Gravity . Does a boson Graviton exist?
January 7, 2014
“Astronomers have discovered the first pulsar with two stars circling it. By watching the three objects orbit one another, observers will soon be able to perform the best-ever test of the “strong equivalence principle”, which is a key prediction of Albert Einstein’s general theory of relativity.
Like the Newtonian theory of gravity that came before it, Einstein’s general theory of relativity says that gravity does not discriminate: it accelerates all objects equally, no matter what their size, shape or composition. Apollo 15 astronaut Dave Scott demonstrated this so-called equivalence principle on the Moon in 1971 by dropping a hammer and a falcon’s feather, which hit the lunar surface simultaneously.
The strong equivalence principle of general relativity goes further, saying that gravity should accelerate all objects in the same way even if the objects hold themselves together with their own gravity. In other words, the gravitational self-energy that binds a planet or star together should have no effect on how it is accelerated. This is unlike theories that seek to topple general relatively and predict a small deviation related to gravitational self-energy called the Nordtvedt effect.”
“The most exacting test of the strong equivalence principle performed so far involves tracking the Earth and the Moon. As they orbit the Sun, both are continually falling through the solar gravitational field. Einstein’s theory says that the Earth and the Moon should behave the same, even though the Earth has greater self-gravity. Precise laser-ranging measurements of the distance between the two bodies back this up by revealing no evidence of the Nordtvedt effect.”
- Does Graviton exist?
- The three other known forces of nature are mediated by elementary particles: electromagnetism by the photon, the strong interaction by the gluons, and the weak interaction by the W and Z bosons. The hypothesis is that the gravitational interaction is likewise mediated by an – as yet undiscovered – elementary particle, dubbed the graviton. In the classical limit, the theory would reduce to general relativity and conform to Newton’s law of gravitation in the weak-field limit.