physics about universe

1. As explained in the paragraph you quoted, this is because of the phenomenon called "Doppler red shift".

When an object emitting light wave is receding, because the direction of motion of the object is in opposite direction to that of the propagation of light waves, a wavefront emitted by the object will be at a longer distance from the preceding wavefront than if the object is not moving. As such, the distance between two successive wavefronts thus increases, leading to a lengthening of the wavelength.

2. In theory, it is possible. But the speed of the galaxy needs to be very high, reaching 3/4 of the speed of light.

Taking the wavelengths of red and violet light to be 700 nm and 400 nm respectively

using the Doppler shift formula,
change of wavelrngth/original wavelength = speed of galaxt/speed of light
(700-400)/400 = v/c, where v is the receding speed of the galaxy, and c is the speed of light
thus, v = 3c/4 = 2.25 x 10^8 m/s

上面你抄錄嗰段已經講咗啦，係doppler effect，用笛聲解釋，當聲源接近時，波長變短，頻率變高，相反變低。光波論與聲波有同一特性，當星系遠離時，光波長增加，頻率變低，顏色趨向偏紅，謂之紅移。咁星系會唔會變成紅色呢﹖你先考慮救護車例子，你認為救護車笛聲係由低變高向你而嚟，再由高變低遠你而去﹖抑或一路都冇變化﹖