7 Theories About What Creates Gravity — And None of Them Fully Work

Right now, as you read this, gravity is acting on you. It has been acting on you continuously since the moment you were born. It will act on you until the moment you die. Every person who has ever lived has experienced it without interruption. It has governed the structure of the observable universe since the first fraction of a second after the Big Bang. It holds the atmosphere to the planet, the Moon in its orbit, the solar system in its configuration, and 2 trillion galaxies in the large-scale structure of everything that exists. It is the oldest, most studied, most universally experienced force in nature. And nobody knows what it is. Not approximately. Not with minor gaps remaining. At the level of fundamental physics — what produces gravity, what mediates it, whether it is quantized, whether it curves spacetime or emerges from spacetime or is spacetime — physics does not have a complete answer. It has seven attempts. None of them fully work. Newton's force law worked for 200 years and broke at 43 arcseconds in Mercury's orbit. Einstein's general relativity resolved Mercury and broke at its own singularities — the places where its equations produce infinities and stop working. Quantum field theory attempts to incorporate gravity produce infinities that cannot be removed by the techniques that work for every other force. String theory produces a mathematically consistent quantum gravity and makes no testable predictions. Loop quantum gravity fixes the singularities and may lose the smooth spacetime that makes general relativity work at large scales. Modified gravity explains galaxy rotation curves without dark matter and fails at every larger scale. And the last theory on this list does not just fail to explain gravity. It suggests that the question — what creates gravity — may be the wrong question entirely. That gravity is not a thing that is created. That it is what spacetime does when something else entirely is happening at a level that no confirmed theory currently describes. 337 years of physics. Seven attempts. The most mathematically sophisticated scientific discipline in human history. The most universally experienced phenomenon in the history of human existence. Still no complete answer.