开始翻译 Einstein@Home 主题站

Youth

http://www.einsteinathome.org/ask/archive/prop-qa1.html

What amplitude, frequency and wavelength gravity waves are we expecting to find?
Submitted by Kostas from Australia

我们所期望寻找到的引力波的振幅、频率和波长分别是多少？
由来自澳大利亚的 Kostas 提交

Each detector can find them only in a certain range of frequencies.

每种探测器都只能在特定的频率范围找到引力波。

LIGO and the other ground-based detectors are sensitive to frequencies from a few tens of Hertz (cycles per second) to a few thousand Hertz. These are the frequencies the human ear is sensitive to, but the amplitudes are much smaller. Your ear can pick up sound waves from air pressure changes as small as one part per ten billion. The strongest signals LIGO might see are less than a part in ten billion of THAT - maybe a thousand times less, though we hope not. These signals have wavelengths from ten miles to about the diameter of the Earth.

LIGO 和其它的地基探测器对从几十赫兹（每秒的周期数）到几千赫兹的频率都是敏感的。这些频率人耳也能感觉得到，但其振幅要小得多。你的耳朵可以从空气气压的几百亿分之一的变化中提取出声波。而 LIGO 可能看到的最强的信号也要比前者的几百亿分之一还要小 － 也许只有千分之一，虽然我们也不希望这样。这些信号的波长范围从几十英里到地球的直径。

LISA, which will share the Earth's orbit around the Sun, will find waves at frequencies from a tenth of a Hertz down to a ten-thousandth of a Hertz. This means wavelengths up to ten times the diameter of the Earth's orbit. LISA's biggest signals will be from galaxies colliding, with amplitudes thousands of times those of the LIGO signals. That's still a few billionths of the fractional pressure changes your ear can detect.

和地球一道绕着太阳运行的 LISA 将可以看到频率从十分之一赫兹到万分之一赫兹的引力波。也就是说对应的波长将达到地球绕日轨道直径的十倍。LISA 探测的信号将来自银河系的碰撞，其振幅将是 LIGO 信号的几千倍。而这仍然只有你的耳朵能探测到的压力变化的几十亿分之一。

The next frequency window is around a few billionths of a Hertz, or periods of years. Any signals here would have wavelengths about the distance from the Sun to the next star. We'll look for these with a "pulsar timing array." Pulsars are spinning stars which act as very good clocks and are scattered around our galaxy. "Array" means we'll look at lots of them for years (we're just starting). If a gravitational wave at these frequencies passes between us and the pulsars, it makes a pattern of changes in their apparent spin rates as it distorts spacetime between us and the pulsars in different directions. Such waves would be coming from the early universe, which we don't know much about, so we can't predict the amplitudes well.

接下来的一个频率窗口是在几十亿分之一赫兹的范围，其周期是若干年。而对应的波长将和太阳到邻近恒星的距离差不多。我们将使用“脉冲星时间校准阵列”来寻找这些信号。脉冲星是分布在我们银河系各处的自旋恒星，可以看作是非常好的时钟。“阵列”表示我们将花费多年的时候来进行观察（我们刚刚才开始）。如果有一个该频率范围内的引力波在我们和脉冲星中间穿过，它将在不同方向扭曲我们和脉冲星之间的时空结构，我们观测到的脉冲星自旋速率也将以一定模式发生变化。

Last but not least are frequencies around a billionth of a billionth of a Hertz. These waves have waved only a few periods over the entire age of the universe and have wavelengths about the size of the universe. They'll show up as patterns in the cosmic microwave background (the fading glow from the Big Bang from the edge of the universe). We haven't seen the pattern yet, so the waves must be pretty small. But they're coming from right after the Big Bang when the universe was microscopic, so if we find them with a future satellite we'll learn something drastically new.

