Gravity and gravitons

[Single Serving Jack]

New member here, may as well dive in with an new thread and a question!

I've just read an article in the New Scientist magazine about detecting gravitons. Here is the link, it's a subscriber only article I'm afraid:

http://www.newscientistspace.com/art...gravitons.html

The basic idea in the article is that the force of gravity is transmitted by particles (as stated by quantum theory) called gravitons, but they are so unlikely to actually interact with other matter (as the gravitational force is so weak compared to other forces) they are practically impossible to ever detect.

My question (most likely pretty basic but what the hell) is that I thought gravity was a manifestation of the curvature of space-time made by the mass of bodies, and in effect a moon orbiting a planet, or an apple falling to the ground was simply following a straight line in space-time. Clearly I need a bit of direction here as I'm not seeing the link between that and gravitons. This is all something to do with relativity and quantum theory, right? Or maybe not.


Here's the paper that the article is actually about: www.arxiv.org/abs/gr-qc/0601043

[Single Serving Jack]

New member here, may as well dive in with an new thread and a question!

I've just read an article in the New Scientist magazine about detecting gravitons. Here is the link, it's a subscriber only article I'm afraid:

http://www.newscientistspace.com/art...gravitons.html

The basic idea in the article is that the force of gravity is transmitted by particles (as stated by quantum theory) called gravitons, but they are so unlikely to actually interact with other matter (as the gravitational force is so weak compared to other forces) they are practically impossible to ever detect.

My question (most likely pretty basic but what the hell) is that I thought gravity was a manifestation of the curvature of space-time made by the mass of bodies, and in effect a moon orbiting a planet, or an apple falling to the ground was simply following a straight line in space-time. Clearly I need a bit of direction here as I'm not seeing the link between that and gravitons. This is all something to do with relativity and quantum theory, right? Or maybe not.


Here's the paper that the article is actually about: www.arxiv.org/abs/gr-qc/0601043

[Choobus]

Quantum therory has nothing to say about gravity one way or another. The fledgling theories of quantum gravity are untested.

Relativity neither neeeds nor wants gravitons. Geodesics in spacetime are perfectly adequate.

[Choobus]

Quantum therory has nothing to say about gravity one way or another. The fledgling theories of quantum gravity are untested.

Relativity neither neeeds nor wants gravitons. Geodesics in spacetime are perfectly adequate.

[Single Serving Jack]

The article says:

"According to quantum theory, all forces are transmitted by particles - the photon for the electromagnetic force, the W and Z bosons for the weak force and gluons for the strong force.... Yet no one has ever seen the particle thought to convey gravity."

I are confused.

[Single Serving Jack]

The article says:

"According to quantum theory, all forces are transmitted by particles - the photon for the electromagnetic force, the W and Z bosons for the weak force and gluons for the strong force.... Yet no one has ever seen the particle thought to convey gravity."

I are confused.

[a different tim]

Well, hang on, I thought relativity did predict gravity waves. And by QM all waves can also be seen as particles, so relativity does predict gravitons.

Am I on the wrong track here, or is this what you meant by only needing gravitions with QM, Choob??

[a different tim]

Well, hang on, I thought relativity did predict gravity waves. And by QM all waves can also be seen as particles, so relativity does predict gravitons.

Am I on the wrong track here, or is this what you meant by only needing gravitions with QM, Choob??

[Choobus]

yes, but quantum theory is limited. The best quantum theory is QCD. that links up Electromagnetism and the strong and weak nuclear forces. There's no gravity, so quantum theory does not have the foundation to say that "all forces are transmitted by particles". It can certainly claim that "all forces described by quantum theory are transmitted by particles", but gravity aint one of them.

[Choobus]

yes, but quantum theory is limited. The best quantum theory is QCD. that links up Electromagnetism and the strong and weak nuclear forces. There's no gravity, so quantum theory does not have the foundation to say that "all forces are transmitted by particles". It can certainly claim that "all forces described by quantum theory are transmitted by particles", but gravity aint one of them.

[Choobus]

A proper description of gravity waves would include the structure of spacetime, which is unknown and is the subject of quantum gravity and string theories. None of these theories have been tested. Relativity does predict gravity waves, but there is much that is not known about them. They have never been detected so they might not even exist. If they do exist they would be more like a water wave than a light wave. That is, they don't need a messanger particle because they travel via a medium (just as light was once thought to travel through the luminiferous ether). So spacetime itself modulates the wave, but nothing actually moves. This is totally different from the kinds of waver the QM talks about, which have no medium and are therefore amenable to both wave and particle descriptions.

[Choobus]

A proper description of gravity waves would include the structure of spacetime, which is unknown and is the subject of quantum gravity and string theories. None of these theories have been tested. Relativity does predict gravity waves, but there is much that is not known about them. They have never been detected so they might not even exist. If they do exist they would be more like a water wave than a light wave. That is, they don't need a messanger particle because they travel via a medium (just as light was once thought to travel through the luminiferous ether). So spacetime itself modulates the wave, but nothing actually moves. This is totally different from the kinds of waver the QM talks about, which have no medium and are therefore amenable to both wave and particle descriptions.