Which rate of Universe expansion are we currently using?

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    Expansion Rate Universe
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Discussion Overview

The discussion centers around the current rates of the universe's expansion, specifically the values of Hubble's constant (H0) that have been proposed in recent studies. Participants explore the implications of these rates for calculations related to cosmic distance and the age of the universe, as well as the reliability of different measurements.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants mention rates of 67, 71, and 74 for Hubble's constant, with a consensus that 74 is not currently accepted.
  • One participant argues that the latest Hubble data suggests the discrepancy in measurements is unlikely to be a fluke, with a probability of 1 in 100,000.
  • Another participant expresses uncertainty about the role of Hubble's constant in calculating the age of the universe and distances.
  • It is noted that the cosmic distance ladder methods primarily utilize Hubble's constant for distance calculations.
  • Some participants discuss the origins of the 67 and 71 values, attributing them to different studies, including one from 2001 that used stars and another that measured the Cosmic Microwave Background (CMB).
  • One participant mentions that the 2018 Planck Collaboration data set is still in use, providing a value of H0 = 67.4 ± 0.5 km/s/Mpc, emphasizing the interdependence of parameters within the LCDM model.
  • There is a suggestion that data analysis often combines error constraints from various experiments to yield a combined result, reflecting the uncertainty in settling on a single value.
  • Some participants indicate that different groups may prefer different values based on the context, with Hubble results being more reliable for current expansion and Planck results being better for early universe conditions.
  • One participant expresses interest in accessing studies related to the rates discussed.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a single rate for the universe's expansion, with multiple competing views and ongoing uncertainty regarding the best value to use in different contexts.

Contextual Notes

The discussion highlights the complexity of measuring Hubble's constant and the interrelation of various cosmological parameters, as well as the ongoing debates in the field regarding the reliability of different measurements.

Who May Find This Useful

This discussion may be of interest to those studying cosmology, astrophysics, or anyone curious about the current understanding of the universe's expansion and the methodologies used in related research.

HankDorsett
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TL;DR
Including the most recent study I've heard about 3 different rates
The rates I've come across are 67, 71 and 74. Obviously it's not 74 as it was just announced. Is it one of these other numbers, something else? I'm only asking out of curiosity.
 
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HankDorsett said:
Obviously it's not 74 as it was just announced.

That's not necessarily correct as the latest Hubble data lowers the possibility that the recently calculated discrepancy is only a fluke to 1 in 100,000.
 
Tghu Verd said:
That's not necessarily correct as the latest Hubble data lowers the possibility that the recently calculated discrepancy is only a fluke to 1 in 100,000.
it's quite possible I have an incorrect assumption here. For some reason I thought we use this rate to help calculate other things. Age of the universe? Distance?
 
Tghu Verd said:
Mostly distance as I understand the objective, as part of the "cosmic distance ladder" methods: https://en.wikipedia.org/wiki/Cosmic_distance_ladder
That's partially where my question was coming from. I think we got 67 from an original study that measured CMB. I think a 2001 study using stars gave us 71. After the release of the 2001 study did we switch over to it or stick with the original calculations?
 
HankDorsett said:
That's partially where my question was coming from. I think we got 67 from an original study that measured CMB. I think a 2001 study using stars gave us 71. After the release of the 2001 study did we switch over to it or stick with the original calculations?
For large scales I think we are still using the 2018 Planck Collaboration data set, with ##H_0=67.4## +- 0.5 km/s/Mpc. One must remember that the whole dataset as a unit is consistent with the LCDM model and one cannot just change one parameter, like ##H_0##, without changing at least some of the rest.
 
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Jorrie said:
For large scales I think we are still using the 2018 Planck Collaboration data set, with ##H_0=67.4## +- 0.5 km/s/Mpc. One must remember that the whole dataset as a unit is consistent with the LCDM model and one cannot just change one parameter, like ##H_0##, without changing at least some of the rest.
Thanks for your response and providing the link. Although I wasn't able to understand much of what the link talked about it did show me something. The more you learn the more you realize you need to learn.
 
HankDorsett said:
Summary: Including the most recent study I've heard about 3 different rates

The rates I've come across are 67, 71 and 74. Obviously it's not 74 as it was just announced. Is it one of these other numbers, something else? I'm only asking out of curiosity.
It really depends. Usually the way this is done in actual data analysis is to simply combine the error constraints of the different experiments together to provide a combined result. When there's a disconnect between different data sets, they may publish separate results which are combined with each.

Honestly, I think the best answer is, "We don't know, so we don't try to settle on either result."

And if you are only using the ##H_0## constraint, usually redoing some data analysis with a different input value of ##H_0## is as simple as pushing a button, so there's no real reason to only consider one of them.
 
It depends on who you mean by "we". Some people use the Hubble result, some people use the Planck result, and the people involved in this topic use both (plus the other measurements) and compare the results. For the expansion now the Hubble results should be more reliable, for things that happened in the early universe the Planck results will be better.
 
  • #10
Thanks for all of your replies. By chance, can someone provide links to the studies surrounding this rate? As I was catching up to this post I was wondering how cool would it have been to be a fly on the wall as they went through these studies.
 

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