1. What is gravity?

2. We all know about gravity We see and experience its effects every day Not just on Earth… http://grcimagenet.grc.nasa.gov/GRC DigitalImages/1995/1995_02395L.jpg [NASA]

3. But in the solar system…and beyond [NASA]

4. Gravity is a force that attracts everything to everything else The strength of the force depends on: –The mass of the objects –The distance between them So planets like Earth and Jupiter have nearby moons orbiting them While they in turn orbit the distant, but more massive Sun [NASA]

5. But what actually is gravity? Does it work the same over cosmic distances as it does in our solar system? [NASA]

6. Newton made a good job of describing how gravity acts between objects, and his ideas work fine in most situations Einstein made a breakthrough by describing gravity as a bending of space-time… …so how does that work? [NASA]

7. Imagine a canon ball sitting on a trampoline – that’s like the Sun bending space-time Flick a marble along the trampoline past the canon ball and it travels around the canon ball in a circle – that’s the Earth orbiting the Sun From the marble’s point of view, it’s going in a straight line along a flat surface OK, the marble slows down and falls in towards the canon ball because of friction, but take away the friction and it would carry on orbiting the canon ball forever

8. Einstein’s view of gravity is holding up well to experimental evidence But it means gravity is a different kind of force to the other three fundamental forces in quantum physics, which each have a mass less “carrier particle” The electromagnetic force, for instance, is carried by photons Could there be a particle that transmits the force of gravity? A graviton? If so, it will be hard to spot because gravity is a very weak force at the atomic scale

9. In 2011 a fleet of 3 laser- linked probes will search for gravitational waves travelling through space They’re ripples in space-time caused by galaxies merging or black holes colliding Einstein’s theory predicts they should exist But could they also provide evidence for gravitons? [NASA]

10. Particle detectors at the LHC might reveal phenomena that support the existence of gravitons [CERN]