Any experimental evidence of Doppler shift in light?

In summary, there have been many experiments that have proven the Doppler shift of light on fast moving objects. This phenomenon has been observed and measured using both acoustical and optical methods. The police radar guns also use this principle to measure the velocity of moving objects. Even very slight differences in frequency can be accurately detected and measured, making it possible to observe the red shift of distant galaxies. The experiment to prove this involved measuring the spectrum of the sun's limb moving towards and away from us, which rotates at a few km per second.
  • #1
Crazy Tosser
182
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Were there any experiments that proved doppler shift of light on a fast moving object - that it has higher frequency if the object is moving towards you and lower if the object is moving away?
 
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  • #2
Many, many experiments. I even did this in college. It's not hard.
 
  • #3
Ever been caught by a police radar trap?
 
  • #4
Excuse me, I always thought police trap was sound waves, not light waves. And how was the experiment performed, Vanadium?
 
  • #5
Crazy Tosser said:
Excuse me, I always thought police trap was sound waves, not light waves.
Police radar guns use radar (ie radio waves = light) they measure the difference in frequency between the outgoing signal and the doppler shifted return. It's very easy in electronics to accurately measure small frequency differences between two signals - much easier than measuring pulse time of flight for instance.

You can do an easy experiment on acoustical doppler shift by just spinning a buzzer around your head on a wire. Optical / radio needs a bit more equipment but it's still an ugrad lab practical.
 
  • #6
Ok, so a 30 mph difference in speed produces a measurable difference in frequency of light? >.< You would think that stars that travel at thousands km/sec away from us would not even be seen?
 
  • #7
Crazy Tosser said:
Ok, so a 30 mph difference in speed produces a measurable difference in frequency of light?
There is a trick to measure slight differences in two frequencies.
Imagine you have a very long sin wave drawn on a chart - now add another very long wave with a tiny difference in frequency and put it next to the first. They will line-up almost perfectly at the start.
But if they differ by 1 part in a million then after a 1/2 million waves the top of one will line up with the bottom of another - this is very easy to detect.
Since the rader gun is sending billions of wavelengths /second it only has to sample a fraction of a second to line up a million waves.

You would think that stars that travel at thousands km/sec away from us would not even be seen?
Speed of light is 300,000km/s so 3000km/s is only a 1% shift. Stars are a continuum source so as 1% of the visible light is moved into the IR another 1% of the UV is moved into the visible. You do see the effect in very distant galaxies - they are red shifted out of the visible into the infrared.
 
  • #8
Crazy Tosser said:
And how was the experiment performed, Vanadium?

Measuring the spectrum of the limb of the sun that is moving away from us, and comparing it to the limb of the sun that is moving towards us. The sun rotates at a few km per second, so it's about a 10 ppm effect. It's quite straightforward, actually.
 

1. What is the Doppler shift in light?

The Doppler shift in light is a phenomenon where the wavelength of light appears to change due to the relative motion between the light source and the observer. This shift can either be towards the blue end of the spectrum (blue shift) or towards the red end (red shift).

2. How is the Doppler shift in light measured?

The Doppler shift in light can be measured using a spectrometer, which separates light into its individual wavelengths. By analyzing the position of the spectral lines, scientists can determine if the light source is moving towards or away from the observer.

3. Is there any experimental evidence of Doppler shift in light?

Yes, there is strong experimental evidence of the Doppler shift in light. This phenomenon has been observed in various astronomical objects, such as stars, galaxies, and even the cosmic microwave background radiation. It has also been demonstrated in laboratory experiments using moving light sources.

4. How does the Doppler shift in light affect our understanding of the universe?

The Doppler shift in light plays a crucial role in our understanding of the universe. By studying the red and blue shifts of light from distant objects, scientists can determine the velocity and direction of their motion. This has helped us map the structure and expansion of the universe and discover the existence of dark matter and dark energy.

5. Can the Doppler shift in light be used to measure the speed of light?

No, the Doppler shift in light cannot be used to directly measure the speed of light. This is because the Doppler shift is dependent on the relative motion between the light source and the observer, and the speed of light is constant regardless of the observer's motion. However, the Doppler shift can be used to indirectly measure the speed of objects in the universe, which can then be used to study the effects of gravity and the expansion of the universe.

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