Gravity question

[Mookow]

What speed does the "force of gravity" act at? IE, is it instantaneous, or does it apply itself at a speed lower than 'c'?

I have been sitting here trying to figure out an experiment that would test this, but since gravitational force is so weak at a particle level, and rapidly accelerating a planet is difficult, I dont know what form a good experiment would take. Maybe if you could accurately measure the force of the moon while on earth, and then compare that to the observed angle to the moon, correct that for the time that light takes to reach the earth, and then see... but I dont know if the pull of the moon as felt from earth's surface is enough to be accurately measurable (ie, I know that the moon is why we have tides, but does the moon exert enough force on a object that we can accurately measure the direction [which, for this question, would seem to be more important than the magnitude of the pull] it is being pulled in to a very small degree of uncertainty).

 

[CTho9305]

Watch a supernova explosion?

 

[Mookow]

Originally posted by: CTho9305
Watch a supernova explosion?

A supernova isnt directional, though, is it (at least I dont recall seeing any asymetrical supernovas in my astronomy classes)? I would think that it wouldnt make much of a difference in felt gravitational force, unless you are close enough to detect the loss of (extra due to the supernova) mass as it is converted into energy, and then you'd have to deal with all the EM energy hitting your measuring instruments. I dont know how long it takes for the freshly created EM radiation to exit the supernova, though, since from my astronomy class I remember it takes a long, long time for a photon created in the sun's center to exit the sun, due to all the matter in the way (ie, it gets re-emitted a lot and doesnt travel in a straight line), so maybe you'd have time. Still, there is the problem of actually getting close to a star before it goes into supernova (ie, traveling out there and waiting around for it to happen, which since we cant accurately, in the perspective of human lifetimes, predict when a star is going to go nova)

 

[PowerMacG5]

Newton believed the force of Gravity was an instantaneous force, while modern science has proven it has not. For example, Newton believed that if the Sun exploded, we would feel it instantly, but would not see it for 8 minutes or so (the time it takes light to travel from the sun to the Earth). However, modern science says we will see and feel it at the same time.

 

[RossGr]

In the frame work of General Relativity the speed of gravity = c. To my knowledge there has been no experimental verification of this. It is a result of GR much as a constant c is a result of Maxwells equations. If and when the gravition is observed we may then be cabable of measuring the speed of gravity.

 

[RadixTwo]

Couldn?t you just measure the tide in a clean room swimming pool filled with distilled water and watch where the moon is to find out?
I like that sentence...

 

[RadioactiveHamzter]

I remember hearing about how they measured the speed of gravity, by comparing the gravitational effect of Jupiter with it's actual position. The managed to confirm that gravity travelled at least 95% the speed of light (don't remember the exact value, it was somewhere in that region though).

 

[RossGr]

The jury is still out on the Jupiter measurements. Last I heard there was a lot disageement between people who know a lot more about it then I. Until it has been throughly analyzed and proven valid I will have to remain skeptical.

 

[sao123]

Gravity is instantanious for this reason...

Gravity fields are continuous and infinite. Since every particle in the universe exerts a gravity field on every other particle in the universe...All particles are already subjected to all the gravitational fields that exist in the universe. There is no area without gravity (only microfractional in magnitude). The only thing that ever changes is the magnitude of the gravitational field. Since there is no beginning or no end..there can be no how soon does gravity take effect... And since the magnitude vector field is continuous in D^3...all changes are instantaneous

 

[Mingon]

Gravity is instantanious for this reason...

I would have to disagree, the speed with which gravity effects something at a great distance is not (in my understanding) instantaneous hence it must have a velocity.

 

[sao123]

Heres a proof by contradiction for you.

In order for gravity to have a speed at which it acts on something, there would have to be a point at which it is not acting.

1) Meaning that there has to be a point where gravity does not exist.

2)However gravity acts as G = 1/D^2. As D-> infinity...G approaches zero, yet never reaches it. Therefore 1 is false.

3)Since there can be no area where gravity does not effect. The speed at which gravity acts on a moving particle is now irrelevent because gravity has always been in effect everywhere the particle has been since the particle in question came into existence.

