The spin = 2 graviton questions are interesting, but note that all quantum spin has the property of taking 4 pi rotation and so this is not just a property of spin = 2 particles like gravitons. There are in fact many spin = 2 atoms and molecules and of course, two photons also form a spin = 2 particle whenever they are coincident.
Feynman simply showed that a hypothetical graviton would necessarily show spin = 2 angular momentum or helicity. The massless notion is akin to a massless photon, but that means rest mass since the graviton would still carry momentum just like a photon. Note that in quantum matter action just like all quantum action, a rotation of 4 pi is equivalent to a quantum phase shift of 4 pi. In space and time, Science uses spinors or dirac matrices to represent spin since that spin is a separable coordinate from location and momentum. In matter action, of course quantum phase is also separable as a third orthogonal coordinate of SO(3).
Here are selected comments that have to do with graviton spin:
Dr. Agnew,
The paper takes off immediately from a premise that detection of a massless helicity-two particle being evidence of the existence of gravitons. Do you concur with that and in what regard to 'matter, action & quantum phase'. Also is a helicity-two particle meant by definition to be a 4 pi rotation of quantum spin states?
thanx j
John,
can the helicity in a spin2 particle(a solitonic character) be seen as a quantization in itself? In a way the em-force is also such because it requires two rotations to come back to the same orientation.
Ulla.
Ulla,
That goes to my question of what is meant by a "massless helicity spin two particle"; as referred to in the first paragraph of the article 'The noise of Gravitons' by Parikh, Wilczek & Zahariade. The attendant footnote is for a 1963 Feynman paper, 'Quantum theory of gravitation', which I have not hunted up and was hoping someone with greater familiarity with the long history of Quantum Mechanics could give a concise statement of the contention by the authors and a description of how 'helicity-two' is treated geometrically and analytically. The opening premise of the article is broadly sweeping in that it literally says, "Feynman famously showed" that 'consistency in the quantum mechanics of a massless helicity-two particle leads one to Einstein gravity'. So I am just seeking some clarification.
My personal preferences of paradigms differs from the article's approach, but that's not the issue. The article won first place in the Gravity Research Foundation's 2020 contest so if that is a preferred direction in that organization's inquiries, it would be good to understand more of the thinking that drives it. Other than that, I think it is always necessary that clear consensus on definition of terms be accepted, so while I am most accustomed to speaking of a rotation of two full circular turns as "4 pi" and a "spin two" meaning the additive 1/2 pi = 90 degree methodology in the spin coordinate system adding up to a single full circular rotation, I am wondering if 'Helicity-two' means a non-zero torque of two full axial rotations giving a 4 pi spinor state restoration of the initial polarity.
Ulla,
Expanding on my previous post, and taking that as how I read the article; if you follow what they present in the way of blanket statements of functions integrating over partial differentials ( perhaps mimicking the forms in the complexities of GR ) it seems that what the authors are attempting in argument to do is to 'split' the 4pi spinor state into two 2pi events at a distance so that the electromagnetic opposing polarities would equate as gravitational attraction.
I do not attempt to take "particle" literally in quantum mechanics, QM was never intended to be the least bit realistic. 'Exchange particles' only make sense to me if I treat the term to mean more like "an integral partial value" of some prescribed effect associated with a presumed material point. I watched a good PBS program on the invention of alphabets in which it was pointed out that the great innovative leap that took communication from pictographs to sound symbols was the very human amusement in making puns. So even with the Higgs I don't try to envision realistic particles quantum mechanically, I see them more like "partial calls" jrc