Re: How do red shifts and blue shift prove the expainsion of the universe?

Hi Veki,

Light from moving objects can appear to be redshifted or blueshifted. If the light is redshifted, the object is moving away from you, the observer. The speed of light is so fast that we can't see this effect with our eyes, but we can hear a similarDoppler shift in sound when an ambulance races by.

Curiously, we observe redshifts in nearly all galaxies, indicating that they are moving away from us. This is nothing personal, but just an effect of the expanding universe. The reason we can infer that the universe is expanding is that the redshifts are larger at greater distances. To understand why, imagine that you stand still while a few hundred people run away from you. After a few hours, the people furthest from you are the ones who run the fastest. Although the analogy is far from perfect, you can think of the size scale of the universe as the distance between runners. This scale increases even though the runners themselves stay the same size. A better analogy is the surface of a balloon which you can try out at home!