What are gravitational waves?
A gravitational wave is a ripple in the geometry of spacetime, the settled count of records shaking. The world here is a network of observers that compare records and repair any disagreement, and geometry is the summary of settled regions, fixed by which records read which and how many there are. In OPH's account that summary answers to energy, and it can ripple. A ripple holds no knot of disagreement for repair to keep maintaining. LIGO caught the first one on 14 September 2015, from two black holes merging over a billion light years away. The detector's four-kilometer arms changed length by about a thousandth of the width of a proton, the finest length measurement anyone has made. In 2017 a wave from two merging neutron stars reached Earth together with the flash of light from the same collision, which showed that gravitational waves travel at the speed of light.
Also in Chapter 34: Why Was Newton Right for Two Hundred Years?, Chapter 25: Why Does Gravity Look Like Geometry?.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read chapter 28: What Is a Particle, What Is a Wave, and Why Does It Look Like Both?watch a universe make its own particles