Doppler Effect: Light Blueshifted When Source Moving Towards Observer

Click For Summary
SUMMARY

The discussion centers on the Doppler Effect, specifically regarding light blueshift when the source moves towards the observer. Participants clarify that regardless of the observer's state of motion, a light source moving towards the observer results in a blueshift. The conversation emphasizes the importance of precise formulations in relativity, highlighting that there is no absolute rest frame. The original poster acknowledges their misunderstanding and corrects their approach to the problem.

PREREQUISITES
  • Understanding of the Doppler Effect in physics
  • Familiarity with the principles of special relativity
  • Knowledge of light behavior and wave properties
  • Ability to formulate and solve equations related to motion
NEXT STEPS
  • Study the mathematical derivation of the relativistic Doppler Effect
  • Explore the implications of relative motion in special relativity
  • Learn about the concept of reference frames in physics
  • Investigate real-world applications of the Doppler Effect in astrophysics
USEFUL FOR

Physics students, educators, and anyone interested in understanding the principles of light behavior and the Doppler Effect in the context of special relativity.

kent davidge
Messages
931
Reaction score
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?
 
Physics news on Phys.org
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.
 
kent davidge said:
I've worked out the equations

Not correctly. If you did it correctly, a source moving towards you would be blueshifted.
 
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.
 
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.
 
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.
 

Similar threads

Undergrad Doppler effect in transparent media and the index of refraction
  • · Replies 11 ·
Replies
11
Views
1K
High School Why is the constant speed of light so unique?
  • · Replies 19 ·
Replies
19
Views
1K
Undergrad Relativistic Doppler effect and refraction
  • · Replies 10 ·
Replies
10
Views
1K
High School Michelson Morley experiment and the Doppler effect
  • · Replies 21 ·
Replies
21
Views
2K
Undergrad Physics Error in Larry Niven's "Neutron Star
  • · Replies 28 ·
Replies
28
Views
3K
Undergrad What is the four-momentum of a photon?
  • · Replies 17 ·
Replies
17
Views
3K
Undergrad What was the role of frequency in the Michelson-Morley experiment's null result?
  • · Replies 3 ·
Replies
3
Views
1K
Undergrad Doppler Effect on Light: Constant Speed of Light Confusion
  • · Replies 9 ·
Replies
9
Views
3K
High School Speed of light seen by a moving observer
  • · Replies 24 ·
Replies
24
Views
2K
Undergrad [SR] light shot at an angle in a moving train
  • · Replies 5 ·
Replies
5
Views
1K