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Q & A: what is the cosmological constant?

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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
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.

(published on 12/26/2012)

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