Quantum gravity force violations

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Discussion Overview

The discussion centers around the potential violations of C, P, and T symmetries in the context of quantum gravity and its comparison with other fundamental forces, particularly the weak interaction. Participants explore theoretical implications and the nature of these symmetries across different forces.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether quantum gravity exhibits C, P, and T violations similar to the weak interaction.
  • Another participant asserts that both electromagnetic and strong forces respect C, P, and T symmetries and expresses certainty that gravity does as well, citing mass equivalence between particles and antiparticles as a reason for C symmetry.
  • This same participant further argues that Einstein's equations are time reversal invariant, suggesting that T symmetry holds, and infers that P symmetry should also hold by CPT invariance.
  • Another participant humorously notes the uniqueness of the weak force in violating C, P, and T symmetries and prompts further inquiry into the reasons behind this.
  • A later reply claims that the weak force's chiral nature is a result of experimental demands, describing it as a gauge theory with two representations of SU(2).
  • Another participant elaborates on the chiral nature of the weak force, discussing the decomposition of SU(4) into two copies of SU(2) and the implications for 4-component spinors and helicity.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of gravity concerning C, P, and T symmetries, with some asserting that gravity respects these symmetries while others raise questions about the nature of quantum gravity. The discussion remains unresolved regarding the specifics of symmetry violations across forces.

Contextual Notes

Participants do not provide definitive conclusions about the implications of symmetry violations or the nature of quantum gravity, leaving several assumptions and dependencies on definitions unaddressed.

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Apart from C, P and T violation in weak interaction, do the same violations occur for the other three forces, in particular, the quantum gravity force?
 
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Both EM and strong force respect C, P and T. I am pretty certain that gravity also respects them: a particle has the same mass as its antiparticle so its gravitational pull is the same (C). I think Einstein's equations are time reversal invariant so (T) holds, hence (P) should also hold by CPT.
 
zefram_c said:
Both EM and strong force respect C, P and T. I am pretty certain that gravity also respects them: a particle has the same mass as its antiparticle so its gravitational pull is the same (C). I think Einstein's equations are time reversal invariant so (T) holds, hence (P) should also hold by CPT.

Why then is the weak force the only force to violate C, P and T symmetry? Isn't that funny?
 
The answer is that experiment demands it..

So by construction the theory is chiral, eg its a gauge theory in the yangmills sense with two representations of SU(2)

Su(2) (left) * Su(2) (right)
 
Haelfix said:
So by construction the theory is chiral, eg its a gauge theory in the yangmills sense with two representations of SU(2)

Su(2) (left) * Su(2) (right)

And that is because SU(4) the double cover of the Poincare group, just happens to decompose into two copies of SU(2), so the 4-component spinors have their first two components acted on independently of their last two. Left and right helicity.
 

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