4)The laws of conservation of mass and energy say you cant create matter or energy only convert between them.
4b)Gravity acts upon mass & energy alike. Therefore since the particle has always existed in one form of mass or energy which it was always affected by gravity.

5)So the speed of gravity does cannot exist.

 

[killedradiostar]

if it does not have instantaneous action at a distance, it will act much like the electromagnetic interaction. in other words, gravitational waves (distortions in spacetime) will be propagated by large disturbances to gravitational fields (shake a black hole). gravity is believed to act through the graviton, which is the messenger particle for gravity; it travels at speed c.

experiments are being done to test this.

 

[killedradiostar]

Originally posted by: sao123In order for gravity to have a speed at which it acts on something, there would have to be a point at which it is not acting.

what about the electromagnetic field? its interaction is not finite, yet it has an associated speed of interaction.

 

[sao123]

what about the electromagnetic field? its interaction is not finite, yet it has an associated speed of interaction.

The difference between magnetism and gravity so far is
The interaction of a magnetic field may be infinite in space, but it is not constant in time. Magnetic fields are defined by the spin of an electron in an orbit of an atom.

When the spin of electrons in 2 atoms are aligned, they produce an attractive force. When they are opposite, the produce a repelling force. Known fact: the spin of an electron can arbitrarily change (for any number of reasons) at any time. Every time this attraction/repelling force changes, there must be a beginning and an end, which at this point can be a measured as your speed effect.

However since gravity is infinate in both space and constant in time (as known to this point) there is no change, no beginning or end (only pure continuity) and therefore no measurable speed effect.

gravity is believed to act through the graviton, which is the messenger particle for gravity;

If all four basic forces are believed to be fundamental in nature...why is gravity the only one explained with a messenger particle? And exactly how does this messenger particle cause an attractive force? Generally when two particles (mass or massless) interact the particles are either reflected or become absorbed.


if you would

(shake a black hole)

the only explaination for any type of delayed affect you might notice is that there are so many other forces at work.
The biggest reason is Inertia - Its not that the gravity isnt working instantly...its just that gravity is weak, to instantly overcome the inertial property of mass.

BTW...Isnt there a quantifiable way of describing inertia besides mass? In other words...what is the anti force/accelleration per time unit value of a quantified amount of mass.

 

[RossGr]

Sao123.
Yours is not the commonly accepted theory.

For one electron spin has little to do with generation of electoMagnetic radition. A photon is generated each time an electron loses enegry in a transition. Has nothing to do with spin.

How do you know there is not an end to gravitional influence? This is an assumption, and it is not even clear that it matters.

Once again, from General Realativity the speed of gravity is c.

 

[sao123]

The fundamental theory for equating the universal magnetic field and the universal gravitational field is...

All atoms consist of a number of negatively charged electrons, orbiting around a positively charged nucleus. These electrons possess a quantity known as spin The combination of orbital and spin motions is called the angular momentum of the electron. The angular momentum of an electron is a vector quantity, meaning it has direction. The motion of the electron produces a current, which in turn generates a tiny magnetic field in the direction given by the angular momentum. All matter creates a magnetic field... The sum of all these indivdual fields equals the universal magnetic field.

ANTI COPYRIGHT DISCLAIMER HERE...
This is not my own knowledge or research...
When i find the reference where this information came from, I will post it.

 

[MrPickins]

Originally posted by: sao123
Heres a proof by contradiction for you.

In order for gravity to have a speed at which it acts on something, there would have to be a point at which it is not acting.

1) Meaning that there has to be a point where gravity does not exist.

What about if a most of a large mass was very quickly converted to energy (as in a supernova)? Gravity would still be acting the whole time, but the decreased mass of the object would cause a change in the intensity of the gravity field (I think ), then you could measure the speed as a function of the change instead of an off/on situation....

Of course, all this is speculation from a very moderately educated mind.

 

[killedradiostar]

Originally posted by: sao123If all four basic forces are believed to be fundamental in nature...why is gravity the only one explained with a messenger particle? And exactly how does this messenger particle cause an attractive force? Generally when two particles (mass or massless) interact the particles are either reflected or become absorbed.

if i'm not mistaken, the photon is generally accepted as the electromagnetic messenger particle, the W and Z bosons are the weak force messengers, and i forget the strong force one :x

interesting comment on the EM field, btw, good stuff

 

[glugglug]

Gravity bends light (it accelerates the photons the same as more massive matter). So if the speed of gravitational field expansion was tied to the "speed of light", gravity would be slowing itself down as the field expanded from the source at its center, and the gravitational field would be unable to escape a black hole.

