# Tag Info

### What is expanding and contracting in LIGO? The space between the arms, the arms themselves, or both?

LIGO measures the path length of light travelling between its test masses. The experiment is built in such a way that the motion of the test masses (in the direction of the light path) is (almost) ...
• 12.6k

### What is expanding and contracting in LIGO? The space between the arms, the arms themselves, or both?

You don't really need the curved space picture to understand LIGO. In the presence of a gravitational wave two masses that normally hang straight down towards the centre of the earth feel slightly ...
• 55.3k

### Do gravitational waves cause matter to radiate?

Let us assume that our gravitational waves are described by a linearized Einstein equation, so that the metric is of the form $$g_{\mu\nu} = \eta_{\mu\nu} + h_{\mu\nu}$$ Where $\eta_{\mu\nu}$ is the ...
• 2,008

### GW luminosity depends on the 3rd time derivative but quadrupole formula depends on the 2nd time derivative?

This is in fact a pretty subtle issue. Instead of trivializing this question, let's rephrase it with a concrete example: Because one can easily mimic sin cos functions with piece-wise quadratic ...
• 305
1 vote

### Noise in gravitational wave detections

What is the meaning of 'realisation'? It is the value you would get upon detection or observation. i.e., another way of saying that given the probability distribution $p(n)$, then the probability of ...
• 30.1k
1 vote

### Do gravitational waves cause matter to radiate?

It depends on your exact setup but in theory you could arrange for gravitational waves to generate electromagnetic radiation, however in practice I don't think this scenario is very plausible to occur ...
• 52.3k

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