Understanding Einstein-Hilbert Action: Detailed Explanation from an Expert

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Discussion Overview

The discussion revolves around the Einstein-Hilbert action in the context of general relativity, focusing on its appropriateness and the reasoning behind its formulation. Participants seek to understand the derivation of field equations from this action and the intuition behind Hilbert's choice of this specific action, exploring both theoretical and conceptual aspects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asks for a detailed explanation of why the Einstein-Hilbert action is considered appropriate and how it yields the correct equations.
  • Another participant notes that the field equations can be derived by setting variations of the action with respect to the metric equal to zero, referencing common practices in general relativity texts.
  • A different participant expresses curiosity about the intuition behind Hilbert's choice of this action, seeking deeper insights into the reasoning involved.
  • One participant suggests that the Ricci scalar is a simple scalar that encodes the curvature of spacetime, implying its relevance to the action.
  • Another participant summarizes that the action is favored because it is simple, general, and encodes essential information needed for the field equations, while also expressing their intrigue about the topic of variational mechanics.

Areas of Agreement / Disagreement

Participants express a shared interest in understanding the Einstein-Hilbert action, but there is no consensus on the deeper intuition behind its formulation or the specific reasons for its appropriateness.

Contextual Notes

Some participants highlight the need for more insight into the principles of variational mechanics and the motivations behind the choice of the action, indicating that their understanding is still developing.

Who May Find This Useful

This discussion may be useful for those interested in general relativity, variational principles in physics, and the foundational aspects of gravitational theories.

Terilien
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Can someone explain to me why this is the appropriate action?It makes some sens that that would be used, but I'd like a detailed explanation from someone familiar with the topic.

Why is it the one that yields the proper equations?
 
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Well, for a start, you can derive the field equations by setting variations of this action with respect to the metric equal to zero. This is done in many GR texts.
 
Yes but what is the intuition behind it? What lead hilbert to choose that particular action?
 
Can you think of a simpler scalar that encodes the curvature of spacetime? The Ricci scalar is a fairly obvious choice.
 
So essentially it used because its the simplest, most general(encodes curvature) involves the inverse metric, the ricci tensor, etc.. and such. So essentially its simple and encodes all the information that we may want tin the field equations...


This is the first time I've emcountered this topic(variational mechanics) so it seems quite exotic. Its very interesting though.

It would however be nice, to gain whatever insight I can into this principle and this topic in general.
 
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