Can the Doppler Effect Explain Redshift in Light?

In summary, the speed of light is constant, regardless of the relative velocity of the observer. This is an observation, not an assumption.
  • #1
Combsbt
10
0
I do not fully understand the Doppler effect in light.
A theoretical question:

If I was traveling near the speed of light, towards a source of light. Would all the wavelengths in the visible spectrum be shortened and therefor, everything shifting towards red?

I thought the speed of light was supposedly constant, no matter the relative velocity of the observer.
 
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  • #2
Combsbt said:
If I was traveling near the speed of light, towards a source of light. Would all the wavelengths in the visible spectrum be shortened and therefor, everything shifting towards red?
The observed wavelengths will be shorter, which means a shift towards blue.

I thought the speed of light was supposedly constant, no matter the relative velocity of the observer.
The speed is constant. It's the observed wavelength that changes, not the speed.
 
  • #3
Oh yeah, red is longer wavelength...

What I don't understand is how the speed of the wave propagation can remain constant relative to the observer. It seems that if you are moving towards the source, your relative velocity would be higher.
 
  • #4
Combsbt said:
What I don't understand is how the speed of the wave propagation can remain constant relative to the observer. It seems that if you are moving towards the source, your relative velocity would be higher.
That the speed of light is independent of the speed of the source or observer is counterintuitive. It requires special relativity to make sense of it all.
 
  • #5
Oh I see, so that property is an assumption.
 
  • #6
Combsbt said:
Oh I see, so that property is an assumption.

No, it's an observation.
 
  • #7
Vanadium 50 said:
No, it's an observation.

Einstein said:
"The insight fundamental for the special theory of relativity is this: The assumptions relativity and light speed invariance are compatible if relations of a new type ("Lorentz transformation") are postulated for the conversion of coordinates and times of events... The universal principle of the special theory of relativity is contained in the postulate: The laws of physics are invariant with respect to Lorentz transformations (for the transition from one inertial system to any other arbitrarily chosen inertial system). This is a restricting principle for natural laws..."

Einstein seemed to think differently.
 
  • #8
Einstein assumed the constancy of the speed of light in deriving the special theory of relativity. Since then it has been tested (observed) experimentally in various ways. The link below refers to many of them.

Experimental Basis of Special Relativity
 
  • #9
Combsbt said:
Einstein seemed to think differently.

Rather than playing word games and "quote the physicist", I think your time would be better spent understanding the physics, rather than the connotation of the word. There are already many sources (and many threads on here) on why the simple Galilean addition of velocities will not work at relativistic speeds.

Zz.
 
  • #10
Found a video on youtube with a visual explanation of special relativity. Seemed to clear some things up for me with my original question. Here it is if anyone is interested.

_http://www.youtube.com/watch?v=C2VMO7pcWhg&feature=related
 

1. What is the Doppler effect in light?

The Doppler effect in light refers to the phenomenon where the frequency of light waves appears to change when the source of light is moving relative to the observer. This results in a shift in the wavelength of light, which can be observed as a change in color.

2. How does the Doppler effect in light work?

The Doppler effect in light is caused by the relative motion between the source of light and the observer. When the source of light is moving towards the observer, the frequency of the light waves appears to increase, resulting in a shorter wavelength and a higher color. Similarly, when the source of light is moving away from the observer, the frequency appears to decrease, resulting in a longer wavelength and a lower color.

3. What is the difference between the Doppler effect in sound and light?

The main difference between the Doppler effect in sound and light is the medium through which the waves travel. Sound waves require a medium, such as air, to propagate, while light waves can travel through a vacuum. Additionally, the speed of sound waves is much slower than the speed of light, resulting in a more noticeable effect for sound compared to light.

4. How is the Doppler effect in light used in astronomy?

The Doppler effect in light is used in astronomy to determine the motion and speed of celestial objects, such as stars and galaxies. By analyzing the shift in the wavelength of light emitted by these objects, scientists can calculate their velocity and direction of motion.

5. Can the Doppler effect in light be observed in everyday life?

Yes, the Doppler effect in light can be observed in everyday life, such as when a police car or ambulance passes by with its sirens on. As the vehicle moves towards the observer, the frequency of the sound waves increases, resulting in a higher pitch. This same effect can also be observed with light, where the color of a moving object appears to change as it approaches or moves away from the observer.

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