New measurement of the Hubble Parameter

In summary: But it's not always possible to do that, and sometimes it's more important to be able to say "This uncertainty is really big, but we still don't know what's going on."In summary, the paper employs Bayesian statistics, but the method used is not explained. The error bars say there is 68% chance that Hubble parameter is between 61 and 82, a 95% chance that it is between 54 and 96, and a 99.7% chance that it is between 47 and 110. However, since the error bars are extrapolations, they are not very reliable.
  • #1
windy miller
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TL;DR Summary
New measurement of Hubble Parameter from GW
I just saw a new paper on measuring the Hubble Parameter : https://arxiv.org/pdf/1908.06060.pdf
It seems they are agreeing with Planck which I understand would speak largely against the idea of new physics from the Hubble tension.
However it says +14 and -7 next to the estimate. I presume these are the error bars. Are they saying it could be as high as 82 or as low as 61? Is that right? in which case I guess this paper isn't very conclusive . Over the years as they get more measurement the error bars will come down and we'll see where the chips land. So we shouldn't get very excited by this result. Is that right?
 
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  • #2
Those look to be the one-sigma error bars. So it is saying there is 68% chance that H0 is between 61 and 82, a 95% chance that it is between 54 and 96, and a 99.7% chance that it is between 47 and 110. So, as you say, it is inconclusive and nothing to get excited about. Yes, as more GW events come in, the measurements will get better and the error bars will come down. However, this will take a long time, since it's going to take hundreds of events before the errors in these measurements get small enough to be able to weigh in on the current discrepancy.
 
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thanks
 
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The paper says it employs a method of Bayesian analysis explained by "Gray et al", but that reference is "TBD". Is there a standard method of Bayesian statistics used by cosmologists?

The thread https://www.physicsforums.com/threa...rpretation-and-credibility-confidence.975683/ asks for an interpretation of "prior" in a paper about cosmology. It would nice for someone to answer the question, but the paper it asks about ( https://arxiv.org/pdf/1709.10504.pdf ) doesn't explain the statistical methods it uses.
 
  • #5
phyzguy said:
Those look to be the one-sigma error bars. So it is saying there is 68% chance that H0 is between 61 and 82, a 95% chance that it is between 54 and 96, and a 99.7% chance that it is between 47 and 110. So, as you say, it is inconclusive and nothing to get excited about. Yes, as more GW events come in, the measurements will get better and the error bars will come down. However, this will take a long time, since it's going to take hundreds of events before the errors in these measurements get small enough to be able to weigh in on the current discrepancy.
Extrapolating error bars like that doesn't really work that well, unfortunately. The asymmetry means that the errors are highly non-Gaussian, so applying Gaussian assumptions is doomed to fail.

Even with symmetric distributions, the real errors often get pretty far off once you get to the 3-sigma level, as most error distributions are pretty highly non-Gaussian. Typically, the real errors tend to be "fatter" than a Gaussian distribution, meaning that there's higher probability of large deviations from the mean than you'd expect. For instance, you might expend from a Gaussian distribution that values above 110 would occur with around 0.3% probability, given this experiment, but in reality the probability might be around 1%.

This is a big reason why theorists I knew back when I worked in physics basically took the view, "Let's just try to get the error bars so tight that there really isn't any doubt as to what's going on."
 

Related to New measurement of the Hubble Parameter

1. What is the Hubble Parameter and why is it important?

The Hubble Parameter, also known as the Hubble constant, is a measurement of the rate at which the universe is expanding. It is important because it helps us understand the age and evolution of the universe, as well as the distribution of matter and energy within it.

2. How is the Hubble Parameter measured?

The Hubble Parameter can be measured using various methods, including observations of the cosmic microwave background radiation, the redshift of galaxies, and the brightness of standard candles such as Type Ia supernovae. These measurements are then used to calculate the Hubble constant.

3. What is the significance of a new measurement of the Hubble Parameter?

A new measurement of the Hubble Parameter can provide more accurate and precise data, which can help refine our understanding of the universe and potentially challenge existing theories. It can also help us better estimate the expansion rate of the universe and its age.

4. How does the Hubble Parameter relate to dark energy and dark matter?

The Hubble Parameter is closely related to dark energy and dark matter, as these are two unknown components that contribute to the expansion of the universe. By measuring the Hubble Parameter, scientists can gain insight into the properties and effects of these mysterious substances.

5. What are the potential implications of a significant difference in the Hubble Parameter from previous measurements?

A significant difference in the Hubble Parameter from previous measurements could indicate the need for a new understanding of the universe and its expansion. It could also lead to further research and discoveries about the nature of dark energy and dark matter, and potentially challenge existing theories and models of the universe.

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