Anticitizen said:If two objects, let's say two pool balls (or giant balls of neutronium for that matter), are placed in a closed universe that contains no other matter or energy, at rest with one another, is there a distance at which they exert absolutely no gravitational pull on each other? Or will there be some sort of gravitational interaction, regardless of how small, that will slowly pull them together given enough time?
Count Iblis said:
Anticitizen said:Antenna Guy, just to get this straight, you're saying that there is no point at which a gravitational field dissapates completely?
A spacetime curve, regardless of distance, will stretch across the universe given enough time for it to stretch at C?
Assuming an infinite, unbounded universe, wouldn't that imply some sort of infinite gravitational energy of some sort?
Anticitizen said:Oh, and by spacetime curve I refer to the warping in spacetime caused by mass. Is there a far away enough point where the 'depression' would end and spacetime would be 'flat' again, as if the objects didn't exist at all as far as spacetime was concerned?
Anticitizen said:I'm subscribing to the high-school textbook model of a ball placed on a sheet of rubber which causes a curvature or depression in the sheet, aka spacetime.
Anticitizen said:Yes, and I'm willing to allow any passage of time for the propogation of the gravitational effect in this thought experiment.
Did you really mean to say this? If ball A has mass (inertial resistance) M and ball B attracts it with a force (gravitational pull) F then ball B will change ball A's acceleration by F/M. No matter how small F is, as long as there is gravitational pull, it will affect the movement.ok123jump said:We have two theories which essentially agree on the outcome. Newton's Gravity and Einstein's Curved Spacetime.
If you had a closed Universe with two pool balls and no other matter, you would still have to worry about inertia. As such, there should be some critical value out in space where the force of attraction (due to Gravity or Spacetime Curvature) would not overcome inertial resistance to movement.
They will always exert a "gravitational pull" on each other - but it will not always influence the movement of the other. At least... that's what we know of these matters thus far.
According to theory (both Newtonian and general relativity) there is no distance limit to gravity, it goes on forever. However it does get less and less, and eventually it will be so weak you couldn't measure it. Indeed quantum theory says (in a horribly gross oversimplification) that very tiny values can't be reliably measured at all.Anticitizen said:If two objects, let's say two pool balls (or giant balls of neutronium for that matter), are placed in a closed universe that contains no other matter or energy, at rest with one another, is there a distance at which they exert absolutely no gravitational pull on each other? Or will there be some sort of gravitational interaction, regardless of how small, that will slowly pull them together given enough time?
I think this is irrelevant to what's being asked. You're assuming that two masses magically appear out of nowhere, contrary to all known laws of classical physics.Antenna Guy said:Then we are back where we started. The two objects would exert absoloutely no gravitational pull on each other until t=d/c.
DrGreg said:Antenna Guy said:Then we are back where we started. The two objects would exert absoloutely no gravitational pull on each other until t=d/c.
I think this is irrelevant to what's being asked. You're assuming that two masses magically appear out of nowhere, contrary to all known laws of classical physics.
HallsofIvy said:Did you really mean to say this? If ball A has mass (inertial resistance) M and ball B attracts it with a force (gravitational pull) F then ball B will change ball A's acceleration by F/M. No matter how small F is, as long as there is gravitational pull, it will affect the movement.
Under GR, in a closed spacetime all objects must come together eventually.Anticitizen said:If two objects, let's say two pool balls (or giant balls of neutronium for that matter), are placed in a closed universe that contains no other matter or energy, at rest with one another, is there a distance at which they exert absolutely no gravitational pull on each other? Or will there be some sort of gravitational interaction, regardless of how small, that will slowly pull them together given enough time?
A gravitational field is a region in space where an object with mass experiences a force due to the presence of another object with mass. This force is known as the force of gravity.
The strength of a gravitational field is measured by the force per unit mass at a given point in the field. This is known as the gravitational field strength.
The relationship between mass and gravitational field is that the greater the mass of an object, the stronger its gravitational field will be. This means that objects with more mass will experience a greater force of gravity.
A uniform gravitational field is one where the gravitational field strength is constant at all points, such as the gravitational field near the surface of a planet. A non-uniform gravitational field is one where the field strength varies at different points, such as the gravitational field near a massive object like a black hole.
The strength of a gravitational field decreases as the distance between objects increases. This is known as the inverse-square law, which states that the force of gravity is inversely proportional to the square of the distance between two objects.