How long does it take for gravity to have an effect?

[mozirry]

Say you are in space and in a void area where gravitational forces are having limited or no impact on your movement at all.

If an incredibally dense or massive objected suddenlty "spawned" in near you, say near earth orbit, would gravity immediately pull at you or would it gradually pull at you?

 

[Gibsons]

According to current theory, gravitational force travels at the speed of light.

 

[PolymerTim]

Originally posted by: mozirry
Say you are in space and in a void area where gravitational forces are having limited or no impact on your movement at all.

If an incredibally dense or massive objected suddenlty "spawned" in near you, say near earth orbit, would gravity immediately pull at you or would it gradually pull at you?

Recent thread for your viewing pleasure.

 

[Nathelion]

If a massive object "spawned" near you, you'd be ripped to shreds The gravity wave as the object suddenly appears would be discontinuous (that is, there is no gravity at first and then "instantaneously" lots of it), so you'd have an essentially infinite force gradient at the wavefront. As this wavefront propagates through the space occupied by your body, even small molecules would find themselves subjected to tremendous stresses when the wavefront passes through as some of the atoms in the molecule find themselves in the "new" gravity field while others are still outside it (at least for some small period of time). If the object is sufficiently massive, and I imagine it wouldn't take much mass (although it's kind of hard to test, proteins and other large structures would be malformed and/or break apart, and you would die a presumably slow and painful death. If the object is really massive, you would simply be torn into microscopic pieces, which may actually be quite a bit more pleasant when it comes down to it.

 

[degibson]

Originally posted by: Nathelion
If a massive object "spawned" near you, you'd be ripped to shreds The gravity wave as the object suddenly appears would be discontinuous (that is, there is no gravity at first and then "instantaneously" lots of it), so you'd have an essentially infinite force gradient at the wavefront. As this wavefront propagates through the space occupied by your body, even small molecules would find themselves subjected to tremendous stresses when the wavefront passes through as some of the atoms in the molecule find themselves in the "new" gravity field while others are still outside it (at least for some small period of time). If the object is sufficiently massive, and I imagine it wouldn't take much mass (although it's kind of hard to test, proteins and other large structures would be malformed and/or break apart, and you would die a presumably slow and painful death. If the object is really massive, you would simply be torn into microscopic pieces, which may actually be quite a bit more pleasant when it comes down to it.

This sounds like a lot of fun! Fortunately, the force would vary by ~1/R^2, and since it moves forward at C, the integral impulse would might be survivable at moderate distance, depending on the mass of the spawned object.

 

[bobsmith1492]

Of course you're starting from the assumption that it is physically possible for matter to spontaneously appear which I would posit is false, hence, it is meaningless to theorize on the resulting effects.

 

[AllGamer]

in nature all matter have its own gravity

so naturally if 2 items are floating in space, once they are close enough, both will mutually attract each other

 

[Smilin]

Originally posted by: Gibsons
According to current theory, gravitational force travels at the speed of light.

For example if the sun suddenly disappeared the Earth would keep going in an ellipse for about 8 minutes then go straight.

 

[hellokeith]

Originally posted by: Smilin

Originally posted by: Gibsons
According to current theory, gravitational force travels at the speed of light.

For example if the sun suddenly disappeared the Earth would keep going in an ellipse for about 8 minutes then go straight.

Except for that the Earth does not revolve around an 8-minute-retarded Sun position, nor has the speed of the effect of gravity has not been conclusively proven.

 

[Ticky]

Originally posted by: bobsmith1492
Of course you're starting from the assumption that it is physically possible for matter to spontaneously appear which I would posit is false, hence, it is meaningless to theorize on the resulting effects.

Massive energy-mass conversion? Might make a very creative weapon....

 

[Smilin]

Originally posted by: hellokeith

Originally posted by: Smilin

Originally posted by: Gibsons
According to current theory, gravitational force travels at the speed of light.

For example if the sun suddenly disappeared the Earth would keep going in an ellipse for about 8 minutes then go straight.

Except for that the Earth does not revolve around an 8-minute-retarded Sun position,

Why do you say that?

nor has the speed of the effect of gravity has not been conclusively proven.

The speed of gravity has been shown conclusively to be finite. The exact speed has been shown to be the speed of light within a few percent while observing binary pulsars.

We still haven't conclusively proven Newton's theory of gravity either. It all depends on your standards I guess

 

[Skraeling]

which is why gravity is only a theory and not a law (I think).

 

[hellokeith]

Originally posted by: Smilin
The speed of gravity has been shown conclusively to be finite. The exact speed has been shown to be the speed of light within a few percent while observing binary pulsars.

I really think you should go read the multipage thread I made on this subject some months ago. And no, measuring the decaying orbits of pulsars is far from conclusive in any objective person's mind, including NASA scientists (which I quoted in my speed of gravity thread).

