I recently used another venue to ask about the speed of gravity, specifically if the speed of gravity is constant or if it is subject to refraction when passing through media, akin to light.

The response stated the speed of gravity was constant. Refraction in light occurs because it takes time for light to interact with particles and this interaction doesn't occur with gravity.

My understanding is that gravitational waves interact with each other. Considering particles have mass and mass has gravity, it seems to me that a gravitational wave passing through media containing mass would interact with the gravity field and that interaction would take time - thus one portion of the wave would interact before another, effectively gravitational refraction.

Am I mistaken in my assumption that a gravitational wave interacts with with a gravity field or that an interaction would be in linear time?

  • $\begingroup$ I think you might be confusing diffraction and dispersion. $\endgroup$
    – S. McGrew
    Oct 26, 2018 at 2:32
  • $\begingroup$ Thank you, I was confusing "difraction" with "refraction" but not dispersion. Diffraction being applicable to the follow up question, refraction for the initial. Updating now. $\endgroup$ Oct 26, 2018 at 2:55

1 Answer 1


There still appears to be some confusion at your end about how diffraction, refraction, and dispersion relate to each other. However it looks like the gist of your question is "can the direction of travel of a gravitational wave be altered by its interaction with matter?"

The simple answer is "yes". The path of a gravitational wave propagating past a galaxy cluster or a black hole should be bent just like the path of a light wave, and for the same reasons.

If your question is more directed at what would happen to a gravitational wave passing through, e.g., a wedge of ordinary matter (analogous to a prism in optics), I don't know. I could tell you my guess, but that is probably an improper answer in this forum. All I can say with confidence is that ordinary matter per se should be very nearly transparent to gravitational waves and have essentially no effect at all on the passage of a gravitational wave. What definitely will have an effect is the strong gravitational fields already known to deflect and focus light.

  • $\begingroup$ Thank you for the explanation. I spent some more time reading up on difraction, refraction and dispersion. If I was confused before then I continue to be confused... That... Or, I failed to accurately state my question. $\endgroup$ Nov 5, 2018 at 16:55
  • $\begingroup$ When you work out how to state your question, please post it and you're sure to get some answers. $\endgroup$
    – S. McGrew
    Nov 5, 2018 at 20:23

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