Tagged Questions

A theory that describes how matter interacts dynamically with the geometry of space and time. It was first published by Einstein in 1915 and is currently used to study the structure and evolution of the universe, as well as having practical applications like GPS.

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Can one shed light on the velocity of the photon through the fourth dimension x4 using limits? [duplicate]

THIS QUESTION IS COMPLETELY DIFFERENT!! IT DISCUSSES LIMITS!! To begin with, please study the mathematics from Brian Greene’s book An Elegant Universe. The upshot is that the faster an object moves ...
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Can we exit the event horizon of merging black holes?

I have an intuitive scenario. Consider we have a spaceship just below the event horizon of a BH, which is merging with another black hole. Finally, the singularities merge and we have a single black ...
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Stress-Energy tensor of a static, spherically symmetric, perfect fluid

I am trying to derive the equation for the interior mass of a spherically symmetric, static, perfect fluid in general relativity, $$\frac{\mathop{dM}}{\mathop{dr}} = 4\pi r^2 \rho(r).$$ This question ...
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What is the metric of a constant electromagnetic (pure electric or pure magnetic) field?

For example, imagine a magnetic field $B_x$ directing in $\hat{x}$ direction filling all the space. What is its associated metric field? I can construct the electromagnetic stress-energy tensor for ...
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Space-Time Curvature Depends on Relative Speed

When the mass of a planet causes the curvature of space-time we see that an approaching free-falling object deviates its path towards the planet. We also see the amount of that deviation depends on it'...
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Black Hole Scattering of Low-Frequency Light

What is the far-field interference pattern for low-frequency (i.e., the wavelength is much larger than the Schwarzschild radius) electromagnetic plane wave radiation about a point mass? I envision a ...
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Can revolving movement also generate gravitational waves? [on hold]

If an object revolves around a circular path at the speed of light could it still generate gravitational waves and what would be the simulation in inner area?
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Ricci scalar for Black Hole

What is the value of Ricci scalar at $r=0$ inside Black Hole? Since $R_{\mu \nu}=0$ is vacuum solution and valid outside event Horizon of black hole where there is no mass energy density. But inside ...
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Does gravity cause the gravity of another mass to curve?

For example say star 1 is at position x, however star 2 causes gravitational lensing on star 1's light that is traveling toward you and you now see star 1 at position y. Will star 1's gravity move you ...
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Is spacetime flat inside a spherical shell?

In a perfectly symmetrical spherical hollow shell, there is a null net gravitational force according to Newton, since in his theory the force is exactly inversely proportional to the square of the ...
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How much additional light does Earth receive from the Sun due to Earth's gravitational field?

I was reading about how gravity affects light, and that got me wondering how much additional light is collected by the Sun due to the Earth's gravitational field. Is it a significant amount of light (...
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Relativity, and Lenz's law with respect to the Lorentz force acting on a wire?

For this system: It's simple for me to predict the induced EMF, and if the wire were connected to a complete circuit(for current $I$ to flow), the opposing Lorentz force($-F$): However, if the ...
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Stationary v/s Static

Blau, in his GR book, says that a stationary and spherically symmetric metric is automatically static. He says this easily follows from the fact that for a stationary metric, and in spherical symmetry,...
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Solving the Friedmann Equation [closed]

Through substituting for values of $\rho$ and $k$, I have: $$H^2=\left(\frac{\dot{a}}{a}\right)^2=\frac{8\pi G C}{3a^4} + \frac{\Lambda c^2}{3}$$ $a=a(t)$, and $a(t=0)=0$. Note that $C$ is a ...
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How long can a particle survive inside of the horizon of a black hole?

By examining the causal structure of a Schwarzschild black hole, one can see that a particle in region II is unable to escape to $r=\infty$. Such diagrams do not show, however, how long a particle ...
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Chasing someone who has fallen into a black hole

Assume that my friend and I decided to explore a black hole. I parked the spaceship in a circular orbit safely away from the horizon. He puts on his spacesuit with a jet pack and carefully travels ...
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How can the size of the universe change over time when time is part of the universe?

Bit of an awkward way to phrase it, but basically: Time in relativity is just one of four dimensions of space-time. Nothing really special about it. Yet the universe was once smaller than it is now ...
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Do objects with mass travel faster than light inside a black hole? [closed]

Does an object with mass travel faster than light inside a black-hole?
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Trace of a Tensor

What is the significance of defining the trace of a tensor as $g^{\alpha\beta} R_{\alpha\beta}$ instead of $R_{\alpha\alpha}$ on a Riemannian manifold?
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How do wormholes work?

Firstly, I understand that we have no observational evidence for 'wormholes'. They are theorised solutions to general relativity equations. That said, if macroscopic wormholes do exist---how do they ...
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Does the general theory of relativity imply time dilation across the whole universe? [duplicate]

If not, why is my idea below not possible? The general theory of relativity tells us that time is slowed down by gravitational fields. We bounced radar signals off planets further from the sun, and ...