Question about equivalence principle

In summary: I'm not sure. If you could clarify what you're getting at, that would be helpful.In summary, the equivalence principle states that the laws of physics are the same in all situations where an observer is stationary. This principle is based on the assumption that there is no difference between the situations of an observer in a closed space capsule and an observer in a rocket accelerating towards the center of the universe.
  • #1
knightq
23
0
Let me restate my problem in a more clear way i think.
Situation A: a accelerated rocket in flat spacetime. the observer in the rocket could think he is in a gravitation field equivalently.All experiments he do are like in a gravitation field downward.

SituationB: a apple falls down under the gravitation force from the tree, or "in GR way", caused by the curved spacetime which is disturbed by the earth.
Can I say that the gravity in A is different from in B? or the gravity in B is real , in the sense that it is caused by another object. After all what we called gravity is a interaction of two bodies , no matter you intepreted as curved spacetime or force, which both demand a source (the Earth in B).Obviously in case A there is no such a source.
 
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  • #2
The idea is as you as an observer in a closed capsule cannot differentiate between Situation-A and Situation-B. This is called the principle of equivalence.

After the formulation of space-time continuum in Special theory of relativity, the immediate afterthought was "What happens to space-time during acceleration?". The mathematics showed curvature of space-time during acceleration.

Because of the principle of equivalence, instead working with the unknowns in gravity, we can as well work with a simple system of acceleration. Equations will be applicable in both cases.

Einstein did this and got GTR.

Makes sense?

cheers!
KANNAN
 
  • #3
kannank said:
After the formulation of space-time continuum in Special theory of relativity, the immediate afterthought was "What happens to space-time during acceleration?". The mathematics showed curvature of space-time during acceleration.
The rindler metric has accelerated observes but the intrinsic geometry of rindler space is flat. The presence of intrinsic curvature is seen with the non -vanishing of the Riemann Curvature tensor and is related to mass - energy distributions / fluxes as per the EFEs.
 
  • #4
WannabeNewton said:
The rindler metric has accelerated observes but the intrinsic geometry of rindler space is flat. The presence of intrinsic curvature is seen with the non -vanishing of the Riemann Curvature tensor and is related to mass - energy distributions / fluxes as per the EFEs.

I didn't get a word you said. Yet, you must be right. The 'observable' space-time must be a 'Riemann Curvature tensor' thingy. Yes?
 
  • #5
kannank said:
After the formulation of space-time continuum in Special theory of relativity, the immediate afterthought was "What happens to space-time during acceleration?". The mathematics showed curvature of space-time during acceleration.

Because of the principle of equivalence, instead working with the unknowns in gravity, we can as well work with a simple system of acceleration. Equations will be applicable in both cases.

Einstein did this and got GTR.

Makes sense?

acceleration do not generate curvature, it can be treat just in special relativity.And do you answer my question?
 
  • #6
kannank said:
I didn't get a word you said. Yet, you must be right. The 'observable' space-time must be a 'Riemann Curvature tensor' thingy. Yes?

There are flat space - times that describe accelerated observers so acceleration does not directly generate curvature. Curvature is generated by mass - energy as is quantified by the field equations of GR. The tensor in question quantifies curvature and if it vanishes then you can say you are dealing with flat space - time, a lack of acceleration does not imply the same.
 
  • #7
hey everybody, please answer my question...
 
  • #8
knightq said:
Let me restate my problem in a more clear way i think.
Situation A: a accelerated rocket in flat spacetime. the observer in the rocket could think he is in a gravitation field equivalently.All experiments he do are like in a gravitation field downward.

SituationB: a apple falls down under the gravitation force from the tree, or "in GR way", caused by the curved spacetime which is disturbed by the earth.
Can I say that the gravity in A is different from in B?

or the gravity in B is real , in the sense that it is caused by another object. After all what we called gravity is a interaction of two bodies , no matter you intepreted as curved spacetime or force, which both demand a source (the Earth in B).Obviously in case A there is no such a source.

I'm not quite sure what your question is, here.

The first part seems to be a pretty good summary of the equivalence principle. (But not phrased as a question).

In the second part seems to be that you're looking for GR to be just like Newtonian theory, with some sort of "force between bodies" defined.

So I guess my best shot at an answer at this point would be that you're on the right track in part 1 as far as understanding what is usually meant by the equivalence principle in basic textbooks, and getting off on a speculative track in part 2, where you start talking about "force between bodies".

You could conceivably be trying to talk about Mach's principle in part 2, I suppose.
 
