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> And so they're not expected to be the same. Still there was a kind of hope that there would be just one Hubble constant eventually, resulting from both measu

by acqq 8y ago

> And so they're not expected to be the same. Still there was a kind of hope that there would be just one Hubble constant eventually, resulting from both measurements, that some kind of unexpected error would be discovered on one (or both) of the sides. But what's happening is illustrated on the picture subtitled "Modern measurement tensions..." in the second link, plus the newest result from the Riess' paper: "74.03 +/- 1.42 km/s/Mpc" with "an uncertainty of 1.91%" which you should imagine appearing to the right of the picture, with the dot at 74 and much narrower red bar. So, looking at that picture again, we have the "blue" and the "red" results for years already that don't converge and keep doing so, although both approaches use always more advanced techniques. But, quoting from the second link: "It is possible that the ways we measure the expansion rate of the Universe are actually revealing something novel about the nature of the Universe itself. Something about the Universe could be changing with time" "Some options include: - our local region of the Universe has unusual properties compared to the average (which is already disfavored), - dark energy is changing in an unexpected fashion over time, - gravity behaves differently than we've anticipated on cosmic scales, - or there is a new type of field or force permeating the Universe." "The option of evolving dark energy is of particular interest and importance, as this is exactly what NASA's future flagship mission for astrophysics, WFIRST, is being explicitly designed to measure." But also: https://en.wikipedia.org/wiki/Wide_Field_Infrared_Survey_Telescope https://en.wikipedia.org/wiki/Wide_Field_Infrared_Survey_Tel... "The Trump administration's proposed FY2019 budget would terminate WFIRST" "Again the Trump administration proposed to terminate WFIRST in its FY2020 budget proposal to Congress" And finally, from the OP article: "Distinguished University of Chicago astrophysicist Wendy Freedman" "spent five years looking at different stars than Riess to come up with a third calculation of the expansion rate. They just submitted their work to the same journal. Freedman wouldn’t reveal her number but said it is between the two other figures."

mirimir 8y ago
Thanks. I was thinking of a recent post[0] pointing to a NASA press release.[1] And this part in particular: > As the team's measurements have become more precise, their calculation of the Hubble constant has remained at odds with the expected value derived from observations of the early universe's expansion. Those measurements were made by Planck, which maps the cosmic microwave background, a relic afterglow from 380,000 years after the big bang. > The measurements have been thoroughly vetted, so astronomers cannot currently dismiss the gap between the two results as due to an error in any single measurement or method. Both values have been tested multiple ways. > "This is not just two experiments disagreeing," Riess explained. "We are measuring something fundamentally different. One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding. If these values don't agree, there becomes a very strong likelihood that we're missing something in the cosmological model that connects the two eras." 0) https://news.ycombinator.com/item?id=19768990 https://news.ycombinator.com/item?id=19768990 1) https://www.nasa.gov/feature/goddard/2019/mystery-of-the-universe-s-expansion-rate-widens-with-new-hubble-data/ https://www.nasa.gov/feature/goddard/2019/mystery-of-the-uni... Edit: > But, quoting from the second link: ResearchGate doesn't like my IP address. What's the URI?
- acqq 8y ago
  I see. Yes, the two sides are measuring different things. Still note that the major news there is effectively: "Riess's team reduced the uncertainty in their Hubble constant value to 1.9% from an earlier estimate of 2.2%." I fail to see that as something that can bring us to conclude anything exactly at this moment but that still more different approaches to measurements are needed. Maybe that Freedman's, or using WFIRST, if it manages to be, or, in the HN link you give, as ncmncm writes, LIGO: https://news.ycombinator.com/item?id=19773731 https://news.ycombinator.com/item?id=19773731 After more measurements, maybe the theory indeed will have to be more complex than what just "one and only" Hubble constant could allow. Still, the values are close enough that even as different as they're now I'm confident that everything we learned up to now is mostly right. In the cosmological scales there are maybe some adjustments to come, but anything that affects us is really good known.
  - XorNot 8y ago
    Being mostly right is an exciting place to be in physics though. Newtonian dynamics was mostly right for orbital mechanics till relativity after all. Hopefully when we find out why we're currently mostly but not completely right, it'll be equally significant.
  - sanxiyn 8y ago
    I am very excited about Wendy Freedman's number. Her program is called CCHP(Carnegie-Chicago Hubble Program). The first paper was in 2016: https://arxiv.org/abs/1604.01788 https://arxiv.org/abs/1604.01788. The idea is to use only Population II stars, while Adam Riess's number uses Population I stars. If the number is in between, that's really cool.

by acqq 8y ago

mirimir 8y ago

Thanks. I was thinking of a recent post[0] pointing to a NASA press release.[1] And this part in particular: > As the team's measurements have become more precise, their calculation of the Hubble constant has remained at odds with the expected value derived from observations of the early universe's expansion. Those measurements were made by Planck, which maps the cosmic microwave background, a relic afterglow from 380,000 years after the big bang. > The measurements have been thoroughly vetted, so astronomers cannot currently dismiss the gap between the two results as due to an error in any single measurement or method. Both values have been tested multiple ways. > "This is not just two experiments disagreeing," Riess explained. "We are measuring something fundamentally different. One is a measurement of how fast the universe is expanding today, as we see it. The other is a prediction based on the physics of the early universe and on measurements of how fast it ought to be expanding. If these values don't agree, there becomes a very strong likelihood that we're missing something in the cosmological model that connects the two eras." 0) https://news.ycombinator.com/item?id=19768990 https://news.ycombinator.com/item?id=19768990 1) https://www.nasa.gov/feature/goddard/2019/mystery-of-the-universe-s-expansion-rate-widens-with-new-hubble-data/ https://www.nasa.gov/feature/goddard/2019/mystery-of-the-uni... Edit: > But, quoting from the second link: ResearchGate doesn't like my IP address. What's the URI?

acqq 8y ago
I see. Yes, the two sides are measuring different things. Still note that the major news there is effectively: "Riess's team reduced the uncertainty in their Hubble constant value to 1.9% from an earlier estimate of 2.2%." I fail to see that as something that can bring us to conclude anything exactly at this moment but that still more different approaches to measurements are needed. Maybe that Freedman's, or using WFIRST, if it manages to be, or, in the HN link you give, as ncmncm writes, LIGO: https://news.ycombinator.com/item?id=19773731 https://news.ycombinator.com/item?id=19773731 After more measurements, maybe the theory indeed will have to be more complex than what just "one and only" Hubble constant could allow. Still, the values are close enough that even as different as they're now I'm confident that everything we learned up to now is mostly right. In the cosmological scales there are maybe some adjustments to come, but anything that affects us is really good known.
- XorNot 8y ago
  Being mostly right is an exciting place to be in physics though. Newtonian dynamics was mostly right for orbital mechanics till relativity after all. Hopefully when we find out why we're currently mostly but not completely right, it'll be equally significant.
- sanxiyn 8y ago
  I am very excited about Wendy Freedman's number. Her program is called CCHP(Carnegie-Chicago Hubble Program). The first paper was in 2016: https://arxiv.org/abs/1604.01788 https://arxiv.org/abs/1604.01788. The idea is to use only Population II stars, while Adam Riess's number uses Population I stars. If the number is in between, that's really cool.