Recent content by shubham agn

Hello! I am in 3rd year of engineering in Biochemical engineering. I want go for a Ph.D in High Energy Physics in the US (and I will be an international applicant). So, I will have to write both the General GRE and Physics GRE. I want to know how important is the General GRE score. Do I need to...

Hello! The Einstein field equation relates the curvature of space-time to the energy tensor of mass-energy. This is fine. These field equations are derived by varying the Hilbert action. Now the Hilbert action is an integral of scalar curvature (R) over volume. So, when we vary this action, we...

Thanks Nugatory and pervect!

Ok. So I think I understand it now. To compute even the magnitude of the 3-velocity along the geodesic, I will need the metric. Now just one more query : In cartesian coordinates in flat space-time, the minimum spatial between two neighbouring points is given by (dx)^2 +(dy)^2 +(dz)^2. But now...

Ok. So, if the components of the 3-velocity are v(x), v(y) and v(z) then is it not true that the magnitude of the "speed" V is given by V^2 = v(x)^2 + v(y)^2 + v(z)^2 ? I mean does the validity of the above equation depend on what the metric is?

I was just thinking of the 3-velocity. Its components are clearly ∂x/∂t, ∂y/∂t, ∂z/∂t. I can find these since the (x,y,z,t) is given to me and I don't need the metric for that. Thus I can find the magnitude of the 3-velocity (without knowing the metric) and compare it with 'c' (the speed of light).

Hello! Please help: A world line is given to us. It is known that it is a geodesic. The metric, however, is not known. Since we don't know the metric, it should not be possible to tell whether the geodesic is spacelike/timelike/null (Right?) But since the geodesic is known (x,y,z,t), we can find...

Thanks Shyan, jedishrfu and stewards!

Hello! I am reading GR and got confused about the principle of General Covariance. The principle of General Covariance says that the laws of physics take the same form in all reference frames. Since the laws are same in all reference frames, any experiment performed should give identical...

Thank you all for your replies! They were indeed helpful!

Hii! Newton's law of gravity is ∇.(∇Φ) = 4πGρ. A book on GR gives a suggestion to make it Lorentz covariant by using de' Alembertian operator on 'Φ' in the LHS of above equation instead of Laplacian. Then it explains that this won't work because we have to include in 'ρ' all the energy...

Dear Jackson, what I mean to say is the following: Let us say the original flux through the loop is 10 Wb. Now, nature abhors a change in flux, so it will try to maintain it at 10 Wb at all times. Now, we decrease the flux to 9 Wb in a small time. Because of this changing flux, there will be an...

Let us say we are decreasing the magnetic flux through a perfect conducting loop by varying the magnetic field. Then there will be an induced emf and as you rightly said, its magnitude will be very large on account of the very small resistance of the loop. So this induced emf will manage to...

Thank you!

Hi! I am in second year of my college. I want to pursue theoretical physics and plan to work on things like String theory and High Energy Physics. Now I was trying to get a summer project in Physics and I have been offered an opportunity to do a project in theoretical Plasma Physics. Is it right...