The distance duality relation

The distance duality relation tells us how, assuming that photons propagate on null geodesics in a pseudo-Riemannian spacetime and that their number is conserved, luminosity and angular diameter distances are related, via where dL is the luminosity distance, dA the angular diameter distance and z the redshift. This relation was introduced by Etherington in 1933, …

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Standard sirens, Cobaya and Beethoven’s 9th: Madrid week two

As of tomorrow, I'll have been in Madrid for two weeks! Time really does fly. The weather is still freezing and there's fresh snow on the hills behind campus (as you can hopefully see in the header image, which I took on my commute this morning). This week I made a proper start on the …

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