How can BAO and SN constraints be compared for measuring dark energy?

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Discussion Overview

The discussion focuses on comparing Baryon Acoustic Oscillations (BAO) and Supernova (SN) measurements in the context of measuring dark energy. Participants explore the methodologies, advantages, and limitations of each approach within cosmological studies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that to achieve competitive constraints on dark energy, changes in H(z) must be observed at the 1% level, which would lead to statistical errors in the dark energy equation of state on the order of 10%.
  • Another participant emphasizes the need for accurate calibration of the standard ruler over the universe's age and volume, along with ultra-precise measurements.
  • BAO measurements are proposed as providing a more accurate standard ruler for estimating H(z) than supernovae, contingent on sufficient galaxy observations.
  • Questions are raised regarding the superiority of BAO over supernovae for distance measurement and their independence from SN1A measurements.
  • One participant asserts that BAO measurements are completely independent of SN1A measurements and contribute to dark energy measurement by assessing the rate of expansion over time.
  • It is argued that BAO is better due to the abundance of galaxies compared to supernovae, which have higher individual measurement errors. However, the value of supernova measurements is acknowledged, with the claim that combining both methods yields better results than either alone.
  • A link to a chart comparing constraints from BAO and SN is provided, suggesting visual data on their relationship.

Areas of Agreement / Disagreement

Participants express differing views on the comparative effectiveness of BAO and SN measurements for dark energy constraints. While some agree on the advantages of BAO, others question the extent of its superiority and the independence from supernova measurements. The discussion remains unresolved regarding the optimal approach for measuring dark energy.

Contextual Notes

Participants highlight the need for precise calibration and measurement techniques, but the discussion does not resolve the specific methodologies or assumptions underlying the comparisons made.

wolram
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How do BAO help us measure dark energy?

thank you for all the help PF members give in the cosmology forum.
 
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This is what i have found so far.

To get competitive constraints on dark energy we need to be able to see changes in H(z) at the 1% level -- this would give us statistical errors in the DE equation of state of O(10%).
  • We need to be able to calibrate the ruler accurately over most of the age of the universe.
  • We need to be able to measure the ruler over much of the volume of the universe.
  • We need to be able to make ultra-precise measurements of the ruler.
 
BAO measurements provide an accurate standard ruler that can be used to estimate H(z) more accurately than supernovae, with enough galaxy observations.
 
But how are they better than supernova for distance measurement and are they independent of
sn1a? and how do they help us measure DE.
 
Last edited:
They are completely independent of SN1A measurements. They help to measure DE by measuring the rate of expansion over time.

They're better primarily because there are huge numbers of galaxies out there, but only so many supernovae. Also, each individual supernova has a lot of error.

This isn't to say that supernova measurements are worthless. SN and BAO measurements have very different error properties, so that the combination of the two is significantly better than either one by itself.
 

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