Page 26 - GALIET PHYSICS BLOSSOMS III

This can be illustrated with a balloon27 as done in class.
InflationàBig Bang
A balloon expands from a point just as the Big Bang, comprising the whole universe, expands
from a point.
• We can:
o drawcirclesonit,ortapecoinstoitssurface.
o imagine that these circles or coins are galaxies, and that the balloon itself
is the “fabric” of our universe.
o noticethateverypointontheballoonisjustthesameaseveryotherpoint
(the cosmological principle).
o imaginethatweliveinoneofthethreedarkcoloredgalaxies.
Fig. 728
o noticethatwedwellrelativetoourneighbors.
o inflatetheballoonandthinkthattheuniverseexpands.
o seeothercoin-galaxiesrecedefromus,andnoticethefollowing:
§ The farthest galaxies recede faster. As the coins recede, the distance between any two of them increases proportionally to the distance between them. Thus the universe expands according to Hubble’s law.
§ The coins-galaxies do not expand along with the balloon anymore than the earth, stars, or galaxies since their own internal forces hold them.
• When we notice the recession of galaxies, we discover that:
o This recession is not special given that the cosmological principle posits
that no viewer, neither you nor I, has a privileged position.
o Thereisnocentertotheuniverse’sexpansion.
o Thereisnoparticularpositionorpointfromwhereexpansionbegan.
o We all see a general expansion or Hubble’s law with the same Hubble’s
constant.
DeflationàBig Crunch
27 Bennet, Donahue, Schneider, Voit. The Cosmic Perspective. 6th Edition. Volume II. Stars and Galaxies. 666. See also Figure 26.5.
28 Bennet, Donahue, Schneider, Voit. The Cosmic Perspective. 6th Edition. Volume II. Stars and Galaxies. 666. Also Figure 26.5.
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