Recent content by extrads

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    Graduate The physics meaning of the light cones tipping over

    There is a connection between the origin and the points in the light cone.That is to say,there is a casual relationship between them.I think normal light cone means light which travels to the right side and to the left side have the same speed.Then in certain spacetime,eg. at the point of strong...
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    Graduate Smaller but Larger? Understand Warped Physics in Higher Dimensions

    So you mean the expanding spatial volume has something to do with higher or extra dimensions ? And what is your favorite method of transportation?
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    Graduate Smaller but Larger? Understand Warped Physics in Higher Dimensions

    What is this real application of?
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    Graduate Smaller but Larger? Understand Warped Physics in Higher Dimensions

    yes,it is.
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    Graduate Smaller but Larger? Understand Warped Physics in Higher Dimensions

    Smaller,but Larger?? You may have a look at the attachments,which are the key parts of my problem. And the full text is here:http://arxiv.org/pdf/gr-qc/9905084v5.pdf How to understand "The outermost surface of the warp bubble will have an area corresponding to a radius of approximately...
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    Graduate How Would Physics Change Without Covariant and Contravariant Tensors?

    If the notions of covariant and contravariant tensors were not introduced,what would happen?E.g. what form will the Einstein E.q. Guv=8πTuv be changed into ?
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    Graduate Stress–energy tensorT^uv in theory and in practice

    yeah,that's the point.Different situation in metric,different result.And I think an another point is ...the matter may be not perfect fluid...
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    Graduate Stress–energy tensorT^uv in theory and in practice

    Oh,sorry,I focused my attention to how to explain the unitarity(normalization) condition and forgot to check it...spacelike vector is not a good example.By the way,do u think spacelike vector and closed timelike curves could exist in nature (in reality)?
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    Graduate Stress–energy tensorT^uv in theory and in practice

    Not exactly...I think if the metric is not diagonal, |g00| may be not equal to |g00| ,and the equation above I quoted may be not correct.
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    Graduate Stress–energy tensorT^uv in theory and in practice

    But for perfect fluid ,T00=ρU0U0+p(g00+U0U0) and according to 3#,then it=ρ/g00+p(g00+1/g00),where p is presure.
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    Graduate Stress–energy tensorT^uv in theory and in practice

    I just want this equation to be the unitarity(normalization) condition.E.g. Uu=(1,2,0,0) and (C,2C,0,0) are different in mathematics,but they have the similar physical meaning.So in order to make work easy,we use (1,2,0,0) to represent (C,2C,0,0)
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    Graduate Stress–energy tensorT^uv in theory and in practice

    I'm confused about the equation I quoted...Why?
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    Graduate Stress–energy tensorT^uv in theory and in practice

    That's it!
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    Graduate Stress–energy tensorT^uv in theory and in practice

    Yeah,I agree the observer should measure it locally and so on,but I'm afraid this generalization is a matter of unitarity.e.g.guvUuUv=+/-1.I think another generalization is Uu=(1,a,0,0),that is to say,orthogonality or diagonal metric is not needed...In that case,ρ is not necessarily equal to T00...
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    Graduate Stress–energy tensorT^uv in theory and in practice

    The observer and the object has the same four-velocity U^u as (1,0,0,0),which means they are relatively static.Then the the observer measures a point A of the object's energy density,which is ρ. My question is,the ρ is T^00 or T_00 at the point A?