graviton spin

[Rev. Green]

I have always assumed the spin of the graviton to be 2, but Peter Rowlands, in his book Zero to Infinity, makes an excellent case for the graviton to have spin 1. What is the argument for spin 2?

[jake-the-peg]

http://www.physicsforums.com/archive/index.php /t-91769.html

What's the argument for spin 1?

I thought that would imply the existance of a repulsive as well as attractive gravity - or is that the argument?

[Rev. Green]

Jake is, of course, correct that spin 1 implies a bi-directional force. I don�t understand the book well enough to summarize, but page 318 explains why gravity is observed as unidirectional. Page 382 describes the spin 1 particle as the generator for the inertial reaction � so I am perhaps mistaken in calling it a graviton. Chapters 17 and 18 are also relevant. The explanation is convincing. It avoids the problem of re-normalisation, gives a possible explanation of the instantaneity of collapse of the wave-function, explains inertia, etc.

Is the fact that gravity is always observed to be attractive the only evidence for the graviton being spin 2? I had hoped that a spin 2 particle was needed to complete a group.

(If anyone intends to read Zero to Infinity leave chapter 1 to last or else it will appear pure numerology.)

[jake-the-peg]

No the reason it's thought to be spin 2 comes out of string theory. Where it's represented by a tensor of rank 2.

Looks an interesting book I bight give it a try - in return let me make a reccomendation.

Check out Roger Penrose's Road to reality. It gives a mathematical background to physics starting from relatively simple ideas such as complex numbers and calculus through the mathematics of relativity all the way through to string theory.

It's not easy but you really don't need to be a professional mathematician and it bridges the gap between popular science and formal academic text books in a remarkable way

[Rev. Green]

Many thanks Jake. I'll give it a try, but I'm agnostic about string theory.

One good idea from the book - though I think it is already well known - is that if you use quaternion representation you need only complex number multiplication, you don't need dot products or cross products i.e. the normal rules of quaternion multiplication ij=k etc. automatically give you dot and cross products for the real and imaginary parts.