最后一个频率范围是在几十亿分之一的几十亿之一赫兹。这些引力波在宇宙产生以后只传播了几个周期，其波长范围和宇宙的尺度相近。这些信号的表现形式是宇宙微波背景（来自宇宙边缘的大爆炸所产生的余热）中的模式。我们还没未见过这些模式，因此它们一定是相当微弱的。但因为它们是来自大爆炸之后宇宙还处于微观状态的时候，如果我们能找到它们，我们将了解一些全新的知识。

Youth

呵呵，不麻烦，这个系列写得还是比较通俗的，翻译后自己也能了解不少东西：）

已经翻译好，大家帮忙校一下，有不少量词译得比较头晕：）

引用 碧城仙 在 2006-7-15 20:00 时的帖子:
还是麻烦 Youth 翻译吧，下周一我再更新对应的几个页面。

Rojer

而 LIGO 可能看到的最强的信号也要比前者的几百亿分之一还要小 － 也许只有千分之一，虽然我们也不希望这样
表述成“或许还要再小一千倍”比较好。

LISA 探测的信号将来自银河系的碰撞
银河系多数单指我们所在的这个星系，觉得用“星系的碰撞”好些。

Such waves would be coming from the early universe, which we don't know much about, so we can't predict the amplitudes well.
这些波来自我们尚不太了解的早期宇宙，因此还不能很好的预测其振幅。
漏了一句：）

(the fading glow from the Big Bang from the edge of the universe)
（来自宇宙边缘的大爆炸所产生的余热）
“宇宙边缘的大爆炸”怎么觉得不太合适，“来自大爆炸来自宇宙的转折处的余热”如何？

Youth

多谢帮忙：）

前三个严重同意，最后一个感觉还有些拗口，意思也不太明确，这里的edge是不是指的就是宇宙起源的时候？要不翻译成“来自宇宙起源时大爆炸的余热”？

Rojer

起源意思上也说得过去

碧城仙

149~155 已更新，原来的最新问题归类到广义相对论，现在的最新问题归类到引力波的属性。
http://boinc.equn.com/einstein/ask/archive/index.htm
http://boinc.equn.com/einstein/ask/archive/relativity-qa3.html
http://boinc.equn.com/einstein/ask/archive/prop-qa1.html

Youth

专家问答部分又有更新了:

广义相对论部分新增:
http://www.einsteinathome.org/ask/archive/relativity-qa4.html
http://www.einsteinathome.org/ask/archive/relativity-qa5.html

引力波的属性 -> 引力波 新增:
http://www.einsteinathome.org/ask/archive/gw-qa2.html

Rojer

我先认领最后这个
http://www.einsteinathome.org/ask/archive/gw-qa2.html
吧...

Rojer

不知道我对原理那部分的理解对不对，马上要外出，匆忙了点……


If gravitational waves are successfully detected, can we expect that knowledge to lead to new kinds of technological advancements?
Submitted by Jo from the USA
引力波是否曾被成功的探测到了，能期望这些知识引发新的技术进步么？
由来自USA的 Jo 提交

Even though we haven't detected gravitational waves yet, there have already
been technical advancements spun off from the search effort.
虽然我们至今还没有探测到引力波，但是已经从搜索的成果中衍生出了新技术。

The first spinoff I know of is from the 1970s and is called Pound-Drever locking. It was a big practical improvement in using laser interferometers to measure small distances. In principle an interferometer measures length changes by letting the mirrors swing freely and counting the light/dark cycles in the output (the light leaking out of the end) to see how many light wavelengths a mirror moved. In practice an interferometer is more sensitive if you keep it locked, or force the length between the mirrors to stay a certain number of wavelengths of light of the laser that's beamed into it. And it's easier to keep it locked if you mess up the laser very slightly. You can see how much the mirrors want to move due to gravitational waves (or anything else) by watching how much power is needed to hold them in lock. Ron Drever developed it with LIGO in mind, but people working with other precision measurements quickly saw its potential and now it's fairly common in industrial settings.
我知道的第一个衍生物是来自1970年代被称作 Pound-Drever 锁的东西。它是使用激光干涉仪测量微小距离的一个巨大进步。干涉仪测量长度改变的原理是让镜子自由的摆动，并根据输出端明/暗的循环（光在末端的泄漏）计算出一面镜子移动了多少波长。实际上如果把干涉仪锁定或迫使镜子间的距离保持在一个确定长度上，也就是注入其中的光的确定波长数目，那它会变得更敏感。并且当你把激光变得很微弱的时候会更容易保持锁定状态。你可以通过观察保持镜子锁定所需的能量来确定引力波想要把反射镜移动多少。Ron Drever 有意将它运用到 LIGO 上，不过其他从事紧密测量的人们很快发现了这项技术的前景，如今该技术在工业中用的很普遍了。

