- #1
thehangedman
- 69
- 2
The analogy always used is to draw two points on the surface of a balloon and then blow air in the balloon. The points move away as the balloon expands. The issue I have with this is: now draw a "meter stick" on the surface of the balloon. It expands too, at the same rate, so that the number of meters between the two points doesn't actualy change as the balloon expands.
So, what gives? Are the points really moving apart? What is broken with the analogy as compared the the actual theory? If there is no change in the distance, as measured in the system itself (as opposed to the person standing outside the system, looking down at the balloon), then how can there be a red shift?
Also, with the balloon, the universe would actually be compact. If you walk in any direction you eventually end up where you started. How does a compact universe differ from one with constant curvature? I've seen and read explanations of Kaluza-Klein but none of them talk about curvature in that fifth dimension...
So, what gives? Are the points really moving apart? What is broken with the analogy as compared the the actual theory? If there is no change in the distance, as measured in the system itself (as opposed to the person standing outside the system, looking down at the balloon), then how can there be a red shift?
Also, with the balloon, the universe would actually be compact. If you walk in any direction you eventually end up where you started. How does a compact universe differ from one with constant curvature? I've seen and read explanations of Kaluza-Klein but none of them talk about curvature in that fifth dimension...