According to equivalence principle, we cannot distinguish gravity with inertial force. Let's assume that there is space shuttle which contain observer and electron. There is some force that is gravity or inertial force that we cannot distinguish. But if the force is gravity, electron will not emit electromagnetic wave.(Both of case, electron is not moving in observer's viewpoint.) However, if it is inertial force it will emit electromagnetic wave. It does not match with the principle. What is wrong in my thought?enter image description here

  • $\begingroup$ Whether an electron emits or does not emit photons depends on the frame of reference. This is the same in gravity or acceleration. The equivalence principle holds. $\endgroup$ – safesphere May 26 '18 at 16:27
  • $\begingroup$ > "if the force is gravity, electron will not emit electromagnetic wave." What makes you say that? If charge is falling in gravity field, I would expect it to produce acceleration field in the frame of the Earth, which could be enough to say it radiates. $\endgroup$ – Ján Lalinský May 26 '18 at 17:33
  • $\begingroup$ @JánLalinský I edited my question with picture. $\endgroup$ – ABC May 27 '18 at 4:24
  • $\begingroup$ So, you are considering an electron at rest on Earth and an electron at rest in accelerating spacecraft. You should state this clearly in the question. Equivalence principle says that it is not possible by any experiment in the spacecraft to discover that it is accelerating rather than standing still in Earth's gravity field. How would you use the electron to tell the spaceship is accelerating? Electron won't produce oscillating EM wave such as the one on the picture, in either case. $\endgroup$ – Ján Lalinský May 27 '18 at 8:58
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    $\begingroup$ The general claim "accelerated charge radiates" is meant to say that from the viewpoint of inertial frame there is radiation field around the accelerated charge. In the reference frame of the spaceship (which is not inertial, and which must be used to use the equivalence principle) the field will look differently, and perhaps the same way as it looks in the spaceship standing still in the Earth's gravity. So I do not see violation of equivalence principle. $\endgroup$ – Ján Lalinský May 27 '18 at 9:04

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