Then there are engineering things. LIGO's 4km arms have been called (correctly) "the biggest holes in the Earth's atmosphere." Building them pushed vacuum technology to the limit and then redefined the limit. The engineering firms who did it learned lessons I'm sure they'll apply on future projects, which will look easy by comparison.
举个工程方面的例子。工程曾上把 LIGO 的4千米测量臂称作“地球大气中最大的洞”（确实如此）。它们的建造把真空技术推到了极限，随后重新定义了新的极限。建造它的工程公司从中学到了不少，我相信他们会运用到以后的项目中，这个一比较就能看出来。

These spinoffs would have happened eventually even without the search for gravitational waves. But having that exciting goal attracted some very bright people to work on the problems who otherwise would have been interested in something else. And because the gravitational wave application is much more challenging than the practical applications, these people had to push much harder than if they were working on the practical stuff directly. Similarly, I don't expect the eventual detection of gravitational waves to directly produce any practical spinoffs. But the excitement it will generate will get more people interested in pushing lasers and vacuum technology and other things related to detection, which will indeed produce practical spinoffs.
即使没有对引力波的搜索，这些衍生出的东西最终还是会出现的。不过这个令人兴奋的目标吸引了一些非常聪明的人来解决遇到的难题，他们即使不从事该项工作也同样会被其他的事情吸引。并且由于引力波应用同实际应用相比更具挑战性，这些人们不得不投入比直接处理实际材料更多的努力。同样的，我并不期望对引力波的最终发现能直接产生任何实际的副产品。但是令人激动的是它会促使人们对推动激光和真空技术以及其他与探测相关的事物感兴趣，这才是真正产生实际附带效益的地方。

Youth

感觉spinoff还是翻译成副产品更合适些：）

The first spinoff I know of is from the 1970s and is called Pound-Drever locking. It was a big practical improvement in using laser interferometers to measure small distances. In principle an interferometer measures length changes by letting the mirrors swing freely and counting the light/dark cycles in the output (the light leaking out of the end) to see how many light wavelengths a mirror moved. In practice an interferometer is more sensitive if you keep it locked, or force the length between the mirrors to stay a certain number of wavelengths of light of the laser that's beamed into it. And it's easier to keep it locked if you mess up the laser very slightly. You can see how much the mirrors want to move due to gravitational waves (or anything else) by watching how much power is needed to hold them in lock. Ron Drever developed it with LIGO in mind, but people working with other precision measurements quickly saw its potential and now it's fairly common in industrial settings.

我知道的第一个副产品是来自1970年代被称作 Pound-Drever 锁的东西。它是使用激光干涉仪测量微小距离的一个巨大进步。干涉仪测量长度改变的原理是让镜子自由的摆动，并根据输出端明/暗环的变化数目（光在末端的泄漏）计算出一面镜子移动了多少波长。实际上如果把干涉仪锁定或者说迫使镜子间的距离固定在一个确定的值，也就是注入光的确定波长数目，那它将更为灵敏。而且如果你非常细微地调节激光，会更容易保持锁定状态。你可以通过观察保持镜子锁定所需的能量来确定引力波想要把反射镜移动多少。Ron Drever 有意将它运用到 LIGO 上，不过其他从事精密测量的人们很快发现了这项技术的前景，如今该技术在工业中用的很普遍了。

Then there are engineering things. LIGO's 4km arms have been called (correctly) "the biggest holes in the Earth's atmosphere." Building them pushed vacuum technology to the limit and then redefined the limit. The engineering firms who did it learned lessons I'm sure they'll apply on future projects, which will look easy by comparison.

还有就是工程方面的例子。LIGO 的4千米测量臂曾经被称作“地球大气中最大的洞”（确实如此）。它们的建造把真空技术推到了极限，随后重新定义了新的极限。建造它的工程公司从中学到了不少，我相信他们会运用到以后的项目中，这个和建造 LIGO 相比较应该要容易得多。

These spinoffs would have happened eventually even without the search for gravitational waves. But having that exciting goal attracted some very bright people to work on the problems who otherwise would have been interested in something else. And because the gravitational wave application is much more challenging than the practical applications, these people had to push much harder than if they were working on the practical stuff directly. Similarly, I don't expect the eventual detection of gravitational waves to directly produce any practical spinoffs. But the excitement it will generate will get more people interested in pushing lasers and vacuum technology and other things related to detection, which will indeed produce practical spinoffs.

