The motion of galaxy clusters in the distant Universe has just yielded the largest-scale test yet of the laws of gravity.
Across scales that span hundreds of millions of light-years, gravity continues to behave the way Isaac Newton predicted in his universal law of gravitation.
According to this law, every particle in the Universe exerts a gravitational force on other particles proportional to its mass, and inversely proportional to the square of the distance between the centers of mass of the two particles.
Observing this effect in galaxy clusters billions of light-years away strengthens our current understanding of gravity – and it also strengthens the case for the mysterious theoretical source of unexplained gravitational pull known as dark matter.
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