The Daily Cow

We'd like to consider physical phenomenons like electromagnetic waves (light, UV, etc) to be instant, because in our approximated world they are. But through an elementary physics education, we learn that they are not. They take time to travel. Magnetic force should also propagate at the same speed because electric fields and magnetic fields do.

So what about gravity? Shouldn't it act in a way that's similar to magnetic and electric forces? What I mean is, does gravity travel instantaneously or at a specific speed? If the latter, is the speed our beloved universal constant--c?

Scenario One

Specifically, consider the following definitions, assumptions and simplifications:

• The Sun and the Earth are single points in space, an assumption often made in physics to simply calculations
• r is the distance between the center of the Sun and the center of the Earth
• M is the mass of the Sun and m is the mass of the Earth at time t₀
• The Sun burns mass at a nearly-constant rate k kg/s (such that k > 0)
• It takes t seconds for light to travel from the Sun (the "center", in this simplified model) to the Earth.
• G is the gravitational constant

The question is: at time t₀ is the magnitude of the force between the Sun and the Earth F₀=GMm/r², or F₁=G(M+t*k)m/r² (where F₁ > F₀)? That is, does the Earth feel the effect of the gravity from the Sun before the burning of t*k kg of mass, or the gravity at the exact point in time during which it is measured (from Earth)?

Scenario Two

If you don't like that more-rigorous physical approach, consider this: The Sun suddenly disappears from the center of our solar system. Does the Earth fly off immediately (without the gravity of the Sun to pull it in), or does it do so t seconds later?

What Do I Think?

I would like to think that gravity also propagates as electromagnetic waves do, but I have no convincing reasons why it should. Any inputs? Anyone taking theoretical physics? Astronomy? Anything that would give you the expertise to enlighten me on this? Any constructive input would be greatly appreciated.

Disclaimer

Perhaps this question touches relativistic topics which may provide us with a more definite answer. but I am not in the position to take that into consideration. If anyone has something to add, please do so.