即使没有对引力波的搜索，这些副产品最终还是会出现的。不过这个令人兴奋的目标吸引了一些非常聪明的人来解决遇到的难题，如果他们不从事该项工作，就会被其他的事情吸引。并且由于引力波应用同实际应用相比更具挑战性，这些人不得不投入比实际应用更多的努力。同样的，我并不期望对引力波的最终发现能直接产生任何实际的副产品。但是令人激动的是它会促使人们对推动激光和真空技术以及其他与探测相关技术的进步感兴趣，这才是真正产生实际附带效益的地方。

Rojer

嗯、嗯，Youth 改的不错，连错字都纠正了。^^

Youth

下面这个翻译得比较粗糙...

http://www.einsteinathome.org/ask/archive/relativity-qa4.html

I was always under the impression that gravity was a field. How can something be both a field and a wave?
Submitted by Eamon from Australia

我印象中引力应该是一个场。为什么它可以既是场又是波？
由澳大利亚的Eamon提交

Waves are just a certain behavior of a field when it changes in a certain way with respect to location in space and time. Fields can do other things besides wave, like not change with time or change in non-wavy ways. Every physical field has to be able to wave as a result of the finite speed limit (the speed of light) and conservation of energy. There is a nice conceptual summary of the argument in the gravitational waves section of this web site.

波只是场的一种特定行为，也就是它在时空中的位置按一定方式进行改变。但场能做到的并不仅仅是波，它还可以不随时间变化或者不像波那样进行变化。由于光速的限制和能量守恒，任何物理场都必须能传播。关于这方面的概念在本站的引力波部分有很好的描述。

Mathematically speaking, a field is a number (or set of numbers) which depends on location in space and time. In physics, the fundamental fields we are interested in yield numbers which are the answers to questions like "If I put a little charge here, how hard and in which direction would it get pushed?" (The charge has to be little so that its own field doesn't disturb the existing field which you are trying to measure.) For example, the answer to the question "How hard (per unit charge) will this little electric charge get pushed, depending where I put it and when?" is the electric field. If you change "electric charge" in the question to "mass," the answer is the gravitational field.

从数学上讲，场是特定于时空中某个位置的一个数值（或者是一个数值集）。而从物理上讲，我们感兴趣的基本场所产生的数值可以用来回答类似于这样的问题：“如果我在这里放置一个小电荷，它将受到多大的哪个方向的推力？”（这个电荷必须非常小，这样它自己的场才不至于打乱你所有测量的场。）举个例子，如果问题是“依赖于我何时将小电荷放置在何处，它将受到多大的推力（单位电荷）？”，那答案是电场。而如果你将问题中的“电荷”换成“质量”，那答案将是引力场。

Actually, that last one was for Newton's theory of gravity. Einstein's relativistic theory is conceptually different because different observers may disagree on how hard the push is and which direction it goes, since they can have different ideas of motion. But mathematically you can still phrase it in terms of a field, which turns out to be related to the geometry of spacetime. That field must allow for the possibility of waves, which means it must be possible to have waves in spacetime itself. Those are the gravitational waves that Einstein@Home is trying to detect.

实际上，后一个问题对应的是牛顿的重力理论。而爱因斯坦的相对论在概念上是不同的，因为推力的大小和方向在不同的观测者看来可能都是不一样的。但从数学上讲你仍然可以用场来进行描述，将它和时空结构联系起来。这个场必须允许波的存在，这意味着它在时空中必然有可能存在波。而这也就是 Einstein@Home 正试图寻找的引力波。

So what's different between waves and the other things fields can do? Obviously they "wave": Some number goes up and down with respect to time and position. What's not so obvious is that this means waves can move energy around (and information and other things) even through empty areas (no masses, charges, etc). They're how distant parts of the universe communicate with each other, which is why they're so important to astronomy.

