On 9/13/2024 7:58 PM, Alan Grayson wrote:


On Friday, September 13, 2024 at 8:48:25 PM UTC-6 Brent Meeker wrote:




    On 9/13/2024 7:10 PM, Alan Grayson wrote:


    On Friday, September 13, 2024 at 4:03:45 PM UTC-6 Brent Meeker wrote:




        On 9/13/2024 4:56 AM, Alan Grayson wrote:


        On Friday, September 13, 2024 at 4:06:49 AM UTC-6 Alan
        Grayson wrote:

            On Thursday, September 12, 2024 at 11:07:49 PM UTC-6
            Alan Grayson wrote:

                On Thursday, September 12, 2024 at 11:00:21 PM UTC-6
                Brent Meeker wrote:




                    On 9/12/2024 9:21 PM, Alan Grayson wrote:


                    On Thursday, September 12, 2024 at 3:55:45 AM
                    UTC-6 Quentin Anciaux wrote:



                        Le jeu. 12 sept. 2024, 11:53, Alan Grayson
                        <[email protected]> a écrit :



                            On Thursday, September 12, 2024 at
                            2:40:56 AM UTC-6 Quentin Anciaux wrote:

                                I just gave you a full proof that
                                as long as the expansion is uniform
                                and expansion rate > 0, then it
                                follows objects will sooner or
                                later recess from each other at
                                speed > c.


                            What was the justification for the
                            geometric progression? I made no such
                            assumption in my "proof".


                        As explained multiple times and in the
                        quote you made, expansion is uniform and
                        happens at every point in space.


                    What bothers me about your method is that
                    you*assume* a geometric increase in the
                    separation distance, when, IMO, that's the
                    variable that must be calculated (which I did).
                    So no matter how many times you affirm your
                    proof as valid, I can't agree. AG

                    You didn't calculate the expansion parameter,
                    which is the Hubble constant.  It's an observed
                    value.

                    Brent


                Why must I do that, when I just want to show that
                eventually the recessional velocity exceeds c? Also,
                I don't see why theta is fixed, when the end of the
                arc defines the position of the receding galaxy. AG


            Now I am not sure I proved the recessional velocity is
            greater than c, after some time has passed. If the
            sphere is expanding, then the distance between any two
            fixed points on the sphere will increase as time passes.
            But that was obvious due to the expansion. What's wrong,
            if anything? AG


        Now I see the light. We've been struggling to prove that a
        receding galaxy will fall out of view if the universe is
        expanding, but all the so-called "proofs" fail, but for
        different reasons. What Quentin offers is not a proof. He's
        just repeating a result done by someone else,*using
        mathematics*, which he believes (and might be true). Brent
        is mistaken in his apparent belief that the proof of concept
        requires appeal to Hubble's law. This is also mistaken IMO
        since the result to be proven depends *exclusively* on the
        *geometry *of an expanding sphere. Finally, my proof also
        fails, since it's obvious that the arclength, s,  between
        two galaxies on an expanding  sphere, will obviously
        increase as the sphere expands. That is, ds/dt will
        obviously be positive since the arclength is increasing.
        IOW, a constantly increasing arclength s, assuming a
        uniformly expanding sphere, necessarily yields ds/dt > 0,
        but it does NOT demonstrate that the velocity of the
        receding galaxy eventually increases to be greater than c.
        When I have the energy, I will calculate the *second time
        derivative* of the arclength, s, hopefully to demonstrate,
        that for a uniformly expanding sphere, the *four* terms of
        the second derivative of s, imply a*positive acceleration*.
        This will establish that eventually the receding galaxy will
        pass out of view for the observer on the assumed stationary
        galaxy. Comments welcome. AG
        It's already proven that ds/dt=ks  => s=j*exp(kt) where k
        with dimensions of 1/time and j is an arbitrary constant of
        integration with the same dimensions as s.  Going to second
        derivatives won't gain any more.

        Brent


    We have different objectives. Your equation represents Hubble's
    law, but what I want to show is that Hubble's law is the inherent
    result of the geometry of an expanding sphere. So I believe going
    to the second derivative will demonstrate this. BTW, what's your
    argument that theta is a constant? AG
    Notice I didn't mention Hubble's law and avoided using H.  I
    deliberately used j and k for undetermined constants.


But you didn't pull that equation out of the proverbial hat. You assumed the recessional velocity ds/dt depends linearly on s,  which is what Hubble measured. AG


    Theta's constant under the assumption that it's the angle between
    two points that at FIXED on the expanding surface.


Yes, the two points are fixed but the distance between them, s. increases due to the increase in the spatial separation, so I contend that rather than assuming Hubble's law, I am trying to show that it is a property of an expanding sphere. This, as I recall, was your claim ages ago when we discussed this issue. AG

But it's not a property of an expanding sphere without the condition that the expansion has a constant proportional rate; so the relative distances keep the same proportions.  The further away something is the faster it is moving away.  That's why your first assumption ds/dt=const gives a result inconsistent with Hubble's law, it doesn't keep theta constant for every point.

Brent

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