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Thread: New Hubble measurements confirm universe is expanding faster than expected

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    New Hubble measurements confirm universe is expanding faster than expected

    Once again this question will involve some discussion, hence posting it here.

    Does the following finding really refute dark energy thus the whole GR?

    “The new measurements, published April 25 in the Astrophysical Journal Letters, reduce the chances that the disparity is an accident from 1 in 3,000 to only 1 in 100,000 and suggest that new physics may be needed to better understand the cosmos.”

    https://phys.org/news/2019-04-hubble...se-faster.html


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    Quote Originally Posted by philippeb8 View Post
    Does the following finding really refute dark energy thus the whole GR?
    I'm not sure where you get that idea from. There is nothing in the article that says either of those things.

    It has been known for a long time that there appears to be a discrepancy between the value of the Hubble constant measured from the CMB and that measured by observing the red-shifts of galaxies. This study appears to have greatly improved the accuracy of the latter measurement and confirmed that the discrepancy exists.

    As these measurements confirm that the universe is expanding, they do not undermine GR. As they do not contradict the accelerating expansion, they do not undermine dark energy.

    Excitingly, though, they might be hints of new physics.

    Some more background on the issue here: https://astronomynow.com/2018/07/13/...bble-constant/

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    Quote Originally Posted by Strange View Post
    Excitingly, though, they might be hints of new physics.
    Thanks but to what probability?


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    Quote Originally Posted by philippeb8 View Post
    Thanks but to what probability?


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    Greater than zero, if the history of science is any guide. There is always a chance that new physics will be needed to explain things that turn up as observations improve. That could be anything from a modest modification to GR to a whole new paradigm.

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    Quote Originally Posted by Hornblower View Post
    Greater than zero, if the history of science is any guide. There is always a chance that new physics will be needed to explain things that turn up as observations improve. That could be anything from a modest modification to GR to a whole new paradigm.
    Ok. I was not aware of their notation but I thought it was computable.


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    Quote Originally Posted by Strange View Post
    As these measurements confirm that the universe is expanding, they do not undermine GR. As they do not contradict the accelerating expansion, they do not undermine dark energy.
    Indeed. In fact, they show the acceleration of the expansion to be larger than expected, even after accounting for dark energy. You can see from the article that one proposed explanation for the discrepancy is to have dark energy be more pronounced than current models.
    Conserve energy. Commute with the Hamiltonian.

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    Quote Originally Posted by Grey View Post
    Indeed. In fact, they show the acceleration of the expansion to be larger than expected, even after accounting for dark energy. You can see from the article that one proposed explanation for the discrepancy is to have dark energy be more pronounced than current models.
    So this assumption implies the dark energy distribution is not necessarily uniform?


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    Quote Originally Posted by philippeb8 View Post
    So this assumption implies the dark energy distribution is not necessarily uniform?
    Again, where do you get that from?

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    Quote Originally Posted by Strange View Post
    Again, where do you get that from?
    A wild guess here.


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    Quote Originally Posted by philippeb8 View Post
    A wild guess here.
    There is no evidence for that guess.

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    Quote Originally Posted by Strange View Post
    There is no evidence for that guess.
    That’s fine. But my main interests were related to the probability of the veracity of that article. I’ll try to dig in to this when I have some free time.


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    Quote Originally Posted by philippeb8 View Post
    But my main interests were related to the probability of the veracity of that article.
    Do you doubt the accuracy of the journalism? Or do you doubt the scientific results that it reports?

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    Quote Originally Posted by Strange View Post
    Do you doubt the accuracy of the journalism? Or do you doubt the scientific results that it reports?
    Sorry I meant: I am interested into the probability of the veracity of the “need for new physics” statement.


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    Quote Originally Posted by philippeb8 View Post
    Sorry I meant: I am interested into the probability of the veracity of the “need for new physics” statement.
    It is impossible to say.

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    Quote Originally Posted by Strange View Post
    It is impossible to say.
    Ok. I assumed that they were using some common notation I was unfamiliar with in their measurement of the discrepancy.


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    Quote Originally Posted by philippeb8 View Post
    Ok. I assumed that they were using some common notation I was unfamiliar with in their measurement of the discrepancy.
    Not sure what notation you mean. But that won't tell us anything about whether new physics is required. The only thing that will do that is either an explanation based on current physics (therefore no new physics required) or an explanation based on new physics which is confirmed by further evidence and observation (in other words: new physics).

    Until we either have a new theory or it is shown that a new theory is not required, we have no idea if a new theory is required or not.

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    like dough rising in the oven
    Finally, the press moves away from the deeply misleading balloon model of expansion.
    Now they just need to add some poppy seeds and call them galaxy clusters.

    I'm not seeing any new physics being needed, beyond actually arriving at an understanding of dark matter and dark energy; both which have had us befuddled since what, the late 1990's?

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    Quote Originally Posted by Strange View Post
    Not sure what notation you mean. But that won't tell us anything about whether new physics is required. The only thing that will do that is either an explanation based on current physics (therefore no new physics required) or an explanation based on new physics which is confirmed by further evidence and observation (in other words: new physics).

    Until we either have a new theory or it is shown that a new theory is not required, we have no idea if a new theory is required or not.
    I was referring to this statement specifically:

    “The new measurements, published April 25 in the Astrophysical Journal Letters, reduce the chances that the disparity is an accident from 1 in 3,000 to only 1 in 100,000 and suggest that new physics may be needed to better understand the cosmos.”

    But if new physics is really required then the way we think will need to be improved. PM if you have a question on this statement.


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    Quote Originally Posted by philippeb8 View Post
    But if new physics is really required then the way we think will need to be improved. PM if you have a question on this statement.
    That statement makes absolutely no sense. So I have no questions about it.

