Understanding Spin-2 Bosons & Graviton Theory of Gravity

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SUMMARY

The discussion focuses on the graviton theory of gravity, emphasizing that a graviton must be a Spin-2 boson, which is fundamentally different from Spin-1 and Spin-0 bosons. The graviton is described as a rank-2 tensor field, with its polarization tensor derived from two polarization vectors, indicating its helicity of ±2. The conversation also highlights that current graviton theories primarily reproduce Newtonian gravity rather than General Relativity, with effective field descriptions being the most viable approach. Participants agree that a comprehensive theory of quantum gravity that aligns with General Relativity remains elusive.

PREREQUISITES
  • Understanding of General Relativity and its implications on gravity.
  • Familiarity with quantum field theory concepts, particularly bosons and their spins.
  • Knowledge of tensor fields and their mathematical representations.
  • Basic comprehension of the differences between scalar, vector, and tensor fields.
NEXT STEPS
  • Research the mathematical foundations of Spin-2 bosons and their role in quantum gravity.
  • Explore effective field theories of gravity and their implications on classical gravity models.
  • Study the differences between linearized gravity and full General Relativity.
  • Investigate current literature on graviton theories and their compatibility with established physics.
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Physicists, researchers in theoretical physics, and students interested in the intersection of quantum mechanics and general relativity, particularly those exploring the nature of gravity and bosonic fields.

  • #31
The electromagnetic field is an antisymmetric rank two tensor field therefore (not but) it is a vector field. Just count the number of components. Antisymmetric means its diagonal is zero. There remains one triangular block which has 3 + 2 + 1 = 6 independent components. These are the electric field and magnetic field vector.
Gravity is a symmetric rank two tensor, it's diagonal is not zero. It therefore has 6 (upper triangular block) + 4 (diagonal) = 10 independent components (the metric tensor). A spin n field has (n(
The solutions to Einstein's equations are NOT waves in general (no pun) since these are non-linear equations. But if you neglect nonlinear terms you can obtain wave-like solutions, those were detected recently. Nonlinear in this context means the graviton creates and is subject to gravitational attraction. That makes gravity similar to a non-Abelian gauge interaction such as QCD. In contrast EM is an Abelian gauge theory because the photon has no charge and therefore cannot interact with the electrons that produced it.
 
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  • #32
Of course, photons interact with electrons. That's how we detect them all the time.

Also your counting is misleading since both the photon and the graviton are massless fields and thus they have only two physical polarization states (except for scalar fields which have of course only 1).
 
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