Doppler Effect: Light Blueshifted When Source Moving Towards Observer

In summary, the conversation discusses the concept of blueshifting when a light source and observer are in motion towards each other, and how this remains the same regardless of which is considered to be "at rest." The importance of being precise in formulating questions and sharing one's own work in the relativity forums is also emphasized.
  • #1
kent davidge
933
56
If I and the light source are both moving toward one another, I see light blueshifted. What if I'm at rest and the source moving towards me?
 
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  • #2
At rest relative to what? You have asked enough questions in the relativity forums to know that there is no absolute rest and that being precise in formulations is important. You should also post your own work, not just say that you "seem to get" something.
 
  • #3
kent davidge said:
I've worked out the equations

Not correctly. If you did it correctly, a source moving towards you would be blueshifted.
 
  • #4
Orodruin said:
At rest relative to what?
Self evident. I do not believe I would have to make that explicit to a experienced physicist like you.
Vanadium 50 said:
a source moving towards you would be blueshifted.
Indeed, as soon as I posted this question, I realized where I was going wrong, and got the correct result.
 
  • #5
Orodruin said:
At rest relative to what?
kent davidge said:
Self evident. I do not believe I would have to make that explicit to a experienced physicist like you.
Not only is the answer not self-evident, but I am unable to imagine any possible answer. As you posed the problem, there are only two things to consider: you and the light source, and these certainly are not at rest relative to one another.
 
  • #6
The original poster says they've found their error so this thread is closed.
The key point here is that it is the exact same physical situation whether we think in terms of the light source approaching the observer or the observer approaching the light source; neither is more "at rest" than the other.
As always, if you have more to say on the topic, PM me or any other mentor.
 

FAQ: Doppler Effect: Light Blueshifted When Source Moving Towards Observer

1. What is the Doppler Effect?

The Doppler Effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the source of the wave. This effect is commonly observed in sound waves, but it also applies to electromagnetic waves, such as light.

2. How does the Doppler Effect affect light?

The Doppler Effect affects light by causing a shift in its wavelength, known as blueshift or redshift, depending on the direction of the relative motion between the source of light and the observer. When the source of light is moving towards the observer, the light is blueshifted, meaning its wavelength becomes shorter and its frequency increases.

3. What causes light to be blueshifted when the source is moving towards the observer?

The blueshift of light when the source is moving towards the observer is caused by the compression of the waves in the direction of motion. This compression results in a decrease in the wavelength of the light, leading to a higher frequency and a shift towards the blue end of the spectrum.

4. How is the Doppler Effect used in astronomy?

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

5. Can the Doppler Effect be observed in everyday life?

Yes, the Doppler Effect can be observed in everyday life, particularly in sound waves. For example, when an ambulance or a train passes by, the sound of its siren or horn appears to change in pitch as it approaches and then moves away from the listener. This is due to the Doppler Effect, which also applies to other types of waves, including light.

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