0
$\begingroup$

I was reading a paper from arxiv (https://arxiv.org/abs/1312.5798) when I stumbled upon this passage at pag 4

"However, even at low redshifts, there are limitations to how well the Type Ia supernova data can be interpreted with an empirical model such as $\Lambda$CDM, because the data cannot be determined independently of the assumed cosmology--- the supernova luminosities must be evaluated by optimizing at least 4 parameters simultaneously with those in the adopted model. This renders the data compliant to the underlying theory..."

but I know that supernovae distances are calculated by comparing the observed flux with the luminosity through the relation

$$ F = \frac{L}{4 \pi S_k (r)^2 (1+z)^2} $$

where $ 4 \pi S_k (r)^2 $ is the proper area and the $(1+z)^2$ comes from both the redshift of the photon wavelength and the time expansion, so i thought that the only thing that could influence the measure should be the value of the curvature parameter $ k$ , so what does the author mean with "optimizing at least 4 parameters simultaneously with those in the adopted model" ? thanks

$\endgroup$
3
  • $\begingroup$ Doesn't the estimate of $z$ depend upon the "choice" of the Hubble constant? $\endgroup$ Commented Jan 18, 2022 at 20:43
  • $\begingroup$ Hi @Alucard: I would like to try to help you regarding your question, but your "the time expansion" confuses me. Please explain what this phrase means. I am familiar with space expansion, but have no idea about time expanding. $\endgroup$
    – Buzz
    Commented Jan 19, 2022 at 16:43
  • $\begingroup$ @buzz ah yes I got that from the book but I did not explain it well, I meant the increase in time between 2 successive detections $\endgroup$
    – Alucard
    Commented Jan 19, 2022 at 18:21

1 Answer 1

0
$\begingroup$

The calculation of z for one supernova depends on the change in frequency of multiple measurements of specific atoms. The value of z does not depend on H_0. The values of z for multiple supernovae (a lot of them) lead to corresponding estimates of distances from Earth. Each combination of z and distance gives a supernova specific value for H_0. The average of these very many values for H_0, one for each supernova, is the calculated cosmological value for H_0. (This is a simplified explanation, more-or-less like is was about a century ago when Edwin Hubble first calculated what has become H_0.)

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.