what is gravity?. we all know about gravity we see and experience its effects every day not just on...
TRANSCRIPT
• We all know about gravity• We see and experience its
effects every day• Not just on Earth…
http://grcimagenet.grc.nasa.gov/GRCDigitalImages/
1995/1995_02395L.jpg[NASA]
• 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]
• But what actually is gravity?• Does it work the same over
cosmic distances as it does in our solar system?
[NASA]
• 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]
• 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
• 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
• 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]
• Particle detectors at the LHC might reveal phenomena that support the existence of gravitons
[CERN]