  • #9
In GR, real gravity that cannot be mimicked by acceleration is called "tidal gravity". One has to do "non-local" experiments to see tidal gravity, whereas the equivalence principle applies only to "local" experiments. In realistic cases, tidal gravity indicates the presence of matter somewhere in the universe. However, GR does contain solutions in which tidal gravity is present even without matter.

http://www.einstein-online.info/spotlights/equivalence_principle
 
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  • #10
Pervect:
my question is that is the gravity the guy in rocket feel is real? in the 2 art I give what i mean by real.
 
  • #11
atyy said:
In GR, real gravity that cannot be mimicked by acceleration is called "tidal gravity". One has to do "non-local" experiments to see tidal gravity, whereas the equivalence principle applies only to "local" experiments. In realistic cases, tidal gravity indicates the presence of matter somewhere in the universe. However, GR does contain solutions in which tidal gravity is present even without matter.

then what the gravity in case A is? if I am a man in the rocket, i want to a explanation of the gravity or the fact every thing around in rocket is falling, how could I explain?

For this statement "In a reference frame that is in free fall, the laws of physics are the same as if there were no gravity at all ", I can understand, you can say there are no gravity at all , all body is go its geodesics, for their own frame, the world are minkowski spacetime.
However i can't understand the inverse statement, "in a gravity-free region of space, objects fall towards the floor if the room we are in is being accelerated"( my situation A). how could I give this a reasonble explanation, i mean what is the cause of this phenomenon?
 
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  • #12
knightq said:
then what the gravity in case A is? if I am a man in the rocket, i want to a explanation of the gravity or the fact every thing around in rocket is falling, how could I explain?

If the man in the rocket does only "local" experiments, he could imagine that he is either accelerating or in a gravitational field. He cannot tell the difference.

If he does "non-local experiments" (let's say he has a slightly bigger rocket), then he can distinguish between the two possibilities.
 
  • #13
But I think that equivalence of gravity and acceleration is not general to global scale. There is never a uniform gravitational field which corresponds to uniform acceleration because there is curvature...
 
  • #14
knightq said:
Let me restate my problem in a more clear way i think.
Situation A: a accelerated rocket in flat spacetime. the observer in the rocket could think he is in a gravitation field equivalently.All experiments he do are like in a gravitation field downward.

SituationB: a apple falls down under the gravitation force from the tree, or "in GR way", caused by the curved spacetime which is disturbed by the earth.
Can I say that the gravity in A is different from in B? or the gravity in B is real , in the sense that it is caused by another object. After all what we called gravity is a interaction of two bodies , no matter you intepreted as curved spacetime or force, which both demand a source (the Earth in B).Obviously in case A there is no such a source.
It appears to me you are comparing apples and oranges.

An observer undergoing constant proper acceleration is not equivalent with an observer free falling, it is equivalent with an observer trying to be stationary in a gravitational field.
 
  • #15
The effect of gravity on an object is it pulls down on every atom, electron and particle. The floor pushing up on an object giving the illusion of gravity (like an elevator that starts to go up) seems to me to be a different phenomenon and not indishtinguishable from gravity. Any serious spaceman with sensitive equipment would be able to measure the difference, unless someone smarter was able to attach miniature booster rockets to every atom in order to mimic gravitation perfectly.:smile:
 

What is the equivalence principle?

The equivalence principle is a fundamental concept in physics which states that the effects of gravitational force and acceleration are indistinguishable. This means that an observer in a gravitational field cannot tell the difference between being in a stationary frame of reference and being in an accelerating frame of reference.

Who proposed the equivalence principle?

The equivalence principle was first proposed by Albert Einstein in his theory of general relativity in 1915. It was later refined and expanded upon by other physicists, such as Niels Bohr and Werner Heisenberg.

How is the equivalence principle used in modern physics?

The equivalence principle is a fundamental principle of general relativity, and is used to explain the behavior of gravity and the motion of objects in the universe. It is also used in other areas of physics, such as in quantum mechanics, where it is applied to the concept of quantum gravity.

Is the equivalence principle a proven theory?

While the equivalence principle has been extensively tested and verified in many experiments, it is still considered a theory and not a proven fact. However, it is widely accepted by the scientific community and is a key foundation for our understanding of the laws of physics.

What are the implications of the equivalence principle?

The equivalence principle has many implications in physics, including the fact that gravity and acceleration are not distinct forces, but rather two different ways of describing the same phenomenon. It also helps to explain the behavior of light and other particles in the presence of gravitational fields, and has played a crucial role in our understanding of the universe and its origins.

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