The Quest for an Ultimate Theory of Gravity
Without gravity the night sky would look very empty. Stars, galaxies, moons, and planets — none of these could exist without gravity holding them together. Neither, for that matter, could the Sun or Earth. It is gravity that pulled together diffuse atoms and built the universe that we see around us today.
Gravity has also been at the heart of our own efforts to understand the nature of reality, from Newton’s formulation of the universal law of gravity to Einstein’s theory of relativity. Today gravity lies at the centre of new problems in science, and holds the key to uncovering what may be the ultimate theory of physics.
For something that has had such a profound effect on humanity, gravity is surprisingly weak. Of the four fundamental forces known to physics, gravity is by far the weakest. This weakness can easily be demonstrated — the magnetic force of a small fridge magnet can easily lift a pin into the air, thus defeating the gravitational force of an entire planet.
The weakness of the gravitational force means it can be almost completely ignored at the level of atoms and molecules. It is only when we look at very big objects — planets, stars and galaxies, that gravity starts to matter. While the other fundamental forces fade away over short distances, the force of gravity can be felt from one side of the galaxy to…
