• Question: What speed does gravity travel at?

    Asked by doppler to Adam, Geoff, Rob, Sheila, Suzie on 21 Mar 2011 in Categories: .
    • Photo: Adam Tuff

      Adam Tuff answered on 20 Mar 2011:

      The current consensus is that you can get gravitational waves (according to Einstein’s theory of General relativity). I think Einstein’s theory of relativity infers that gravity travels at the speed of light.

    • Photo: Suzie Sheehy

      Suzie Sheehy answered on 20 Mar 2011:

      Good question – normally when we learn about gravity in school we learn about ‘newtonian’ gravity, which for most things works perfectly fine. Until you start to think about how it travels!

      Then we need to turn to the great man Einstein, and his theory of General Relativity. It’s in this theory that an object creates a distortion in the curvature of spacetime, which moves outward at the speed of light. That’s what we see as gravity – so, really, we think that gravity travels at the speed of light.

      I’ve had this question (myself) before and had previously looked it up, and I found this link useful in understanding it:
      http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html

      Let me know if you have any other questions, though I did only study general relativity for one term, so can’t promise to know the answers!!

    • Photo: Sheila Kanani

      Sheila Kanani answered on 20 Mar 2011:

      Great question! Essentially the answer is gravity travels at the speed of light, but here is some more information:

      The speed of gravity has not been measured in a lab because the gravitational force is really weak.

      There are two ways of thinking about it.
      1. In Newton’s model, gravity happens in an instant. The force exerted by a massive object points directly toward that object’s present position. Eg, the Sun is 500 light seconds from the Earth but newtonian gravity is a force on Earth due to the Sun’s position “now,” not its position 500 seconds ago.
      2. In general relativity gravity propagates at the speed of light. This means the motion of a massive object creates a distortion in the curvature of “spacetime” and gravity can affect how light travels.

    • Photo: Robert Simpson

      Robert Simpson answered on 21 Mar 2011:

      Gravity travels at about the speed of light. Experiments have been done measuring the decay of pulsars – rapidly spinning, massive dead stars that give off strong radio waves. These experiments show that the effect of gravity travels though space time at the speed of light (at least to within 1% of the speed of light).

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