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    Ok so if there is no probabilistic evidence then the question is answered.


    Thanks!
    philippeb8


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    Quote Originally Posted by philippeb8 View Post
    Ok so if there is no probabilistic evidence then the question is answered.
    The phrase "reduce the chances that the disparity is an accident from 1 in 3,000 to only 1 in 100,000" is about the confidence in the accuracy of the measurement, not the probability that new physics is required (which is unknowable).

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    Quote Originally Posted by Strange View Post
    The phrase "reduce the chances that the disparity is an accident from 1 in 3,000 to only 1 in 100,000" is about the confidence in the accuracy of the measurement, not the probability that new physics is required (which is unknowable).
    Ah ok. Thanks for the clarifications!


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    Quote Originally Posted by philippeb8 View Post
    “The new measurements, published April 25 in the Astrophysical Journal Letters, reduce the chances that the disparity is an accident from 1 in 3,000 to only 1 in 100,000 and suggest that new physics may be needed to better understand the cosmos.”
    I'm pretty sure that this is just stating the confidence in the result, in a less technical way to make it more understandable to a lay reader. Any time you make a series of measurements that seems to show a correlation, there's always a chance that the apparent correlation is just there by chance, and that if you re-did the study with different galaxies, your apparent result wouldn't show up. So when doing something like this, you also make an assessment of how statistically significant the result is.

    So, those probabilities are just the chance that this result is a random outlier. This additional study reducing that probability makes it seem quite likely that they really have measured what they think they measured, and that the universe really is expanding faster than current models suggest that it should be, even when taking dark energy into account. So that means that the models have to be adjusted somehow, but they give a number of possible modifications that have been proposed. Some involve changes to how dark energy or dark matter work, it's also possible in principle that some could involve modifications to general relativity. But we don't know which of those changes are going to work: we'll have to try them out, see which ones work for this observation, and also see which ones are still consistent with other observations.
    Conserve energy. Commute with the Hamiltonian.

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    I get how the "Hubble method" estimates the expansion rate (or the change in the expansion rate). How does the "Planck/CMB" method come up with this estimate?
    Everyone is entitled to his own opinion, but not his own facts.

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    Quote Originally Posted by Cougar View Post
    I get how the "Hubble method" estimates the expansion rate (or the change in the expansion rate). How does the "Planck/CMB" method come up with this estimate?
    I'm pretty sure that you use the variations in the CMB and the scale at which those variations are seen to constrain the parameters of your cosmological model (including things like the ratio of dark energy to dark matter to normal matter), and then the value for the Hubble parameter comes from that model. So I think it's a less direct measurement in a certain sense, which is why ways of resolving the discrepancy can include things that seem pretty subtle, like changing how strongly dark matter interacts with normal matter in your model.
    Conserve energy. Commute with the Hamiltonian.

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    Quote Originally Posted by Squink View Post
    Finally, the press moves away from the deeply misleading balloon model of expansion.
    Now they just need to add some poppy seeds and call them galaxy clusters.

    I'm not seeing any new physics being needed, beyond actually arriving at an understanding of dark matter and dark energy; both which have had us befuddled since what, the late 1990's?
    There is no "deeply misleading balloon model of expansion" in the paper or article. The article has a descriptive "The space between galaxies is stretching, like dough rising in the oven" sentence. There is the slightly misleading balloon analogy where people should be reminded that this is a balloon that is just surface (no exterior or interior).

    The paper is a more accurate measurement of an expanding universe from astronomical observations. It has been known for years that there is a mismatch between the Hubble constant in the early universe (WMAP and Planck data) and late universe (this data). In the last couple of years the accuracy of late measurements has increased enough so that the different values are unlikely to be statistical flukes (the 1 in 100,000 value in the article). That is why new physics as described in the article may be needed.
    So, what could explain this discrepancy?

    One explanation for the mismatch involves an unexpected appearance of dark energy in the young universe, which is thought to now comprise 70% of the universe's contents. Proposed by astronomers at Johns Hopkins, the theory is dubbed "early dark energy," and suggests that the universe evolved like a three-act play.

    Astronomers have already hypothesized that dark energy existed during the first seconds after the big bang and pushed matter throughout space, starting the initial expansion. Dark energy may also be the reason for the universe's accelerated expansion today. The new theory suggests that there was a third dark-energy episode not long after the big bang, which expanded the universe faster than astronomers had predicted. The existence of this "early dark energy" could account for the tension between the two Hubble constant values, Riess said.

    Another idea is that the universe contains a new subatomic particle that travels close to the speed of light. Such speedy particles are collectively called "dark radiation" and include previously known particles like neutrinos, which are created in nuclear reactions and radioactive decays.

    Yet another attractive possibility is that dark matter (an invisible form of matter not made up of protons, neutrons, and electrons) interacts more strongly with normal matter or radiation than previously assumed.
    Last edited by Reality Check; 2019-Apr-29 at 04:05 AM.

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    Looks like there is even more dark energy--the way this reads. Big Rip after all?

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    Quote Originally Posted by publiusr View Post
    Looks like there is even more dark energy--the way this reads. Big Rip after all?
    I don't think you can conclude that from this evidence.
    Conserve energy. Commute with the Hamiltonian.

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    Quote Originally Posted by publiusr View Post
    Looks like there is even more dark energy--the way this reads. Big Rip after all?
    Early dark energy is not current dark energy. See Early Dark Energy Can Resolve The Hubble Tension
    Early dark energy (EDE) that behaves like a cosmological constant at early times (redshifts z≳3000 ) and then decays away like radiation or faster at later times can solve the Hubble tension.
    If we consider dark energy to be a cost of having spacetime, EDE is an extra cost of having spacetime incurred only for the early universe.

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