How can light exhibit the doppler effect?

[RVonse]

According to relativity light must always travel the same speed regardless of the frame of reference. As I understand it, relativity was based entirely on the premise of Michelson-Morely experiment which concluded once and for all that light behaved differently than sound waves through a medium.

 

So how can a doppler shift be observed for stars going towards or away from the earth? If the speed that star light approaches earth is exactly C, then how could there be a red or blue shift? Doppler effect makes sense for sound but not light.

[bascule]

You have to take into account the Special Theory of Relativity. The Doppler effect exhibited by light is relativistic:

 

http://en.wikipedia.org/wiki/Relativistic_Doppler_effect

[swansont]

So how can a doppler shift be observed for stars going towards or away from the earth? If the speed that star light approaches earth is exactly C, then how could there be a red or blue shift? Doppler effect makes sense for sound but not light.

 

A star approaching earth can't be travelling at c.

[Janus]

http://www.scienceforums.net/forums/showpost.php?p=217243&postcount=25

[RVonse]

[url']http://www.scienceforums.net/forums/showpost.php?p=217243&postcount=25[/url]

 

So Are you really saying with the illustrations that the frequency of light has nothing to do with the speed of light? And that the frequency or color will doppler but not the speed which is still constant at C? Kind of like an electromagnetic RF carrier wave that is modulated at a certain frequency (color)?

 

Is that how light behaves?

[RVonse]

A star approaching earth can't be travelling at c.

 

Swansont,

What I meant by that was that light can always be depended to arrive earth traveling at C. And that it always arrives at C even if it comes from a star that is moving high speed approaching earth.

[swansont]

Swansont' date='

What I meant by that was that light can always be depended to arrive earth traveling at C. And that it always arrives at C even if it comes from a star that is moving high speed approaching earth.[/quote']

 

mea culpa. I misread the sentence. (literally didn't see the "light")

[Conceptual]

Light or energy is unique in that it express both the speed of light and finite reference at the same time. The equivilency of mass and energy seems to indicate that its mass associated (m=0) aspect travels at the speed of light. While its distance and time components, expressed as wavelength and frequency, define a non speed of light reference. When light is doppler shifted, the speed of light or its m=0 component remains constant while its distance and time aspects will display the affects of changing between two relativistic references. It is this finite aspect of light that defines inertial reference since what we see is what we know.

 

When we convert energy to mass, the speed of light component or the m=0 aspect of energy becomes finite in mass and velocity. The size or distance aspect of energy will become very small unless one considers the gravitational force an infinite extension of the mass. The time component will become either very transient (laboratory created particles) or will becomes very long in time duration (common matter).