# Shape of a Gravitational Wave

1. Feb 15, 2016

### DiracPool

We've seen the peculiar oscillating shape of the "squeeze-stretch" effect that a gravitational wave (GW) imparts on space and matter. What I am unsure of, however, is how does this wave manifest itself in three dimensions, as well as a few other questions..

1) Does it spread out spherically or, as is hinted at in many of the animations, does it send out like a ripple on the surface of a pond only in the plane of the inspiral event (in reference to the current binary black hole discovery)?

2) Take a look at this video starting at 10 seconds in:

Does that thing look creepy or what? It looks like a large intergalactic earthworm. But notice the ring structure.

3) How big is that ring? Is it the diameter of the black holes themselves? Is it composed of just that one big ring progressing through space like a tube, or does it expand out like a cone, as one might expect sound waves to after talking through a megaphone? Or, does the tube propagate in a spiral fashion as depicted later in the video above?

4) How do the rings overlap? In the earthworm depiction above, it looks just like one tube pointing in one direction. If the GW's are restricted to a plane, do we just have interference in the iconic squeeze-stretch from say two tubes that partially overlap?

2. Feb 15, 2016

### Staff: Mentor

The video shows an analogy of what a gravitational wave is like but don't read too much in the analogy. Its always better to go back to the math that describes it instead.

As you surmised, the wave travels out in all directions. The size of the ellipses are for illustration only, in reality they'd be describing the forces acting on some point in space as the wave passes by. The earthworm analogy is basically showing the wave as it comes at you and the ellipses show how the forces will act on you stretching one direction and squashing in another direction. Other observers would experience the same kind of squash and stretch wherever they were positioned.

Basically, if you could feel a gravity wave and were looking in the direction of the wave source then what you'd feel is something pushing/pulling you side to side and at the same time something pulling/pushing you top to bottom depending on your orientation.

However, some of our Science Advisors will be able to describe it much better than I. Perhaps @bcrowell can correct or clarify my descriptions.

Here's a more detailed discussion of gravitational waves that may help:

http://blog.wolfram.com/2016/02/11/on-the-detection-of-gravitational-waves-by-ligo/

http://news.discovery.com/space/gravitational-waves-vs-gravity-waves-know-the-difference-160208.htm

Last edited: Feb 15, 2016