Measuring the Universe and GR:

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Jan 10, 2018.

  1. paddoboy Valued Senior Member

    Messages:
    21,703
    I'm sure many will be interested in this article and the facts presented supporting GR as the current accepted and evidenced gravitational theory, that has passed all tests and made successful predictions. It appears it will be that way for a long time yet, [despite a prediction by a forumite that it will be superceded and disproved by 2025] as we are no closer to be able to formulate any QGT that can be validated.
    Despite my valuable time taken in presenting the following, I see it as necessary taking into account the many unscientific, unprofessional online criticisms of GR and the great man, by a diverse collection of lay people.

    https://phys.org/news/2018-01-gravitational-universe.html#jCp
    Gravitational waves measure the universe
    January 8, 2018, Harvard-Smithsonian Center for Astrophysics


    Read more at: https://phys.org/news/2018-01-gravitational-universe.html#jCp
    The direct detection of gravitational waves from at least five sources during the past two years offers spectacular confirmation of Einstein's model of gravity and space-time. Modeling of these events has also provided information on massive star formation, gamma-ray bursts, neutron star characteristics, and (for the first time) verification of theoretical ideas about how the very heavy elements, like gold, are produced.

    Read more at: https://phys.org/news/2018-01-gravitational-universe.html#jCp
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    Important if obvious excerpts from the article....
    Knowing how far away it is and how fast the galaxy is moving from us allows scientists to calculate the time since the expansion began – the age of the universe: between about 11.9 and 15.7 billion years given the experimental uncertainties".
    and......

    "The age derived from this single event is consistent with estimates from decades of observations relying on statistical methods using two othersources: thecosmic microwave backgroundradiation (CMBR) and the motions ofgalaxies"
    "With a large statistical sample of gravitational wave events of all types, the current range of values for the age will narrow".


    "Although both the CMBR and the galaxy measurements are each quite precise, they seem to disagree with each other at roughly the ten percent level. This disagreement could just be observational error, but some astronomers suspect it might be a real difference reflecting something currently missing from our picture of the cosmic expansion process, perhaps connected with the fact that the CMBR arises from a vastly different epoch of cosmic time than does the galaxy data. This third method, gravitational wave events, may help solve the puzzle".
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    the paper:
    https://www.nature.com/nature/journal/v551/n7678/full/nature24471.html


    A gravitational-wave standard siren measurement of the Hubble constant:

    On 17 August 2017, the Advanced LIGO1and Virgo2detectors observed the gravitational-wave event GW170817—a strong signal from the merger of a binary neutron-star system3. Less than two seconds after the merger, a γ-ray burst (GRB 170817A) was detected within a region of the sky consistent with the LIGO–Virgo-derived location of the gravitational-wave source4,5,6. This sky region was subsequently observed by optical astronomy facilities7, resulting in the identification8,9,10,11,12,13of an optical transient signal within about ten arcseconds of the galaxy NGC 4993. This detection of GW170817 in both gravitational waves and electromagnetic waves represents the first ‘multi-messenger’ astronomical observation. Such observations enable GW170817 to be used as a ‘standard siren’14,15,16,17,18(meaning that the absolute distance to the source can be determined directly from the gravitational-wave measurements) to measure the Hubble constant. This quantity represents the local expansion rate of the Universe, sets the overall scale of the Universe and is of fundamental importance to cosmology. Here we report a measurement of the Hubble constant that combines the distance to the source inferred purely from the gravitational-wave signal with the recession velocity inferred from measurements of the redshift using the electromagnetic data. In contrast to previous measurements, ours does not require the use of a cosmic ‘distance ladder’19: the gravitational-wave analysis can be used to estimate the luminosity distance out to cosmological scales directly, without the use of intermediate astronomical distance measurements. We determine the Hubble constant to be about 70 kilometres per second per megaparsec. This value is consistent with existing measurements20,21, while being completely independent of them. Additional standard siren measurements from future gravitational-wave sources will enable the Hubble constant to be constrained to high precision.
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    A review:
    Einstein proposed three tests of GR:
    The perihelion precession of Mercury's orbit. VERIFIED

    the deflection of light by the Sun. VERIFIED:

    The gravitational redshift of light. VERIFIED.

