Can energy conservation be violated?

  • #1

Main Question or Discussion Point

I think energy can be created...i agree that energy is not conserved between different reference frames..but i can show you that energy measured in a single frame may wary... Does photon's energy increase when i emit it from a train which is moving at comparable speed and get it reflected back by a mirror on a platform so that i can catch it again in the train? According to doppler effect the frequency of the photon for an observer standing near the mirror is greater to an observer in the train.So to the observer near the mirror, energy of the photon is greater than the energy observed by an observer in train.Similarly when it gets reflected back and reaches the train its frequency is larger than the initial frequency when observed by an observer in train .So obviously energy of photon is increased without doing any work....please correct me if i am wrong somewhere
 

Answers and Replies

  • #2
Ibix
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I think energy can be created
No it can't.

So obviously energy of photon is increased without doing any work....please correct me if i am wrong somewhere
The light bounces off the mirror, and there is energy and momentum transfer there. In the frame of the train the mirror is moving towards the train and is slightly slowed by the reflection. Its kinetic energy is carried away by the light.

[Mentors' note: This post has been edited to remove a loose end from when it was moved from another thread]
 
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  • #3
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So obviously energy of photon is increased without doing any work....please correct me if i am wrong somewhere
As @Ibix mentioned, the mirror is the source of the additional energy. Recall that light exerts pressure on a surface. This pressure reduces the speed of the mirror and thereby transfers both energy and momentum to the light. Energy is conserved in this case.
 
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  • #4
russ_watters
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Answer to the title question: No.

Follow-up: Do you really think that millions of scientists and engineers over the past hundred years could plausibly have all missed something so obvious?
 

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