Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.physics.relativity > #667935

Re: The Ever Expanding Universe

Show all headers | View raw

Ross Finlayson <ross.a.finlayson@gmail.com> posted:

> On 12/23/2025 03:42 PM, Thomas 'PointedEars' Lahn wrote:
> > Ruben Safir wrote:
> >> One of the concepts that have bothered me the most is the idea that the
> >> universe is ever exapanding.
> >
> > [_expanding_]
> >
> > We do not know that.  We know that our universe is expanding now and has
> > been in the past (because we observe the cosmological redshift); but it is
> > uncertain for how long, if at all, this will continue.  The reason for that
> > is that recent observations indicate that the Dark Energy density could be
> > time-dependent (in the current Standard Model of cosmology, it is constant,
> > leading to an exponential expansion).  If it decreases, then gravitation
> > might be able to slow down the expansion after all, and even reverse it,
> > leading to a Big Crunch:
> >
> > <https://www.quantamagazine.org/is-dark-energy-getting-weaker-new-evidence-strengthens-the-case-20250319/>
> >
> >> If space is constantly exanding and we are in space, then our measuring
> >> sticks would also be expanding so we wouldn't be able to see it and
> >> there would be no doppler effect.
> >
> > No.  First of all, you need to realize how large our universe is and how
> > small everything in it is by comparison. 

No, not if we make a meaningful comparison in terms of mass or numbers of atoms.
OK, the volume of the universe is large, but it makes little sense to ignore the
fact that it is overwhelmingly empty. In terms of mass it is only about 10^27 times
larger than the Earth, whereas the Earth is 10^40 times larger than an E. coli
cell. In other words the Earth is _much_ larger on the scale of a bacterial
cell than the universe is on the scale of the Earth.

> > This is best illustrated with numbers:
> >
> > Terra (Earth) is a planet with a diameter of ca. 12'642 km (if you think
> > that is big, read on).  Sol (the Sun) is a star with a diameter of ca.
> > 1'400'000 (1.4 million) km.  The average distance of Terra to Sol is
> > approximately 150'000'000 (150 million) km.  The distance to the next star
> > from Sol, Proxima Centauri, is ca. 4.25 ly (light-years); that is, ca. 4.25
> > times the distance that light travels in vacuum in one Julian year: ca. 40
> > *trillion* (short scale) kilometers. Both those stars are two of
> > approximately 200 billion stars in the Milky Way (each which on average at
> > least one planet) which has a diameter of approximately 200'000 ly.  The
> > Milky Way is one of ca. 200 billion to 2 trillion galaxies in our observable
> > universe which has a diameter of ca. 96 billion light-years.  Our entire
> > universe has a diameter that is at least 500 times as large as the
> > observable one's.
-- 
athel

Back to sci.physics.relativity | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: The Ever Expanding Universe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2025-12-24 00:42 +0100
  Re: The Ever Expanding Universe Ross Finlayson <ross.a.finlayson@gmail.com> - 2025-12-23 20:19 -0800
    Re: The Ever Expanding Universe athel.cb@gmail.com <user12588@newsgrouper.org.invalid> - 2025-12-24 10:49 +0000
      Re: The Ever Expanding Universe Ross Finlayson <ross.a.finlayson@gmail.com> - 2025-12-27 08:42 -0800
  Re: The Ever Expanding Universe The Starmaker <starmaker@ix.netcom.com> - 2025-12-27 22:50 -0800
    Re: The Ever Expanding Universe squalk <sq@net.inv> - 2025-12-28 17:47 +0000
      Re: The Ever Expanding Universe Ross Finlayson <ross.a.finlayson@gmail.com> - 2025-12-28 09:54 -0800
      Re: The Ever Expanding Universe Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2025-12-28 19:51 +0100
        Re: The Ever Expanding Universe The Starmaker <starmaker@ix.netcom.com> - 2025-12-28 11:39 -0800
        Re: The Ever Expanding Universe Maciej Woźniak <mlwozniak@wp.pl> - 2025-12-29 07:03 +0100
        Re: The Ever Expanding Universe Ross Finlayson <ross.a.finlayson@gmail.com> - 2025-12-29 11:44 -0800
          Re: The Ever Expanding Universe Ross Finlayson <ross.a.finlayson@gmail.com> - 2025-12-29 11:57 -0800

csiph-web