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http://www.einsteinathome.org/ask/archive/ligo-qa5.html
What will physicists do if there is still no sign of gravity waves when advanced LIGO is operational? Will they abandon the search or modify the theory?
Submitted by Baharudin from Malaysia
如果在先进LIGO投入使用后仍然找不到引力波，物理学家们将会怎么办？他们会放弃搜索还是对理论进行修改？
由马来西亚的Baharudin提交
If advanced LIGO detects nothing after a year or two, that will be even more revolutionary than if it does. But I wouldn't bet on it.
如果先进LIGO在一两年后还探测不到任何引力波信号，这将比能探测到还更具有革命性，不过我现在仍认为信号应该是能探测到的。
One reason is that we have a lot of indirect evidence for gravitational waves. I talked a little about this here, but let's have some more detail:
原因之一是我们已经有了大量的间接证据可以证明引力波的存在，关于这一点，之前我也稍微提到过，下面我再详细讲一讲：
The most famous example is the Hulse-Taylor pulsar. It's a binary - two neutron stars orbiting each other. We see a periodic radio signal coming from one of them because there's a beam which sweeps across the Earth like a searchlight as the star rotates. That signal is like a GPS clock that lets us track the motions of the stars, and it tells us that they are spiraling in towards each other - the orbit is shrinking very slowly. Gravitational wave emission should shrink the orbit at precisely the rate that's observed, so it's a stunning confirmation of Einstein's theory. That's why Hulse and Taylor got a Nobel Prize in 1993.
最其名的例子就是哈尔斯-泰勒脉冲星。这是一个双星系统，也就是两颗互相围绕对方运转的中子星。因为其中一颗星体发出的射电信号会在星体旋转时扫过地球，我们就可以观测到一个周期性的射电信号。这个信号就像好比全球定位系统的时钟，我们就可以由此跟踪星体的运行，而这个信号告诉我们它们正在以螺旋形式互相靠近，也就是说它们的运行轨道正在缓慢地缩小。由于发射引力波导致的轨道收缩和我们的观测结果相当一致，因此这是爱因斯坦理论的一个相当强有力的证据。因为这个发现，哈尔斯和泰勒最终获得了1993年的诺贝尔奖。
Since then, we've found a lot more binaries like this with better radio searches. LIGO can't detect these particular binaries - it can only detect the last few minutes of inspiral before merger - but we know there are more that we haven't seen in radio. For example, many pulsar beams aren't pointed toward us. But the gravitational waves come out in all directions, so these count for estimating how many inspirals LIGO will detect per year. Putting together everything we infer from observations (like the rate of supernova explosions which turn normal stars to neutron stars) and calculations from astrophysics (like how often a supernova breaks up a binary), we get an estimate of a few mergers per hundred thousand years per galaxy. Since there are a million galaxies within range of advanced LIGO, we expect dozens of mergers per year. There are some uncertainties in this number, but it's very hard to push the rate below one per year.
从那时起，随着射电搜索技术的进步，我们已经发现了更多类似的双星。但这些特殊的双星用LIGO是不能探测到的，它只能探测到双星在合并前最后几分钟的运行情况，不过我们知道一定还有更多我们用射电方法找不到的双星，比如某些脉冲星的波束并没有指向我们，而引力波产生时是在各个方向上都有的，这就可用来估计LIGO每年可以探测的螺旋运行数目。加上我们从观测结果中得到的推断（比如超新星爆炸后将普通星体转变为中子星的几率）以及天体物理学家的计算（比如超新星分解为双星的几率），我们估计出每个星系中每几十万年应该会发生几次双星合并。既然高级LIGO可以看到数以百万计的星系，我们认为每年应该可以观测到几十次的双星合并。这个数字有一定的不确定性，但再怎么少，一年一次总归是有的。
So if advanced LIGO doesn't find a merger after a year, we wouldn't decide to change relativity theory, but we would start taking a hard look at our understanding of the stellar life cycle. And LIGO would keep going, because even without a signal you can set upper limits - a topic I'll come back to in part 2.
因此，如果先进LIGO在一年后还探测不到一次双星合并，我们并不会想去修改相对论，我们会开始好好审视一下我们对恒星生命周期的理解。而LIGO的观测也会继续，因为即便没有信号，我们也可以设定一个上限，我将在下一部分中继续讨论这个主题。
