# Another idea for observing dark energy

1. Feb 17, 2004

### marcus

http://arxiv.org./abs/gr-qc/0402066

these people (at U British Columbia) study an idea for observing the effect of the cosmological constant (dark energy, negative pressure...) on the spectrum of Xrays coming from a black hole

their conclusion is disappointing, the test they study (involving the iron line in the Xray fluorescence) is not sensitive enough to detect such a small dark energy density as the cosmologists say we have.

it is something of a curiosity tho, that they should even think they could see the effect of Lambda in the Xrays from a BH and so I gave the link in case you want to see how their idea goes

BTW the figure they give for cosmologists current estimate of Lambda is in metric units of inverse area (curvature)

1.3E-46 per square kilometer

People seem to have different conventions, depending on where they put a factor of 8pi. I would divide this by a factor of 8pi and say that their figure really means Lambda is 5.17E-48 per sq. km. and
1/Lambda is 1.93E47 sq. km

anybody have any preference as to which version to use? or some suggestion as to how to arrive at a common language for describing the estimated size of the cosmological constant.
(now most people just say "0.73" meaning 73 percent of the critical density, something that is a bit more familiar having been around longer)