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No one is saying the cosmological constant can vary. The idea is simply that if dark energy is dynamical, it clearly cannot be explained by a cosmological const

• sigmoid10 2y ago
  As explained above this scalar field would manifest differently in the equations and basically be something that enters alongside a cosmological constant. Making dark energy or Λ itself vary at the level of the Einstein field equations means you're essentially making an integral constant vary which is not straightforward as people here purport.
  • pdonis 2y ago
    > this scalar field would manifest differently in the equations It shows up in the Einstein Field Equation as part of the stress-energy tensor. That is not a problem at all. > and basically be something that enters alongside a cosmological constant. The "cosmological constant" can just as easily be moved to the RHS of the Einstein Field Equation and also considered part of the stress-energy tensor, yes. There is no issue with that at all. > Making dark energy or Λ itself vary Is something nobody has claimed to be doing, as the GP said, so you are attacking a straw man. "Varying dark energy density" does not mean trying to make the cosmological constant vary. It just means adding some other component of stress-energy whose density does not have to be constant, but which still produces accelerated expansion. Anything with pressure less than minus 1/3 of its energy density will do that. A scalar field is the simplest such thing, but not the only possibility. None of this poses the slightest problem for the Einstein Field Equation.