Therefore, gravity can't be limited to the speed of light.

 

[sao123]

the photon is generally accepted as the electromagnetic messenger particle

I never heard it described this way...but I was acutally thinking of photons in my earlier post...
I think photons are the behavioral particle of when electromagnetic energy interacts with a massed particle.

Generally when two particles (mass or massless) interact the particles are either reflected or become absorbed.

Photons, reflect, refract, vibrate, and can be absorbed (as energy)...but still how could a particle modeled after a photon (think billiard balls) represent an attractive relationship.


The difference...are we talking electromagnetic energy (light, xrays) or electromagnetic fields (vector array over a continuous space) ?
I do not believe photons are the particle expressed when a magnetic field exerts force on a charged particle.

What about if a most of a large mass was very quickly converted to energy (as in a supernova)? Gravity would still be acting the whole time, but the decreased mass of the object would cause a change in the intensity of the gravity field (I think ), then you could measure the speed as a function of the change instead of an off/on situation....

Theoretically if there were absolutely no other forces at work on the affected particle (in the changed field) this would work. However...the particle you are trying to measure the change on is affected by... inertia &/or momentum.

what I am saying is...even if the change in force is instantaneous...it couldnt be detected as instantaneous, because inertia would "temporarily" delay the effect of the immediate change in force (even if for a microsecond) then the measurement is imperfect.

 

[Shalmanese]

A experimental verifcation would be to look at a powerful rotating binary star and compare the phase of the star light to the phase of the gravity wave. The problem is that the effect is so weak that some fairly elaborate equipment needs to be set up and nobody has ponied up the cash to verify it. Theres talk of an experiment in the works but nothing concrete.

 

[RossGr]

Originally posted by: sao123
The fundamental theory for equating the universal magnetic field and the universal gravitational field is...

All atoms consist of a number of negatively charged electrons, orbiting around a positively charged nucleus. These electrons possess a quantity known as spin The combination of orbital and spin motions is called the angular momentum of the electron. The angular momentum of an electron is a vector quantity, meaning it has direction. The motion of the electron produces a current, which in turn generates a tiny magnetic field in the direction given by the angular momentum. All matter creates a magnetic field... The sum of all these indivdual fields equals the universal magnetic field.

ANTI COPYRIGHT DISCLAIMER HERE...
This is not my own knowledge or research...
When i find the reference where this information came from, I will post it.

Where did you tie in gravity?

Perhaps you need to spend a bit more time reading up on quantum theory, yours is a mish mash of correct facts which do not sum to your conclusion.

 

[RossGr]

Originally posted by: glugglug
Gravity bends light (it accelerates the photons the same as more massive matter). So if the speed of gravitational field expansion was tied to the "speed of light", gravity would be slowing itself down as the field expanded from the source at its center, and the gravitational field would be unable to escape a black hole.

Therefore, gravity can't be limited to the speed of light.

Gravity does not accelerate light. Light follows space-time geodesics, that is the shortest path throgh space time. Light merely follows the contures of space-time. It is not the path of light that is skewed but our perspective of space-time.

 

[rgwalt]

The talk in this thread is over my head, but I do know that your computer monitor exerts more gravitational force on you than the moon does.

Ryan

 

[Sahakiel]

Originally posted by: sao123

Photons, reflect, refract, vibrate, and can be absorbed (as energy)...but still how could a particle modeled after a photon (think billiard balls) represent an attractive relationship.

Hm... billiard balls...
If you hit the cue ball just right, you can get it to retrace its path after impact. It's relatively simple.
If you're even more skilled, you can get the target ball to come back.

The difference...are we talking electromagnetic energy (light, xrays) or electromagnetic fields (vector array over a continuous space) ?
I do not believe photons are the particle expressed when a magnetic field exerts force on a charged particle.

Photon, electromagnetic field, same thing, really.