那么波和其它场的行为间有什么不同呢？比较明显的是它们是可以“波动”的：依赖于时间和位置，数值上上下下地发生变化。而另外不那么明显的是这意味着波可以传输能量（还有信息以及其它事物），即便是在真空中（没有质量、电荷等等）。它们是宇宙间相距遥远的部分可以互相联系到一起的原因，这也就是为什么它们在天文学上如此重要的原因。

Youth

再接再厉...还是有些粗糙

http://www.einsteinathome.org/ask/archive/relativity-qa5.html

Do gravitational waves distort both space and time? I can understand the warping of space and trying to measure the difference in stretch, but how do you know a time distortion would not affect the LIGO split laser beam?
Submitted by Dave from the USA

引力波会扭曲时间和空间吗？我能理解空间的扭曲以及如何去测量其差异，但你们如何能够知道时间的扭曲是否会影响 LIGO 中的激光束？
由美国的 Dave 提交

You could say that gravitational waves distort both space and time. It's more precise to say they distort spacetime, and whether you see the distortion as purely space, purely time, or some combination depends on how you're moving (what frame of reference you're in).

你可以说引力波会扭曲时间和空间，但更精确的说它们扭曲的是时空，而你看到的究竟是单纯空间或单纯时间的扭曲，还是空间和时间的某种组合，依赖于你自己是如何移动的（也就是你所在的参照系）。

The usual version of this common question goes something like: "Yesterday you said that LIGO has 4km arms and that a gravitational wave makes the arm length change a little because space is distorted. Today you said that the gravitational wave shows up as a little change in the frequency of the laser light because time is distorted. But if the speed of light is constant and the frequency is changing, the wavelength of the light must be changing too. If the wavelength and the arm length change in the same way, how is that any different from when they don't change?"

这个问题的常见版本类似于：“昨天你们说 LIGO 的臂长为4公里，然后在引力波扭曲了空间后这个长度改变了一丁点。而今天你们又说因为引力波扭曲了时间，导致激光的频率发生了一丁点的改变。但如果光速是恒定的，频率的改变将带来的波长的改变。而如果波长和臂长的改变是相对应的，你们怎么知道是不是本来就什么改变都没有发生过？”

Yesterday I gave an answer that was true in one frame of reference, and today I gave an answer that was true in another. You can pick a frame where the arm length changes and the wavelength doesn't. You can pick another frame where the arm length doesn't change, but the wavelength and frequency do. You can pick a frame in between, where wavelength and arm length change by half as much, and so on. You can't pick one where both change in harmony. What is really measured by the instrument is basically the number of wavelengths that fit into an arm or the number of wave periods it takes light to traverse an arm, and that number is the same in all frames.

昨天我的答案在一个参照系中是正确的，而今天我的答案在另一个参照系中也是正确的。你可以找到一个臂长改变而波长不改变的参照系，你也可以找到一个波长和频率改变但臂长却不改变的参照系，但你永远找不到一个参照系其中波长和臂长的改变是可以相一致的。仪器真正测量的是腔臂长度所对应的波长数或者说激光在腔臂内传播的波长周期的数目，而这个数目在所有参照系中都是相同的。

What's behind the answer is the principle of relativity: Fundamental physical observables are the same in any frame of reference, however it's moving. So you could pick a frame where it's easy to calculate something, or another frame where it's easier to explain what's going on. Or get a result in one frame and use it in another. This switching around is very convenient for physicists to do calculations and becomes second nature to us very quickly, so sometimes we forget it can seem confusing!

这个答案的背后下是相对论的原则：无论一个参照系如何移动，其中基本的物理观察都是相同的。因此你可以选择一个参照系以便你可以更方便地进行计算，或者选择另一个参照系以便你可以更容易地解释某个现象。或者将在一个参照系得到的结果用在另一个参照系中。这种切换在物理学家们做计算时是非常方便的，也就很快变得非常自然，因此有时我们甚至会忘记它看上去可能会让人感到困惑！

碧城仙

157 ～ 163 楼内容已转至服务器，问答部分主页和归档页面也已更新。
请看以下页面：
http://boinc.equn.com/einstein/ask/index.htm
http://boinc.equn.com/einstein/ask/archive/index.htm
http://boinc.equn.com/einstein/ask/archive/relativity-qa4.html
http://boinc.equn.com/einstein/ask/archive/relativity-qa5.html
http://boinc.equn.com/einstein/ask/archive/gw-qa2.html

Youth

大仙辛苦，另外，http://boinc.equn.com/einstein/ask/archive/index.htm这一页中“引力波的属性”这一类别也要对应改叫“引力波了”：）