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Thread: Halve the Hubble constant! (still apears to be 72km/s/Mpc)

  1. #61
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    Quote Originally Posted by john hunter View Post
    H as defined in the previous post a(dot)/a is approx. 1*10^-18 .
    The Hubble parameter H is defined in textbooks as a(dot)/a and is a variable parameter because the scale factor a varies with time. That is why we can differentiate a(t) with respect to time and not always get a trivial value of zero. That variation with time also means that a(t) also varies with redshift. A galaxy at a redshift of z is in the universe with a corresponding a(t). Thus H varies with redshift and we see papers about a H(z). But you know this.
    Matter-dominated universe (with a cosmological constant) derives H(z).
    Utility of observational Hubble parameter data on dark energy evolution equation 3 is H(z) for a flat universe as shown by independent measurements.

    The Andromeda galaxy is not a good example. Bound systems do not experience measurable effects of the expansion of the universe. Atoms have not expanded measurably. The Earth has not expanded measurably. The orbit of the Earth has expanded about 1 part in a septillion over the lifetime of the Solar System. Importantly, galaxies have peculiar velocity that locally can be larger than any cosmological redshift. Andromeda happens to be one of the nearby blue-shifted galaxies.

  2. #62
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    Quote Originally Posted by Reality Check View Post
    it is the Hubble parameter that is defined as a(dot)/a. They Hubble constant is dimensionless as you know and have acknowledged. If you want to create a new symbol for your personal use then it is not the Hubble parameter and you cannot use H.
    You have made it clear that you think the use of the term Hubble constant in the title was wrong. And, from post 7 onwards it's been made clear that the ATM idea is that the rate of expansion a(dot)/a is half the mainstream value.

    You made a mistake saying that the Hubble parameter H(z) is dimensionless, when you meant the 'reduced Hubble parameter' h (see post 53), and another mistake in the quote above...(The Hubble constant has dimensions of km/s/Mpc or s^-1), so maybe it's time to stop the same argument and argue against a(dot)/a being half the accepted value, if that's what you want to do.

    IF08 was answered also in post 50 some repeated here

    The slope of the graph and line is 70km/s/Mpc - it matches the data, slope =2H (defined below) , on the full data graph posted previously.

    Here is the low z part, line of best fit as done by Desmos

    https://www.desmos.com/calculator/c7nnitv3da it matches (best) with 2H = 65.95km/s/Mpc. All this can be seen by looking at the data on the left and the formula at the bottom.
    Last edited by john hunter; 2017-Jul-19 at 10:13 PM.

  3. #63
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    Quote Originally Posted by john hunter View Post
    https://en.wikipedia.org/wiki/Friedmann_equations Just under the section 'Equations' there are two equations and to make the top one have consistent dimensions, it can be seen that the Hubble parameter H has dimensions of seconds^-1.

    You probably meant h (the reduced Hubble parameter) when you claimed the Hubble parameter was dimensionless. They are two different things.
    The dimensionless Hubble parameter = a(dot)/a. The scale factor a has no dimensions. Its time derivative need not have dimensions. For example here is a dimensionless function varying with time: F(t) = (t/t0)2. The time derivative is F(dot)(t) = 2t/t0. As you can see this is also dimensionless. Any a(t) that has times expressed at t/t0 will have a time derivative that has no dimensions.
    The reduced Hubble parameter h definitely has dimensions because it is defined as the Hubble parameter * 100 km s−1 Mpc−1 (read Hubble's law: Dimensionless Hubble parameter).

  4. #64
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    Quote Originally Posted by john hunter View Post
    You have made it clear that you think the use of the term Hubble constant in the title was wrong. And, from post 7 onwards it's been made clear that the ATM idea is that the rate of expansion a(dot)/a is half the mainstream value.
    From post 7 onwards, you have made it clear hat the ATM idea is wrong.
    1. The scale factor a(t) is the relative expansion of the universe. The rate of relative expansion of the universe would be a(dot).
    2. The Hubble parameter defined as a(dot)/a is not a "mainstream value". It is a mainstream definition and is a variable.

    You are still ignoring the basic fact that it is the best fit to the data that determines which model is correct. Even if we accept that your curve is correct, it is useless until you compare its fit to the other models, e.g. with non-zero cosmological constant.
    Last edited by Reality Check; 2017-Jul-19 at 10:28 PM.

  5. #65
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    Quote Originally Posted by Reality Check View Post
    The Hubble parameter H is defined in textbooks as a(dot)/a and is a variable parameter because the scale factor a varies with time. That is why we can differentiate a(t) with respect to time and not always get a trivial value of zero. .
    "The Hubble parameter H is defined in textbooks as a(dot)/a", this is agreed, and the ATM proposal is that it is constant (in time) and has half the mainstream value. H(z) will vary with z, Shaula in a Q&A session said that for a constant H (in time), H(z)=H(1+z). a(dot)/a=constant leads to an exponential relation between scalefactor and time .

