Einstein equivalence principle

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Discussion Overview

The discussion centers on the Einstein equivalence principle, exploring its implications and interpretations. Participants seek clarification on the principle's meaning, its relationship to gravity, and its connection to special relativity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express confusion about the equivalence principle, specifically regarding the idea that a free-falling lift can be considered as experiencing no gravity.
  • One participant states that experiments in a free-falling lift yield the same results as those in a lab in empty space, excluding tidal forces.
  • Another participant emphasizes that a lab in empty space is effectively in free fall and that this perspective was not fully established when Einstein developed general relativity.
  • There is a discussion about Newtonian gravity being an infinite-range force, which leads to the conclusion that weightlessness in a free-falling lab is due to the lab's motion rather than the absence of gravity.
  • One participant argues that Einstein's contribution was to assert that the equivalence of acceleration and gravity is a genuine phenomenon, rather than merely a mathematical artifact.
  • Another participant raises the distinction between the weak equivalence principle and the strong equivalence principle, suggesting that Einstein extended the former to the latter.
  • A participant questions whether special relativity holds true in a free-falling frame, indicating a need for further explanation on this point.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the implications of the equivalence principle, particularly regarding its relationship with special relativity and the historical context of its development. Multiple competing views remain on the interpretations of the principles involved.

Contextual Notes

There are unresolved questions about the implications of special relativity in a free-falling frame and the historical development of the equivalence principle, including the distinction between weak and strong equivalence principles.

Sobi
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I can not understand what exactly this principle says.while reading a book about it ,it was written that einstein abolished gravity by saying the lift is free falling can some explain clearly what does that mean?
 
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Sobi said:
I can not understand what exactly this principle says.while reading a book about it ,it was written that einstein abolished gravity by saying the lift is free falling can some explain clearly what does that mean?

It means that (apart from tidal forces) experiments that you perform in a free falling lift will have the same results as experiments that you perform in a lab in empty space.
 
Smattering said:
It means that (apart from tidal forces) experiments that you perform in a free falling lift will have the same results as experiments that you perform in a lab in empty space.
A lab in empty space would be a lab in free fall.
 
Chalnoth said:
A lab in empty space would be a lab in free fall.

Yes, but as far as I know this view had not been established when Einstein began working in GR.
 
Smattering said:
Yes, but as far as I know this view had not been established when Einstein began working in GR.
Yes, it had. This realization is based upon Newtonian gravity. Newtonian gravity is an infinite-range force, which means that a lab in orbit still experiences gravity. People in that lab only feel weightless because the lab is in free fall.

Einstein's philosophical contribution here was to state that this equivalence between acceleration and gravity is a real thing, not just a trick of the math.
 
It means that if you're in a closed box, you cannot say whether you're in a gravitational field or the box is accelerating. Both have the same effects.
 
Chalnoth said:
Yes, it had. This realization is based upon Newtonian gravity. Newtonian gravity is an infinite-range force, which means that a lab in orbit still experiences gravity. People in that lab only feel weightless because the lab is in free fall.

Einstein's philosophical contribution here was to state that this equivalence between acceleration and gravity is a real thing, not just a trick of the math.

Hm ... I thought the version that was established before Einstein was only the so-called weak equivalence principle (equivalence of inertial and gravitational mass), and it was Einstein who extended this to the strong equivalence principle (invariance of physical laws in nonrotating laboratories freely falling in a uniform gravitational field).
 
it has also written that the free fall is a local inertial frame.well I will accept that any thing inside the lab will feel that it is moving with a constant speed compared to the other things inside the lab,but inside the book it stated that this was a problem for Einstein because then special relativity had to hold true there.i also need an explanation wether special relativity will be true there or not?
 

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