 

[Born2bwire]

Originally posted by: hellokeith

Originally posted by: Smilin
The speed of gravity has been shown conclusively to be finite. The exact speed has been shown to be the speed of light within a few percent while observing binary pulsars.

I really think you should go read the multipage thread I made on this subject some months ago. And no, measuring the decaying orbits of pulsars is far from conclusive in any objective person's mind, including NASA scientists (which I quoted in my speed of gravity thread).

That was only in response to the Jupiter measurements, there are other measurements that support the speed of gravity to be c. In fact, your NASA scientist, who admitted not being an expert on the subject, only really talked about the fact that the speed of propagation is not a hindrance to a Newtonian model. There are still additional experiments with binary pulsars. The difference with these experiments is that the measurement is not a direct measurement like was hoped for with the Jupiter experiment.

http://math.ucr.edu/home/baez/...ity/GR/grav_speed.html

I had this in the other thread but you did not respond to it. Carlip states,

While current observations do not yet provide a direct model-independent measurement of the speed of gravity, a test within the framework of general relativity can be made by observing the binary pulsar PSR 1913+16. The orbit of this binary system is gradually decaying, and this behavior is attributed to the loss of energy due to escaping gravitational radiation. But in any field theory, radiation is intimately related to the finite velocity of field propagation, and the orbital changes due to gravitational radiation can equivalently be viewed as damping caused by the finite propagation speed. (In the discussion above, this damping represents a failure of the "retardation" and "noncentral, velocity-dependent" effects to completely cancel.)

The rate of this damping can be computed, and one finds that it depends sensitively on the speed of gravity. The fact that gravitational damping is measured at all is a strong indication that the propagation speed of gravity is not infinite. If the calculational framework of general relativity is accepted, the damping can be used to calculate the speed, and the actual measurement confirms that the speed of gravity is equal to the speed of light to within 1%. (Measurements of at least one other binary pulsar system, PSR B1534+12, confirm this result, although so far with less precision.)

You can find a few of Carlip's papers weighing in on the Jupiter experiment. Other than the Jupiter stuff, you did not present anything from a valid source that showed that the propagation of gravity was not the speed of light or challenged the validity of GR.

 

[fire400]

Gravity in relations to other dimensions (assuming the theory is true/false), do you think that gravity itself moves or has to absorb something/anything, etc?

 

[Stiganator]

I have a question. Can we measure things faster than light? If we can't , how do we know that the propagation isn't instantaneous and we see it as c because that's as fast as we can measure? Maybe its a stupid question, but anyone know?

I don't recall ever hearing of things faster than light. From what I've gathered over the years, c is basically the speed at which so much energy is added to a piece of matter that it is entirely converted to energy/light and no longer has mass.

 

[Born2bwire]

Originally posted by: Stiganator
I have a question. Can we measure things faster than light? If we can't , how do we know that the propagation isn't instantaneous and we see it as c because that's as fast as we can measure? Maybe its a stupid question, but anyone know?

I don't recall ever hearing of things faster than light. From what I've gathered over the years, c is basically the speed at which so much energy is added to a piece of matter that it is entirely converted to energy/light and no longer has mass.

That'd be rather hard to answer. The current state of physics is that nothing can travel faster than c, so if this is true how can you possibly measure phenomenon that violate this? Fortunately, the consequence of special relativity can be accounted for very accurately using various techniques like the Lorentz transformations. These consequences create unique phenomenon that we can measure and use to work backwards to gain further insight into a process. For example, the radiation emitted by a particle in a synchrotron is patterned in a manner dependent upon it's velocity. Without special relativity, this would not be true. As such, we can use measurements of the radiation pattern and frequency to discern the strength of the magnetic field in the synchrotron. That's how we have a good guess about the magnetic field in the Crab Nebula without ever being able to physically go there and take measurements. For electrodynamics, special relativity causes what are known as retarded potentials. That is, the fields that I see at a point some given distance away from a source are time delayed due to the finite speed of propagation. With EM and electrodynamics, we can measure and observe this retardation since we can actually create and control sources. Not so with gravity. Gravity is more subtle and we are not able to suddenly turn on a gravitational source and control it to give insight into how the fields work. Even at the huge distances of the solar system, the retardation between the Earth and Sun only amounts to 8 minutes. The fact is, the finite propagation of gravity is very inconsequential to simulating the interactions of large bodies like solar systems. So it's very difficult to directly measure the speed of propagation since the impact is potentially very small. However, we can still discern it using indirect measurements, just like how we indirectly discern the magnetic field strength of the Crab Nebula. This is what Carlip was talking in terms of the binary pulsar measurements. More recently, there were some measurements concerning Jupiter and a pulsar. This experiment had hopes of being able to more directly measure the speed of propagation. However, there has been some back and forth about whether or not the experiment was truly successful in doing so.