# Speed of Gravity [closed]

Is the speed of gravity instant? By the speed of gravity, I'm not talking about acceleration.

What I mean is something like this: If I take a vacuum, for example, and put in two objects of the same size, shape, and mass, exactly 1 light year apart. In this vacum, no other objects exist anywhere. Therefore, these two objects will have gravity towards each other. How long will it take before the force of gravity to start acting? One year, (as it's the speed of light) or instantly?

Under both conditions, I have question expanding on them.

If it is instant, then could we theoretically have a machine sensitive enough to pick up gravity of objects outside of our observable universe?

If it's not, then what would happen if an object with high enough gravity (Like super-super-super massive black hole) were to suddenly enter our observable universe. Then would we be hugely affected? What would happen?

## closed as off-topic by SF., Brian Tompsett - 汤莱恩, Philipp, TildalWaveJan 3 '16 at 13:52

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question is about other space sciences (physics, weather, astronomy, etc), and does not directly pertain to space exploration as outlined in the help center." – Philipp, TildalWave
If this question can be reworded to fit the rules in the help center, please edit the question.

• This question might be better suited to Physics SE. – Fred Jan 3 '16 at 10:03
• belongs to Physics.SE......... – SF. Jan 3 '16 at 10:56
• ...and I believe for actual, factual answer we'll have to wait until eLISA sends its results. – SF. Jan 3 '16 at 10:59
• @Hennes -- That is not a good question. You are in essence asking "what do the (known) laws of physics say will happen when those laws are violated?" Mass is a conserved quantity in Newtonian mechanics, so the question doesn't make sense from a Newtonian perspective. Mass-energy is locally conserved in general relativity, so the question doesn't make sense from a relativistic perspective, either. What make make sense is to ask what would happen if the Sun exploded. But that too has already been answered at physics.SE. – David Hammen Jan 3 '16 at 14:30
• @SF. - See, for example, these questions at physics.SE: physics.stackexchange.com/questions/45882/…, physics.stackexchange.com/questions/90507/…, physics.stackexchange.com/questions/22876/…, and also this wikipedia article, en.wikipedia.org/wiki/Electromagnetic_stress%2Denergy_tensor. – David Hammen Jan 3 '16 at 17:01