Galaxies on the Edge: Understanding the Expansion of the Universe

[jimjohnson]

The analogy for the expansion of the universe is explained as raisins (mass, or galaxies) expanding inside an expanding loaf of bread (bread being space), everything is moving away from everything else. This may be a simplistic question, but when the expansion started some raisins were on the outside of others. Where are the raisins on the outer surface, how can all raisins be in the middle? These galaxies would look opposite the expansion and "see" nothing. What am I missing?

 

[mathman]

The analogy is from the SURFACE of the loaf to the VOLUME of space.

 

[jimjohnson]

Sorry, do not understand response, the surface would be 2 dimensions. tks

 

[Feldoh]

What Mathman is saying is that the analogy is an analogy. The analogy is a 2D example of what could happen in 3D.

 

[Studiot]

I think jim asked a very fair question, which is a long way short of an answer.

Jim's pudding analogy is of an expanding euclidian 3D object, not a map from a 2D one to a 3D one.

This issue of the edge galaxies can be addressed in two ways?

How do we know (what evidence is there) that the inhabitants don't see an asymmetric universe?

The second is the current explanation which is by no means proven.

The thinking runs as follows.

Instead of the raisins being distributed throughout your pudding, imagine they are just popped onto the outer surface, as if they were spots painted on a balloon. So the zone of raisins or spots really is a 2D surface in a 3D world. In this model or analogy no raisin sees an asymmetric view as there is no boundary in the 2D of the durface.

Now let the dough rise so the pudding expand. The outer surface gets bigger and all the raisins move farther away from each other. There is stil no boundary so the raisins maintain their viewpoint.

Translating this model to our 3D universe, The most widely accepted explanation of theory and observable facts in modern physics is that our 3D space is 'curved' in 4D, just as the 2D surface of the pudding is curved in 3D.

 

[jimjohnson]

This is hard to visualize but a logical explanation which I have not read before. Thanks for response.