Human hearing is an incredibly useful tool that is regularly used in LIGO. Staff at the observatories often plug the output of the interferometer into an audio-mixer and listen on a pair of headphones. One does not need to pitch up the output since human hearing ranges from 20Hz to 20kHz, which covers the entire spectrum in Dan’s plot up at the top of the post. Audio is used to diagnose problems in detector subsystems and investigate short (non-gravitational wave) blips in the data called glitches. The gravitational wave signals we are looking for, such as coalescence of a binary star system will have frequencies in the audio band. There are few websites where you can listen to simulated signals. Just check out http://www.ligo.org.

LIGO will indeed start a new observational run this month, with a sensitivity about twice that of the previous run (which was, by the way, at better than design sensitivity!). This run will last about 1-1/2 years, so an indisputable “event” just might be seen, but that observation would still be fortuitous. We’re all banking on Advanced LIGO, which will go online in 2014-2015 and will probe a volume of space 1000 times greater than LIGO could; but even then, it will take some time for the observatories to reach optimum sensitivity.

Information is still transmitted – that the ball keeps moving in the same direction, information that there is no change is still information.

“If the ball suddenly accelerates (e.g., it stops moving, or changes direction, or speeds up), then a wave has to propagate to let us know (modulo near field effects).”

I think the point is that near field effects can also transmit information which is not in the form of waves.

What’s the source of the spike in the 5th run between 300 and 400 Hz?

Keep it simple. Move the ball of plutonium into interstellar space, where it can just drift along (inertially!) at constant velocity with no intrinsic angular momentum.

Here is something to think about (and again, consider electrostatics, magnetostatics, and electrodynamics, where the mass of the ball is replaced by a spherically symmetric electric charge). If the ball is moving at constant velocity, then there is an inertial reference frame in which it isn’t moving at all. In this frame the associated field is static; it changes with position (distance from the ball) but not with time. In a different frame the associated field is changing with time.

In fact, in electrodynamics, you actually have an electric and magnetic field vector at each point. Maxwell’s equations determine what the magnitude and direction of the vectors will be. The finite speed of propagation of light is (from this perspective—more about that in a moment) a consequence of Maxwell’s equations. The magnitude and direction of the field vectors at some distance D away from the moving ball will, roughly speaking, reflect where the ball was at an earlier time (a time D / c, where c is the speed of light).

As I indicated, from the perspective of the late 19th century the finiteness of the speed of light—ie, the speed of propagation of electromagnetic “disturbances”—was a consequence of Maxwell’s equations. Of course this is what got Einstein thinking at age 16. He took Galileo’s principle of relativity of inertial frames seriously, but he couldn’t see how Maxwell’s equations could be invariant under the coordinate transformations everyone assumed should apply to Newtonian mechanics (and Newton’s theory of gravitation). He gradually realized that the coordinate transformations had to be different for Maxwell’s equations, in such a way as to leave the speed of light both finite and invariant under those transformations. From this perspective the finite speed of propagation of electromagnetic disturbances is a consequence of the relativistic invariance of the laws governing electrodynamic fields.

However, Einstein felt that Galileo’s relativity had to hold for all the laws of physics, and this could only be possible if Newton’s mechanics, and ultimately his theory of gravitation, were changed. And so he set about reformulating them. Elementary mechanics in the absence of gravitation was comparatively easy. Gravitation presented much deeper difficulties…

If you read I. Shapiro’s 1964 paper where Shapiro delay was introduced, the first para states “the speed of light depends on strength of gravitational potential along its path”
Now same argument applies to gravitational waves.

I’m OK with the idea that the change in the field propagates at the speed of light, as in electrodynamics. Arrow’s comment states what I’m getting at more explicitly, which is this: If this propagating change requires gravitational waves (as Daniel seemed to be saying), why does it seem like it works just as well in the constant velocity case (where, correct me if I’m wrong, no gravitational waves would be produced)?

(Good point that rolling involves acceleration. I guess I should have said “the bowling ball slides along some frictionless ice”, although that’s not a very natural image when it comes to bowling balls.)

The chambers in which the instrument sits are resting on a foundation of several feet of concrete separate from the walls of the building. One also has a complicated passive (and active in Louisiana) seismic isolation system made up of primarily springs and pendula. The beam tube in which the laser is enclosed is itself enclosed within a few inches of concrete. The chambers that hold the optics are placed in buildings in which the temperatures are regulated to within a single degree.

Each noise source has some characteristic frequencies. Large far-away earthquakes shake the ground at frequencies between 0.03 and 0.1Hz, while the wind and traffic show up in the 1-3Hz seismic band. The isolation systems at LIGO do an incredible job reducing the ground motion’s effect on the mirrors by factors more than a million.

At that accuracy, how do you rule out noise? Even wind on the building or heating by the sun could completely rule this domain, so how do you get by?

Try thinking about the analogous question in electrodynamics. The same issue arises there. The underlying theories encompass fields associated with a static configuration of sources, a slowly changing configuration, and rapidly changing configurations (with acceleration). Of course the detailed geometry and distribution of the sources is relevant, in general.

(PS: If the bowling ball is rolling, then most of it is being accelerated around its axis of rotation, although this is beside the point.)