The expanding balloon analogy for cosmological models is shown below at
two different times. A common misconception is that the balloon is
expanding into empty space that is "beyond the Universe" and that it is
expanding from a single point in the center of the balloon. But the
balloon analogy is a 2-dimensional model, and the center of the balloon
and the space around are not part of the 2-dimensional Universe. In our
3-dimensional Universe, these points could only be reached by traveling
in a 4th spatial dimension (not the time dimension of 4-D spacetime),
but there is no evidence that this dimension exists.
This animation shows an expanding universe model with yellow blobs for
galaxies and moving, redshifting photons. The animation starts
at a redshift of 3 when the Universe was 4 times smaller than it is
now, and finishes at the present. Taken literally, the ratio of
the radius of the "balloon" to the Hubble distance c/Ho
implies an Omega = 2 currently and Omega = 1.14 at z = 3.
Note that the galaxies do not expand: bound systems are not
affected by the expansion of the Universe. Also note that the speed
of light relative to the nearby galaxies is a constant - if your browser
is properly using the duration values in the animated GIF file.
FAQ | Tutorial : Part 1 | Part 2 | Part 3 | Part 4 | Age | Distances | Bibliography | Relativity
© 1998 Edward L. Wright. Last modified 8-May-1998