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Doubts in general theory of relativity

  1. Apr 1, 2013 #1
    according to equvalence principle,acceleration can be equvalent to rest in which gravitational field exists. Earth revolves around the sun as sun produces curvature in space-time. What kind of acceleration is the curvature of space-time produced by sun equavalent too?
     
  2. jcsd
  3. Apr 1, 2013 #2
    I think you are seriously messing something up here.
    First of all according to GR objects that have mass /energy curve or bend spacetime by themselves even if they are not accelerating just standing there , just like the floor beneath you feels you just as you are standing there or walking upon it.
    Now acceleration is a different frame.
    Sun produces curvature and earth does too it's just that earth has much smaller mass so the curvature is less and it follows to the body with the strongest curvature which near us happens to be the sun.

    Now if you think can acceleration create similar force to that of gravity , well yes it can to the observer which is accelerating but only as long as you accelerate if you stop accelerating you don't feel the G force anymore and you become stationary , you are moving only with respect to others in your frame of reference you are not moving.
    So the key think here is acceleration both increasing or decreasing in speed.
     
  4. Apr 1, 2013 #3

    Dale

    Staff: Mentor

    Acceleration is equivalent to rest in a gravitational field without tidal effects. If you consider the sun's gravity over a small portion of spacetime where tidal effects are negligible then it is equivalent to acceleration directly away from the sun.
     
  5. Apr 1, 2013 #4
    It's is equivalent to proper acceleration. The curvature "causes" a coordinate acceleration.
     
  6. Apr 1, 2013 #5
    well,i was asking precisely this.. I don't understand what you meant by i am seriously missing.. Ok.i didn't understand you answer.. Let me tell question again. Inorder to create an effect of sun's gravity,what kind of acceleration that object should exhibit?
     
  7. Apr 1, 2013 #6
    To me you understand since you put it this way; "equivalent to rest in which gravitational field exists".
     
  8. Apr 1, 2013 #7
    what do you mean by proper acceleration? Is it object accelerating with respect to galiliean system is a straight line? Is this acceleration curvature of space-time caused by sun when stationery equalent too?
     
  9. Apr 1, 2013 #8
    i actually asked what kind of acceleration equavalent to it.
     
  10. Apr 1, 2013 #9
    no.i was not asking like that.let me use an example. First you need a galilean system of co-ordinates. Then think about a room,inside a man stands.someone pulls the room upwards with a constant force.that man has a ball.he lets go of that ball. A person outside sees this as like this:acceleration is not imparted into the ball,so it is moving uniform.but room is accelerating.so it hits the ground.but observer inside will think that gravitation did this.here you can see that upward acceleration was equavalent to object falling downwards towards the floor.likwise extend this principle to sun and tell me what kind of acceleration is equavalent to sun's gravity on earth?
     
  11. Apr 1, 2013 #10
    by that i actually meant that sun is able to curve space-time when it is stationery.
     
  12. Apr 1, 2013 #11

    Nugatory

    User Avatar

    Staff: Mentor

    Dalespam answered this in #3: straight outwards, away from the sun.
     
  13. Apr 1, 2013 #12
    No friend,i know that!!! But i don't know What kind of acceleration. I want that... I mean directional acceleration or straight line acceleration.. like that.. You can understand what exactly i was saying if you read #9..
     
  14. Apr 1, 2013 #13
    Oh!! Sorry friend,i haven't seen that part of comment as i was reading from the mobile. What does that mean away from the sun?? Can you explain a little easy manner. Away from what???
     
  15. Apr 1, 2013 #14

    Nugatory

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    Staff: Mentor

    Radially outwards, away from the center of the sun, in any direction. If you were standing on the surface of the sun (bad idea, of course - it's hot) the direction would be "up"
     
  16. Apr 1, 2013 #15

    Dale

    Staff: Mentor

    ash64449, your question is very confusingly worded. You are confusing yourself as much as you are confusing all of the rest of us. Let's just skip your question and instead just explain how the equivalence principle works.

    Suppose that you have a UNIFORM gravitational field, meaning that there are no tidal effects present in the gravitational field. That type of gravitational field is experimentally equivalent to an accelerating reference frame without gravity.

    For a person in a small room on the surface of the earth the gravity of the earth is approximately uniform, so you can say that experiments conducted in this room will produce the same results as though he were in a rocket ship accelerating at 1 g far from any gravitating masses.

    For a short period of time in the earth's orbit the gravity of the sun is approximately uniform, but the earth's gravity is not uniform, so it is difficult to treat that situation using the equivalence principle.

    However, consider a related example of a small spaceship orbiting the sun at 1 AU. Inside the spaceship for a short period of time the gravity of the sun is approximately uniform and the spaceship's gravity is negligible, so you can use the equivalence principle. By the equivalence principle, being in free-fall in a uniform field is equivalent to being in an inertial frame far from any gravitating body, so you can say that experiments conducted in this space ship will produce the same results as though he were far from any gravitating masses.
     
  17. Apr 1, 2013 #16
    oh.. Thank you friend.. similar to what i said in #9... Thank you once again!!:smile:
     
  18. Apr 1, 2013 #17
    Yes.This is what i was saying.. am i not fluent or you guys cannot understand what i said... Watch #9 in which i explain equivalence principle.
    i just asked this: Sun has a curved Gravitational field.So Which accelerating reference frame without gravity is equivalent to the Sun's curved Gravitational field?? That is what i was asking. I got the answer...
     
  19. Apr 1, 2013 #18

    Dale

    Staff: Mentor

    And what was the answer? (in your own words)
     
    Last edited: Apr 1, 2013
  20. Apr 1, 2013 #19

    acceleration directly away from the sun.
     
  21. Apr 1, 2013 #20
    just like that if you were standing in the sun,direction is towards the up
     
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