How was the bright line spectrum of hydogen involved with Hubbles development with Big Bang theory?
By noticing that the hydrogen line of distant galaxies was shifted Hubble recognised that they must have a velocity relative to us (Doppler shift). Further studies showed that ALL galaxies were receeding, and that their recession velocity was proportional to their distance. This implied that at some time in the past all galaxies were at the same point in space / time. If this was the case then something must have caused all matter to start moving outwards from that point – hence The Big Bang.
