Final answer:
The notion that we are at the center of the universe's expansion is an observer-dependent effect due to the cosmological redshift caused by the expansion of space itself, as discovered by Edwin Hubble. This implies there is no actual center or edge to the universe's expansion, and each observer in any galaxy would observe similar redshifts in other galaxies, making all galaxies appear to be moving away from them.
Step-by-step explanation:
The perception that we are at the center of the universe's expansion is a consequence of the observation that all other distant galaxies are receding from us, displaying a redshift in their light spectra that suggests they are moving away. This phenomenon, first observed by Edwin Hubble, is due to the expansion of space itself, not because there is an actual center of the universe. In this cosmic expansion, every observer in any galaxy would observe the same effect, which would make them also appear to be at the center of the universe's expansion.
The redshift is not due to a Doppler effect but is instead a cosmological redshift; as space expands, the wavelengths of photons traveling through it are stretched, making the light appear redder the farther the galaxy is. This cosmological principle is an essential part of understanding our universe, negating the existence of a singular central point from which everything is expanding.
The analogy of a balloon being inflated can be used to simplify the explanation: as the surface of the balloon stretches, all points on the surface move away from each other uniformly. Likewise, in the universe, galaxies spread apart as space itself expands, and hence no edge or center to this expansion can be determined. Additionally, the measured redshifts are proportional to distance and not to variables like the size of the galaxy, eliminating alternative explanations like gravitational redshifts related to the mass of individual galaxies.