Recent content by lailola

It means that the area of the cube in the x-y plane is constant for every z. Doesn't it?

Thanks for your answers. Ruta, I don't get why that line element satisfies the first condition.

Hi, I have to write a spacetime line element for the shape of a cube of cosmological dimensions. This cube is expanding like this: i)With time, the cube becomes elongated along the z-axis, and the square x-y shape doesn't change. ii)The line element must be spatially homogeneus. (I don't...

Thank you haushofer, those links have helped me a lot.

With 'normal' units I mean G=c=1

Hello, I have to calculate the gravitational field strength g given by the De Sitter-Schwarzschild spacetime. If G=c=1 I get: R_{00}\simeq -kT_{00}+\frac{1}{2}kT\eta_{00}+\Lambda \eta_{00}\simeq -kT_{00}+\frac{1}{2}kT_{00}\eta^{00}\eta_{00} +\Lambda \eta_{00}\simeq...

Ok, I think now I understand you. Setting dr/d\lambda in the equation in the figure I can get the expression that you've writen. Then, to calculate the proper time measured by the observer I use the Schw. metric again, but this time d\tau is not zero cause, as you said before, now we are...

I think you mean: \frac{dt}{d\tau}=g_{tt}^{-1/2}\rightarrow \Delta\tau=\Delta t (1-2M/r) where t is the time measured by an observer at infinity. And I get that expression from the expression of the Schwarzschild metric. But in this case what I have is (see image). That's why I cannot see...

But there's no proper time. We have a photon, instead of proper time we have to use an affine parameter λ, for example.

Let be a photon in a circular orbit (r=3M). I want to know the period measured by a stationary observer at this radius. Because we are working with a photon we cannot 'talk' about proper time, that's why I don't understand how can I calculate this. If I had a massive particle I could do...

I've already calculated the magnetic field along the axis. But, in the plane? And, what about the electric field? Any help? thanks

You're right, It's the field in the center.

Homework Statement We have an uniformly charged disk with total charge q, which is rotating around its axis with constant angular velocity w. Calculate electric and magnetic field in the axis and in the rotation plane. Calculate the radiated power in one cicle. Homework Equations...

Ok, thank you!

Ok. When i solve the equation it appears an 'x^2' in the denominator. Should I consider separately the two cases (x=0,x≠0 )? And, when I set t=0, does tr have to be negative? Thanks