Confusion about killing horizon in Carroll

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SUMMARY

The discussion centers on the concept of a killing horizon as defined in section 6.3 of Carroll's text, where a null hypersurface Σ is identified by the nullification of a killing vector field χμ. The confusion arises when distinguishing between static and stationary spacetimes, particularly regarding the killing field Kμ = (∂t)μ, which remains non-null at the killing horizon in stationary spacetimes. The resolution indicates that the definition of a killing horizon does not inherently conflict with the properties of the killing field in these contexts.

PREREQUISITES
  • Understanding of general relativity concepts, particularly killing vector fields
  • Familiarity with null hypersurfaces and their significance in spacetime geometry
  • Knowledge of the differences between static and stationary spacetimes
  • Access to Carroll's "Spacetime and Geometry" for reference
NEXT STEPS
  • Study the implications of killing vector fields in general relativity
  • Explore the properties of null hypersurfaces in various spacetime geometries
  • Investigate the distinctions between static and stationary spacetimes in detail
  • Review section 6.3 of Carroll's "Spacetime and Geometry" for deeper insights
USEFUL FOR

This discussion is beneficial for students and researchers in theoretical physics, particularly those focusing on general relativity and spacetime geometry, as well as anyone seeking clarity on the concept of killing horizons and their implications in different spacetime scenarios.

hideelo
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In the opening paragraph of section 6.3 Carroll defines a killing horizon to be a null hypersurface Σ where some killing vector field χμ becomes null. Later (on page 247 if you have the book) when distinguishing between static and stationary space times, he says that in a stationary, but not static spacetime, we still have the killing field Kμ = (∂t)μ , but it won't become null at the killing horizon. How is that possible? By definition that seems wrong. How do you have a killing horizon if that's not where your killing field becomes null?

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