Red Shift/Blue shift
Red Shift- Red shift in the universe is a phenomenon occuring in our universe today. In red shift, the stars and galxies are moving farther away such as red wave lenghts in the visible light spectrum. This leads astronomers to believe that our universe is expanding. Red shift relates to the doppler affect as it represents the light and sound waves strecthing out as the source moves farther away from the observer.
Blue Shift- Blue shift is the complete opposite of red shift, meaning that instead of moving farther apart, they move closer together. This is related to blue wavelengths in the visible light spectrum because they are closer together. This phenomenon is currently not occuring in our universe, meaning that our universe is not shrinking. Blue shift is related to the doppler affect as it represents the light and sound waves squishing together as their source gets closer to the observer.
Relation to big bang theory
Both red shift and blue shift relate to the Big Bang Theory in specific ways. Red shift is related to th Big Bang Theory because it is what happened when the universe started its expansion and is still what is occuring today. Blue shift is related to the Big Bang Theory by it occuring after red shift has ended and the universe has stopped expanding. When this occurs, the universe will come together until it is in the state it was before the big bang.
Side Note- For anyone who doesn't know, the Doppler Effect is the change in frequency of sound waves and/or light waves as the source of those waves gets closer to the observer. In this effect, the wave's frequency gets faster as the source gets closer causing light to seem brighter and sound seem louder, and as the source gets farther away the frequency slows, making light seem dimmer and sound seem softer.