  6. #66
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    Quote Originally Posted by john hunter View Post
    "The Hubble parameter H is defined in textbooks as a(dot)/a", this is agreed, and the ATM proposal is that it is constant (in time) and has half the mainstream value.
    Now wrong three times:
    1. The scale factor a(t) is the relative expansion of the universe. The rate of relative expansion of the universe would be a(dot).
    2. The Hubble parameter defined as a(dot)/a is not a "mainstream value". It is a mainstream definition.
    3. The Hubble parameter varies with time and thus redshift.

    Shaula stated that H(z) varied for a constant H0 (Hubble's constant)
    Quote Originally Posted by Shaula View Post
    You are misunderstanding what is meant by the Hubble parameter. In the simple linear model it is the product of the distance and the Hubble constant.

    If expansion were not accelerating then we'd expect the plot of H(z) to be a straight line. That table is showing that H(z) is not a straight line because the absolute value of the rate of change of the Hubble parameter with z is not constant. And as you get closer to home that rate of change is increasing compared to intermediate distances.
    Shaula also hinted at why your single curve is dubious in the next post:
    Quote Originally Posted by Shaula View Post
    Fitting lines by eye is fraught with danger. If you take the predicted relationships from the accelerating and non-accelerating models you find that the accelerating universe is a better fit. There are straight lines you can (just) fit to the data, but they are all statistically lower confidence than the curved line from the LCDM model. The differences between the two models are small and the data tends to have large uncertainties on it. So we can't rule out either case with 100% confidence. But we can say that the accelerating case is much more likely.
    Last edited by Reality Check; 2017-Jul-19 at 10:39 PM.

  7. #67
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    Quote Originally Posted by Reality Check View Post
    The Hubble parameter defined as a(dot)/a is not a "mainstream value". It is a mainstream definition.
    OK, and when this defined quantity is measured, lets say nowadays, it has a measured value...what would you say that value is?

  8. #68
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    Quote Originally Posted by john hunter View Post
    OK, and when this defined quantity is measured, lets say nowadays, it has a measured value...what would you say that value is?
    You know the answer. Read my posts. Read the thread. Read the papers you have cited.

  9. #69
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    Quote Originally Posted by Reality Check View Post
    You know the answer. Read my posts. Read the thread. Read the papers you have cited.
    If you mean about 72km/s/Mpc from cosmological measurements and about 69km/s/Mpc from galaxies...this ATM proposal is that a(dot)/a is half those values. Just to be clear what it is.

    Hear is another question being asked just for clarification: When you said cosmological considerations, are you talking about very high redshift supernovae or the Plank / WMAP data? What did you mean by 'from galaxies', OHD or something else? Why did you say that most astronomers think the 72km/s/Mpc value will be found correct as Planck has a low value for Hubbles constant. If you saw the match (post 50) of the low redshift data from the new proposal you'll see it has 2H at about 66km/s/Mpc

  10. #70
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    Quote Originally Posted by john hunter View Post
    If you mean about 72km/s/Mpc from cosmological measurements and about 69km/s/Mpc from galaxies...
    That is the measured value of H0: ATM idea wrong 5 times:
    1. The scale factor a(t) is the relative expansion of the universe. The rate of relative expansion of the universe would be a(dot).
    2. The Hubble parameter defined as a(dot)/a is not a "mainstream value". It is a mainstream definition.
    3. The Hubble parameter varies with time and thus redshift.
    4. The measured (and so cannot be any other value without other measurements) value of the Hubble constant H0 is 72km/s/Mpc from cosmological measurements and about 69km/s/Mpc from galaxies.
    5. Your ATM idea is you can change a scientific definition which is wrong.
      Replacing H with 2H is invalid because H has a definition. You can replace H with 2X if you want to get X is the "john hunter" parameter.
    .
    This is what I wrote about the 69/72 values and their probable resolution on 10 July 2017:
    Physicists know that the Hubble constant is not measured to be 72 km/s/Mpc !
    They know that Hubble's constant is measured to have 2 different values of 72 km/s/Mpc from cosmological data and 69 km/s/Mpc from looking at galaxies. However most astronomers think that it is the 72 value that will be confirmed. The distances to galaxies depends on the cosmic distance ladder which is a series of overlapping methods for distance measurements. An early rung is parallax used to measure distances to stars, e.g. leading to the standard candle of Cepheid variable stars used by Hubble. Parallax depends on measuring very small angles accurately.
    It is that the 69 value is more likely to be revised upward to 72 from more precise parallax measurements, e.g. from the Gaia telescope, than the 72 value being revised downward from future cosmological measurements.

  11. #71
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    It has come to our attention that this ATM topic is a repeat of one that was closed...and that one was closed because it was discussed it in an ATM thread prior to that. This thread is therefore closed and an infraction has been issued.

    john hunter,

    If you want to continue this discussion, you must report this closing post and explain why your thread qualifies for an extension under our rules.
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