Re: The Cosmological Constant (CC)

[Brent Meeker]

On 3/11/2025 9:40 PM, Alan Grayson wrote:


On Tuesday, March 11, 2025 at 10:26:37 PM UTC-6 Alan Grayson wrote:

    On Tuesday, March 11, 2025 at 1:41:29 PM UTC-6 Brent Meeker wrote:



        On 3/10/2025 11:48 PM, Alan Grayson wrote:


        On Tuesday, March 11, 2025 at 12:33:36 AM UTC-6 Brent Meeker
        wrote:



            On 3/10/2025 11:04 PM, Alan Grayson wrote:


            On Monday, March 10, 2025 at 11:15:07 PM UTC-6 Brent
            Meeker wrote:



                On 3/9/2025 11:14 PM, Alan Grayson wrote:
                I don't think you understand my question. Without a
                CC, or equivalently setting it to zero, don't we
                get a universe which is in UNSTABLE equilibrium,
                like balancing a pencil of its writing tip, so the
                universe expands or contracts in a very short time
                interval? Isn't this the issue Einstein faced? If
                so, why would he choose a positive CC? AG 

                No, Einstein's model with the CC=0 was static.  The
                model when I was in grad school was an expanding
                universe with the CC=0 but the expansion kinetic
                energy was just balanced by the negative
                gravitational potential, so the universe would
                expand forever but slowing asymptotically toward static.

                Brent


            Now I am totally confused. If E's model was static with
            CC=0,
            Sorry, I miswrote.  I intended to say Einstein had to
            make the CC>0 in order to balance the gravitational
            attraction.

            Brent


        OK. Does setting CC>0 result in unstable equilibrium as I
        think Clark claimed, and discovered by Arthur Eddington? 
        IOW, will the universe suddenly contract if it is expanding? AG
        No, it's unstable as a static universe, which was the general
        opinion of astronomers at the time.  The Milky Way was the
        only known galaxy.  The other smudges in the night sky were
        "nebula".  So Einstein calculated a value for the CC that
        would just balance the gravitational attraction of the Milky
        Way, to explain why it hadn't collapsed.  But this produced an
        unstable equilbrium.  It was about 10yrs later that Hubble
        discovered the universe was much bigger than just the Milky
        Way and it was expanding.

        Brent


    It was Arthur Eddington in 1930 who showed that a static universe
    with CC>0, would be in unstable equilibrium. AG


After Einstein removed the CC from his field equations in recognizing 
that the universe is expanding, did he reintroduce it when realizing 
that empty space is non-existent, that it has energy? When did he do 
that, and was it in reaction to the quantization of the EM field and 
its zero point energy? AG
He never "realized empty space has energy", that's just one way of 
looking at the acceleration of expansion which wasn't discovered till 
the 1990's.  When did he do what?...that thing he didn't do in response 
to the thing he never knew about?  Einstein never believed in zero point 
energy.   It always comes out infinite unless you impose an arbitrary 
cutoff.

Brent

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