Understanding Spin-2 Bosons & Graviton Theory of Gravity

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Discussion Overview

The discussion revolves around the concept of spin-2 bosons, specifically gravitons, and their relation to gravity theories, particularly General Relativity (GR). Participants explore the differences between various types of bosons (spin-0, spin-1, and spin-2), the implications of graviton theories, and the challenges in reconciling quantum mechanics with gravity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions how spin-2 bosons differ from spin-1 and spin-0 bosons, seeking to understand their behaviors and similarities.
  • Another participant expresses skepticism about the existence of a valid graviton theory, suggesting that current theories may only reproduce Newtonian gravity rather than GR.
  • There is a discussion on linearized gravity, with one participant asking if it is simply a linear approximation of GR.
  • Multiple participants provide insights into the nature of the graviton as a rank-2 tensor field, discussing its polarization tensor and helicity.
  • Some participants debate the conceptualization of gravity as an energy field, contrasting Newtonian and Einsteinian views.
  • There is a discussion about the nature of energy, with differing opinions on whether it is a substance or a property of something.
  • Participants reference popularizations by physicists, discussing their limitations and the need for mathematical rigor in understanding concepts like energy and mass.
  • One participant mentions that a theory of quantum gravity exists that incorporates classical GR with quantum corrections, but it does not fully encompass GR near singularities.

Areas of Agreement / Disagreement

Participants express a range of views on the existence and validity of graviton theories, with no consensus reached on the implications of these theories for gravity or their relationship to General Relativity. The discussion remains unresolved regarding the nature of energy and the interpretation of popular science literature.

Contextual Notes

Participants highlight limitations in current graviton theories, including the lack of renormalizability and the challenges in addressing the full scope of General Relativity, particularly near singularities.

  • #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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