Testing the possibility of gravity models other than general relativity may be closer to home than we thought. In an article published on the preprint server arXivA research team has suggested that we can use seismic motions on the Earth itself to test for altered gravity.

We don’t understand 95% of the content of the universe. The unknowns, known collectively as the dark sector, include both dark matter and dark energy. Dark matter appears to be the dominant form of matter in the universe, as each galaxy contains up to 80% of this invisible form of matter. Meanwhile, dark energy is a specific source of energy that fills all of space-time and is responsible for the accelerating expansion of space.

But the claim that dark matter and dark energy are physical entities is based on the assumption that our understanding of gravity is correct. Thanks to Einstein’s general theory of relativity, we now understand gravity best. This theory tells us that gravity is a manifestation of the distortion and warping of space-time itself.

But we know that general relativity is incomplete. We know that black holes collapsed at their centers and at the beginning of the universe. So we know we don’t have the full history of gravity yet. Guided by this, many over the decades have proposed modified theories of gravity that are a number of extensions and refinements of Einstein’s original model.

However, all these extensions face a number of formidable hurdles. We have tested general relativity in many contexts and at many scales, so it is difficult to construct a theory that differs significantly from general relativity to potentially explain dark matter and dark energy while satisfying all known observational constraints.

The more ways we can develop to study altered gravity, the better. And so a research team discovered that we don’t need to look at the stars to test various modified theories of gravity. Instead, we can look down on the Earth. They found that under varying gravitational conditions, seismic waves propagate at different speeds and in different paths on Earth.

Since we know many properties of the Earth, such as its mass and moment of inertia, we can reverse this information to use seismic data to constrain modified gravity theories. So far, the data do not indicate the need to deviate from Einstein’s original work. But the more tools we develop and the more search methods we use, the better.