Orodruin's latest activity
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Orodruin replied to the thread Writing a vector parallel and normal to a unit vector ##\hat n##.I actually think ##\vec A - (\vec A \cdot \hat n)\hat n## is nicer than the double cross product. It also generalises to any dimension. -
Orodruin replied to the thread Writing a vector parallel and normal to a unit vector ##\hat n##.The answer given is a special case for three dimensions. The cross product is not defined in dimensions other than three. The...
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Orodruin replied to the thread I Missing proof of the Shell theorem in General Relativity.There is no object at all in the Schwarzschild spacetime. It is a vacuum solution. The assumptions are spherical symmetry of the...
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Orodruin replied to the thread A Understanding the Gravitational Redshift Caused by a Black Hole.Maintain the same ##r## coordinate and angular coordinates (in standard Schwarzschild coordinates). In other words, observers whose...
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Orodruin replied to the thread I Missing proof of the Shell theorem in General Relativity.No it isn’t. The usual derivation starts by assuming spherical symmetry and a vacuum solution and then proceeds to solve the EFEs under...
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Orodruin replied to the thread What should I do about my academic supervisor?.A good indicator of what? It is a purely citation based metric that comes with all the flaws of such metrics. It certainly has...
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Orodruin replied to the thread I Age of the Universe and the Cosmological Constant.To connect to what I said above, I meant that there is no algebraic closed form expression for the general case. The integral here is in...
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Orodruin replied to the thread I Age of the Universe and the Cosmological Constant.There is no standard formula except if you assume domination by one component. Generally you have to solve the Friedman equations to...
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Orodruin replied to the thread I Age of the Universe and the Cosmological Constant.It is not. Assuming one component dominates the entire expansion history it is a numerical factor multiplied by 1/H. Iirc, this factor...