13
$\begingroup$

In my GR textbook, it states that gravitational waves can undergo interference but not scattering.

I am just starting the chapter on linearised gravity concepts (weak field approximation) and my apologies if this is a duplicate.

My questions are:

  1. Can gravitational waves undergo refraction, as this effect, (at my naive GR level of understanding anyway) is related to the curvature of spacetime.

  2. Is there any intuitive picture of what occurs as a gravitational wave approaches the vicinity of a black hole, but is not scattered.

Improve this question
$\endgroup$
4
  • 3
    $\begingroup$ Scalar fields, vector fields, and tensor fields can all scatter off of black holes. C.f. Teukolsky equation for scattering of gravitational waves off of Kerr. More generally, look up perturbations of fields on black hole backgrounds. You can also find exercises in many GR books on scattering of scalar fields on Schwarzschild black holes which amounts to solving a separable wave equation using a curved space-time wave operator; for example see project 8.2 in Padmanabhan "Gravitation: Foundations and Frontiers". See also superradiance in Kerr. $\endgroup$
    – FenderLesPaul
    Commented Jun 21, 2015 at 21:44
  • $\begingroup$ @FenderLesPaul thanks for that, I will do the exercises and check I read my textbook correctly. (And read other textbooks). $\endgroup$
    – user81619
    Commented Jun 21, 2015 at 21:57
  • $\begingroup$ @AcidJazz What textbook is it? $\endgroup$
    – magma
    Commented Jun 24, 2015 at 0:12
  • $\begingroup$ @magma hi it's Cheng,Ta-Pei , Relativity, Graviation and Cosmology, 2010 edition, OUP, p337 "once gravitational waves are emitted,they will not scatter and will propogate undisturbed from inner core of exploding star ". It's fairly light on math, but a good introduction and I have Hartle and Carroll's online notes $\endgroup$
    – user81619
    Commented Jun 24, 2015 at 7:02

1 Answer 1

Reset to default
1
$\begingroup$

Often when people talk about "gravitational waves" it is in the context of linearized gravity on a flat background. In this case waves do not scatter, refract nor diffract. However, GR is not linear (and does not have a background) and in many cases this approximation does not hold. One way to go a bit beyond this approximation and still keep things tractable is to change the background. One can consider the change to the metric on top of a known stationary solution such as Schwarzschild (outside the horizon). In these cases gravitational waves will behave similar to electromagnetic waves, that is they will propagate along null geodesics.

So specifically for your questions:

  1. Yes, for a suitable definition of refraction in the proper approximation.
  2. Developing intuition regarding black hole is generally quite hard. However, outside the horizon gravitational waves will behave similar to light.
Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.