Quantisation of light and Doppler effect

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SUMMARY

The discussion centers on the quantization of light and the Doppler effect, specifically how the frequency of photons is frame-dependent. Participants clarify that while the energy of light changes with the motion of the source or observer, this does not violate the conservation of energy principle. The analogy of kinetic energy in different frames of reference is used to illustrate that energy measurements can vary based on the observer's frame. The conversation emphasizes the importance of understanding the photon picture in explaining the light Doppler effect.

PREREQUISITES
  • Understanding of quantum mechanics and the concept of photons
  • Familiarity with the Doppler effect in both sound and light
  • Knowledge of frame-dependent measurements in physics
  • Basic principles of energy conservation in different reference frames
NEXT STEPS
  • Research the mathematical formulation of the Doppler effect for light
  • Explore the implications of special relativity on energy and momentum
  • Study the relationship between frequency, wavelength, and energy in quantum mechanics
  • Investigate real-world applications of the light Doppler effect in astronomy
USEFUL FOR

Physicists, students of quantum mechanics, and anyone interested in the principles of light behavior and relativistic effects.

Vibin Narayanan
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Light consists of quanta(small packets of energy). Then how do we explain doppler effect of light the same way we do for sound? What is the valid explanation of light doppler effect which is consistent with the photon picture?
 
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Vibin Narayanan said:
Light consists of quanta(small packets of energy). Then how do we explain doppler effect of light the same way we do for sound? What is the valid explanation of light doppler effect which is consistent with the photon picture?
The frequency of the photon (and hence its energy) is frame-dependent.
 
DrClaude said:
The frequency of the photon (and hence its energy) is frame-dependent.
That's it? I simply didn't get it. Energy changing with the motion of source or observer or both, doesn't violate conservation of energy?
 
Energy is conserved, but it is dependent on the frame. For example, I will measure a ball moving relative to me as having kinetic energy, but in a frame co-moving with the ball, it will have none.
 
Vibin Narayanan said:
That's it? I simply didn't get it. Energy changing with the motion of source or observer or both, doesn't violate conservation of energy?

Nope. Consider yourself in a car moving down the road. If another car comes up behind you 1 mph faster than you're going and taps your bumper, your car is not totaled, despite the fact that you both may be traveling 70+ mph.
 

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