在仪器的敏感波长范围内引力波的效应可能是相当微弱的。不过人们仍然会观察，而且对来自天体的光效应的寻找已经开始。这可能需要相当长的时间，但一旦有人观察到，这将是牵涉到量子引力理论的第一个观察结果。爱因斯坦在他一半的生命中都在寻找它，因此如果有人发现了以光速传播的引力波，你将肯定会在新闻中听到！

Youth

上面两篇有不少地方翻译得不太确定或者说比较随意，大家帮忙挑错吧：）

碧城仙

139、141、142 楼翻译已经更新。感谢 Youth 翻译！
请见：http://boinc.equn.com/einstein/ask/index.htm
http://boinc.equn.com/einstein/ask/archive/index.htm
http://boinc.equn.com/einstein/ask/archive/ligo-qa4.html
http://boinc.equn.com/einstein/ask/archive/sources-qa3.html

Youth

hi！这个页面中“引力波源”的最后一个问答弄错了，但链接是对的：）

http://boinc.equn.com/einstein/ask/archive/index.htm

碧城仙

引用 Youth 在 2006-6-8 09:49 时的帖子:
这个页面中“引力波源”的最后一个问答弄错了，但链接是对的：）

已更改，其他需要修改的地方还请各位多多费心检查。

youyancao

32-36页面无法打开
点击后提示
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碧城仙

引用 youyancao 在 2006-6-10 12:10 时的帖子:
32-36页面无法打开

？？？？？？？？？？？？
什么意思？页面地址是什么？

Youth

ask a physicist 部分又有更新了

原来的最新问题（引力子是否存在？）归类至“引力波源”

新增了一个类别，Properties of Gravitational Waves（引力波的属性）

新的最新问题（What amplitude, frequency and wavelength gravity waves are we expecting to find?）就是这个类别的

碧城仙

还是麻烦 Youth 翻译吧，下周一我再更新对应的几个页面。