    Since those heady days, further predictions of GR have been verified.....
    Lense-Thirring Effect:
    Gravitational waves:
    No scientific model of the Universe will ever be "perfect" even a QGT, but GR is as perfect as we have at this time, and should remain so for a long time yet.
    Of course as per many scientific theories and models, GR is tested every day, even as we speak, and continues to pass with flying colours. As Evolution is a certainty, and Abiogenesis the only scientific answer to the origin of life, GR stands alone at this time.

    Finally, here is a 2017 rundown paper on GR and how it and the man mostly responsible has changed our whole outlook on the universe of which we are a small insignificant part.

    https://arxiv.org/ftp/arxiv/papers/1705/1705.04397.pdf

    Tests of General Relativity:
    A Review By Estelle Asmodelle
    May 4th, 2017

    Abstract

    This report is a literature review of significant and successful tests of general relativity [GR]. The GR predicted value for the perihelion advance of Mercury was ∆f = 43”.03 century-1 and fit well with observation, being the first success of GR. The GR result for the bending of light around the Sun dGR = 1”.75, confirmed by observation, marked the second successful validation of GR. Gravitational Redshift [GvR] was first detected 1925 and is the third successful classical test. The parametrized post-Newtonian [PPN] employs b and g for GR testing. Shapiro delay was also confirmed with g = 1.000021 ± 0.000023, against GR value g = 1, some consider this to be the fourth classical test. So too gravitational time dilation [GvT] was experimentally confirmed in 1971, while GvT for GPS is a daily validation of GR. Frame-dragging and the Geodetic effect have also been confirmed. The strong equivalence principle [SEP] has been confirmed to h = 4.4 × 10-4 , to GR h = 0. Gravitational slip has been constrained to EG = 0.48 ± 0.10 at z = 0.32, against the GR value, EG = 0.30 ± 0.07. The first gravitational wave detection from GW150914, in 2015, has confirmed a long-awaited phenomenon that has taken GR testing to higher precision. Gravitational lensing has also confirmed GR to better than 1%. GR continues to be tested, eliminating competing gravity theories.
     
    Last edited: Jan 10, 2018
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  3. paddoboy Valued Senior Member

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    PS: Before I go into hybernation, if anyone believes that there are any errors, any alterations needed, please take it up with an appropriate professional scientist/physicist: Obviously even scientists are not infallible, but obviously far less infallible then most lay people, at least on the relevant subject.
     
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  5. Michael 345 In China - finding my way :) Valued Senior Member

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    Are professional Scientists MORE professional because they don't watch YouTube for research?

    Or do lay people think they ARE professional because they do watch YouTube for research?

    I suspect the latter because I don't know if Scientists do watch YouTube

    Thanks for the post

    Please Register or Log in to view the hidden image!

     
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  7. Q-reeus Valued Senior Member

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    YouTube idiocy alert warning! Note the following two characters appear on YouTube thus anything they say not to be trusted:

     
    Xelasnave.1947 likes this.
  8. Xelasnave.1947 Valued Senior Member

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    4,444
    True but we can only hope someone can come through with the goods.
    We need to know how mass telld space how to bend on some physical level.

    There no doubt will have to be some alterations to BB theory when QTG is worked out and maybe the need for dark matter may be removed.
    Still the success of GR is to be expected because as an area of study and research it seems absolutely ever aspect and ramification has been studied and there is more than ample funding available to research any aspect a researcher can think of that can be looked at and used as further confirmation of GRs correctness.
    GR certainly has had a long run but I imagine that something better will come up...thats just the way it goes.
    Look at plate tectonics not thete one moment and out pops the idea and everything changed.
    No Noble prize which sucks.
    Alex
     

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