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| Cosmology |
1. The loose terminology that the Universe is expanding really means that space is expanding, and this is signalled by an increase in the cosmic scale factor with time. For a closed, finite Universe this is like the increase of the radius, but for an infinite Universe the scale factor should not be interpreted a radius but instead as a measure of the average separation between galaxies.
3. We are not the center. Because of the expansion of spacetime, any galaxy will appear to be the center as we view from it. Thus all distant galaxies will be redshifted, no matter where we view from.
5. Since light can only travel several hundred kilometers in a time of order 1/1000 of a second, flickering on this timescale implies that the energy source for the gamma-ray burst is no more than several hundred kilometers in diameter. If it were larger, there would be insufficient time for a signal to pass through the object and correlate the flickering intensity because of the finite speed of light.