Expanding Universe ::: Doppler Shift
The sudden change in pitch of a car horn as a car passes by an observer, was first explained in 1842 by Christian Doppler. This effect came to be known as Doppler Effect is the shift in frequency and wavelength of waves which results from a source’s or target’s motion.Although first discovered for sound waves, the Doppler effect holds true for all types of waves including light (and other electromagnetic waves). The Doppler effect for light waves is usually described in terms of colors rather than frequency. A red shift occurs when the source and observer are moving away from each other, and a blue shift occurs when the source and observer are moving towards each other. The red shift of light from remote galaxies is proof that the universe is expanding.Astronomers had previously noticed that nebulae emitted spectral lines of unidentified wavelength. It turned out that these actually were common emission wavelengths, severely Doppler-shifted because their sources were moving away from us, at speeds which could be an appreciable fraction of c. In fact, this "red shift" seemed a universal feature, present in all directions. It also suggested that all distant galaxies are moving away from us - the more distant they were, the faster their motion. Light is a wave that can be described in terms of its frequency, the number of wave peaks that pass by each second. A star zooming toward earth has its light waves squeezed together. We see these light waves as having a higher frequency than normal. Since blue is at the high-frequency end of the visible spectrum, we say the light from an approaching star is shifted toward blue, or blueshifted. Likewise, if a star is zooming away from us, any light it emits gets stretched. You see these stretched-out light waves as having a lower frequency. Since red is at the low-frequency end of the visible spectrum, we say that light from a receding star is shifted toward red, or redshifted.
There are many examples which are infront of our eyes which are yet to be conciously thought of!
The balloon slowly filled with air is the best analogy of expanding universe. Initially, the marks on the balloon are close to each other and as the balloon increases in size the points move away from each other. As an extension to this analogy if the balloon is filled more and more, at some point of time it will burst. And if we compare this to our universe, the universe might come to an end someday. But dont ponder on this much, we won't be able to see something like that because the issue here is when we go in space we measure in light years!! And our life span is going to be a max of 100 yrs!
