Speed of gravity?

[Linguofreak]

Fun fact: such a situation can't even be considered in general relativity, because it contradicts Einstein's equations. Those equations have conservation of energy built-in in themselves in a way, and sudden disappearing of the Sun would violate conservation of energy quite a bit.

But would that matter to how regions outside the sun would react? The laws of physics are violated within the region of space containing the sun, but let's consider that region to be a black box where we leave the exact contents and laws of physics inside the region undefined, and only specify that it reacts with the outside universe in such a way that it appears to have a mass of 1 solar mass.

1) For that apparent mass to disappear, does General Relativity need to be violated outside the "black box sun" (that is, in any region where the density of mass/energy doesn't change)?

2) If the answer to 1) is "no", would there be any gravitational effects noticable at Earth, other than the Sun's gravity cutting out after 8 minutes?

 

[malisle]

Here is a link to the open-access paper published by the Chinese recently, claiming they measured the speed of gravity using eclipses.
Link

 

[Fizyk]

But would that matter to how regions outside the sun would react?

It matters in the sense that this question is similar to asking what would happen on Earth, if suddenly 2+2 would equal 5 on the Sun. You can speculate, but you can't plug that into a theory, because starting with a contradiction leads to nowhere.

This is actually more similar to the situation where Sun disappears than one could think. Conservation of energy emerges in General Relativity from a mathematical identity satisfied by the tensor used for describing the geometry of spacetime. Assuming that Sun just disappears means saying "let's assume that this identity doesn't hold" - and it's just like saying "let's assume that 2+2 is not 4".

 

[asbjos]

I used the scenario of a suddenly missing Sun to create a situation where the question of the speed of gravity would seem natural. Of course, I know that it never will happen, but I wanted to illustrate a situation where speed of gravity would have a practical use.

Thank you to everybody for all your answers and comments!

 

[Astronut25]

What About Dark Flow

[ame="http://en.wikipedia.org/wiki/Dark_flow"]Dark flow[/ame] exerpt
"[T]he matter causing the net motion is outside [the visible universe]"

This would suggest that gravity is FTL, since it travelled to some galaxies before the light did, and travelled the rest of the way as light ahead of the light emitted by the source (which will never get here due to the faster than light expansion of the universe*).

*according to relativity, nothing can travel faster than light, or as I understand it, NOTHING(noun) can travel faster than light. I found The Cassiopeia Project Website a while ago that is pretty good at describing certain things in a simplified manner, which I find useful sometimes. The video I'm referring to is under the Space section, number 15 (Universe)

And what about Black Holes, if gravity can't travel faster than light, then it shouldn't be able to escape itself?

 

[Keatah]

Gravity doesn't "flow" out of black holes. Black holes are like a zit upon the fabric of space, to use the outmoded ball-bearing on a rubber sheet analogy.

 

[Loru]

Gravity doesn't "flow" out of black holes. Black holes are like a zit upon the fabric of space, to use the outmoded ball-bearing on a rubber sheet analogy.

Exactly - spacetime distortion caused by a body isn't affected by itself.

If you add mass, the grafity well gets bigger, therefore event horizon is growing. Sphere of influence too but gravity is a property of spacetime (function of it's curvature) not actual particle interaction (as far as we know since no gravitons have been found yet and I'm not sure there is a place for them in standard model).

 

[blixel]

Theoretically, imagine that the Sun suddenly disappeared.