Local Landmarks & General Relativity

  • Thread starter Thread starter codeman_nz
  • Start date Start date
  • Tags Tags
    Local
codeman_nz
Messages
11
Reaction score
0
General relativity says that nothing can go faster than the speed of light when measured against local landmarks.

What counts as a local landmark? What is the boundary between a local and distant landmark?
 
Physics news on Phys.org
The distance between such local landmarks gets smaller as the spacetime curvature around them, or between them increases. So in flat spacetime it can be any distance, but close to the sun it would be smaller. I suppose the boundary is where the nearby spacetime deviates from flatness by an amount greater than the instrumental error.
 

Thread 'I don't see how a black hole's event horizon can be crossed'

OK, so this has bugged me for a while about the equivalence principle and the black hole information paradox. If black holes "evaporate" via Hawking radiation, then they cannot exist forever. So, from my external perspective, watching the person fall in, they slow down, freeze, and redshift to "nothing," but never cross the event horizon. Does the equivalence principle say my perspective is valid? If it does, is it possible that that person really never crossed the event horizon? The...
View full post »

Thread 'Synchronizing clocks in an inertial frame if light is anisotropic'

ASSUMPTIONS 1. Two identical clocks A and B in the same inertial frame are stationary relative to each other a fixed distance L apart. Time passes at the same rate for both. 2. Both clocks are able to send/receive light signals and to write/read the send/receive times into signals. 3. The speed of light is anisotropic. METHOD 1. At time t[A1] and time t[B1], clock A sends a light signal to clock B. The clock B time is unknown to A. 2. Clock B receives the signal from A at time t[B2] and...
View full post »

Thread 'Is the variation of the metric ##\delta g_{\mu\nu}## a tensor?'

From $$0 = \delta(g^{\alpha\mu}g_{\mu\nu}) = g^{\alpha\mu} \delta g_{\mu\nu} + g_{\mu\nu} \delta g^{\alpha\mu}$$ we have $$g^{\alpha\mu} \delta g_{\mu\nu} = -g_{\mu\nu} \delta g^{\alpha\mu} \,\, . $$ Multiply both sides by ##g_{\alpha\beta}## to get $$\delta g_{\beta\nu} = -g_{\alpha\beta} g_{\mu\nu} \delta g^{\alpha\mu} \qquad(*)$$ (This is Dirac's eq. (26.9) in "GTR".) On the other hand, the variation ##\delta g^{\alpha\mu} = \bar{g}^{\alpha\mu} - g^{\alpha\mu}## should be a tensor...
View full post »

Similar threads

I Quasi-local mass as a measure of the gravitational energy?
Replies
3
Views
1K
I Non-Inertial Relativistic Dynamics
Replies
18
Views
1K
I Locally Inertial Frames: Freefall & Relative Velocities
Replies
26
Views
2K
I General Relativity: Is it Local?
Replies
2
Views
2K
A Dirac on localization of energy in the gravitational field
Replies
16
Views
1K
I How do non-diagonal indices of a metric allow for local flatness?
Replies
22
Views
409
I Are Space and Time Just an Illusion in General Relativity?
Replies
6
Views
3K
B General Relativity and the curvature of space: more space or less than flat?
2
Replies
62
Views
6K
I Doubts about the relativistic description of electrical interactions
Replies
2
Views
1K
I Understanding the Equivalence Principle
Replies
10
Views
1K

Hot Threads

Recent Insights

Back
Top