- #1
- 6,735
- 2,436
In relativistic doppler shift, the energy of the photon is increasing och decreasing, due to realative motion of observer vs emitter. Let say that the photon is redshiftet, does any energy dissapear? 
Doppler and enegry conservation
- Context: Graduate
- Thread starter malawi_glenn
- Start date
-
- Tags
- Conservation Doppler
Click For Summary
Discussion Overview
The discussion revolves around the relativistic Doppler effect and its implications for energy conservation in the context of photon emission and observation. Participants explore how the energy of photons changes due to the relative motion between the observer and the emitter, particularly focusing on redshift and the interpretation of energy in different reference frames.
Discussion Character
- Exploratory
- Debate/contested
- Technical explanation
Main Points Raised
- Some participants assert that while the frequency of a photon decreases (redshift), its energy is not lost; rather, it is a result of the relative motion between the observer and the emitter.
- Others argue that the increase in wavelength implies a loss of energy, suggesting that energy must have disappeared as the wavelength increases.
- A participant questions the invariance of energy, proposing that energy is constant according to both the emitter and observer, yet the measurements differ due to relativistic effects.
- There is a discussion about the nature of energy as an invariant quantity, with some participants asserting that energy is invariant in force-free motion, while others challenge this view by highlighting the relativity of kinetic energy across different frames.
Areas of Agreement / Disagreement
Participants do not reach a consensus on whether energy is conserved in the context of the relativistic Doppler effect. Multiple competing views remain regarding the interpretation of energy changes and invariance in different reference frames.
Contextual Notes
The discussion includes unresolved assumptions about the definitions of energy and how it is measured in different inertial frames. There is also ambiguity regarding the implications of relativistic effects on energy conservation.
Who May Find This Useful
This discussion may be of interest to those studying relativistic physics, particularly in understanding the implications of the Doppler effect on energy and the nature of measurements in different reference frames.
- #2
Danger
Gold Member
- 9,805
- 251
The energy isn't lost. While the frequency decreases, the wavelength increases. Each individual photon retains its initial energy; it just takes a 'longer path' to get here. That's a pretty lousy response. Best wait for ST or other to clear it up.
- #3
- 6,735
- 2,436
Is this what you mean?
When the photon is emitted, its wavelength is less than the wavelength as the observer see it. The energy must have dissapeared, science the wave length is increasing. There must be a relativistic answer to this. Of course the frequency is increasing if wavelength is decreasing.. But that is not the anszer to my question i think. You must compare the initial wave length and the final wavelength.
So i guess that the answer lies in the relativisic area. According to the emitter the photon energy is constant, and according to the observer the photon energy is constant, science we can't follow a photons path. If I would make a guess. But energy is an invariant of motion.. ? That is why Iam asking.
When the photon is emitted, its wavelength is less than the wavelength as the observer see it. The energy must have dissapeared, science the wave length is increasing. There must be a relativistic answer to this. Of course the frequency is increasing if wavelength is decreasing.. But that is not the anszer to my question i think. You must compare the initial wave length and the final wavelength.
So i guess that the answer lies in the relativisic area. According to the emitter the photon energy is constant, and according to the observer the photon energy is constant, science we can't follow a photons path. If I would make a guess. But energy is an invariant of motion.. ? That is why Iam asking.
- #4
HungryChemist
- 140
- 0
malawi_glenn said:In relativistic doppler shift, the energy of the photon is increasing och decreasing, due to realative motion of observer vs emitter. Let say that the photon is redshiftet, does any energy dissapear?
There will be difference in energy measured by emitter and receiver and that is fine. But the "change in energy" is not observed respect to emitter(and receiver). Difference in energy measured b/t two reference frame is not the same thing as the change in energy observed by one frame.
malawi_glenn said:
What makes you think Energy is invariant of motion? For one, kinetic energy is obviously a relative quantity respect to different reference frame.
- #5
Mentz114
- 5,429
- 292
Energy is an invariant of force-free motion, but that energy will be measured differently from different inertial frames.
Similar threads
- · Replies 1 ·
Graduate
Can energy conservation be violated?
- · Replies 3 ·
High School
Work Done By Conservative Forces
- · Replies 1 ·
- · Replies 13 ·
High School
Red shifted tired light doubts
- · Replies 10 ·
- · Replies 1 ·
Undergrad
What is the four-momentum of a photon?
- · Replies 17 ·
- · Replies 10 ·
Undergrad
Sound Doppler shift asymmetry confusion
- · Replies 23 ·
- · Replies 1 ·