Final answer:
The balloon and dots experiment illustrates that there is no 'center' in the universe's expansion, with everything moving away from everything else, analogous to the surface of an expanding balloon where dots represent galaxies moving apart.
Step-by-step explanation:
The main concept demonstrated by the experiment involving a balloon and dots is D. How there does not need to be a 'center' of the universe, and how everything in the universe can still be moving away from everything else. This experiment is a classic analogy used to explain the Big Bang and the subsequent expansion of the universe. As the balloon (representing the universe) expands, the dots on the balloon (representing galaxies) move away from each other in all directions, showing that there is no central point of expansion and echoing the observations made by Edwin Hubble regarding the cosmological red shift and the proportional increase of galaxy speeds with distance. This demonstrates a four-dimensional cosmic expansion, where every point can be seen as the center, refuting the notion of a privileged central position within the universe.