# What is the Cosmological Constant?

*Most recent answer: 12/26/2012*

Q:

I've read from de Sitter invariant special relativity that what is dubbed the cosmological constant in GR would become a fundamental parameter describing the symmetry structure of space-time.
I'm wondering...Would that make it part of the stress-energy tensor or would that be a uniquely separate component of the field equations?

- Devon (age 26)

Lansing

- Devon (age 26)

Lansing

A:

Devon-

You always ask questions close to or beyond the level of our knowledge. Here, though, I think the answer is pretty simple. Mathematically it doesn't make any difference whether you treat this term as an additive extra to the stress-energy tensor or as part of the tensor.

The difference is only psychological- if you treat it as part of the stress-energy tensor that may suggest to you that you ought to be looking for some dynamical field associated with it, perhaps with some experimental implications once you have a more definite idea, etc. There's a nice discussion in Feynman's Character of Physical Law about how sometimes mathematically equivalent theories can trigger different lines of thought about where to go next.

Mike W.

You always ask questions close to or beyond the level of our knowledge. Here, though, I think the answer is pretty simple. Mathematically it doesn't make any difference whether you treat this term as an additive extra to the stress-energy tensor or as part of the tensor.

The difference is only psychological- if you treat it as part of the stress-energy tensor that may suggest to you that you ought to be looking for some dynamical field associated with it, perhaps with some experimental implications once you have a more definite idea, etc. There's a nice discussion in Feynman's Character of Physical Law about how sometimes mathematically equivalent theories can trigger different lines of thought about where to go next.

Mike W.

*(published on 12/26/2012)*