Gravity – The Weakest Force in Charge of Everything

Pick up a small fridge magnet and use it to lift a paperclip off the table, and you've just watched electromagnetism, working through a scrap of moulded plastic and metal, casually beat the gravitational pull of the entire planet Earth. Gravity is, by a staggering margin, the weakest of the four fundamental forces of nature — and yet it's the one that holds you to the ground, keeps the Moon circling Earth, and shapes the large-scale structure of the entire universe. This episode explores that paradox, from Newton's tidy law of universal gravitation through Einstein's stranger and more accurate picture of gravity as curved spacetime, and ends at the edge of what physics still can't explain. You'll come away understanding just how weak gravity really is compared with the other fundamental forces, how Newton's law succeeded for centuries including predicting the discovery of a new planet, why Einstein's general relativity was needed to fix a small but real crack in Newton's picture, what's actually happening during weightlessness and ocean tides, and why unifying gravity with quantum mechanics remains one of the biggest unsolved problems in physics. Talking Science is sponsored by Kinsoft. Visit www.kinsoft.com.au Further reading: NASA – "What Is Gravity?" and general relativity mission pages; Australian Academy of Science – public explainers on Einstein and gravitational physics; Scientific American – features on quantum gravity and unification attempts; Nature – research summaries on tests of general relativity.